This study evaluated the toxicity of pesticide formulations Kraft® 36 EC (active ingredient-a.i. abamectin) and Score® 250 EC (a.i. difenoconazole), and their mixtures in Daphnia magna at different biological levels of organization. Survival, reproduction and biochemical markers (cholinesterase (ChE), catalase (CAT) and lipid peroxidation (LPO)) were some of the endpoints evaluated. Total proteins and lipids were also studied together with energy consumption (Ec). D. magna neonates were exposed for 96 h to Kraft (2, 4, and 6 ng a.i./L) and Score (12.5, 25, and 50 µg a.i./L) for the biochemical experiments, and for 15 days to abamectin (1-5 ng a.i./L) and to difenoconazole (3.12-50 µg a.i./L) to assess possible changes in reproduction. Exposures of organisms to both single compounds did not cause effects to antioxidant and detoxifying enzymes, except for LPO occurring at the highest concentration of difenoconazole tested. For ChE and CAT there was enzymatic induction in mixture treatments organisms, occurring at minor pesticides concentrations for CAT and at the two highest concentrations for ChE. There were no significant differences for total protein in D. magna but lipids showed an increase at the highest concentrations of pesticide mixture combinations. There was a significant increase of Ec in individuals of all treatments tested. In the chronic test, increased fecundity occurred for D. magna under difenoconazole exposures and mixtures. This study demonstrated that mixtures of these pesticides caused greater toxicity to D. magna than when tested individually, except for Ec. Therefore, effects of mixtures are very hard to predict only based on information from single compounds, which most possibly is the result of biological complexity and redundancy in response pathways, which need further experimentation to become better known.
Keywords: Cholinesterase; Energy reserves; Kraft® 36 EC; Oxidative stress; Reproduction; Score® 250 EC.