Insecticide risk assessment in tropical soils: relevant concentrations of fipronil cause high risk to the edaphic community

Abstract Widely used in Brazilian agricultural fields, the insecticide fipronil acts in the arthropods’ nervous system of target and non-target organisms. The present study aimed to estimate fipronil ecological risk to soil organisms, on both natural and artificial soils from tropical environments. For risk calculations, a tiered approach was used. At the screening level (TIER I) data was obtained from the literature and laboratory experiments. For the intermediate level (TIER II), species sensitivity distributions (SSD) curves were generated based on the results from six species of soil invertebrates in both soils. To estimate the risk, the Toxicity-Exposure Ratios (TER) were calculated considering the related toxicity data and the fipronil concentrations 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 safety value). The high risks were observed for both tiers, although more accentuated risk values were obtained using the SSD approach. Hence, it was also discussed here that the mode of action is the factor most influencing the pesticides’ toxicity to non-target organisms and using only one group of organisms to assess the risk of any pesticide may underestimate the risk to the whole community.