Assessment of the ecotoxicological effects of deltamethrin to Daphnia magna: Linking sub-individual and supra-individual parameters

Deltamethrin (DM) is a pyrethroid insecticide, widely used worldwide, and is known to be toxic to diverse aquatic organisms. This work intended to evaluate the ecotoxicological effects of DM in Daphnia magna. To calculate the LC₅₀ and EC₅₀ values, an acute bioassay was conducted with a range of DM concentrations (0.1-150 µg/L). A chronic bioassay was also performed with a range of DM concentrations (18.66-100 ng/L). In both assays, a negative and a solvent control (acetone) were also tested. Life history parameters (reproduction and growth) were evaluated. Biochemical quantifications were also assessed regarding antioxidant and biotransformation capacity, oxidative damage, neurotoxicity, energy reserves content, and genotoxicity. LC₅₀ values and confidence interval at 95 % (CI₉₅) were 64.13 (CI₉₅: 46.40–81.85) and 65.22 (CI₉₅: 43.17–87.27) μg/L, and EC₅₀ values were 0.68 (CI₉₅: 0.54–0.81) and 0.31 (CI₉₅: 0.23–0.39) μg/L, for 24 h and 48 h, respectively. Regarding life-history parameters, only the lower DM concentration tested (18.7 ng/L) induced a significant increase in the rate of population increase (r). A significant increase in the solvent control was recorded for N1 fecundity, reproductive output, and r. Biochemical effects were only observed in terms of antioxidant/detoxification mechanisms (18.7, 32.6, 100 ng/L and solvent control) and oxidative damage (>18.7 ng/L and solvent control) but did not show an evident pattern of oxidative stress promoted by DM. Depletion of energy reserves (glycogen content) was observed from the lowest concentration tested as well as for the solvent control, and DNA damage up to 100 ng/L of DM was also observed. Future investigations (e.g. ecotoxicological studies with exposure of other aquatic organisms to environmentally relevant concentrations for longer exposure periods) would be required to confirm DM’s toxicity under ecologically relevant conditions. Moreover, the solvent effects in an ecotoxicological approach must be clarified.