Screening assessment Petroleum sector stream approach Liquefied Petroleum Gases Stream 4 Petroleum and Refinery Gases (2024)

Environment and Climate Change Canada
Health Canada
February 2017

(PDF Format - 940 KB)

• Synopsis
• 1. Introduction
• 2. Substance identity
• 3. Physical and chemical properties
• 4. Sources
• 5. Uses
• 6. Releases to the environment
  • 6.1. Potential on-site releases from production and storage of LPGs
  • 6.2. Potential releases from transportation of LPGs
  • 6.3. Potential releases from transferring of LPGs
  • 6.4. Potential releases from end-uses of LPGs
• 7. Environmental fate
• 8. Persistence and bioaccumulation
  • 8.1. Environmental persistence
  • 8.2. Potential for bioaccumulation
• 9. Potential to cause ecological harm
  • 9.1. Ecological effects assessment
  • 9.2. Ecological exposure assessment
  • 9.3. Characterization of ecological risk
  • 9.4. Uncertainties in evaluation of ecological risk
• 10. Potential to cause harm to human health
  • 10.1. Exposure assessment
  • 10.2. Health effects assessment
  • 10.3. Characterization of risk to human health
  • 10.4. Uncertainties in evaluation of human health risk
• 11. Conclusion
• References
• Appendicies
  • Appendix A: Petroleum substance grouping
  • Appendix B: Physical and chemical data tables for LPGs
  • Appendix C: air dispersion modelling of potential releases of LPGs
  • Appendix D: modelling results for human exposure to LPGs from representative aerosol products available to consumersa
  • Appendix E: Summary of the health effects information for LPGs and 1,3-butadiene

During the categorization exercise, LPGs under two Chemical Abstracts Service Registry Numbers (CAS RNs) 68476-85-7 and 68476-86-8 were identified as priorities for assessment, as they met the categorization criteria under subsection 73(1) of CEPA and/or were considered as a priority based on other human health concerns. These substances were included in the Petroleum Sector Stream Approach (PSSA) because they are related to the petroleum sector and are complex combinations of hydrocarbons.

LPGs are produced by petroleum facilities (i.e., refineries or natural gas processing facilities) and are a category of light, predominantly saturated, hydrocarbons (mainly C1 to C7). However, the LPGs used in consumer products are predominantly C3 and C4 hydrocarbons. LPGs from refineries may contain unsaturated hydrocarbons, such as propene and butenes. The composition of LPGs varies depending on the sources (e.g., natural gas, crude oil), as well as process operating conditions and processing units used. In order to predict overall behaviour of these complex substances for the purposes of assessing the potential for ecological effects, representative structures have been selected from each chemical class in the substances.

LPGs are used primarily as domestic and industrial fuels, as feedstocks, and as aerosol propellants in products available to consumers. It has been recognized that, given the physical-chemical properties of these substances (i.e., gases with high vapour pressures), releases of LPGs into the atmosphere can occur.

Based on the available information, exposure to LPGs by organisms is considered to be mainly through air (e.g., inhalation). Considering the low toxicities of the components of LPGs to organisms via air for non-cancer endpoints, and low predicted exposure relative to those toxicities, there is a low risk of harm to organisms and the broader integrity of the environment from LPGs. It is concluded that these two LPGs (CAS RNs 68476-85-7 and 68476-86-8) do not meet the criteria under paragraphs 64(a) and (b) of CEPA, as they are not entering the environment in a quantity or concentration or under conditions that have or may have an immediate or long-term harmful effect on the environment or its biological diversity or that constitute or may constitute a danger to the environment on which life depends.

A critical human health effect for the initial categorization of these two LPGs was carcinogenicity, as the European Union has identified petroleum and refinery gases containing 1,3-butadiene at concentrations equal to or greater than 0.1% by weight as carcinogens. 1,3-Butadiene has been identified by Health Canada and several international regulatory agencies as a carcinogen and was added to the List of Toxic Substances in Schedule 1 of CEPA. 1,3-Butadiene was found to be a multi-site carcinogen in rodents, increasing the incidence of tumours at all inhalation concentrations tested. 1,3-Butadiene also exhibits genotoxicity in vitro and in vivo, and a plausible mode of action for induction of tumours involves direct interaction with genetic material.

The general population may be exposed to LPGs through various aerosol products available in the Canadian marketplace that use LPGs as propellants. For characterization of risk of potential long-term inhalation exposure to aerosol products containing LPGs, a margin of exposure was derived based on 1,3-butadiene indoor air levels in non-smoking homes located in four Canadian cities. Compared with the cancer potency of 1,3-butadiene, the margin of exposure is considered adequate to address uncertainties related to health effects and exposure. This approach is considered conservative as multiple sources are likely to contribute to indoor air levels of 1,3-butadiene.

The general population living in the vicinity of LPG cylinder tank filling stations or LPG vehicle refuelling stations may also be exposed to LPGs. Margins of exposure were therefore derived based on potential long-term inhalation exposure to 1,3-butadiene arising from LPG releases during the fuel transfer process and are considered adequate to address uncertainties related to health effects and exposure.

A recent industry submission on testing 1,3-butadiene levels in selected gas streams at natural gas processing facilities indicates that the concentration of 1,3-butadiene was below the detection limit of 1 ppm in most of the samples tested. Based on the lines of evidence indicating a low level of 1,3-butadiene and the low hazard for other predominant gas components, the human health risks due to volatile emissions of petroleum and refinery gases including LPGs from natural gas processing facilities are considered to be low. Accordingly, emissions of LPGs from natural gas processing facilities are not identified as a source of exposure of concern.

On the basis of available information, 1,3-butadiene is considered to be present in these two LPGs when produced by petroleum refineries. These two LPGs are considered to contribute a portion of the 1,3-butadiene releases at petroleum refining facilities, as quantified in the previously published assessment on Site-Restricted Petroleum and Refinery Gases. In that assessment, it was determined that margins between high-end estimates of exposure to 1,3-butadiene and estimates of cancer potency for inhalation exposure to 1,3-butadiene were considered potentially inadequate to address uncertainties related to health effects and exposure.

Based on the contribution of these two LPGs to overall petroleum refinery emissions, it is concluded that these two LPGs (CAS RNs 68476-85-7 and 68476-86-8) meet the criteria in paragraph 64(c) of CEPA as they are entering or may enter the environment in a quantity or concentration or under conditions that constitute or may constitute a danger in Canada to human life or health.

It is concluded that these two LPGs (CAS RNs 68476-85-7 and 68476-86-8) meet one or more of the criteria set out in section 64 of CEPA.

Pursuant to sections 68 and 74 of the Canadian Environmental Protection Act, 1999 (Canada 1999) the Minister of the Environment and the Minister of Health conduct screening assessments of substances to determine whether these substances present or may present a risk to the environment or to human health.

A key element of the Government of Canada's Chemicals Management Plan (CMP) is the Petroleum Sector Stream Approach (PSSA), which involves the assessment of approximately 160 petroleum substances that are considered high priorities for action. These substances are primarily related to the petroleum sector and are considered to be of Unknown or Variable composition, Complex reaction products or Biological materials (UVCBs).

The high-priority petroleum substances fall into nine groups of substances based on similarities in production, toxicity and physicochemical properties (Appendix A). In order to conduct the screening assessments, each high-priority petroleum substance was placed into one of five categories ("streams"), depending on its production and uses in Canada:

• Stream 0: substances not produced by the petroleum sector and/or not in commerce;
• Stream 1: site-restricted substances, which are substances that are not expected to be transported off refinery, upgrader or natural gas processing facility sites^Footnote1;
• Stream 2: industry-restricted substances, which are substances that may leave a petroleum-sector facility and may be transported to other industrial facilities (for example, for use as a feedstock, fuel or blending component), but that do not reach the public market in the form originally acquired;
• Stream 3: substances that are primarily used by industries and consumers as fuels;
• Stream 4: substances that may be present in products available to the consumer.

An analysis of the available data determined that 67 high-priority petroleum substances may be present in products available to consumers under Stream 4, as described above. These 67 substances were further sub-grouped as follows, based on their physical and chemical properties and potential uses: aromatic extracts, gas oils, heavy fuel oils, low boiling point naphthas, natural gas condensates, solvents, petroleum and refinery gases, base oils, petrolatum and waxes, and asphalt. Forty site-restricted petroleum and refinery gases were previously assessed under Stream 1, four were assessed under Stream 2, and two are assessed herein under Stream 4 (as described above).

This screening assessment addresses two substances. These liquefied petroleum gases (LPGs) were identified as priorities for assessment, as they met the categorization criteria under section 73 of CEPA and/or were considered a priority based on human health concerns. These substances were included in the PSSA because they are related to the petroleum sector and are complex mixtures.

According to information submitted under section 71 of CEPA (Environment Canada 2009, 2012), an in-depth literature review and a search of available material safety data sheets (MSDS), these substances can be transported between industrial facilities and they are present in products available to consumers.

An analysis of exposure to LPG exhaust or combustion by-products from its use as a fuel is outside the scope of this assessment, as consideration of the contribution of fuel combustion to air pollution is assessed under different programs within the Government of Canada.

Screening assessments focus on information critical to determining whether substances within a grouping meet the criteria as set out in section 64 of CEPA, by examining scientific information to develop conclusions by incorporating a weight of evidence approach and precaution^Footnote2.

This screening assessment includes consideration of information on chemical properties, environmental fate, hazards, uses and exposure, including additional information submitted by stakeholders. Relevant data were identified up to February 2014 . Empirical data from key studies as well as some results from models were used to reach conclusions. When available and relevant, information presented in assessments from other jurisdictions was considered.

The screening assessment does not represent an exhaustive or critical review of all available data. Rather, it presents the most critical studies and lines of evidence pertinent to the conclusion.

This screening assessment was prepared by staff in the Existing Substances Programs at Health Canada and Environment and Climate Change Canada and incorporates input from other programs within these departments. The human health and ecological portions of this assessment have undergone external written peer review/consultation. Comments on the technical portions relevant to human health were received from scientists selected by Toxicology Excellence for Risk Assessment, including Dr. Susan Griffin (U.S. Environmental Protection Agency), Dr. Calvin Willhite (Risk Sciences International & McLaughlin Centre for Population Health Risk Assessment), Dr. Donna Vorhees (Boston University School of Public Health) and Mr. Robert Lee (Neptune and Company Inc.). While external comments were taken into consideration, the final content and outcome of the screening assessment remain the responsibility of Health Canada and Environment and Climate Change Canada.

The critical information and considerations upon which the screening assessment is based are summarized below.

LPGs are a category of petroleum light hydrocarbons produced from the extraction of natural gases or the refining of crude oils (Benz et al. 1960; Barber 2006; Thompson et al. 2011; Wiley 2007). These substances are gaseous at ambient temperature and pressure, but can be liquefied under pressurized or cooling conditions to be conveniently stored or transported (CONCAWE 1992; Thompson et al. 2011). LPGs are similar in composition to site-restricted (Stream 1) and industry-restricted (Stream 2) petroleum and refinery gases, which have been assessed by the Government of Canada (Environment Canada, Health Canada 2013, 2014a).

Below are generic CAS RN descriptions for 68476-85-7 and 68476-86-8 (NCI 2009). A general substance identity for these CAS RNs is given in Table B-1 in Appendix B. It is recognized that globally different companies may use CAS RNs according to individual preferences and internal precedent.

CAS RN 68476-85-7 is a complex combination of hydrocarbons produced by the distillation of crude oil. It consists of hydrocarbons having carbon numbers predominantly in the range of C₃-C₇ and boiling in the range of approximately -40°C to 80°C.

CAS RN 68476-86-8 is a complex combination of hydrocarbons obtained by subjecting liquefied petroleum gas mix to a sweetening process to convert mercaptan or to remove acidic impurities. It consists of hydrocarbons having carbon numbers predominantly in the range of C₃ through C₇ and boiling in the range of approximately -40°C to 80°C.

Available information indicates that the hydrocarbon range and compositional proportion in the LPGs described by these two CAS RNs can vary significantly. The composition of LPGs varies depending on the types of natural gas or crude oils, process operating conditions, seasonal process issues and economic cycles ; they may contain hydrocarbons from C1 to C8 (Barber 2006; U.S. EPA 2010). Based on limited historical sampling data (1992 -2002) from several U.S. refineries primarily processing heavy sour crude oils from South America, the substances identified under CAS RNs 68476-85-7 and 68476-86-8 can contain hydrocarbons ranging from C₁ to C₈, but predominantly C₁ to C₇ (Petroleum HPV 2009a; U.S. EPA 2010).

LPGs are often simply defined as a mixture of propane and butanes. Statistics Canada (2013a,b) defines LPGs as propane, butane or a combination of the two whereas natural gas liquids (NGLs) are a mixture of ethane, propane and butane from gas plants. The National Energy Board (NEB) defines LPGs as a term for propane and butane whereas NGLs is a term for light hydrocarbons extracted from natural gas, including ethane, propane, butane and pentanes plus (NEB 2013). Similarly, the Canadian Association of Petroleum Producers (CAPP) defines LPG as consisting primarily of propane or butanes or a propane and butane mixture (CAPP 2013).

In addition to saturated hydrocarbon components, the LPGs from petroleum refining processes (e.g., cracking) may contain unsaturated hydrocarbons, such as propene, butenes and dienes (Benz et al. 1960; CONCAWE 1992; Thompson et al. 2011; Wiley 2007). There are limited data on the 1,3-butadiene content of the LPGs under the CAS RNs identified in this screening assessment report. One recent report by Petroleum HPV (2009a) presents a 1,3-butadiene level ranging from 0 to 0.1% w/w for CAS RNs 68476-85-7 and 68476-86-8. A search of MSDS indicates that the 1,3-butadiene level can vary from 0 to 0.3% w/w in LPGs used as a refinery feedstock (Valero 2012). 1,3-Butadiene was selected as a high hazard component in the Stream 1 and Stream 2 petroleum and refinery gases screening assessments (Environment Canada, Health Canada 2013, 2014a).

Although the substances identified under CAS RNs 68476-85-7 and 68476-86-8 can contain hydrocarbons ranging from C₁ to C₈, LPGs used in the public market with a narrow hydrocarbon range can be identified under the same CAS RNs. Available information indicates that, compared to the composition of LPGs produced at petroleum facilities, LPGs used in products available to consumers often consist of a much narrower hydrocarbon range, predominantly C₃ to C₄, i.e., propane, butanes, propene, butene, and their mixtures (Benz et al. 1960; Lewis 2007; Pohanish 2008; Petroleum HPV 2001, 2009a; Wiley 2007; Thompson et al. 2011). The presence of light hydrocarbons (less than C₃) in the final products should be avoided to enhance the capability of being liquefied under moderate conditions (pressurized or refrigerated). Similarly, the amount of higher hydrocarbons (greater than or equal to C₅) should be minimized to avoid over-condensation in the gas lines or products (e.g., aerosol products). Due to such specifications, potential exposure to benzene and hexane in the LPG end products is therefore not expected (Petroleum HPV 2001, 2009a). Trace amounts of odourants (e.g., mercaptan substances) may be added in the end-use LPG products as a safety precaution to enhance leak detection (CONCAWE 1992).

LPGs used as aerosol propellants usually consist of only propane, n-butane and isobutane with little or no unsaturated hydrocarbons (Barber 2006; Diversified CPC International 2012). In some MSDS, CAS RN 68476-85-7 or CAS RN 68476-86-8 is used to refer to isobutane, or a mixture of propane and isobutane, or a combination of propane, n-butane and isobutane (Farnam Companies 2007; Magic American Products 2008; LPS Laboratories 2008; GOJO Industries 2010; Petro-Canada Lubricants Inc. 2011).

LPGs used as home heating and cooking fuel or automotive fuel consist primarily of propane and butane (Lee et al. 2002; Gasca et al. 2004; Bozkurt et al. 2008). The mixture ratio varies among countries and/or climates. A larger quantity of propane can be added in winter (Bozkurt et al. 2008; Na and Kim 2001).

For LPGs used as a transportation fuel, propane, n-butane and isobutane are the major components, with the remaining minor components consisting of pentanes, alkenes, ethane and hexanes. However, their composition can vary significantly depending on their origin. Blake and Rowland (1995) compared the composition of LPGs as a vehicle fuel from Mexico City collected in February 1993 to one from Los Angeles collected in April 1995. The authors reported that the LPG vehicle fuel from Mexico City contained approximately 0.26% w/w propene, 5% w/w butenes and 0.1% w/w 1,3-butadiene. In contrast, the sample from Los Angeles showed 1.6% w/w of propene and less than 0.01% w/w of butenes and 0.01% w/w of 1,3-butadiene. Na et al. (2004) also compared LPGs used as a vehicle fuel from Korea, the United States, Egypt and Mexico. LPGs from Korea and the United States had a higher content of propane, whereas LPGs from Egypt and Mexico had a higher level of butanes. On the basis of 13 samples of LPG fuels collected from different distribution centres in Mexico City, Gamas et al. (2000) reported that C1 to C6 paraffins accounted for 98.9 mol% (~98.8% w/w) with the remaining as propene at 0.49 mol% (~0.41% w/w), isobutene at 0.62 mol% (~0.7% w/w) and 1,3-butadiene at 0.02 mol% (~0.02% w/w).

The information considered in this screening assessment represents the typical characteristics of LPGs. LPGs may also contain ethene . Since releases of ethene from the petroleum sector have been addressed in a separate screening assessment (Environment Canada, Health Canada 2014b), it is not further considered in this assessment.

As shown in Table 3-1, the vapour density of LPGs is higher than that of air. This means that LPGs are heavier than air and can settle in low points and may accumulate in confined spaces in the case of a leak. In addition, due to their low boiling points, once released into the atmosphere, liquid LPGs in contact with the skin can cause cold burns due to rapid evaporation (CONCAWE 1992).

LPGs are gaseous at environmentally relevant temperatures and, if released to the environment, they will quickly disperse and separate. The C5 alkane, alkene and cyclic components that are liquids at ambient temperatures have high vapour pressures, so they will also evaporate quite readily from soil or water.

To predict the environmental behaviour and fate of LPGs, representative structures were chosen from each chemical class contained within the mixture (Table B-2 in Appendix B). Give that the types of petroleum hydrocarbons found in petroleum and refinery gases are similar to those found in LPGs, representative structures similar to the petroleum and refinery gases were used. Petroleum and refinery gases are mainly composed of C₁-C₆ hydrocarbons, which can be alkanes, isoalkanes, alkenes, cycloalkanes, cycloalkenes, dienes and cyclodienes. These components are all well-understood simple structures. The proportion of each component for a particular CAS RN can be highly variable within a facility or among different facilities; this makes prediction of the physical and chemical properties of such substances inexact. Detailed physical-chemical properties of the individual selected representative structures are given in Table B-2 (Appendix B).

The LPGs considered in this screening assessment are produced in petroleum facilities. Raw gas extracted at the wellheads of natural gas, condensate or oil wells is delivered to gas processing facilities for further purification and separation into individual products (e.g., natural gas, ethane, LPGs, condensates). According to a literature search and information submitted under section 71 of CEPA, LPGs can be produced from natural gas processing facilities as well as from various crude oil treatment processes in petroleum refineries, such as distillation, cracking or reforming . LPGs can also be generated from plants located near the main natural gas pipeline network, with any LPGs remaining in the natural gas being recovered (Purvin & Gertz 2007). Some stand-alone fractionation plants can separate raw gas streams into individual LPG products (e.g., propane/butane mixture) for commercial markets (Cheminfo 2009).

According to information submitted under section 71 of CEPA (Environment Canada 2012), in 2010, the total quantity of LPGs manufactured in Canada under CAS RNs 68476-85-7 and 68476-86-8 was between 1 and 10 million tonnes, the total imported quantity was between 10000 and 100000 tonnes, and the total transport and export quantities were both less than 1 million tonnes.

In addition to the information submitted under section 71 of CEPA, other production data on LPGs in Canada and worldwide were also considered. Statistics Canada (2013c) reported that the total production volume of LPGs from refineries was approximately 2.2×10⁶ m³ (~ 1 million tonnes) in 2010. The total production of NGLs from natural gas processing facilities, including ethane, propane and butane, was approximately 2.8×10⁷ m³ (more than 10 million tonnes) in 2010. However, these data may not be specific to the two CAS RNs identified in this screening assessment report. In the United States, each of the two CAS RNs, are considered to be high production volume (HPV) chemicals, having been reported to have a total production and/or import volume of 1 billion lb. (~ 0.45 million tonnes) or greater (U.S. EPA 2010). Similarly, both CAS RNs have been identified by the Organisation for Economic Co-operation and Development (OECD) as HPV chemicals, with 1000 tonnes or more produced per year (OECD 2004). In 2009, the global production of LPGs was 244 million tonnes with North America as the major producer (24% of total production) (Thompson et al. 2011). In North America, 60% of LPG production was from natural gas processing with the remainder from petroleum refineries.

LPGs have widespread uses in industry, transportation, commerce, residences and agriculture. According to information submitted under section 71 of CEPA (Environment Canada 2012) as well as information gathered during an additional public literature search, the LPGs identified under CAS RNs 68476-85-7 and 68476-86-8 are used as a feedstock for chemical plants and petroleum refineries, domestic fuel, as well as a propellant in various types of aerosol products, including industrial blowing agents, lubricants, paints and coating products, household cleaning products, fabric treatments, automotive care products, adhesives and sealants, hair spray products, and pesticides.

One major use identified from the literature and the section 71 submission is as a chemical feedstock. For example, LPGs are used as a raw material for production of ethene, or are used to produce butane that is further blended into gasoline to increase the volatility and octane number of the fuel (CONCAWE 1992; Competition Commission 2006; Wiley 2007; Cheminfo 2009; Thompson et al. 2011). In the United States, about 35% of total LPG consumption is as a feedstock for the petrochemical industry (Wiley 2007). LPGs can also be used directly (without blending) as a high-quality fuel in industry for heating, cutting or soldering (Sullivan 1992; Thompson et al. 2011).

LPGs are used as a fuel for heating or cooking in Canada and other countries. As an end-use, LPGs are often stored in cylinders, as a convenient or mobile source for small domestic appliances such as portal space heaters, cookers, blow lamps, camping equipment and cigarette lighters (Ames and Crowhurst, 1988; Barber 2006; AFROX 2013). In Canada, LPGs are used as a fuel for barbecue tanks or for refrigerators in recreational vehicles where electricity is unavailable (Enviroharvest 2012). LPGs are also used for crop drying and powering farm equipment (Sullivan 1992; Competition Commission 2006).

LPGs are used as an alternative automotive fuel to lower vehicle exhaust emissions in some countries. In 1994, there were approximately 140 000 LPG-driven vehicles in Canada (Liu et al. 1997). More recently, LPGs have become the least competitive transportation fuel as compared to conventional fossil fuels. The number of LPG-driven fleets in Canada declined substantially, and by 2010, there were no LPG-driven passenger vehicles used in Canada (Transport Canada 2010; World LP Gas Association 2012). However, commercial taxi fleets, front-line police vehicle fleets, para-transit service fleets and mail courier company fleets in Canada still use propane or LPGs as fuels (Propane Facts 2008; Wheels.ca 2013). Some terms, such as "autogas", "liquefied petroleum gases", "liquefied propane gases", "auto propane" and "propane fuel " are sometimes used interchangeably when referring to motor fuels. The ratio of propane to butane in LPG motor fuels can vary from 20/80 up to 100% propane only (Beer et al. 2006). For example, HD5 is one special type of engine fuel, consisting predominantly of propane (> 90 % v/v). LPGs are also used as a vehicle fuel by non-road vehicles (e.g., fork lift trucks) (Sullivan 1992; Competition Commission 2006).

LPGs are also found as a propellant in a variety of aerosol products available to consumers, including household cleaners, hair spray products, fabric treatment products, adhesives and paints. In addition, CAS RNs 68476-85-7 and 68476-86-8 are used as a propellant in pesticides, in therapeutic products and in the manufacturing of a coating material for food packaging in Canada. CAS RN 68476-86-8 is present as a formulant at 6 to 10 % by weight in three chemical sanitizers and one insecticide in Canada (a propane-butane mix) with a 1,3-butadiene level of less than 0.1% by weight (personal communication with Health Canada's Pest Management Regulatory Agency Feb. 2011 and Sept. 2013). In Canada, CAS RN 68476-85-7 was listed in the Therapeutic Products Directorate's internal non-medicinal ingredients database as a non-medicinal ingredient used as a propellant in disinfectant products (for hard surface) (personal communication with Health Canada's Therapeutic Product Directorate, May 2010). CAS RN 68476-85-7 has also been identified as a processing aid in Canada for manufacturing a coating used in food packaging, and no direct contact of residues of CAS RN 68476-85-7 with food is expected (personal communication with Health Canada's Food Directorate, June 2013).

The composition of LPGs (even under the same CAS RN) varies depending upon the products they are used for. For example, the product used for domestic heating is primarily composed of propane (U.S. EPA 2008a), whereas high-grade or refined LPGs used for laboratory work and as an aerosol propellant contain predominantly propane and butane (Barber 2006; CONCAWE 1992; Hartop et al. 1991; U.S. EPA 2008a; Thompson et al. 2011). The CAS RNs 68476-85-7 and 68476-86-8 noted in MSDSs for aerosol consumer products often refer to propane, butanes or a combination of the two (Farnam Companies 2007; Magic American Products 2008; LPS Laboratories 2008; GOJO Industries 2010; Petro-Canada Lubricants Inc. 2011).

Potential releases of LPGs include releases within facilities from activities associated with their production and processing, releases related to their transportation between industrial facilities, and release during consumer uses.

Following production at natural gas processing facilities or petroleum refineries, LPGs are liquefied under pressurized or refrigerated conditions for storage or transportation as a final LPG product. Traditionally, large quantities of LPGs are transported under pressurized conditions by pipeline, rail, truck and ship to large-scale LPG users (e.g., industrial facilities, large commercial users ) or to distribution terminals of wholesalers. From the large distribution terminals, the LPGs can be transported in pressurized road tankers to other LPG suppliers or to secondary or local distribution depots for retail sale. Small quantities of LPGs can then be delivered in specially-designed pressurized cylinders, such as barbecue tanks, to domestic end-users (Sullivan 1992; Barber 2006; Thompson et al. 2011; Wiley 2007). The potential release of LPGs can occur at any point in the LPG distribution chain, as well as from end-use products. These releases are expected to be directly to air , with any potential spills to water or soil expected to evaporate quickly if they occur . Exposure is therefore considered solely via air.

With such a high volatility, LPGs released into the environment will rapidly disperse in the atmosphere and are unlikely to cause ground or water pollution (CONCAWE 1992). The general physical and chemical properties of LPGs indicate that if released, their vapour can accumulate in low-lying areas as LPGs are heavier than air.

LPGs are not reportable under either the Canadian National Pollutant Release Inventory (NPRI 2013 ) or the U.S. Toxics Release Inventory (TRI 2013).

Petroleum facilities are highly regulated under various jurisdictions, and voluntary non-regulatory measures implemented by the petroleum industry are in place to manage potential releases (SENES 2009). Regulatory and non-regulatory tools are in place to prevent or reduce potential releases (both controlled and unintentional releases) of petroleum substances from petroleum facilities, including the LPGs identified in this screening assessment.

Despite the fact that some measures and practices are in place to reduce releases of petroleum substances within facilities, it has been recognized that fugitive releases of LPGs into the atmosphere can occur from compressor seals, processing valves, flanges etc., due to the much higher volatility (lower boiling point) and higher mobility of gases compared with liquids (U.S. EPA 1995; CAPP 2007; CPPI 2007; CCME 1993). Fugitive releases tend to occur more frequently when processing equipment is not properly maintained or operated and could go undetected or unfixed for periods ranging from days to months (CCME 1993; CAPP 2007). Once released, LPGs disperse quickly into the air.

Therefore, there is a potential for exposure of the general population and the environment in the vicinity of petroleum sector facility sites to LPGs. Detailed analysis of human exposure was conducted using a gas dispersion model (see the Potential to Cause Harm to Human Health section).

Due to their flammability and volatility, special requirements are needed for storing and handling LPGs. LPGs are usually stored under pressurized conditions (Purchon 1980; Thompson et al. 2011; Wiley 2007). The equipment for storing LPGs is fabricated according to appropriate codes with additional requirements for inspection, safety considerations and emergency guidelines. The Liquefied Petroleum Gases Bulk Storage Regulations made under the Canada Transportation Act set out standards for the placement of storage tanks, and additional requirements for the storage equipment, inspection, safety considerations and emergency guidelines (Canada 2013). Individual provinces can also have legislative requirements for the transport and storage of LPGs. As a result of stringent requirements for the design and operation of such pressurized storage systems, the potential for evaporative emissions of gaseous substances has been reduced (OECD 2009). The potential exposure of the general population to any release from the pressurized storage of LPGs, under normal operating conditions, is therefore considered to be minimal and is not assessed further in this report.

In addition to potential unintentional on-site releases, releases may also occur during the transportation of LPGs between facilities. In general, three operating procedures are involved during the process of transportation: loading, transit and unloading. Loading and unloading of LPGs are normally conducted on industrial sites. To reduce the transported volumes and the potential for release, gases are normally transported as liquids through pressurized pipelines (Environment Canada 2009) or in pressurized containers (Noyes 1992; Kraus 1998; Miesner and Leffler 2006; Environment Canada 2009). Releases from pipeline loading and unloading processes are considered as part of operational releases by the National Energy Board (NEB 2008a, b). Pipeline loading is associated with pumping a liquid or compressing a gas stream into a pipeline system. Loading operations occur at an inlet station where storage tanks, pumps or compressors are normally located. Unloading operations occur at an outlet station where liquid streams may enter into tanks, but gas streams can enter directly into a distribution network.

Apart from the releases from loading and unloading processes, the potential releases from auxiliary pipeline components are also part of the operational releases defined by NEB (2008a,b). The auxiliary components include pump/compressor stations located along the pipelines to assist the movement of products through the pipelines and valve stations equipped along the pipelines for pipeline protection and maintenance.

No equations or data are available with respect to evaporative emissions from loading LPGs into pressurized vessels. The U.S. EPA's AP 42 (U.S. EPA 2008a) states that "High-pressure storage tanks can be operated so that virtually no evaporative or working losses occur. No appropriate correlations are available to estimate vapour losses from pressure tanks". Due to the high safety and inspection standards generally applied to pressurized pipeline and container systems, regular releases from these types of pressurized systems are unlikely under normal operating conditions (European Commission 2006; U.S. EPA 2008a; OECD 2009). Therefore, only releases from pipelines are considered in this screening assessment. The potential sources of release to the environment are from unintentional leaks that occur during processing, handling and transport. These substances are gaseous at environmentally relevant temperatures, so ambient air is considered to be the primary receiving medium for all releases of LPGs.

Further details on potential releases of LPGs from pipelines have been addressed in a previous assessment on industry-restricted petroleum and refinery gases (Environment Canada, Health Canada 2011). Pipeline releases of industry-restricted petroleum and refinery gases were found not to be a concern for environmental exposure in that assessment. LPGs belong to the petroleum group "petroleum and refinery gases" and have similar composition and properties as those previously assessed. Due to the nature of the available information used in the assessment of industry-restricted petroleum and refinery gases (Environment Canada, Health Canada 2014a), the estimate of releases from pipelines was not restricted to the CAS RNs covered by the assessment, but instead covered all petroleum and refinery gases, including the LPGs being assessed herein. Thus, releases of LPGs from pipelines are not considered further in this assessment.

For fuel uses, such as refuelling LPG-powered vehicles or filling a LPG barbecue tank, transferring of LPGs into a pressurized container is commonly required. Due to the high mobility and volatility of gaseous substances, there is a potential for releases of LPGs during the filling/handling process from nozzle disconnection or outage/bleeder vapour valves (to indicate whether the 80% capacity limit is reached) (Sullivan 1992; Purchon 1980).

Sullivan (1992) estimated the emissions of LPGs associated with LPG transfer operations (e.g., filling LPGs into cylinders or small storage tanks or vehicles) in several different use categories, including agricultural, commercial, engine fuel, industrial and residential , as well as from LPG distribution systems in California. The LPGs were mainly composed of propane with a small amount of butane. In this study, an average of 0.064 % v/v of total LPG used was emitted into the atmosphere from transfer processes. Based on the quantity used in each use category, the emissions from engine fuel use were approximately 0.101 % v/v, with emissions ranging from 0.044 to 0.057 % v/v for the remaining five categories.

Similarly, Sosa et al. (2009) reported that fugitive releases of LPGs, due to handling and transfer processes, contributed to ambient air levels of propane and butanes. Gasca et al. (2004) examined the contribution of LPG emissions to ambient air due to domestic combustion, fugitive emissions from cylinder distribution, and leaks from domestic appliances.

For LPG-driven vehicles, Gasca et al. (2004) and Schifter et al. (2000) examined evaporative emissions that originate from LPG fuel trapped between the vapourizer and the mixing system once the engine is stopped. The vapour consists of 43% w/w propane, 49% w/w butanes (n-butane and isobutane), 1% w/w pentane, and 1.5% w/w alkenes with no 1,3-butadiene identified at the detection level.

Potential long-term exposure to LPG releases from the fuel transfer process (e.g., refuelling LPG-powered vehicles or refilling LPG barbecue tanks) is considered in the Potential to Cause Harm to Human Health section.

The bulk of the substances identified as components of LPGs are gaseous at environmentally relevant temperatures and, if released to the environment, they will volatilize and escape into ambient air.

C1-C6 alkanes have boiling points from -162 to 69°C. The individual components of LPGs are characterized by moderate water solubilities (9.5 to 735 mg/L), very high vapour pressures (2.0×10⁴ to 6×10⁷ Pa), very high Henry's Law constants (7.5×10³ to 1.8×10⁵ Pa·m³/mol), low log K_ow values (1.1 to 3.9) and low to moderate log K_oc values (1.6 to 3.4) (Table B-2 in Appendix B).

If released to air, all components of LPGs are expected to remain in air, as they are highly volatile.

Based on the water solubility of these components (9.5 to 735 mg/L), if a release occurs to water, these components would dissolve in water. However, volatilization from water is expected to occur quickly given their high vapour pressures and high Henry’s Law constants . The majority of LPGs are composed of propane, butane and isobutane, and each of these components are highly volatile and will volatilize quickly from water. LPGs are not expected to sorb significantly to suspended solids and sediments given their low to moderate estimated log K_oc values (Table B-2 in Appendix B).

If released to soil, the alkanes and alkenes are expected to volatilize. Most components of LPGs are expected to have low to negligible sorption to soil (i.e., expected to be highly mobile) given their low to moderate estimated log K_oc values and high vapour pressures. If released to moist soil surfaces, these components are expected to volatilize given their high to very high Henry's Law constants and vapour pressures.

No empirical data on the persistence of LPGs were found. Because LPGs have similar components as the industry-restricted petroleum and refinery gases, assessed previously, data on the environmental persistence of industry-restricted petroleum and refinery gases were used in the determination of persistence for LPG components (Environment Canada, Health Canada 2011).

Based on Environment Canada, Health Canada (2011), the atmospheric half-lives of most components, including propane, butane and isobutane, of these LPGs are greater than or equal to 2 days via reactions with hydroxyl. In contrast, they have relatively short half-lives in water, soil and sediments and therefore are not expected to persist in these media for long durations.

No experimental bioaccumulation factor (BAF) or bioconcentration factor (BCF) for consumer-related LPGs or their components were found. Therefore, as LPGs consist of similar components as petroleum and refinery gases, data on the bioaccumulation potential of industry-restricted petroleum and refinery gases were used in the determination of bioaccumulation of LPG components (Environment Canada, Health Canada 2011). A predictive approach was applied using available BAF and BCF models.

Based on the available kinetic-based modelled values (Environment Canada, Health Canada 2011), the components of LPGs have very low bioaccumulation potential (BAF/BCF less than 200 L/kg).

Terrestrial organisms may be exposed to LPGs through air. Toxicity data for rodents were available for LPGs and components of LPGs (Appendix E), and toxicity data for terrestrial organisms to 1,3-butadiene, a component of LPGs, were also available in Canada (2000).

Experimental data available on effects via inhalation in laboratory animals indicate that LPGs have very low acute, subchronic, reproductive, developmental and neurological toxicity to rodents (lowest observed adverse effect concentration (LOAEC) greater than 500000 mg/m³; Table E-1, Appendix E).The major components of LPGs also have very low acute toxicities to rodents (LC50s greater than 100000 mg/m³), as summarized in Appendix E. Small mammals are also not especially sensitive to these major components over longer periods of time , with reproductive and developmental LOAECs in rodents above 7000 mg/m³.

1,3-Butadiene, a minor component of LPGs, was identified as the component of LPGs having the highest toxicity. Exposure to 1,3-butadiene for 7h caused a depletion of cellular non-protein sulfhydryl content of liver, lung or heart in mice, with a lowest-observed-effect level (LOEL) of 100 ppm (221 mg/m³) (Deutschmann and Laib 1989). In a 2-year study conducted by the U.S. National Toxicology Program (NTP1993), there was a significant increase in the incidence of ovarian atrophy in female mice exposed for up to 2 years to all concentrations tested (i.e., greater than or equal to 6.25 ppm [greater than or equal to 13.8 mg/m³]).1-3-Butadiene has low toxicity to plants, with low to no adverse effects reported when plants were exposed to 1,3-butadiene at 2210 mg/m³ for 7 days (Heck and Pires 1962). When exposed for 21 days, no adverse effects were observed at 22.1 mg/m³ (Heck and Pires 1962).

Due to the much greater toxicity of 1,3-butadiene to mammals compared to other components of LPGs, 1,3-butadiene is used to estimate the risk of LPGs to the environment from atmospheric exposure to LPGs. The chronic lowest observed adverse effect level (LOAEL) for rodents of 13.8 mg/m³ (13800 μg/m³) (NTP 1993) will be used as the chronic critical toxicity value (CTV) for the terrestrial toxicity of LPGs.

Based on the high volatilization from aquatic environments, an aquatic exposure scenario was not developed. Two exposure scenarios for terrestrial mammals via chronic inhalation were developed: exposure due to unintentional releases from petroleum facilities and exposure near filling stations. Due to the significantly higher toxicity of 1,3-butadiene to mammals compared to other LPG components, 1,3-butadiene concentrations in the environment were estimated for exposure.

Estimated concentrations of 1,3-butadiene in air as determined in the human health section (section 10.1.1 for releases from petroleum facilities and section 10.1.3 for releases from filling stations) were used. Annual concentrations were estimated at various distances from these facilities. The highest annual concentrations estimated for any distance from the petroleum facilities and from filling stations are used here as worst-case scenarios for chronic exposure from these facilities. For releases from petroleum refining facilities, the highest annual concentration of 1,3-butadiene was 0.44 µg/m³ at 200 m (Table C-2, Appendix C). For releases from filling stations, the highest annual concentration of 1,3-butadiene was 0.86 µg/m³ at a distance of 10 m from the filling station (Table C-4, Appendix C).

The approach taken in this ecological screening assessment was to examine available scientific information and develop conclusions based on a weight-of-evidence approach as required under CEPA.

As these substances are composed of gases, exposure of aquatic organisms to these substances in the event that they are released to the aquatic environment is extremely unlikely due to their rapid volatilization from water.

In a scenario in which LPGs are released to soil via pipeline transport, these substances are not expected to remain in soil, but rather will partition readily to air. Therefore, an exposure scenario involving the release of LPGs to soil was not developed. Exposure to LPGs is most likely via inhalation. LPGs themselves, along with their major components, have very low acute (greater than 100000 mg/m³) and chronic (greater than 7000 mg/m³) toxicities via inhalation, such that it is highly unlikely that animals would be exposed to toxic concentrations. A minor component of LPGs, 1,3-butadiene, was identified as having much greater toxicity to organisms. However, estimated concentrations of 1,3-butadiene near petroleum facilities and filling stations are orders of magnitude below those that cause toxicity.

Therefore, based on the information presented in this screening assessment, the LPGs included in this screening assessment are unlikely to be causing ecological harm to organisms or the broader integrity of the environment. It is concluded that these LPGs (CAS RNs 68476-85-7 and 68476-86-8) do not meet the criteria under paragraphs 64(a) or 64(b) of the Canadian Environmental Protection Act, 1999 (CEPA) as they are not entering the environment in a quantity or concentration or under conditions that have or may have an immediate or long-term harmful effect on the environment or its biological diversity or that constitute or may constitute a danger to the environment on which life depends.

The proportions of each component in each LPG assigned a specific CAS RN are generally not known. LPG components fall within the C₁ to C₈ range, though the majority of components are in the C₃ to C₇ range. However, the low ecological toxicity of most of these components makes this information gap relatively unimportant for the assessment of ecological risk.

There is uncertainty concerning the exposure of terrestrial organisms to LPGs. As exposure information for LPGs from petroleum facilities and filling stations was not available, effect, exposure and risk for a high-hazard component of LPGs were characterized.

The general physical-chemical properties of LPGs indicate that when these substances are released they rapidly disperse into ambient air, and the individual components of LPGs will separate and partition in accordance with their own physical-chemical properties. As such, inhalation would be the primary potential route of exposure and is therefore the focus of the exposure assessment. Dermal and oral exposures are not expected to be significant routes of exposure.

1,3-Butadiene is a high-hazard component that is found in some LPG streams. An analysis of limited samples collected from U.S. refineries from 1992 to 2002 indicated the potential presence of 1,3-butadiene at up to 0.1% by weight (w/w) for the LPGs identified under CAS RNs 68476-85-7 and 68476-86-8 (U.S.EPA 2010). Information submitted under section 71 of CEPA indicates that for the individual substances butane and isobutane, the residual level of 1,3-butadiene ranged from non-detectable to less than 1% by weight but was typically below 0.1% by weight (Environment Canada 2007). 1,3-Butadiene is the basis for the classification of CAS RNs 68476-85-7 and 68476-86-8 as carcinogens by the European Union if the level of 1,3-butadiene is equal to or greater than 0.1% by weight (European Commission 2008a, 2009; European Union 2008).

Available information indicates that compared to LPGs consumed in industrial settings as feedstocks or industrial fuels, there is a narrower range of hydrocarbons in the LPGs used in marketplace products, especially when they are used as aerosol propellants. (Barber 2006; CONCAWE 1992; Hartop et al. 1991; U.S.EPA 2008a; Thompson et al. 2011). As a propellant or domestic fuel (that is, for use in cooking, heating or transportation), LPGs identified under CAS RNs 68476-85-7 and 68476-86-8 are often referred to as isobutane or a combination of propane, n-butane and isobutane (Magic American Products 2008; LPS Laboratories 2008; GOJO Industries 2010; Farnam Companies 2007). MSDSs searches for consumer aerosol products containing LPGs gave no indication of 1,3-butadiene above 0.1%. Furthermore, according to the information submitted under section 71 of CEPA (Environment Canada 2007), 1,3-butadiene has been reported to be present in butane and isobutane as a residual at a level of non-detectable to less than 1% by weight, with a typical level below 0.1% w/w. Therefore, one approach taken in this screening assessment considered that 1,3-butadiene may be present in LPGs as a residual of up to 0.1%w/w.

The annual average concentrations of 1,3-butadiene in ambient air have been reported by various sources as less than 0.05 μg/m³ and up to 0.4 μg/m³, depending on location. In general, automotive emissions are a major contributor to 1,3-butadiene levels in ambient air (Canada 2000). Curren et al. (2006) reported that the average annual 1,3-butadiene concentration at urban sites in Canada between 1995 and 2003 was 0.22 μg/m³. Additional monitoring data for 1990-2008 collected from the Clean Air Strategic Alliance data warehouse in Alberta (CASA 2008) indicate that the average annual concentrations in central Edmonton, east Edmonton and central Calgary were 0.33 μg/m³, 0.17 μg/m³ and 0.31 μg/m³, respectively. As reported by the National Air Pollution Surveillance Network (NAPS, 2012), the annual concentration of 1,3-butadiene in ambient air in 2009 ranged from 0.028-0.293 µg/m³ for rural and urban areas across Canada.

Additional Canadian studies were available that measured the levels of 1,3-butadiene in both outdoor air and indoor air in Windsor, Regina, Halifax and Edmonton during the summer and winter seasons (Health Canada 2010a, 2010b, 2012 and 2013). Indoor measurements were taken in the family or living rooms of selected residential homes and the concurrent outdoor measurements were taken in the backyards. The 45-48 non-smoking participant homes in Windsor were monitored between January 2005 and August 2006 with samples collected every 24h for five consecutive days. Personal air samples were also taken every 24h for five consecutive days in the 2005 study. Method detection limits (MDL) were 0.055 µg/m³ (2005) and 0.043 µg/m³ (2006) and 1,3-butadiene was detected in over 90% of the samples. In the Regina study, a total of 146 homes, of which 34 homes had at least one smoking participant, were monitored in both the winter and summer of 2007 with one 24-h sample and one 5-day sample collected from each household. The MDL was 0.05 µg/m³ and the detection frequency of 1,3-butadiene was 65% and 100%, based on the season that the air samples were taken. In the Halifax study, 50 non-smoking homes were monitored in both the winter and summer of 2009 with samples collected every 24h for seven consecutive days. The MDL was 0.022 µg/m³ and the detection frequency was 83% and 98%, based on the season of sampling. In the Edmonton study, 50 non-smoking homes were monitored in both the winter and summer of 2010 with samples collected every 24h for seven consecutive days. The MDL values were 0.018 µg/m³ (summer) and 0.017 µg/m³ (winter) and the sample detection frequency was above 95%.

The outdoor air measurements from the four Canadian studies showed that the levels of 1,3-butadiene for the winter monitoring periods could be up to twice as high as the summer measurements (Health Canada 2010a, 2010b, 2012, 2013). The 50^thpercentile concentrations of 1,3-butadiene from these studies ranged from 0.024 to 0.07 μg/m³, with 95^thpercentile values ranging from 0.025 to 0.385 μg/m³ (Health Canada 2010b). Such outdoor measurement values are in line with the other monitoring data across Canada (Curren et al. 2006; CASA 2007; NAPS 2012). For the assessment of risk of exposure to modelled emissions from a petroleum facility herein, an ambient background level of 0.22 μg/m³ 1,3-butadiene from Curren et al. (2006) was used as a benchmark, and is consistent with the background value selected in the Stream 1 petroleum and refinery gases assessment (Environment Canada, Health Canada 2013).

The indoor air measurements from the four Canadian studies showed the 50^thpercentile values of 1,3-butadiene from non-smoking homes to range from 0.04 to 0.134 μg/m³, and the 95^thpercentile values to range from 0.16 to 0.59 μg/m³ (Health Canada 2010a, 2010b, 2012, 2013). In comparison, a much higher level of 1,3-butadiene was observed from 34 homes with at least one smoker in the Regina study, as shown by the 50^thpercentile values of 0.947 μg/m³ (winter) and 0.657 μg/m³ (summer), with 95^thpercentile values of 4.577 μg/m³ (winter) and 9.177 μg/m³ (summer) (Health Canada 2010b).

Compared to the recent studies on selected homes in Windsor, Regina, Halifax and Edmonton, other older studies that measured the indoor air level of 1,3-butadiene have shown higher MDLs and lower detection frequencies. Zhu et al. (2005) measured the 24h indoor 1,3-butadiene levels from 75 residential houses in Ottawa, Canada from November 2002 to March 2003. The MDL was 0.32 µg/m³ and detection frequency was 32%. The authors reported a concentration range from below the MDL up to 3.65 µg/m³ with 1.64 µg/m³ as the 90^thpercentile. Weisel et al. (2008) also examined the 24h indoor air concentrations of 1,3-butadiene in 100 homes of suburban and rural areas of New Jersey, U.S. between December 2003 and April 2006 with MDLs of 0.44 to 1.1 µg/m³. Only 7 of 100 samples were tested above the MDL with a 95^th percentile of 1.3 µg/m³. The highest value was 4.4 µg/m³.

The indoor level of 1,3-butadiene in Canadian homes can be attributed to various sources including the use of aerosol products, possible vehicle exhaust from attached garages, and cooking activities (combustion by-products) (Canada 2000). For the purpose of assessing risk from potential long-term exposure to LPGs from the use of aerosol products inside the home, the highest 50^th percentile value of 1,3-butadiene for Canadian non-smoking homes was selected from air sampling studies conducted inside homes located in four Canadian cities. This level, 0.134 µg/m³, is derived from the Regina study (Health Canada 2010b) and is considered to represent a conservative indoor air level of 1,3-butadiene to which multiple sources contribute inside the home.

As discussed in the "Releases to the Environment" section, potential sources of releases of LPGs include unintentional fugitive releases from petroleum facilities, releases during transportation of the substances, releases from transfer of LPGs into pressurized containers (e.g., refuelling LPG vehicle fuel tanks or refilling barbecue tanks), as well as releases from products containing LPGs as aerosol propellants.

LPGs originate from petroleum refineries and natural gas processing facilities and thus upgraders are not included in this assessment. Like previously assessed Stream 1 and Stream 2 petroleum and refinery gases (Environment Canada, Health Canada 2013 2014a), LPGs are a portion of total petroleum and refinery gases generated from petroleum facilities. LPGs may disperse into the air in the vicinity of a facility via fugitive emissions from, for example, process equipment, valves and flanges. It is recognized that releases of LPGs represent a fraction of the total fugitive releases of petroleum and refinery gases from a petroleum facility, and it is not possible to determine the proportion of total releases that are LPGs. As such, total releases of all petroleum and refinery gases containing 1,3-butadiene were characterized in the Stream 1 petroleum and refinery gases screening assessment report (Environment Canada, Health Canada 2013) and, therefore, potential exposure of the general population living in the vicinity of a petroleum refinery or natural gas processing plant to unintentional releases of LPGs (identified under the CAS RNs 68476-85-7 and 68476-86-8 ) has already been considered. Given the potential presence of 1,3-butadiene in these two LPGs, fugitive releases of LPGs may contribute to 1,3-butadiene concentrations in ambient air in the vicinity of petroleum facilities.

A recent report describes a mobile method (the "Aerodyne Mobile Laboratory") that was used to detect and quantify industrial emissions, including 1,3-butadiene, from point sources (Knighton et al. 2012). However, detailed information on the estimation of total fugitive releases of 1,3-butadiene from petroleum and refinery gases at a facility in Canada was provided in the Stream 1 petroleum and refinery gases screening assessment report (Environment Canada, Health Canada 2013). SCREEN3, a tier-one air dispersion model developed by the U.S. EPA (SCREEN3 1996), was used to model the contribution of 1,3-butadiene to ambient air associated with petroleum facility fugitive releases. The results are adopted herein and are provided in Appendix C (Tables C-1 and C-2). A summary of the estimated total releases of 1,3-butadiene on which the conclusion is based is presented below.

The results of the modelled dispersion profile of 1,3-butadiene, based on distance from the release source, demonstrate that at 200 m, annual concentrations from all petroleum and refinery gases (including Stream 1 and Stream 2 petroleum and refinery gases and the LPGs in this report) contributed to ambient air by these facilities are approximately 0.44 μg/m³ on the high end (based on a ratio of 1,3-butadiene to benzene of 1:85 ) and approximately 0.17 μg/m³ on the low end (based on a ratio of 1,3-butadiene to benzene of 1:216). The modelled concentration decreases as the distance from the release source increases. It is estimated that for the high end ratio, the contribution of 1,3-butadiene to air associated with unintentional releases of the total petroleum and refinery gases will be equivalent to the average annual Canadian ambient urban air concentration of 0.22 μg/m³ at a distance of 500 m from the release source. For the low end ratio, the estimated contribution of 1,3-butadiene to air from unintentional releases of petroleum and refinery gases is 0.088 μg/m³ at 500 m from the release source. Map analysis has determined that the general population may reside approximately 200 m from a potential source of release. Accordingly, releases of petroleum and refinery gases from petroleum facilities may result in long-term exposure of a limited proportion of the general population to above-background levels of 1,3-butadiene. Recent air monitoring results of sites near Canadian petroleum facilities (Simpson et al. 2013) corroborated and validated the estimated 1,3-butadiene levels obtained using SCREEN3 modelling for locations in the vicinity of a petroleum facility.

SCREEN3 is recognized as being a conservative dispersion model compared to more advanced models that require highly detailed inputs. Thus, AERSCREEN (U.S. EPA 2011a) was also used in order to conduct a sensitivity analysis. AERSCREEN is the screening model based onAERMOD (U.S. EPA 2011a). The model produces estimates of "worst-case" 1-h concentrations for a single source, without the need for hourly meteorological data, and also includes conversion factors to estimate "worst-case" 3-h, 8-h, 24-h and annual concentrations. AERSCREEN is intended to produce concentration estimates that are equal to or greater than the estimates produced byAERMOD, without a fully developed set of meteorological and terrain data (U.S. EPA 2011a). The modelling results are provided in Appendix C (Tables C-5 and C-6). 1,3-Butadiene emissions modelled with AERSCREEN at a distance of 200 m from a refinery produced estimates of 0.55 μg/m³ on the high end (based on a ratio of 1,3-butadiene to benzene of 1:85), and approximately 0.21 μg/m³ on the low end (based on a ratio of 1,3-butadiene to benzene of 1:216). AERSCREEN results suggest that the values generated by SCREEN3 are valid.

Natural gas processing facilities have different feedstocks, processing units, and operating conditions compared to petroleum refineries. A recent industry submission on testing the level of 1,3-butadiene in selected gas streams from natural gas processing facilities indicates that the concentration of 1,3-butadiene in most gas samples was below the detection limit of 1ppm, with a single sample determined to be above the detection limit (CAPP 2014). Based on these analytical data, in combination with the lines of evidence previously submitted by industry on the absence of 1,3-butadiene in natural gas streams, and on the removal of 1,3-butadiene from the U.S. EPA list of pollutants of concern from oil and natural gas production facilities and natural gas transmission and storage facilities, the level of 1,3-butadiene in LPGs produced by natural gas processing facilities is expected to be low. Therefore, human exposure to 1,3-butadiene due to fugitive emissions of petroleum and refinery gases,including LPGs from natural gas processing facilities, is not expected.

According to information received under section 71 of CEPA and literature review, LPGs can be transported by truck, rail, ship and pipeline (Environment Canada 2012; Thompson et al. 2011).

Pressurized or refrigerated containers are used for delivering LPGs to various users (Thompson et al. 2011; Wiley 2007). The U.S. EPA’s AP 42 (U.S. EPA 2008b) states that "High-pressure storage tanks can be operated so that virtually no evaporative or working losses occur. No appropriate correlations are available to estimate vapour losses from pressure tanks". The shipment of pressurized gaseous substances generally requires stringent safety measures due to their physical–chemical properties. For example, under the Transportation of Dangerous Goods Regulations of the Transportation of Dangerous Goods Act, 1992, Transport Canada requires a series of standards, developed by Transport Canada, the Canadian Standards Association or the Canadian General Standards Board, for safety devices and for the design, manufacture, inspection and operation of authorized means of containment involved in the transportation of gases by rail, road and water. As well, equipment used for loading or unloading the means of containment, such as transfer hoses or loading arms, must meet design standards for appropriate pressures and temperatures (Canada 2001a). Due to the high safety and inspection standards generally applied to pressurized pipeline and container systems, regular releases from these types of pressurized systems are unlikely under normal operating conditions (European Commission 2006; U.S. EPA 2008b; OECD 2009).

There is relevant legislation in place at the federal and provincial levels for handling gaseous hydrocarbons, which is intended to reduce or prevent releases from these operations. Some of the measures outlined in these provisions apply to means of containment (i.e., transportation vessel), means of transportation (i.e., transportation vehicle) and handling equipment for transporting pressurized gases, and they indicate that each means of containment and transportation must meet specified design and safety standards. It is recognized, however, that fugitive releases of gaseous substances can occur due to their high volatility and high mobility. For example, poor maintenance of a threaded connection that may be used between a loading arm and a pressurized tank could result in fugitive leaks. Replacing threaded connections with flange connections can help reduce such releases (Hendler et al. 2006).

Potential exposure of the general population to fugitive releases during the transportation process is considered limited and accounted for by the exposures to LPGs as detailed and assessed below.

As LPGs are normally stored in pressurized containers with stringent requirements for design and operation (there exist various provincial regulations), potential exposure of the general population to any fugitive emissions from such pressurized containers is not expected. However, it is recognized that a release can occur during the transfer of LPGs between containers or during a filling process, such as filling barbecue gas tank cylinders (Sullivan 1992; CONCAWE 2012). Transfer operations are typically conducted by professionals with training in the safe handling of LPGs. In addition, LPG cylinder filling stations have declined in number, generating a growing popularity of cylinder exchange services provided to customers as a convenient way to exchange an empty tank for one that was previously filled by a professional. These factors have reduced the potential for exposure of the general population to LPGs from the transfer process.

Exposure to LPGs may occur in the general population living in the vicinity of LPG cylinder tank filling stations. The filling stations can be for vehicle refuelling or for filling non-vehicle tanks, such as barbecue tanks, and are located at commercial outlets and some hardware stores. Additionally, LPG transfer may occur at centralized depots prior to delivery to the consumer market. A conservative exposure analysis was developed for considering these types of filling scenarios.

The number of LPG-powered vehicles used by the general public in Canada is unclear. Transport Canada (2010) states that as of 2010, there are no passenger vehicles running on LPG . However, commercial taxi fleets, front-line police vehicle fleets, para-transit service fleets, and a fraction of mail courier company fleets in Canada are reported to use propane or LPGs as fuel (Propane Facts 2008; Wheels.ca 2013). The terms LPG and "automotive propane" are sometimes used interchangeably in referring to alternative vehicle fuels. Other off-road vehicles, such as industrial fork-lifts and some agricultural vehicles, are also known to use LPGs (Sullivan 1992; Competition Commission 2006).

Some larger home and hardware stores provide LPG filling services. Particularly in high-demand months such as during the summer, large numbers of customers bring in empty barbecue tanks either for refilling or for direct exchange with a previously filled tank. LPG released during each cylinder tank filling process and the subsequent dispersion of this released gas in the vicinity of homes near the stores can be a potential source of long-term exposure for nearby residents.

Sullivan (1992) estimated LPG emission rates for filling of different-size stand-alone LPG storage tanks and for vehicle fuel tanks. These emissions occur at the time of nozzle disconnection and are also due to the presence of outage valves. Using factors provided by Sullivan and additional conservative assumptions regarding the number of filling events occurring at a high-throughput site, a value of 27 g per event was estimated to be a typical loss of LPGs to the atmosphere for either a single filling of a barbecue tank or a vehicle fuel tank (losses are independent of the size and purpose of the fuel tank, but dependent on the nature of the connections involved in the transfer process). Similarly, CONCAWE (2012) suggested an "inhalation transfer factor" of 0.0005 for filling a vehicle tank with 45 kg of LPGs. The emission estimate based on CONCAWE (2012) (i.e., 22.5 g/transfer) is similar to the value of 27 g/transfer calculated using parameters given by Sullivan (1992). Therefore, a total emission of 27 g of LPG per transfer event is used to characterize the risk of potential exposure in the vicinity of LPG filling stations.

The dispersion of LPGs in ambient air in the vicinity of filling stations was modelled using SCREEN3 (1996), which was developed by the U.S. EPA and which has been used in previous screening assessments (e.g., Environment Canada, Health Canada 2013). Detailed input parameters used for modelling the dispersion of LPGs for a filling scenario are listed in Table C-3. The estimated concentrations of LPGs, as well as 1,3-butadiene, contributed to ambient air are presented in Table C-4. Estimates include the maximum concentrations within 1 h and 24 h, and they account for both changing wind directions and the intermittent nature of the events. Annual estimates of 1,3-butadiene in ambient air are also determined by assuming 0.1% (w/w) of 1,3-butadiene in LPG fuels. The Liquefied Petroleum Bulk Storage Regulations under the Canada Transportation Act stipulate that the distance of LPG loading and unloading racks be not less than 200 ft (61 m) from a residence (Canada 2013). As presented in Table C-4, the annual upper-bounding estimates of 1,3-butadiene at 60 m from the LPG filling station is 0.12 µg/m³, which is below the ambient air background of 0.22 µg/m³ reported by Curren et al. (2006).

LPGs are one of the most common aerosol propellants used in products available to consumers (Diversified CPC International 2012). In an aerosol can, LPGs are pressurized into liquid form and mixed with a liquid product. Once the pressure in the can is reduced (e.g., the nozzle is depressed and the valve opens), LPGs vapourize, forming a gas phase in the headspace of the can that exerts pressure on the liquid, effectively pushing the liquid product out of the can. As the liquid (a mixture of product and LPGs) leaves the can, the propellant rapidly expands into gas, which can further atomize the product to form a fine spray (CAPCO 2011). Accordingly, inhalation is the primary route of exposure to LPGs used as propellants.

LPGs identified under CAS RNs 68476-85-7 and 68476-86-8 are used as aerosol propellants in a variety of products across multiple brands. Based on a literature search, a summary of aerosol products containing LPGs (CAS RNs 68476-85-7 or 68476-86-8) as propellants is provided in Table 10-1, including the LPG concentration range by weight upon which the short-term exposure analysis is based.

^a The information in the table is based on an MSDS search unless specified otherwise.

^b Personal communication with Health Canada Pest Management Regulatory Agency, September 2013.

One monitoring study is available that measured indoor air levels of LPGs resulting from use of a spray product. Hartop et al. (1991) measured the concentration of LPGs in the breathing zone of an adult user and of an accompanying child (bystander) after 10 seconds of spraying with a hair spray product that contained 26% LPGs (a mixture of propane, n-butane and isobutane) as the propellant. The spray was conducted in a room (21 m³) without ventilation and with the door open as well as closed. The air samples were collected at heights of 1.5 m and 0.8 m from the floor and were measured by infra-red spectroscopy. The authors reported that the time weighted average concentrations of LPGs over 10 minutes from the beginning of the spray (TWA10) were 73 ppm (~130 mg/m³ at 1.5 m from the floor) for the adult user, and 80 ppm (144 mg/m³ at 0.8 m from the floor) for the bystander. The status of the room door (open/closed) had no significant impact on the TWA10 values. As the hair spray product used in this study contained a similar level of LPGs as the products listed in Table 10-1, the measured TWA10 of 144 mg/m³ is adopted to represent an exposure that might occur for short-term use of similar products.

LPG exposures from other aerosol products were modelled with ConsExpo, version 4.1 (ConsExpo 2006). ConsExpo is a multi-tiered predictive model used to derive estimates of exposure to substances in products available to consumers via inhalation, dermal contact and oral ingestion. The IHMod version 0.198 model created by the American Industrial Hygiene Association (AIHA 2009) was also considered. Since the predictions of the LPG concentration from IHMod were similar to those from ConsExpo, only the estimates from the ConsExpo model are presented here.

As a conservative approach, a representative upper-bounding exposure scenario was selected from each use category, based on concentration, use amount, or frequency. Short-term inhalation upper-bounding exposure estimates for each representative use pattern is presented in Appendix D (includes default input parameters). A summary of upper-bounding estimates for short-term inhalation exposure (i.e., amortized over 24h) to representative aerosol products that are commonly used is presented in Table 10-2 below.

The European Commission previously classified LPGs, identified by CAS RNs 68476-85-7 and 68476-86-8, as Category 1 carcinogens ("known to be carcinogenic to humans") and Category 2 mutagens ("should be regarded as if they are mutagenic to man") if 1,3-butadiene content is equal to or greater than 0.1% by weight (ESIS 2008; European Commission 2008a). The equivalent re-classifications of these substances by the European Commission in 2009 were Category 1A carcinogens ("known to have carcinogenic potential for humans, classification is largely based on human evidence") and Category 1B mutagens ("regarded as if they induce heritable mutations in the germ cells of humans") (European Commission 2008b, 2009).

Health effects information is limited for the LPGs identified under CAS RNs 68476-85-7 and 68476-86-8. A limited number of studies are available for exposure to highly refined LPG found in aerosol products containing any combination of propane, n-butane and isobutane. Toxicological information for other petroleum and refinery gases in the PSSA (i.e., Stream 1 and Stream 2 petroleum and refinery gases) that are similar from both a process and a physical-chemical perspective was not found. Various organizations have therefore characterized the toxicity of these substances by examining the petroleum and refinery gas component classes including alkanes, alkenes (or olefins), alkadienes, alkynes, aromatics, mercaptans and inorganics (CONCAWE 1992; ECB 2000a,b; Petroleum HPV 2009a,b; U.S.EPA 2010). Available literature relevant to the LPGs and their individual components was therefore considered in the preparation of the screening assessment. An overview of health effects information is provided in Appendix E. Only a summary of the critical information upon which the conclusion is based is presented herein.

No studies are available to assess the acute inhalation toxicity of LPGs identified under CAS RNs 68476-85-7 and 68476-86-8. One study on a mixture of propane (17.1% v/v), n-butane (2.5% v/v) and isobutane (80.4% v/v) indicated an LC₅₀ of approximately 1 227 000 mg/m³ (539 600 ppm) (Aviado et al. 1977).

Acute exposure of rabbits to high levels of LPGs indicated potential toxicity. Neocortical changes and cardiac damage were reported at approximately 540 000 mg/m³ after male rabbits were continuously exposed to a mixture of ethane, propane, n-butane, propene and isobutane for 120 min (Komura et al. 1973). Yoshino et al. (1984) conducted histological and cytological analysis of the central nervous system of male rabbits after a 4h exposure to a mixture of LPG (containing greater than or equal to 95% propane) and oxygen and nitrogen. Reversible neuropathological changes were observed at 1 260 000 mg/m³, as characterized by cytoplasmic vacuolation with reduced stainability in the V (5^th) layer of the cerebral cortex, and a high-grade vacuolation of the rough endoplasmic reticulum in the peripheral region of the neurons observed at the ultrastructure level.

A no-observed-adverse-effect concentration (NOAEC) of 18 230 mg/m³ was identified for systemic effects, neurotoxicity, reproductive and developmental toxicity, following inhalation exposure of male and female rats to CAS RN 68476-85-7 for 6h/day, 5 days/week for 13 weeks. No dose or exposure-related changes in organ weights, or haematological or clinical parameters were seen (Petroleum HPV 2009b; U.S.EPA 2010). Neurotoxicity was examined but no LPG-related effects on the functional observational battery parameters or motor activity were observed. Similarly, a NOAEC of 18 230 mg/m³ was established based on an analysis of reproductive and developmental effects. At this dose level, there was an increased incidence of abnormal sperm (4-12% of 200 sperms evaluated, with the effect occurring in 4 of 10 animals) but there was no concurrent effects on sperm count motility. Thus, such incidences of abnormal sperm were considered to be incidental and non-treatment related (Petroleum HPV 2009b; U.S.EPA 2010).

In another study on inhalation exposure of pregnant rats to CAS RN 68476-85-7 for 6h/day from gestation days 6 to 19 (Petroleum HPV 2009b; U.S. EPA 2010 ), no treatment -related effects were observed at the highest dose tested , and a NOAEC of 19020mg/m³ was identified.

LPGs have not demonstrated evidence of genotoxicity in an in vivo micronucleus assay and in an in vitro Ames assay. CAS RN 68476-85-7 exhibited negative results for micronuclei induction, as reported by the Petroleum HPV (2006, 2009b) and U.S. EPA (2010). There are no studies on CAS RNs 68476-85-7 and 68476-86-8 for in vitro genotoxicity. Only one study is available that examined the in vitro mutagenicity of gas mixtures of propane, isobutane and n-butane using the Ames assay with and without metabolic activation (Kirwin and Thomas 1980). The mixture exhibited negative mutagenicity, under both experimental conditions, after 6h exposure to the gas mixture.

An epidemiology (cross-sectional) study by Sirdah et al. (2013) that characterized health effects of LPGs on workers at LPG filling and distribution stations was identified. This study included a questionnaire interview and haematological and biochemical analyses of venous blood samples. The authors reported that LPG workers were at a higher risk of health-related symptoms and clinical abnormalities, as shown by high health-related complaints and significantly increased levels of some haematological parameters (e.g., red blood cell counts, haemoglobin), as well as elevated levels of urea and creatinine (measures of kidney function ) and aspartate aminotransferase (AST) and alanine aminotransferase (ALT) (measures of liver function). The exposure metrics used in the study are not known . Confounding factors of such studies include concurrent exposures to other substances (e.g., vehicle exhaust).

Aydin and Özçakar (2003) reported a case of acute hepatitis associated with an exposure to a mixture of propane and butane during the filling of gas cylinders in an enclosed space. The symptoms resolved 10 days after cessation of exposure. Exposure time and exposure metrics were not reported in the study.

Two case studies have been reported on the use of aerosol products containing LPGs as a propellant. Weibrecht and Rhyee (2011) reported an acute pulmonary injury after a male was exposed to a spray product containing 1-10% (w/v) of LPGs for 15 minutes in an enclosed garage, with symptoms of coughing, light headedness, shortness of breath, near-synocope, chest wall tightness, vomiting, diarrhea, chills and tremor. Similarly, another case study was identified of a male repeatedly exposed to an adhesive spray containing 30-35% of butane/propane/isobutane in a poorly ventilated garage over 2 years (Pyatt et al. 1998). The authors reported effects on the liver and the central nervous system, as shown by malaise and paraesthesia in the left upper limb, and higher levels of serum alkaline phosphatase (AP) and gamma-glutamyl-transferase (γ-GT) values. All the effects and symptoms reported in these two case studies were resolved after cessation of exposure. The exposure metrics in these studies are not known and the results are confounded by likely exposure to the other substances (the actual substances that comprise the product such as the adhesive material) present in the spray cans.

Due to limited information on the health effects of petroleum and refinery gases or LPGs, available literature relevant to the individual components present in LPGs is considered. Petroleum and refinery gases have been previously evaluated for mammalian health effects based on the assessment of individual components found in the gaseous state of these substances (API 2001a, 2009a,b; CONCAWE 2005; Petroleum HPV 2009a; U.S.EPA 2010). The results of the component evaluation facilitated the characterization of potential hazards associated with LPG mixtures. Generally, there can be multiple potentially hazardous components at various concentrations in the petroleum and refinery gases; therefore, the component that is the most highly hazardous for a particular endpoint (and present in the greatest quantity) is generally used to characterize the hazard associated with the mixture (API 2009a,b).

A brief summary of the health effects of the component classes is presented in Appendix E-2. A review of the health effects data for the predominant components of LPGs, including propane, butanes, butenes, and ethane, was undertaken as part of this screening assessment. These LPG components typically exhibit low toxicity, having high LC50 values and high NO(A)ECs and LO(A)ECs in repeated-dose studies.

For alkane components (propane, butane, isobutane), LC₅₀ values range from 570000 to over 800000 mg/m³ (Shugaev 1969; Clark and Tinson 1982), and in vitro genotoxicity assays are negative (Petroleum HPV 2009b; U.S. EPA 2010). Mixtures of butane/pentane or isobutane/isopentane have associated NOECs of 11943 mg/m³ in subchronic exposure assays in rats (Aranyi et al. 1986). Butane and isobutane both have associated NOAECs of 21500 mg/m³ in assays of short-term exposure and maternal/developmental toxicity, and butane exhibited a NOAEC of 21700 mg/m³ for reproductive toxicity in SD rats (Petroleum HPV 2009b; U.S. EPA 2010). Inhalation exposure to propane has elicited some effects in animals including hematological changes in female SD rats after 2- or 4-week exposure (84 or 168 h) to 21900 mg/m³ (Petroleum HPV 2009b). Reproductive effects in rats have been noted for propane exposure of 7180 mg/m³ (decreased live pups) and for isobutane exposures of 21700 mg/m³ (reduced fertility index and increased post-implantation loss) (Petroleum HPV 2009b; U.S. EPA 2010). However, given that concordant effects are not seen with similar exposures to ethane, butane or other low molecular weight gases, the toxicological relevance of these effects is questionable.

Other predominant components of LPGs, such as alkenes, produce similarly negative results or unremarkable effects in toxicological assays (see Appendix E-2 for more details). Substances expected to be present only at very low levels in LPGs, such as benzene, may be associated with hazardous endpoints, but are considered not to be present at concentrations that would pose an unacceptable risk.

For the characterization of the potential risk to human health from exposure to LPGs, this screening assessment focuses on a specific component considered to conservatively represent the greatest hazard to human health. The alkadiene 1,3-butadiene was previously selected as the high-hazard component that best represents the critical health effects of petroleum and refinery gases (Environment Canada, Health Canada 2013). 1,3- Butadiene has been reported to be potentially present in LPGs (identified under CAS RNs 68476-85-7 and 68476-86-8) that are produced at petroleum refineries (U.S. EPA 2010).

1,3-Butadiene has been classified as a carcinogen by several national and international agencies. For example, the Government of Canada concluded that 1,3-butadiene met the criteria under section 64(c) of CEPA on the basis of a plausible mode of action for induction of tumours involving direct interaction with genetic material (Canada 2000). The International Agency for Research on Cancer (IARC 2008) also classified 1,3-butadiene as carcinogenic to humans(Group 1). The U.S. EPA (2002) concluded that 1,3-butadiene is carcinogenic to humans by inhalation , while the U.S. National Toxicology Program (NTP 2011a) classified 1,3-butadiene as a known human carcinogen due to sufficient evidence of carcinogenicity in humans . For its part, the European Commission classified 1,3-butadiene as a carcinogen (Category 1A: known to have carcinogenic potential for humans), but also as a mutagen (Category 1B: be regarded as if they induce heritable mutations in the germ cells of humans”) (European Commission 2008b, 2009). Based on toxicity data generated in animals, 1,3-butadiene is also in the highest (most comprehensive) category that describes the weight-of-evidence scheme in the Guidelines for Mutagenicity Risk Assessment (U.S. EPA 1986).

1,3-Butadiene was subsequently added to the List of Toxic Substances in Schedule 1 of CEPA. Appendix E-3 contains a summary of the critical health effects information on 1,3-butadiene. The critical literature for characterizing the human health effects of 1,3-butadiene as a potential high-hazard component of LPGs is presented here.

In an NTP study, the carcinogenic potential of inhaled 1,3-butadiene has been clearly demonstrated in a 2-year inhalation study in B6C3F1 mice exposed to 1,3-butadiene at concentrations of 0-625 ppm (0-1380 mg/m³) in a 103-week study. 1,3-Butadiene was found to be a potent carcinogen, inducing common and rare tumours at a variety of sites in mice. In most cases, there was evidence of an exposure-response relationship in the tumour incidence and the involvement of a genotoxic mechanism. A statistically significant increase in the incidence of alveolar/bronchiolar adenocarcinomas or carcinomas in females was observed at 6.25 ppm (13.8 mg/m³) (NTP 1993; EURAR 2002; U.S. EPA 2002). As tumour induction was observed at all concentrations examined, it is likely that exposures lower than 6.25 ppm (13.8 mg/m³) would also cause cancer in mice (U.S. EPA 2002).

Also, mice were more sensitive to reproductive effects than rats, possibly due to production in mice of reactive 1,3-butadiene metabolites that are not formed to the same degree in rats (NTP 1993; Henderson 2001; Filser et al. 2007; Grant et al. 2010). Adverse reproductive/developmental effects are observed at lower concentrations tested in mice when compared to rats (NTP 1993). This single long-term inhalation study in rats suggests that 1,3-butadiene is also a multisite carcinogen in the rat; however, the effects were observed at air concentrations that were two to three orders of magnitude higher than in the mouse. The resistance of the rat to ovarian toxicity of 1,3-butadiene is likely due to decreased ability of the rat to produce 1,2:3,4-diepoxybutane (DEB) from 1, 3-butadiene. In a more recent study, Filser et al (2007) were unable to detect DEB in venous blood of male Sprague-Dawley rats (detection limit 0.01 µmol/L) when they were exposed to 1200 ppm (~2650 mg/m³) for 6 h, whereas DEB was detected in B6C3F1 mice at a concentration of 3.2 µmol/L after exposure to 1280 ppm BD (~2830 mg/m³) for 6 h.

Humans are more similar to rats than mice for 1, 3-butadiene metabolism in that they do not readily produce the diepoxide metabolite (Henderson 2001). Although there are marked differences in inter-species sensitivity to the carcinogenic properties of 1,3-butadiene, that may be explained by differences in metabolism, the available data does unequivocally indicate that 1,3-butadiene is a multisite carcinogen (Owen 1981; Owen et al. 1987; Owen and Glaister 1990; U.S. EPA 2002).

Several epidemiological investigations of the carcinogenicity of 1,3-butadiene have been conducted and have served as the basis for assessment of the weight of evidence for causality of associations based on traditional criteria (Canada 2000; EURAR 2002; U.S. EPA 2002). The investigation by Delzell et al. (1995, 1996), which was a large, high quality, cohort mortality study, portrays a clear association between exposure to 1,3-butadiene in the styrene-butadiene rubber industry and leukemia in humans.

Overall, on the basis of the available rodent and human evidence, it can be considered that 1,3-butadiene has the potential to induce tumours via a mode of action involving direct interaction with genetic material (Canada 2000; EURAR 2002; U.S. EPA 2002).

The Government of Canada has previously developed estimates of carcinogenic potency associated with inhalation exposure to 1,3-butadiene. A tumorigenic concentration (TC₀₁) of 1.7 mg/m³ was derived from the epidemiological investigation of Delzell et al. (1995), and the quantitative estimate of carcinogenic potency (TC05) derived on the basis of data in experimental animals was 2.3 mg/m³ for the most sensitive tumour site in mice (Canada 2000). More recently, an inhalation unit risk factor of 5×10^-7 (μg/m³)-1 has been calculated by the Texas Commission on Environmental Quality (TCEQ) based on updated human leukemia data (Grant et al. 2009).

LPGs listed under CAS RNs 68476-85-7 and 68476-86-8 were identified as high priorities for action during categorization of the DSL because they were determined to present the greatest or intermediate potential for exposure of individuals in Canada, and were considered to present a high hazard to human health. A critical effect for the initial categorization of LPGs was carcinogenicity, based primarily on classifications by international agencies. The European Union considers LPGs containing 1,3-butadiene at concentrations equal to or greater than 0.1% by weight to be carcinogens. Measured concentrations of 1,3-butadiene in the gaseous state for the two LPG substances identified in this assessment ranged from non-detectable to 0.1% by weight (U.S.EPA 2010). According to information submitted under section 71 of CEPA, the residual level of 1,3-butadiene in butane or isobutane ranges from non-detectable to less than 1% by weight, and typically less than 0.1% by weight (Environment Canada 2007).

1,3-Butadiene has been identified by Health Canada and several international regulatory agencies as a carcinogen, and was added to the List of Toxic Substances in Schedule 1 of CEPA. 1,3-Butadiene was found to be a multi-site carcinogen in rodents by inhalation, increasing the incidence of tumours at all concentrations tested. Epidemiological studies provide further evidence for an association between exposure to 1,3-butadiene in occupational environments and leukemia in humans. 1,3-Butadiene also exhibits genotoxicity in vitro and in vivo, and a plausible mode of action for induction of tumours involves direct interaction with genetic material.

Based on its carcinogenicity and presence in LPGs, 1,3-butadiene is considered to be the component representing the highest health concern for long-term inhalation exposure to LPGs. A quantitative estimate of carcinogenic potency (TC05 = 2.3 mg/m³) for 1,3-butadiene for the inhalation route of exposure was previously determined, and represents the level that causes a 5% increase in tumours or mortality in mice (Canada 2000). The TC05 is used to characterize risk to the general population by deriving margins of exposure for potential long-term exposure to fugitive releases of LPGs containing 1,3-butadiene. Petroleum facilities, LPG transfer stations (where LPG tanks or LPG-powered automobiles are refuelled), and the use of aerosol products (that contain LPG as propellants) are potential sources of long-term exposure to 1,3-butadiene associated with LPG releases.

Limited studies were identified on which to base the characterization of risk for short-term inhalation exposures to LPGs. The highest inhalation NOAEC for LPGs of 19 000 mg/m³ was based on absence of maternal and developmental toxicity and is used for short-term risk characterizations through comparisons with the estimated short-term inhalation exposures (i.e., 24h or TWA10) to LPGs from the use of aerosol products.

LPGs identified under CAS RNs 68476-85-7 and 68476-86-8 are produced at petroleum refining and natural gas processing facilities. Fugitive releases of LPGs from petroleum refineries may contribute to the overall 1,3-butadiene concentrations in ambient air in the vicinity of the facilities. However, it is not possible to determine the proportion of such releases specifically associated with these two CAS RNs. Therefore, any risk associated with on-site fugitive releases of these two CAS RNs has been captured by the risk characterization of the total petroleum and refinery gases released at a facility in the assessment of Stream 1 petroleum and refinery gases (Environment Canada, Health Canada 2013) (summarized below).

Both air dispersion modelling and calculations based on the application of emission factors indicate that unintentional releases of petroleum and refinery gases contribute to the overall 1,3-butadiene concentration in ambient air in the vicinity of petroleum refineries that produce or use these substances. The estimated 1,3-butadiene concentrations decline with increasing distance from these release sources. A conservative approach estimates the 1,3-butadiene concentration to be comparable to or below the Canadian urban average concentration at distances equal to or greater than 500 m from the centre of the release source. Using the estimates of carcinogenic potency previously developed by the Government of Canada (Canada 2000), together with the high and low end estimates of exposure derived from dispersion modelling of 1,3-butadiene as a high-hazard component of the petroleum and refinery gases, margins of exposure (MOEs) were derived for increasing distances from the release source (a distance of 200 m is illustrated in Table 10-3). 1,3-butadiene to benzene ratios of 1: 85 and 1:216 were used for high end and low end exposure estimates, respectively. Map analysis has determined that the general population may reside approximately 200 m from a potential source of release. Accordingly, this distance has been selected to characterize risk to the general population.

For the high end of the exposure range, at a distance of 200 m from the centre of the release source, the margin of exposure is 5300. At 500 m, the margin of exposure is 10 500, which equates to an exposure concentration equal to the Canadian average annual ambient air concentration of 0.22 μg/m³ found in urban centres. Although the magnitude of risk would vary with the cancer potency metrics selected (TC₀₅; unit risks derived by U.S. EPA and Texas Commission on Environmental Quality based on linear low-dose extrapolation models etc.), use of a conservative cancer potency metric is considered appropriate given the uncertainties in the health effects database. For the high end of the exposure range, the margin of exposure at 200 m from the release source is considered potentially inadequate to address uncertainties in the health effects and exposure databases for petroleum and refinery gases.

Therefore, fugitive emissions of LPGs (CAS RNs 68476-85-7 and 68476-86-8) produced from petroleum refineries contribute to the overall site emissions of 1,3-butadiene as estimated above, accordingly contributing to the potentially inadequate margins of exposure.

Sampling results from natural gas processing facilities show that the levels of 1,3-butadiene were below the detection limit (less than 1 ppm) in most gas streams, and were below 5ppm in all samples (CAPP 2014). Given the low hazard of the other predominant gas components, the human health risks from potential exposure to fugitive emissions of petroleum and refinery gases, including LPGs from natural gas processing facilities, are expected to be low.

The general population can be exposed to LPGs through indoor air during and after intermittent or frequent use of aerosol products containing LPGs as propellants.

For the characterization of risk of potential long-term inhalation exposure to LPGs released from the use of various aerosol products over time, the MOE was determined by comparing the highest 50^thpercentile of 0.134 µg/m³ for Canadian indoor air levels of 1,3-butadiene in non-smoking homes with the TC05 of 2.3 mg/m³ (2300 µg/m³) for 1,3-butadiene, resulting in an MOE of 17 000. This approach is considered conservative as multiple sources likely contribute to the indoor air level of 1,3-butadiene. This MOE is considered adequate to address uncertainties related to health effects and exposure.

The MOEs for short-term inhalation exposure to LPGs from different aerosol products are presented in Table 10-4. The MOEs were derived by comparing the estimated 24h LPG concentration in indoor air from the use of each product with the highest LPG NOAEC of 19 000 mg/m³. As shown in Table 10-4, MOE estimates range from 135 to 552 300. Given the absence of adverse effects (i.e., the MOE is based on a NOAEC ) and the conservative assumptions taken within the assessment , the MOEs are considered adequate to address uncertainties related to health effects and exposure.

The composition of LPGs can vary depending on the source of crude oil or natural gas, operating conditions, seasonal process issues and economic cycles. Therefore, the hazard properties of LPGs may change based on the levels of component substances.

Canadian monitoring data for 1,3-butadiene in the vicinity of petroleum facilities was not identified. Therefore, general population exposures were estimated in part using computer models. There is inherent uncertainty in estimates derived with models (assumptions made in the various exposure analyses are listed in Appendix C).

It is assumed that all the estimated facility releases of 1,3-butadiene are attributed to the petroleum and refinery gases, and that a portion of these releases stem from the two LPGs considered in this assessment. Quantitative information for each LPG CAS RN present at petroleum refinery facilities was not available to attribute relative contributions to total facility releases of 1,3-butadiene.

Based on the information presented in this screening assessment, it is concluded that the LPGs listed under CAS RNs 68476-85-7 and 68476-86-8 are unlikely to be causing ecological harm to organisms or the broader integrity of the environment. Therefore, it is concluded that these two LPGs (CAS RNs 68476-85-7 and 68476-86-8) do not meet the criteria under paragraphs 64(a) and (b) of CEPA as they are not entering the environment in a quantity or concentration or under conditions that have or may have an immediate or long-term harmful effect on the environment or its biological diversity or that constitute or may constitute a danger to the environment on which life depends.

Based on the information presented in this final screening assessment, it is concluded that these two LPGs (CAS RNs 68476-85-7 and 68476-86-8) meet the criteria under paragraph 64(c) of CEPA as they are entering or may enter the environment in a quantity or concentration or under conditions that constitute or may constitute a danger in Canada to human life or health.

It is concluded that these two LPGs (CAS RNs 68476-85-7 and 68476-86-8) meet one or more of the criteria set out in section 64 of CEPA.

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^a These groups were based on classifications developed by CONCAWE and a contractor's report presented to the Canadian Petroleum Products Institute (CPPI) (Simpson 2005).

^b LPGs are considered to be in the petroleum and refinery gases group.

Abbreviations:
K_oc = organic carbon-water partition coefficient; K_ow = octanol-water partition coefficient; exp., experimental data.

^a All data on melting point, boiling point, vapour pressure, K_ow and water solubility are experimental. Henry's Law constants are calculated based on experimental data. K_ow data are from Hansch et al. (1995); melting point, boiling point and vapour pressure data are from Daubert and Danner (1994), Riddick et al. (1986), Yalkowsky and He (2003) and McAuliffe (1966).

Abbreviation: DIAL = differential absorption, light detection and ranging.

^a See Environment Canada, Health Canada (2013) for detailed information on estimation of potential releases from a petroleum facility.

^b Aerial photo analysis and professional judgement.

^c Chambers et al. (2008).

^d NPRI (2000-2007) and TRI (2011).

^e Professional judgement.

^f Curry et al. (1993).

^g Emissions were specified at a high level (above 15 m) and a low level (3 m) to represent the heights of equipment involving unintentional releases of 1,3-butadiene. It is assumed that 80% of the unintentional releases occur above 15 m, accounting for the common discharging points, such as the top of a distillation column. The final concentration of 1,3-butadiene results from the combined high-level and low-level emissions.

^h U.S. EPA (1992) and professional judgement.

ⁱ Default value in SCREEN3.

^a Assumptions made in the modelling:

• All unintentional releases of 1,3-butadiene from a petroleum facility are assumed to be attributed to the unintentional emission of total petroleum and refinery gases and originate from processing areas rather than bulk storage facilities.
• Both LPGs identified under CAS RNs 68476-85-7 and 68476-86-8 are flagged as potentially containing 1,3-butadiene and are considered to comprise a fraction of the previously characterized Stream 1 petroleum and refinery gases.
• The ratio of 1,3-butadiene to benzene(1:85 as a high end exposure range and 1:216 as a low end exposure range) in unintentional emissions is assumed to be constant over different processing units.
• Unintentional emission heights of 1,3-butadiene are assumed to be 15 m and 3 m, with 80% of total emissions occurring above 15 m and 20% of emissions occurring at 3 m.
• Considering the fact that the release sources are actually multiple point sources spatially distributed over the processing area, the effective processing area used for calculation of emission rate is assumed to be 80% of the total process area.
• Total processing area is assumed to be 300 m×100 m.
• Adjustment factor 0.2 is used for estimation of maximum concentration over a year based on the highest 1h concentration.

^a Professional judgement for filling stations

^b Estimated based on the release factor reported by Sullivan (1992)

^c Conservative professional judgement for a high-throughput BBQ cylinder tank filling station

^d Curry et al. (1993)

^e U.S. EPA (1992) and professional judgement.

^f Default value in SCREEN3.

^a Aerial photo analysis and professional judgement.

^b Chambers et al. 2008.

^c NPRI (2000–2007) and TRI (2007).

^d Curry et al. 1993.

^e Emissions were specified at a high level (above 15 m) and a low level (3 m), in order to represent the heights of equipment involving fugitive releases of 1,3-butadiene. It is assumed that 80% of the fugitive releases occur at 15 m, accounting for the common discharging points, such as the top of a distillation column. The final concentration of 1,3-butadiene results from the combined high-level and low-level emissions.

^f Professional judgement.

^g Statistics Canada data (http://www.statcan.gc.ca/tables-tableaux/sum-som/l01/cst01/phys08b-eng.htm).

^h Default value in AERSCREEN.

ⁱ U.S. EPA (1992) and professional judgement.

^a Assumptions made in the modelling:

1. All releases of 1,3-butadiene from a petroleum facility are assumed to be attributed to the emissions of site-restricted petroleum and refinery gases and originate from processing areas rather than tank farms.
2. Both LPGs identified under CAS RNs 68476-85-7 and 68476-86-8 are flagged as potentially containing 1,3-butadiene and are considered to comprise a fraction of the previously characterized Stream 1 petroleum and refinery gases.
3. The ratio of 1,3-butadiene to benzene in fugitive emissions is assumed to be constant over different processing units.
4. Fugitive emission heights of 1,3-butadiene are assumed to be 15 m and 3 m, with 80% of total emissions occurring at 15 m and 20% of emissions occurring at 3 m.
5. Total processing area is assumed to be 300 m × 100 m.
6. Adjustment factor 0.2 is used for estimation of maximum concentration over a year based on the highest 1-h concentration.

^a From each use category, only the products with a high concentration, a high use frequency or a high use quantity are selected for high-end exposure modelling.

^b Using "instantaneous release mode" of "exposure to vapour" in ConsExpo (RIVM 2005). All values for input parameters are from ConsExpo factsheets (RIVM 2005) unless specified.

^c Values of max. weight fraction of LPGs in products are from the maximum level reported in the MSDS for each representative consumer aerosol product.

^d Assuming a maximum level of 1,3-butadiene in LPG is 0.1 % w/w, then the estimates for 1,3-butadiene air concentration from each product scenario is 0.1%×estimates for LPGs.

^e Amortized mean concentration over a year is presented for those products with a high use frequency (i.e., equal to or more than once per month).

^f ECETOC (2012).

^g U.S.EPA (2011b).

^h Professional judgement based on product information

ⁱ Versar (1986).

^j Environment Canada, Health Canada (2010).

^a LC₅₀, median lethal concentration; LD₅₀, median lethal dose; LAEC, lowest-observed-adverse-effect concentration; LOAEL, lowest-observed-adverse-effect level; NOAEC, no-observed-adverse-effect concentration; NOAEL, no-observed-adverse-effect level.

^b The following formula was used for conversion of provided values into mg/m³ in air: (x ppm×MM)/24.45, assuming at 1atm and 25°C.

^c Molar mass (MM) of CAS RN 68476-85-7 reported to be 44.6 g/mol (U.S. EPA 2010).

Alkanes

As propane, n-butane and isobutane are the predominant components present in LPGs, key observations from toxicological studies on inhalation exposure to these components are summarized here.

In humans, it has been observed that alkanes of low molecular weight (e.g., methane) can cause displacement of oxygen for acute exposures at high concentrations, which may lead to asphyxiation. At higher molecular weights, substances such as propane can act as mild depressants on the central nervous system (API 2001a). In experimental animals, LC₅₀ values for alkanes range from 658 mg/L (658000 mg/m³) (butane, 4h), 570 000 ppm (isobutane, 15-min.) to greater than 800000 ppm (1440000 mg/m³) (propane, 15-min.), depending on the substance, concentration and duration of acute exposure (Shugaev 1969; Clark and Tinson 1982). The European Commission has classified butane and isobutane as category 1A carcinogen ("known to have carcinogenic potential for humans") and category 1B mutagen ("known to induce heritable mutations or to be regarded as if they induce heritable mutations in the germ cells of humans") if each of them contains a concentration of 1,3-butadiene greater than or equal to 0.1% by weight (European Commission 2008b, 2009).

For short-term exposure, a short-term NOAEC/LOEC of 12 168 ppm (21 900 mg/m³) was identified for propane based on decreased weight gain in male rats and increases in hemoglobin concentration, hematocrit, erythrocytes and absolute eosinophils in female SD rats after 4-week exposure at 6h/day and 7 days/week. A NOAEC of greater than 9100 ppm (21 500 mg/m³) for butane or isobutane were reported in separate studies at 6h/day, 7 days/week for 4 weeks (Petroleum HPV 2009b).

For reproductive toxicity, a LOAEC of 3990 ppm (7180 mg/m³) was reported based on a decrease in the number of live pups and increase in the number of stillborn pups when SD female rats were exposed to propane at 6h/day, 7 days/week for 2 weeks prior to mating, during mating and on gestation days 0-19. Similarly, a LOAEC of 9148 ppm (21 700 mg/m³) was reported for SD female rats exposed to isobutane at 6h/day, 7 days/week for 2 weeks prior to mating, during mating and on gestational days 0-19, as shown by a reduction in fertility index and an increase in post-implantation loss. Similar testing methodology was applied to n-butane in a separate study and a NOAEC of 9157 ppm (21 700 mg/m³) was reported for reproductive toxicity (Petroleum HPV 2009b; U.S. EPA 2010).

For developmental toxicity, a NOAEC/LOEC of maternal toxicity at 12 168 ppm (21 900 mg/m³) was identified for propane based on increases in hemoglobin concentration, hematocrit, erythrocytes and absolute eosinophils observed in SD female rats following exposure to propane gas at 6h/day, 7 days/week for 2 weeks prior to mating, during mating and on gestational days 0 to 19. Following the similar testing methodology, a NOAEC of greater than 9100 ppm (21500 mg/m³) was identified for n-butane and isobutane for their maternal/developmental toxicity (Petroleum HPV 2009b; U.S. EPA 2010).

For in vitro genotoxicity, negative results for gene mutation were exhibited in vitro Ames assay for propane and butanes. No in vivo genotoxicity studies are available on propane or butanes (n-butane and isobutane) (Petroleum HPV 2009b; U.S. EPA 2010).

A few inhalation studies are available on a mixture of C₃ to C₅. Rats were exposed to mixtures of alkanes (50% butane / 50% pentane; 50% isobutane / 50% isopentane) via inhalation for 90 days in a study designed to investigate kidney effects; a NOEC of 4489 ppm (11 943 mg/m³)^Footnote3, ^Footnote4 (highest dose tested) was identified (Aranyi et al. 1986). Negative mutagenicity results were observed for various alkanes (propane, n-butane, isobutane, n-pentane and isopentane) tested via the Ames assay, although toxicity was observed in three of the gases (n-pentane, isopentane and isobutane) at various concentrations (Kirwin and Thomas 1980).

Alkenes

In experimental animals exposed by inhalation, concentrations of up to 25-70% propene and 15-40% butene induced anesthesia in rats, cats and mice (Brown 1924; Riggs 1925; Virtue 1950), while narcosis was noted in mice exposed to up to 70% isobutene via inhalation (Von Oettingen 1940). Acute toxicity values (LC₅₀) are noted to range from 65000 ppm (111 736 mg/m³)⁶ (propene; molecular weight (MW) = 42.03 g/mol) to 620 mg/L (620 000 mg/m³) (isobutene) (Shugaev 1969; Conolly and Osimitz 1981).

Short-term toxicity studies show that oral exposure to isobutene results in a NOAEL of 150 mg/kg body weight (kg-bw) per day, despite the occurrence of significant biochemical changes that fall into the historical control range (Hazleton Laboratories 1986). Short-term exposure by inhalation resulted in changes to hematology in rats exposed for a few days to 60% ethene (approximately 690 000 mg/m³) (Fink 1968) as well as clinical and biochemical changes in rats exposed for 70 days to 100 ppm (115 mg/m³)⁶ ethene (MW of ethene = 28.02 g/mol) (Krasovitskaya and Maliarova 1968). Exposure to propene resulted in a lowest NOEL value of 10 000 ppm (17 190 mg/m³)⁶ for 28-day exposure to multiple concentrations of propene (MW = 42.03 g/mol) up to 17190 mg/m³ (DuPont 2002).

The lowest LOEC identified for subchronic toxicity is 500 ppm (1146 mg/m³)⁶ in a 14-week study in which male and female B6C3F1 mice and F344/N rats were exposed by inhalation to isobutene (MW = 56.10 g/mol) at concentrations up to 8000 ppm (18 336 mg/m³)6, resulting in significant increases in absolute and relative right kidney weights in female mice. In male mice, the absolute right kidney weight was increased at 1000 and 8000 ppm (2292 and 18 336 mg/m³)⁶. In female rats, there was a significant increase in relative liver weights from 500 ppm (1146 mg/m³)6 and in absolute liver weights from 1000 ppm (2292 mg/m³)⁵. In male rats, a significant increase in relative right kidney weight was observed from 500 ppm (1146 mg/m³)⁶, with an increase in absolute right kidney weight at 4000 ppm (9168 mg/m³)⁶ (NTP 1998). In addition, a 90-day continuous inhalation study conducted in newborn rats caused delays in coat appearance, tooth development and eye opening, as well as hypertension, inhibition of cholinesterase activity and behavioural changes, at an ethene (MW = 28.02 g/mol) concentration of 2.62 ppm (3 mg/m³)⁶ ( Krasovitskaya and Maliarova 1968).

With regard to developmental toxicity, NOEC values of 5000 ppm (5750 mg/m³) for ethene (MW = 28.02 g/mol), 10 000 ppm (17190 mg/m³) 6 for propene (MW = 42.03 g/mol) and 5000 ppm (11 460 mg/m³)⁶ for 2-butene (MW = 54.04 g/mol) were identified in rats exposed by inhalation (Waalkens-Berendsen and Arts 1992; Aveyard 1996). Effects on reproductive organs were observed in male rats exposed to isobutene via inhalation over 14 weeks; these include a significant increase in left epididymal weight and a decrease in epididymal sperm motility at 8000 ppm (18336 mg/m³)⁶. In addition, female rats were reported to have an increased estrus length with a related decrease in diestrus length; however, the length of the estrus cycle was not noted to change (NTP 1998).

Both propene and ethene have been classified as Group 3 carcinogens (not classifiable as to their carcinogenicity to humans) by IARC (1994 a,c). For propene, a two-year inhalation study (concentrations up to 10000 ppm [17 190 mg/m³; MW for propene = 42.03 g/mol])⁶ showed the occurrence of hemangiosarcoma in male and female mice as well as lung tumours (negative trend with increasing concentration) in male mice. No tumours were observed under the same protocol in rats (Quest et al. 1984; NTP 1985). A second inhalation study in mice (78 weeks) and rats (104 weeks) conducted with up to 5000 ppm (8600 mg/m³)⁶ propene showed no differences in tumour incidence compared with controls (Ciliberti et al. 1988). For ethene, a two-year study in rats did not result in increased tumour incidence at concentrations up to 3000 ppm (3438 mg/m³; MW of ethene = 28.02 g/mol)⁶ (Hamm et al. 1984). Chronic exposure of male and female F344 rats and B6C3F1 mice to isobutene at levels up to 8000 ppm (18336 mg/m³; MW of isobutene = 54.04 g/mol)⁶ for 104 weeks was noted to cause an increased incidence of thyroid gland follicular cell carcinoma in male rats (NTP 1998). In addition, an increased incidence of hyaline degeneration in the nose of rats and mice was reported (NTP 1998).

Ethene, propene and 1-butene were all noted to cause an increased incidence of DNA adducts in vivo (Segerback 1983; Tornqvist et al. 1989; Filser et al. 1992; Eide et al. 1995; Zhao et al. 1999; Rusyn et al. 2005; Pottenger et al. 2007), but no micronuclei were induced when rats and mice were exposed to ethene, propene or isobutene (Vergnes and Pritts 1994; NTP 1998; Pottenger et al. 2007). When ethene, 1-butene, 2-butene or isobutene were administered in vitro, negative results were obtained for mutagenicity in bacteria (Landry and Fuerst 1968; Hamm et al. 1984; Shimizu et al. 1985; Victorin and Stahlberg 1988; Wagner et al. 1992; Araki et al. 1994; NTP 1998), mouse lymphoma cells with and without activation (Staab and Sarginson 1984), micronuclei induction without activation (Jorritsma et al. 1995), chromosomal aberrations with and without activation (Riley 1996; Wright 1992) and cell transformation with and without activation (Staab and Sarginson 1984).

Other components

The refinery gases (as part of the API grouping of petroleum gases) are noted to contain alkadienes, alkynes, aromatics, inorganics and mercaptans in addition to alkanes and alkenes, although as less abundant components in the petroleum stream (API 2001b). Many of these components are described below.

Alkadienes

As noted in the health effects section of the screening assessment, a member of the alkadienes, 1,3-butadiene, is classified as both a carcinogen and a mutagen by multiple national and international agencies (Canada 2000; IARC 2008; U.S. EPA 2002; NTP 2011a; EURAR 2002; ESIS 2008). A thorough review of the human health effects of 1,3-butadiene was previously done under the Priority Substances List (PSL) 2 assessment (Canada 2000). 1,3-butadiene was subsequently added to the List of Toxic Substances - Schedule 1 of CEPA. Alkadienes have been observed to have narcotic properties at high concentrations and low general toxicity (Sandmeyer 1981).

Another member of the alkadienes (2-methyl-1,3-butadiene or isoprene) is also classified as a carcinogen (Group 2B: possibly carcinogenic to humans; Category 2: suspected human carcinogen, may cause cancer and "…reasonably anticipated to be a human carcinogen", as well as a mutagen. (IRAC 1999; ESIS 2008; NTP 2011b). Isoprene is noted to have reproductive effects in mice (testicular atrophy, similar to those observed after 1,3-butadiene exposure) as well as developmental effects (reduced fetal body weight, increased incidence of supernumerary ribs) (Mast et al. 1989, 1990). Isoprene has also been reported to have effects on mortality, body weight, organ weight, hematology and histopathology (stomach hyperplasia, olfactory degeneration, thymic atrophy, hepatocellular foci changes, alveolar hyperplasia, spinal cord degeneration) in mice after short- and long-term inhalation exposures (Melnick et al. 1990, 1994, 1996). On the basis of carcinogenicity, for which there may be a probability of harm at any level of exposure, Health Canada concluded that isoprene should be considered as a substance that may be entering the environment in a quantity or concentration or under conditions that constitute or may constitute a danger in Canada to human life or health (Environment Canada, Health Canada 2008).

Alkynes

Ethyne or acetylene is a simple asphyxiant (HSDB 2008); effects observed in humans after inhalation include intoxication, aggressiveness and unconsciousness at high concentrations (U.S. EPA 2008c).

Acetylene is noted to cause increased mortality in various species of experimental animals, as well as intoxication or anesthesia. Effects in the liver (LOAEC = 266.3 mg/L (266 300 mg/m³), kidneys and spleens of rats were observed following repeated exposure via inhalation. Genotoxic effects were not observed in vitro (US EPA 2008c).

Aromatics

Benzene is noted to be a carcinogen, as classified by the Government of Canada (carcinogenic to humans; CEPA - List of Toxic Substances) (Canada 1993), IARC (1987) (Group 1: carcinogenic to humans), the European Commission (Category 1 carcinogen: may cause cancer) (ESIS 2008), the U.S. National Toxicology Program (NTP 2011c) (known human carcinogen) and the U.S. EPA (2008d) (Group A). In addition, benzene has been classified as a mutagen as Category 1B (be regarded as if they induce heritable mutations in the germ cells of humans) (European Commission 2008b, 2009).

Inorganics

Hydrogen sulphide has been evaluated by the International Programme on Chemical Safety (IPCS) in both an Environmental Health Criteria monograph (IPCS 1981) and a Concise International Chemical Assessment Document (IPCS 2003). In addition, the U.S. Agency for Toxic Substances and Disease Registry (ATSDR 2006) has generated a toxicological profile on hydrogen sulphide. The Government of Canada is currently assessing the potential impacts of hydrogen sulphide on human health from various uses and sources.

Ammonia has been evaluated by the IPCS (1986), ATSDR (2004) and the Organisation for Economic Co-operation and Development (OECD) Screening Information Dataset (SIDS) program (OECD 2007). In addition, ammonia has been evaluated by the Government of Canada under the Priority Substances List program for its presence in the aquatic environment, where "conclusions drawn on the basis of a more robust data set on environmental effects would also be protective of human health" (Canada 2001b).

Both nitrogen and carbon dioxide have been noted to be inert pesticide ingredients by the U.S. EPA (2004b). Carbon monoxide has been classified by the European Commission as a Category 1 reproductive toxin (ESIS 2008) and has also been reviewed by IPCS (1999).

Mercaptans

Two mercaptans noted to be components of petroleum and refinery gases have been evaluated or reviewed by various international or national agencies; however, for the purposes of this hazard assessment, an evaluation of these component substances will not be included.

Methanethiol or methyl mercaptan has been reviewed by ATSDR (1992) and included in a review of aliphatic and aromatic sulphides and thiols by the Joint FAO/WHO Expert Committee on Food Additives (JECFA) (WHO 2000). In addition, both methanethiol and ethanethiol are substances scheduled for evaluation under the OECD SIDS program, but a final review has not been made available at this time (OECD 2000).

^a LOAEC, lowest-observed-adverse-effect concentration.

^b Conversion of the provided value into mg/m³ was completed using the formula: x ppm (MW)/24.45.