Diuron and diazinon alter the behavior of zebrafish embryos and larvae in the absence of acute toxicity

Abstract

The use of zebrafish for aquatic vertebrate (eco)toxicity testing allows the assessment of effects on a wide range of biological levels - from enzymes to sensory organs and behavioral endpoints. The present study investigated the effects of the insecticide diazinon and the herbicide diuron regarding the acute toxicity and behavior of zebrafish embryos and larvae. After conducting the fish embryo toxicity test, three concentrations (1, 2 and 3.5 mg L^-1 for diazinon and 1, 2 and 3.8 mg L^-1 for diuron) were evaluated for effects on embryonic spontaneous movement and heartbeat, larval light-dark transition response, and thigmotaxis. Although the modes-of-action are different, both pesticides proved to be moderately toxic to early life stages of zebrafish with 96 h LC₅₀ of approximately 6.5 mg L^-1 and similar EC₅₀ values of approximately 4 mg L^-1. Changes in behavioral endpoints were detected 24 h of exposure, suggesting that behavioral measurements can serve as sensitive and early indicators of pesticide exposure. Changes in behavior, such as decrease in spontaneous coiling movements of embryos and reduction of thigmotaxis in larvae, were pronounced for diuron, indicating the usefulness of the application of behavioral endpoints to assess the effects of other herbicides. In the case of diazinon, the effects were less prominent, but the detected changes in ratios between activity in light and darkness also point to the possibility of using behavioral changes for evaluation of insecticide effects. The obtained results support the usage of behavioral endpoints in zebrafish embryos and larvae for the detection of early effects of pesticides.

Keywords: Behavior assessment; Danio rerio; Diazinon; Diuron; Embryo toxicity; Sublethal effects.