Toxicity in Neonicotinoids to Folsima candida and Eisenia andrei

Elevated temperature magnifies the acute and chronic toxicity of clothianidin to Eisenia fetida

Pesticide residue and thermal stress resulting from global climate change are parallel stressors for soil fauna. However, it remains ambiguous how elevated temperatures and pesticides can interact to threaten soil fauna. In the study, the acute and chronic clothianidin (CTD) toxicity to earthworms (Eisenia fetida) at different temperatures, and the effect of increasing temperature on antioxidant defense mechanisms in response to CTD were investigated. The acute toxicity of CTD was exacerbated by increased temperature in both filter paper contact tests (a decrease in the 48-h median lethal concentration (LC50) from 0.077 μg/cm2 at 20 °C to 0.009 μg/cm2 at 30 °C) and natural soil tests (a decrease in the 48-h LC50 from 0.774 mg/kg at 20 °C to 0.199 mg/kg at 30 °C). Exposure to CTD or high temperature (30 °C) triggered reactive oxygen species (ROS) overgeneration and increased antioxidant enzyme activities in earthworms; and the effect was particularly pronounced after exposure to both higher temperatures and CTD. At 20 and 25 °C, there was no significant change in the growth and reproduction of E. fetida after 56-d exposure to CTD-contaminated soil. However, the combined effect of CTD and high temperature (30 °C) significantly reduced the weight change rate, cocoon number, hatching rate, and number of juveniles on day 56. These results indicated that elevated temperature could aggravate acute and chronic CTD toxicity to earthworms. The findings emphasize that evaluating changes in pesticide toxicity under global warming is worth further investigation.

Joint toxic mechanism of clothianidin and prochloraz in the earthworm (Eisenia fetida)

Pesticides are typically present as combinations within soil ecosystems and have detrimental effects on untamed surroundings. However, the collective impacts and fundamental mechanisms of pesticides on soil living beings are currently inadequately assessed. In our current work, we evaluated the interactive consequences of clothianidin (CLO) and prochloraz (PRO) on earthworms (Eisenia fetida) using several toxicological tests, such as acute adverse effects, biocatalytic activity, and alterations in transcriptional activity. The findings revealed that CLO (with a 14-day LC50 value of 6.08 mg kg-1) exhibited greater toxicity compared to PRO (with a 14-day LC50 value of 79.41 mg kg-1). Moreover, the combinations of CLO and PRO had synergistic acute effects on E. fetida. Additionally, the activities of POD, CAT, and GST were significantly varied in most instances of single and mixed treatments when compared to the control. Surprisingly, the transcriptional levels of four genes (gst, sod, crt, and ann), related to oxidative load, metabolic detoxification systems, endoplasmic reticulum, and oxytocin neuropeptide, respectively, were also altered in response to single and mixture exposures, as compared to the control. Alterations in enzyme activity and gene transcriptional level could serve as early indicators for detecting co-exposure to pesticides. The findings of this research offered valuable holistic understanding regarding the toxicity of pesticide combinations on earthworms. Further research should be conducted to investigate the persistent effects of pesticide mixtures on terrestrial invertebrates in order to draw definitive conclusions about the associated risks.

Toxicity evaluation of neonicotinoids to earthworm (Eisenia fetida) behaviors by a novel locomotion tracking assay

Pesticides are substances used for controlling, preventing, and repelling pests in agriculture. Among them, neonicotinoids have become the fastest-growing class of insecticides because of their efficiency in targeting pests. They work by strongly binding to nicotinic acetylcholine receptors (nAChRs) in the central nervous system of insects, leading to receptor blockage, paralysis, and death. Despite their selectivity for insects, these substances may be hazardous to non-target creatures, including earthworms. Although earthworms may be invasive in some regions like north America, they contribute to the development of soil structure, water management, nutrient cycling, pollution remediation, and cultural services, positively impacting the environment, particularly in the soil ecosystem. Thus, this study aimed to develop a novel earthworm behavior assay since behavior is a sensitive marker for toxicity assay, and demonstrated its application in evaluating the toxicity of various neonicotinoids. Here, we exposed Eisenia fetida to 1 and 10 ppb of eight neonicotinoids (acetamiprid, clothianidin, dinotefuran, imidacloprid, nitenpyram pestanal, thiacloprid, thiametoxam, and sulfoxaflor) for 3 days to observe their behavior toxicities. Overall, all of the neonicotinoids decreased their locomotion, showed by a reduction of average speed by 24.94-68.63% and increment in freezing time movement ratio by 1.51-4.25 times, and altered their movement orientation and complexity, indicated by the decrement in the fractal dimension value by 24-70%. Moreover, some of the neonicotinoids, which were acetamiprid, dinotefuran, imidacloprid, nitenpyram, and sulfoxaflor, could even alter their exploratory behaviors, which was shown by the increment in the time spent in the center area value by 6.94-12.99 times. Furthermore, based on the PCA and heatmap clustering results, thiametoxam was found as the neonicotinoid that possessed the least pronounced behavior toxicity effects among the tested pesticides since these neonicotinoid-treated groups in both concentrations were grouped in the same major cluster with the control group. Finally, molecular docking was also conducted to examine neonicotinoids' possible binding mechanism to Acetylcholine Binding Protein (AChBP), which is responsible for neurotransmission. The molecular docking result confirmed that each of the neonicotinoids has a relatively high binding energy with AChBP, with the lowest binding energy was possessed by thiametoxam, which consistent with its relatively low behavior toxicities. Thus, these molecular docking results might hint at the possible mechanism behind the observed behavior alterations. To sum up, the present study demonstrated that all of the neonicotinoids altered the earthworm behaviors which might be due to their ability to bind with some specific neurotransmitters and the current findings give insights into the toxicities of neonicotinoids to the environment, especially animals in a soil ecosystem.

Spent coffee grounds as a suitable alternative to standard soil in ecotoxicological tests

Eisenia andrei is considered in OECD and ISO guidelines to be a suitable replacement for Eisenia fetida in ecotoxicological assays. This suggests that other alternative materials and methods could also be used in standard procedures for toxicity testing. The guidelines also favor using less time-consuming procedures and reducing costs and other limitations to ecotoxicological assessments. In recent years, spent coffee grounds (SCG) have been used to produce vermicompost and biochar and as an additive to organic fertilizers. In addition, the physicochemical characteristics of SCG indicate that the material is a suitable substrate for earthworms, with the organisms performing as well as in natural soil. In the present study, a battery of ecotoxicological tests was established with unwashed and washed SCG and a natural reference soil (LUFA 2.2). The test substrates were spiked with different concentrations of silver nitrate. Survival and reproduction of the earthworm E. andrei were assessed under different conditions, along with substrate basal respiration (SBR) as a proxy for microbial activity. Seedling emergence and the germination index of Lepidium sativum were also determined, following standard guidelines. Exposure to silver nitrate had similar effects on earthworm survival and reproduction, as the estimated effective concentrations (EC10 and EC50) in unwashed SCG and LUFA 2.2 overlapped. A hormetic effect was observed for SBR in LUFA 2.2 spiked with 12.8 mg/kg but not in unwashed SCG. Both SBR and root development were inhibited by similar concentrations of silver nitrate in washed SCG. The findings indicate that unwashed SCG could potentially be used as a substrate in E. andrei toxicity tests and support the eventual inclusion of this material in the standard guidelines.

Identification of point and nonpoint emission sources of neonicotinoid pollution in regional surface water

Neonicotinoid insecticides are widely applied in farmland, with high detection rates in soils and surface waters, posing potential risks to biodiversity and human health. As a nonpoint emission, surface runoff is widely regarded as the major source of neonicotinoid pollution in surface waters, but few studies have determined the point source contribution to rivers that may be primarily from wastewater treatment plants (WWTPs). Here, we collected the surface water from eight river basins in Zhejiang Province of China and quantified residual concentrations of eight widely commercialized neonicotinoids. Four of these were detected in all samples, with concentrations of dinotefuran and nitenpyram of 119 ± 166 and 87.6 ± 25.3 ng/L, respectively, representing more than 90 % of the total (282 ± 174 ng/L). Neonicotinoid residues were higher in tributaries due to nearby farmland and more dilution effects in the mainstream, and the residues were higher in lower reaches which can be explained by the water flow direction. Significant spatial differences in neonicotinoid distribution between surface water and agricultural soils result from environmental factors (e.g., water turbidity, precipitation, temperature) impacting migration and transport processes. Neonicotinoid residues in surface water showed a significant positive correlation with total WWTP emissions after adjusting for environmental factors. Conversely, no significant association was observed with cropland density (a nonpoint emission source), indicating that point emission source (contributing 20.6 %) predominantly influenced neonicotinoid residue spatial variation in river basin-scale surface water.

Integument colour change: Tracking delayed growth of Oppia nitens as a sub-lethal indicator of soil toxicity

Growth is an important toxicity end-point in ecotoxicology but is rarely used in soil ecotoxicological studies. Here, we assessed the growth change of Oppia nitens when exposed to reference and heavy metal toxicants. To assess mite growth, we developed an image analysis methodology to measure colour spectrum changes of the mite integument at the final developmental stage, as a proxy for growth change. We linked the values of red, green, blue, key-black, and light colour of mites to different growth stages. Based on this concept, we assessed the growth change of mites exposed to cadmium, copper, zinc, lead, boric acid, or phenanthrene at sublethal concentrations in LUFA 2.2 soil for 14 days. Sublethal effects were detected after 7 days of exposure. The growth of O. nitens was more sensitive than survival and reproduction when exposed to copper (EC50growth = 1360 mg/kg compared to EC50reproduction = 2896 mg/kg). Mite growth sensitivity was within the same order of magnitude to mite reproduction when exposed to zinc (EC50growth = 1785; EC50reproduction = 1562 mg/kg). At least 25% of sublethal effects of boric acid and phenanthrene were detected in the mites but growth was not impacted when O. nitens were exposed to lead. Consistent with previous studies, cadmium was the most toxic metal to O. nitens. The mite growth pattern was comparable to mite survival and reproduction from previous studies. Mite growth is a sensitive toxicity endpoint, ecologically relevant, fast, easy to detect, and can be assessed in a non-invasive fashion, thereby complimenting existing O. nitens testing protocols.

Changes in soil microbial communities after exposure to neonicotinoids: A systematic review

Neonicotinoids are a group of nicotine-related chemicals widely used as insecticides in agriculture. Several studies have shown measurable quantities of neonicotinoids in the environment but little is known regarding their impact on soil microbial populations. The purpose of this systematic review was to clarify the effects of neonicotinoids on soil microbiology and to highlight any knowledge gaps. A formal systematic review was performed following PRISMA (Preferred Reporting Items for Systematic Review and Meta-Analyses) guidelines using keywords in PubMed, SCOPUS and Web of Science. This resulted in 29 peer-reviewed articles, whose findings diverged widely because of variable methodologies. Field-based studies were few (28%). Imidacloprid was the most widely used (66%) and soil microbial communities were most sensitive to it. Spray formulations were used in 83% of the studies and seed treatments in the rest. Diversity indices were the most frequently reported soil microbial parameter (62%). About 45% of the studies found that neonicotinoids had adverse impacts on soil microbial community structure, composition, diversity, functioning, enzymatic activity and nitrogen transformation. Interactions with soil physicochemical properties were poorly addressed in all studies. The need for more research, particularly field-based research on the effects of neonicotinoids on soil microorganisms was highlighted by this review.

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.

Physiological and behavioral assessment of Metaphire posthuma in response to clothianidin insecticide: Insights from molecular and biochemical analysis

In the present study, Clothianidin [(E) - 1-(2 - chloro-1,3 - thiazol - 5-ylmethyl) - 3-methyl - 2- nitroguanidine] (CLO) was selected as a soil pollutant and earthworm was employed as a test organism. The various responses like biochemical and detoxification process of earthworm Metaphire posthuma towards Clothianidin at lethal and sublethal doses were studied using OECD-standardized toxicological guidelines. The present study examined the toxicity of CLO to earthworms after 28 days of exposure at conc. 0, 1.5, 3, 6, 12 and 24 mg kg-1 in a soil mixture. Biochemical markers including Guaiacol peroxidase (POD), Superoxide dismutase (SOD), Catalase (CAT), Glutathione S-transferase (GST) and content of Malondialdehyde (MDA) in earthworms were measured. Acute toxicity tests revealed that CLO caused a concentration-dependent increase in mortality with LC50 (Lethal concentration) values of 10.960 and 8.201 mg kg-1 for 7th and 14th day respectively. The earthworms were exposed to CLO contaminated soil for 56 days and reflecting the significant decrease in earthworm growth, cocoon and hatchling production. Moreover, enzyme activities such as CAT, SOD, POD and MDA content were significantly enhanced with the increased concentration and exposure period of CLO. Molecular docking studies indicated that CLO primarily interacts to the junction site of SOD and in active centres of CAT, POD and GST. As a result, the current findings imply that the sub chronic CLO exposure can induce variations in physiology and avoidance behaviour of earthworms, oxidative stress as well as alterations in enzyme activities.

Validation of biomarkers for neonicotinoid exposure in Folsomia candida under mutual exposure to diethyl maleate

Neonicotinoid insecticides are harmful to non-target soil invertebrates, which are crucial for sustainable agriculture. Gene expression biomarkers could provide economic and high-throughput metrics of neonicotinoid exposure and toxicity to non-target invertebrates. Thereby, biomarkers can help guide remediation efforts or policy enforcement. Gene expression of Glutathione S-Transferase 3 (GST3) has previously been proposed as a biomarker for the neonicotinoid imidacloprid in the soil ecotoxicological model species Folsomia candida (Collembola). However, it remains unclear how reliably gene expression of neonicotinoid biomarkers, such as GST3, can indicate the exposure to the broader neonicotinoid family under putative GST enzymatic inhibition. In this work, we exposed springtails to two neonicotinoids, thiacloprid and imidacloprid, alongside diethyl maleate (DEM), a known GST metabolic inhibitor that imposes oxidative stress. First, we determined the influence of DEM on neonicotinoid toxicity to springtail fecundity. Second, we surveyed the gene expression of four biomarkers, including GST3, under mutual exposure to neonicotinoids and DEM. We observed no effect of DEM on springtail fecundity. Moreover, the expression of GST3 was only influenced by DEM under mutual exposure with thiacloprid but not with imidacloprid. The results indicate that GST3 is not a robust indicator of neonicotinoid exposure and that probable GST enzymatic inhibition mediates the toxicity of imidacloprid and thiacloprid differentially. Future research should investigate biomarker reliability under shifting metabolic conditions such as provided by DEM exposure.

Individual and combined toxicity of imidacloprid and two seed dressing insecticides on collembolans Folsomia candida

The aim of this study was to examine the chronic toxicity of imidacloprid (IMI), clothianidin (CLO) and fipronil (FIP) as a single exposure, as well as binary mixtures of IMI with CLO or FIP toward collembolans Folsomia candida, which are fauna present in the soil. Chronic toxicity assays were performed following an ISO guideline in a Tropical Artificial Soil (TAS), and the influence on the number and growth of the juveniles produced were determined. The range of nominal concentrations used in the tests with the individual compounds was 0.08-1.28 mg/kg (IMI), 0.079-1.264 mg/kg (FIP) and 0.007-0.112 mg/kg (CLO), whereas the mixture assays were performed with half the value used in the tests with individual compounds. Based upon single exposures, IMI produced a similar impact of reducing reproduction by 50% (EC₅₀ ranging from 0.74 to 0.85 mg/kg) compared to FIP (EC₅₀ = 0.78 mg/kg), whereas CLO was the most toxic to F. candida (EC₅₀ = 0.08 mg/kg). Their mixtures generally resulted in a diminished effect on reproduction, as evidenced by the higher EC₅₀ values. In contrast, in the case of the IMI+FIP combination at high concentrations at the EC₅₀ level, a synergistic effect on toxicity was observed. The single exposure to the three insecticides and the mixture of IMI-FIP also decreased the size of generated juveniles, which was evidenced by the reduction in the proportion of large juveniles and increased proportion of small juveniles. However, both binary mixtures (IMI-FIP and IMI-CLO) presented antagonistic effects as evidenced by less than expected reductions in growth. Data on the toxic effects of IMI in a mixture with other seed dressing insecticides to collembolans provides useful information to environmental risk assessors by diminishing the uncertainties on the ecological risk of exposure to pesticides, enabling soil management degradation by utilizing multiple insecticides.

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.

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; EC_{50_60%WHC} = 0.010 mg kg^-1) and 27 °C (EC_{50_30%WHC} = 0.006 mg kg^-1; EC_{50_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 (EC_{50_30%WHC} = 0.040 mg kg^-1; EC_{50_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.

Biomarker development for neonicotinoid exposure in soil under interaction with the synergist piperonyl butoxide in Folsomia candida

Pesticide toxicity is typically assessed by exposing model organisms to individual compounds and measuring effects on survival and reproduction. These tests are time-consuming, labor-intensive, and do not accurately capture the effect of pesticide mixtures. Moreover, it is unfeasible to screen the nearly infinite combinations of mixtures for synergistic effects on model organisms. Therefore, reliable molecular indicators of pesticide exposure have to be identified, i.e., biomarkers. These biomarkers can form the basis of rapid and economical screening procedures to assess the toxicity of pesticides even under synergistic interaction with other pollutants. In this study, we screened the expression patterns of eight genes for suitability as a biomarker for neonicotinoid exposure in the soil ecotoxicological model Folsomia candida (springtails). Springtails were exposed to the neonicotinoids imidacloprid and thiacloprid either alone or with various levels of piperonyl butoxide (PBO), which inhibits cytochrome P450 enzymes (CYPs): a common point of synergistic interaction between neonicotinoid and other pesticides. First, we confirmed PBO as a potency enhancer for neonicotinoid toxicity to springtail fecundity, and then used it as a tool to confirm biomarker robustness. We identified two genes that are reliably indicative for neonicotinoid exposure even under metabolic inhibition of CYPs by PBO, nicotinic acetylcholine receptor-subunit alpha 1 (nAchR) and sodium-coupled monocarboxylate transporter (SMCT). These results can form the basis for developing high-throughput screening procedures for neonicotinoid exposure in varying mixture compositions.

Pesticide effects on the abundance of springtails and mites in field mesocosms at an agricultural site

The use of pesticides to protect crops often affects non-target organisms vital to ecosystem functioning. A functional soil mesofauna is important for decomposition and nutrient cycling processes in agricultural soils, which generally have low biodiversity. To assess pesticide effects on natural soil communities we enclosed intact soil cores in situ in an agricultural field in 5 cm wide mesocosms. We used two types of mesh lids on the mesocosms, allowing or preventing migration of mesofauna. The mesocosms were exposed to the insecticide imidacloprid (0, 0.1, 1, and 10 mg/kg dry soil) and left in the field for 20 days. Overall, regardless of lid type, mesocosm enclosure did not affect springtail or mite abundances during the experiment when compared with undisturbed soil. Imidacloprid exposure reduced the abundance of both surface- and soil-living springtails in a concentration-dependent manner, by 65-90% at the two highest concentrations, and 21-23% at 0.1 mg/kg, a concentration found in some agricultural soils after pesticide application. Surface-living springtails were more affected by imidacloprid exposure than soil-living ones. In contrast, neither predatory nor saprotrophic mites showed imidacloprid-dependent changes in abundance, concurring with previous findings indicating that mites are generally less sensitive to neonicotinoids than other soil organisms. The possibility to migrate did not affect the springtail or mite abundance responses to imidacloprid. We show that under realistic exposure concentrations in the field, soil arthropod community composition and abundance can be substantially altered in an organism-dependent manner, thus affecting the soil community diversity.

Neonicotinoid pollution in marine sediments of the East China Sea

Neonicotinoid insecticides are widely and exceedingly applied in farmlands worldwide and are ubiquitous in various environments, including surface water, soil, river sediments, etc. However, few studies reported neonicotinoid residues in the marine environment. Considering the large application of neonicotinoids in China, here, we collected marine sediments in offshore and far sea areas of the East China Sea, including the Hangzhou Bay and the area along the Zhejiang Province coast, and measured the concentrations of nine commercialized neonicotinoids. The total concentration of neonicotinoids was 11.9 ± 6.22 ng/g (dry weight) (range: 4.77-29.9 ng/g), which was higher than other regions reported in previous studies. Neonicotinoid residues found in far sea areas were statistically lower than those in offshore areas. Nitenpyram and dinotefuran were the dominant compounds, contributing to >75 % of the total residue. It is thought that the flux of the Yangtze River is the main source of the neonicotinoid pollution in the East China Sea and the sediment is the sink of neonicotinoid residue from mainland China. Neonicotinoid residues were found to be negatively correlated with sediment pH, and positively correlated with microbial diversity and nitrate content. Based on structural equation modeling, we also illustrated the associations between neonicotinoid residues and different factors, suggesting that the change in sediment pH and microbial diversity were related to the degradation of neonicotinoid residues. Actinobacteriota, Chloroflexi, and Nitrospirota were found to be the key bacterial community at the phylum level on the degradation of neonicotinoids. Our findings provide new insights into the understanding of spatial distribution, source, and migration of neonicotinoids and their impacts on marine microorganisms.

Collembola are Among the Most Pesticide-Sensitive Soil Fauna Groups: A Meta-Analysis

Pesticides are a major concern because of their deleterious impacts on biodiversity and on the ecological functions provided by living organisms. Although earthworms are well studied, smaller-sized organisms, such as Collembola, also contribute to the agroecosystem functioning, and their sensitivity to pesticides makes them good bioindicators of soil quality. Using data from 21 publications, we performed a meta-analysis to compare the pesticide sensitivity of Collembola with other soil invertebrate groups and discuss the relevance of including tests on representatives of this microarthropods group in European regulation tests. We defined a paired observation as the median lethal concentration or the median effect concentration values for both Collembola species and another soil fauna group (Acari, enchytraeids, earthworms, isopods, and nematodes) under a unique combination of author, year, substance, and type of soil (61 and 57 paired observations for reproduction and lethal effects). In some studies, paired comparisons were available for several groups of soil fauna. We demonstrated that Collembola are among the most sensitive soil fauna groups to a variety of pesticides, notably for effects on reproduction, mostly compared with earthworms and enchytraeids. Because there are several modes of exposure and explaining factors, we suggest moving from a single-species study to a food-chain approach integrating different taxonomic groups. Differences between soil fauna groups in sensitivity or response to pesticides could have effects on soil communities and also on soil functions. Environ Toxicol Chem 2022;41:2333-2341. © 2022 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Field mixtures of currently used pesticides in agricultural soil pose a risk to soil invertebrates

Massive use of pesticides in conventional agriculture leads to accumulation in soil of complex mixtures, triggering questions about their potential ecotoxicological risk. This study assessed cropland soils containing pesticide mixtures sampled from conventional and organic farming systems at La Cage and Mons, France. The conventional agricultural field soils contained more pesticide residues (11 and 17 versus 3 and 11, respectively) and at higher concentrations than soils from organic fields (mean 6.6 and 10.5 versus 0.2 and 0.6 μg kg^-1, respectively), including systemic insecticides belonging to neonicotinoids, carbamate herbicides and broad-spectrum fungicides mostly from the azole family. A risk quotient (RQ_i) approach evaluated the toxicity of the pesticide mixtures in soil, assuming concentration addition. Based on measured concentrations, both conventional agricultural soils posed high risks to soil invertebrates, especially due to the presence of epoxiconazole and imidacloprid, whereas soils under organic farming showed negligible to medium risk. To confirm the outcome of the risk assessment, toxicity of the soils was determined in bioassays following standardized test guidelines with seven representative non-target invertebrates: earthworms (Eisenia andrei, Lumbricus rubellus, Aporrectodea caliginosa), enchytraeids (Enchytraeus crypticus), Collembola (Folsomia candida), oribatid mites (Oppia nitens), and snails (Cantareus aspersus). Collembola and enchytraeid survival and reproduction and land snail growth were significantly lower in soils from conventional compared to organic agriculture. The earthworms displayed different responses: L. rubellus showed higher mortality on soils from conventional agriculture and large body mass loss in all field soils, E. andrei showed considerable mass loss and strongly reduced reproduction, and A. caliginosa showed significantly reduced acetylcholinesterase activity in soils from conventional agriculture. The oribatid mites did not show consistent differences between organic and conventional farming soils. These results highlight that conventional agricultural practices pose a high risk for soil invertebrates and may threaten soil functionality, likely due to additive or synergistic "cocktail effects".

Long-Term Effects of Imidacloprid, Thiacloprid, and Clothianidin on the Growth and Development of Eisenia andrei

Recently, the high toxicity of neonicotinoids to the survival and reproduction of adult earthworms has become apparent in standard 56-day toxicity tests. The persistence of some neonicotinoids and/or their repeated application may lead to long-term exposure, possibly also affecting other parts of the life cycle of earthworms. The present study aimed at providing insight into the sublethal effects of imidacloprid, thiacloprid, and clothianidin on juvenile Eisenia andrei exposed for 16 weeks in Lufa 2.2 soil. Significant effects on growth and maturation were observed for all compounds. Exposure to 0.125 mg imidacloprid/kg dry soil and 0.03125 and 0.0625 mg thiacloprid/kg dry soil significantly affected the growth of the earthworms, while significant maturation effects were observed at 0.03125 mg/kg dry soil for imidacloprid and thiacloprid and 0.25 mg clothianidin/kg dry soil. The 16-week no-observed-effect concentrations (NOECs) found in the present study were lower than previously reported NOECs for effects on earthworm reproduction. Predicted environmental concentrations after a single application exceeded the observed NOECs for effects on earthworm maturation in the case of imidacloprid and thiacloprid and for effects on earthworm growth in the case of thiacloprid and clothianidin. Environ Toxicol Chem 2022;41:1686-1695. © 2022 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

QSAR models for soil ecotoxicity: Development and validation of models to predict reproductive toxicity of organic chemicals in the collembola Folsomia candida

Soil pollution is a critical environmental challenge: the substances released in the soil can adversely affect humans and the ecosystem. Several bioassays were developed to investigate the soil ecotoxicity of chemicals with soil microbes, plants, invertebrates and vertebrates. The 28-day collembolan reproduction test with the springtail Folsomia candida is a recently introduced bioassay described by OECD guideline 232. Although the importance of springtails for maintaining soil quality, toxicity data for Collembola are still limited. We have developed two QSAR models for the prediction of reproductive toxicity induced by organic compounds in Folsomia candida using 28 days NOEC data. We assembled a dataset with the highest number of compounds available so far: 54 compounds were collected from publicly available sources, including plant protection products, reactive intermediates and industrial chemicals, household and cosmetic ingredients, drugs, environmental transformation products and polycyclic aromatic hydrocarbons. The models were developed using partial least squares regression (PLS) and the Monte Carlo technique with respectively the open source tools Small Dataset Modeler and CORAL software. Both QSAR models gave good predictive performance even though based on a small dataset, so they could serve for the ecological risk assessment of chemicals for terrestrial organisms.

Low Doses of Imidacloprid Induce Oxidative Stress and Neural Cell Disruption in Earthworm <i>Eisenia fetida</i>

Imidacloprid is a widely used pesticide that belongs to the class of neonicotinoids. There is a piece of rising evidence that neonicotinoids exert cytotoxic effects in non-target organisms including vertebrate species such as mammals. Nevertheless, dose-limiting toxicity and molecular mechanisms of neonicotinoids' deleterious effects are still poorly understood. In accord to imidacloprid fate in the environment, the most of used pesticide is absorbed in the soil. Therefore, earthworms, which are prevailing soil organisms, could be considered as a target of neonicotinoids toxicity. The earthworm’s simple nervous system is a prospective model for neurotoxicological studies. We exposed earthworms to imidacloprid in a paper contact test with a doses range of 0.1‑0.4 µg/cm2 for 14 days. In the present work, we studied the imidacloprid effect on oxidative stress generation and neuronal marker neuron-specific enolase (NSE) expression. The exposure to imidacloprid induced a dose-dependent decrease in NSE. Both reactive oxygen species production and lipid peroxidation level were upregulated as well. Observed NSE decline suggests imidacloprid-caused disturbance in earthworm neuron cells. Obtained data have shown that relatively low doses of imidacloprid are potent to induce cytotoxicity in neurons. Furthermore, neurotoxicity could be recognized as one of an individual scenario of the general imidacloprid toxicity. Thus, presented results suggest the cytotoxicity of imidacloprid low doses in non-target organisms and hypothesize that NSE downregulation could be estimated as a biomarker of neonicotinoid cytotoxicity in a nervous system of non-insect species.

Low Doses of Imidacloprid Induce Oxidative Stress and Neural Cell Disruption in Earthworm <i>Eisenia fetida</i>

Imidacloprid is a widely used pesticide that belongs to the class of neonicotinoids. There is a piece of rising evidence that neonicotinoids exert cytotoxic effects in non-target organisms including vertebrate species such as mammals. Nevertheless, dose-limiting toxicity and molecular mechanisms of neonicotinoids' deleterious effects are still poorly understood. In accord to imidacloprid fate in the environment, the most of used pesticide is absorbed in the soil. Therefore, earthworms, which are prevailing soil organisms, could be considered as a target of neonicotinoids toxicity. The earthworm’s simple nervous system is a prospective model for neurotoxicological studies. We exposed earthworms to imidacloprid in a paper contact test with a doses range of 0.1‑0.4 µg/cm2 for 14 days. In the present work, we studied the imidacloprid effect on oxidative stress generation and neuronal marker neuron-specific enolase (NSE) expression. The exposure to imidacloprid induced a dose-dependent decrease in NSE. Both reactive oxygen species production and lipid peroxidation level were upregulated as well. Observed NSE decline suggests imidacloprid-caused disturbance in earthworm neuron cells. Obtained data have shown that relatively low doses of imidacloprid are potent to induce cytotoxicity in neurons. Furthermore, neurotoxicity could be recognized as one of an individual scenario of the general imidacloprid toxicity. Thus, presented results suggest the cytotoxicity of imidacloprid low doses in non-target organisms and hypothesize that NSE downregulation could be estimated as a biomarker of neonicotinoid cytotoxicity in a nervous system of non-insect species.

Toxicity of clothianidin to common Eastern North American fireflies

Background

Previous research suggests that fireflies (Coleoptera: Lampyridae) are susceptible to commonly used insecticides. In the United States, there has been a rapid and widespread adoption of neonicotinoid insecticides, predominantly used as seed coatings on large-acreage crops like corn, soy, and cotton. Neonicotinoid insecticides are persistent in soil yet mobile in water, so they have potential to contaminate firefly habitats both in and adjacent to application sites. As a result, fireflies may be at high risk of exposure to neonicotinoids, possibly jeopardizing this already at-risk group of charismatic insects.

Methods

To assess the sensitivity of fireflies to neonicotinoids, we exposed larvae of Photuris versicolor complex and Photinus pyralis to multiple levels of clothianidin-treated soil and monitored feeding behavior, protective soil chamber formation, intoxication, and mortality.

Results

Pt. versicolor and Pn. pyralis larvae exhibited long-term intoxication and mortality at concentrations above 1,000 ng g^-1 soil (1 ppm). Under sub-lethal clothianidin exposure, firefly larvae fed less and spent less time in protective soil chambers, two behavioral changes that could decrease larval survival in the wild.

Discussion

Both firefly species demonstrated sub-lethal responses in the lab to clothianidin exposure at field-realistic concentrations, although Pt. versicolor and Pn. pyralis appeared to tolerate higher clothianidin exposure relative to other soil invertebrates and beetle species. While these two firefly species, which are relatively widespread in North America, appear somewhat tolerant of neonicotinoid exposure in a laboratory setting, further work is needed to extend this conclusion to wild populations, especially in rare or declining taxa.

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.

Differences in kinetic metabolomics in Eisenia fetida under single and dual exposure of imidacloprid and dinotefuran at environmentally relevant concentrations

Metabolomic responses of earthworms to neonicotinoids are important for understanding their molecular-level toxicity and assessing their ecological risks, but little is known until now. We investigated impact of imidacloprid (IMI, 52.6 ng/g) and dinotefuran (DIN, 52.5 ng/g) on Eisenia fetida metabolomics under single- and dual-compound exposure scenarios for one to four weeks. Dissimilar metabolites and anti-stress strategies were found for different neonicotinoids and exposure scenarios. Specifically, IMI exposure first increased myo-inositol and UDP-glucuronate associated with transmembrane absorption and transformation to IMI-urea, and then increased glutathione and fourteen amino acids (TCA cycle precursors) to resist stress and replenish energy. In contrast, worms exposed to DIN first prepared TCA cycle intermediates from glucosamine-6-phosphate and amino acids, suppressed urea cycle and DIN transformation, and then alleviated oxidative stress by increasing carnosine, nicotinate-D-ribonucleotide and nicotinamide-β-riboside. Dual exposure increased four eicosanoids by 1.6-1.9-fold, possibly associated with membrane lipid peroxidation; the amino acids consumed to balance the energy metabolism exhibited a wave-like pattern. This study first systematically revealed the compound/time/exposure scenario- dependent effects of trace neonicotinoids on earthworm metabolomics and advanced the understanding of their action modes. Neonicotinoid transformation was closely related to worms' metabolic profiles, providing important insights in contaminant fate in soil ecosystems.

A Multiple Life-History Trait-Based and Time-Resolved Assessment of Imidacloprid Effects and Recovery in the Widely Distributed Collembolan Folsomia quadrioculata

Life-history traits determine individual fitness and the fate of populations. Imidacloprid, a widely used neonicotinoid insecticide, which persists in soil for more than 100 d at biologically relevant levels, may affect nontarget and ecologically important species, such as collembolans. In the present study, we determined the sublethal effects of short-term imidacloprid exposure and postexposure recovery in the collembolan Folsomia quadrioculata, which occurs abundantly across the northern hemisphere. We assessed survival, egg production, and hatching success in adult springtails exposed for 14 d through the diet to imidacloprid, followed by a 28-d postexposure phase. Survival and hatching success were high throughout the experiment in all the treatments, with no clear concentration dependence. However, egg production declined during the exposure phase and nearly stopped between 8 and 14 d in all the treatments (except the control) but resumed during the postexposure phase. Moreover, the resumption of egg production showed a concentration-dependent delay. Our findings suggest that low imidacloprid exposures can restrict reproduction, with potentially severe consequences for the population, notwithstanding the partial recovery in egg production. Environ Toxicol Chem 2021;40:139-147. © 2020 SETAC.

Bringing ecology into toxicology: Life-cycle toxicity of two neonicotinoids to four different species of springtails in LUFA 2.2 natural soil

Collembolans comprise one of the most abundant groups of soil invertebrates within the arthropods. The parthenogenetic species Folsomia candida (Willem, 1902) is the most well-studied representative, being used since the beginning of the 1960s as a model organism for assessing toxicity of chemicals in soil. In this paper we aimed at answering three questions by exposing four different species of springtails (F. candida, Folsomia fimetaria, Sinella curviseta and Heteromurus nitidus) to the neonicotinoids imidacloprid and thiacloprid: i) How representative as a model organism is F. candida for species of springtails that reproduce sexually? (ii) How suitable are other species of springtails to be used as model organisms for ecotoxicological testing? (iii) Is it possible to use the life history of these species to extrapolate the impact of neonicotinoids on the population level? Our results showed that F. candida is a good model organism, despite being the most sensitive species tested, when analysing both endpoints - survival and reproduction. The tests performed with S. curviseta and H. nitidus showed that they could be used as surrogates in ecotoxicity tests, and also to predict how their population might be affected after being exposed to chemicals. The adjustments made to the test performed with F. candida: introducing adults (20-22 days old) into the test jars and exposing them for 21 days instead of 28 days, proved to be as efficient as the standardized test guideline (OECD 232, 2009).

Toxicity of imidacloprid to collembolans in two tropical soils under different soil moisture

Shifts in precipitation regimes due to the predicted climate changes can alter the water content in tropical soils and, consequently, may influence the toxicity of pesticides to soil fauna. This study assessed the influence of soil moisture content on the toxicity of the insecticide imidacloprid to the collembolans Folsomia candida in two tropical soils and evaluated the risk of this active ingredient for this species in the soils tested through the toxicity exposure ratio approach. Acute and chronic toxicity tests with F. candida were performed using an Entisol and an Oxisol. The soils were spiked with increasing imidacloprid concentrations while simulating normal water availability (60% of the water holding capacity [WHC]) and water restriction (30 or 45% WHC) for the tests. In the Oxisol, the reduction of soil moisture content significantly increased the toxic effects of imidacloprid on F. candida's survival (LC₅₀ at 45% WHC = 23.8 vs. LC₅₀ at 60% WHC >64 mg kg^-1) and reproduction (effective concentration causing reductions in species reproduction of 50% [EC₅₀] at 45% WHC = 0.32 vs. EC₅₀ at 60% WHC = 2.83 mg kg^-1), but in the Entisol no clear influence of the soil moisture on the toxicity of imidacloprid for collembolans was found. A significant risk for F. candida was observed in the Oxisol only when in water restriction, whereas in the Entisol it occurred regardless of soil moisture, suggesting that the imidacloprid hazard and risk for F. candida may be increased if soil moisture decreases due to climate changes, depending on the soil type.