Influence of existing site contamination on sensitivity of Rhinella fernandezae (Anura, Bufonidae) tadpoles to Lorsban®48E formulation of chlorpyrifos.

Effects of the widely employed insecticide Lorsban(®)48E formulation of chlorpyrifos (CPF) was studied on Rhinella fernandezae tadpoles, a native species of Argentina, Brazil, Paraguay and Uruguay, under the hypothesis of a differential response of organisms from ponds of two sites with different degree of anthropogenic disturbance: S1 an unpolluted area, and S2 area with high degree of antropogenic disturbance. To collect a representative sample of the genotypic variability of each population, small portions from six clutches were taken randomly from each site when the period of clutching was finished. Embryos and tadpoles were maintained under controlled laboratory conditions. Toxicity tests were conducted under standardized conditions to study acute and chronic lethal (mortality) and sublethal effects (behavior, growth, and abnormalities), within the range of concentrations of 0.010 to 5 mg/L. Chronic effects were assessed with organisms from one of the demes (S1). CPF showed high toxicity on the tadpoles, inducing lethal and sublethal effects at 96 h exposure within a narrow range of concentrations from 0.066 to 0.887 mg/L. Results indicate that R. fernandezae tadpoles are below the 30th percentile in the species sensitivity distribution of existing data. The acute LC50, NOEC, and LOEC values were 0.151, 0.066, and 0.133 mg/L for S1, and 0.293, 0.177, and 0.266 mg/L for S2, respectively. Considering all acute end-points evaluated, the effects of CPF showed no significant differences (p = 0.3484) between the studied populations. CPF has more severe effects at higher concentrations than at higher times of exposure. Contaminants in S2 do not seem to induce local adaptation. Sublethal effects data and measured environmental concentrations indicate potential risk for populations inhabiting agroecosystems.