Priority Substances List - Statement of the Science Report for Ethylene Glycol

Synopsis

Ethylene glycol (CAS No. 107-21-1) is a colourless, odourless, relatively non-volatile liquid. It has a low vapour pressure and is completely miscible in water.

Ethylene glycols (mono-, di- and tri-) are produced by three companies in Canada, which had a total annual capacity of 850 kilotonnes in 1996. Ethylene glycol is used primarily as an antifreeze agent but is also used, for example, in the manufacture of polyethylene terephthalate, in natural gas processing and as a component of paints. Natural levels of ethylene glycol are considered to be insignificant relative to amounts released from anthropogenic sources. The highest reported releases of ethylene glycol to the environment are to land from aircraft deicing/anti-icing operations, with subsequent release to the aquatic environment. Current management practices at the major airports in Canada have resulted in a trend of decreased releases in recent years. Other sources of releases to water include paper products and steel industries. Releases to air occur during ethylene glycol production, during natural gas processing and from paints and coatings manufacture. Ethylene glycol is also injected underground as a means of disposal from natural gas processing operations.

Once released into the environment, ethylene glycol partitions mainly into surface water or groundwater. It does not bioaccumulate or persist in the environment, primarily due to biodegradation. Half-lives in air, water, groundwater and soil are estimated to typically range from 0.35 to 3.5 days, from 2 to 12 days, from 4 to 24 days, and from 2 to 12 days, respectively, but may exceed these ranges, depending on the environmental conditions. Ethylene glycol is not expected to deplete the ozone layer, it has a low potential to contribute to ground-level ozone formation, and its potential contribution to climate change is negligible. Ethylene glycol has been found to biodegrade rapidly in the aquatic environment and therefore has the potential to induce depletion of the dissolved oxygen (DO) in receiving waters.

Given that ethylene glycol tends to partition to the aquatic environment, with little transfer to soil or air expected, and because the majority of ethylene glycol is released to the aquatic environment from aircraft deicing and anti-icing, the potential for effects is greatest for aquatic organisms. In assessing the risk, consideration is given to the time and frequency of exposure. From the available studies, the induction of effects on algae and amphibians is selected to represent the most sensitive measurement endpoints for inducing potential population-level impacts on aquatic organisms and is used as a basis for generating the Estimated No-Effects Values (ENEVs). Indirect effects from oxygen depletion following ethylene glycol release was also examined using the Streeter-Phelps oxygen sag model and probabilistic analysis.

The direct comparison of current exposure concentrations predicted to occur in the aquatic environment with the ENEVs suggests that adverse effects are unlikely when consideration is given to the seasonal nature of releases, ambient temperatures, metabolic rates and duration of exposure. Examination of potential indirect effects through oxygen depletion suggests a low potential for DO levels to drop below the Canadian water quality guideline (9.5 mg/L) under very infrequent, maximal loading conditions. Although, based on the present characterization, it is evident that harmful environmental effects are unlikely to result from exposure to ethylene glycol in Canada, effects related to depletion of DO levels in receiving waters are possible under conditions of maximum loading at some Canadian airports. It is therefore recommended that current efforts to reduce releases of ethylene glycol during aircraft deicing/anti-icing operations (e.g., glycol mitigation plans and glycol operational management plans) continue to be strengthened, with the aim of reducing further the instances when ethylene glycol concentrations in stormwaters exceed the CEPA effluent guideline of 100 mg total glycol/L.

Monitoring data upon which to base estimates of exposure of the general human population in Canada to ethylene glycol were not identified. Population exposure estimates are, therefore, extremely limited. Intakes in air and soil in the vicinity of a point source were estimated based on modelled data, and that in food was based on reported concentrations in a limited range of foodstuffs from other countries. Dermal absorption was also estimated for a limited range of products for which data on the proportion of ethylene glycol in the product were identified.

Based on short-term and long-term studies conducted by the oral route in experimental animals, the kidney is the principal target site for effects of ethylene glycol. Consistently, degenerative non-neoplastic changes in the kidney have been observed at lowest doses in a range of species. Based on an extensive database, ethylene glycol induces slight reproductive effects and developmental toxicity, including teratogenicity, in rodents exposed by the oral route, although at doses greater than those associated with renal effects.

Therefore, a Tolerable Intake has been derived for this substance, based on a Benchmark Dose calculated for non-neoplastic renal effects in animals and an uncertainty factor. However, owing to limitations of available studies, this Tolerable Intake is uncertain. Based on highly uncertain estimates, exposure of some age groups in the vicinity of a point source or of adults through absorption from some consumer products exceeds the Tolerable Intake. A Tolerable Intake is the level of intake to which it is believed a person may be exposed daily over a lifetime without deleterious effect. To reduce the considerable uncertainty, in critical areas, research on exposure in the vicinity of point sources and progression of renal lesions in toxicity studies is considered a priority. Characterization of the distribution and ranges of ethylene glycol in consumer products in Canada is also recommended.