As aquatic environments associated with conventional agriculture are exposed to various pesticides, it is important to identify any possible interactions that modify their effects when in a mixture. We applied avoidance tests with Danio rerio, exposing juveniles to three relevant current use pesticides: chlorpyrifos (CPF), chlorothalonil (CTL) and glyphosate (Gly), individually and in binary mixtures (CPF-Gly and CTL-Gly). Our goal was to identify the potential of contaminants to trigger the avoidance response in fish and detect any changes to that response resulting from binary mixtures. Avoidance was assessed for three hours using an open gradient system with six levels of increasing concentrations. Fish avoided environmentally relevant concentrations of the three compounds. The avoidance of CPF [AC50 = 7.95 (3.3-36.3) µg/L] and CTL [AC50 = 3.41 (1.2-41.6) µg/L] was evident during the entire period of observation. In the case of Gly, the response changed throughout the experiment: initially (until 100 min) the fish tolerated higher concentrations of the herbicide [AC50 = 52.2 (12.1-2700) µg/L] while during the later period (after 100 min) a clearer avoidance [1.5 (0.8-4.2) µg/L] was observed. The avoidance recorded using CPF and CTL alone was attenuated by the presence of Gly. Applying an additive concentration model, Gly initially acted synergistically with the other two compounds, although this interaction was not observed during the later period. Avoidance gives us an idea of how the distribution of populations may be altered by contamination, our results suggest that in some mixtures this response may be inhibited, at least temporarily, thus masking the ecological risk of the exposure.
Keywords: Avoidance; Behaviour; Fish; Mixtures; Pesticide.
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