INTERNAL LETHAL CONCENTRATIONS OF HALOBENZENES WITH FISH (GAMBUSIA-AFFINIS)

The internal lethal concentration is a potential measure of toxicity w hich could be usefully applied in environmental toxicology and risk as sessment. Using halobenzenes, which are common environmental contamina nts, and represented test compounds, experiments were conducted in aqu aria with the mosquitofish (Gambusia affinis). The average internal le thal concentration (ILC50) for four representative halohydrocarbons, 1 ,4-diBB, 1,2,3-triCB, 1,2,4-triBB, and pentaCB, were consistent with t hose previously observed, i.e., 2.3-8.3 mmol kg(-1) fish over exposure time periods of 10.4 to 633 hr. However, the ILC50 for all the compou nds is not constant but decreases with increasing exposure time period with a mean first-order rate constant of (4.21 +/- 0.70) x 10(-3) hr( -1). The time dependency of the ILC50 is inconsistent with the critica l internal concentration hypothesis which requires the ILC50 to reach a constant critical value when lethality occurs. The life expectancy o f the fish from the beginning of chemical exposure could possibly be r elated to the ILC50-exposure time relationship. (C) 1997 Academic Pres s.