Fipronil Risk Assessment in Tropical Soils: Relevant Concentrations Cause High Risk to the Edaphic Community

Widely used in agricultural fields, fipronil acts in the arthropods’ nervous systems. Although advances have been noticed, little is known about the effects of the insecticide to non-target soil organisms, especially considering specific parameters from tropical environments. This is the first study considering ecologically relevant tropical conditions to assess the environmental risk of fipronil to the terrestrial ecosystem. The present study aimed to estimate fipronil’s ecological risk to soil organisms through a tiered approach. At the screening level (TIER I) data were obtained from both the literature and laboratory experiments. For the intermediate level (TIER II), species sensitivity distributions (SSD) curves were generated based on ecotoxicological data from six species of soil invertebrates in two soil types. To estimate the risk, the Toxicity-Exposure Ratios (TER) were calculated at each tier considering the related toxicity data and the fipronil concentrations, which were measured and predicted in the field. Results showed that ecologically relevant concentrations of fipronil lead to a high risk for the edaphic community (above 100 times higher than the established safety value). The high risks were observed for both tiers, although at TIER II (SSD approach) it was at least 2.5 times higher than at TIER I. It was also discussed here that the pesticide mode of action is the factor most influencing toxicity; the estimated risk considering artificial soil was comparable to that with the natural soil; and estimating risk using only one species (as performed in the tropics) may underestimate the risk to the edaphic community.