Metabolic response of earthworms (Pheretima guillemi) to silver nanoparticles in sludge-amended soil

Picoxystrobin causes mitochondrial dysfunction in earthworms by interfering with complex enzyme activity and binding to the electron carrier cytochrome c protein

Picoxystrobin (PICO) poses a great threat to earthworms due to its widespread use in agriculture and its stability in soil. Mitochondria may be a sensitive target organ for the toxic effects of PICO on worms. Therefore, evaluating the effect of PICO on mitochondria can further understand the toxic mechanism of PICO to earthworms. Here, we investigated the mechanism of mitochondrial toxicity of PICO to earthworms at environmentally relevant concentrations (62.5, 125 and 250 μg/kg). Transmission electron microscopy observed that PICO disrupted mitochondrial ultrastructure. PICO reduced mitochondrial membrane potential and inhibited the expression of mitochondrial dynamics proteins of 51 kDa (MiD51). PICO interfered with the electron transport chain (ETC) complex activity and the relative transcription of its subunits. In particular, PICO inhibited complex III activity, cytochrome c (Cyt c, an electron carrier protein that transfers electrons from complex III to complex IV) activity, and ATP level. These changes were observed at PICO concentrations as low as 62.5 μg/kg. Molecular docking analysis indicated that PICO can directly bind to Cyt c with a minimum free energy of -7.84 kcal/mol, thus hindering electron transfer in the ETC. This study confirmed that PICO induces mitochondrial dysfunction in earthworms and contributes to effective pesticide management.

Assessing the presence of microplastic in agriculture soils irrigated with treated waste waters using Lumbricus sp.: Ecotoxicological effects

Global water scarcity entailed the use of treated wastewater (TWW) in agriculture, however, this water can vehiculate numerous pollutants into soil and further crops such as microplastics (MPs). To date, few studies had quantified the accumulation of MPs in soils and earthworms after irrigation with TWW as well as their toxicological effects. Hence, the main objective of the present work is to evaluate the toxicity of MPs using Lumbricus sp. earthworms collected from TWW irrigated soils with an increasing gradient of time (5 years, 16 years and 24 years). MPs determination in soil, as well as in earthworms were performed. The intestinal mucus was quantified, and cytotoxicity (Lysosomal membrane stability (LMS), Catalase (CAT) and glutathione-S-Transferase (GST) activities), neurotoxicity (Acetylcholinesterase activity (AChE)) and genotoxicity (Micronuclei frequency (MNi)) biomarker were assessed. Our results revealed that the use of TWW rendered MPs accumulation in earthworms' tissues and induce alteration on the intestinal mucus. An important cytotoxicity time-depending was observed being associated with an increase on genotoxicity. Overall, the present investigation highlights the ecotoxicological risk associated with the use of TWWs as an important driver of MPs and consequently measures are necessary to reduce MPs in wastewater treatment plans to improve this non-conventional water quality.

Endocrine system, cell growth and death, and energy metabolism induced by Sb(III) exposure in earthworm (Pheretima guillemi) revealed by transcriptome and metabolome analysis

Antimony (Sb) is known for its severe and extensive toxicity, and earthworms are considered important indicator organisms in soil ecosystems. Therefore, the present study investigated the mechanism of toxicity of the Sb at different concentrations (50, 200 mg/kg) on earthworms using biochemical indicators, pathological sections, as well as metabolomics and transcriptomics analyses. The results showed that as the exposure concentration increased, both the antioxidant system of earthworms, extent of intestinal damage, and their metabolomic characteristics were significantly enhanced. In the 50 and 200 mg/kg Sb treatment group, 30 and 177 significant differentially changed metabolites (DCMs) were identified, respectively, with the most DCMs being down- and up-regulated, respectively. Metabolomics analysis showed that the contents of dl-tryptophan, glutamic acid, glycine, isoleucine, l-methionine, involved in the protein digestion and absorption as well as aminoacyl-tRNA biosynthesis were significantly up-regulated under the 200 mg/kg treatment. At the transcriptional level, Sb mainly affected the immune system, nervous system, amino acid metabolism, endocrine system, and carbohydrate metabolism in earthworms. The integration of transcriptomic and metabolomic data indicated that high doses of Sb regulated the metabolites and genes related to the oxidative phosphorylation pathway in earthworms. Overall, these results revealed global responses beyond the scope of conventional toxicity endpoints and facilitated a more in-depth and comprehensive assessment of the toxic effects of Sb.

Effects of biochar-derived dissolved organic matter on the gut microbiomes and metabolomics in earthworm Eisenia fetida

The ecological risks of biochar-derived dissolved organic matter (DOM) to soil invertebrates at different organismal levels remains limited. This study comprehensively explored the ecological risks of biochar-derived DOM on earthworm gut through assessments of enzyme activity response, histopathology, gut microbiomes, and metabolomics. Results demonstrated that DOM disturbed the digestive enzymes in earthworm, especially for 10% DOM300 groups. The integrated biomarker response v2 (IBRv2) indicated that the perturbation of earthworm digestive enzymes induced by DOM was both time-dependent and dose-dependent. Pathological observations revealed that 10% DOM300 damaged intestinal epithelium and digestive lumen of earthworms. The significant damage and injury to earthworms caused by DOM300 due to its higher concentrations of heavy metal ions and organic substrates (e.g., toluene, hexane, butanamide, and hexanamide) compared to DOM500 and DOM700. Analysis of 16S rRNA from the gut microbiota showed a significant decrease in genera (Verminephrobacter, Bacillus, and Microbacteriaceae) associated with inflammation, disease, and detoxification processes. Furthermore, 10% DOM300 caused the abnormality of metabolites, such as glutamate, fumaric acid, pyruvate, and citric acid, which were involved in energy metabolism, These findings contributed to improve our understanding of the toxic mechanism of biochar DOM from multiple perspectives.

Evidence of interregional similarity in crayfish metabolomes at reference sites: Progress towards the metabolome as a biomonitoring tool

It has been proposed that biomonitoring may benefit from the use of metabolomics (the study of all small molecules in an organism) to detect sub-lethal organism stress through changes in the metabolite profile (i.e., the metabolome). However, to integrate the metabolome into biomonitoring programs the amount of natural variability among and within populations of indicator taxa must be established prior to generating a reference condition. This study determined variation in the metabolome among ecoregion and stream of origin in the northern crayfish (Faxonius virilis) and if that variation inhibited detection of stressor effects at sites exposed to human activities. We collected crayfish from seven minimally disturbed streams (i.e., reference streams), distributed across three level II ecoregions in central Canada and compared their metabolomes. We found ecoregion and stream origin were poor predictors of crayfish metabolomes. This result suggests crayfish metabolomes were similar, despite differing environmental conditions. Metabolomes of crayfish collected from three stream sites exposed to agricultural activity and municipal wastewater (i.e., test sites) were then compared to the crayfish metabolomes from the seven reference streams. Findings showed that crayfish metabolomes from test sites were strongly differentiated from those at all reference sites. The consistency in the northern crayfish metabolome at the studied reference streams indicates that a single reference condition may effectively detect impacts of human activities across the sampled ecoregions.

Co-exposure to UV-aged microplastics and cadmium induces intestinal toxicity and metabolic responses in earthworms

Aged microplastics (MPs) alter the interaction with heavy metals due to changes in surface properties. However, the combined toxicological effects of aged MPs on heavy metals in soil remain poorly understood. In this study, earthworms were employed as model animals to investigate the effects of aged MPs on the biotoxicity of cadmium (Cd) by simulating the exposure patterns of original and UV-aged MPs (polylactic acid (PLA) and polyethylene (PE)) with Cd. The results showed that UV-aging decreased the zeta potential and increased the specific surface area of the MPs, which enhanced the bioaccumulation of Cd and caused more severe oxidative stress to earthworms. Meanwhile, the earthworm intestines exhibited increased tissue damage, including chloragogenous tissue congestion lesions, and typhlosole damage. Furthermore, the combined exposure to UV-aged MPs and Cd enhanced the complexity of the microbial network in the earthworm gut and interfered with endocrine disruption, membrane structure, and energy metabolic pathways in earthworms. The results emphasized the need to consider the degradation of MPs in the environment. Hence, we recommend that future toxicological studies use aged MPs that are more representative of the actual environmental conditions, with the results being important for the risk assessment and management of MPs.

Pollution Status and Associated Risk Assessment of Heavy Metals in Sewage Sludge in the Yangtze River Delta, China

The risk assessment of heavy metals (HMs) in sewage sludge (SS) is essential before land application. Six HMs in nineteen SS collected in the Yangtze River Delta were analyzed to assess risks to environment, ecosystem, and human health. HMs concentrations were ranked in the order of Zn > Cu > Cr > Ni > Pb > Cd, with Cu, Zn, and Ni in a total of 16% of samples exceeding the legal standard. Zn showed greatest extractability according to EDTA-extractable concentrations. HMs in 16% of SS samples posed heavy contamination to the environment with Zn as the major pollutant. HMs in 26% of samples posed ecological risk to the ecosystem and Cd was the highest risky HM. The probabilistic health risk assessment revealed that HMs posed carcinogenic risks to all populations, but non-carcinogenic risks only to children. This work will provide fundamental information for land application of SS in this area.

The effects of polyethylene microplastics on the growth, reproduction, metabolic enzymes, and metabolomics of earthworms Eisenia fetida

The existing data regarding the effects of polyethylene (PE) microplastics (MPs) smaller than 5 mm in size on earthworms are insufficient to fully comprehend their toxicity. In this study, earthworms Eisenia fetida were exposed to artificially added PE at a concentration ranging from 0.05 to 20 g/kg soil (0.005%-2%) for 60 days to determine the concentration range causing negative effects on earthworms and to uncover the potential toxic mechanisms. The individual growth, reproduction, and metabolic enzyme activities, including phase I enzymes (cytochrome P450 [CYP] 1A2, 2B6, 2C9, and 3A4), and phase II metabolic enzymes (superoxide dismutase (SOD), catalase (CAT), and glutathione sulfotransferase (GST)), and metabolomics were measured. The observed variations in responses of multiple cross-scale endpoints indicated that individual indices are less responsive to PE MPs than metabolic enzymes or metabolomics. Despite the absence of significant alterations in growth inhibition based on body weight, PE MPs at concentrations equal to or exceeding 2.5 g/kg were found to exert a toxic effect on earthworms, which was evidenced by significant changes in metabolic enzyme activities (CYP1A2, 2B6, 2C9, and 3A4, SOD, CAT, and GST) and important small molecule metabolites screened based on metabolomics, likely due to the bioaccumulation of PE. The toxicity of PE MPs to earthworms is inferred to be associated with neurotoxicity, oxidative damage, decreased detoxification capacity, energy metabolism imbalance, and impaired amino acid and purine metabolism due to bioaccumulation. The findings of this study will enhance our understanding of the molecular toxicity mechanisms of PE MPs and contribute to a more accurate assessment of the ecological risks posed by PE MPs in soil.

Blockage of ATPase-mediated energy supply inducing metabolic disturbances in algal cells under silver nanoparticles stress

Adenosine triphosphate (ATP) generation of aquatic organisms is often subject to nanoparticles (NPs) stress, involving extensive reprogramming of gene expression and changes in enzyme activity accompanied by metabolic disturbances. However, little is known about the mechanism of energy supply by ATP to regulate the metabolism of aquatic organisms under NPs stress. Here, we selected extensively existing silver nanoparticles (AgNPs) to investigate their implications on ATP generation and relevant metabolic pathways in alga (Chlorella vulgaris). Results showed that ATP content significantly decreased by 94.2% of the control (without AgNPs) in the algal cells at 0.20 mg/L AgNPs, which was mainly attributed to the reduction of chloroplast ATPase activity (81.4%) and the downregulation of ATPase-coding genes atpB and atpH (74.5%-82.8%) in chloroplast. Molecular dynamics simulations demonstrated that AgNPs competed with the binding sites of substrates adenosine diphosphate and inorganic phosphate by forming a stable complex with ATPase subunit beta, potentially resulting in the reduced binding efficiency of substrates. Furthermore, metabolomics analysis proved that the ATP content positively correlated with the content of most differential metabolites such as D-talose, myo-inositol, and L-allothreonine. AgNPs remarkably inhibited ATP-involving metabolic pathways, including inositol phosphate metabolism, phosphatidylinositol signaling system, glycerophospholipid metabolism, aminoacyl-tRNA biosynthesis, and glutathione metabolism. These results could provide a deep understanding of energy supply in regulating metabolic disturbances under NPs stress.

Responses and detoxification mechanisms of earthworm Amynthas hupeiensis to metal contaminated soils of North China

Metal contamination is widespread, but only a few studies have evaluated the toxicological risks of metals (Cd, Cu, and Pb) in earthworms from farmlands in North China (Hebei province). Amynthas hupeiensis, the dominant species in the study area, was used to determine the responses and detoxification mechanisms of uncontaminated (CK), and low (LM)-, and high (HM)-metal-contaminated soils following 7-, 14-, and 28-days exposure. Metal toxicity in LM and HM soils inhibited the biomass of A. hupeiensis. The concentrations of Cd in A. hupeiensis bodies indicated accumulated Cd appeared to remain steady with prolonged exposure, while Cu/Pb increased significantly with soil levels. Bioaccumulation occurred in the order Cd > Pb > Cu in LM soil, and in the order Cd > Cu ≈ Pb in HM soil, which was attributed to differences in available fractions between LM and HM soils. Physiological levels of biomarkers in A. hupeiensis were determined, including total protein (TP), glutathione (GSH), glutathione peroxidase (GPx), acetylcholinesterase (AChE), and malondialdehyde (MDA). Deviations in GSH, GPx, and AChE were considered to denote sensitive biomarkers using the IBRv2 index. Metabolomics data (1H nuclear magnetic resonance-based) revealed changes in metabolites following 28-days exposure to LM and HM soils. Differences in metabolism in A. hupeiensis following exposure to LM and HM were related to energy metabolism, amino acid biosynthesis, glycerophospholipid metabolism, inositol phosphate metabolism, and glutathione metabolism. Metal stress from LM and HM soils disturbed osmoregulation, resulting in oxidative stress, destruction of cell membranes and inflammation, and altered levels of amino acids required for energy by A. hupeiensis. These findings provide biochemical insights into the physiological and metabolic mechanisms underlying the ability of A. hupeiensis to resist metal stress, and for assessing the environmental risks of metal-contaminated soils in farmland in North China.

Toxicity of ionic liquids against earthworms (Eisenia fetida)

Ionic liquids (ILs) are widely used in frontier fields because of their highly tunable properties. Although ILs may have adverse effects on organisms, few studies have focused on their effect on earthworm gene expression. Herein we investigated the toxicity mechanism of different ILs towards Eisenia fetida using transcriptomics. Earthworms were exposed to soil containing different concentrations and types of ILs, and behavior, weight, enzymatic activity and transcriptome were analyzed. Earthworms exhibited avoidance behavior towards ILs and growth was inhibited. ILs also affected antioxidant and detoxifying enzymatic activity. These effects were concentration and alkyl chain length-dependent. Analysis of intrasample expression levels and differences in transcriptome expression levels showed good parallelism within groups and large differences between groups. Based on functional classification analysis, we speculate that toxicity mainly occurs through translation and modification of proteins and intracellular transport functions, which affect protein-related binding functions and catalytic activity. KEGG pathway analysis revealed that ILs may damage the digestive system of earthworms, among other possible pathological effects. Transcriptome analysis reveals mechanisms that cannot be observed by conventional toxicity endpoints. This is useful to evaluate the potential environmental adverse effects of the industrial use of ILs.

Changes in Gut Microbiota Structure: A Potential Pathway for Silver Nanoparticles to Affect the Host Metabolism

Silver nanoparticles (AgNPs) are one of the most widely used NPs. Their adverse effects on either the host or its gut microbiota (GM) have been examined. Nevertheless, whether the GM plays any role in AgNP toxicity to the host remains unclear. In the present study, AgNPs were administered to mice by oral gavage once a day for 120 days. A significant dose-dependent accumulation of Ag in the liver was observed, with a steady state reached within 21 days. The AgNPs changed the structure of the GM, mainly with respect to microorganisms involved in the metabolism of energy, amino acids, organic acids, and lipids, as predicted in a PICRUST analysis. Effects of the AgNPs on liver metabolism were also demonstrated, as a KEGG pathway analysis showed the enrichment of pathways responsible for the metabolism of amino acids, purines and pyrimidine, lipids, and energy. More interestingly, the changes in GM structure and liver metabolism were highly correlated, evidenced by the correlation between ∼23% of the differential microorganisms at the genus level and ∼60% of the differential metabolites. This implies that the metabolic variations in liver as affected by AgNPs were partly attributable to NP-induced changes of GM structure. Therefore, our results demonstrate the importance of considering the roles of GM in the toxicity of NPs to the host in evaluations of the health risks of NPs.

Effects of multi-walled carbon nanotubes in soil on earthworm growth and reproduction, enzymatic activities, and metabolomics

Increased production and environmental release of multi-walled carbon nanotubes (MWCNTs) increase soil exposure and potential risk to earthworms. However, MWCNT toxicity to earthworms remains unclear, with some studies identifying negative effects and others negligible effects. In this study, to determine whether exposure to MWCNTs negatively affects earthworms and to elucidate possible mechanisms of toxicity, earthworms were exposed to sublethal soil concentrations of MWCNTs (10, 50, and 100 mg/kg) for 28 days. Earthworm growth and reproduction, activities of cytochrome P450 (CYP) isoforms (1A2, 2C9, and 3A4) and antioxidant enzymes (superoxide dismutase (SOD), catalase (CAT), and glutathione-s-transferase (GST)), and metabolomics were determined. Effects of MWCNTs on earthworms depended on exposure concentration. Exposure to MWCNTs did not significantly affect growth and reproduction of individual earthworms. Exposure to 50 mg/kg MWCNTs significantly increased activities of CYP2C9, CYP3A4, SOD, CAT, and GST but clearly reduced levels of L-aspartate, L-asparagine, and glutamine. With exposure to 100 mg/kg MWCNTs, toxic effects on earthworms were observed, with significant inhibition in activities of CYP isoenzymes and SOD, significant reductions in L-aspartate, L-asparagine, glutamine, and tryptophan, and simultaneous accumulations of citrate, isocitrate, fumarate, 2-oxoglutarate, pyruvate, D-galactose, carbamoyl phosphate, formyl anthranilate, hypoxanthine, and xanthine. Results suggest that toxicity of MWCNTs to earthworms is associated with reduced detoxification capacity, excessive oxidative stress, and disturbance of multiple metabolic pathways, including amino acids metabolism, the tricarboxylic acid cycle, pyruvate metabolism, D-galactose metabolism, and purine metabolism. The study provides new insights to better understand and predict the toxicity of MWCNTs in soil.

Effects of ecotoxicity of penoxsulam single and co-exposure with AgNPs on Eisenia fetida

Penoxsulam (PNX) and silver nanoparticles (AgNPs) are likely to coexist in soils due to continuous use. However, the ecotoxicity of PNX in earthworms and the effect of AgNPs on PNX toxicity are unknown. Therefore, the toxicity of PNX (0.05, 0.5, and 2.5 mg/kg) single and co-exposure with AgNPs (10 mg/kg) after 28 and 56 days on Eisenia fetida (E. fetida) was investigated from biochemical, genetic, histopathological, and transcriptomic aspects. The results showed that the low concentration of PNX (0.05PNX) had almost no effect on the biochemical level of E. fetida. However, the addition of AgNPs resulted in 0.05PNX causing E. fetida to produce excessive reactive oxygen species, and the activity of antioxidant and detoxification enzymes were interfered, resulting in lipid peroxidation and DNA damage. From the genetic level, even the lowest concentration of PNX can significantly interfere with the expression of functional genes, thus inducing oxidative stress and apoptosis and inhibited reproductive behavior in E. fetida. The integrated biomarker response results at the biochemical and genetic levels showed that the comprehensive toxicity of PNX and PNX + AgNPs on E. fetida was PNX dose-dependent. And the toxicity of all co-exposure groups was greater than that of the PNX only exposure groups. Furthermore, the addition of AgNPs significantly increased the damage of PNX on E. fetida intestinal tissue. Meanwhile, transcriptomic analysis showed that PNX + AgNPs had a greater effect on E. fetida than PNX single, and multiple pathways related to oxidative stress, inflammation, and cellular process regulation were disturbed. These results provide a basis for comprehensive evaluation of the ecotoxicity of PNX and confirm that the AgNPs does increase the ecotoxicity of PNX in soil environment.

Earthworm half-pipe assay: A new alternative in vivo skin corrosion test using invertebrates

As a result of the efforts to introduce the principle of the 3Rs (replacement, reduction, and refinement) into animal testing, alternative in vitro skin corrosion test methods have been developed and standardized globally. However, alternative in vitro skin corrosion test methods have some limitations in terms of the use of humanely killed rats or commercial models and kits. The present study focused on the applicability of invertebrates as alternative in vivo skin models. Even though earthworm skin comprises the same biomolecules as human skin, the possibility of using earthworm skin as an alternative for skin testing remains unexplored. In this study, we developed a half-pipe tool for earthworm skin corrosion testing and optimized the test protocol. Subsequently, the applicability of the earthworm half-pipe assay for corrosion testing with six chemicals, including inorganic acids, organic acids, and alkalis, was investigated using stereomicroscopy and electron microscopy. It was observed that the specific concentrations for earthworm skin corrosion were lower than those for animal or in vitro tests. Therefore, the sensitivity of the earthworm half-pipe assay indicates that it could be useful as a screening tool before conducting in vivo animal tests or in vitro skin tests. This new method can contribute to research on alternative skin corrosion tests by reducing ethical issues, time, and cost while achieving effective results.