Lw. Masten et al., STRATEGIES EMPLOYED TO DETERMINE THE ACUTE AQUATIC TOXICITY OF ETHYL BENZENE, A HIGHLY VOLATILE, POORLY WATER-SOLUBLE CHEMICAL, Ecotoxicology and environmental safety, 27(3), 1994, pp. 335-348
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.