Biochemical stress response in tetradifon exposed Daphnia magna and its relationship to individual growth and reproduction

Environmental risk assessment of chemicals toxicity requires the use of costly and labor-intensive chronic data and short-term tests provide additional information. Energy budget is used by the animals for their growth, reproduction, and metabolism and it is reduced in case of toxic stress. Tetradifon acaricide is frequently used in the European Mediterranean region and it is implicated in aquatic environmental pollution. Previous studies showed that the EC50-24 h of tetradifon on Daphnia magna was 8.92 mg/L. Based on that, D. magna were exposed to sublethal tetradifon concentrations of 0.10, 0.18, 0.22 and 0.44 mg/L for five days in order to investigate their effect on intermediate metabolism. Caloric content was determined as biomarker of tetradifon toxicity. Results were analyzed using one-way analysis of variance (ANOVA) and Duncan's significant difference test was used to find differences between groups (α was set at p = 0.05). Daphnids energy content decreased as tetradifon concentration increased. At 120-h caloric content was depleted > 51% at pesticide concentrations of 0.18 mg/L and higher. In order to determine a possible link between the 5-d test and the 21-d chronic test, animals under short-term test were exposed to the same pesticide concentrations known to cause adverse effects on reproduction, growth and survival. Results from the present study indicated a good correlation between the proposed 5-day test and daphnid energy budget. Comparison between both, caloric content results and the chronic effect values obtained using life-table studies, suggested a good fit between them. These studies can be used as earlier, predictive and useful tests with comparable results to the classic chronic ones. Our results indicate that caution must be done about the use of tetradifon in the aquatic environment.