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Priority Substances List Assessment Report- 1,3-Butadiene
2.0 Summary of Information Critical to Assessment of "Toxic" under CEPA 1999
2.1 Identity and physical/chemical properties
1,3-Butadiene is also known as butadiene, alpha-gamma-butadiene, buta-1,3-diene, bivinyl, divinyl, erythrene, vinylethylene, biethylene and pyrrolylene. Its Chemical Abstracts Service (CAS) registry number is 106-99-0, and its Registry of Toxic Effects of Chemical Substances (RTECS) number is EI9275000.
The chemical and physical characteristics of butadiene are shown in Table 1. Ranges of reported values have been discussed by Mackay et al. (1993) and are presented in the environmental Supporting Document (Environment Canada, 1998). At room temperature, butadiene is a colourless, flammable gas with a mild aromatic odour. It has a high vapour pressure, a moderately low water solubility and a low octanol/water partition coefficient (Kow) (Mackay et al., 1993).
2.2 Entry characterization
2.2.1 Production and uses
Butadiene is produced during the combustion of organic matter in both natural processes and human activities. In addition, it is produced commercially for use in the chemical polymer industry.
In 1994, there was one Canadian commercial producer of butadiene (located in Sarnia, Ontario), with a production capacity of 120 kilotonnes and actual domestic production of 103.7 kilotonnes. Butadiene is purified by an extraction distillation process from a crude petroleum butadiene stream. Importation into Canada from the United States was 1.7 kilotonnes in 1994. The Canadian domestic use of butadiene in 1994 amounted to 105.4 kilotonnes (98.3 kilotonnes for total domestic demand and 7.1 for export sales) (Camford Information Services, 1995).
The largest end use of butadiene in Canada is the production of polybutadiene rubber (51.4 kilotonnes; 52.3% of total Canadian consumption for 1994) (Camford Information Services, 1995). Other derivatives produced include styrene-butadiene latexes (31.0 kilotonnes; 31.5% of total Canadian consumption for 1994), nitrile-butadiene rubbers (10.0 kilotonnes; 10.2% for 1994), acrylonitrile-butadiene-styrene terpolymer (3.4 kilotonnes; 3.5% for 1994) and specialty styrene-butadiene rubbers (2.5 kilotonnes; 2.5% of total Canadian consumption for 1994).
Results from a survey of industry carried out under the authority of Section 16 of CEPA indicated generally similar commercial data for 1996 (Environment Canada, 1997c).
Butadiene has a long history of use, notably related to production of polymers. Several industrial and commercial products are manufactured with it or may contain it as a component. Examples include tires, car sealants, plastic bottles and food wrap, epoxy resins, lubricating oils, hoses, drive belts, moulded rubber goods, adhesives, paint, latex foams for carpet backing or underpad, shoe soles, moulded toys/household goods, medical devices and chewing gum (CEH-SRI International, 1994; OECD, 1996).
2.2.2 Sources and releases
Estimates of emissions are highly variable, depending on the method of estimation and the quality of the data upon which they are based. Total Canadian emissions for 1994 were estimated to range between 12 917 and 41 622 tonnes (Environment Canada, 1998). Major uncertainties are associated with estimates for combustion sources, notably forest fires.
2.2.2.1 Natural sources
Butadiene is released from biomass combustion, especially forest fires. Total global emission of butadiene from biomass combustion was estimated to be 770 000 tonnes per year (Ward and Hao, 1992). Releases from forest fires in Canada were estimated to range between 3607 and 26 966 tonnes, which constituted 49.3% (range of estimates is 28-65%) of the total annual emissions of butadiene in Canada (CPPI, 1997). Forest fires are sporadic events, both in time and space. As indicated below, the atmospheric half-life of butadiene is short (hours). Thus, while forest fires are an important local source of butadiene soon after their occurrence, they likely contribute little to the concentrations consistently measured in urban or industrial areas.
2.2.2.2 Anthropogenic sources
All internal combustion engines may produce butadiene as a result of incomplete combustion. The amount generated and released depends primarily on the composition of fuel, the type of engine, the emission control used (i.e., presence and efficiency of catalytic converter), the operating temperature, and the age and state of repair of the vehicle (Environment Canada, 1996a). Cyclohexane, 1-hexene, 1-pentene and cyclohexene have been identified as primary fuel precursors for butadiene (Schuetzle et al., 1994). As well, very low levels of butadiene itself may be present in gasoline and in liquefied petroleum gas (Environment Canada, 1998).
Butadiene can also enter the environment from any stage in the production, storage, use, transport or disposal of products with residual, free or unreacted butadiene. Data on Canadian industrial emissions have been collected for industrial processes, plastic products industries, refined petroleum and coal products industries, and chemical and chemical products industries as part of the National Pollutant Release Inventory (NPRI) (Environment Canada, 1996b, 1997d). Emissions other than those reported to the NPRI may occur, including from combustion of other fuels (e.g., natural gas, oil and wood), prescribed forest burning, cigarettes, waste incineration, releases from polymer products, releases from the use and disposal of products containing butadiene, and spillage (Ligocki et al., 1994; Environment Canada, 1996c; OECD, 1996).
The following amounts of butadiene were estimated to have been released into the Canadian environment in 1994 from transportation and related sources (Environment Canada, 1996b; CPPI, 1997): 3376-7401tonnes from on-road gasoline- and diesel-powered motor vehicles (with about 45-89% of those releases from gasoline engines and 11-55% from diesel engines); 150-258 tonnes from aircraft; 84-1689 tonnes from off-road motor vehicles; 84 tonnes from lawnmowers; 40 tonnes from the marine sector; and 17 tonnes from the rail sector. Data on releases from on-road motor vehicles in 1994 were estimated by modelling (Mobile 5C model), using assumptions outlined in Environment Canada (1996b). It can be expected that the rates of release of butadiene from automotive sources have and will continue to change; most current and planned modifications to automotive emission control technology and gasoline quality would lead to decreases in the releases of butadiene and other VOCs.
In addition, data from NPRI for 1994 (Environment Canada, 1996b) listed a total of 270.4 tonnes released from the chemical and chemical products industries. Of this, 270.3 tonnes were released into air, 0.058 tonnes into water (St. Clair River, Ontario) and 0.002 tonnes onto land. There were releases of 17.5 tonnes into air from the plastic products industries. A total of 22.3 tonnes was released from the refined petroleum and coal products industries, of which 22.2 tonnes were released into air. Off-site transfer of wastes (material sent for final disposal or treatment prior to final disposal) from industrial sites in Canada in 1994 was estimated to include a total of 131.3 tonnes of butadiene, with 128.7 tonnes being sent to incineration, 2.1 tonnes to landfill and 0.5 tonnes to municipal sewage treatment plants (Environment Canada, 1996b). Based on 1995 NPRI data (Environment Canada, 1997d), the amount of butadiene estimated to have been released into the Canadian environment was 225.8 tonnes from industrial on-site uses, with 0.058 tonnes released into water, 0.002 tonnes into land and 225.4 tonnes into air. Releases into air included air fugitive releases (172.8 tonnes), air stack releases (36.3 tonnes), air storage releases (4.8 tonnes), air spill releases (1.1tonnes) and other air releases (10.4 tonnes).
Based on data in NPRI, it was estimated that the total release of butadiene from fuel distribution in 1994 was 24 tonnes (Environment Canada, 1996b), although gasoline and diesel fuel contain little butadiene.
CPPI (1997) estimated that releases into the Canadian environment in 1994 were 1191 tonnes from prescribed forest burning, 3706 tonnes from wood space heating, 11 tonnes from natural gas/oil space heating and 1-9 tonnes from cigarettes.
2.3 Exposure characterization
2.3.1 Environmental fate
2.3.1.1 Air
Since butadiene is released primarily to air, its fate in that medium is of primary importance. Butadiene is not expected to persist in air, since it oxidizes rapidly with several oxidant species. Destruction of atmospheric butadiene by the gas-phase reaction with photochemically produced hydroxyl radicals is expected to be the dominant photo-initiated pathway. Products that can be formed include formaldehyde, acrolein and furan. Destruction by nitrate radicals is expected to be a nighttime process in urban areas. Acrolein, trans-4-nitroxy-2-butenal and 1-nitroxy-3-buten-2-one have been identified as products of this reaction. Reaction with ozone is also rapid but less important than reaction with hydroxyl radicals. The products from the reaction of butadiene with ozone are acrolein, formaldehyde, acetylene, ethylene, formic acid, formic anhydride, carbon monoxide, carbon dioxide, hydrogen gas, hydroperoxyl radical, hydroxyl radical and 3,4-epoxy-1-butene (Atkinson et al., 1990; Howard et al., 1991; McKone et al., 1993; U.S. EPA, 1993).
Estimated average atmospheric half-lives for photo-oxidation of butadiene range from 0.24 to 10 hours (Darnell et al., 1976; Lyman et al., 1982; Atkinson et al., 1984; Howard et al., 1991; Mackay et al., 1993). However, half-lives for butadiene in air can vary considerably under different conditions. Estimations for atmospheric residence time in several U.S. cities ranged from 0.4 hours under clear skies at night in the summer to 2000 hours (83 days) under cloudy skies at night in the winter. Daytime residence times for different cities within a given season varied by factors of 2-3. Nighttime residence times varied by larger factors. The differences between summer and winter conditions were large at all sites, with winter residence times 10-30 times greater than summer residence times (U.S. EPA, 1993). Because of the long residence times under some conditions, especially in winter under cloudy conditions, there is a possibility of day-to-day carryover. Nonetheless, given the generally short daytime residence times, the net atmospheric lifetime of butadiene is short, and there is generally limited potential for long-range transport of this compound.
It is predicted from its physical/chemical properties that when butadiene is released into air, almost all of it will exist in the vapour phase in the atmosphere (Eisenreich et al., 1981; Environment Canada, 1998). Wet and dry deposition are not expected to be important as transfer processes. Evaporation from rain may be rapid, and the compound is returned to the atmosphere relatively quickly unless it is leached into the soil.
2.3.1.2 Water
Volatilization, biodegradation and oxidation by singlet oxygen are the most prominent processes involved in determining the fate of butadiene in water. The estimated half-lives of butadiene by reaction in water range from 4.2 to 28 days (Howard et al., 1991; Mackay et al., 1993).
2.3.1.3 Sediment
The processes that are most prominent in determining the environmental fate of butadiene in sediment are biotic and abiotic degradation. The estimated half-lives of butadiene by reaction in sediment range from 41.7 to 125 days (Mackay et al., 1993).
2.3.1.4 Soil
Based on its vapour pressure and its solubility, volatilization of butadiene from soil and other surfaces is expected to be significant. Butadiene's organic carbon/water partition coefficient indicates that it should not adsorb to soil particles to a great degree and would be considered moderately mobile (Kenaga, 1980; Swann et al., 1983). However, the rapid rate of volatilization and the potential for degradation in soil suggest that it is unlikely that butadiene will leach into groundwater. The estimated half-life of butadiene by reaction, given by Howard et al. (1991) and Mackay et al. (1993), ranges from 7 to 41.7 days.
2.3.1.5 Biota
There are no measured bioconcentration factors. Butadiene is metabolized by the mixed-function oxidase system in higher organisms, which contributes to the expected lack of accumulation by many organisms. Estimated bioconcentration factors for butadiene in fish have been reported to range from 4.6 to 19 (Lyman et al., 1982; OECD, 1996). Even though estimation methods likely overestimate the true bioconcentration potential for a readily metabolized substance, they indicate that butadiene is not expected to bioconcentrate in aquatic organisms or to biomagnify in the aquatic food chain.
There are no reported measurements of plant-root bioconcentration in soils. However, McKone et al. (1993) estimated the uptake of butadiene by roots from soil solution to be 1.84 L/kg, which is the ratio of butadiene concentration in root (mg/kg, fresh mass) to concentration in soil solution (mg/L). The partition coefficient of butadiene concentration in roots (mg/kg, fresh mass) to concentration in soil solids (mg/kg) was estimated to range from 0.32 to 15 (dimensionless). The partition coefficient of butadiene concentration in whole plants (mg/kg, fresh mass) to concentration in soil solids (mg/kg) was estimated to range from 0.1 to 2.9 (dimensionless). The steady-state plant/air partition coefficient for foliar uptake of butadiene in plant leaves was estimated to be 0.63 m3/kg. There are no reported bioaccumulation data for any terrestrial invertebrates.
2.3.1.6 Environmental distribution
Fugacity modelling was conducted to provide an overview of key reaction, intercompartment and advection (movement out of a system) pathways for butadiene and of overall distribution in the environment. A steady-state, non-equilibrium model (Level III fugacity modelling) was run using the methods developed by Mackay (1991) and Mackay and Paterson (1991). Assumptions, input parameters and results are presented in Environment Canada (1998).
Based on butadiene's physical/chemical properties, Level III fugacity modelling predicts that (Environment Canada, 1998):
- when butadiene is released into air, the distribution of mass is almost 100% in air, with very small amounts in soil and water;
- when butadiene is released into water, the distribution of mass is 98.1% in water, with small amounts in air;
- when butadiene is released into soil, the distribution of mass is 47.6% in soil, 51.5% in air and 0.9% in water.
Modelling predictions do not purport to reflect actual expected measurements in the environment but rather indicate the broad characteristics of the fate of the substance in the environment and its general distribution between media. Thus, when butadiene is discharged into air or water, most of it is expected to be found in the medium receiving the discharge directly. For example, if butadiene is discharged into air, almost all of it will exist in the atmosphere, where it will react rapidly and will also be transported away. If butadiene is discharged to water, it will react in water, and some will also evaporate into air. If butadiene is discharged to soil, most will be present in air or soil, where it will react (Mackay et al., 1993; Environment Canada, 1998).
2.3.2 Environmental concentrations
2.3.2.1 Ambient air
Butadiene was detected (detection limit 0.05 µg/m3) in 7314 (or 80%) of 9168 24-hour samples collected between 1989 and 1996 under the National Air Pollution Surveillance (NAPS) program from rural, suburban and urban locations (n = 47) in seven provinces (Dann, 1997). The mean concentration in all samples was 0.3 µg/m3 (in the calculation of the mean, a value of one-half the detection limit was assumed for samples in which levels were below the detection limit), and the maximum concentration measured was 14.1 µg/m3. Concentrations of butadiene in ambient air corresponding to the 50th and 95th percentiles of the NAPS data set were 0.21 and 1.0 µg/m3, respectively. There was a seasonal variation in the mean concentration of butadiene in ambient air, with levels being lower during the late spring and early summer months. This seasonal variation in mean concentration was more pronounced for suburban NAPS sites than for urban sites. There is no evidence that concentrations of butadiene in ambient air in Canada have been increasing or decreasing in a systematic manner during the 1990s.
Concentrations of butadiene were determined in 1611 samples of outdoor air from 25 sites within 14 cities, towns or rural locations in Ontario between 1990 and 1994 (Steer, 1996). Butadiene was detected in 37% of the samples (detection limits 0.04-0.1 µg/m3). The frequency of detection was much higher at downtown sites than at rural sites. The mean concentration in all samples was 0.1 µg/m3 (in the calculation of the mean, a value of one-half the detection limit was assumed for samples in which levels were below the detection limit), and the maximum concentration measured was 1.7 µg/m3. Concentrations of butadiene in ambient air corresponding to the 50th and 95th percentiles of this data set were 0.05 and 0.3 µg/m3, respectively.
Butadiene has been detected at concentrations generally less than 2 µg/m3 in a low percentage of samples of outdoor air collected during several small studies conducted during the 1990s in Toronto (Bell et al., 1991), Windsor (Bell et al., 1993) and Hamilton (Hamilton-Wentworth, 1997) in Ontario and in Edmonton and Fort Saskatchewan, Alberta (Conor Pacific Environmental, 1998). The highest reported concentration of butadiene in outdoor air in Canada (i.e., 28 µg/m3 in a 30-minute sample) was measured in 1995 within 1 km of an industrial point source of discharge to the atmosphere in Sarnia, Ontario (MOEE, 1995). Butadiene was detected in 78% of samples collected at various distances downwind from the point source, but in only 38% of samples collected upwind (detection limit 0.11 µg/m3 for 30-minute air samples). Concentrations decreased with distance from the source. At distances between 1 and 3 km downwind of the source, the concentrations of butadiene in ambient air corresponding to the 50th and 95th percentiles of this data set were 0.62 and 6.4 µg/m3, respectively, while the levels corresponding to the 50th and 95th percentiles of samples at distances of 1 km and greater (upper end of the range not specified) were 0.48 and 2.6 µg/m3, respectively.
Butadiene has also been detected in air in enclosed structures. Concentrations of butadiene between 4 and 49 µg/m3 were measured during the winter months of 1994-95 in Canadian underground parking garages (Environment Canada, 1994) because of its presence in vehicle exhaust. Similarly, butadiene was frequently detected in samples from 10 parking structures in California, with the maximum concentration being 28 µg/m3 (Wilson et al., 1991). Butadiene has also been detected in urban road tunnels during rush hours in Australia (mean concentration 28 µg/m3; Duffy and Nelson, 1996) and Sweden (mean concentrations 17 µg/m3 and 25 µg/m3 in two tunnels; Barrefors, 1996). Butadiene was measured at concentrations ranging from 0.2 to 28 µg/m3 in 96 of 97 5-minute air samples collected from a pumping island at randomly identified self-service filling stations in California (Wilson et al., 1991).
2.3.2.2 Indoor air
Concentrations of butadiene in the air of indoor environments are highly variable and depend largely on individual activities and circumstances, including the use of consumer products (e.g., cigarettes), the infiltration of vehicle exhaust from nearby traffic and possibly from attached garages, and, reportedly, cooking activities involving heated fats and oils. While data are inadequate to determine the relative contributions of each of these potential indoor sources, the highest concentrations of butadiene in indoor air in Canada have generally been detected in indoor environments contaminated with environmental tobacco smoke (ETS).
Butadiene was detected in 45% of indoor air samples in the Windsor Air Quality Study (Bell et al., 1993) but in only 7.5% of outdoor air samples, using the same sampling and analytical methodologies (detection limits 0.08-0.14 µg/m3). A maximum concentration of 1.2 µg/m3 was measured outdoors. Mean concentrations in indoor air from "non-smoking" locations ranged from 0.3 to 1.6 µg/m3, while mean concentrations in indoor air from "smoking" locations ranged from 1.3 to 18.9 µg/m3. A maximum indoor concentration of 36.9 µg/m3 was measured in a bingo hall. The frequency of detection of butadiene was 75-100% at non-residential indoor sampling sites where ETS was present.
Concentrations of butadiene were measured in 57 randomly chosen homes in Hamilton, Ontario, during 1993 (Hamilton-Wentworth, 1997). In 34 pairs of concurrent 24-hour samples of indoor and outdoor air, butadiene was detected in 38% of the indoor samples but in only 9% of the outdoor samples. Limits of detection ranged from 0.08 to 0.14 µg/m3. A concentration equivalent to one-half the limit of detection was assumed for the concentration of butadiene in samples in which it was not detected for calculation of median and mean concentrations. The mean concentration of butadiene was nine times higher indoors (i.e., 0.27 µg/m3) than outdoors (i.e., 0.03 µg/m3). The maximum concentrations in indoor and outdoor air were 1.5 µg/m3 and 0.13 µg/m3, respectively. Butadiene was detected in 16% of samples from "non-smoking" homes (maximum concentration 1.0 µg/m3) and in 50% of samples from "smoking" homes (maximum concentration 1.2 µg/m3).
Concentrations of butadiene were measured in a multimedia exposure study in several Canadian cities during 1996 and 1997. In the pilot study phase, butadiene was detected in 25% of 24-hour samples of indoor air, but in none of the 44 concurrent 24-hour outdoor air samples (detection limit 0.6 µg/m3) (Cao, 1997). In the second phase of this study, butadiene was detected in 22% of 24-hour samples of indoor air and in only 9% of the 50 concurrent 24-hour outdoor air samples (detection limit 0.9 µg/m3) (Conor Pacific Environmental, 1998). The maximum concentration of butadiene in the indoor air of the 94 residences was 19.2 µg/m3, while the maximum concentration in outdoor air was 2.1 µg/m3. Butadiene was detected in 10% of the indoor air samples from homes (n = 57) where cigarette smoking did not occur (mean concentration <1 µg/m3; censored data) and in 43% of the indoor air samples from homes (n = 37) where cigarette smoking did occur during the sample collection (mean concentration 2.5 µg/m3; censored data).
2.3.2.3 Surface water
No data on concentrations of butadiene in Canadian lake, river, estuarine or marine waters were identified in the literature. Butadiene is being monitored in effluents discharged into the St. Clair River from the butadiene production plant in Sarnia, Ontario. It was detected only twice, at 2 and 5 µg/L, in 2103 composite samples of aqueous effluent taken every 4 hours in 1996 (detection limit 1 µg/L). In daily sampling of effluents from the four individual outfalls (detection limit 1 µg/L in 736 samples and 50 µg/L in 789 samples), butadiene was detected in only three samples, at concentrations of 21, 80 and 130 µg/L (Bayer Inc., 1997).
Using the approaches of Mackay (1991), partition coefficients were calculated for a closed system at steady-state equilibrium at 25°C (Environment Canada, 1998). Under such conditions, it was predicted that for the highest concentration measured in outdoor air in Canada (28 µg/m3), the concentration of butadiene expected in water would be 9.3 × 10-3 µg/L.
2.3.2.4 Groundwater
Butadiene was detected but not quantified in a groundwater plume near a waste site in Quebec where refinery oil residues and a variety of organic chemicals had been dumped (Pakdel et al., 1992).
2.3.2.5 Drinking water
There are no data available concerning the presence of butadiene in drinking water in Canada or elsewhere. In an investigation on whether the use of polybutylene pipe in water distribution systems is likely to result in the contamination of drinking water with butadiene, Cooper (1989) did not detect the substance in water from these types of pipes (no further information was presented in the secondary account [CARB, 1992] of this study).
2.3.2.6 Soil and sediment
No data were identified regarding concentrations of butadiene in soil or sediment. Using the approaches of Mackay (1991), partition coefficients were calculated for a closed system at steady-state equilibrium at 25°C (Environment Canada, 1998). Under such conditions, it was predicted that for the highest concentration measured in outdoor air in Canada (28 µg/m3), the concentrations of butadiene expected in bulk soil and bulk sediment would be 7.5 × 10-6 and 1.5 × 10-5 µg/g (dry weight), respectively.
2.3.2.7 Food
There are no data available concerning the presence or concentrations of butadiene in food in Canada. In the United States, the migration of butadiene from rubber-modified plastic containers to food was investigated by McNeal and Breder (1987). Butadiene was detected in some of the containers, but was generally not detected in the foods (detection limits 1-5 ng/g). Similarly, in the United Kingdom, butadiene was not detected (detection limit 0.2 ng/g) in five brands of soft margarine, although its presence was demonstrated (at concentrations ranging from <5 to 310 ng/g) in the plastic containers (Startin and Gilbert, 1984). Butadiene has been detected in the emissions from heated cooking oils, including Chinese rapeseed, peanut, soybean and canola oils, at levels ranging from 23 to 504 µg/m3 (Pellizzari et al., 1995; Shields et al., 1995).
2.3.2.8 Consumer products
Data on emissions of butadiene from potential indoor sources such as styrene-butadiene rubber were not identified.
Butadiene has been detected in both mainstream smoke and sidestream smoke from cigarettes in Canada and the United States. For 18 brands of Canadian cigarettes, the mean butadiene content ranged from 14.3 to 59.5 µg/cigarette (overall mean concentration 30.0 µg/cigarette) in the mainstream smoke and from 281 to 656 µg/cigarette (overall mean concentration 375 µg/cigarette) in the sidestream smoke, according to "preliminary" data (Labstat, Inc., 1995). The U.S. DHHS (1989) reported that the vapour phase of mainstream smoke of non-filtered cigarettes contained butadiene at levels of 25-40 µg/cigarette. Brunnemann et al. (1989) measured butadiene levels ranging from 16 to 75 µg/cigarette in mainstream smoke from seven brands of cigarettes and levels ranging from 205 to 361 µg/cigarette in the sidestream smoke from six types of cigarettes. As discussed in Section 2.3.2.2, the presence of ETS contributes to elevated levels of butadiene in indoor air.
2.4 Effects characterization
2.4.1 Ecotoxicology
Owing to the high vapour pressure, flammable/ explosive nature and relatively rapid abiotic and biotic degradation of butadiene, few experimental toxicity data are available, particularly for aquatic organisms. Instead, many of the data have been derived using modelling based on quantitative structure-activity relationships (QSAR). The reliability of the data is dependent on the model used; data reported below were derived using models for non-polar narcotics or organic volatiles. Experimental data for substances chemically or toxicologically related to butadiene can be used to verify the reliability of the modelled data.
There is no experimental information in the literature on the effects of butadiene on aquatic plants or invertebrates. Predicted acute and chronic toxicity data for these groups are presented in Table 2. Toxicity information for the alga Selenastrum capricornutum is available for a structurally similar chemical, 1,3-pentadiene, with a 96-hour EC50 of 174.6 mg/L for growth rate and 245.8 mg/L for growth inhibition (OECD, 1996). The measured 48-hour EC50 for the invertebrate Daphnia exposed to 1,3-pentadiene was 221.5 mg/L (OECD, 1996).
No valid aquatic toxicity tests have been carried out in which fish were exposed to butadiene. A 24-hour Median Tolerance Limit(LC50) of 71.5 mg/L for pinfish (Lagodon rhomboides) is frequently quoted for butadiene, but the actual chemical tested was cyano-1,3-butadiene (Daugherty and Garrett, 1951), and so the result is not relevant to this assessment. Predicted acute and chronic toxicity values for freshwater fish are presented in Table 2. Information on toxicity is available for the structurally similar chemicals 1,3-pentadiene and isoprene (3-methyl-1,3-butadiene) (OECD, 1996). For 1,3-pentadiene,the 96-hour LC50 for fathead minnow (Pimephales promelas) was 139.9 mg/L. For isoprene, the 96-hour LC50s ranged from 42.5 mg/L for bluegill (Lepomis macrochirus) to 240 mg/L for the guppy (Poecilia reticulata) (OECD, 1996).
| Test organism | Endpoint | Toxicity value | Reference2 |
|---|---|---|---|
| Freshwater algae - Acute/chronic | |||
| algae green | 72-hour EC50 | 32.6 g/L | Bol et al., 1993* |
| algae | 96-hour EC50 | 27.4 g/L | Galassi and Vighi,1981* |
| Freshwater invertebrate - Acute | |||
| Daphnia sp. | 48-hour EC 50 | 44.9 g/L | Bol et al., 1993* |
| Daphnia sp. | 48-hour EC 50 | 43.8 g/L | Hermens et al., 1984* |
| Daphnia sp. | 48-hour EC 50 | 24.8 g/L | IUCLID, 1996 |
| Freshwater invertebrate - Chronic | |||
| Daphnia sp. | 21-day NOEC reproduction /growth |
9.2 mg/L | Bol et al., 1993* |
| Daphnia sp. | 16-day EC50 production | 2.2 mg/L | Hermens et al., 1984* |
| Freshwater fish - Acute | |||
| fathead minnow ( Pimephales promelas ) | 96-hour LC 50 | 42.8 mg/L | Bol et al., 1993* |
| fathead minnow ( Pimephales promelas ) | 96-hour LC 50 | 49.8 mg/L | IUCLID, 1996 |
| fathead minnow ( Pimephales promelas ) | 96-hour LC 50 | 40.9 g/L | Veith et al., 1983* |
| bluegill ( Lepomis macrochirus ) | 96-hour LC 50 | 37.8 g/L | IUCLID, 1996 |
| channel catfish (Ictalurus punctatus) | 96-hour LC 50 | 21.4 mg/L | IUCLID, 1996 |
| rainbow trout (Oncorhynchus mykiss) | 96-hour LC 50 | 22.4 mg/L | IUCLID, 1996 |
| Freshwater fish - Chronic | |||
| fathead minnow (Pimephales promelas)and zebra fish (Danio rerio) | 21-day NOEC | 4.5 mg/L | Bol et al., 1993* |
| fish | 30-day survival, growth | 5.3 mg/L | U.S. EPA, 1991* |
| fathead minnow (Pimephales promelas) | 32-day MATC | 7.3 mg/L | IUCLID, 1996 |
| Saltwater fish - Acute | |||
| sheepshead minnow (Cyprinodon variegatus) |
96 hour LC50 | 9.3 mg/L | Zaroogian et al., 1985* |
| Terrestrial plant - Acute/chronic | |||
| coleus, sorghum, soybean | 7-day NOEC3 | 2210 g/m3 | Heck and Pires, 1962 |
| cotton, cowpea, tomato | 7-day LOEC 3 | 2210 g/m3 | Heck and Pires, 1962 |
| cotton, coleus, tomato |
21-day NOEC 3 | 22.1 g/m3 | Heck and Pires, 1962 |
| cotton, tomato | 21-day LOEC3 | 221 g/m3 | Heck and Pires, 1962 |
| Soil invertebrate - Chronic | |||
| earthworm (Eisenia fetida) | 14-day LC50 | 335 mg/kg (dry soil) | McCarty, 1997 |
The toxicity of butadiene to several species of terrestrial plants has been determined experimentally by Heck and Pires (1962), including effects on growth and development of cotton, cowpea, tomato, coleus, sorghum and soybean. When plants were exposed to butadiene at 2210 mg/m3 for 7 days, no injury was reported for coleus, sorghum and soybean, and only slight injury was reported in cotton, cowpea and tomato. When exposed for 21 days to butadiene, no injury was seen in coleus, cotton and tomato exposed to 22.1 mg/m3, and no significant (<5%) injury was seen in cotton and tomato exposed to 221 mg/m3. The authors summarized the results as 0% injury on exposure to 22.1 mg/m3 and only slight (<5%) injury on exposure to both 221 and 2210 mg/m3. The nature of the injury was not stated. The butadiene tested was >99% pure, with impurities including t-butyl catechol, n-butane, butenes and acetylene.
Although there is no information on experimental toxicity for soil invertebrates, modelling was used to estimate a 14-day LC50 of 335 mg/kg (dry mass) for earthworm (Table 2) (McCarty, 1997). No information on the effects of butadiene on birds or wild mammals by any route of exposure was identified. Data for laboratory mammals and other organisms pertinent to the human health assessment are presented in Section 2.4.3.
1 All but terrestrial plant data are estimated using QSAR modelling, assuming a log Kow value of 1.99.
2 For those references marked with an asterisk, the values presented in the table were calculated using the equations/methods outlined in the references (i.e., the values themselves are not contained in the references).
3 Experimental observations.
