Modeling temperature-dependent life-cycle toxicity of thiamethoxam in Chironomus riparius using a DEB-TKTD model.

The neonicotinoid insecticide thiamethoxam (TMX) is widely used to protect crops against insect pests. Despite some desirable properties such as its low toxicity to birds and mammals, concerns have been raised about its toxicity to non-target arthropods, including freshwater insects like chironomids. Whereas multiple studies have investigated chronic effects of neonicotinoids in chironomid larvae at standardized laboratory conditions, a better understanding of their chronic toxicity under variable temperatures and exposure is needed for coherent extrapolation from the laboratory to the field. Here, we developed a quantitative mechanistic effect model for Chironomus riparius, to simulate the species' life history under dynamic temperatures and exposure concentrations of TMX. Laboratory experiments at four different temperatures (12, 15, 20, 23 °C) and TMX concentrations between 4 and 51 µg/L were used to calibrate the model. Observed concentration-dependent effects of TMX in C. riparius included slower growth, later emergence, and higher mortality rates with increasing concentrations. Furthermore, besides a typical accelerating effect on the organisms' growth and development, higher temperatures further increased the effects associated with TMX. With some data-informed modeling decisions, most prominently the inclusion of a size dependence that makes larger animals more sensitive to TMX, the model was parametrized to convincingly reproduce the data. Experiments at both a constant (20 °C) and a dynamically increasing temperature (15-23 °C) with pulsed exposure were used to validate the model. Finally, the model was used to simulate realistic exposure conditions using two reference exposure scenarios measured in Missouri and Nebraska, utilizing a moving time window (MTW) and either a constant temperature (20 °C) or the measured temperature profiles belonging to each respective scenario. Minimum exposure multiplication factors leading to a 10% effect (EP10) in the survival at pupation, i.e., the most sensitive endpoint found in this study, were 25.67 and 21.87 for the Missouri scenario and 38.58 and 44.64 for the Nebraska scenario, when using the respective temperature assumptions. While the results illustrate that the use of real temperature scenarios does not systematically modify the EPx in the same direction (making it either more or less conservative when used as a risk indicator), the advantage of this approach is that it increases the realism and thus reduces the uncertainty associated with the model predictions.

Physiological responses of oxidative damage, genotoxicity and hematological parameters of the toxic effect of neonicotinoid-thiamethoxam in Oreochromis niloticus.

The purpose of investigation assessed the impacts of neonicotinoid thiamethoxam (TMX) at sublethal concentrations in hematological profile and renal function of Oreochromis niloticus. In the experiment, fish were exposed to TMX in four groups (0, 50, 100 and 150 ppm) for 7 days. At the end of the experiment, biochemical analysis of blood samples showed that the parameters indicating renal function showed a significant increase in serum enzymes ALT, AST, ALP and metabolites (BUN, urea, uric acid, creatinine and cortisol) concentrations, while albumin concentration decreased in a dose-dependent manner compared to the control group. In parallel with the decrease in Na+, K+ and Ca+2 in blood ion levels, there was a significant decrease in the activity of Na+/K+ ATPase, Ca+2 ATPase and AChE enzyme, levels of GSH and HSP70 in kidney tissue in TMX groups compared to the control group. It was determined that the toxic effect of TMX caused a significant increase in TBARS, PC, 8-OHdG levels, respectively. In conclusion, our study shows that TMX causes dose-dependent toxic effects, with knock-on effects on physiological processes regarding the hematological profile and renal function of O. niloticus.

The protective role of L-carnitine on oxidative stress, neurotransmitter perturbations, astrogliosis, and apoptosis induced by thiamethoxam in the brains of male rats.

Synthetic organic insecticides such as pyrethroids, organophosphates, neonicotinoids, and others have the potential to disrupt ecosystems and are often toxic to humans. Thiamethoxam (TMX), a neonicotinoid insecticide , is a widely used insecticide with neurotoxic potential. L-Carnitine (LC) is regarded as the "gatekeeper" in charge of allowing long-chain fatty acids into cell mitochondria. LC is an endogenous chemical that is renowned for its prospective biological activity in addition to its role in energy metabolism. This study investigated the protective effects of LC against TMX-induced neurotoxicity in male Wistar rats. For 28 days, animals were divided into four groups and treated daily with either LC (300 mg/kg), TMX (100 mg/kg), or both at the aforementioned doses. Our results revealed marked serum lipid profile and electrolyte changes, declines in brain antioxidants and neurotransmitters (acetylcholine, dopamine, and serotonin levels) with elevations in thiobarbituric acid reactive substances and proinflammatory cytokine levels, as well as acetylcholinesterase and monoamine oxidase brain activity in TMX-treated rats. TMX also increased the expression of caspase-3 and glial fibrillary acidic protein. In contrast, pretreatment with LC attenuated TMX-induced brain injury by suppressing oxidative stress and proinflammatory cytokines and modulating neurotransmitter levels. It also ameliorated the expression of apoptotic and astrogliosis markers. It could be concluded that LC has antioxidant, anti-inflammatory, anti-astrogliosis, and anti-apoptotic potential against TMX neurotoxicity.

Modulatory role ulexit against thiamethoxam-induced hematotoxicity/hepatotoxicity oxidative stress and immunotoxicity in Oncorhynchusmykiss.

Contamination of the aquatic environment with different insecticides is a major concern in the aquatic ecosystem today. For this reason, in the designed study, Thiamethoxam (TMX) for which there is limited information on its negative effects on Oncorhynchus mykiss was investigated, its effects on hematotoxicity, oxidative status, cytotoxicity, DNA damage and apoptotic status indicators in blood/liver tissue. However, the antitoxic potential of ulexite (UX) supplementation in the elimination of TMX-mediated toxicity has been determined. LC50-96h value determined for TMX 0.73 mg/L has been determined. As a result of hematology profile, TMX application, RBC, Hgb and Hct values showed a temporal decrease compared to the control group, while increases were determined in MCV, MCH and MCHC values. It was determined that the inhibition/induction of hematological parameters was slowed down by adding UX to the medium. During the trial (48th and 96th hours), it was noted that TMX induced cortisol level, while UX supplementation slowed this induction at 48th hour. Antioxidant enzyme activities were significantly inhibited by TMX application, and MDA and MPO values increased as a result of the stimulation of ROS. It was determined that UX added to the medium showed activity in favor of antioxidants and tried to inhibit MDA and MPO levels. When Nrf-2, one of the inflammation parameters, was compared with the administration and control groups, it was determined that it inhibited depending on time, TNF-α, IL-6, DNA damage and apoptosis were induced, and UX suppressed this situation. The results obtained were evaluated as statistically meaningful. Briefly, it was determined that TMX induced oxidative damage in all tissues at 48th - 96th hours, whereas UX mitigated this situation. The results provide possible in vivo evidence that UX supplements can reduce TMX-mediated oxidative stress and tissues damage in O. mykiss blood and liver tissues.

Proteomic analysis reveals oxidative stress-induced activation of Hippo signaling in thiamethoxam-exposed Drosophila.

Thiamethoxam (THIA) is a widely used neonicotinoid insecticide. However, the toxicity and defense mechanisms activated in THIA-exposed insects are unclear. Here, we used isobaric tags for relative and absolute quantitation (iTRAQ) proteomics technology to identify changes in protein expression in THIA-exposed Drosophila. We found that the antioxidant proteins Cyp6a23 and Dys were upregulated, whereas vir-1 was downregulated, which may have been detoxification in response to THIA exposure. Prx5 downregulation promoted the generation of reactive oxygen species. Furthermore, the accumulation of reactive oxygen species led to the induction of antioxidant defenses in THIA-exposed Drosophila, thereby enhancing the levels of oxidative stress markers (e.g., superoxide dismutase, glutathione S-transferase, and glutathione) and reducing catalase expression. Furthermore, the Hippo signaling transcription coactivator Yki was inactivated by THIA. Our results suggesting that Hippo signaling may be necessary to promote insect survival in response to neonicotinoid insecticide toxicity.

Short communication: Is there a difference in the sensitivity of Africanised and European honeybees to thiamethoxam or dimethoate?

The similarity of sensitivity of adult Africanised and European honeybees following acute oral exposure to thiamethoxam has been questioned. Data collated from adult acute contact and oral toxicity testing of a range of thiamethoxam containing products (solo and mixtures) shows that the toxicity of these products to Africanised honeybees can be directly predicted from the toxicity of the active substances to European honeybees. Similarly, the acute contact and oral toxicity of dimethoate to Africanised bees lies within the same range as European honeybees. There are no major differences in the sensitivity of Africanised and European honeybee individuals to thiamethoxam and dimethoate.

Comparative toxicity of two neonicotinoid insecticides at environmentally relevant concentrations to telecoprid dung beetles.

Dung beetles (Coleoptera: Scarabaeinae) frequently traverse agricultural matrices in search of ephemeral dung resources and spend extended periods of time burrowing in soil. Neonicotinoids are among the most heavily applied and widely detected insecticides used in conventional agriculture with formulated products designed for row crop and livestock pest suppression. Here, we determined the comparative toxicity of two neonicotinoids (imidacloprid and thiamethoxam) on dung beetles, Canthon spp., under two exposure profiles: direct topical application (acute) and sustained contact with treated-soil (chronic). Imidacloprid was significantly more toxic than thiamethoxam under each exposure scenario. Topical application LD50 values (95% CI) for imidacloprid and thiamethoxam were 19.1 (14.5-25.3) and 378.9 (200.3-716.5) ng/beetle, respectively. After the 10-day soil exposure, the measured percent mortality in the 3 and 9 µg/kg nominal imidacloprid treatments was 35 ± 7% and 39 ± 6%, respectively. Observed mortality in the 9 µg/kg imidacloprid treatment was significantly greater than the control (p = 0.04); however, the 3 µg/kg imidacloprid dose response may be biologically relevant (p = 0.07). Thiamethoxam treatments had similar mortality as the controls (p > 0.8). Environmentally relevant concentrations of imidacloprid measured in airborne particulate matter and non-target soils pose a potential risk to coprophagous scarabs.

Potential Risk of Residues From Neonicotinoid-Treated Sugar Beet Flowering Weeds to Honey Bees (Apis mellifera L.).

In 2018 the European Union (EU) banned the three neonicotinoid insecticides imidacloprid, clothianidin (CLO), and thiamethoxam (TMX), but they can still be used if an EU Member State issues an emergency approval. Such an approval went into effect in 2021 for TMX-coated sugar beet seeds in Germany. Usually, this crop is harvested before flowering without exposing non-target organisms to the active ingredient or its metabolites. In addition to the approval, strict mitigation measures were imposed by the EU and the German federal states. One of the measures was to monitor the drilling of sugar beet and its impact on the environment. Hence we took residue samples from different bee and plant matrices and at different dates to fully map beet growth in the German states of Lower Saxony, Bavaria, and Baden-Württemberg. A total of four treated and three untreated plots were surveyed, resulting in 189 samples. Residue data were evaluated using the US Environmental Protection Agency BeeREX model to assess acute and chronic risk to honey bees from the samples, because oral toxicity data are widely available for both TMX and CLO. Within treated plots, we found no residues either in pools of nectar and honey crop samples (n = 24) or dead bee samples (n = 21). Although 13% of beebread and pollen samples and 88% of weed and sugar beet shoot samples were positive, the BeeREX model found no evidence of acute or chronic risk. We also detected neonicotinoid residues in the nesting material of the solitary bee Osmia bicornis, probably from contaminated soil of a treated plot. All control plots were free of residues. Currently, there are insufficient data on wild bee species to allow for an individual risk assessment. In terms of the future use of these highly potent insecticides, therefore, it must be ensured that all regulatory requirements are complied with to mitigate any unintentional exposure. Environ Toxicol Chem 2023;42:1167-1177. © 2023 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Thiamethoxam evoked neural oxido-inflammatory stress in male rats through modulation of Nrf2/NF-kB/iNOS signaling and inflammatory cytokines: Neuroprotective effect of Silymarin.

Thiamethoxam (TMX), a neonicotinoid insecticide, is a widely used insecticide with neurotoxic potential. Silymarin (SM), a milk thistle-derived flavonoid, is known with its promising biological activities. This study explored the neuroprotective effects of SM against TMX-triggered cortical injury in male rats. Animals were divided into four groups and treated daily either with SM (150 mg/kg), TMX (78.15 mg/kg), or both at the aforementioned doses for 28 days. Our results revealed marked declines in cortical SOD and CAT activities with elevations in MDA, IL-1b and TNF-α levels in TMX-treated rats. Further, TMX induced down-regulation in the gene expressions of Sod, Cat, Gpx, and Nrf-2, with up-regulation in the gene expressions of IL-1b, IL-6, iNOS, TNF-α and NF-kB. Interestingly, pre-treatment with SM provided a notable neuroprotective action against TMX-mediated cortical damage that indicates its promising antioxidant and anti-inflammatory activities. This effect may be mediated by Nrf2/NF-kB/iNOS signalling and suppression of excess free radicals and production of inflammatory cytokines. In brief, SM could be a promising therapeutic agent against TMX-mediated neural complication via its antioxidant and anti-inflammatory properties. PRACTICAL APPLICATIONS: The using of neonicotinoids as thiamethoxam is recently increased and is associated with brain damage. TMX induced excessive oxidative and inflammatory damage. Therefore, new therapeutic approaches are needed to counteract its adverse effects on the nervous system. SM, a flavonoid, is extracted from the seeds and fruits of milk thistle. Due to its potent antioxidative activity, SM have been applied to mitigate the oxidative stress as well as inflammatory disorders. Herein, we examined the potential therapeutic role of SM against TMX-induced brain oxidative stress and inflammation in rats through evaluating oxidative markers, inflammatory response, and histopathological changes in the brain cortical tissue.

Assessment of Global DNA Methylation in SH-SY5Y Cells Exposed to the Neonicotinoid Insecticides Imidacloprid and Thiamethoxam.

Neonicotinoid insecticides, known for their selectivity and low mammalian toxicity, have been widely used in recent years as alternatives to organophosphate insecticides. Although neonicotinoids are generally considered to be safe, data show that they can cause harmful effects on human and environmental health. Due to the lack of information on their mechanism of toxicity, the effects of imidacloprid and thiamethoxam on DNA methylation as the most used marker for epigenetic effects were investigated in human neuroblastoma (SH-SY5Y) cells. The cells were exposed to imidacloprid and thiamethoxam in concentrations of 100, 200, and 500 µM for 24 hours, then global DNA methylation and expression of genes involved in global DNA methylation (DNMT1, DNMT3a and DNMT3b) were investigated. Global DNA methylation significantly increased after imidacloprid exposure at 100 µM, and thiamethoxam exposures at 200 µM and 500 µM (>1.5-fold). Imidacloprid significantly decreased the expression of DNMT1 and DNMT3a, whereas thiamethoxam did not cause any significant changes in the expression of DNMT genes. Our findings suggested that alteration in global DNA methylation may be involved in the toxic mechanisms of imidacloprid and thiametoxam.

Evaluation of the risk of human exposure to thiamethoxam by extrapolation from a toxicokinetic experiment in rats and literature data.

Previous studies suggest that exposure to thiamethoxam (TMX) may cause adverse effects to human. However, the distribution of TMX in various organs of human body and the associated risk are little-known. This study aimed to explore the distribution of TMX in human organs by extrapolation from a toxicokinetic experiment in rats and to assess the associated risk based on literature data. The rat exposure experiment was performed using 6-week female SD rats. Five groups of rats were oral-exposed to 1 mg/kg TMX (water as solvent) and executed at 1 h, 2 h, 4 h, 8 h and 24 h after treatment, respectively. The concentrations of TMX and its metabolites in rat liver, kidney, blood, brain, muscle, uterus and urine were measured in different time points using LC-MS. Data on concentrations of TMX in food, human urine and blood as well as human cell-based in vitro toxicity of TMX were collected from the literature. After oral exposure, TMX and its metabolite clothianidin (CLO) were detected in all organs of the rats. The steady-state tissue-plasma partition coefficients of TMX for liver, kidney, brain, uterus and muscle were 0.96, 1.53, 0.47, 0.60 and 1.10, respectively. Based on literature analysis, the concentration of TMX in human urine and blood for general population were 0.06-0.5 ng/mL and 0.04-0.6 ng/mL, respectively. For some people, the concentration of TMX in human urine reached 222 ng/mL. By extraplation from rat experiment, the estimated concentrations of TMX in human liver, kidney, brain, uterus and muscle for general population were 0.038-0.58, 0.061-0.92, 0.019-0.28, 0.024-0.36 and 0.044-0.66 ng/g, respectively, well below the relevant concentrations for cytotoxic endpoints (HQs ≤ 0.012); however, for some people they could be up to 253.44, 403.92, 124.08, 158.40 and 290.40 ng/g, respectively, with very high developmental toxicity (HQ = 5.4). Therefore, the risk for highly exposed people should not be neglected.

Joint toxic effects of thiamethoxam and flusilazole on the adult worker honey bees (Apis mellifera L.).

Insect pollinators are routinely exposed to a complex mixture of many pesticides. However, traditional environmental risk assessment is only carried out based on ecotoxicological data of single substances. In this context, we aimed to explore the potential effects when worker honey bees (Apis mellifera L.) were simultaneously challenged by thiamethoxam (TMX) and flusilazole (FSZ). Results displayed that TMX possessed higher toxicity to A. mellifera (96-h LC50 value of 0.11 mg a. i. L-1) than FSZ (96-h LC50 value of 738 mg a. i. L-1). Furthermore, the mixture of TMX and FSZ exhibited an acute synergistic impact on the pollinators. Meanwhile, the activities of SOD, caspase 3, caspase 9, and PPO, as well as the expressions of six genes (abaecin, dorsal-2, defensin-2, vtg, caspase-1, and CYP6AS14) associated with oxidative stress, immune response, lifespan, cell apoptosis, and detoxification metabolism were noteworthily varied in the individual and mixture challenges than at the baseline level. These data revealed that it is imminently essential to investigate the combined toxicity of pesticides since the toxicity evaluation from individual compounds toward honey bees may underestimate the toxicity in realistic conditions. Overall, the present results could help understand the potential contribution of pesticide mixtures to the decline of bee populations.

A Time-course Transcriptional Kinetics of Genes in Behavior, Cortisol Synthesis and Neurodevelopment in Zebrafish Larvae Exposed to Imidacloprid and Thiamethoxam.

Agricultural use of neonicotinoid insecticides, neuroactive nitroguanidine compounds, has been detected everywhere in the global, posing significant hazard to nontarget organisms. This work studied the developmental neurotoxicity of zebrafish larvae exposed to imidacloprid (IMI) and thiamethoxam (THM), ranging from 0.05 µg L- 1 to 50 µg L- 1 for 35 days. Transcriptions of genes belonging to the behavior, neurodevelopment and cortisol synthesis in zebrafish larvae were monitored. The qPCR data demonstrated that with exposure time increased, the transcription of behavior related genes was down-regulated in both IMI and THM groups, such as macf1, cdh6 and syt10. Additionally, IMI and THM significantly up-regulated the transcriptions of actha, and down-regulated il1rapl1b and pi4k2a at 35 dpf. Importantly, IMI markedly enhanced the transcripiton of gfap, shha, nkx2.2a and nestin in a time dependent manner. This work provided the foundation for understanding zebrafish larvae's neurotoxicity induced by IMI and THM.

Embryonic Exposure to Thiamethoxam Reduces Survival and Alters Neurobehavior of Fathead Minnows.

Thiamethoxam is a commonly used neonicotinoid insecticide that acts as a nicotinic acetylcholine receptor (nAChR) agonist. Although vertebrates are less sensitive to neonicotinoid insecticides than invertebrates, some neonicotinoids have been shown to cause neurobehavioral changes in larval fishes. In the present study, we examine the neurobehavioral toxicity of acute and chronic exposure to environmentally relevant concentrations of thiamethoxam in fathead minnows at two different life stages. Whereas acute exposure of embryos to thiamethoxam does not appear to stimulate spontaneous contractions within 1 min, chronic exposure of embryos to 1.57 µg or more thiamethoxam/L caused increased mortality as well as a subtle increase in spontaneous contraction frequency (SCF), which was negatively correlated with early hatching success. Chronic exposure of embryos to 155 µg thiamethoxam/L impaired predator escape response, and chronic exposure to 0.02-14.61 µg thiamethoxam/L impaired foraging efficiency of some fish. Fathead minnows exposed to thiamethoxam beginning post hatch did not experience changes to measured health or neurobehavioral indicators. Taken together, our findings indicate that embryonic life stages are more sensitive to thiamethoxam exposure than later larval life stages. Because early exposure to thiamethoxam can cause deficits in predatory escape behaviors and may impair foraging success, further study of the potential direct and nondirect impacts of thiamethoxam on wild fish populations is warranted. Environ Toxicol Chem 2022;41:1276-1285. © 2022 SETAC.

Biotoxicity Evaluation of a Cationic Star Polymer on a Predatory Ladybird and Cooperative Pest Control by Polymer-Delivered Pesticides and Ladybird.

Although employing nanocarriers for gene/drug delivery shows great potential in agricultural fields, the biotoxicity of nanocarriers is a major concern for large-scale applications. Herein, we synthesized a cationic star polymer (SPc) as a pesticide nanocarrier/adjuvant to evaluate its safety against a widely used predatory ladybird (Harmonia axyridis). The application of SPc at extremely high concentrations nearly did not influence the hatching of ladybird eggs but it led to the death of ladybird larvae at lethal concentration 50 (LC50) values of 43.96 and 19.85 mg/mL through the soaking and feeding methods, respectively. The oral feeding of SPc downregulated many membrane protein genes and lysosome genes significantly, and the cell membrane and nucleus in gut tissues were remarkably damaged by SPc application, revealing that the lethal mechanism might be SPc-mediated membrane damage. Furthermore, the oral feeding of SPc increased the relative abundance of Serratia bacteria in ladybird guts to result in bacterial infection. Coapplication of ladybird and SPc-loaded thiamethoxam/matrine achieved desired control efficacies of more than 80% against green peach aphids, revealing that the coapplication could overcome the slow-acting property of ladybirds. To our knowledge, this is the first attempt to investigate the polymer-mediated lethal mechanism toward natural enemies and explore the possibility of coapplying SPc-loaded pesticides and natural enemies for pest management.

Fate of thiamethoxam from treated seeds in mesocosms and response of aquatic invertebrate communities.

Thiamethoxam is a neonicotinoid insecticide widely applied in the Canadian Prairies. It has been detected in surface waters of agro-ecosystems, including wetlands, but the potential effects on non-target invertebrate communities in these wetlands have not been well characterized. In an effort to understand better the fate of thiamethoxam in wetlands and the response of invertebrates (zooplankton and emergent insects), model systems were used to mimic wetland flooding into planted fields. Outdoor mesocosms were treated with a single application of thiamethoxam-treated canola seeds at three treatment levels based on a recommended seeding rate (i.e., 6 kg/ha; 1×, 10×, and 100× seeding rate) and monitored over ten weeks. The mean half-life of thiamethoxam in the water column was 6.2 d. There was no ecologically meaningful impact on zooplankton abundances or community structure among treatments. Statistically significant differences were observed in aquatic insect abundance between control mesocosms and the two greatest thiamethoxam treatments (10× and 100× seeding rate). The observed results indicate exposure to thiamethoxam at environmentally relevant concentrations likely does not represent a significant ecological risk to abundance and community structure of wetland zooplankton and emergent insects.

Integrative analysis of transcriptomics and metabolomics reveals the hepatotoxic mechanism of thiamethoxam on male Coturnix japonica.

Thiamethoxam (TMX), a representative neonicotinoids, is widely used for seed coating. The consumption of TMX-coated seeds posed threat to birds during crop sowing. The hepatotoxicity of TMX has been reported in mammals, however, no clear evidence showed TMX-induced toxic effects on bird liver. In this study, male Japanese quails (Coturnix japonica) were exposed to 20 or 200 mg/kg TMX-treated bird feed for 28 days. Results showed that Clothianidin (CLO), a TMX metabolite preferred to accumulate in quail plasma and liver, and inflammatory cell infiltration was found in quail livers. Oxidative stress-related biological processes were significantly enriched in both TMX treatment groups through transcriptomics analysis. Moreover, integrative analysis of transcriptomics and metabolomics indicated ferroptosis and DNA damage was implicated in hepatotoxicity caused by high- and low-concentration of TMX exposure, respectively. High-dose TMX treatment decreased CAT activity and GSH concentration and increased expression of the ferroptosis-related gene. In addition, the up-regulation of 8-OHdG concentration and DNA repair-related genes expression demonstrated low-dose TMX triggered oxidative DNA damage. The present results highlight the toxicity of TMX to bird livers and contribute to a better understanding of the TMX toxic mechanism in birds.

Acute and Chronic Effects of Clothianidin, Thiamethoxam and Methomyl on Chironomus dilutus.

Organism tolerance thresholds for emerging contaminants are vital to the development of water quality criteria. Acute (96-h) and chronic (10-day) effects thresholds for neonicotinoid pesticides clothianidin and thiamethoxam, and the carbamate pesticide methomyl were developed for the midge Chironomus dilutus to support criteria development using the UC Davis Method. Median lethal concentrations (LC50s) were calculated for acute and chronic exposures, and the 25% inhibition concentrations (IC25) were calculated for the chronic exposures based on confirmed chemical concentrations. Clothianidin effect concentrations were 4.89 µg/L, 2.11 µg/L and 1.15 µg/L for 96-h LC50, 10-day LC50 and 10-day IC25, respectively. Similarly, thiamethoxam concentrations were 56.4 µg/L, 32.3 µg/L and 19.6 µg/L, and methomyl concentrations were 244 µg/L, 266 µg/L and 92.1 µg/L. Neonicotinoid effect concentrations compared favorably to previously published 96-h and 14-day LC50 concentrations, and methomyl effect concentrations were within the acute survival range reported for Chironomus species and other organisms.

Acute Toxicity of Insecticide Thiamethoxam to Crayfish (Astacus leptodactylus): Alterations in Oxidative Stress Markers, ATPases and Cholinesterase.

Thiamethoxam (Thmx) is a globally used neonicotinoid pesticide contaminated in freshwater ecosystems with residues detected in fishery products. Astacus leptodactylus is a popular freshwater crustacean that is cultivated and exported in many countries. In this study, we investigated the acute toxic effects of Thmx on A. leptodactylus using various biomarkers (acetylcholinesterase, carboxylesterase, glutathione S-transferase, glutathione, superoxide dismutase, glutathione peroxidase, glutathione reductase, and adenosinetriphosphatases). The 96-h LC50 value of Thmx was calculated as 8.95 mg active ingredient L-1. As the dose of Thmx increased, oxidative stress was induced by the inhibition/activation of antioxidant enzymes, while the activities of acetylcholinesterase, carboxylesterase and adenosinetriphosphatases were inhibited. As a result, it can be said that Thmx has highly toxic effects on crayfish, therefore they are under threat in the areas where this pesticide is used.

Juvenile African Clawed Frogs (Xenopus laevis) Express Growth, Metamorphosis, Mortality, Gene Expression, and Metabolic Changes When Exposed to Thiamethoxam and Clothianidin.

Neonicotinoids (NEO) represent the main class of insecticides currently in use, with thiamethoxam (THX) and clothianidin (CLO) primarily applied agriculturally. With few comprehensive studies having been performed with non-target amphibians, the aim was to investigate potential biomarker responses along an adverse outcome pathway of NEO exposure, whereby data were collected on multiple biological hierarchies. Juvenile African clawed frogs, Xenopus laevis, were exposed to commercial formulations of THX and CLO at high (100 ppm) and low (20 ppm) concentrations of the active ingredient. Mortality, growth, development, liver metabolic enzyme activity, and gene expression endpoints were quantified. Tadpoles (n > 1000) from NF 47 through tail resorption stage (NF 66) were exposed to NEO or to NEO-free media treatments. Liver cell reductase activity and cytotoxicity were quantified by flow cytometry. Compared to control reference gene expressions, levels of expression for NEO receptor subunits, cell structure, function, and decontamination processes were measured by RT-qPCR by using liver and brain. Mortality in THX high was 21.5% compared to the control (9.1%); the metabolic conversion of THX to CLO may explain these results. The NF 57 control tadpoles were heavier, longer, and more developed than the others. The progression of development from NF 57-66 was reduced by THX low, and weight gain was impaired. Liver reductases were highest in the control (84.1%), with low NEO exhibiting the greatest reductions; the greatest cytotoxicity was seen with THX high. More transcriptional activity was noted in brains than in livers. Results affirm the utility of a study approach that considers multiple complexities in ecotoxicological studies with non-target amphibians, underscoring the need for simultaneously considering NEO concentration-response relationships with both whole-organism and biomarker endpoints.