Effect of phenanthrene on the biological characteristics of earthworm casts and their relationships with digestive and anti-oxidative systems

Cadmium and pyrene in the soil modify the properties of earthworm-mediated soil

Earthworms are pivotal in soil ecosystems due to their crucial role in shaping soil characteristics through casts and burrow walls. Previous research has predominantly focused on the direct impact of soil pollution on live earthworms, overlooking the subsequent effects on earthworm-mediated soil, such as casts and burrow walls. Using 2D-terraria as incubation containers and the geophagous earthworm species Metaphire guillelmi, this study assessed the change in various properties of earthworm-mediated soil in both uncontaminated soils and Cd- and Pye-contaminated soils. Overall, both Cd and Pye overall improved the ammonium nitrogen (NH4+-N), Olsen's phosphorus (Olsen-P) levels, and invertase and catalase activities while decreasing catalase activities in earthworm-mediated soil. They also fluctuating affected the pH, soil organic matter (SOM) content, soil urease, alkaline phosphatase activities, and microbial functional genes in the cast and burrow walls. These results indicated that earthworms remained crucial "ecosystem engineers" even in polluted soil. Additionally, differences were observed in the responses of properties between casts and burrow walls, showing unequal contributions of transit-through-gut and burrowing processes to soil modification. Specifically, transit-through-gut was found to have a more significant influence on soil NH4+-N and Olsen-P content compared to burrowing behavior. Regarding the pattern of microbial functional genes in earthworm-associated compartments, results revealed that they differed significantly in casts from those in bulk soil and burrow walls under unpolluted conditions, with pollution-enhancing disparities among compartments. Furthermore, NH4+-N and Olsen-P content, urease, and catalase activities in burrow walls and/or casts were identified as potential biomarkers for soil pollution, exhibiting a clear dose-effect relationship. Developing such biomarkers could address ethical concerns related to conventional earthworm biomarkers that require sacrificing earthworms. This study provides insights into the consequences of soil pollution on earthworm-mediated soil components, highlighting the importance of considering the indirect effects of contaminants on soil ecosystems.

Combined effects of cadmium and sulfamethoxazole on Eisenia fetida: Insights into accumulation, subcellular partitioning, biomarkers and toxicological responses

Cadmium (Cd) and sulfamethoxazole (SMX) frequently coexist in farmlands, yet their synergistic toxicological impacts on terrestrial invertebrates remain unexplored. In this study, earthworms were exposed to artificial soils percolated with Cd (5 mg/kg), SMX (5 mg/kg) or combination of them for 7 days, followed by a 12-day elimination phase in uncontaminated soil. The uptake of Cd and SMX by the earthworms, along with their subcellular distribution, was meticulously analyzed. Additionally, a suite of biomarkers-including superoxide dismutase (SOD), catalase (CAT), malondialdehyde (MDA), and weight loss-were evaluated to assess the health status of the earthworms and the toxicological effects of the Cd and SMX mixture. Notably, the cotreatment with Cd and SMX resulted in a significantly higher weight loss in Eisenia fetida (41.25 %) compared to exposure to Cd alone (26.84 %). Moreover, the cotreatment group exhibited substantially higher concentrations of Cd in the total internal body, fraction C (cytosol), and fraction E (tissue fragments and cell membranes) in Eisenia fetida compared to Cd alone counterparts. The combined exposure also significantly elevated the SMX levels in the total body and fraction C compared with the SMX-only treated earthworms. Additionally, Eisenia fetida subjected to the combined treatment showed markedly increased activities of SOD, CAT, and MDA compared to those treated with Cd alone. The effect addition indices (EAIs), ranging from 1.00 to 2.23, unequivocally demonstrated a synergistic effect of the combined treatments. Interestingly, relocating the earthworms to clean soil did not mitigate the observed adverse effects. These findings underscore the increased risk posed by the Cd-SMX complex to terrestrial invertebrates in agricultural areas.

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.

Combined inhibitory effects of microcystin-LR and microcystin-RR on growth and development in zebrafish larvae

Microcystins (MCs) are the most widespread, frequently found, and seriously toxic cyanobacterial toxins in aquatic environments. Microcystin-leucine-arginine (MCLR) and microcystin-arginine-arginine (MCRR) are the most studied MCs. Normally, their levels are low and they coexist in the environment; however, they may also interact with each other. The developmental toxicity of MCLR in the presence of MCRR in the early life stage of zebrafish (from 2 to 120 h post fertilization) was investigated for the first time in this study. Our findings revealed that MCRR treatment marginally elevated thyroxine (T4) and 3,5,3'-triiodothyronine (T3) levels, whereas MCLR treatment alone resulted in a significant increase in T3 and T4 levels, indicating a cooperative effect. Furthermore, clear changes in the expression levels of genes involved in growth and development, accompanied by growth inhibition, were observed after co-treatment with MCRR and MCLR. In addition, zebrafish larvae subjected to MCRR and/or MCLR treatment showed increased levels of superoxide dismutase, glutathione, and malondialdehyde, and decreased levels of catalase in the MCRR + MCLR group, indicating oxidative stress and lipid peroxidation. Thus, we investigated the synergistic developmental toxicity of MCRR and MCLR during the early life stages of zebrafish development.

Butyl benzyl phthalate exposure impact on the gut health of Metaphire guillelmi

Agricultural films are extensively utilized in high-intensity agriculture, with China's annual usage reaching 1.5 million tons. Unfortunately, the recovery rate is less than 60%, leading to an inevitable accumulation of plastic mulch in agricultural soils. This accumulation primarily introduces butyl benzyl phthalate (BBP) into soil ecosystems, whose specific effects remain largely unclear, thereby posing potential risks. The present study focuses on the exposure impact of BBP on earthworms, Metaphire guillelmi, a commonly found endogenic earthworm within real farmland, as it provides insight into the direct interaction between biota gut health and contaminants. Specifically, we studied the biomarkers related to oxidative stress, the digestive system, and neurotoxicity within the gut of Metaphire guillelmi, and the integrated biological response (IBR) index was utilized to track these markers at different timeframes after BBP exposures. Our findings indicate that BBP exposures lead to oxidative damage, digestive system inhibition, and neurotoxicity, with IBR indexes of 14.6 and 17.3 on the 14th and 28th days, respectively. Further, the underlying mechanisms at a molecular level through molecular docking were investigated. The results showed that the most unstable interaction was with the Na+K+-ATPase (binding energy: -2.25 kcal-1), while BBP displayed stable bonds with superoxide dismutase and 8-hydroxydeoxyguanosine via hydrogen bonds and hydrophobic interaction. These interactions resulted in changes in protein conformation and their normal physiological functions, offering new insights into the molecular mechanism underlying enzymatic activity changes. This study has significant implications for the prediction of toxicity, environmental risk assessment, and the establishment of regulations related to BBP.

Combination of Biochar and Trichoderma harzianum Can Improve the Phytoremediation Efficiency of Brassica juncea and the Rhizosphere Micro-Ecology in Cadmium and Arsenic Contaminated Soil

Phytoremediation is an environment-friendly method for toxic elements remediation. The aim of this study was to improve the phytoremediation efficiency of Brassica juncea and the rhizosphere soil micro-ecology in cadmium (Cd) and arsenic (As) contaminated soil. A field experiment was conducted with six treatments, including a control treatment (CK), two treatments with two contents of Trichoderma harzianum (T1: 4.5 g m-2; T2: 9 g m-2), one biochar treatment (B: 750 g m-2), and two combined treatments of T1B and T2B. The results showed Trichoderma harzianum promoted the total chlorophyll and translocation factor of Brassica juncea, while biochar promoted plant biomass compared to CK. T2B treatment showed the best results, which significantly increased Cd accumulation by 187.49-308.92%, and As accumulation by 125.74-221.43%. As a result, the soil's total Cd content was reduced by 19.04% to 49.64% and total As contents by 38.76% to 53.77%. The combined amendment increased the contents of soil available potassium, phosphorus, nitrogen, and organic matter. Meanwhile, both the activity of glutathione and peroxidase enzymes in plants, together with urease and sucrase enzymes in soil, were increased. Firmicutes (dominant bacterial phylum) and Ascomycota (dominant fungal phylum) showed positive and close correlation with soil nutrients and plant potentially toxic elements contents. This study demonstrated that phytoremediation assisted by biochar and Trichoderma harzianum is an effective method of soil remediation and provides a new strategy for enhancing plant remediation efficiency.

Enhanced removal of phenanthrene and nutrients in wetland sediment with metallic biochar: Performance and mechanisms

Polycyclic aromatic hydrocarbon (PAHs) are persistent organic pollutants and pose high risk in aquatic environment. The utilization of biochar is a strategy for PAHs-contaminated remediation but is challenging due to the adsorption saturation and reoccurrence of PAHs desorbed back into water. In this study, iron (Fe) and manganese (Mn) were provided as electron acceptors for biochar modification to enhance anaerobic biodegradation of phenanthrene (Phe). Results revealed that, the Mn(Ⅳ) and Fe(Ⅲ) modification improved the removal of Phe by 24.2% and 31.4% than that of biochar, respectively. Additionally, nitrate removal was improved by 19.5% with Fe(Ⅲ) amendment. The Mn-and Fe-biochar decreased Phe contents by 8.7% and 17.4% in sediment, 10.3% and 13.8% in biochar than that of biochar. Much higher DOC contents were observed with Mn- and Fe-biochar, which provided bioavailable carbon source for microbes and contributed to microbial degradation of Phe. The greater degree of humification, higher proportions of humic and fulvic acid like components in metallic biochar participated in electron transport and further enhancing the degradation of PAHs. Microbial analysis proved the high abundance of Phe-degrading bacteria (e.g. PAH-RHD_α, Flavobacterium and Vibrio), nitrogen removal microbes (e.g. amoA, nxrA, and nir), Fe and Mn bioreduction or oxidation (e. g. Bacillus, Thermomonas, Deferribacter) with metallic biochar. Based on the results, the Fe and Mn modification, especially Fe-modified biochar provided well performance for PAHs removal in aquatic sediment.

How does the internal distribution of microplastics in Scylla serrata link with the antioxidant response in functional tissues?

Crabs can live in diverse lifestyles in both water and benthic environments, which are the basin of microplastics (MPs) inputs. Edible crabs with large consuming quantity, e.g., Scylla serrata were subjected to accumulate MPs in their tissues from surrounding environments and generate biological damages. However, no related research has been conducted. In order to accurately assess the potential risks to both crabs and humans consuming MPs contaminated crabs, S. serrata were exposed to different concentrations (2, 200 and 20,000 μg/L) of polyethylene (PE) microbeads (10-45 μm) for 3 days. The physiological conditions of crabs and a series of biological responses, including DNA damage, antioxidant enzymes activities and their corresponding gene expressions in functional tissues (gills and hepatopancreas) were investigated. PE-MPs accumulated in all tissues of crabs with concentration- and tissue-dependent manner, which was assumed to be via the internal distribution initialized by gills' respiration, filtration and transportation. Significantly increased DNA damages were observed in both gills and hepatopancreas under exposures, however, the physiological conditions of crabs showed no dramatic alterations. Under low and middle concentration exposures, gills energetically activated the first line of antioxidant defense to against oxidative stress, e.g., superoxide dismutase (SOD) and catalase (CAT), but lipid peroxidation damage still occurred under high concentration exposure. In comparison, SOD and CAT composed antioxidant defense in hepatopancreas tended to collapse under severe MPs exposure and the defense mechanism attempted to switch to the secondary antioxidant response by compensatively stimulating the activities of glutathione S-transferase (GST), glutathione peroxidase (GPx) and the content of glutathione (GSH). The diverse antioxidant strategies in gills and hepatopancreas were proposed to be closely related to the accumulation capacity of tissues. The results confirmed the relation between PE-MPs exposure and antioxidant defense in S. serrata, and will help to clarify the biological toxicity and corresponding ecological risks.

Effects of secondary release of chromium and vanadium on soil properties, nutrient cycling and bacterial communities in contaminated acidic paddy soil

Although the contamination situation of chromium (Cr) and vanadium (V) have been revealed, the effects of their re-release on ecological risk in contaminated acidic paddy soil are unclear. To evaluate the effects, we assigned soil microcosms across three different concentration (100, 200, 300 mg/L) and introduced Cr and V alone or combination into an already slightly contaminated acidic soil. We found that Cr and V alone or interacted to increased soil bioavailable-metals, changed soil properties and nutrients to varying degrees. Meanwhile, soil ammoniacal nitrogen (NH₄⁺-N) and nitrate nitrogen (NO₃^--N) contents, nitrogen (N) -cycling enzyme activities, microbial mass N were significantly influenced by Cr addition. Which demonstrated that Cr re-release may disturb soil N cycle. However, V alone significantly improved soil NO₃^--N contents, cellulase and dehydrogenase activities, soil respiration intensity and microbial mass carbon: nitrogen. Meanwhile, V addition also decreased bacterial diversity while Cr addition increased bacterial diversity and shaped new bacterial community, some V(V) and Cr (VI) reducing bacteria were identified. Heatmap of Pearson correlation and Redundancy analysis showed that NH₄⁺-N, NO₃^--N, Potassium, Phosphorus, and Cr played an important role in bacterial community structure. These findings suggested that re-release of Cr and V disturbed soil function and raised ecological risks, and the power to destroy the ecosystem stability originated from Cr was much stronger than V. This study was contributed to understand the effects of Cr and V re-release on microecology in contaminated acidic agricultural soil.

Heat stress delays detoxification of phenanthrene in the springtail Folsomia candida

Climate change has intensified the occurrence of heat waves, resulting in organisms being exposed to thermal and chemical stress at the same time. The effects of mild heat shock combined with sublethal concentrations of phenanthrene (PHE) on defense mechanisms in springtails Folsomia candida were investigated. The transcription of Heat Shock Protein 70 (HSP70) was significantly upregulated by heat shock but tended to reach the control levels after 42 h of recovery. The transcription of cytochrome P450 3A13 (CYP3A13) was upregulated 3-13 fold by PHE but suppressed by heat shock. The suppression by heat shock might contribute to the reduced detoxification of PHE during high-temperature exposure. In line with this, we found that the internal PHE concentration was approximately 70% higher in heat-shocked springtails than in animals kept at control temperature. In general, the transcription of genes encoding enzymes of detoxification phase Ⅱ (glutathione S-transferase 3) and phase Ⅲ (ABC transporter 1) and the activity of antioxidant defense enzymes (superoxide dismutase and catalase) were less influenced than genes encoding phase I detoxification mechanisms (CYP3A13). These results indicate that heat shock delays the detoxification of PHE in springtails.

Adverse effects of microplastics on earthworms: A critical review

Microplastics are widely distributed in terrestrial environments and have been known to adversely affect earthworms. Based on 65 publications, we summarized the effects of microplastics on the growth, behavior, oxidative responses, gene expression, and gut microbiota of earthworms. Since microplastics are often present simultaneously with other pollutants, especially heavy metals and hydrophobic organic chemicals (HOCs), the interactions and combined effects of microplastics and these pollutants on earthworms have also been discussed. It has been shown that earthworms can selectively ingest microplastics, preferring to those with smaller particle size (especially smaller than 50 μm) and biodegradable compositions. Generally, microplastics with higher concentrations (especially those > 0.5%, w/w) and smaller sizes (e.g., 100 nm) have greater adverse effects on earthworms. Additionally, microplastics can facilitate the accumulation of heavy metals and organic pollutants by earthworms and pose severer damages. Current knowledge gaps and perspectives for future work are pointed out.

Effects of polyethylene, polyvinyl chloride, and polystyrene microplastics on the vermitoxicity of fluoranthene in soil

Polycyclic aromatic hydrocarbons (PAHs) and microplastics (MPs) may coexist in soil. Consequently, the toxicity of PAHs to "soil engineers" earthworms (vermitoxicity), may be influenced by various MPs. However, studies on this issue are scarce. In particular, the differential effect of MPs of different polymers on the vermitoxicity of PAHs remains unclear. Therefore, a series of microcosm experiments were conducted to evaluate the potential vermitoxicity of fluoranthene (Fla) in the presence of polyethylene (PE), polyvinyl chloride (PVC), and polystyrene (PS) MPs at an environmentally relevant concentration (125 mg kg^-1). The results indicated that Fla exerted vermitoxicity and MPs enhanced the adverse effects. Specifically, after the introduction of MPs, the 14-d LC₅₀s of Fla on earthworms decreased from 130.9 to 98.0-123.6 mg kg^-1; in addition, the growth inhibition rates improved from 5.37%-15.34% to 15.63%-33.38%, and the avoidance rate increased by 10%-100% at the same exposure doses in most cases. In most cases, the neutral red retention time was shortened by 14.3%-47.9%, indicating that the integrity of the coelomocytes' lysosomal membrane had worsened. The affected antioxidant enzyme activity and improved malondialdehyde content indicated enhanced oxidative damage in the treatments containing MPs. However, the aggravation of the vermitoxicity varied by MPs type and toxicological endpoints. Overall, Fla + PS MPs exerted the greatest effect on the mortality of earthworms. On the contrary, PVC and PE MPs exhibited higher subacute effects on the vermitoxicity of Fla. Our study also demonstrated that MPs at environmentally relevant doses may directly induce vermitoxicity. In particular, damaged coelomocytes' lysosomal membrane stability by MPs was second reported to the best of our knowledge. Our results revealed the differences in the effects of various MPs on the vermitoxicity of PAHs, which provides new data in assessing the ecological effects of PAHs and MPs in soils.

Size effects of polystyrene microplastics on the accumulation and toxicity of (semi-)metals in earthworms

Microplastics (MPs) are plastic fragments less than 5 mm, which may have adverse impacts on organisms. In this study, we investigated the impacts and mechanisms of polystyrene MPs (10 μm and 100 μm) and nanoplastics (NPs, 100 nm) with different concentrations (10 mg/kg and 100 mg/kg) in soil on the uptake of metal Cd and semi-metal As in earthworms, Eisenia fetida. MPs facilitated the accumulation of (semi-)metals via damaging the integrity of earthworm intestine, and earthworms accumulated more (semi-)metals in MP treatment groups than NP treatment groups, especially in group of 100 mg/kg of 10 μm MP with concentrations of 1.13 mg/kg and 32.7 mg/kg of Cd and As, respectively. Higher genotoxicity to earthworms was observed for MPs than NPs. Antioxidant enzymes activity and their mRNA gene relative expression levels indicated that MPs with high concentration induced severer damage to earthworms, thus resulting in the increased accumulation of (semi-)metals by earthworms. In addition, proteomic and metabolomic analysis revealed that MPs (100 ppm of 10 μm) disturbed the earthworm immune and metabolic systems, resulting in the highest accumulation of (semi-)metals in earthworms. This study clarifies the influence mechanisms of MPs with different sizes and levels on the accumulation of (semi-)metals by terrestrial invertebrates.

Effects of fluoranthene on digestive enzymes activity and relative growth rate of larvae of lepidopteran species, Lymantria dispar L. and Euproctis chrysorrhoea L

Fluoranthene is one of the most abundant polycyclic aromatic hydrocarbon pollutants in the environment and it may accumulate in plant leaves which are the main food source for phytophagous insect species. The aim of this study was to establish the effects of dietary fluoranthene on specific activities of digestive enzymes and expression of their isoforms in the midgut, and the relative growth rates of Lymantria dispar and Euproctis chrysorrhoea larvae. Exposure to fluoranthene led to significantly decreased trypsin activity in the midgut of larvae of both species. Leucine aminopeptidase activity decreased significantly in the midgut of L. dispar larvae exposed to the lower concentration of fluoranthene, but that enzyme activity showed the opposite trend in E. chrysorrhoea larvae. There was no pollutant induced changes in lipase activity in L. dispar, while elevated enzyme activity was recorded in the midgut of E. chrysorrhoea larvae exposed to the lower concentration of fluoranthene. Different patterns of expression of enzyme isoforms were noticed. Relative growth rates of both species significantly decreased in fluoranthene treated larvae. These responses indicate to the significance of relationships between physiological changes and fitness-related traits in L. dispar and E. chrysorrhoea larvae affected by pollutant, and contribute to understanding the mechanisms of their adjustment to stressful conditions.

Remediation of soils and sediments polluted with polycyclic aromatic hydrocarbons: To immobilize, mobilize, or degrade?

Polycyclic aromatic hydrocarbons (PAHs) are generated due to incomplete burning of organic substances. Use of fossil fuels is the primary anthropogenic cause of PAHs emission in natural settings. Although several PAH compounds exist in the natural environmental setting, only 16 of these compounds are considered priority pollutants. PAHs imposes several health impacts on humans and other living organisms due to their carcinogenic, mutagenic, or teratogenic properties. The specific characteristics of PAHs, such as their high hydrophobicity and low water solubility, influence their active adsorption onto soils and sediments, affecting their bioavailability and subsequent degradation. Therefore, this review first discusses various sources of PAHs, including source identification techniques, bioavailability, and interactions of PAHs with soils and sediments. Then this review addresses the remediation technologies adopted so far of PAHs in soils and sediments using immobilization techniques (capping, stabilization, dredging, and excavation), mobilization techniques (thermal desorption, washing, electrokinetics, and surfactant assisted), and biological degradation techniques. The pros and cons of each technology are discussed. A detailed systematic compilation of eco-friendly approaches used to degrade PAHs, such as phytoremediation, microbial remediation, and emerging hybrid or integrated technologies are reviewed along with case studies and provided prospects for future research.

Toxic mechanism on phenanthrene-induced cytotoxicity, oxidative stress and activity changes of superoxide dismutase and catalase in earthworm (Eisenia foetida): A combined molecular and cellular study

Phenanthrene (PHE) is an important organic compound, which is widespread in the soil environment and exhibits potential threats to soil organisms. Toxic effects of PHE to earthworms have been extensively studied, but toxic mechanisms on PHE-induced cytotoxicity and oxidative stress at the molecular and cellular levels have not been reported yet. Therefore, we explored the cytotoxicity and oxidative stress caused by PHE in earthworm coelomocytes and the interaction mechanism between PHE and the major antioxidant enzymes SOD/CAT. It was shown that high-dose PHE exposure induced the intracellular reactive oxygen species (ROS) generation, mediated lipid peroxidation, reduced total antioxidant capacity (T-AOC) in coelomocytes, and triggered oxidative stress, thus resulted in a strong cytotoxicity at higher concentrations (0.6-1.0 mg/L). The intracellular SOD/CAT activity in cells after PHE exposure were congruent with that in molecular levels, which the activity of SOD enhanced and CAT inhibited. Spectroscopic studies showed the SOD/CAT protein skeleton and secondary structure, as well as the micro-environment of aromatic amino acids were changed after PHE binding. Molecular docking indicated PHE preferentially docked to the surface of SOD. However, the key residues Tyr 357, His 74, and Asn 147 for activity were in the binding pocket, indicating PHE more likely to dock to the active center of CAT. In addition, H-bonding and hydrophobic force were the primary driving force in the binding interaction between PHE and SOD/CAT. This study indicates that PHE can induce cytotoxicity and oxidative damage to coelomocytes and unearthes the potential effects of PHE on earthworms.

Polystyrene microplastics impact the occurrence of antibiotic resistance genes in earthworms by size-dependent toxic effects

Microplastics (MPs) and antibiotic resistance genes (ARGs) are two classes of emerging and prevalent contaminants in terrestrial environments. To date, effects of MPs on the occurrence of ARGs in terrestrial invertebrates remain uncertain. Here we exposed earthworms to a soil amended with polystyrene MPs at two environmentally relevant concentrations to elucidate the occurrence and mechanisms of ARGs in earthworms impacted by MPs with different sizes. Nano-size and 10 mg/kg of 100 µm MPs slightly affected the occurrence of ARGs in earthworms. Highest abundance of ARGs was found in the presence of 10 mg/kg of 10 µm MPs, whereas 100 mg/kg of 10 µm MPs significantly changed the profile of ARGs. Metagenomics sequencing and toxicity tests indicated that MPs caused toxicity and influenced the abundance of microbial community in earthworms, resulting in the changes of ARGs. Results of proteomics and metabolomics demonstrated that 100 mg/kg of 10 µm MPs changed the microenvironment of earthworm gut, built a new homeostatic process, and thus increased the abundance of key bacterial that carried a variety of ARGs. This study highlights the size-dependent toxic effects of MPs and their impacts on the transfer of ARGs in terrestrial environments.

Single and combined effects of phenanthrene and polystyrene microplastics on oxidative stress of the clam (Mactra veneriformis)

Toxicity of single organic pollutants or microplastics on organisms have been reported widely, however, their combined toxicity on bivalves was rarely investigated. In this paper, single and combined effects of phenanthrene (Phe, 20 μg·L^-1 and 50 μg·L^-1) and polystyrene (PS, 17 μm and 150 μm with 1 mg·L^-1) microplastics on oxidative stress of the clam Mactra veneriformis were assayed under laboratory conditions with biomarkers including superoxide dismutase (SOD), glutathione-S-transferase (GST) and malondialdehyde (MDA). We found that Phe or PS single stress source could induce oxidative stress to clams. Besides, exposed to Phe 50 μg·L^-1 or PS 150 μm caused the reduced expression of SOD and GST activities, leading to potential oxidative injury in clams. At each Phe concentration level, the order of single and combined toxicity on clams was Phe + PS 150 μm > Phe ≈ Phe + PS 17 μm. Phe exhibited a stronger toxic effect on clams than PS. Under joint exposure stress, the toxicity influence of Phe is still dominant. Furthermore, MDA and GST could be considered the most sensitive oxidative stress biomarkers in clams under Phe or PS single and combined exposures, respectively.

Effects of biochar and thermally treated biochar on Eisenia fetida survival, growth, lysosomal membrane stability and oxidative stress

Despite its known positive impacts when added to soil, the negative effects of biochar on earthworms are not fully understood. Here, we investigated the toxicity of nine biochars of three feedstock origins, animal (cow dung), plant (corncob) and microorganism (sewage sludge), produced at three pyrolysis temperatures (350 °C, 550 °C and 750 °C) on earthworms. Vermitoxicity was first assessed using acute toxicity test, neutral red retention time (NRRT) assay and oxidative stress response assay. Furthermore, we evaluated whether the thermal treatment of biochars could reduce their vermitoxicity using an acute toxicity assay. We found that, according to LC₅₀ and earthworm weight loss, cow dung biochar was more toxic than corncob or sewage sludge biochar; thus, production feedstock is apparently important to biochar vermitoxicity. Furthermore, NRRTs indicated cow dung biochar disrupted lysosomal membrane stability in earthworm coelomocytes, providing further evidence for the toxicity of this biochar to earthworms. Disturbed antioxidant enzyme activities and elevated malondialdehyde content showed that earthworm suffer oxidative stress, also implying a potential vermitoxicity. However, thermal treatment of cow dung biochar substantially improved its LC₅₀ and decreased earthworm weight loss, implying that the PAHs in this biochar might be damage factors and that heating could reduce the potential toxicity of biochar. Besides, NRRT assay was first used to evaluate the effects of biochar on earthworms and clear dose-effect relationships indicated that NRRT assay might be a useful tool for assessing the potential negative effects of biochar. Overall, given the different effects of various biochars, including toxicity, reported here, our findings will help improve understanding of biochar vermitoxicity mechanisms, serve to improve biochar ecological risk assessments and provide a reference for the proper application of biochar amendments.

Molecular and biochemical evaluation of effects of malathion, phenanthrene and cadmium on Chironomus sancticaroli (Diptera: Chironomidae) larvae

In-vitro effects of sub-lethal concentrations of malathion, phenanthrene (Phe) and cadmium (Cd) were tested on Chironomus sancticaroli larvae in acute bioassays by measuring biochemical and molecular parameters. Malathion was evaluated at 0.001, 0.0564 and 0.1006 mg L^-1; Phe at 0.0025, 1.25 and 2.44 mg L^-1; and Cd at 0.001, 3.2 and 7.4 mg L^-1. The recovery test carried out at the highest concentration of each compound showed that survival of larvae exposed to Phe ranged from 4% to 5%, while the effects of malathion and Cd were irreversible, not allowing the emergence of adults. Results showed that malathion and Cd inhibited AChE, EST-α and ES-β activities at the two highest concentrations. Phe at 0.0025, 1.25 and 2.44 mg L^-1; and Cd at 3.2 and 7.4 mg L^-1 inhibited glutathione S-transferase activity. Oxidative stress was exclusively induced by the lowest concentration of malathion considering SOD activity once CAT was unaffected by the stressors. Lipid peroxidation was registered exclusively by malathion at the two highest concentrations, and total hemoglobin content was only reduced by Cd at the two highest concentrations. The relationship among biochemical results, examined using the PCA, evidenced that malathion and Cd concentrations were clustered into two groups, while Phe only formed one group. Four hemoglobin genes of C. sancticaroli were tested for the first time in this species, with Hemoglobin-C being upregulated by malathion. The toxicity ranking was malathion > Phe > Cd, while biochemical and molecular results showed the order malathion > Cd > Phe. Our results highlight the importance of combining different markers to understand the effects of the diverse compounds in aquatic organisms.

Size effects of microplastics on accumulation and elimination of phenanthrene in earthworms

Microplastics (MPs) are a class of emerging contaminants with diverse sizes. They influence the behavior of pollutants in the environment and cause harmful effects on organisms. To date, the size effects of MPs on the accumulation of organic pollutants by terrestrial invertebrates remain unclear. Here, we study the impacts and mechanisms of polystyrene MPs on the accumulation and elimination of phenanthrene in earthworms. Results showed that larger-size MPs (10 and 100 µm) facilitated the accumulation of phenanthrene by earthworms in the first week, whereas 100 nm MPs inhibited the elimination of phenanthrene in earthworms afterwards. Higher genotoxicity to earthworms was observed for co-exposure of micron-size MPs and phenanthrene, and 10 µm MPs were detected at the highest concentration and caused the most serious DNA damage to earthworm coelomocytes. Biomarkers and their mRNA gene expression levels suggested that larger-size MPs caused severer damage to earthworms, thus leading to increased accumulation of phenanthrene by earthworms at the beginning. Moreover, high-throughput 16S rRNA gene sequencing indicated that nano-size MPs significantly inhibited phenanthrene-degrading bacteria in earthworms, resulting in the highest residual concentration of phenanthrene. This study highlights the size effects of MPs and their impacts on the accumulation of organic pollutants by terrestrial organisms.

Toxicity assessment of Fluoranthene, Benz(a)anthracene and its mixed pollution in soil: Studies at the molecular and animal levels

An increasing amount of Fluoranthene (Fla) and Benz(a)anthracene (BaA) is being produced and used, eventually entering the soil sediments. The accumulation of Fla and BaA will cause poisoning to typical enzymes (α-Amylase) and organisms (Eisenia fetida) in soil. However, the studies about exploring and comparing the different effects of Fla, BaA and their joint effect at different levels are rarely reported. In this paper, the different effects of Fla, BaA and their mixed pollutant on α-Amylase were evaluated and compared at the molecular level, and the effect of Fla-BaA to the antioxidant system of earthworm (Eisenia fetida) was investigated from the aspects of concentration and exposure time at the animal level. The results showed that Fla-BaA had the greatest influence on the skeleton structure and the microenvironment of amino acid residue of α-Amylase compared to Fla and BaA, and in the mixed pollutant system, the joint effect mode was additive mode. The inhibitory effect of Fla-BaA on the activity of α-Amylase was also stronger than that of the system alone. The assays at the animal level showed that low concentrations (below 5 mg/kg) of Fla-BaA increased the activity of GSH-Px and SOD while high concentrations inhibited their activity. The POD that was activated throughout the experiment period suggested its key role in the earthworm antioxidant system. Changes in T-AOC and MDA showed that long-term and high-dose of Fla-BaA exposure inhibited the antioxidant capacity of Eisenia fetida, causing lipid peroxidation and damage to cells.