Toxicological interactions of cadmium and four pesticides on early life stage of rare minnow (Gobiocypris rarus).

Abstract

Although chemicals have been traditionally regulated on an individual basis in aquatic ecosystems, they often co-exist as different types of complex mixtures. Laboratory assays were conducted for assessing the responses of rare minnow (Gobiocypris rarus) to individual and mixture chemicals [trace element cadmium (Cd), thiamethoxam, deltamethrin, malathion and prochloraz]. Data obtained from 96 h semi-static toxicity assays implied that deltamethrin elicited the highest toxic effect on the various developmental phases (larval, juvenile and adult phases) of G. rarus with LC50 values ranging from 0.00061 to 0.25 mg a.i. L-1, followed by prochloraz, malathion and Cd with 96-h LC50 values ranging from 0.49 to 1.1, from 7.1 to 26, and from 7.6 to 15 mg a.i. L-1, respectively. Thiamethoxam elicited the lowest toxic effect on the organisms with 96-h LC50 values ranging from 38 to 202 mg a.i. L-1. Larval phase was not always the most sensitive period in the three detected phases to most of chemicals. Chemical combinations containing deltamethrin and malathion displayed synergetic responses to the larvae of G. rarus. Besides, the binary mixtures of Cd-deltamethrin and Cd-prochloraz also exhibited synergetic response to rare minnows. Our results indicate that extra information is necessary to develop practical criteria for selecting chemical combinations that require legislative attention according to their likelihood to exert synergetic responses. Thence, more investigations on mixture toxicities of various chemicals should be taken as a priority for producing synergetic interaction to improve the environmental risk assessment of chemicals.