Does cadmium affect the toxicokinetics of permethrin in Chironomus dilutus at sublethal level? Evidence of enzymatic activity and gene expression

Co-exposure to cadmium and triazophos induces variations at enzymatic and transcriptional levels in Opsariichthys bidens

Heavy metals and pesticides are significant pollutants in aquatic environments, often leading to combined pollution and exerting toxic effects on aquatic organisms. With the rapid growth of modern industry and agriculture, heavy metal cadmium (Cd) and pesticide triazophos (TRI) are frequently detected together in various water bodies, particularly in agricultural watersheds. However, the combined toxic mechanisms of these pollutants on fish remain poorly understood. This experiment involved a 21-day co-exposure of Cd and TRI to the hook snout carp Opsariichthys bidens to investigate the toxic effects on liver tissues at both enzymatic and transcriptional levels. Biochemical analysis revealed that both individual and combined exposures significantly increased the content or activity of caspase-3 (CASP-3) and malondialdehyde (MDA). Moreover, the impact on these parameters was greater in the combined exposure groups compared to the corresponding individual exposure groups. These findings suggested that both individual and combined exposures could induce mitochondrial dysfunction and lipid peroxidation damage, with combined exposure exacerbating the toxicological effects of each individual pollutant. Furthermore, at the molecular level, both individual and combined exposures upregulated the expression levels of cu-sod, cat, and erβ, while downregulating the expression of il-1. Similar to the patterns observed in the biochemical parameters, the combined exposure group exhibited a greater impact on the expression of these genes compared to the individual exposure groups. These results indicated that exposure to Cd, TRI, and their combination induced oxidative stress, endocrine disruption, and immunosuppression in fish livers, with more severe effects observed in the combined exposure group. Overall, the interaction between Cd and TRI appeared to be synergistic, shedding light on the toxic mechanisms by which fish livers responded to these pollutants. These findings contributed to the understanding of mixture risk assessment of pollutants and were valuable for the conservation of aquatic resources.

UDP-glucuronosyltransferase is involved in susceptibility of Chironomus kiiensis Tokunaga, 1936 (Diptera: Chironomidae) to insecticides

UDP-glucuronosyltransferases (UGTs) could transform various exogenous and endogenous compounds, which help detoxification of pesticides in insects. To investigate the role of UGTs in the detoxification metabolism of insecticides in Chironomus kiiensis, CkUGT302M1, CkUGT302N1, CkUGT308N1 and CkUGT36J1 genes were identified with 1449-1599 bp encoding 482-532 amino acids. Four UGT genes shared 40.86∼53.36% identity with other homologous insect species, and expressed in all developmental stages, notably in the larval and adult stages. Expression of CkUGTs was higher in the gastric caecum, midgut and head. Moreover, CkUGTs expression and activity were significantly increased in C. kiiensis larvae in exposure to sublethal concentrations of carbaryl, deltamethrin and phoxim, respectively. To further explore the functions of UGT genes, the CkUGT308N1 was effectively silenced in 4th instar C. kiiensis larvae by RNA interference, which resulted in the mortality of dsCkUGT308N1 treated larvae increased by 71.43%, 111.11% and 62.50% under sublethal doses of carbaryl, deltamethrin and phoxim at the 24-h time point, respectively. The study revealed that the CkUGT308N1 gene in C. kiiensis could contribute to the metabolism of pesticides and provide a scientific basis for evaluating the water pollution of pesticides.

A Reduced Model for Bioconcentration and Biotransformation of Neutral Organic Compounds in Midge

A bioconcentration factor (BCF) database and a toxicokinetic model considering only biota-water partitioning and biotransformation were constructed for neutral organic chemicals in midge. The database contained quality-reviewed BCF and toxicokinetic data with variability constrained to within 0.5 to 1 log unit. Diverse conditions in exposure duration, flow set-up, substrate presence, temperature, and taxonomic classification did not translate into substantial variability in BCF, uptake rate constant (k₁ ), or depuration rate constant (k_T ), and no systematic bias was observed in BCFs derived in unlabeled versus radiolabeled studies. Substance-specific biotransformation rate constants k_M were derived by difference between the calculated biota-water partitioning coefficient (K_BW ) and experimental BCF for developing a midge biotransformation model. Experimental midge BCF was modeled as BCF = K_BW /(1 + k_M/ k₂ ) with log k_M (k_M in h^-1 ) = -0.37 log K_OW - 0.06T (in K) + 18.87 (root mean square error [RMSE] = 0.60), log k₁ (k₁ in L kg_wet.wt^-1  h^-1 ) = -0.0747 W (body weight in mg_wet.wt ) + 2.35 (RMSE = 0.48). The K_BW value was estimated using midge biochemical composition and established polyparameter linear free energy relationships, and the diffusive elimination rate constant (k₂ ) was computed as k₂  = k₁ /K_BW. The BCF model predicted >85% of BCFs that associated with neutral organic compounds (log K_OW  = 1.46 - 7.75) to within 1 log-unit error margin and had comparable accuracy similar to amphipod or fish models. A number of outliers and critical limitations of the k_M model were identified and examined, and they largely reflected the inherent limitation of difference-derived k_M , the lack of chemical diversity, and inadequate temperature variation in existing data. Future modeling efforts can benefit from more BCF and toxicokinetic observations of BCF on structurally diverse chemicals for model training, validation, and diagnosis. Environ Toxicol Chem 2021;40:57-71. © 2020 SETAC.

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.

Toxicological interactions of cadmium and four pesticides on early life stage of rare minnow (Gobiocypris rarus)

Although chemicals have been traditionally regulated on an individual basis in aquatic ecosystems, they often co-exist as different types of complex mixtures. Laboratory assays were conducted for assessing the responses of rare minnow (Gobiocypris rarus) to individual and mixture chemicals [trace element cadmium (Cd), thiamethoxam, deltamethrin, malathion and prochloraz]. Data obtained from 96 h semi-static toxicity assays implied that deltamethrin elicited the highest toxic effect on the various developmental phases (larval, juvenile and adult phases) of G. rarus with LC₅₀ values ranging from 0.00061 to 0.25 mg a.i. L^-1, followed by prochloraz, malathion and Cd with 96-h LC₅₀ values ranging from 0.49 to 1.1, from 7.1 to 26, and from 7.6 to 15 mg a.i. L^-1, respectively. Thiamethoxam elicited the lowest toxic effect on the organisms with 96-h LC₅₀ values ranging from 38 to 202 mg a.i. L^-1. Larval phase was not always the most sensitive period in the three detected phases to most of chemicals. Chemical combinations containing deltamethrin and malathion displayed synergetic responses to the larvae of G. rarus. Besides, the binary mixtures of Cd-deltamethrin and Cd-prochloraz also exhibited synergetic response to rare minnows. Our results indicate that extra information is necessary to develop practical criteria for selecting chemical combinations that require legislative attention according to their likelihood to exert synergetic responses. Thence, more investigations on mixture toxicities of various chemicals should be taken as a priority for producing synergetic interaction to improve the environmental risk assessment of chemicals.

Joint toxic impacts of cadmium and three pesticides on embryonic development of rare minnow (Gobiocypris rarus)

Although rare minnow (Gobiocypris rarus) has been employed in many toxicological investigations, most of them have only assessed the impacts of single chemical. In our current work, we investigated the single and joint toxic impacts of heavy metal cadmium (Cd) and three pesticides (thiamethoxam, bifenthrin, and tebuconazole) on G. rarus embryos. Results from the 96-h semi-static toxicity assay exhibited that bifenthrin possessed the highest intrinsic toxic effect on rare minnows with an LC₅₀ value of 1.86 mg L^-1, followed by tebuconazole with LC₅₀ values of 4.07 mg L^-1. Contrarily, thiamethoxam elicited the least toxic effect with an LC₅₀ value of 351.9 mg L^-1. Seven chemical mixtures (four binary mixtures of Cd-bifenthrin, thiamethoxam-bifenthrin, thiamethoxam-tebuconazole, and bifenthrin-tebuconazole, two ternary mixtures of Cd-thiamethoxam-tebuconazole and thiamethoxam-bifenthrin-tebuconazole, and one quaternary mixture of Cd-thiamethoxam-bifenthrin-tebuconazole) displayed synergistic impacts with equivalent concentration and equitoxic ratio on G. rarus. Our results offered valuable insights into ecological risk assessment of these chemical combinations to aquatic vertebrates. The simultaneous existence of a few chemicals in the aquatic ecosystem might result in elevated toxicity, leading to severe harm to the non-target organisms compared with single compound. The observed synergistic interactions underlined the necessity to revise water quality standards, in which the detrimental joint effects of these chemicals are likely to be underestimated.

The influence of nanoplastics on the toxic effects, bioaccumulation, biodegradation and enantioselectivity of ibuprofen in freshwater algae Chlorella pyrenoidosa

Plastic pollution has become a pressing issue due to its persistence in the environment. Smaller plastics are more easily ingested, potentially exerting greater influences on organisms. In this study, the effects of polystyrene nanoplastics (NP) on the toxic effects, bioaccumulation, biodegradation and enantioselectivity of ibuprofen (IBU) in algae Chlorella pyrenoidosa were explored. The influences on the growth rate, chlorophyll a, total antioxidant capacity (T-AOC), reactive oxygen species (ROS) and lipid peroxidation (MDA) were evaluated after 96 h of exposure to a combination of polystryene NP (1 mg L^-1) and IBU (5-100 mg L^-1). The results indicated that the inhibitory effect of IBU on C. pyrenoidosa growth was alleviated in the presence of NP. For instance, the 96 h-IC₅₀ value for rac-IBU in the treatment lacking NP was 45.7 mg L^-1, and the corresponding value in the treatment containing NP was 63.9 mg L^-1. The co-exposure of NP led to a significant enhancement of T-AOC and slight reduction of ROS and MDA compared with the individual exposure (IBU) group, suggesting a decreased oxidative stress. In addition, treatment with NP led to a decreased bioaccumulation and accelerated biodegradation of IBU in C. pyrenoidosa and enhanced removal in the medium. The enantioselective toxicity, bioaccumulation and biodegradation of IBU were observed both in the absence and presence of NP. S-IBU exhibited a greater toxicity, and R-IBU was preferentially accumulated and degraded in C. pyrenoidosa. No interconversion of the two enantiomers occurred regardless of the presence of NP. This consequence implied that the influence of coexistent NP should be considered in the environmental risk assessment of pharmaceuticals and personal care products in aquatic environments.

Characterisation of GST genes from the Hyphantria cunea and their response to the oxidative stress caused by the infection of Hyphantria cunea nucleopolyhedrovirus (HcNPV)

The fall webworm, Hyphantria cunea (Drury) (Lepidoptera: Noctuidae), is a major pest found in forests. In this study, the effects of Hyphantria cunea nucleopolyhedrovirus (HcNPV) infection on the transcription levels and activities of glutathione S-transferases (GSTs) in H. cunea were determined. In the present study, 18 GST family genes were identified from the H. cunea transcriptome dataset by using bioinformatic analyses. These GST genes were classified into cytosolic (15 genes) and microsomal (three genes) classes. The 15 cytosolic GST genes belonged to four different subclasses (epsilon, sigma and delta). The all GST genes, especially GSTe4, showed high expression levels in egg and 1st~4th instar larval stage while their low expression levels in 5th~7th instar larvae using real-time quantitative PCR analysis. However, the expression levels of the 18 GST genes were varied after exposure to sublethal doses of HcNPV. The expression levels of most GSTs were downregulated and upregulated at low and high concentrations of HcNPV, respectively. The corresponding total GST activities also showed similar patterns. In H. cunea, changes in the expression levels and enzymatic activities of GSTs after exposure to HcNPV indicated that they may have important functions in the defense against HcNPV, and the stress, which may be reflected by the high GST enzymatic activities.

Changes of enzyme activity and gene expression in embryonic zebrafish co-exposed to beta-cypermethrin and thiacloprid

Pesticides often occur as mixtures of complex compounds in water environments, while most of studies only focus on the toxic effects of individual pesticides with little attention to the joint toxic effects. In the present study, we aimed to the mixture toxicity of beta-cypermethrin (BCY) and thiacloprid (THI) to zebrafish (Danio rerio) employing multiple toxicological endpoints. Results displayed that the 96-h LC₅₀ values of BCY to D. rerio at various developmental stages ranged from 2.64 × 10 (1.97 × 10-3.37 × 10) to 6.03 × 10³ (4.54 × 10³-1.05 × 10⁴) nM, which were lower than those of THI ranging from 2.97 × 10⁴ (1.96 × 10⁴-4.25 × 10⁴) to 2.86 × 10⁵ (2.19 × 10⁵-5.87 × 10⁵) nM. Mixtures of BCY and THI exhibited synergistic response in embryonic zebrafish. Meanwhile, the enzyme activities of antioxidants (CAT and SOD) and detoxification enzyme (CarE), endogenous T-GSH and MDA contents, as well as gene expressions (tsh, crh, cxcl and bax) involved in oxidative stress, cellular apoptosis, immune system and endocrine system were obviously changed in the mixture exposure compared with the respective BCY or THI treatment. Consequently, the increased toxicity of pesticide mixture suggested that the toxicological data acquired from individual pesticide tests might underrate the toxicity risk of pesticides that actually arise in the real environment. Taken together, our present study provided evidence that mixture exposure of BCY and THI could induce additional toxic effect compared with their respective individual pesticides on D. rerio, offering valuable insights into the toxic mechanism of pesticide mixture.

Lethal toxicity and gene expression changes in embryonic zebrafish upon exposure to individual and mixture of malathion, chlorpyrifos and lambda-cyhalothrin

Pesticides are usually present as mixtures in water environments. Evaluating the toxic effects of individual pesticide may not be enough for protecting ecological environment due to interactions among substances. In this study, we aimed to examine the lethal doses and gene expression changes in zebrafish (Danio rerio) upon exposure to individual and mixture pesticides [malathion (MAL), chlorpyrifos (CHL) and lambda-cyhalothrin (LCY)]. Individual pesticide toxicity evaluation manifested that the toxicity of the three pesticides to D. rerio at various developmental stages (embryonic, larval, juvenile and adult stages) followed the order of LCY > CHL > MAL. On the contrary, the least toxicity to the animals was discovered from MAL. Most of the tested pesticides displayed lower toxicities to the embryonic stage compared with other life stages of zebrafish. Synergistic effects were monitored from two binary mixtures of LCY in combination with MAL or CHL and ternary mixture of MAL + CHL + LCY. The expressions of 16 genes involved in oxidative stress, immunity system, cell apoptosis and endocrine disruption at the mRNA level revealed that embryonic zebrafish were influenced by the individual or mixture pesticides. The expressions of Tnf, P53, TRα, Crh and Cyp19a exerted greater variations upon exposure to pesticide mixtures compared with their individual compounds. Collectively, the transcriptional responses of these genes might afford early warning biomarkers for identifying pollutant exposure, and the data acquired from this study provided valuable insights into the comprehensive toxicity of pesticide mixtures to zebrafish.

Effects of phenol on glutathione S-transferase expression and enzyme activity in Chironomus kiiensis larvae

Detoxifying enzyme mRNAs are potentially useful stress biomarkers. Glutathione S-transferase (GST) metabolises lipophilic organic contaminants and mitigates oxidative damage caused by environmental pollutants. Herein, 12 Chironomus kiiensis GSTs (CkGSTs1-6, CkGSTt1-2, CkGSTd1-2, CkGSTm1-2) were cloned and grouped into sigma, theta, delta and microsomal subclasses. Open reading frames (450-699 bp) encode 170-232 amino acid proteins with predicted molecular masses of 17.31-26.84 kDa and isoelectric points from 4.94 to 9.58. All 12 GSTs were expressed during all tested developmental stages, and 11 displayed higher expression in fourth-instar larvae than eggs. GST activity after 24 h of phenol exposure was used to estimate environmental phenol contamination. After exposure to sublethal concentrations of phenol for 48 h, expression and activity of CkGSTs were inhibited in C. kiiensis larvae. Expression of CkGSTd1-2 and CkGSTs1-2 varied with phenol concentration, indicating potential use as biomarkers for monitoring environmental phenol contamination.

Bioconcentration, metabolism and the effects of tetracycline on multiple biomarkers in Chironomus riparius larvae

The antibiotic tetracycline (TC) is widespread in surface waters, but few data are available regarding its adverse effects on aquatic insects. In this study, we investigated the bioconcentration, metabolism, and effects of TC on Chironomus riparius larvae exposed to different concentrations of TC (1.83, 18.5 and 174 μg L^-1) for 48 h. The bioconcentration factors were 3.65, 0.74 and 0.23 in larvae with exposure to 1.83, 18.5 and 174 μg L^-1 TC, respectively. High concentration ratios of the metabolites anhydrotetracycline (0.56-0.60), 4-epitetracycline (0.43-0.69), and 4-epianhydrotetracycline (0.50-0.55) to the unmetabolized compound were found. Additionally, the activities of superoxide dismutase and glutathione S-transferase were markedly inhibited with a significant increase in malondialdehyde contents at high exposure concentrations of TC (18.5 and 174 μg L^-1). Moreover, significant up-regulation of heat shock genes (hsp70 and hsp27), the ecdysone receptor gene, and the E74 early ecdysone responsive gene was observed at all exposure concentrations except for hsp70 at 1.83 μg L^-1. Collectively, these results suggested that TC was quickly absorbed and metabolized by C. riparius and resulted in molecular and biochemical disturbances.

iTRAQ-based quantitative proteomic analysis identified Eno1 as a cadmium stress response gene in Propsilocerus akamusi (Tokunaga) hemolymph

Propsilocerus akamusi (Tokunaga) is a common species of midge in Siberia, Japan, and China and an important prey species for fish and aquatic birds. Furthermore, this species has been shown to have an extraordinary capacity to resist cadmium (Cd) toxicity. In this study, isobaric tags for relative and absolute quantitation (iTRAQ) coupled liquid chromatography tandem mass spectrometry (LC-MS/MS) was used to analyze relative changes in the P. akamusi hemolymph proteome following exposure to a sublethal concentration of Cd²⁺. The results showed that Cd²⁺ stress affects energy metabolism in P. akamusi. After examining the differentially expressed proteins (DEPs), only one up-regulated protein associated with metabolism, α-enolase (Eno1) was identified and further isolated and characterized. Sequence alignments showed that the deduced P. akamusi Eno1 amino acid sequence is highly conserved, with similarities of 77-95% noted when compared to other Dipteran Eno1 sequences. Furthermore, prolonged Cd²⁺ exposure impacted Eno1 transcription, protein expression and enzyme activity levels. These results suggest that Eno1 may play a role in the response to Cd²⁺ stress in P. akamusi.

Evaluation of joint effects of cyprodinil and kresoxim-methyl on zebrafish, Danio rerio

Aquatic organisms are usually exposed to a mixture of pesticides instead of individual chemicals. However, risk assessment of pesticides is traditionally based on toxicity data of individual compounds. In this study, we aimed to examine the joint toxicity of two fungicides cyprodinil (CYP) and kresoxim-methyl (KRM) to zebrafish (Danio rerio) using a systematic experimental approach. Results from 96-h semi-static test indicated that the LC₅₀ values of KRM to D. rerio at multiple life stages (embryonic, larval, juvenile and adult stages) ranged from 0.034 (0.015-0.073) to 0.61 (0.39-0.83) mg a.i. L^-1, which were higher than those of CYP ranging from 1.05 (0.88-1.52) to 4.42 (3.24-6.02) mg a.i. L^-1. Pesticide mixtures of CYP and KRM exhibited synergistic effect on embryonic zebrafish. The activities of carboxylesterase (CarE) and cytochrome P450 (Cyp450) were significantly altered in most of the individual and combined exposures compared with the control group. The expressions of seven genes (Mnsod, cyp17, crhr 2, crh, gnrhr 4, gnrhr 1 and hmgrb) were significantly altered upon exposure to combined pesticides compared with their individual pesticides. Collectively, these findings suggested joint effects should be considered in the risk assessment of pesticides and development of water quality criteria for the protection of aquatic environment.

Joint toxic effects of triazophos and imidacloprid on zebrafish (Danio rerio)

Pesticide contamination is more often found as a mixture of different pesticides in water bodies rather than individual compounds. However, regulatory risk evaluation is mostly based on the effects of individual pesticides. In the present study, we aimed to investigate the individual and joint toxicities of triazophos (TRI) and imidacloprid (IMI) to the zebrafish (Danio rerio) using acute indices and various sublethal endpoints. Results from 96-h semi-static test indicated that the LC₅₀ values of TRI to D. rerio at multiple life stages (embryonic, larval, juvenile and adult stages) ranged from 0.49 (0.36-0.71) to 4.99 (2.06-6.81) mg a.i. L^-1, which were higher than those of IMI ranging from 26.39 (19.04-38.01) to 128.9 (68.47-173.6) mg a.i. L^-1. Pesticide mixtures of TRI and IMI displayed synergistic response to zebrafish embryos. Activities of carboxylesterase (CarE) and catalase (CAT) were significantly changed in most of the individual and joint exposures of pesticides compared with the control group. The expressions of 26 genes related to oxidative stress, cellular apoptosis, immune system, hypothalamic-pituitary-thyroid and hypothalamic-pituitary-gonadal axis at the mRNA level revealed that zebrafish embryos were affected by the individual or joint pesticides, and greater changes in the expressions of six genes (Mn-sod, CXCL-CIC, Dio1, Dio2, tsh and vtg1) were observed when exposed to joint pesticides compared with their individual pesticides. Taken together, the synergistic effects indicated that it was highly important to incorporate joint toxicity studies, especially at low concentrations, when assessing the risk of pesticides.

Global occurrence of pyrethroid insecticides in sediment and the associated toxicological effects on benthic invertebrates: An overview

Pyrethroids are the third most applied group of insecticides worldwide and are extensively used in agricultural and non-agricultural applications. Pyrethroids exhibit low toxicity to mammals, but have extremely high toxicity to fish and non-target invertebrates. Their high hydrophobicity, along with pseudo-persistence due to continuous input, indicates that pyrethroids will accumulate in sediment, pose long-term exposure concerns to benthic invertebrates and ultimately cause significant risk to benthic communities and aquatic ecosystems. The current review synthesizes the reported sediment concentrations of pyrethroids and associated toxicity to benthic invertebrates on a global scale. Geographically, the most studied area was North America, followed by Asia, Europe, Australia and Africa. Pyrethroids were frequently detected in both agricultural and urban sediments, and bifenthrin and cypermethrin were identified as the main contributors to toxicity in benthic invertebrates. Simulated hazard quotients (HQ) for sediment-associated pyrethroids to benthic organisms ranged from 10.5±31.1 (bifenthrin) to 41.7±204 (cypermethrin), suggesting significant risk. The current study has provided evidence that pyrethroids are not only commonly detected in the aquatic environment, but also can cause toxic effects to benthic invertebrates, and calls for better development of accurate sediment quality criteria and effective ecological risk assessment methods for this emerging class of insecticides.