The spread of pesticides in water bodies integrated into agricultural landscapes may prevent some areas from being colonized. In this study, the effects on the colonization responses of D. magna exerted by gradients of realistic environmental concentrations of the pesticides chlorpyrifos, terbuthylazine and their mixtures were tested in a novel multicompartment non-forced exposure system. Furthermore, the effects of both pesticides and their mixtures on the swimming behavior and the neurotransmission activity of D. magna were analyzed using a traditional forced exposure system. The synthesis and concentration of the main environmental metabolites of terbuthylazine were also analyzed. Results confirmed that D. magna exposed to mixture gradients were able to detect the pollutants and their colonization dynamics were drastically inhibited. The swimming behavior increased in D. magna exposed to the highest concentration of the mixture treatment. AChE activity was only significantly inhibited in the D. magna exposed to the highest concentration of chlorpyrifos. Changes in swimming behavior could not be directly related to the effects on AChE. Furthermore, the synthesis of the metabolite terbuthylazine 2-hydroxy during the course of the experiments was confirmed. These results demonstrate the importance of integrating pesticide mixtures in both non-forced and forced exposure systems during ecotoxicological assays.
Keywords: Cladocera; Colonization response; Mixture; Non-forced exposure; Pesticides; Toxicity.
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