Avaliação ecotoxicológica de fipronil em solos tropicais: efeitos sobre Folsomia candida (COLLEMBOLA)

Abstract

Fipronil is synthetic insecticide used in commercial formulations as seed dressing. This active ingredient (a.i.) acts on insect central nervous system by blocking the neurotransmitter GABA. Despite its efficiency in controlling agricultural pests, several ecotoxicological studies have demonstrated its toxic potential for non-target soil species, which plays important functions in the terrestrial ecosystem. However, the toxicity and ecological risk of the formulations containing this insecticide are not yet fully known on brazilian tropical soils. In order to study the environmental hazard/risk of fipronil for a non-target invertebrate species in the soil, this work assessed the effects of this a.i. on the reproduction (chronic toxicity) of springtails Folsomia candida in TAS (Tropical Artificial Soil), Entisol and Oxisol. The assays were performed according to ISO 11267/2014 by using increasing concentrations of a.i., through Shelter®, a seed dressing commercial formulation (0.25; 0.5; 1.0; 2.0 and 4.0 mg kg-1) and a control treatment (without contaminant). The commercial formulation containing fipronil was toxic to springtails in all soils, however, this effect was even greater in Entisol (EC50 = 0.20 mg kg -1), followed by SAT (EC50 = 0.39 mg kg -1) and Oxisol (EC50 = 1.28 mg kg -1). The ecological risk formulation for F. candida was significant in all tested soils (Hazard Quotient – HQ >1), being the highest risk also verified in Entisol > TAS > Oxisol. When calculated the Toxicity-Exposure Ratio (TER), no ecological risk was found only in Oxisol. The results suggest that toxicity may be lower in soils that present mainly high levels of clay and silt, probably because of the chemical retention of fipronil molecule in the soil, and consequently lower availability for non-target organisms. Through the ecological risk methodologies, it was found that the exposure of springtails can present higher risks in soils with lower clay and silt content as in Entisol, therefore, more studies should be carried out, such as evaluations at semifield or field level to confirm if these effects will occur under more realistic exposure conditions. It can be concluded that differences toxicity of fipronil occur in reproduction of F. candida between tropical soils.