Toxicity of fipronil to Folsomia candida in contrasting tropical soils and soil moisture contents: effects on the reproduction and growth.

This study assessed the influence of three tropical soil types and soil moisture content on the toxicity and risk of the insecticide fipronil to collembolans Folsomia candida. Chronic toxicity tests were performed in a Tropical Artificial Soil (TAS), an Oxisol and an Entisol spiked with increasing concentrations of fipronil to assess the effects on the reproduction and growth of the species. The soil moisture contents were kept at 60% (standard condition) and 30 or 45% (water restriction) of their water holding capacity (WHC). The toxicity of fipronil on collembolans reproduction was about three times higher in Entisol compared to TAS or Oxisol. Higher toxicities were also found in the drier TAS (EC50 30%WHC = 0.20 vs EC50 60%WHC = 0.70 mg kg-1) and Oxisol (EC50 45%WHC = 0.27 vs EC50 60%WHC = 0.54 mg kg-1), while in Entisol lower impacts were found in the drier samples (EC50 30%WHC = 0.41 vs EC50 60%WHC = 0.24 mg kg-1). For all tested soils, the size of generated collembolans was reduced by the fipronil concentrations, regardless of soil moisture. However, the drier condition increased the effect on the growth in TAS and Entisol for some concentrations. A significant risk of exposure was found in TAS and Oxisol at drier conditions and, for Entisol, regardless of the soil moisture. The toxic effects and risk of fipronil on collembolans were higher in the natural sandy soil. The soil moisture content increase or decrease the toxicity of the insecticide for collembolans, depending on soil type.

A systematic review of the toxic effects of a nanopesticide on non-target organisms: Estimation of protective concentrations using a species sensitivity distribution (SSD) approach - The case of atrazine.

Nanopesticides, such as nanoencapsulated atrazine (nATZ), have been studied and developed as eco-friendly alternatives to control weeds in fields, requiring lower doses. This review contains a historical and systematic literature review about the toxicity of nATZ to non-target species. In addition, the study establishes protective concentrations for non-target organisms through a species sensitivity distribution (SSD) approach. Through the systematic search, we identified 3197 publications. Of these, 14 studies addressed "(nano)atrazine's toxicity to non-target organisms". Chronological and geographic data on the publication of articles, characterization of nATZ (type of nanocarrier, size, polydispersity index, zeta potential), experimental design (test species, exposure time, measurements, methodology, tested concentrations), and toxic effects are summarized and discussed. The data indicate that cell and algal models do not show sensitivity to nATZ, while many terrestrial and aquatic invertebrates, aquatic vertebrates, microorganisms, and plants have high sensitivity to nAZT. The SSD results indicated that D. similis is the most sensitive species to nATZ, followed by C. elegans, E. crypticus, and P. subcapitata. However, the limitations in terms of the number of species and endpoints available to elaborate the SSD reflect gaps in knowledge of the effects of nATZ on different ecosystems.

Can the increase in atmospheric temperature enhance the toxicity and risk of fipronil for collembolans in tropical soils?

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 (EC50-based) were found at 27 °C (EC50 TAS = 0.81, 0.70, 0.31 mg kg-1; EC50 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 (EC50 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 (EC10-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.

Role of climatic factors in the toxicity of fipronil toward earthworms in two tropical soils: effects of increased temperature and reduced soil moisture content.

The aim of this study was to assess the effect of temperature on the toxicity of fipronil toward earthworms (Eisenia andrei) in two Brazilian soils (Entisol and Oxisol) with contrasting textures. In the case of Entisol, the influence of soil moisture content on toxicity was also investigated. Earthworms were exposed for 56 days to soils spiked with increasing concentrations of fipronil (8.95, 19.48, 38.22, 155.61, and 237.81 mg kg-1 for Entisol; 12.99, 27.94, 48.42, 204.67, and 374.29 mg kg-1 for Oxisol) under scenarios with different combinations of temperature (20, 25 and 27 °C) and soil moisture content (60 and 30% of water holding capacity (WHC) for Entisol and 60% WHC for Oxisol). The number of juveniles produced was taken as the endpoint, and a risk assessment was performed based on the hazard quotient (HQ). In Entisol, at 60% WHC the fipronil toxicity decreased at 27 °C compared with the other temperatures tested (EC50 = 52.58, 48.48, and 110 mg kg-1 for 20, 25, and 27 °C, respectively). In the case of Oxisol at 60% WHC, the fipronil toxicity increased at 27 °C compared with other temperatures (EC50 = 277.57, 312.87, and 39.89 mg kg-1 at 20, 25, and 27 °C, respectively). An increase in fipronil toxicity was also observed with a decrease in soil moisture content in Entisol at 27 °C (EC50 = 27.95 and 110 mg kg-1 for 30% and 60% WHC, respectively). The risk of fipronil was only significant at 27 °C in Entisol and Oxisol with water contents of 30% and 60% WHC, respectively, revealing that higher temperatures are able to increase the risk of fipronil toxicity toward earthworms depending on soil type and soil moisture content. The results reported herein show that soil properties associated with climatic shifts could enhance the ecotoxicological effects and risk of fipronil for earthworms, depending on the type of soil.

Chronic effects of clothianidin to non-target soil invertebrates: Ecological risk assessment using the species sensitivity distribution (SSD) approach.

This study aimed to assess the chronic toxicity and risk of clothianidin in a seed dressing formulation to non-target soil invertebrates. The toxicity assays were performed with two oligochaetes (earthworms Eisenia andrei and enchytraeids Enchytraeus crypticus) and three collembolans (Folsomia candida, Proisotoma minuta and Sinella curviseta) species following ISO protocols. Risk assessment (via Hazard Quotient approach - HQ) was based on the hazardous concentrations for 95% of the species (HC5), derived from chronic Species Sensitivity Distributions (SSD) for clothianidin, and on its predicted environmental concentrations (PEC). Four SSD scenarios were generated with literature and/or this study data, following different data selection criteria (i.e., general, only data from tests using similar formulations, similar soils, or identical soil/formulation). In our experiments, a higher clothianidin toxicity (EC50-based) was found for collembolans (varying from 0.11 to 0.28 mg kg-1 between species) followed by the earthworms (4.35 mg kg-1), while the enchytraeids were the least sensitive (33.5 mg kg-1). HQ indicated a significant risk of clothianidin to soil invertebrates because the estimated PEC were at least 16.6 times higher than HC5 and are expected to affect the whole group of collembolans. Despite the criteria for data inclusion have influenced the HC5 values, no substantial changes were observed for the risk outcomes. To our knowledge, this is the first study assessing the chronic ecological risk of clothianidin to beneficial soil fauna based on a probabilistic SSD approach. Data from this study can help to derive more reliable protection thresholds for clothianidin in soils.

Effect of temperature on the toxicity of imidacloprid to Eisenia andrei and Folsomia candida in tropical soils.

The influence of temperature on the chronic toxicity and risk of imidacloprid to soil non-target species was assessed in tropical soils. Earthworms Eisenia andrei and collembolans Folsomia candida were exposed to a tropical artificial soil (TAS) and two natural tropical soils from Brazil (Entisol and Oxisol) with increasing concentrations of imidacloprid under atmospheric temperatures of 20, 25 and 28 °C. The effect of temperature on the reproduction of both species was assessed through the number of juveniles and earthworm's growth, and the risk associated was estimated through the Toxicity-Exposure Ratio (TER). Toxicity of imidacloprid increased with temperature in all tested soils, being generally lower in TAS soil (EC50s of 1.48, 0.66 and 0.40 mg kg-1 for E. andrei and 0.3, 0.2 and 0.06 mg kg-1 for F. candida at 20, 25 and 28 °C, respectively) compared to Entisol (EC50s of 0.19, 0.03 and 0.14 mg kg-1 for E. andrei and 0.04, 0.02, 0.01 mg kg-1 for F. candida at 20, 25 and 28 °C, respectively) and Oxisol (EC50s of 0.21, 0.07, 0.06 mg kg-1 for E. andrei and 0.16, 0.09, 0.06 mg kg-1 for F. candida at 20, 25 and 28 °C, respectively) within each temperature for both species. These values indicate that properties of TAS may not be representative of natural/local soils to adequately estimate the toxicity of pesticides to non-target soil species. At higher temperatures, the variability of imidacloprid toxicity between soils was lower, which suggests that the influence of soil properties on imidacloprid toxicity was overshadowed by temperature. TER values revealed that risk is also greater at higher temperatures. Data reported enforce the need for the inclusion of more realistic conditions in single-species tests in prospective risk assessment of pesticides to avoid underestimation of risk to non-target species.