Follow-up Report on a PSL1 Substance for Which There Was Insufficient Information to Conclude Whether the Substance Constitutes a Danger to the Environment
1,1,2,2-Tetrachloroethane
Environment Canada
May 2003
Table of Contents
- List of Acronyms and Abbreviations
- Synopsis
- 1.0 Introduction
- 2.0 Entry Characterization
- 3.0 Exposure Characterization
- 4.0 Effects Characterization
- 5.0 Assessment of “Toxic” UnderCEPA 1999
- 6.0 References
- Appendix A: Molecular Structures of 1,1,2,2-tetrachloroethane and its Structural Analogues
- Appendix B: Search Strategies Employed for Identification of Relevant Data
| Acronym or abbreviation | Definition |
|---|---|
| BCF | bioconcentration factor |
| CEPA | Canadian Environmental Protection Act |
| CEPA 1999 | Canadian Environmental Protection Act, 1999 |
| CTV | Critical Toxicity Value |
| EEV | Estimated Exposure Value |
| ENEV | Estimated No-Effects Value |
| kg-bw | kilogram body weight |
| PSL | Priority Substances List |
| PSL1 | first Priority Substances List |
1,1,2,2-Tetrachloroethane, which appeared on the first Priority Substances List (PSL1), was assessed to determine whether it should be considered “toxic” as defined under the Canadian Environmental Protection Act (CEPA). It was concluded that 1,1,2,2-tetrachloroethane was not “toxic” under Paragraph 11(b) of CEPA; however, there was insufficient information to conclude whether 1,1,2,2-tetrachloroethane constituted a danger to the environment under Paragraph 11(a). Information was lacking about the potential effects of the substance on terrestrial biota.
No information is available concerning the effects of 1,1,2,2-tetrachloroethane on wildlife. Based on currently available toxicity studies conducted on laboratory animals, it is unlikely that wildlife would be adversely affected by the concentrations of 1,1,2,2-tetrachloroethane reported in the Canadian environment. No information was identified on the potential effects of 1,1,2,2-tetrachloroethane on plants exposed through the atmosphere. Based on toxicity information available for several PSL1 substances that are structurally similar to 1,1,2,2-tetrachloroethane, it is concluded that terrestrial plants are unlikely to be adversely affected by the concentrations of the substance reported in the Canadian atmosphere.
Based on the information currently available, it is proposed that 1,1,2,2-tetrachloroethane is 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. Therefore, 1,1,2,2-tetrachloroethane is not considered “toxic” as defined in Paragraph 64(a) of the Canadian Environmental Protection Act, 1999. The results of the U.S. National Toxicology Program (NTP) study will be evaluated when they become available, as they could affect the assessment of potential effects of 1,1,2,2-tetrachloroethane on wildlife.
1,1,2,2-Tetrachloroethane appeared on the first Priority Substances List (PSL1) of the Canadian Environmental Protection Act (CEPA), published in the Canada Gazette, Part I, on February 11, 1989. Assessments were performed to determine whether the substance should be considered “toxic” as defined under CEPA and were completed in 1993 (Government of Canada, 1993a). It was concluded that 1,1,2,2-tetrachloroethane does not constitute a danger to the environment on which human life depends; therefore, it was not found to be “toxic” under Paragraph 11(b) of CEPA. Available information was insufficient to conclude whether 1,1,2,2-tetrachloroethane constituted a danger to the environment under Paragraph 11(a) of CEPA. In particular, information was lacking about whether concentrations of 1,1,2,2-tetrachloroethane in air would adversely affect terrestrial biota (plants and wildlife) in Canada.
A literature search was undertaken to identify recent information on the toxicity of 1,1,2,2-tetrachloroethane to terrestrial plants through atmospheric exposure. Recent information about releases of 1,1,2,2-tetrachloroethane from industrial sources and data on concentrations of 1,1,2,2-tetrachloroethane in air from across Canada were obtained from Canadian databases.
This report examines this new information about the entry of and exposure to 1,1,2,2-tetrachloroethane in the Canadian environment to determine if the substance is likely to have a harmful effect on wildlife. The report also examines information on structural analogues of 1,1,2,2-tetrachloroethane that were PSL1 substances in order to determine if the substance is likely to have a harmful effect on terrestrial plants through atmospheric exposure.
A draft follow-up report was made available for a 60-day public comment period (between September 28 and November 27, 2002). No comments were received.
No on-site environmental releases of 1,1,2,2-tetrachloroethane were reported to the National Pollutant Release Inventory in 1996 (NPRI, 1999).
The Canadian Chemical Producers’ Association (1999) reported total emissions of 1,1,2,2-tetrachloroethane of 2 tonnes from member companies in 1998 and 0.42 tonnes in 1997.
3.1 Environmental Fate
1,1,2,2-Tetrachloroethane has a low bioaccumulation potential. Its bioconcentration factor (BCF) is calculated to be 21–72 using the method of Veith et al. (1980), based on its octanol/water partition coefficient (Kow) of 2.39 (Government of Canada, 1993a). A measured BCF of 8 was reported for bluegill, Lepomis macrochirus, exposed to 9.6 µg 1,1,2,2-tetrachloroethane/L for 14 days (Barrows et al., 1980, cited in Government of Canada, 1993a). The metabolic half-life of 1,1,2,2-tetrachloroethane in the fish was quite short, less than 1 day, accounting for the measured BCF being lower than the estimated BCF.
3.2 Environmental Concentrations
3.2.1 Ambient Air
1,1,2,2-Tetrachloroethane was detected (detection limit 0.1 µg/m3) in 2283 (or 25%) of 9178 24-hour samples collected from 1994 to 1999, inclusive, from rural, suburban and urban locations in seven provinces under the National Air Pollution Surveillance program (Dann, 1999). The highest 24-hour average concentration measured was 1.7 µg/m3, in a sample collected at Sarnia, Ontario, in 1998. This value is higher than the previously reported high of 0.86 µg/m3, measured in a sample from Ottawa, Ontario (Environment Canada, 1992, cited in Government of Canada, 1993a).
3.2.2 Surface Water
1,1,2,2-Tetrachloroethane has been detected in surface waters in Canada, with the highest reported concentration being 4.0 µg/L (COARGLWQ, 1986, cited in Government of Canada, 1993a).
3.2.3 Biota
No data have been identified concerning the concentration of 1,1,2,2-tetrachloroethane in aquatic or terrestrial biota in Canada. Based on the measured BCF of 8 and the maximum reported concentration in Canadian surface water of 4.0 µg/L, the concentration of 1,1,2,2-tetrachloroethane in biota should not exceed 32 µg/kg-bw.
4.1 Terrestrial Plants
No information was identified concerning the effects of 1,1,2,2-tetrachloroethane on terrestrial plants.
In the absence of toxicity data for 1,1,2,2-tetrachloroethane, one approach is to use substances similar in structure to 1,1,2,2-tetrachloroethane as surrogates. Toxicity data are available for several PSL1 substances that are similar in structure to 1,1,2,2-tetrachloroethane. They are tetrachloroethylene, trichloroethylene and 1,2-dichloroethane.Appendix A presents the molecular structures of these substances.
4.1.1 Tetrachloroethylene
The principal photodegradation product of chloroethylenes is trichloroacetic acid, a known herbicide (Frank, 1990; Frank et al., 1990, 1992; all cited in Government of Canada, 1993b). Chlorosis (bleaching of needles) occurred in Norway spruce, Picea abies, following exposure to 3–6 µg tetrachloroethylene/m3 for 1–2 weeks (Frank, 1990, cited in Government of Canada, 1993b). Concentrations of the photosynthetic pigments chlorophyll-a and ?-carotene were reduced by 52% and 58%, respectively, when Norway spruce needles were irradiated with visible/ultraviolet radiation and exposed to tetrachloroethylene at a concentration of 14 µg/m3 for 5 hours (Frank and Frank, 1986, cited in Government of Canada, 1993b).
4.1.2 Trichloroethylene
The principal photodegradation product of chloroethylenes is trichloroacetic acid, a known herbicide (Frank, 1990; Frank et al., 1990, 1992; all cited in Government of Canada, 1993b). Concentrations of the photosynthetic pigments chlorophyll-a and ?-carotene were reduced by 32% and 41%, respectively, when Norway spruce needles were irradiated with visible/ultraviolet radiation and exposed to trichloroethylene at a concentration of 10.8 µg/m3 for 5 hours (Frank and Frank, 1986, cited in Government of Canada, 1993c). Exposure to trichloroethylene and radiation separately had no effect on the photosynthetic pigments, implying that photodegradation products were responsible for the effect.
4.1.3 1,2-Dichloroethane
1,2-Dichloroethane was both lethal and mutagenic to barley after an exposure of 3000 µg/m3 for 24 hours (Ehrenberg et al., 1974, cited in Government of Canada, 1994).
4.2 Wildlife
No information was identified concerning the effects of 1,1,2,2-tetrachloroethane on birds or wild mammals. Some information on the effects of 1,1,2,2-tetrachloroethane on laboratory animals was presented in Government of Canada (1993a).
Exposure to 50 000 µg 1,1,2,2-tetrachloroethane/m3 for approximately 5 weeks resulted in neurological effects and alterations in biochemical parameters and organ weights in rats (Schmidt et al., 1975, cited in Government of Canada, 1993a).
Histopathological damage was reported in the liver, kidney, testicles and thyroid gland of rats receiving oral doses of 3200–50 000 µg 1,1,2,2-tetrachloroethane/kg-bw per day for periods ranging from 2 to 150 days (Gohlke et al., 1977, cited in Government of Canada, 1993a). The results of this study were not well documented, so an effect level could not be validated (Government of Canada, 1993a).
The preliminary results of subchronic studies conducted by the U.S. National Toxicology Program (NTP, 1994) have been identified (see Health Canada Follow-up Report on 1,1,2,2-tetrachloroethane). Results of this study will be reviewed when they become available, as they could be relevant to the assessment of potential effects of 1,1,2,2-tetrachloroethane on wildlife.
The environmental risk assessment of a PSL substance is based on the procedures outlined in Environment Canada (1997). Analysis of exposure pathways and subsequent identification of sensitive receptors are used to select environmental assessment endpoints (e.g., adverse reproductive effects on sensitive fish species in a community). For each endpoint, a conservative Estimated Exposure Value (EEV) is selected and an Estimated No-Effects Value (ENEV) is determined by dividing a Critical Toxicity Value (CTV) by an application factor. A conservative (or hyperconservative) quotient (EEV/ENEV) is calculated for each of the assessment endpoints in order to determine whether there is potential ecological risk in Canada. If these quotients are less than one, it can be concluded that the substance poses no significant risk to the environment, and the risk assessment is completed. If, however, the quotient is greater than one for a particular assessment endpoint, then the risk assessment for that endpoint proceeds to an analysis where more realistic assumptions are used and the probability and magnitude of effects are considered. This latter approach involves a more thorough consideration of sources of variability and uncertainty in the risk analysis.
5.1 Assessment Endpoints
The assessment endpoints in this report are adverse effects on terrestrial plants exposed to 1,1,2,2-tetrachloroethane through the air and adverse effects on wildlife.
5.2 Terrestrial Plants
For a hyperconservative risk characterization for terrestrial plants, the EEVis 1.7 µg/m3, the highest 24-hour average concentration of 1,1,2,2-tetrachloroethane reported in the Canadian atmosphere from 1994 to 1999.
Phytotoxicity data are available for three PSL1 substances that are similar in structure to 1,1,2,2-tetrachloroethane: tetrachloroethylene, trichloroethylene and 1,2-dichloroethane. TheCTV is 10.8 µg/m3, the concentration of trichloroethylene that caused significant reductions in the concentration of photosynthetic pigments in Norway spruce needles after an exposure period of 5 hours. Adverse effects on conifers have been reported at lower concentrations of tetrachloroethylene, but only following longer exposure periods. Elevated concentrations of 1,1,2,2-tetrachloroethane in Canada appear to be transitory (see below), so the main concern is for effects from acute exposure. Dividing the CTVby a factor of 100 (to account for the use of trichloroethylene toxicity as a surrogate for 1,1,2,2-tetrachloroethane toxicity, extrapolation from laboratory to field conditions, and interspecies and intraspecies variations in sensitivity) gives anENEV of 0.1 µg/m3.
The hyperconservative quotient (EEV/ENEV) is then 1.7/0.1 = 17. It is therefore necessary to further assess the likelihood that 1,1,2,2-tetrachloroethane will cause harm to terrestrial vegetation in Canada as a result of atmospheric exposure.
About 1500 air samples have been collected from various urban, suburban and rural sites across Canada each year and analysed for 1,1,2,2-tetrachloroethane, among a number of other substances (Dann, 1999). As stated above, the maximum reported concentration of 1,1,2,2-tetrachloroethane was 1.7 µg/m3, from a sample collected in 1998. The maximum concentrations of 1,1,2,2-tetrachloroethane in 1999, 1997, 1996, 1995 and 1994 were 0.14 µg/m3, 0.24 µg/m3, 0.196 µg/m3, 0.22 µg/m3 and 0.17 µg/m3, respectively. The 99th percentile concentrations in 1999, 1998, 1997, 1996, 1995 and 1994 were 0.09 µg/m3, 0.05 µg/m3, 0.08 µg/m3, 0.08 µg/m3, 0.077 µg/m3 and 0.05 µg/m3, respectively. In 1999, 1570 air samples were collected from 37 sites. 1,1,2,2-Tetrachloroethane concentrations exceeded 0.1 µg/m3 at two sites. At these sites, the 95th percentile concentration was below 0.1 µg/m3. Concentrations of 1,1,2,2-tetrachloroethane therefore appear to be elevated in only a few places in Canada and for only limited periods of time. It is therefore unlikely that terrestrial plants would be significantly affected by the concentrations of 1,1,2,2-tetrachloroethane occurring in the Canadian atmosphere.
5.3 Wildlife
Wildlife can be exposed to 1,1,2,2-tetrachloroethane through inhalation or orally through ingestion of the substance in food or water.
The EEV for inhalation is 1.7 µg/m3, the highest 24-hour average concentration of 1,1,2,2-tetrachloroethane reported in the Canadian atmosphere from 1994 to 1999.
The CTV for inhalation is 50 000 µg/m3, the lowest concentration of 1,1,2,2-tetrachloroethane reported to have adverse effects on laboratory animals. Dividing the CTV by a factor of 10 (to account for the extrapolation from laboratory to field conditions and interspecies and intraspecies variations in sensitivity) gives an ENEV of 5000 µg/m3.
The hyperconservative quotient (EEV/ENEV) is then 1.7/5000 = 0.00034. 1,1,2,2-Tetrachloroethane is therefore unlikely to cause harm to wildlife in Canada as result of inhalation.
For wildlife exposed to 1,1,2,2-tetrachloroethane by ingestion, the EEVs are 32 µg/kg-bw, the highest estimated whole-body concentration of 1,1,2,2-tetrachloroethane in biota (Section 3.2.3), and 4 µg/L, the maximum reported concentration in Canadian surface water.
The CTV is 3200 µg 1,1,2,2-tetrachloroethane/kg-bw per day, the lowest concentration reported to have adverse effects on laboratory animals. Dividing the CTV by a factor of 10 (to account for the extrapolation from laboratory to field conditions and interspecies and intraspecies variations in sensitivity) gives an ENEV of 320 µg/kg-bw per day.
To reach the ENEV of 320 µg/kg-bw per day, an animal would, each day, have to eat 10 times its own weight of food containing 1,1,2,2-tetrachloroethane at a concentration of 32 µg/kg (320 µg/kg-bw per day divided by 32 µg/kg = 10) or drink 80 times its own weight of water containing 4 µg 1,1,2,2-tetrachloroethane/L (320 µg/kg-bw per day divided by 4 µg/L = 80), assuming that all of the 1,1,2,2-tetrachloroethane in the food and water was assimilated. It is therefore unlikely that wildlife would be adversely affected by the concentrations of 1,1,2,2-tetrachloroethane occurring in the Canadian environment.
The results of the NTP subchronic study will be evaluated when they become available.
5.4 Discussion of uncertainty
The ENEVfor terrestrial plants was based on the toxicity of trichloroethylene. 1,1,2,2-Tetrachloroethane could be a more potent toxicant than trichloroethylene; however, the principal photodegradation product of chloroethylenes is trichloroacetic acid, a known herbicide.
None of the mammalian toxicity studies identified was of sufficient quality to determine a No-Observed-Adverse-Effect Level or a Lowest-Observed-Adverse-Effect Level for 1,1,2,2-tetrachloroethane. The lowest exposure value reported to have an adverse effect, 3200 µg/kg-bw per day, was considerably lower than the lowest effect levels reported for the analogues of 1,1,2,2-tetrachloroethane that were included on PSL1(tetrachloroethylene, trichloroethylene and 1,2-dichloroethane). A Lowest-Observed-Effect Level of 20 000 µg/kg-bw per day was reported for tetrachloroethylene, based on hepatic damage in mice exposed orally 5 days per week for 6 weeks (Buben and O’Flaherty, 1985, cited in Government of Canada, 1993a). The results of the NTP subchronic study will be evaluated when they become available.
Atmospheric concentrations of 1,1,2,2-tetrachloroethane in Canada are quite low but appear to be increasing somewhat, as the maximum reported concentration was 1.7 µg/m3 in 1998, up from 0.17 µg/m3 in 1994. The maximum reported concentration in 1999, however, was lower, 0.14 µg/m3. Continued monitoring of 1,1,2,2-tetrachloroethane is needed.
Despite limitations in the data relating to the environmental effects of and exposure to 1,1,2,2-tetrachloroethane, data available at this time are considered adequate for reaching a conclusion on the environmental risk of 1,1,2,2-tetrachloroethane in Canada.
5.5 Conclusions
CEPA 199964(a): Based on currently available data, it is proposed that 1,1,2,2-tetrachloroethane is 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. Therefore, 1,1,2,2-tetrachloroethane is not considered “toxic” as defined in Paragraph 64(a) ofCEPA 1999. This conclusion will be re-examined when the results of the NTP study become available.
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| Chemical structure | Name |
|---|---|
| CHCl2CHCl2 | 1,1,2,2-tetrachloroethane |
| CH2ClCH2Cl | 1,2-dichloroethane |
| Cl2C=CCl2 | tetrachloroethylene |
| HClC=CCl2 | trichloroethylene |
Data relevant to the toxicity of 1,1,2,2-tetrachloroethane and its atmospheric breakdown products to terrestrial vegetation was sought using the following on-line searches in August 1999: CAB (Commonwealth Agriculture Bureaux), CAPLUS (Chemical Abstracts Service) and ECOTOX (Ecological Toxicity Database).