Environmental toxicity of three fungicides and their photoderivatives on freshwater crustaceans

The fungicides Carboxin, Oxycarboxin and Furalaxyl occur mainly on the soil, even if surface-waters are subjected to contamination due to phenomena of run off with continuous exposure of non-target aquatic organisms. Carboxin and Furalaxyl undergo photooxidation that may induce the conversion of pesticides into noxious derivatives. These photoproducts may constitute a further potential risk for aquatic biota. Here we report the effects of the three pesticides and their photoproducts, obtained by sunlight exposure in water, on freshwater crustaceans. The photoderivatives were isolated by chromatographic techniques and/or identified by spectroscopic means. All the compounds were tested to evaluate acute and chronic toxicity on freshwater crustaceans. Thamnocephalus platyurus, Daphnia magna and Ceriodaphnia dubia were used in acute bioassays, while chronic tests were performed only on Ceriodaphnia dubia. The acute results about the parent compounds showed that Furalaxyl was particularly active on T. platyurus (LC50=0.46 mg/L), while Carboxin and Oxycarboxin were less toxic, showing the highest effect on C. dubia (LC50=10.32 mg/L and 8.63 respectively). A different behavior was found for the photoderivatives, in fact the 2(5H)-furanone (the main photoproduct obtained from Furalaxyl) was one-fold more toxic than the parent compound while the main photoproduct obtained from Carboxin, the sulfoxide, was found to be less toxic than the parent compound. Chronic data demonstrated that Carboxin and Furalaxyl had a toxic potential in the same order found for acute toxicity towards T. platyurus while an EC50=0.02 was found for Oxycarboxin. The Furalaxyl photoderivative showed a toxicity two order of magnitude higher than the parent compound (EC50=0.0065 mg/L). From these data it appears that the risk characterization of pesticides have to consider their potential photochemical changes that may or not lead to a toxicological activation process and interfere with fate and effects on non-target organisms.