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Ambient Water Quality Guidelines for Ethylbenzene
Introduction
Ethylbenzene is a colourless liquid at room temperature with a gasoline-like aroma. It occurs naturally in coal, tar and petroleum and is found in consumer products such as paint, ink, pesticides and gasoline. In Canada, ethylbenzene is used for producing styrene and as a solvent in the chemical and rubber industries.
Ethylbenzene can enter aquatic environments during production, usage, storage, transportation and spills. It is released into the air from burning oil, gas and coal and is generally associated with smog. Physical, chemical and biological breakdown removes ethylbenzene from all media so there is little tendency for it to accumulate in environmental compartments. Ethylbenzene is resistant to hydrolysis, and photolysis of ethylbenzene in water is minimal. It binds moderately to soil and aquatic sediments and thus may leach into ground water if released to land. Ethylbenzene is volatile with a half-life of up to two weeks in water. The log octanol-water partition coefficient (Kow) is 3.2.
Ethylbenzene has been detected throughout North America in effluents from municipalities, industries, industrialized river basins, ground water, sediments, soil and water.
In performing toxicity testing, the most sensitive freshwater species to ethylbenzene reported in the literature was Daphnia magna with a 48 hour EC50 of 1.8 mg/L for immobilization. Three separate studies conducted independently reported the 48 hour EC50s for immobilization of this species ranged from 1.8 to 2.1 mg/L. One study reported a 24 hour EC50 (immobilization) of 2.2 mg/L. A 96 hour LC50 of 4.2 mg/L was reported for rainbow trout, Oncorhynchus mykiss, in soft water whereas a 72 hour EC50 of 4.6 mg/L for growth inhibition was reported for the green algae Selenastrum capricornutum.
In marine water, sensitive species included the Atlantic silversides, Mendidia mendidia, and Mysid shrimp, Mysidopsis bahia. The no observed effects concentration (NOEC) using survival of Atlantic silversides was 3.3 mg/L, while the lowest concentration at which there was a statistical difference in survival from the control group was 5.9 mg/L after 96 hours. For Mysid shrimp, the NOEC (survival) was 1.0 mg/L, while the lowest observed effects concentration (LOEC) was 2.7 mg/L after a 96-hour exposure.
Recommended Guidelines
1. DRINKING WATER SUPPLY
An aesthetic objective of 0.0024 mg/L for ethylbenzene in drinking water has been recommended by the Federal-Provincial Subcommittee on Drinking Water, Health Canada (1993) and is adopted for ambient conditions.
Rationale
This concentration yields no objectionable taste or smell, or no adverse health effects. Without treatment prior to entering a water distribution system, ethylbenzene concentrations will change little from ambient concentrations, especially when time from withdrawal to use is small. Therefore, the recommended concentration for water distribution systems will be the ambient water quality concentration for ethylbenzene.
2. FRESHWATER AQUATIC LIFE
The maximum concentration of ethylbenzene should not exceed the BC guideline of 0.2 mg/L. This guideline has been revised from the CCME guideline of 0.09 mg/L.
Rationale
We found that the data quality from the researchers considered by CCME was satisfactory. There were three independent studies on the most sensitive species Daphnia magna that derived similar concentration levels to ensure confidence in the endpoint. In developing their guideline, the CCME applied a safety factor of 20:1. However, studies indicate that ethylbenzene has high volatility, low bioaccumulation potential and would not be expected to remain in the environment for prolonged periods of time (half-life is up to two weeks in water). The LOEC/NOEC ratios for freshwater aquatic life is expected to be low as in the marine environment, although such data were not available for freshwater species. Therefore, the recommended guideline is based on a reduction in the applied safety factor from 20:1 to 10:1.
3. MARINE AND ESTUARINE LIFE
The maximum concentration of ethylbenzene should not exceed 0.25 mg/L. This guideline has been revised from the CCME guideline of 0.02 mg/L.
Rationale
The critical study used by the CCME to derive the guideline was classified as secondary data. In BC, we eliminated this study for determining the BC guideline as the concentrations were not measured at the end of the test. This is due to rapid and large losses in the compound concentration (greater than 99% after 24 hours), which precluded accurately predicting concentrations at any time interval. The next lowest critical study had a 96 hour LC50 of 2.6 mg/L for Mysid shrimp, Mysidopsis bahia.
The safety factor used by CCME was reduced from 20:1 to 10:1 for BC based on ethylbenzene's short half-life and low potential to bioaccumulate. We felt further justified in reducing the safety factor since there were paired data showing ratios of 96 hour LC50 (LOEC) to NOEC values of <3:1.
4. CROP IRRIGATION
No water quality guideline for this use is recommended as there are insufficient data on the adverse effects of ethylbenzene in irrigation water.
5. LIVESTOCK WATERING
Due to lack of data, guidelines for livestock watering was not recommended at this time in BC.
