Modeling acute and chronic toxicity of nonpolar narcotic chemicals and mixtures to Ceriodaphnia dubia.

The response of the daphnid Ceriodaphnia dubia to six widely used industrial chemicals acting through nonpolar narcosis and a mixture was determined. Toxicological effect levels were based on reasonably steady-state, measured concentrations. Reproductive IC50S were 149 microM benzene, 82 microM trichloroethylene, 35 microM toluene, 31 microM ethylbenzene, 26 microM m-xylene, and 4 microM tetrachloroethylene. A QSAR describing 2-day LC50S as a function of log Kow accounted for 90.97% of the variation in response across chemical. A similar QSAR for chronic effects on reproduction accounted for 78.92%. Mixtures of benzene, trichloroethylene, and toluene had effects at concentrations below their individual LOELs. Observed effects of 20/24 mixtures tested fell within the 95% prediction interval for a concentration-addition model of joint action derived from tests with individual components. However, the observed response differed significantly from the predictive relationship. In general, the predictive relationship overestimated mixture toxicity. Fitted relationships reduced observed error by as much as 82% compared to the predictive model.