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Priority Substances List Assessment Report for 2-Ethoxyethanol
3.0 Assessment of "Toxic" under CEPA
3.1 CEPA 1999 64(a): Environment
The environmental risk assessment of a PSL substance is based on the procedures outlined in Environment Canada (1997a). 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.
3.1.1 Assessment endpoints
In Canada, most environmental releases of 2-ethoxyethanol are to the atmosphere. Based on its predicted environmental partitioning, assessment endpoints for 2-ethoxyethanol relate to terrestrial organisms, including terrestrial wildlife and soil organisms, and aquatic organisms.
3.1.2 Environmental risk assessment
3.1.2.1 Terrestrial organisms
3.1.2.1.1 Wildlife
For a conservative risk characterization for terrestrial biota, the EEV is 860 ng/m3, the highest concentration of 2-ethoxyethanol reported in Canada (near an automotive plant in Windsor) (OMEE, 1994).
The CTV is 50 ppm (1.8 x 108 ng/m3), the concentration that had minimal fetotoxic effects on rats and rabbits in inhalation studies. Dividing this CTV by a factor of 100 (to account for the extrapolation from laboratory to field conditions and interspecies and intraspecies variations in sensitivity) gives an ENEV of 0.5 ppm (1.8 x 106 ng/m3).
The conservative quotient is calculated as follows:
Therefore, concentrations of 2-ethoxyethanol in air in Canada are unlikely to cause adverse effects on populations of wildlife.
3.1.2.1.2 Soil organisms
For a conservative risk characterization for soil organisms, the EEV is 4.15 x 10-4 ng/g, the estimated concentration of 2-ethoxyethanol in soil using ChemCAN modelling based on reported releases in 1995. This value is believed to be conservative because releases of 2-ethoxyethanol in Canada appear to have significantly decreased since 1995.
No information was identified regarding the toxicity of 2-ethoxyethanol to soil organisms. Van Leeuwen et al. (1992) used quantitative structure-activity relationships to estimate that a sediment concentration of 2800 ng 2-ethoxyethanol/g would be hazardous to 5% of benthic species (HC5). Using this sediment HC5 value as a CTV and an application factor of 100 (to account for the extrapolation from benthic to soil organisms) gives an ENEV of 28 ng/g for soil organisms.
The conservative quotient is calculated as follows:
Therefore, concentrations of 2-ethoxyethanol in soil in Canada are unlikely to cause adverse effects on populations of soil organisms.
3.1.2.2 Aquatic organisms
For a conservative risk characterization for aquatic organisms, the EEV is 2.2 x 10-5 µg/L, the estimated concentration of 2-ethoxyethanol in water using ChemCAN modelling based on reported releases in 1995. This value is believed to be conservative because releases of 2-ethoxyethanol in Canada appear to have significantly decreased since 1995.
The CTV for aquatic organisms is 7.7 x 106 µg/L, the 48-hour IC50 for Daphnia magna. Dividing this CTV by a factor of 100 (to account for the conversion of a short-term IC50 to a long-term no-effects value, extrapolation from laboratory to field conditions, and interspecies and intraspecies variations in sensitivity) gives an ENEV of 7.7 x 104 µg/L.
The conservative quotient is calculated as follows:
Therefore, concentrations of 2-ethoxyethanol in water in Canada are unlikely to cause adverse effects on populations of aquatic organisms.
3.1.2.3 Discussion of uncertainty
There are several sources of uncertainty in this environmental risk assessment. Few data on environmental concentrations of 2-ethoxyethanol in Canada or elsewhere were identified; limited monitoring data were identified for air only. The EEV for wildlife exposure is considered to be conservative, as it was based on the maximum concentration measured near an industrial facility in Windsor. In addition, 2-ethoxyethanol was not detected in ambient air in the multimedia exposure study in Canada (Conor Pacific Environmental Technologies, 1998) or in a survey of six locations in the United States (Sheldon et al., 1988).
In view of the lack of adequate monitoring data, the ChemCAN4 model was used to estimate concentrations of 2-ethoxyethanol in the other environmental compartments (i.e., soil and water), based on the highest reported recent release of the substance in Canada, which occurred in 1995. Kane (1993) compared measured environmental concentrations of five industrial chemicals and six pesticides with environmental concentrations estimated for the substances by the ChemCAN model.
Sixty percent of the measured environmental concentrations were within 1 order of magnitude of predicted values, and 75% were within 2 orders of magnitude. In the only relevant study identified from other countries, the concentration of 2-ethoxyethanol in a polluted river in Japan ranged up to 1200 µg/L (Yasuhara et al., 1981), a value that is an order of magnitude lower than the ENEV for aquatic organisms.
No information was identified regarding the toxicity of 2-ethoxyethanol to soil organisms or to terrestrial wildlife through atmospheric exposure. An estimation of a hazardous concentration to benthic species was the basis for the assessment of risk to soil organisms. The results of an inhalation toxicity study using a laboratory strain of rats were used for the assessment of risk to terrestrial biota. To account for these uncertainties, application factors were used in the environmental risk assessment to derive ENEVs.
Conservative risk quotients were very small for all environmental assessment endpoints. Therefore, despite the data gaps regarding the 2-ethoxyethanol on soil organisms and terrestrial wildlife, the data available at this time are considered adequate for drawing a conclusion about the environmental risk of the substance in Canada.
3.2 CEPA 1999 64(b): Environment upon which life depends
2-Ethoxyethanol does not deplete stratospheric ozone, and its potential for contributing to climate change is negligible. The potential of 2-ethoxyethanol for creation of photochemical ozone (smog) is moderate, but the low quantities of 2-ethoxyethanol in the atmosphere are unlikely to make its contribution significant relative to that of other smog-forming substances.
3.3 CEPA 1999 64(c): Human health
3.3.1 Estimates of potential exposure in humans
The limitations of the available monitoring data for 2-ethoxyethanol preclude the development of reliable estimates of typical exposure of the general population; instead, crude upper-bounding estimates of exposure to 2-ethoxyethanol from environmental media and consumer products have been developed in order to characterize potential exposure from these pathways.
The only environmental media for which available monitoring data allowed even crude estimation of exposure were air and water. Upper-bounding estimates of intake of 2-ethoxyethanol from these media by six age groups in the general population of Canada are presented in Table 2. These estimates are based on the limits of detection in air and tap water from the limited Canadian multimedia exposure study in which concentrations of 2-ethoxyethanol were below the limits of detection in all samples analysed (Conor Pacific Environmental Technologies, 1998). Although confidence in the results of this survey is low, comparison with estimates of intake in air and water on the basis of results of fugacity modelling and in ambient air based on the data from the Windsor study indicates that this approach is conservative in deriving upper-bounding estimates of intake in air. Based on these values, the average adult in Canada would be exposed to airborne levels of 2-ethoxyethanol no greater than 3.6 µg/m3 and would not ingest more than 0.005 µg/kg-bw per day in drinking water, although it is recognized that these values likely overestimate exposure.
Since no monitoring data are available, it is not possible to determine the contribution of food to the overall intake of 2-ethoxyethanol. However, 2-ethoxyethanol is released primarily to air from industrial activities and through volatilization from consumer products and is unlikely to partition to food from air due to its volatility and very low octanol/water partition coefficient (log Kow of -0.32). In addition, if intake in food is estimated on the basis of extrapolation from the results of fugacity modelling, this value would be several orders of magnitude less than the upper-bounding estimates calculated for air and drinking water on the basis of the limits of detection in the multimedia study. Likewise, exposure to 2-ethoxyethanol in soil is likely to be negligible in comparison with that in air, based on its release patterns and the relatively small quantities ingested.
| Route of exposure | Upper-bounding estimates of intake of 2-ethoxyethanol by various age groups in the general population (µg/kg-bw per day) | |||||
|---|---|---|---|---|---|---|
| 0-6 months 1 | 7 months-4 yrs 2 | 5-11 yrs 3 | 12-19 yrs 4 | 20-59 yrs 5 | 60+ yrs 6 | |
| Ambient air 7 | 0.13 | 0.27 | 0.21 | 0.12 | 0.10 | 0.09 |
| Indoor air 8 | 0.87 | 1.87 | 1.46 | 0.83 | 0.71 | 0.62 |
| Drinking water 9 | 0.005 10 | 0.002 | 0.002 | 0.001 | 0.001 | 0.001 |
| Total | 1.0 | 2.1 | 1.7 | 0.9 | 0.8 | 0.7 |
- Assumed to weigh 7.5 kg, to drink 0.8 L of water per day and to breathe 2.1 m3 of air per day (EHD, 1998).
- Assumed to weigh 15.5 kg, to drink 0.7 L of water per day and to breathe 9.3 m3 of air per day (EHD, 1998).
- Assumed to weigh 31.0 kg, to drink 1.1 L of water per day and to breathe 14.5 m3 of air per day (EHD, 1998).
- Assumed to weigh 59.4 kg, to drink 1.2 L of water per day and to breathe 15.8 m3 of air per day (EHD, 1998).
- Assumed to weigh 70.9 kg, to drink 1.5 L of water per day and to breathe 16.2 m3 of air per day (EHD, 1998).
- Assumed to weigh 72.0 kg, to drink 1.6 L of water per day and to breathe 14.3 m3 of air per day (EHD, 1998).
- Based on the limit of detection for 2-ethoxyethanol in 50 ambient air samples collected outside of Canadian residences, 3.6 µg/m3 (Conor Pacific Environmental Technologies, 1998). The average Canadian is assumed to spend 3 hours of every day outdoors (EHD, 1998).
- Based on the detection limit (3.6 µg/m3) for 2-ethoxyethanol in 50 indoor air samples collected in Canadian residences (Conor Pacific Environmental Technologies, 1998). The average Canadian is assumed to spend 21 hours of every day indoors (EHD, 1998).
- Based on the detection limit (0.05 µg/L) for 2-ethoxyethanol in 50 drinking water samples collected in Canadian residences (Conor Pacific Environmental Technologies, 1998).
- Based on the assumption that infants were exclusively formula fed and consumed 800 mL of formula that was prepared with tap water.
Note: Insufficient data were available to estimate intake from soil or food.
Limited available recent data do not indicate that 2-ethoxyethanol or its acetate are commonly present in consumer products in Canada. Based primarily on earlier data, direct exposure to 2-ethoxyethanol and 2-ethoxyethyl acetate might result from the use of a variety of consumer products containing these substances. Both inhalation and dermal absorption would be expected to be important routes of exposure for such consumer products, since many of those that might contain 2-ethoxyethanol or its acetate can contact the skin. Because most of the consumer products for which data are available are used primarily by adults, the estimated exposures have been derived for this age class only. (The differences among age classes in intake from a given medium as a result of age-specific differences would be small in relation to the variation in exposure from the various sources, in any case.) Upper-bounding estimates of intake of 2-ethoxyethanol (on a per event basis as well as average daily intakes based on annual event frequencies) from exposure to household cleaning products and nail polish were developed from product use scenarios (Versar Inc., 1986), assuming 100% absorption for the product contacting the skin and for the inhaled product and 100% transfer of 2-ethoxyethanol from the product into air (in view of the lack of adequate data to support more refined estimates) (Table 3). These estimates should be interpreted with caution in view of the limited available information on the presence and concentrations of 2-ethoxyethanol and its acetate in consumer products currently used in Canada and should be considered as upper-bounding estimates only, as actual exposure is very likely much lower. Indeed, as discussed above, 2-ethoxyethanol was not detected in a recent investigation conducted by Health Canada of emissions of glycol ethers from several consumer products (Cao, 1999).
The worst-case estimate for exposure through use of a household cleaning product that is used on an almost daily basis (all-purpose spray cleaner, the only cleaning product for which composition data was available) was 1.6 or 0.5 mg/kg-bw per event or per day via inhalation and dermal absorption, respectively. Concentrations in indoor air resulting from use of such products could range up to 190 mg/m3, assuming complete volatilization.
It should be noted that these estimates have been made for only a limited range of media and few products for which at least some data were available. In addition, they do not represent typical or likely current exposures, since the limitations of the available data preclude development of such estimates; most are instead upper-bounding estimates of potential exposure.
3.3.2 Human health hazard characterization
Little information was identified on the effects of 2-ethoxyethanol in humans. However, although the epidemiological data are not conclusive, the results of available investigations in occupationally exposed populations are suggestive of effects on the blood and on sperm production in men (Cullen et al., 1983; Welch and Cullen, 1988; Welch et al., 1988; Ratcliffe et al., 1989; Veulemans et al., 1993; Kim et al., 1999). There is consistent evidence from short-and long-term toxicological studies in all species of experimental animals investigated that hematological, male reproductive and developmental effects are associated with exposure to 2-ethoxyethanol or its acetate by the oral, inhalation and dermal routes. The results of mechanistic studies suggest that metabolic activation to the acetic acid metabolite, EAA, is required for the induction of these effects. For example, co-exposure to substances that interfere with metabolism via alcohol or aldehyde dehydrogenases (e.g., toluene, xylene and ethanol) reduced the magnitude of testicular atrophy in male rats (Chung et al., 1999) and the effects on neurological development in rats exposed to 2-ethoxyethanol in utero (Nelson et al., 1982a,b, 1984). Metabolism via alcohol and aldehyde dehydrogenases to EAA is the principal metabolic pathway in both humans and laboratory animals; indeed, there is some evidence, although limited, that humans may have greater potential than rats for formation of EAA and slower clearance than in rats. Therefore, although there is only limited evidence of effects on the blood and sperm production in occupationally exposed human populations, based on the consistent evidence in experimental animals and the similarity in metabolism across species, hematopoietic, reproductive (in males) and developmental toxicity are considered critical effects for 2-ethoxyethanol.
3.3.3 Human health risk characterization
As discussed above in Section 1.0, due principally to the limitations of available monitoring data, upper-bounding estimates of exposure are compared with conservative effect levels for critical effects as a basis for characterization of rather crude margins of exposure.
Based on evaluation of available data, hematological, reproductive and developmental effects are considered critical endpoints for assessment of potential risk to humans associated with exposure to 2-ethoxyethanol. Statistically significant alterations in blood parameters were observed in shipyard painters exposed to a mean 2-ethoxyethyl acetate concentration of 3.03 ppm (equivalent to 11 mg 2-ethoxyethanol/m3), 5 although the authors suggested that the magnitude of these changes was not of biological significance (Kim et al., 1999). With respect to reproductive effects, in the only relevant studies in which exposure was quantified, reduced sperm production was observed in workers exposed to mean 2-ethoxyethanol concentrations of 9.9 mg/m3 (Welch et al., 1988) and 24 mg/m3 (Ratcliffe et al., 1989), although these men were also exposed to several other substances. In investigations in experimental animals, effect levels for hematological, reproductive and developmental effects were generally greater than concentrations associated with effects in the epidemiological studies (i.e., lowest LOELs of 184 mg/m3 and 94 mg/kg-bw per day), which is consistent with the limited data that suggest that humans form the putatively active metabolite to a greater extent than do rats and clear the metabolite more slowly. Therefore, risk to human health is characterized through comparison of the upper-bounding estimates of population exposure with the levels associated with effects in exposed workers.
| Consumer product | Assumptions | Estimated intake (mg/kg-bw per event) | Estimated average daily intake (mg/kg-bw per day) |
|---|---|---|---|
| Nail polish | Dermal 1
|
0.04 | 0.03 |
| All-purpose spray cleaner | Inhalation 2
|
1.6 [estimated indoor air concentration of 190 mg/m3] |
1.6 |
Dermal 1
|
0.5 | 0.5 |
- Estimates of intake by dermal absorption of 2-ethoxyethanol in liquid consumer products are based on the assumptions that a portion of the skin contacts the liquid and the amount absorbed is directly proportional to the area of exposed skin. It is assumed that all of the ingredient present in the liquid is absorbed through the skin. Standard exposure scenarios for dermal absorption of ingredients of liquid consumer products (e.g., Versar Inc., 1986; U.S. EPA, 1997) often include recommended skin surface areas and surface film thickness depending on the type of product and the manner in which it is used. For example, in Versar Inc. (1986), surface areas assumed are 400 cm2 for both palms of adult hands for scenarios involving some liquid cleaning products. Experimental data for surface film thickness are often not available for some types of consumer products and are estimated by analogy with other liquid substances.
- Estimates of intake by inhalation are based on the assumptions that the ingredient is completely and instantaneously released from the applied product, the concentration is homogenous throughout the assumed volume, and no air exchange occurs between this volume and adjacent areas. Standard exposure scenarios for inhalation intakes of volatile ingredients of consumer products used in indoor spaces (e.g., Versar Inc., 1986; U.S. EPA, 1997) often include recommended room volumes intended to be representative of the areas within a residence where the products are typically used. For example, in Versar Inc. (1986), a room volume of 20 m3 is assumed for tasks involving all-purpose liquid spray cleaners.
Based on comparison of the concentration associated with effects in humans in the study in which exposure was best characterized (i.e., alterations in hematological parameters in Kim et al., 1999) of 11 mg/m3 with the upper-bounding estimates of exposure levels in air in Canada of 3.6 µg/m3 (based on the detection limit in the multimedia exposure study by Conor Pacific Environmental Technologies, 1998), the margin between effect level and exposure is about 3000. (Note: If this effect level is compared with the highest concentration of 2-ethoxyethanol detected outside of an automotive plant in Windsor [i.e., the maximum level detected in ambient air in Canada, 0.86 µg/m3], this margin would be even greater.) With respect to ingestion, although no epidemiological investigations of the effects of ingested 2-ethoxyethanol in humans were identified, the margin between the intake equivalent to inhalation of 2-ethoxyethanol at a concentration of 11 mg/m3 (assuming 100% absorption) and the upper-bounding estimate of intake in drinking water is about 6 orders of magnitude. Margins between exposure and the effect levels from studies in animals would be even greater. Although intake of 2-ethoxyethanol in food could not be estimated, it is considered unlikely to be greater than these upper-bounding estimates for air or drinking water. These margins between upper-bounding estimates of exposure and the conservative effect levels are considered adequate to account for the uncertainties in the database (including exposure estimates and interindividual variation in response).
However, upper-bounding estimates of exposure to 2-ethoxyethanol through use of some consumer products could approach or exceed the effect levels for health effects in humans. For example, upper-bounding estimates of indoor air concentrations resulting from use of all purpose spray cleaners containing the substance (the only household cleaning product for which information on composition was available) are more than an order of magnitude greater than these effect levels. However, the degree of confidence in these estimates of exposure from consumer products is considered to be extremely low (see Section 3.3.4), and they are very likely gross overestimates of actual exposure from products currently being used in Canada. Therefore, confirmation that 2-ethoxyethanol is not present in consumer products in Canada is a high priority.
3.3.4 Uncertainties and degree of confidence in the human health risk characterization
Due to the paucity of data on levels of 2-ethoxyethanol in environmental media in Canada, there is a high degree of uncertainty in the estimates of exposure that have been developed in this assessment. While conservative upper-bounding estimates of exposure were determined on the basis of the detection limits reported in the multimedia exposure study, it is not known if these values grossly overestimate environmental levels or if the population is exposed to concentrations approaching these levels, although predicted concentrations in ambient air and drinking water based on fugacity modelling were several orders of magnitude below these detection limits, and levels were lower in the small survey of ambient air in Windsor (in which confidence is greater) than the detection limit reported for the multimedia study. In addition, although these data are considered adequate as a basis for developing crude bounding estimates of exposure, the methodology employed in the multimedia study is considered experimental, for which confidence is low. Recoveries were often low (only 43% for 2-ethoxyethanol in air), concentrations in "blanks" were high, etc. There is a high degree of confidence, though, that this approach is conservative, based on comparison with other results. It should also be noted that uptake of 2-ethoxyethanol vapour via dermal absorption has not been considered in these estimates of exposure. As well, the contribution of food and soil to overall intake of 2-ethoxyethanol is unknown, as no relevant data were identified, although predictions based on fugacity modelling suggest that intake from these sources is likely much less than the upper-bounding estimates of intake from air and drinking water upon which the conclusions presented here are based.
There is an extremely low degree of confidence in the estimates of exposure to 2-ethoxyethanol from consumer products, due to the uncertainties regarding the presence and concentrations of the substance in products currently used in Canada. Therefore, it is likely that the values presented here greatly overestimate potential current exposures. These estimates were also determined based on the conservative assumptions of complete transfer of 2-ethoxyethanol from the product to air and 100% absorption of the inhaled substance and the amount contacting the skin. While 2-ethoxyethanol was not detected in emissions from a range of products recently tested by Health Canada (Cao, 1999), confirmation that it is not present in consumer products in Canada is desirable.
There is a moderate to high degree of confidence in the characterization of the health hazards associated with exposure to 2-ethoxyethanol for the purposes of identifying critical effects for risk characterization. Hematological, reproductive and developmental effects were consistently observed in investigations in experimental animals.
Hematological and reproductive effects have also been observed in occupationally exposed human populations, although the database in humans is somewhat limited. Additional investigations of exposed workers, in which exposure to 2-ethoxyethanol is quantified, would be helpful in further characterizing risks to humans, particularly since there is some indication that humans may be more sensitive than animal species to effects induced by this substance (additional research on the relative toxicokinetics would also be desirable). However, there is some uncertainty concerning the effects of 2-ethoxyethanol following long-term exposure, as no adequate chronic studies in animals are available. Likewise, no epidemiological investigations of the potential effects in humans in which both magnitude and duration of exposure to 2-ethoxyethanol were considered have been identified.
3.4 Conclusions
CEPA 1999 64(a):
Based on conservative estimates of exposure and effects in Canada, risk quotients for terrestrial wildlife, soil organisms and aquatic organisms are less than one. The environmental risks associated with estimated concentrations of 2-ethoxyethanol likely to be found in Canada therefore appear to be low. Therefore, available data indicate that it is unlikely that 2-ethoxyethanol is entering or may enter 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, and it is not considered to be "toxic" as defined in CEPA 1999 Paragraph 64(a).
CEPA 1999 64(b):
2-Ethoxyethanol is not involved in the depletion of stratospheric ozone and likely does not contribute significantly to climate change. Because of its very low estimated concentration in air in Canada, it is unlikely to play a significant role in tropospheric ozone production. Therefore, based on available data, it has been concluded that 2-ethoxyethanol is not entering the environment in a quantity or concentration or under conditions that constitute or may constitute a danger to the environment on which life depends, and it is not considered to be "toxic" as defined in CEPA 1999 Paragraph 64(b).
CEPA 1999 64(c):
Based on comparison of upper-bounding estimates of exposure in the general environment with conservative effect levels, it is concluded that 2-ethoxyethanol is not entering the general environment in a quantity or concentration or under conditions that constitute or may constitute a danger in Canada to human life or health. Therefore, 2-ethoxyethanol is not considered to be "toxic" as defined in Section 64(c) of the Canadian Environmental Protection Act (CEPA, 1999). Although 2-ethoxyethanol was not detected in emissions from a range of consumer products in Canada, acquisition of additional more representative information on its use in consumer products in Canada is desirable.
Overall conclusion:
Based on critical assessment of relevant information, 2-ethoxyethanol is not considered to be "toxic" as defined in Section 64 of CEPA 1999.
3.5 Considerations for follow-up (further action)
Although 2-ethoxyethanol was not detected in emissions from a range of products tested by Health Canada, information on its use in consumer products marketed in Canada is sparse. It is recommended, therefore, that additional information on patterns of use of consumer products containing 2-ethoxyethanol in Canada and levels of the compound in these products be sought. Depending upon the results of such investigations, it may be necessary to conduct a fuller assessment, including refined estimates of exposure and full dose-response analyses.
5 Since the acetate moiety of 2-ethoxyethanol is rapidly converted to 2-ethoxyethanol in the body, with similar resulting health effects, it was considered appropriate to develop effect levels on the basis of studies in which the toxicity of 2-ethoxyethyl acetate was investigated, converting the exposure levels of the acetate to equivalent concentrations or doses of 2-ethoxyethanol on a relative molecular weight basis.
