STRATEGIES EMPLOYED TO DETERMINE THE ACUTE AQUATIC TOXICITY OF ETHYL BENZENE, A HIGHLY VOLATILE, POORLY WATER-SOLUBLE CHEMICAL

Studies are described in which ethyl benzene (EB) was tested to determ ine its acute toxicity to three marine organisms, Atlantic silversides (Menidia menidia), mysid shrimp (Mysidopsis bahia), and diatoms (Skel etonema costatum), and to one freshwater algae (Selenastrum capricornu tum). The respective 96-hr median lethal concentration (LC50) values a nd 95% confidence intervals for EB in the flow-through studies with fi sh and mysid shrimp were 5.1 (4.4-5.7) mg/liter and 2.6 (2.0-3.3) mg/l iter. While the 96-hr median effective concentrations (EC50's) for gro wth inhibition and 95% confidence intervals for the static studies wit h diatoms and algae were 7.7 (5.9-10.0) mg/liter and 3.6 (1.7-7.6) mg/ liter, respectively. Problems were encountered in all four studies as a result of the high volatility and poor water solubility of EB in wat er and an apparent ''salting out'' effect noted in seawater. This effe ct was found particularly true in the diatom and algae studies where t he salinity was increased with the addition of culture medium. Measure s are described which were used to overcome this stability problem wit h EB. These included sealing the test systems tight without any air sp aces to prevent the collection of EB vapors. Also, increased mixing of EB in the test solutions was found to be essential in the flow-throug h studies to maintain stable levels. In the case of the diatom and alg al studies, since current EPA test guidelines were judged to be inadeq uate to overcome EB volatility from the test medium, a new closed test system had to be developed and employed, after validation with a nonv olatile reference toxicant in the new and conventional static test sys tems. The results of these studies indicate that previous reports unde restimated the potential acute aquatic toxicity of EB by at least one order of magnitude. The implications of these findings are discussed i n relation to the potential environmental impact of EB and the resulta nt regulatory actions. (C) 1994 Academic Press, Inc.