Toxicogenomics provides insights to toxicity pathways of neonicotinoids to aquatic insect, Chironomus dilutus

Nickel oxide nanoparticles decrease the accumulation of atrazine in earthworms

Nickel oxide nanoparticles (NiO-NPs) are common nanomaterials that may be released into the environment, affecting the toxicity of other contaminants. Atrazine (ATZ) is a commonly used herbicide that can harm organisms due to its persistence and bioaccumulation in the environment. Although the toxicity of ATZ to earthworms is well-documented, the risk of co-exposure with NiO-NPs increases as more nanoparticles accumulate in the soil. In this study, we investigated the effects and mechanisms of NiO-NPs on the accumulation of ATZ in earthworms. The results showed that after day 21, the antioxidant system of the cells under ATZ treatment alone was adversely affected, with ROS content 36.05 % higher than that of the control (CK) group. However, the addition of NiO-NPs reduced the ROS contents in the earthworms by 0.6 %- 32.3 %. Moreover, analysis of earthworm intestinal sections indicates that NiO-NPs mitigated cellular and tissue damage caused by ATZ. High-throughput sequencing revealed that NiO-NPs in earthworm intestines increased the abundance of Pseudomonas aeruginosa and Aeromonas aeruginosa. Additionally, the enhanced function of the ABC transport system in the gut resulted in lower accumulation of ATZ in earthworms. In summary, NiO-NPs can reduce the accumulation and thus the toxicity of ATZ in earthworms. Our study contributes to a deeper understanding of the effects of NiO-NPs on co-existing pollutants.

Prediction of Potential Risk for Flupyradifurone and Its Transformation Products to Hydrobionts

Flupyradifurone (FPF) is considered the latest generation of neonicotinoid insecticides. Here, we investigated the toxicity and ecological risk of FPF and its aerobic transformation products (TPs) to aquatic species using the method of prediction. We found that FPF exhibited moderate or high toxicity to some aquatic species. The 5% hazardous concentration of FPF was 3.84 μg/L for aquatic organisms. We obtained 91 aerobic TPs for FPF, and almost half of FPF TPs exhibited toxicity to fish or Daphnia. Eleven of the TPs of FPF exhibited a high or moderate risk to aquatic ecosystems. All FPF TPs with high and moderate risks contained a 6-chloropyridine ring structure, indicating that the derivant of a pyridine ring exhibits potential risks to aquatic ecosystems. Our results provide insight into the potential risk of FPF to aquatic ecosystems and could be used to help set criteria to control pollution caused by FPF.

Toxicokinetics Explain Differential Freshwater Ecotoxicity of Nanoencapsulated Imidacloprid Compared to Its Conventional Active Ingredient

Agricultural applications of nanotechnologies necessitate addressing safety concerns associated with nanopesticides, yet research has not adequately elucidated potential environmental risks between nanopesticides and their conventional counterparts. To address this gap, we investigated the risk of nanopesticides by comparing the ecotoxicity of nanoencapsulated imidacloprid (nano-IMI) with its active ingredient to nontarget freshwater organisms (embryonic Danio rerio, Daphnia magna, and Chironomus kiinensis). Nano-IMI elicited approximately 5 times higher toxicity than IMI to zebrafish embryos with and without chorion, while no significant difference was observed between the two invertebrates. Toxicokinetics further explained the differential toxicity patterns of the two IMI analogues. One-compartmental two-phase toxicokinetic modeling showed that nano-IMI exhibited significantly slower elimination and subsequently higher bioaccumulation potential than IMI in zebrafish embryos (dechorinated), while no disparity in toxicokinetics was observed between nano-IMI and IMI in D. magna and C. kiinensis. A two-compartmental toxicokinetic model successfully simulated the slow elimination of IMI from C. kiinensis and confirmed that both analogues of IMI reached toxicologically relevant targets at similar levels. Although nanopesticides exhibit comparable or elevated toxicity, future work is of utmost importance to properly understand the life cycle risks from production to end-of-life exposures, which helps establish optimal management measures before their widespread applications.

Quantitative differentiation of toxicity contributions and predicted global risk of fipronil and its transformation products to aquatic invertebrates

Biotransformation often alters chemical toxicity, yet its impacts on risk assessment are hardly quantified due to the challenges in acquiring internal exposure-based thresholds for chemicals that are readily metabolizable. Here, we integrated toxic unit and toxicokinetics to quantitatively assess toxicity contributions and potential risk of both parent compound and transformation products (TPs) to aquatic organisms, using fipronil (FIP) as a representative toxicant. In aquatic invertebrates Chironomus dilutus and Hyalella azteca, approximately 90 % of FIP was transformed to fipronil sulfone (SUL). FIP and SUL exhibited similar intrinsic toxicity to these organisms, which was contrary to conventional perception that SUL was more toxic than FIP. However, biotransformation was still important in risk assessment because the TP had 10-fold slower depuration rate than FIP. The amphipod H. azteca was found to be as sensitive to FIPs as the insect C. dilutus, which was previously considered ten times more sensitive based on external thresholds. This discrepancy has led to overlooking the toxicity of FIP to H. azteca in regional risk assessments. Lastly, we predicted the lethal risk of FIPs in global surface water. When using external thresholds for prediction, FIPs in 3.4 % of the water samples were lethally toxic to H. azteca, and the percentage of water samples at risk increased to 14 % when internal thresholds were used and SUF dominated the risk. This study presents an improved method for quantifying aquatic risk of readily metabolized toxicants. Our findings underscore the urgency of considering TPs in water quality assessments, especially for sensitive species that are at risk in the environment.

Impacts of neonicotinoid insecticides on bumble bee energy metabolism are revealed under nectar starvation

Bumble bees are an important group of insects that provide essential pollination services as a consequence of their foraging behaviors. These pollination services are driven, in part, by energetic exchanges between flowering plants and individual bees. Thus, it is important to examine bumble bee energy metabolism and explore how it might be influenced by external stressors contributing to declines in global pollinator populations. Two stressors that are commonly encountered by bees are insecticides, such as the neonicotinoids, and nutritional stress, resulting from deficits in pollen and nectar availability. Our study uses a metabolomic approach to examine the effects of neonicotinoid insecticide exposure on bumble bee metabolism, both alone and in combination with nutritional stress. We hypothesized that exposure to imidacloprid disrupts bumble bee energy metabolism, leading to changes in key metabolites involved in central carbon metabolism. We tested this by exposing Bombus impatiens workers to imidacloprid according to one of three exposure paradigms designed to explore how chronic versus more acute (early or late) imidacloprid exposure influences energy metabolite levels, then also subjecting them to artificial nectar starvation. The strongest effects of imidacloprid were observed when bees also experienced nectar starvation, suggesting a combinatorial effect of neonicotinoids and nutritional stress on bumble bee energy metabolism. Overall, this study provides important insights into the mechanisms underlying the impact of neonicotinoid insecticides on pollinators, and underscores the need for further investigation into the complex interactions between environmental stressors and energy metabolism.

Low concentration chlorantraniliprole-promoted Ca2+ release drives a shift from autophagy to apoptosis in the silk gland of Bombyx mori

The novel pesticide chlorantraniliprole (CAP) is widely used for pest control in agriculture, and the safety for non-target organisms of trace residues in the environment has received widespread attention. In the present study, exposure to low concentrations of CAP resulted in abnormal silk gland development in the B. mori, and induced the release of intracellular Ca2+ in addition to the triggering of Ca2+-dependent gene transcription. Moreover, the CAP treatment group exhibited down-regulation of oxidative phosphorylation and antioxidant enzyme-related genes in the silk gland, resulting in peroxide accumulation. Furthermore, transcript levels of autophagy-related genes were significantly up-regulated and protein levels of LC3-I and LC3-II were up-regulated, indicating an increase in autophagy. The protein levels of ATG5 and NtATG5 were also significantly up-regulated. While the protein levels of caspase3 and active caspase3 were significantly up-regulated consistent with the transcript levels of key genes in the apoptotic signaling pathway, ultimately affecting silk protein synthesis. Overall, these findings indicate that low concentration CAP induced abnormal development in the silk gland of B. mori by causing intracellular Ca2+ overload, which inhibits oxidative phosphorylation pathway and the removal of reactive oxygen species, leading to a driving a shift from autophagy to apoptosis. The findings herein provided a basis for evaluating the safety of CAP environmental residues on non-target organisms.

Occurrence and water-sediment exchange of systemic insecticides and their transformation products in an agriculture-dominated basin

Neonicotinoids (NEOs) and fipronil (FIP) are ubiquitous in aquatic environment, yet the transformation and water-sediment exchange are largely unknown for these systemic insecticides and their transformation products (TPs). Herein, occurrence, field-based partitioning coefficients, and fugacity fractions (ff) of NEOs, FIP, and their TPs were analyzed in the drainage and receiving rivers near a rice paddy field. NEOs and FIPs were frequently detected in the sediments with concentrations of TPs being often higher than the parent compounds. Average ff values of NEOs (0.944-1.00) were larger than those of FIPs (0.399-0.716), indicating NEOs had a greater tendency to diffuse from sediment into water. Similar as well-studied hydrophobic compounds, hydrophobicity was the main factor impacting the water-sediment exchange of moderately hydrophobic FIPs. Alternatively, electrostatic interactions governed the fate of hydrophilic NEOs in water-sediment system. The log Kd values of NEOs were positively correlated with their N/C ratios (p < 0.05), possibly because the negatively charged sediments (zeta potential were from -19.1 ± 0.6 to -5.84 ± 0.57 mV) generated electrostatic attraction with amino functional group. Our study highlighted the ubiquitousness of TPs and distinct water-sediment interaction for moderately hydrophobic and hydrophilic insecticides in an agriculture-dominated watershed.

Melatonin Supplementation during In Vitro Maturation of Porcine Oocytes Alleviates Oxidative Stress and Endoplasmic Reticulum Stress Induced by Imidacloprid Exposure

Imidacloprid (IMI) is an endogenous neonicotinoid insecticide widely used in agriculture and has attracted researchers' attention because of its risks to the environment and human health. Melatonin (MT) is an antioxidant hormone produced by the pineal gland of the brain. Studies have shown that it has a variety of physiological functions and plays a crucial role in the development of animal germ cells and embryos. The potential protective effects of MT against oocyte damage caused by neonicotinoid pesticide toxicity remain unclear. In this study, we report the toxicity of IMI against, and its effects on the quality of, porcine oocytes and the protective effect of MT on IMI-exposed oocytes. The results show that IMI exposure adversely affected oocyte maturation, while MT supplementation ameliorated its toxic effects. Specifically, IMI exposure increased oxidative stress (OS), endoplasmic reticulum stress (ERS), and apoptosis, which may affect polar body expulsion rates and blastocyst formation. Also, IMI exposure reduced oocyte cleavage rates and the number of cells in blastocysts. However, all of these toxic effects can be restored after a melatonin supplementation treatment. In conclusion, these results suggest that melatonin has a protective effect on IMI-induced defects during porcine oocyte maturation.

Two-Compartmental Toxicokinetic Model Predicts Interspecies Sensitivity Variation of Imidacloprid to Aquatic Invertebrates

Interspecies sensitivity to the same chemical can be several orders of magnitude different. Quantifying toxicologically internal levels and toxicokinetic (TK) parameters is critical in elucidating the interspecies sensitivity. Herein, a two-compartmental TK model was constructed to characterize the uptake, distribution, and elimination kinetics toward interspecies sensitivity to an insecticide, imidacloprid. Imidacloprid exhibited the highest lethality to the insect Chironomus dilutus, followed by Lumbriculus variegatus, Hyalella azteca, and Daphnia magna. Interspecies sensitivity of imidacloprid to these invertebrates varied by ∼1000 folds based on water concentrations (LC50). Remarkably, the sensitivity variation decreased to ∼50 folds based on the internal residues (LR50), highlighting the critical role of TK in interspecies sensitivity. A one-compartmental TK model failed to simulate the bioaccumulation of imidacloprid in these invertebrates except for D. magna. Instead, a two-compartmental model successfully simulated the slow elimination of imidacloprid in the remaining three species by internally distinguishing the highly dynamic (C1) and toxicologically available (C2) fractions. We further showed that the species sensitivity of the invertebrates to imidacloprid was significantly related to C2, demonstrating that C2 was toxicologically available and responsible for the toxicity of imidacloprid. This mechanistic-based model bridged the internal distribution of organic contaminants in small invertebrates and the associated toxic potency.

Sex-specific alterations in adaptive responses of Chironomus columbiensis triggered by imidacloprid chronic and acute sublethal exposures

The use of imidacloprid is a common pest control practice in the Neotropical region. However, the imidacloprid unintended sublethal effects on Neotropical aquatic non-target arthropods and undesirable consequences for aquatic environments remain unclear. Here, we assessed the susceptibility of Chironomus columbiensis (Diptera: Chironomidae) larvae to the neonicotinoid imidacloprid and evaluated whether sublethal exposure types would trigger sex-dependent adaptive responses (e.g., emergence, body mass, reproduction, wing morphology). We conducted a concentration-mortality curve (96 h of exposure) and established chronic and acute sublethal exposure bioassays. While chronic sublethal exposures consisted of exposing individuals during their entire larval and pupal stages, the acute sublethal exposures represented a single short duration (24 h) exposure episode during either the first or fourth larval instar. Our results revealed that chronic sublethal exposure reduced the body mass of males, while acute sublethal exposures during the first instar resulted in heavier males than those that were not exposed to imidacloprid. Chronic exposure also reduced the reproduction of males and females, while the acute sublethal exposure only affected the reproduction of individuals that were imidacloprid-exposed on their later larval instar. Chronic and acute sublethal exposures did differentially affect the wing properties of C. columbiensis males (e.g., increased size when chronically exposed and highly asymmetric wings when acutely exposed in early larval phase) and females (e.g., highly asymmetric wings when chronically and acutely exposed). Collectively, our findings demonstrated that imidacloprid can cause unintended sublethal effects on C. columbiensis, and those effects are dependent on sex, exposure type, and developmental stage.

The effect of TiO2NPs on cloransulam-methyl toxicity to earthworm (Eisenia fetida)

Cloransulam-methyl is a new herbicide and has broad application prospect. However, the effect of cloransulam-methyl on earthworm have yet to be clarified. As more and more titanium dioxide nanoparticles (TiO₂NPs) enter the soil, cloransulam-methyl and TiO₂NPs have a risk of co-exposure, but the effect of TiO₂NPs on cloransulam-methyl toxicity is unknown. In the study, the ecotoxicity of cloransulam-methyl (0.1, 1 mg kg^-1) on earthworm and the effect of TiO₂NPs (10 mg kg^-1) on cloransulam-methyl toxicity was investigated after exposure for 28 and 56 d. Exposure tests showed cloransulam-methyl and cloransulam-methyl + TiO₂NPs promoted the accumulation of reactive oxygen species, malondialdehyde and 8-hydroxydeoxyguanosine, increased the activities of superoxide dismutase and catalase, resulted in lipid peroxidation and DNA damage. Besides, the results at the genetic level showed cloransulam-methyl and cloransulam-methyl + TiO₂NPs altered the expression of physiologically-related genes, which demonstrated that cloransulam-methyl and cloransulam-methyl + TiO₂NPs induced oxidative stress and cell apoptosis, and disturbed the normal reproduction in earthworm. The results of comprehensive toxicity comparison indicated cloransulam-methyl and TiO₂NPs co-exposure has higher toxicity compared to cloransulam single exposure. Our results suggest that TiO₂NPs can enhance the toxicity of cloransulam-methyl on Eisenia fetida in terms of oxidative stress, cell apoptosis and reproduction aspects. Based on above studies, it is of great importance for evaluating the risk of cloransulam-methyl co-exposure with TiO₂NPs in soil.

Differential Production of Nitric Oxide and Hydrogen Peroxide among Drosophila melanogaster, Apis mellifera, and Mamestra brassicae Immune-Activated Hemocytes after Exposure to Imidacloprid and Amitraz

Invertebrates have a diverse immune system that responds differently to stressors such as pesticides and pathogens, which leads to different degrees of susceptibility. Honeybees are facing a phenomenon called colony collapse disorder which is attributed to several factors including pesticides and pathogens. We applied an in vitro approach to assess the response of immune-activated hemocytes from Apis mellifera, Drosophila melanogaster and Mamestra brassicae after exposure to imidacloprid and amitraz. Hemocytes were exposed to the pesticides in single and co-exposures using zymosan A for immune activation. We measured the effect of these exposures on cell viability, nitric oxide (NO) production from 15 to 120 min and on extracellular hydrogen peroxide (H₂O₂) production after 3 h to assess potential alterations in the oxidative response. Our results indicate that NO and H₂O₂ production is more altered in honeybee hemocytes compared to D. melanogaster and M. brassicae cell lines. There is also a differential production at different time points after pesticide exposure between these insect species as contrasting effects were evident with the oxidative responses in hemocytes. The results imply that imidacloprid and amitraz act differently on the immune response among insect orders and may render honeybee colonies more susceptible to infection and pests.

Sublethal chlorantraniliprole exposure induces autophagy and apoptosis through disrupting calcium homeostasis in the silkworm Bombyx mori

The intensive application of chlorantraniliprole (CAP) leaves residues in the environment, posing a potential threat to non-target organisms. In the present study, we investigated the adverse effects of sublethal CAP exposure on Bombyx mori. Sublethal CAP (0.02 mg/L) was shown to induce the release of intracellular Ca²⁺ in BmN cells. Meanwhile, Ca²⁺ -dependent genes were induced in the midgut at 72 h after CAP (0.01 mg/L) exposure, and damaged mitochondria, autophagosomes, nuclear membrane rupture and condensed chromatin were observed. Moreover, the key genes in the oxidative phosphorylation pathway were significantly down-regulated. The transcript levels of autophagy-related genes ATG6 and ATG8 were significantly up-regulated, and the protein levels of LC3-II and ATG7 were significantly increased by 3.72- and 3.33-fold, respectively. Additionally, the transcript levels of the upstream genes in the apoptosis pathway (calpain and Apaf-1) were significantly up-regulated, the protein levels of the downstream gene caspase 3 and its cleaved form were significantly up-regulated by 1.97- and 4.55-fold, respectively, consistent with the elevated caspase 3 activity at 72 h. Collectively, these findings demonstrate that intracellular Ca²⁺ release induced by sublethal CAP inhibits oxidative phosphorylation pathway, which causes mitochondrial dysfunction, leading to autophagy and apoptosis in the midgut of B. mori.

Microporous carbon for fast and simple electrochemical detection of imidacloprid insecticide in fruit and water samples

Herein, a fast and sensitive electrochemical sensor was developed for imidacloprid detection using low-cost disposable microporous carbon screen-printed electrodes. The electrochemical behaviour of imidacloprid at the microporous material was investigated in detail. The developed sensor allowed imidacloprid detection in the linear range of 0.00-1.00 mM with a sensitivity of 14.43 ± 0.42 μA mM^-1 and a detection limit of 2.54 μM (3s _B/m). The sensor showed excellent selectivity and high tolerance to possible interference from other tested insecticides and ions. Excellent repeatability (3.42%, n = 3) and reproducibility (2.23%, n = 3) were demonstrated. Application of the sensor in various fruit and water samples without any treatment showed 96.2-103.0% recoveries. The developed sensor further revealed that the most effective method for removing imidacloprid residue from fruit samples was via washing with a mixture of 5% w/v NaCl and 5% w/v bicarbonate at 40 °C.

Salinity-induced ionoregulatory changes in the gill proteome of the mayfly, Neocloeon triangulifer

Ecologists have observed declines in the biodiversity of sensitive freshwater organisms in response to increasing concentrations of major ions (salinization). Yet, how changing salinities physiologically challenge aquatic organisms, such as mayflies, remains remarkably understudied. Moreover, it is not well understood the degree to which species respond and acclimate to salinity changes. Our lab is developing the Baetid mayfly, N. triangulifer, as a model organism for physiological research. We have previously described acclimatory changes in both ion flux rates and altered mRNA transcript levels in response to chronic exposures to elevated major ion concentrations at the whole animal level. In the present study, we use shotgun proteomics to identify the specific proteins associated with apical ion transport and how their abundance changes in response to chronic salinity exposures in gills. Gills were isolated from the penultimate nymphal stage of N. triangulifer reared under control culture conditions, elevated NaCl (157 mg L^-1 Na), elevated CaCl₂ (121 mg L^-1 Ca), elevated Ca/MgSO₄ (735 mg L^-1 SO₄). These conditions mirrored those from previously published physiological work. We also acutely exposed nymphs to dilute (50% dilution of culture water with deionized water) to explore proteomic changes in the gills in response to dilute conditions. We report 710 unique peptide sequences among treatment groups, including important apical ion transporters such as Ca-ATPase, Na/K ATPase, and V-ATPase. Treatment with elevated NaCl and Ca/MgSO₄ appeared to cause more significant differential protein expression (452 and 345, respectively) compared to CaCl₂ and dilute groups (134 and 17, respectively). Finally, we demonstrated the breadth of physiological functions in gills by exploring non-transport related pathways found in our dataset, including ATP synthesis, calcium signaling, and oxidative stress response. We discuss our results in the context of freshwater salinization and the challenges of working with non-model species without fully sequenced and annotated genomes.

Associations Between Mild Cognitive Impairment and Whole Blood Zinc and Selenium in the Elderly Cohort

Some studies have shown that an imbalance in trace element homeostasis can lead to cognitive dysfunction, but data are lacking. The purpose of this study was to investigate the association between whole blood zinc (Zn), selenium (Se), copper-zinc ratio (Cu/Zn), copper-selenium ratio (Cu/Se), and zinc-selenium ratio (Zn/Se) and mild cognitive impairment (MCI) in elderly Chinese individuals. The study was based on the Elderly Health and Controlled Environmental Factors Cohort in Lu'an, Anhui Province, China, from June to September 2016. The cognitive function of the elderly was determined by the Mini-Mental State Examination (MMSE) and activities of daily living (ADL) scales. The concentrations of Zn, Cu, and Se in the whole blood were measured by inductively coupled plasma-mass spectrometry (ICP-MS). Binary logistic regression was used to analyze the associations between trace elements and MCI. A total of 1006 participants with an average age of 71.70 years old were included in this study. Compared with healthy people, MCI patients had higher whole blood Zn levels and lower Se levels, and Cu/Zn, Cu/Se, and Zn/Se were also significantly different. Binary logistic regression analysis showed that Zn, Cu/Se, and Zn/Se exposure in the third tertile was associated with an increased risk of MCI, while Se exposure in the third tertile was associated with a reduced risk of MCI. After adjustment for sex, age, marital status, BMI, and living status, whole blood Zn, Se, Cu/Zn, Cu/Se, and Zn/Se were significantly associated with MCI risk, especially in elderly women.

The multigenerational effects of clothianidin on Chironomus xanthus: Larvae exposed to this acetylcholine super agonist show no clear resistance

Clothianidin (CLO) is an insecticide belonging to the second-generation class of neonicotinoids. In this study, we evaluated how CLO affects the survival and the complete life cycle of the tropical insect Chironomus xanthus, a non-target species, considering the Parental (P) and Filial (F1) generations. We found a 48 h-lethal concentration (LC₅₀) of CLO of 3.78 µg/L. The lowest observed effect concentrations (LOECs) were: i) for body growth and head capsule width in P generation = 47.3 ng/L CLO; ii) for body growth and head capsule width in F1 generation larvae = 80 and 36.4 ng/L CLO, respectively; iii) for cumulative emergence it was 80 ng/L CLO in the P generation, while there was no significant difference in the F1 generation; iv) for total developmental time for males and females = 61.53 ng/L in P generation; v) in the F1 generation, the LOEC was determined to be 36.4 ng/L for males and 80 ng/L for females; vi) The number of total hatched eggs and total hatched eggs/female had LOECs of 36.4 ng/L CLO for both generations. Our study reveals that environmentally relevant concentrations of the CLO-based insecticide are highly toxic to C. xanthus. It also shows that the F1 generation, resulting from parents exposed to CLO was not clearly resistant to the insecticide. This fact might be explained by the different effects observed for males and females of F1 generation. Understanding the sub-types of acetylcholine receptors present on target and non-target insect species and toxicological effects of neonicotinoids seems to be desirable for the insecticide industry to deal with insect pests and the environmental protection of non-target organisms.

Long-Term Exposure to Neonicotinoid Insecticide Acetamiprid at Environmentally Relevant Concentrations Impairs Endocrine Functions in Zebrafish: Bioaccumulation, Feminization, and Transgenerational Effects

Neonicotinoid insecticides have attracted worldwide attention due to their ubiquitous occurrence and detrimental effects on aquatic organisms, yet their impacts on fish reproduction during long-term exposure remain unknown. Here, zebrafish (F0) were exposed to a neonicotinoid, acetamiprid, at 0.19-1637 μg/L for 154 d. Accumulation and biotransformation of acetamiprid were observed in adult fish, and the parent compound and its metabolite (acetamiprid-N-desmethyl) were transferred to their offspring. Acetamiprid caused slight survival reduction and significant feminization in F0 fish even at the lowest concentration. Hormone levels in F0 fish were remarkedly altered, that is, gonad 17β-estradiol (E2) significantly increased, while androstenedione decreased. The corresponding transcription of steroidogenic genes (ar, cyp19b, fshβ, gnrh2, gnrh3, and lhβ) were significantly upregulated in the brain and gonad of the females but downregulated in the males. The vtg1 gene expression in the liver of male fish was also upregulated. In addition to F0 fish, parental exposure to acetamiprid decreased hatchability and enhanced malformation of F1 embryos. Chronic exposure to acetamiprid at environmentally relevant concentrations altered hormone production and the related gene expression of the hypothalamic-pituitary-gonad (HPG) axis in a sex-dependent way, caused feminization and reproductive dysfunction in zebrafish, and impaired production and development of their offspring.

Sulfoxaflor, Zn2+ and their combinations disrupt the antioxidant and osmoregulatory (Ca2+-ATPase) system in Daphnia magna

BACKGROUND

The oxidative- and osmoregulatory stress-inducing potential of binary mixtures of sulfoxaflor (SUL), a recently developed sulfoximine insecticide, and Zn²⁺ was aimed to evaluate in Daphnia magna with different exposure regimes.

METHODS

Animals were exposed to different SUL concentrations (1.25, 2.5, 10, and 25 mg/L) for 7 days. In vivo 48 h and in vitro effects of single and binary mixtures of SUL (25 and 50 mg/L) and Zn²⁺ (40 µg/L) were also determined. Furthermore, Ca²⁺-ATPase, oxidative stress biomarkers (catalase, CAT; superoxide dismutase, SOD; glutathione peroxidase, GPX; glutathione S-transferase, GST; reduced glutathione, GSH; thiobarbituric acid reactive substances, TBARS), and morphometric characteristics were measured.

RESULTS

Variable response patterns were observed due to exposure duration and regime, toxicant type, and concentration. Marked effects of SUL were observed, especially in subacute exposure, and 25 mg/L SUL concentration can be considered as a threshold level. Stimulation of GST activity was the most typical response, followed by declined SOD activity and GSH levels. GPX activity and TBARS levels responded differently depending upon the exposure type. Subacute and in vitro effects of SUL and Zn²⁺ produced similar responses except for some cases. Ca²⁺-ATPase activity was altered differently upon subchronic duration, though inhibited by in vitro SUL+Zn effect. Subchronic SUL exposure increased body weight and length up to 25 mg/L, contrary to the observed decrease at higher concentrations.

CONCLUSIONS

Single and binary mixtures of SUL and Zn²⁺ caused damage to the antioxidant and osmoregulatory system due to their oxidative potential on cellular targets (biomarkers). The current data emphasized that investigating the SUL toxicity with the Zn²⁺ combination based on the multi-biomarker approach is essential in the realistic evaluation of SUL toxicity in toxicological research.

Different cellular mechanism of imidacloprid and acetamiprid by a combined targeted lipidomics and metabolomics approach in Neuro-2a cells

As commonly used neonicotinoid insecticides for pest control, imidacloprid (IMI) and acetamiprid (ACE) posed neurotoxicity effects on living organisms. However, researches of the differences in toxicity mechanism between these two neonicotinoid insecticides are still limited. In this study, different cellular metabolism perturbations and redox homeostasis damages induced by IMI and ACE exposure in Neuro-2a cells were investigated. Distinct elevation of lactate dehydrogenase (LDH) activity and caspase 7 level demonstrated the influences on necrosis and apoptosis. There were 21 and 12 metabolites screened out as potential biomarkers after IMI and ACE exposure, including lipids and amino acids. Remarkable decrease of lipid hydroperoxides (LOOH) and increase of reactive oxygen species (ROS) generation were found only in the ACE20 group. Interference with glutathione metabolism pathway was further validated by detecting GPx (glutathion peroxidase), GSH (reduced glutathione) and GSSG (oxidized glutathione) levels. Taken together, the metabolic interferences and oxidative damages in ACE20 group were significantly different from the other three exposure groups. These results help to explore the toxicity mechanism of neonicotinoid insecticides from multiple perspectives. This study provides scientific basis for evaluating toxicity of different neonicotinoid insecticides.

Effects of chronic exposure to microcystin-LR on life-history traits, intestinal microbiota and transcriptomic responses in Chironomus pallidivittatus

Microcystins (MCs) are the most widely distributed cyanobacterial toxins that can exert adverse effects on aquatic organisms, but aside from the study of the harmful effect of cyanobacterial blooms, little is known about the effect of released MCs on the growth and development of chironomid larvae. To assess the harmful effect and the toxic mechanism of MCs on midges, the life-history traits, intestinal microbiota, and transcriptome of Chironomus pallidivittatus were analyzed after chronic exposure to 30 μg/L of MC-LR. Exposure inhibited larvae body length by 35.61% and wet weight by 21.92%, increased emergence time of midges, damaged mitochondria in the intestine, promoted oxidative stress, dysregulated lipid metabolism of chironomid larvae, and increased detoxification enzymes glutathione S-transferase (GST) and superoxide dismutase (SOD) by 32.44% and 17.41%, respectively. Exposure also altered the diversity and abundance of the intestinal microbiota, favoring pathogenic and MC degradation bacteria. RNA sequencing identified 261 differentially expressed genes under MC-LR stress, suggesting that impairment of the peroxisome proliferator-activated receptor signaling pathway upregulated fatty acid biosynthesis and elongation to promote lipid accumulation. In addition, exposure-induced detoxification and antioxidant responses, indicating that the chironomid larvae had the potential ability to resist MC-LR. To our knowledge, this is the first time that lipid accumulation, oxidative stress, and detoxification have been studied in this organism at the environmentally relevant concentration of MC-LR; the information may assist in ecological risk assessment of cyanobacterial toxins and their effects on benthic organisms.

A rapid evidence assessment of the potential risk to the environment presented by active ingredients in the UK's most commonly sold companion animal parasiticides

A number of parasiticides are commercially available as companion animal treatments to protect against parasite infestation and are sold in large volumes. These treatments are not intended to enter the wider environment but may be washed off or excreted by treated animals and have ecotoxic impacts. A systematic literature review was conducted to identify the existing evidence for the toxicity of the six most used parasiticides in the UK: imidacloprid, fipronil, fluralaner, afoxolaner, selamectin, and flumethrin. A total of 17,207 published articles were screened, with 690 included in the final evidence synthesis. All parasiticides displayed higher toxicity towards invertebrates than vertebrates, enabling their use as companion animal treatments. Extensive evidence exists of ecotoxicity for imidacloprid and fipronil, but this focuses on exposure via agricultural use and is not representative of environmental exposure that results from use in companion animal treatments, especially in urban greenspace. Little to no evidence exists for the ecotoxicity of the remaining parasiticides. Despite heavy usage, there is currently insufficient evidence to understand the environmental risk posed by these veterinary treatments and further studies are urgently needed to quantify the levels and characterise the routes of environmental exposure, as well as identifying any resulting environmental harm.

Neonicotinoids: mechanisms of systemic toxicity based on oxidative stress-mitochondrial damage

Neonicotinoids are the most widely used pesticides in the world. However, research studies have shown that it can affect the cognitive abilities and health of non-target bees and other wild pollinators by inducing DNA damage, apoptosis and mitochondrial damage, injure to its central nervous system, and it is even developmentally neurotoxic to mammals and humans, with mitochondria being an important target of neonicotinoids. Therefore, this article reviews the role of mitochondrial morphology, calcium ions (Ca²⁺) homeostasis, respiratory function, apoptosis, and DNA damage in neonicotinoids-induced systemic toxicity. Additionally, it evaluates the protective effects of various active substances including vitamin C, N-acetylcysteine (NAC), curcumin (CUR), glutathione reduced (GSH), caffeic acid phenethyl ester (CAPE), resveratrol, and thymoquinone (TQ) on neonicotinoids-induced toxicity. This review manuscript found that mitochondria are important targets to neonicotinoids. Neonicotinoids can cause DNA damage, apoptosis, protein oxidation, and lipid peroxidation in non-target organisms by altering mitochondrial Ca²⁺ homeostasis, inhibiting mitochondrial respiration, and inducing reactive oxygen species (ROS) production. Several active substances (vitamin C, NAC, CUR, GSH, resveratrol, CAPE, and TQ) play a protective role against neonicotinoid-induced systemic toxicity by inhibiting ROS signaling pathways, apoptosis, and lipid peroxidation. This review manuscript emphasizes the importance and urgency of the development of neonicotinoid antidotes, emphasizes the prospect of the application of targeted mitochondrial antidotes, and prospects the development of neonicotinoid antidotes in order to provide some strategies for the prevention of neonicotinoid toxicity.

Impact of imidacloprid exposure on the biochemical responses, transcriptome, gut microbiota and growth performance of the Pacific white shrimp Litopenaeus vannamei

The widespread use of neonicotinoid insecticides, such as imidacloprid, in agriculture is one of the key factors for the drop in the survival of invertebrates, including decapod crustaceans. However, there is currently a lack of comprehensive studies on the chronic toxicity mechanisms in decapod crustaceans. Here, the concentration-dependent effects of imidacloprid on the physiology and biochemistry, gut microbiota and transcriptome of L. vannamei , and the interaction between imidacloprid, gut microbiota and genes were studied. Imidacloprid caused oxidative stress, leading to reduced growth and to immunity and tissue damage in L. vannamei . Imidacloprid increased the gut pathogenic microbiota abundance and broke the steady state of the gut microbiota interaction network, resulting in microbiota function disorders. Chronic imidacloprid exposure induced overall transcriptome changes in L. vannamei . Specifically, imidacloprid caused a large number of differentially expressed genes (DEGs) to be significantly downregulated. The inhibition of autophagy-related pathways revealed the toxic process of imidacloprid to L. vannamei . The changes in phase I and II detoxification gene expression clarified the formation of a detoxification mechanism in L. vannamei . The disturbance of circadian rhythm (CLOCK) caused by imidacloprid is one of the reasons for the increase in gut pathogenic microbiota abundance.

Target and Suspect Screening of Urinary Biomarkers for Current-use Pesticides: Application of a Simple Extraction Method

Pesticide residues pose a great threat to human health. Biomonitoring with urine samples has often been used to assess pesticide exposure to humans, and identifying appropriate biomarkers is a premise of success. Current-use pesticides (CUPs) including neonicotinoids tend to be transformed in an organism, and thus the biomonitoring studies focusing on parent compounds alone may underestimate their risk. It is imperative to develop effective methods to analyze CUPs and their metabolites simultaneously and to identify viable metabolites as urinary biomarkers. For analyzing xenobiotics in urine, we optimized CH₃ COCH₃ -MgSO₄ extraction coupled with a high-performance liquid chromatography-tandem mass spectrometry detection method. The method had sensitive method detection limits (0.11-1.39 ng/ml), low matrix effects, and satisfactory recovery and precision (49.4% ± 7.2%-99.8% ± 17.8%) for neonicotinoids and their metabolites. Application of the method for real samples showed that children living in rural areas in South China were ubiquitously exposed to CUPs, including neonicotinoids, fipronil, and chlorpyrifos, and urinary residues were mainly in the form of metabolites. Suitable biomarkers were identified for individual neonicotinoids, including imidacloprid-olefin and imidacloprid-guanidine for imidacloprid, acetamiprid-N-desmethyl for acetamiprid, thiacloprid-amide for thiacloprid, and N-desmethyl-thiamethoxam and thiamethoxam for thiamethoxam. Three metabolites were mainly reported in urine samples, including imidacloprid-urea, thiacloprid-amide, and N-desmethyl-thiamethoxam. In addition, the method was also applied for suspect screening, and an additional metabolite (clothianidin-desmethyl-nitrosoguanidine) was identified, showing its potential application in suspect analysis. Environ Toxicol Chem 2022;41:73-80. © 2021 SETAC.

Exposure to imidacloprid induce oxidative stress, mitochondrial dysfunction, inflammation, apoptosis and mitophagy via NF-kappaB/JNK pathway in grass carp hepatocytes

Imidacloprid (IMI) is a neonicotinoid compound widely used in agriculture production, causing surface water pollution and threatening non-target organisms. The aim of this study was to analyze the effects of IMI on grass carp (Ctenopharyngodon idellus) liver cell (L8824) injury. The L8824 cells were exposed to different doses of IMI (65 mg/L, 130 mg/L and 260 mg/L) for 24 h. Our results demonstrated that exposure IMI significantly suppressed the activity of anti-oxidant enzymes (SOD, CAT and T-AOC) and accumulated oxidase (MDA) levels, and promoting reactive oxygen species (ROS) generation in L8824 cells. Additionally, mitochondrial membrane potential (ΔΨ m), mitochondria-derived ROS and ATP content and the MitoTracker Green indicated that IMI aggravated mitochondrial dysfunction, thereby inducing inflammation and enhancing pro-inflammatory genes (NF-kappaB, TNFα, IL-1β and IL-6) expressions. However, the addition of 2 mM N-acetyl-l-cysteine (NAC) can reverse these adverse effects of high-dose IMI- induced. Hence, ROS is the main factor of IMI-induced mitochondrial dysfunction and inflammation. We further found that exposure to IMI induced apoptosis, which is characterized by promoting release of cytochrome c (Cyt-C), and increasing the expression of Bcl-2-Associated X (BAX), cysteinyl aspartate specific proteinases (Caspase 9 and 3), decreasing Bcl-2 level. Immunofluorescent staining, qRT-PCR and Western Blot results indicated that IMI exposure also activated mitophagy, which was demonstrated by the expression of mitophagy-related genes (BNIP3, LC3B and P62). Conversely, scavenging JNK by SP600125(10 μM) alleviated the expression of mitochondrial apoptosis and mitophagy-related gene induced by high-dose IMI. Therefore, these results of study demonstrated that IMI-induced oxidative stress to regulate mitochondrial dysfunction, thus causing inflammation, mitochondrial apoptosis and mitophagy in grass carp hepatocytes through NF-kappaB/JNK pathway.

Probing the biological toxicity of pyrene to the earthworm Eisenia fetida and the toxicity pathways of oxidative damage: A systematic study at the animal and molecular levels

Pyrene (Pyr), a widely used tetracyclic aromatic hydrocarbon, enters soil in large quantities and causes environmental pollution due to its production and mining. In order to systematically study the biotoxicity of pyrene to model organisms Eisenia fetida in soil, experiments were carried out from four dimensions: animal, tissue, cell and molecule. Experimental results proved that the mortality rate increased with increasing concentration and time of exposure to pyrene, while the mean body weight and spawning rate decreased. Meanwhile, when the pyrene concentration reached 900 mg/kg, the seminal vesicle and longitudinal muscle of the earthworm showed obvious atrophy. Experimental results at the cellular level showed that pyrene induced cell membrane damage and Ca²⁺ influx triggered mitochondrial membrane depolarization and a surge in ROS levels. Oxidative stress causes damage to proteins and lipids and DNA inside cells. When the mortality rate was 91.67 %, the Olive Tail Movement (OTM) of the comet experiment reached 15. The results of molecular level tests showed that pyrene inhibited the activity of Cu/Zn-superoxide dismutase (Cu/Zn-SOD) mainly by changing the microenvironment and secondary structure of amino acid Tyr 108. The weakened function of direct antioxidant enzymes may be the root cause of the excessive increase of reactive oxygen species (ROS) in cells. The systematic approach used in this study enriches the network of toxic pathways in toxicological studies, and basic data on the biological toxicity of pyrene can provide support for future soil contamination detection.

Combined lethal toxicities of pesticides with similar structures to Caenorhabditis elegans are not necessarily concentration additives

Studies have shown that the mixture toxicity of compounds with similar modes of action (MOAs) is usually predicted by the concentration addition (CA) model. However, due to the lack of toxicological information on compounds, more evidence is needed to determine whether the above conclusion is generally applicable. In general, the same type of compounds with similar chemical structures have similar MOAs, so whether the toxicities of the mixture of these compounds are additive needs to be further studied. In this paper, three types of pesticides with similar chemical structures (three organophosphoruses, two carbamates and two neonicotinoids) that may have similar MOAs were selected and five binary mixture systems were constructed. For each system, five mixture rays with different concentration ratios were designed by the direct equipartition ray design (EquRay) method. The mortality of Caenorhabditis elegans was regarded as the endpoint for the toxicity exposure to single pesticides and binary mixtures. The combined toxicities were evaluated simultaneously using the CA model, isobologram and combination index. The structural similarity of the same type of pesticides was quantitatively analyzed according to the MACCS molecular fingerprint and the slope of dose-response curve at pEC₅₀. The results show that the toxicities of neonicotinoid mixtures and carbamate mixtures are almost antagonistic. The entire mixture system of dichlorvos and dimethoate produced synergism, and four of the five mixture rays of dimethoate and methamidophos induced antagonism, while among the mixture rays of dichlorvos and methamidophos, different concentrations showed different interaction types. The results of structural similarity analysis show that the size of structural similarity showed a certain quantitative relationship with the toxicity interaction of mixtures, that is, the structural similarity of the same type of pesticides may show an additive action in a certain range.

Physiological Effects of Neonicotinoid Insecticides on Non-Target Aquatic Animals-An Updated Review

In this paper, we review the effects of large-scale neonicotinoid contaminations in the aquatic environment on non-target aquatic invertebrate and vertebrate species. These aquatic species are the fauna widely exposed to environmental changes and chemical accumulation in bodies of water. Neonicotinoids are insecticides that target the nicotinic type acetylcholine receptors (nAChRs) in the central nervous systems (CNS) and are considered selective neurotoxins for insects. However, studies on their physiologic impacts and interactions with non-target species are limited. In researches dedicated to exploring physiologic and toxic outcomes of neonicotinoids, studies relating to the effects on vertebrate species represent a minority case compared to invertebrate species. For aquatic species, the known effects of neonicotinoids are described in the level of organismal, behavioral, genetic and physiologic toxicities. Toxicological studies were reported based on the environment of bodies of water, temperature, salinity and several other factors. There exists a knowledge gap on the relationship between toxicity outcomes to regulatory risk valuation. It has been a general observation among studies that neonicotinoid insecticides demonstrate significant toxicity to an extensive variety of invertebrates. Comprehensive analysis of data points to a generalization that field-realistic and laboratory exposures could result in different or non-comparable results in some cases. Aquatic invertebrates perform important roles in balancing a healthy ecosystem, thus rapid screening strategies are necessary to verify physiologic and toxicological impacts. So far, much of the studies describing field tests on non-target species are inadequate and in many cases, obsolete. Considering the current literature, this review addresses important information gaps relating to the impacts of neonicotinoids on the environment and spring forward policies, avoiding adverse biological and ecological effects on a range of non-target aquatic species which might further impair the whole of the aquatic ecological web.

Neonicotinoid insecticides triggers mitochondrial bioenergetic dysfunction via manipulating ROS-calcium influx pathway in the liver

Extensive use of neonicotinoids insecticides (NNIs) rapidly garnered widespread attention in the toxicology, since they have been found in human samples, including urine, blood, breast milk and hair. However, the precise mechanism is not completely clear regarding the NNIs-induced hepatotoxicity. In this study, we exposed male mice to three neonicotinoids (dinotefuran (DIN), nitenpyram (NIT) and acetamiprid (ACET) for 30 days. Our results showed that NNIs remarkably induced morphological damage in the liver. Simultaneously, we found that three neonicotinoids could activate the store operated Ca2+ entry (SOCE) in the liver. Further results confirmed that reactive oxide species (ROS) scavenger n-acetylcysteine (NAC) attenuated DIN-induced calcium ion (Ca2+) overload and S-phase arrest via restoring protein expression of SOCE and S phase related genes in L02 hepatocytes. Moreover, we found that NAC obviously combated mitochondrial dysfunction caused by DIN via restoring mitochondrial membrane potential. Meanwhile, DIN treatment significantly increased pyruvate content, impaired the activities of tricarboxylic acid (TCA) cycle rate-limiting enzymes and inhibited adenosine triphosphate (ATP) generation, but these effects were reversed by Serca specific activator CDN1163. Collectively, perturbation of redox states can be recognized as the center of S-phase arrest and Ca2+ overload after NNIs exposure. In this regard, Ca2+ homeostasis dysregulation is a causative event of mitochondrial bioenergetic dysfunction in the liver. These data provides a new perspective for understanding NNI-induced hepatotoxicity mechanisms.

Joint toxicity of imidacloprid and azoxystrobin to Chironomus dilutus at organism, cell, and gene levels

Pesticides occur in the environment as mixtures, yet the joint toxicity of pesticide mixtures remains largely under-explored and is usually overlooked in ecological risk assessment. In the current study, joint toxicity of a neonicotinoid insecticide (imidacloprid, IMI) and a strobilurin fungicide (azoxystrobin, AZO) was investigated with Chironomus dilutus over a wide range of concentrations and at different effect levels (organism, cell, and gene levels). The two pesticides, both individually and in combination, were found to induce oxidative stress and cause lethality in C. dilutus. Median lethal concentrations for IMI and AZO were 3.98 ± 1.17 and 52.9 ± 1.1 μg/L, respectively. Mixtures of the two pesticides presented synergetic effects at environmentally relevant concentrations whilst antagonistic effects at high concentrations, showing concentration-dependent joint toxicity. Investigation on the expressions of 12 genes (cyt b, coi, cox1, cyp4, cyp12m1, cyp9au1, cyp6fv1, cyp315, gst, Zn/Cu-sod, Mn-sod, and cat) revealed that the two pesticides impaired mitochondrial respiration, detoxification, and antioxidant system of C. dilutus, and the joint effects of the two pesticides were likely due to an interplay between their respective influences on these physiological processes. Collectively, the synergistic effects of the two pesticides at environmentally relevant concentrations highlight the importance to incorporate combined toxicity studies into ecological risk assessment of pesticides.

Multi-Level Gene Expression in Response to Environmental Stress in Aquatic Invertebrate Chironomids: Potential Applications in Water Quality Monitoring

In freshwater ecosystems, aquatic invertebrates are influenced continuously by both physical stress and xenobiotics. Chironomids (Diptera; Chironomidae), or non-biting midges, are the most diverse and abundant invertebrates in freshwater habitats. They are a fundamental link in food chains of aquatic ecosystems. Chironomid larvae tolerate stress factors in their environments via various physiological processes. At the molecular level, environmental pollutants induce multi-level gene responses in Chironomus that regulate cellular protection through the activation of defense processes. This paper reviews literature on the transcriptional responses of biomarker genes to environmental stress in chironomids at the molecular level, in studies conducted from 1991 to 2020 (120 selected literatures of 374 results with the keywords "Chironomus and gene expression" by PubMed search tool). According to these studies, transcriptional responses in chironomids vary depending on the type of stress factor and defensive responses associated with antioxidant activity, the endocrine system, detoxification, homeostasis and stress response, energy metabolism, ribosomal machinery, apoptosis, DNA repair, and epigenetics. These data could provide a comprehensive overview of how Chironomus species respond to pollutants in aquatic environments. Furthermore, the transcriptomic data could facilitate the development of genetic tools for water quality and environmental monitoring based on resident chironomid species.

Transcriptomic analysis reveals common pathways and biomarkers associated with oxidative damage caused by mitochondrial toxicants in Chironomus dilutus

A variety of chemicals are capable of provoking mitochondrial dysfunction and thereby contribute to metabolic disorder related effects in wildlife and human. For better identifying new mitochondrial toxicants and assessing mitochondria-related risk, an in-depth understanding of toxic mechanisms and biomarkers should be attained. In the current study, a representative mitotoxicant, azoxystrobin, was assessed for lethal and sublethal outcomes in Chironomus dilutus after 96-h exposure and the toxic mechanism was explored. Global transcriptomic profiles by RNA-sequencing revealed that ampk, acc1, atp2a, gsk3b, pi3k, fak, atr, chk1, and map3k5 were the key genes which involved in the toxic action of azoxystrobin and could serve as potential molecular biomarkers. A major network of common toxicity pathways was then developed for mitotoxicants towards aquatic insects. In particular, calcium ion-PI3K/AKT and cAMP-AMPK-lethality pathways were demonstrated, in addition to the well-known mitochondrial electron transfer-oxidative damage-apoptosis pathway. These analyses could help developing adverse outcome pathways that integrate toxicological information at various levels and support more effective risk assessment and management of mitotoxicants.

Insights into the Toxicity and Degradation Mechanisms of Imidacloprid Via Physicochemical and Microbial Approaches

Imidacloprid is a neonicotinoid insecticide that has been widely used to control insect pests in agricultural fields for decades. It shows insecticidal activity mainly by blocking the normal conduction of the central nervous system in insects. However, in recent years, imidacloprid has been reported to be an emerging contaminant in all parts of the world, and has different toxic effects on a variety of non-target organisms, including human beings, due to its large-scale use. Hence, the removal of imidacloprid from the ecosystem has received widespread attention. Different remediation approaches have been studied to eliminate imidacloprid residues from the environment, such as oxidation, hydrolysis, adsorption, ultrasound, illumination, and biodegradation. In nature, microbial degradation is one of the most important processes controlling the fate of and transformation from imidacloprid use, and from an environmental point of view, it is the most promising means, as it is the most effective, least hazardous, and most environmentally friendly. To date, several imidacloprid-degrading microbes, including Bacillus, Pseudoxanthomonas, Mycobacterium, Rhizobium, Rhodococcus, and Stenotrophomonas, have been characterized for biodegradation. In addition, previous studies have found that many insects and microorganisms have developed resistance genes to and degradation enzymes of imidacloprid. Furthermore, the metabolites and degradation pathways of imidacloprid have been reported. However, reviews of the toxicity and degradation mechanisms of imidacloprid are rare. In this review, the toxicity and degradation mechanisms of imidacloprid are summarized in order to provide a theoretical and practical basis for the remediation of imidacloprid-contaminated environments.