Efeito da aplicação de lodo de estação de tratamento de esgoto no solo sobre a toxicidade do imidacloprido para folsomia candida

Abstract

Imidacloprid is an active ingredient (a.i.) widely used as an insecticide for the chemical treatment of agricultural seeds in Brazil. However, the toxic effects of this insecticide, in non-target organisms, in soils treated with sewage sludge are not well known. This study aimed to assess the toxic potential of the imidacloprid in springtails (Folsomia candida) in a soil previously treated with sludge of wastewater treatment plant (WWTP), on the survival and reproduction of springtails. Chronic toxicity tests were chosen to assess the effects of the WWTP sludge doses on the toxic potential of imidacloprid on the reproduction of the F. candida in Oxisol, at 20 ± 2 °C. The WWTP sludge doses L0, L1, L2, L3, L4 and L5 correspond to 0, 20, 40, 80, 160, and 320 g sludge/kg dry soil (application 20 t/ha), respectively, and with doses of imidacloprid concentrations (0,25, 0,50, 1, 2 e 4 mg/kg soil) were compared by using the analysis of variance (ANOVA), followed by Dunnet’s test. The concentrations causing a reduction effect of 50% in the population (EC50) were estimated by non-linear regression models. The chronic toxicity for F. candida was observed in the presence of imidacloprid regardless of the tested sludge dose. It was found a reduction in the reproduction at imidacloprid concentrations of 0.25 mg/kg for sludge L0 (no sludge added), 0.5 mg/kg for doses L4 and L5 and 1 mg/kg for L1, L2 and L3. The EC50 values obtained were 0.349 mg/kg, 0.940 mg/kg, 1.083 mg/kg, 1.108 mg/kg, 1.069 mg/kg and 1.231 mg/kg, for the sludge doses L0, L1, L2, L3, L4 and L5, respectively, indicating a gradual reduction of the insecticide’s toxicity in the soil as the increased sludge doses increased. Furthermore, the higher WWTP sludge doses applied (from L2 to L5) in uncontaminated soil samples (control without the insecticide) reduced the number of generated juveniles, when compared to the control (L0), also indicating that in soils without the insecticide contamination, attention must be paid on the dosage of sludge applied for agricultural purposes.