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PurposeImidacloprid is a widely used seed dressing insecticide in Brazil. However, the effects of this pesticide on non-target organisms such as soil fauna still present some knowledge gaps in tropical soils. This study aimed to assess the toxicity and risk of imidacloprid to earthworms Eisenia andrei and collembolans Folsomia candida in three contrasting Brazilian tropical soils.Materials and methodsAcute and chronic toxicity assays were performed in the laboratory with both species in a tropical artificial soil (TAS) and in two natural soils (Oxisol and Entisol), at room temperature of 25 °C. The ecological risk was calculated for each species and soil by using the toxicity exposure ratio (TER) and hazard quotient (HQ) approaches.Results and discussionAcute toxicity for collembolans and earthworms was higher in Entisol (LC50 = 4.68 and 0.55 mg kg−1, respectively) when compared with TAS (LC50 = 10.8 and 9.18 mg kg−1, respectively) and Oxisol (LC50collembolans = 25.1 mg kg−1). Chronic toxicity for collembolans was similar in TAS and Oxisol (EC50 TAS = 0.80 mg kg−1; EC50 OXISOL = 0.83 mg kg−1), whereas higher toxicity was observed in Entisol (EC50 = 0.09 mg kg−1). In chronic assays with earthworms, imidacloprid was also more toxic in Entisol (EC50 = 0.21 mg kg−1) when compared to TAS (EC50 = 1.89 mg kg−1). TER and HQ values indicated a significant risk of exposure of the species to imidacloprid in all soils tested, and the risk in Entisol was at least six times higher than in Oxisol or TAS.ConclusionsThe toxicity and risk of imidacloprid varied significantly between tropical soils, being the species exposure to this pesticide particularly hazardous in very sandy natural soils such as Entisol.

We evaluated the toxicity and risk (via toxicity exposure ratio approach — TER) of the insecticide fipronil to collembolan’s growth and reproduction in three tropical soils, under increasing atmospheric temperatures. Chronic toxicity tests were performed with Folsomia candida in tropical artificial soil (TAS), oxisol, and entisol spiked with increasing concentrations of fipronil, at three room temperature scenarios: a standard (20 ± 2 °C), a tropical condition (25 ± 2 °C) and a global warming simulation (27 ± 2 °C). Temperatures influenced the fipronil effects on the species reproduction differently between soil types. In TAS and oxisol the highest toxicities (EC 50 -based) were found at 27 °C (EC 50 TAS = 0.81, 0.70, 0.31 mg kg −1 ; EC 50 OXISOL = 0.52, 0.54, 0.40 mg kg −1 ; at 20, 25, and 27 °C, respectively). In entisol, the toxicity at 27 °C was lower compared to 25 and 20 °C (EC 50 ENTISOL = 0.33, 0.24, 0.12 mg kg −1 , respectively). Fipronil concentrations also increased the proportion of small juveniles (growth reduction) in all tested soils. However, this effect was greater (EC 10 -based) at higher temperatures (25 and/or 27 °C), regardless of the soil type. TER approach revealed a significant risk of fipronil in entisol, regardless of the tested temperature, while in other soils the risk was found significant only at the higher temperatures (25 and 27 °C for TAS, and 27 °C for oxisol). These results indicate that exposures to fipronil at high temperatures (e.g., those resulting from climate change) can threaten F. candida populations, depending on the soil type.