In Costa Rica, agriculture is one of the most important economic activities. Chlorpyrifos and difenoconazole have been identified as agrochemicals widely used in banana and pineapple crops in the Caribbean area of the country and are constantly recorded in aquatic ecosystems. The toxicity of these pesticides in Parachromis dovii was studied. Median lethal concentrations (LC50s) for each substance were obtained from 96-h acute tests. Then, fish were exposed to sublethal concentrations of both substances (10% of LC50), individually and in mixture, to evaluate biomarker responses. Ethoxyresorufin-O-deethylase (EROD), catalase, and glutathione S-transferase activities as well as lipid peroxidation were measured in liver and gill tissues as markers of biotransformation and oxidative stress processes. Cholinesterase activity in brain and muscle tissue was also quantified as a biomarker of toxicity. The LC50s were 55.34 μg/L (95% confidence interval [CI] 51.06-59.98) for chlorpyrifos and 3250 μg/L (95% CI 2770-3810) for difenoconazole. Regarding the biomarkers, a significant inhibition of brain and muscle cholinesterase activity was recorded in fish exposed to 5.50 μg/L of chlorpyrifos. This activity was not affected when fish were exposed to the mixture of chlorpyrifos with difenoconazole. Significant changes in lactate dehydrogenase activity were observed in fish exposed to 325 μg/L of difenoconazole, whereas fish exposed to the mixture showed a significant increase in EROD activity in the liver. These results suggest harmful effects of chlorpyrifos insecticide at environmentally relevant concentrations. There is also evidence for an interaction of the 2 substances that affects the biotransformation metabolism at sublethal levels of exposure.
and Coastal Management Aquatic environments associated with conventional agriculture are exposed to contamination with mixtures of pesticides. In this context, where substances with different biocide activities are frequently present, it is important to identify possible interactions that enhance their effects when in 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 and the mixtures to trigger avoidance response in fish. Avoidance was assessed for a period of three hours using an open gradient system with six levels of increasing concentrations of the substances. Fish avoided environmentally relevant concentrations of the three compounds. The avoidance of CPF 3) µg/L] and CTL ) µg/L] was evident during the whole period of observation, with fish preferring the cleaner part of the system. In the case of Gly, a biphasic response was observed: fish initially (until 100 min) tolerated higher concentrations of the herbicide [AC50= 52.2 (12.1 -2700) µg/L] and a clearer avoidance [1.5 (0.8 -4.2) µg/L] was observed during the late period (after 100 min). The clear avoidance response observed with CPF and CTL alone was attenuated with the presence of Gly. Applying a mathematical model, the interactions of the mixtures were assessed and we observed that Gly acted synergistically with the other two compounds regarding the avoidance response of fish; but during the late period, the interaction was antagonistic with both substances. Although the avoidance is a response that prevents organisms of being continuously exposed to contaminants and gives us an idea about how the distribution of populations can be altered by contamination, our results suggests that in a context of mixtures the avoidance response can be impaired, making organisms more susceptible to toxicity.
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