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 tim