Physiological Perturbations in Several Generations of Daphnia magna Straus Exposed to Diazinon

Abstract

Daphnia magna was exposed to sublethal diazinon concentrations (0.05, 0.1, 0.5, 0.75, and 1.0 ng/L) for 21 days. The algae Nannochloris oculata (5×105 cells/mL) was used to feed the daphnids. Chronic toxicity tests were carried out using neonates of F1 (first brood) and F1 (third brood) offspring generations from parentals (F0) preexposed to the organophosphate. The effect of diazinon on survival, reproduction, and growth was monitored for the selected daphnid generations. The parameters used to evaluate pesticide effect on reproduction were mean total young per female, mean brood size, time to first reproduction, mean number broods per female, and intrinsic rate of natural increase (r). Survival and growth (body length) were also determined after 21 days of exposure to the pesticide. Reproduction as well as survival was significantly reduced when diazinon concentration increased in the medium. This effect was greater in F1 (first) and F1 (third) offspring compared to the parental generation (F0) daphnids. The intrinsic rate of natural increase (r) decreased with increasing concentrations of diazinon, especially in those animals from the first and third brood. However, the growth of the exposed organisms decreased in the same order of magnitude in all generations tested. The maximum acceptable toxicant concentration (MATC) was calculated for F0, F1 (first), and F1 (third) generations of D. magna exposed to the pesticide using as parameter of evaluation the intrinsic rate of natural increase (r). The interpolation of these results gave MATC values of 0.62 and 0.07 ng/L pesticide for F0–F1 (first) generations and F1 (third) generation, respectively. Therefore, F1 (third) generation seems to be more sensitive to diazinon than generations F0 and F1 (first). The EC50 values have been derived for some selected parameters on the generations of D. magna exposed to diazinon. EC50 values decreased in F1 (first) and F1 (third) generations compared to the parental generation F0. Expanding the reproduction tests to several generations revealed important information on chronic toxicity that could add to an increased cost-effectiveness in the protection of aquatic environments.