Behavioral Response in Toxicity Assessment of the Insecticide Decis® 2.5 EC toward Freshwater Zooplankton

Abstract

Chemical crop protection agents are widely applied in modern agricultural practice. As a result of surface runoff, these insecticides penetrate into rivers, ponds, and lakes, where they become a serious threat to aquatic organisms. The aim of the study was to determine the toxicity of increasing concentrations of the insecticide Decis® 2.5 EC to Daphnia magna and Heterocypris incongruens, which are components of freshwater zooplankton. The observed effect was immobilization of organisms, which were not able to swim after gentle agitation of the liquid for 15 sec. It was found that up to 135 min, increasing Decis® 2.5 EC concentrations inhibited the swimming of tested organisms. Initially, up to 135 min, Heterocypris incongruens was more sensitive to the tested insecticide. After 135 min of the experiment, ostracods acclimatized to the tested xenobiotic. However, after 360 min, the immobilization of organisms increased proportionally to the concentrations of Decis® 2.5 EC. The most toxic concentrations were 15 × 10−3% and 30 × 10−3%. The lowest observed effect concentration of Decis® 2.5 EC that reduced the swimming of daphnia and ostracod by more than 20% was >0.91 × 10−3% (0.23 mg L−1 of deltamethrin). This experiment demonstrated that Daphnia magna and Heterocypris incongruens are good bioindicators of freshwaters polluted with Decis® 2.5 EC.