| Field and laboratory studies were conducted to determine the utility of a novel risk assessment approach based on the combination of probabilistic ecological risk assessment and toxic equivalent methods (PERA-TE approach). Field experiments were conducted in freshwater microcosms (12 m3). Ternary mixtures composed of organophosphorus insecticides (azinphos-methyl, diazinon and chlorpyrifos) having similar modes of toxic action, and mixtures exhibiting different modes of toxic action (composed of chlorpyrifos, endosulfan, and trifluralin) were assessed using both concentration-response and ANOVA designs. Endpoints included mortality of fathead minnows (Pimephales promelas), and AChE inhibition. The TE mixtures were normalized based on the 10th centile of the most toxic substance, and based on factors of the 90th centile, extrapolated from measured environmental concentration data obtained from Ohio and Ontario surface water monitoring studies. Laboratory tests using static renewal methods, and based on the toxic unit (TU) model, were conducted to determine the interactive effects following exposure to the same ternary mixtures. (Abstract shortened by UMI.)... |
