Influence of temperature and soil moisture on the toxic potential of clothianidin to collembolan Folsomia candida in a tropical field soil.

Climate change can alter the toxic effects of pesticides on soil invertebrates. However, the nature and magnitude of the influence of climatic factors on clothianidin impacts in tropical soils are still unknown. The influence of increasing atmospheric temperature and the reduction in soil moisture on the toxicity and risk of clothianidin (seed dressing formulation Inside FS®) were assessed through chronic toxicity tests with collembolans Folsomia candida in a tropical field soil (Entisol). The risk of clothianidin for collembolans was estimated using the Toxicity-Exposure Ratio (TER) approach. Organisms were exposed to increasing clothianidin concentrations at 20, 25 and 27 °C in combination with two soil moisture conditions (30 and 60% of the maximum water holding capacity-WHC). The effect of temperature and soil moisture content on clothianidin toxicity was verified through the number of F. candida juveniles generated after 28 days of exposure to the spiked soil. The toxicities estimated at 25 °C (EC50_30%WHC = 0.014 mg kg-1; EC50_60%WHC = 0.010 mg kg-1) and 27 °C (EC50_30%WHC = 0.006 mg kg-1; EC50_60%WHC = 0.007 mg kg-1) were 2.9-3.0-fold (25 °C) and 4.3-6.7-fold (27 °C) higher than those found at 20 °C (EC50_30%WHC = 0.040 mg kg-1; EC50_60%WHC = 0.030 mg kg-1), indicating that clothianidin toxicity increases with temperature. No clear influence of soil moisture content on clothianidin toxicity could be observed once the EC50 values estimated at 30% and 60% WHC, within the same temperature, did not significantly differ. A significant risk was detected in all temperatures and soil moisture scenarios studied, and the TER values indicate that the risk can increase with increasing temperatures. Our results revealed that temperature could overlap with soil moisture in regulating clothianidin toxicity and reinforce the importance of including climatic factors in the prospective risk assessment of pesticides.

Rapid Communication: oxidative stress induced by mixed exposure to glyphosate and silver nanoparticles.

The aim of this study was to examine oxidative stress induced by the binary mixture of silver nanoparticles (AgNP) and glyphosate (Gly) in Daphnia magna by measurement of reactive oxygen species (ROS) production, glutathione (GSH) levels, enzyme activities of catalase (CAT) and superoxide dismutase (SOD) as well as malondialdehyde (MDA) content. Acute exposure of Daphnia magna to binary mixture of AgNP and Gly resulted in significant biochemical responses indicative of oxidative damage. This response seemed to be related to imbalance in enzymatic/non-enzymatic antioxidant enzymes associated with intracellular overproduction of ROS and significant increase in MDA levels, indicating that the integrity and function of the cell membrane was damaged. These changes adversely affected the fitness and survival of Daphnia magna and negatively influenced offspring growth and reproduction.

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.

Ecotoxicological evaluation of swine manure disposal on tropical soils in Brazil.

Swine production in Brazil results in a great volume of manure that normally is disposed of as agricultural fertilizer. However, this form of soil disposal, generally on small farms, causes the accumulation of large amounts of manure and this results in contaminated soil and water tables. To evaluate the effects of increasing concentrations of swine manure on earthworms, several ecotoxicological tests were performed using Eisenia andrei as test organism in different tropical soils, classified respectively as Ultisol, Oxisol, and Entisol, as well as Tropical Artificial Soil (TAS). The survival, reproduction and behavior of the earthworms were evaluated in experiments using a completely randomized design, with five replications. In the Ultisol, Oxisol and TAS the swine manure showed no lethality, but in the Entisol it caused earthworm mortality (LOEC=45 m(3)ha(-1)). In the Entisol, the waste reduced the reproductive rate and caused avoidance behavior in E. andrei (LOEC=30 m(3)ha(-1)) even in lower concentrations. The Entisol is extremely sandy, with low cation exchange capacity (CEC), and this may be the reason for the higher toxicity on soil fauna, with the soil not being able to hold large amounts of pollutants (e.g. toxic metals), but leaving them in bioavailable forms. These results should be a warning of the necessity to consider soil parameters (e.g. texture and CEC) when evaluating soil contamination by means of ecotoxicological assays, as there still are no standards for natural soils in tropical regions. E. andrei earthworms act as indicators for a soil to support disposal of swine manure without generating harm to agriculture and ecosystems.

Are the Brazilian prevention values for copper and zinc in soils suitable for protecting earthworms against metal toxicity?

The current Brazilian copper (Cu) and zinc (Zn) prevention values (PV) for soil quality do not take into account the ecotoxicological impacts on soil organisms, which suggests these guiding values may not be protective of soil ecological trophic levels. This study assessed the acute (mortality) and chronic toxicity (reproduction), as well as the cumulative (bioaccumulation) potential of Cu and Zn (pseudo-total and available fractions) for earthworms Eisenia andrei in a Tropical Artificial Soil (TAS) and two tropical field soils (Oxisol and Alfisol). Toxicity data based on pseudo-total fractions were compared to PV. The Lowest Observed Effect Concentrations (LOEC) for the mortality endpoint were found at Cu and Zn concentrations higher than their PV (60 and 300 mg kg-1, respectively), regardless of the soil type. However, concentrations lower than PV reduced the reproduction of E. andrei by 20% (compared to the controls) for Cu in all tested soils (EC20s from 31.7 to 51.2 mg kg-1) and by 50% for Zn in Oxisol and Alfisol (EC50s = 225 and 283 mg kg-1, respectively). In TAS, only the EC20 (273 mg kg-1) for Zn was lower than PV. Increases of Cu in earthworm tissues occurred at concentrations higher than PV in all tested soils (LOEC values from 70 to 107 mg kg-1). The same was observed for Zn in TAS (LOEC = 497 mg kg-1), while in the field soils, the increases of Zn in earthworm tissues were lower than PV (LOEC = 131 and 259 mg kg-1 in Alfisol and Oxisol, respectively). We suggest the following: (1) The current Brazilian PV for Cu and Zn are not protective for earthworms (E. andrei) in the field soils tested; (2) PV derived from ecotoxicological assays in artificial soil cannot be representative for Brazilian field soils; (3) Using PV based on the pseudo-total fraction, without a soil-type normalizing factor, may limit the representativeness of this threshold for different soil types.

The use of sewage sludge as remediation for imidacloprid toxicity in soils.

This study investigated the influence of the sewage sludge (SS) soil amendment on the chronic toxicity of imidacloprid (through the seed dressing formulation MUCH 600 FS®-600 g active ingredient L-1) to collembolans Folsomia candida. Individuals 10-12 days old were exposed to two contrasting tropical soils (Oxisol and Entisol) amended with SS doses (0, 20, 40, 80, 160, and 320 g SS kg-1 soil; the SS doses have low intrinsic toxicity, which was checked before its application) in a full factorial combination with five imidacloprid concentrations (varying from 0.25 to 4 mg kg-1 in Oxisol and 0.03-0.5 mg kg-1 in Entisol) plus a control. None of the SS doses (without imidacloprid) in both soils reduced the number of generated juvenile collembolans. The imidacloprid concentrations reducing the collembolan reproduction in 50% (EC50) in Oxisol and Entisol without SS were 0.49 and 0.08 mg kg-1, respectively. However, the EC50 values generally increased with increasing SS doses in soils, varying from 1.03 to 1.41 in Oxisol and 0.07 to 0.21 in Entisol. The SS-amended soils showed 2.1- to 2.9-fold lower imidacloprid toxicity (EC50-based) in Oxisol and 1.8- to 2.7-fold lower toxicity in Entisol. Our results suggest the most effective SS doses alleviating the imidacloprid toxicity (EC50-based) to collembolans are 20 g kg-1 in Oxisol and 80 g kg-1 in Entisol. These results indicate that the tested SS has the potential to be employed as a soil amendment agent by reducing the toxicity of imidacloprid to the reproduction of F. candida.

Locomotion behavior testing as a complementary tool in Collembola avoidance assays with neurotoxic insecticides.

This study aimed (1) to assess the ability of collembolans Folsomia candida to avoid soils contaminated with three seed dressing insecticides imidacloprid, clothianidin, and fipronil; (2) to assess the effects of the insecticides on collembolans' locomotion behavior; (3) to check if changes in the locomotion behavior would explain the avoidance/preference responses; and (4) to evaluate the possibility to use locomotion behavior as toxicity biomarker of the tested insecticides. Avoidance and locomotion behavior assays with collembolans F. candida were performed with commercial seed dressing formulations of three insecticides (imidacloprid, clothianidin, and fipronil). Results showed no avoidance behavior at any concentration, while a "preference" was observed with increasing concentrations of the three tested insecticides. Significant reductions in the locomotion of exposed collembolans were observed at ≥ 1 mg kg-1 for imidacloprid (18-38%) and fipronil (29-58%) and ≥ 4 mg kg-1 for clothianidin (10-47%). At the higher insecticide concentrations, the collembolans had their trajectories restricted to smaller areas, with a tendency for circular movements. Our results confirm that the "preference" for contaminated soils with neurotoxic substances is likely due to locomotion inhibition impairing the ability of organisms to escape. This effect highlights that only avoidance assays may be not sufficient to assure the safety of some substances and confirm the potential of locomotion behavior as a sensitive toxicity biomarker for neurotoxic insecticides.

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.

Ecotoxicity of imidacloprid to soil invertebrates in two tropical soils with contrasting texture.

Imidacloprid is one of the most commercialized insecticides in agriculture in the world, with a broad spectrum of action. However, little is known about the effects of commercial formulations containing this active ingredient (a.i.) on non-target organisms in tropical soils. Our objective was to assess the toxicity based on the predicted environmental concentration (PEC) of imidacloprid, in the avoidance behaviour of earthworms and collembolans as well as in the reproduction of collembolans, in two representative soils of the Brazilian Cerrado with contrasting texture (clayey Oxisol and sandy Entisol). Ecotoxicity tests were carried out according to ISO protocols to assess the avoidance behaviour of earthworms (Eisenia andrei) and avoidance and reproduction of collembolans (Folsomia candida). In the earthworm's avoidance test, more than 80% of the individuals were found in the control, in all tested concentrations, indicating a possible habitat function loss in both soils. The avoidance behaviour of collembolans was observed in both soils, being more expressive (up to 75% of escape) in Oxisol. In Entisol, only the two highest concentrations were avoided (up to 63%). There was a negative effect on the reproduction of collembolans in both soils, with a higher EC50 value (0.255 mg kg-1) in Oxisol than in Entisol (0.177 mg kg-1), demonstrating higher toxicity in the sandy soil. These differences were attributed to the contrasting texture of the studied soils, probably due to lower retention of the a.i. in the sandy soil, causing an increased bioavailability. This study demonstrated that imidacloprid can be highly toxic to soil invertebrates, even in soil concentrations lower than those expected from recommended dose, causing an impact on the edaphic organisms and, consequently, compromising its functions in the soil ecosystem.

Ecotoxicological assessment of Fluazuron: effects on Folsomia candida and Eisenia andrei.

The cattle production in Brazil has increased considerably in the last years, mainly due to the control of parasite infestation of the animals, which cause loss of productivity to the sector. Fluazuron is an active ingredient (a.i.) of the benzoylurea class used to control ticks in cattle. As this a.i. has been found unchanged in animal feces, which may present a risk to edaphic organisms, this study aimed to assess the effects of fluazuron on survival, reproduction, and behavior of the soil invertebrates Folsomia candida and Eisenia andrei, through ecotoxicological assays. We carried out bioassays in a tropical artificial soil (TAS) spiked with increasing doses of the insecticide. Earthworm mortality was found only at the highest tested fluazuron concentration (LOEC = 160 mg a.i. kg-1 dry soil and NOEC = 80 mg kg-1), while the reproduction of F. candida and E. andrei was reduced at lower fluazuron concentrations (EC50 = 4.48 mg kg-1 and EC50 = 20.8 mg kg-1, respectively). Avoidance behavior was detected for both species at lower concentrations than those that caused impacts on reproduction, indicating that the substance may affect the soil habitat function. Since the possible adverse effects of fluazuron on edaphic fauna are still unknown or neglected, this study also warns about the possible harmful effect of veterinary pharmaceutical products on edaphic fauna.

Ecotoxicological impact of arsenic on earthworms and collembolans as affected by attributes of a highly weathered tropical soil.

High levels of heavy metals in soils may impose serious impacts on terrestrial organisms. In Brazil, the prevention values for evaluating the ecological risk of these elements are based only on soil chemical analyses and/or on data from ecotoxicological assays performed in soils of temperate regions. However, the attributes of the Brazilian highly-weathered tropical soils can influence the availability of heavy metals for soil fauna, resulting in different toxic values. To provide more accurate ecotoxicological risk values for arsenic (As) in tropical soils, we assessed the impacts of sodium arsenate (Na2HAsO4·7H2O) on the reproduction of earthworms (Eisenia andrei) and collembolans (Folsomia candida), as well as on As bioaccumulation and growth (weight loss) of E. andrei in a tropical artificial soil (TAS) and in an Oxisol. In TAS, As doses reduced the reproduction of the species and promoted weight loss of earthworms. On the other hand, the reproductions of the species as well as the earthworm growth were not altered by As in the Oxisol. The effective concentrations that reduce the reproduction of E. andrei and F. candida by 50 % (EC50) obtained in TAS (22.7 and 26.1 mg of As kg-1 of dry soil, respectively) were lower than those in the Oxisol (>135 mg kg-1, for both species). Although there was As bioaccumulation in earthworms in both soils, the internal concentrations in the earthworms were much higher in the oligochaetes exposed to arsenic in TAS. All these differences were attributed to the higher availability of As in the TAS, compared to the Oxisol, which increased the exposure of the species to the metal. The lower availability in the Oxisol was related to higher contents of type 1:1 silicate minerals and Fe and Al oxides and hydroxides, which strongly bind to As. These results highlight the importance of using tropical soils of humid regions to derive the Brazilian ecological risk prevention values for heavy metals, since the toxicity values are specific for these soils.