Exploring the bioavailability of nickel in a soil system: Physiological and histopathological toxicity study to the earthworms (Eisenia fetida)

Environmental-related doses of afidopyropen induced toxicity effects in earthworms (Eisenia fetida)

Afidopyropen has high activity against pests. However, it poses potential risks to the soil ecology after entering the environment. The toxicity of afidopyropen to earthworms (Eisenia fetida) was studied for the first time in this study. The results showed that afidopyropen had low level of acute toxicity to E. fetida. Under the stimulation of chronic toxicity, the increase of reactive oxygen species (ROS) level activated the antioxidant and detoxification system, which led to the increase of superoxide dismutase (SOD) and glutathione S-transferase (GST) activities. Lipid peroxidation and DNA damage were characterized by the increase of malondialdehyde (MDA) and 8-hydroxy-2'-deoxyguanosine (8-OHdG) contents. Meanwhile, the functional genes SOD, CAT, GST, heat shock protein 70 (HSP70), transcriptionally controlled tumor protein (TCTP), and annetocin (ANN) played a synergistic role in antioxidant defense. However, the comprehensive toxicity of high concentration still increased on the 28th day. In addition, strong histopathological damage in the body wall and intestine was observed, accompanied by weight loss, which indicated that afidopyropen inhibited the growth of E. fetida. The molecular docking revealed that afidopyrene combined with the surface structure of SOD and GST proteins, which made SOD and GST become sensitive biomarkers reflecting the toxicity of afidopyropen to E. fetida. Summing up, afidopyropen destroys the homeostasis of E. fetida through chronic toxic. These results provide theoretical data for evaluating the environmental risk of afidopyropen to soil ecosystem.

The combined effects of polystyrene nanoplastics with nickel on oxidative stress and related toxic effects to earthworms from individual and cellular perspectives

Nanoplastics may adsorb other pollutants in the environment due to their high specific surface area and small size. We used earthworms as experimental organisms to evaluate the ecotoxicity of NPs and Ni combined pollution at the individual and cellular levels. The results showed that when only 20 mg/L Ni2+ was added to the combined pollution system, the antioxidant system of earthworm coelomocytes was destroyed to a certain extent, the ROS level increased, the cell viability decreased significantly, and the redox balance was destroyed. With the introduction of PS-NPs and the increase of concentration, the oxidative damage in the coelomocytes of earthworms gradually increased, and finally tended to be stable when the maximum concentration of 50 mg/L PS-NPs and Ni were exposed together. At the animal level, the activities of CAT and SOD decreased within 28 days of exposure, and the combined pollution showed a synergistic effect. At the same time, it promoted the synthesis of GST in earthworms, improved their detoxification ability and reduced oxidative damage. The changes of T-AOC and MDA showed that the combined pollution caused the accumulation of ROS and caused more serious toxicological effects. With the increase of exposure time, the antioxidant system of earthworms was continuously destroyed, and the oxidative damage was serious, which induced more serious lipid peroxidation and caused the damage of earthworm body wall structure.

Toxicity of carbon nanofibers in earthworms (Lumbricus terrestris) naturally infected with Monocystis sp

Although the ecotoxicity of carbon-based nanomaterials (CBNs) is known, the potential effect of carbon nanofibers (CNFs) on edaphic organisms has been insufficiently explored. Thus, we aimed at the ecotoxicity of CNFs (at 10 and 100 mg/kg) in Lumbricus terrestris earthworms naturally infected with Monocystis sp. After 28 days of exposure, treatments did not affect the survival rate. However, we observed a significant loss of body biomass, and Monocystis sp. infection in seminal vesicles was potentiated by exposure to CNFs. Earthworms exposed to CNFs showed a redox imbalance in the seminal vesicle, muscle, and intestine and an alteration in nitric oxide production in these organs. In muscles, we also noticed a significant reduction in AChE activity in earthworms exposed to CNFs. The histopathological analyses revealed the treatments' significant effect on the structures of the different evaluated tissues. Although we did not notice a concentration-response for several of the biomarkers, when taken together and after the application of Integrated Biomarker Response (IBR) and principal component analysis (PCA), we noticed that the response of earthworms to CNFs at 100 mg/kg showed a more significant deviation from the unexposed group. This was mainly determined by inhibiting antioxidant activity in the seminal vesicle, biochemical biomarkers assessed in muscle and intestine, and histomorphometric muscle biomarkers from earthworms exposed to CNFs at 100 mg/kg. Thus, we demonstrate that CNFs increase the parasite load of Monocystis sp. of adult L. terrestris earthworms and induce biochemical and histopathological changes, especially at 100 mg/kg. Our results point to the additional impact these nanomaterials can have on the health of earthworms, signaling the need for greater attention to their disposal and ecotoxicological effects on soil organisms.

Toxicity of leachate from smoked cigarette butts to terrestrial animals: A case study on the earthworm Eisenia fetida

Cigarette butts, as easily overlooked littered wastes, have been evaluated for toxicity in various researches. In this study, we investigated the toxic effects of smoked cigarette butt leachate (SCBL) on the earthworm Eisenia fetida. The results showed the following: 1) E. fetida avoided SCBL in artificial soil, and the avoidance rate was positively correlated with the concentration of SCBL but negatively correlated with the exposure time; 2) the LD50 of SCBL on earthworms at 36 and 48 h of exposure were 3.71 × 10-4 and 2.67 × 10-4 butts/cm2, respectively. Moreover, both the body surface and intestinal tissues of E. fetida were damaged after exposure to SCBL; 3) the survival rates of E. fetida exposed to artificial soil with an SCBL of 3.6 butts/kg for 7 and 14 days were 80.00 ± 7.07 % and 68.00 ± 4.47 %, respectively; and 4) the mean biomass of the surviving E. fetida in all treated groups decreased with increasing SCBL concentration and exposure time. We concluded that SCBL exerted significant negative effects on soil animals, and suggested that SCBs should be collected, detoxified, and reused before entering the natural environment.

A 50-year systemic review of bioavailability application in Soil environmental criteria and risk assessment

Bioavailability has become a critical factor in improving ecological risk assessment and environmental remediation efficiency in contaminated soil research. However, the soil environmental quality standards and risk assessment procedures used in most countries are still based on the total amount of pollutants for lacking sufficient understanding of the exposure pathways and action mechanisms of pollutants. we collected relevant literature from the Web of Science database, spanning the period from 1950 to 2021 by using Citespace to analyze the scientific development of bioavailability. As of January 09, 2022, the database contained 118,813 publications on bioavailability. The review summarizes the progress in bioavailability research and emerging trends, including exploring advanced analytical techniques, advancing modeling approaches, and integrating interdisciplinary approaches to better understand the fate and behavior of pollutants in complex environmental matrices. In particular, the review emphasizes the need for better integration of bioavailability concepts into soil environmental reference, risk assessment procedures, and environmental remediation strategies. Overall, this review emphasized the necessity of incorporating the concept of bioavailability into soil environmental reference, risk assessment procedures, and environmental remediation strategies.

Effects of a Neonicotinoid on Indigenous Earthworm Perionyx excavatus Biochemical and Histopathological Alterations

Acetamiprid is a broad-spectrum insecticide, belonging to the neonicotinoid compounds group, which has been extensively applied throughout the globe. Recently, indiscriminate use of these compounds was reported to cause fatal impacts on non-targeted soil organisms. Hence, the present study aimed to examine the impact of acetamiprid on Indian indigenous earthworm, Perionyx excavatus. Acute toxicity revealed an LC₅₀ concentration of 0.25 µg/cm² for filter paper test/72 h and 400 µg/kg for artificial soil test/14 days. Oxidative stress (ROS) and various biomarkers including superoxide dismutase, catalase, glutathione S-transferase, malondialdehyde content and DNA damage were measured. The results of the biomarker responses confirmed the acetamiprid exposure can cause toxicity to P. excavatus. In addition, cell density (20 × 10² cell mL/mg) and cell viability (40%) were significantly (p < 0.05) reduced. Further, the ecotoxicological assessment made through this study can be utilized as good evidence to toxicity of neonicotinoids to non-targeted indigenous organisms.

Ecotoxicological effects of soil lithium on earthworm Eisenia fetida: Lethality, bioaccumulation, biomarker responses, and histopathological changes

Lithium is an emerging environmental contaminant in the current low-carbon economy, but little is known about its influences on soil invertebrates. In this work, earthworm Eisenia fetida was exposed to soils treated with different levels of lithium for 7 d, and multiple ecotoxicological parameters were evaluated. The results showed that mortality was dose-dependent and lithium's median lethal content (LC₅₀) to earthworm was respectively 865.08, 361.01, 139.36, and 94.95 mg/kg after 1 d, 2 d, 4 d, and 7 d exposure. The bioaccumulation factor based on measured exogenous lithium content (BF_exog) respectively reached 0.79, 1.01, 1.57, and 1.27 with the increasing lithium levels, suggesting that lithium accumulation was averagely 1.16-fold to the exogenous content, and 74.42%∼81.19%, 14.54%∼18.23%, and 2.26%∼8.02% of the lithium in exposed earthworms were respectively retained in the cytosol, debris, and granule. Then, lithium stress stimulated the activity of superoxide dismutase, peroxidase, catalase, acetylcholinesterase, and glutathione S-transferase as well as the content of 8-hydroxy-2-deoxyguanosine and metallothionein, indicating the generation of oxidative damage, while the content of reactive oxygen species and malondialdehyde decreased. Finally, lithium introduced histopathological changes, including the degenerated seminal vesicle and muscle hyperplasia, as well as high or extreme nuclear DNA damage. This study confirmed the obvious bioaccumulation and toxic effects caused by soil lithium via ecotoxicological data, providing new theoretical insights into understanding the ecological risks of lithium to soil invertebrates.

Effect of different exposure times and doses of cyantraniliprole on oxidative stress and genotoxicity in earthworms (Eisenia fetida)

Cyantraniliprole, the second generation of diamide insecticides, is widely used to control various pests, which will certainly result in adverse effects on earthworms in soil. In this study, after exposure with six doses of cyantraniliprole (0, 0.5, 1, 2.5, 5, and 10 mg kg^-1) by artificial soil method, six biomarkers, four functional genes, and histopathological changes of Eisenia fetida were measured on the 7th, 14th, 21st, and 28th days. The comprehensive toxicity was assessed by the IBR version 2 (IBRv2) method. The results showed that the reactive oxygen species (ROS) level was induced significantly. The superoxide dismutase (SOD) activity was activated in 7-28 days. The catalase (CAT) and glutathione S-transferases (GST) activities were also activated in the initial 14 days. The 8-hydroxy-2'-deoxyguanosine (8-OHdG) and malondialdehyde (MDA) contents in the high treatment increased until the late stage of exposure. On the 28th day, the metallothionein (MT) and calreticulin (CRT) genes were up-regulated, the transcriptionally controlled tumor protein (TCTP) gene was down-regulated. The SOD gene showed a good correlation with SOD activity. Extensive histopathological damage was found in the endoderm and ectoderm of E. fetida. The 5 and 10 mg kg^-1 treatments showed higher comprehensive toxicity than the 0.5, 1, and 2.5 mg kg^-1 treatments on the 28th day. These results suggest that cyantraniliprole exerted certain subchronic toxic effects of oxidative stress, DNA damage, and histopathological changes to E. fetida, which provided theoretical basis for rational use of cyantraniliprole and evaluation of its safety to soil environment.

Combined toxicity of Cd and 2,4-dichlorophenoxyacetic acid on the earthworm Eisenia andrei under biochar amendment

Due to anthropogenic activities, various pollutants can be found in agricultural soil, such as cadmium (Cd) and 2,4-dichlorophenoxyacetic acid (2,4-D). They are highly toxic and can have a negative impact on soil fertility. For remediation strategies, biochar has acquired considerable attention due to its benefits for agriculture. However, we should recognize the ecological risk posed by biochar use. In addition, little is known about its non-desirable effects on soil organisms such as earthworms, especially in the case of soil remediation. In this study, earthworms (Eisenia andrei) were exposed to soil contaminated with Cd (0.7 mg/kg), (2,4-D) (7 mg/kg), and a mixture of the two in the presence and absence of biochar (2%). A 7- and 14-day incubation experiment was carried out for this purpose. Cd and 2,4-D uptakes in earthworms' tissues, oxidative stress, cytotoxic response, DNA damage, histopathological changes, and gene expression level were assessed. Results suggested that biochar increased the bioavailability of Cd and 2,4-D and the frequency of micronuclei (MNi) and decreased the lysosomal membrane stability (LMS) in earthworms. Also, histopathological examination detected numerous alterations in animals exposed to the contaminants without any amelioration when biochar was added. The biochemical response of earthworms in terms of oxidative stress demonstrates that in the presence of biochar, animals tend to alleviate the toxicity of Cd and 2,4-D. This was also supported by transcriptomic analyses where expression gene levels related to oxidative stress were upregulated in earthworms exposed to Cd and 2,4-D + biochar. The present investigation brought new insights concerning the use of biochar in agriculture.

The Typical Polybrominated Diphenyl Ethers (PBDEs) and Heavy Metals Distributions in a Formal e-Waste Dismantling Site

Understanding the release of pollutants from the formal e-waste dismantling site could provide the basic information and potential risk to guide the normative regulation of the process. In this study, the distribution of typical polybrominated diphenyl ethers (PBDEs) and heavy metals in a relocating site of a formal e-waste dismantling company was firstly investigated down to the saturated zone, with a maximum depth of 3.0 m. The mean concentrations of Σ₁₃PBDEs were ranged from 2.815 to 7.178 ng/g, with a peak value of 7.178 ng/g in storage area. BDE-209 was the predominant congener of PBDEs in the soil, with the value ranged from 1.688 to 2.483 ng/g. A higher pollution of PBDEs and HMs was presented in the storage area. The risk assessment of PBDEs mostly posed a low environmental risk (RQ ≤ 0.01) and pentaBDE was found to be the most harmful driver for the potential environmental risk.

Radium uptake by earthworms E. fetida after exposure to contaminated soil

Radium-226 is one of the most important radionuclides for assessing the radiation exposure in terrestrial ecosystems in terms of its significant contribution to the internal and total dose rates. A laboratory culture of Eisenia fetida was exposed to soil contaminated with ²²⁶Ra and ²³⁸U during two months. These nuclides entered the soil as a result of industrial radium production (Vodny, Komi Republic, Russia). The concentrations of ²²⁶Ra and ²³⁸U were 89000 ± 9000 and 2130 ± 270 Bq kg^-1 of soil. Bioaccumulation of ²²⁶Ra was investigated in E. fetida exposed to the radioactive soil or to a mixture containing the same radioactive soil diluted with peat and sand. The activity concentrations of ²²⁶Ra in E. fetida were higher after exposure to the contaminated soil compared to the mixture. The literature data on the radium accumulation in earthworms were considered also. Our experiments showed that the concentration ratio (CR) of ²²⁶Ra in E. fetida varied from 5.5 × 10^-4 to 4.5 × 10^-3 Bq kg^-1 f.w./Bq kg^-1 d.w. The average CRs were (6.7 ± 1.7) × 10^-4 for the earthworms E. fetida from the soil mixture and (3.2 ± 1.2) × 10^-3 for those from the radioactive soil. These CRs for ²²⁶Ra were up to two orders of magnitude lower than the values calculated by us from the results obtained by other researchers for natural earthworm populations in areas with lower levels radioactivity.

Influence of aged and pristine polyethylene microplastics on bioavailability of three heavy metals in soil: Toxic effects to earthworms (Eisenia fetida)

Virgin microplastics (MPs) would undergo aging process when entering environment, the adsorption capability of pollutants onto MPs may change during the aging process. To better understand the influence of aged polyethylene microplastics (PE-MP) on the bioavailability of three heavy metals (Zn, Pb, and Cd) in soil, hydrogen peroxide exposure (3% H₂O₂) and ultraviolet irradiation methods were employed to simulate the aging process. After aging process, different amount (0.1%, 1%, 10%) of PE-MP (pristine or aged) was added into soil to assess the ability of soil (containing PE-MP) adsorbing heavy metal. Moreover, different amount (0.01%, 0.1%, 1%) of PE-MP (pristine or aged) was added into soil to cultivate the earthworms to assess the impact of PE-MP on bioavailability of three heavy metals. Results indicated that the aged and virgin PE-MP had similar capability to adsorb heavy metal, the adsorption ability of Zn²⁺, Pb²⁺, and Cd²⁺ to pristine PE-MP were 2.42, 7.47, and 7.76 mg/g, respectively. The concentration of Zn or Pb in earthworms in treatments of metal +1% PE-MP was slightly higher than that in single metal (Zn or Pb) treatment, moreover, the concentration of Cd in earthworms in treatment of Cd + 1% PE-MP was significantly (p < 0.05) higher than that in single Cd treatment, exhibiting that 1% of PE-MP enhanced the bioavailability of heavy metals in soil. However, heavy metal concentrations in earthworms in treatments of metal + pristine PE-MP showed insignificant (p > 0.05) difference with those in treatments of metal + aged PE-MP, indicating that the aging process in this study did not change the environmental influence of PE-MP on heavy metals bioavailability. Superoxide dismutase activity, reactive oxygen species level, malondialdehyde content, and related gene expression in earthworms showed that PE-MP and heavy metals would bring toxic synergy to earthworms, therefore, the influence of MPs should be comprehensively considered when determining the environmental risk of heavy metals in soil.

Site-specific ecological risk assessment of metal-contaminated soils based on the TRIAD approach

Ecological risk assessment based on scientific data is crucial for understanding causal relationships between chemical pollution and environmental risks. Simultaneously, a balance is required between socioeconomic factors and scientific evidence. The TRIAD approach, which incorporates three lines of evidence (LoE)-chemical (Chem-LoE), ecotoxicological (Ecotox-LoE), and ecological (Eco-LoE)-was applied in five sites of an abandoned mine for site-specific soil ecological risk assessment (SERA). In combination, the three LoEs showed that two sites had extremely high risks, one site had moderate risk, and the other site had low risk. At all sites, Chem-LoE exhibited high-integrated risk values. In Ecotox-LoE and Eco-LoE, some species were not affected despite high metal concentrations in the soil samples collected from the sites, indicating that the bioavailability of metals differed according to the physiochemical properties of the soil medium. This study is significant as multiple analyses were performed considering ecosystem structure to reduce uncertainty in SERA. The results provide information to support effective decision-making risk management to protect the soil ecosystem. Moreover, these findings will be useful in establishing policies and priorities for soil risk management.

Hydrogen-Rich Water Alleviates the Nickel-Induced Toxic Responses (Inflammatory Responses, Oxidative Stress, DNA Damage) and Ameliorates Cocoon Production in Earthworm

In recent years, studies investigating the protective effect of hydrogen-rich water (HRW) against different diseases and the toxicity of some substances have attracted increasing attention. Here, we assessed the effects of hydrogen-rich water on different nickel-induced toxic responses (reactive oxygen species (ROS), tumor necrosis factor-alpha (TNF-α), and 8-hydroxy-2'-deoxyguanosine (8-OHdG) of stress responses, histopathological changes) and cocoon production in earthworm model. Earthworms were randomly divided into two main groups: water (W) group including control (CW: ultrapure water), 10 (10W), 200 (200W), and 500 (500W), and hydrogen-rich ultrapure water (HRW) group including control (CHRW: hydrogen-rich ultrapure water), 10 (10HRW), 200 (200HRW), and 500 (500HRW) mg of nickel chloride kg-1 soil for 14 days. We found that cocoon production was less affected by the nickel exposure of earthworms in the 500HRW group compared to the 500W group. The ROS levels in 200HRW and 500HRW groups were less than that of 200W and 500W, respectively. The epithelial degeneration, epithelial necrosis, and necrosis in muscle fibers in tissues of earthworm were less damaged in 200HRW and 500HRW groups compared to 200W and 500W, respectively. HRW groups significantly reduced the expression of 8-OHdG induced by nickel exposure and inflammatory cytokine response including TNF-α. The study showed that hydrogen-rich water could alleviate the toxic effects of nickel-induced oxidative and inflammatory damages in earthworms. The HRW treatment known for its cheap and eco-friendly propertıes without any negative effects on the ecosystem can be used as a green method for alleviating the toxification effects of heavy metals in contaminated soil and increasing cocoon production of earthworms.

Biochemical, transcriptomic, gut microbiome responses and defense mechanisms of the earthworm Eisenia fetida to salt stress

The accumulation of sodium chloride (NaCl) in soil is a worldwide problem with detrimental effects on the survival of soil animals. The effects of NaCl on earthworms remain unclear. Here, we show that the growth rate, cocoon production rate, annetocin precursor (ANN) mRNA level, and superoxide dismutase and catalase activities in earthworms were reduced under NaCl stress, whereas the mortality rate, reactive oxygen species (ROS) and malondialdehyde activity level increased. Histological damage to the earthworm body wall and intestine were observed under NaCl stress. NaCl stress increased DNA damage in the seminal vesicle and coelomocytes. The mRNA level of lumbrokinase, 1,3-beta-glucanse, coelomic cytolytic factor (CCF1), and alpha-amylase was significantly down-regulated, whereas that of earthworm excitatory peptides2 (EEP2) was up-regulated. From 16 S rRNA sequencing, the earthworm gut microbiota diversity decreased under NaCl stress. However, Verminephrobacter, Kluyvera, Lactobacillus, and Ochrobactrum increased under NaCl stress. These findings contribute to the risk assessment of the salt stress on soil organisms.

Ecotoxicological Effects of Bimetallic PdNi/MWCNT and PdCu/MWCNT Nanoparticles onto DNA Damage and Oxidative Stress in Earthworms

Bimetallic nanoparticles are synthesized using two different metal elements and used recently in many fields. However, limited studies related to the ecotoxic effects of nanoparticles available in the literature. The purpose of this study is to synthesize and characterize bimetallic PdCu/MWCNT and PdNi/MWCNT NPs and investigate their ecotoxic effects on earthworms. For this purpose, we injected approximately 20 µL of various concentrations of bimetallic PdCu/MWCNT and PdNi/MWCNT NPs (1, 10, 100, 1000, and 2000 mg/L) into the coelomic space of earthworms. We evaluated survival rate, malformations, reactive oxygen species (ROS) level, 8-OHdG content, and histopathological changes in earthworms at the 48th hour after exposure. PdCu/MWCNT and PdNi/MWCNT NPs were characterized by scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray diffraction (XRD) pattern, and Raman-scattering spectroscopy. Toxicological examinations showed that PdCu/MWCNT NPs reduced the survival rate of earthworms (2000 mg/L, 84%) and caused various malformations (various lesions, thinning, swelling, and rupture), but nonsignificant effects of survival rate and malformations were observed in earthworms using PdNi/MWCNT NPs. The histopathological examinations of earthworm tissues exposed with PdNi/MWCNT determined that tissues in all treatment groups had a normal histological appearance. However, at a concentration of 2000 mg/L of PdCu/MWCNT NPs, atrophy in the longitudinal muscle layer and less degenerative cells in the epidermis layer were observed in earthworm tissues. It was determined that PdNi/MWCNT and PdCu/MWCNT NPs caused significant increases in ROS levels and 8-OHdG activity in earthworm tissues after 48 h. Finally, our results demonstrated that the toxicity of PdNi/MWCNT NPs was detected to be lower than PdCu/MWCNT NPs. However, both nanoparticles may pose a toxicological risk at high concentrations (1000 and 2000 mg/L). These findings will provide valuable information to studies on the use of PdNi/MWCNT NPs in wastewater treatment systems, industrial and medical fields, which have been determined to have less ecotoxicological risk.

Physiochemical responses of earthworms (Eisenia fetida) under exposure to lanthanum and cerium alone or in combination in artificial and contaminated soils

Rare earth elements inevitably release into the soil due to their widespread application. However, it is unclear how they affect the soil animals. The study surveyed the growth and physiological responses of earthworm (Eisenia fetida) exposed into artificial soils spiked with La, Ce, and their mixture, and actual mine soil collected from an abandoned La-Ce mining area (Mianning, Sichuan). The results showed that the 1000-1200 mg/kg combined exposure in two soils induced significant histopathological and phenotypic changes of earthworms. Concentration significantly affected the superoxide dismutase (SOD), peroxidase (POD), malondialdehyde (MDA), and protein of E. fetida and the effects differentiated with the prolonging duration. These indicators were negatively affected under the La stress ≥800 mg/kg (SOD, POD, and protein), the 1200 mg/kg (SOD), Ce stress ≥1000 mg/kg (protein), and the combination ≥800 mg/kg (SOD, POD) and ≥1000 mg/kg (protein). Artificial combination had -15.04% (SOD), 8.87% (POD), 5.64% (MDA), and -8.34% (protein) difference compared with the contamination soil, respectively. Overall, E. fetida respond sensitively under the La and Ce stress, the antioxidant defense system and the lipid peroxidation were stimulated, and the artificial soil might overestimate eco-toxicological effect.

Earthworm Eisenia fetida potential for sewage sludge amended soil valorization by heavy metal remediation and soil quality improvement

Sewage sludge reuse in agriculture is increasing, however it can be an important route for contaminants to enter the environment. The aim of this study was to evaluate earthworm Eisenia fetida capability to reduce heavy metal content in the sewage sludge (SS) amended soil and increase soil fertility in terms of soil nutrients content. Adult earthworms were introduced into aged SS amended soil (0-200 Mg ha^-1) and left for 65 days. Earthworms have stabilized soil pH and accelerated organic matter mineralization. The concentrations of most heavy metals during the vermiremediation sharply decreased, K and Mg decreased to a moderate extent, whereas Ca content has increased. The highest removal efficiency was detected for Ni, Co and Mn (> 80%), bioconcentration factors were as follows Zn > Co > Cu > Ni > Mn > Cr. The content of major nutrients (S, P) was substantially higher compared to the initial values. The most efficient remediation and soil quality improvement was achieved under the doses of 25-50 Mg ha^-1. Higher (≥ 100 Mg ha^-1) doses might restrict this technique application because of earthworm mortality and retarded growth. Overall, the study shows that vermiremediation might be a sustainable technique for ecological stabilization of SS amended soil and converting to usable for agricultural needs.

Is the climate change mitigation effect of enhanced silicate weathering governed by biological processes?

A number of negative emission technologies (NETs) have been proposed to actively remove CO₂ from the atmosphere, with enhanced silicate weathering (ESW) as a relatively new NET with considerable climate change mitigation potential. Models calibrated to ESW rates in lab experiments estimate the global potential for inorganic carbon sequestration by ESW at about 0.5-5 Gt CO₂  year^-1 , suggesting ESW could be an important component of the future NETs mix. In real soils, however, weathering rates may differ strongly from lab conditions. Research on natural weathering has shown that biota such as plants, microbes, and macro-invertebrates can strongly affect weathering rates, but biotic effects were excluded from most ESW lab assessments. Moreover, ESW may alter soil organic carbon sequestration and greenhouse gas emissions by influencing physicochemical and biological processes, which holds the potential to perpetuate even larger negative emissions. Here, we argue that it is likely that the climate change mitigation effect of ESW will be governed by biological processes, emphasizing the need to put these processes on the agenda of this emerging research field.

Individual and histopathological responses of the earthworm (Eisenia fetida) to graphene oxide exposure

The increasing production and applications of graphene oxide (GO) inevitably lead to its entry into the environment. However, its potential toxicity to soil invertebrates is not yet completely known. Herein, the harmful effects of GO on the growth, survival, reproduction, and ultrastructure of earthworms were thoroughly evaluated through acute and chronic toxicity experiments. In the acute toxicity experiments, earthworms were exposed to different concentrations of GO using two test methods: filter paper contact test and natural soil contact test. The lethal concentrations (LC₅₀) for GO at 24-h and 48-h exposure were 2.52 and 2.36 mg mL^-1, respectively, in the filter paper contact test and the LC₅₀ on day 14 was 68.8 g kg^-1 in the natural soil test. Histopathological observation demonstrated that serious skin and intestinal damage occurred with increasing GO concentrations. In the chronic toxicity test, earthworm growth rate and reproduction were investigated after exposure to 0, 5, 10, 20 and 30 g kg^-1 GO in natural soil for 28 and 56 d. Earthworm growth was significantly inhibited after 7, 14, 21 and 28 d of GO exposure. The effect was more significant with increasing GO concentrations and exposure days. Moreover, GO exposure significantly decreased the reproductive capacity of earthworms. When earthworms were exposed to 20 g kg^-1 GO for 56 d, the number and hatching rate of cocoons and the number of juveniles decreased by approximately half compared with the control. These findings indicate the potential health risk of GO to E. fetida under high concentrations and long exposure times in soil. Thus, the potential risks associated with the application of GO should receive considerable attention. This study can provide valuable information for assessing the toxicity of carbon nanomaterials in terrestrial ecosystems.

Toxicity and bioavailability of antimony to the earthworm (Eisenia fetida) in different agricultural soils

Laboratory experiments in which earthworms were exposed to four different Sb spiked agricultural soils (acidic, neutral, alkaline and calcareous alkaline soil) were conducted in a climate-controlled room. The study surveyed the toxicity of Sb to the Eisenia fetida at the individual (mortality, growth inhibition, Sb accumulation), physiological (enzymatic activities), subcellular and tissue levels (histological damage), and for the induction of an avoidance response of Sb. The results showed that earthworms clearly avoided Sb spiked soil, and the avoidance response tended to be correlated to the exposure dose. The EC₅₀ values of the net avoidance response in the four soils were as followed: S1 (acidic soil, 135 ± 37 mg kg^-1) < S3 (alkaline soil, 430 ± 114 mg kg^-1) < S4 (calcareous alkaline soil, 455 ± 29 mg kg^-1) < S2 (neutral soil, 946 ± 151 mg kg^-1). Different toxic effects of Sb to earthworms cultivated in the four types of soils were observed. Antimony was more toxic in a sandy alkaline soil than that in the other three soils tested. The LC₅₀ of the 28 d mortality ranged as follows: S3 (22.2 ± 0.1 mg kg^-1) < S2 (372 ± 177 mg kg^-1) < S4 (491 ± 140 mg kg^-1) < S1 (497 ± 29 mg kg^-1). Changes in oxidative stress and the subcellular distribution of Sb in earthworms induced by Sb exposure differed between soil types. Additionally, histological damage in earthworm's epidermis and intestine were observed under Sb stress. Mortality, growth inhibition and Sb accumulation in the earthworms tended to increase with Sb exposure regardless of soil type and were all significantly correlated with the exposure dose. The growth inhibition and Sb concentration in tissues of earthworms were sensitive indicators of Sb bioavailability. The relatively comprehensive toxicological data provided herein can contribute to the toxicity threshold and assessment of bioavailability of Sb contaminated agricultural soil, and then to the ecological risk assessments.

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.

Bio-interaction of nano and bulk lanthanum and ytterbium oxides in soil system: Biochemical, genetic, and histopathological effects on Eisenia fetida

The massive application of rare earth elements (REEs) in electronic industries cause their inevitable release into the environment; however, its effects on soil biota remain largely unaddressed. We investigated the E. fetida detoxification potential of nano and bulk La₂O₃ and Yb₂O₃ and their potential impact on biochemical and genetic markers at 50, 100, 200, 500 and 1000 mg kg^-1 concentration. We found that earthworms bioremediate 3-15% La₂O₃ and Yb₂O₃ contaminated soil at low and medium levels, while this potential was limited at higher levels. Nano and bulk La₂O₃ and Yb₂O₃ treatment induced neurotoxicity in earthworm by inhibiting acetylcholinesterase by 49-65% and 22-36% at 500 and 1000 mg kg^-1, respectively. Nano La₂O₃ proved to be highly detrimental, mainly through oxidative stress and subsequent failure of antioxidant system. Nano La₂O₃ and Yb₂O₃ at 100 mg kg^-1 significantly down-regulated the expression of annetocin mRNA in the parental and progeny earthworms by 50% and 20%, which is crucial for earthworm reproduction. Similarly, expression level of heat shock protein 70 (HSP70) and metallothionein was significantly upregulated in both generations at medium exposure level. Histological observations showed that nano REEs at 200 mg kg^-1 induced drastic changes in the intestinal epithelium and typhlosole of E. fetida. To date, our results enhance the understanding of interaction between REEs and earthworms.

Influence of polyethylene-microplastic on environmental behaviors of metals in soil

Microplastics (MPs) in terrestrial ecosystems have attracted increasing attention all over the world. The adsorption-desorption behavior and bioavailability of metals in soil would affect its toxicity to organisms. However, the influences of MPs on adsorption-desorption behavior between metals and soil as well as bioavailability of metals in soils are scarcely investigated. Herein, different percentage (0, 0.1%, 1%, 10%) of polyethylene-microplastic (PE-MP) were thoroughly mixed into the soil to investigate the impacts of PE-MP on adsorption-desorption and bioavailability of metals (Zn²⁺, Pb²⁺) in the soil. A series of characterization were carried out to determine the change of PE-MP before and after adsorption to investigate the mechanisms. When MP100 (average size: 129 μm) content in soil increased to 10%, the adsorption capacities of soil with Pb²⁺ and Zn²⁺ were 3.73 and 4.56 mg/g, respectively, which were significantly (p < 0.05) lower than that of pure soil. When MP300 (average size: 293 μm) content in soil increased to 10%, the extraction fraction of Zn²⁺ and Pb²⁺ from soil by diethylenetriaminepentaacetic acid reached 12.35% and 23.96%, respectively, which were significantly (p < 0.05) higher than that of pure soil, indicating high concentration (10%) of MPs in soil would decrease the adsorption capability of soil to metals and increase the mobility of metals in terrestrial environment. However, when MPs content in soil was 0.1%, the extraction fraction of Zn²⁺ and Pb²⁺ showed no significant difference with that of pure soil, indicating that actual MPs in soil is unlikely to bring significant influence on metal bioavailability.

Bioaccumulation and potential ecotoxicological effects of trace metals along a management intensity gradient in volcanic pasturelands

The particularities of volcanic soils raise the need to better understand the link between soil agricultural management intensity and trace metal bioaccumulation. The Azores are a region characterized by volcanic soils, which were changed in different degrees according to the intensity of the agricultural practices. The main objective of this study was to assess the potential ecotoxicological effects of the trace metals present in volcanic pastureland soils along a gradient of management intensity (i.e., semi-natural, permanent and reseeded), using earthworms (Eisenia fetida) as biological indicators. For this purpose earthworms were exposed during 7, 14, 28 and 56 days to soils from the three types of pastures. At each exposure time, we quantified trace element bioaccumulation (As, Cd, Co, Cr, Cu, Hg, Li, Mn, Mo, Ni, Pb, Rb, U, V and Zn) and the activities of superoxide dismutase and acetylcholinesterase in earthworm tissues. Overall, the results showed that the type of pastureland management significantly increased the soil contents in trace metals: V, Co, Ni and Zn in semi-natural pasturelands; As, Cd and Hg in reseeded pasturelands; and, Rb and U in both permanent and reseeded pasturelands. The soil physicochemical properties observed in the reseeded pastureland systems (higher electric conductivity values associated with a moderately acid pH value) modulated the metal bioavailability, from soil to biota, leading to a greater Hg bioaccumulation in earthworm tissues. The long-term exposure (56 days) of earthworms to reseeded pastureland soil was associated with adverse biological effects (intensification of AChE activity and decrease of SOD activity), encompassing key processes such as neurotransmission and antioxidant defence mechanisms in resident soil biota (earthworms). This study point towards the increased importance of semi-natural and permanent pastureland management, over the intensive management (reseeded pasturelands), in favour of more sustainable ecosystems.

Impacts of polyethylene microplastics on bioavailability and toxicity of metals in soil

In this study, we investigated the bioavailability and toxicity of metals (Cu and Ni) in the soil containing polyethylene microplastics (PE-MPs). The bioavailability of the metals determined by the five-step chemical sequential extraction method increased with the addition of MPs (0.1%, 1%, 10%) in the soil, which was confirmed by the adsorption-desorption characteristics. To further examine the bioavailability and toxicity of metals, earthworms (Eisenia fetida) were exposed to soil containing Cu²⁺ (100 mg/kg) or Ni²⁺ (40 mg/kg) with different amounts (0.01%, 0.05%, and 0.1%) of PE-MPs for 21 days. The highest concentrations of Cu²⁺ and Ni²⁺ in earthworms reached to 73.3 and 36.3 mg/kg, respectively. Moreover, metal concentrations in earthworms increased with MP contents in the soil, which was consistent with the bioavailability measured by the sequential extraction method. Furthermore, changes in biomarkers including peroxidase (POD), catalase (CAT) and superoxide dismutase (SOD) activity, malondialdehyde (MDA) contents, and related gene expression levels in earthworms suggested that the pollutants caused toxicity to earthworms. Overall, MPs increased the bioavailability of metals in the soil and the toxic effects to earthworms. These findings provide insights regarding the impacts of MPs on the bioavailability of metals and the combined toxic effects of these two kinds of pollutants on terrestrial animals.

Oxidative stress, growth inhibition, and DNA damage in earthworms induced by the combined pollution of typical neonicotinoid insecticides and heavy metals

Heavy metals pollution of soil and widespread application of neonicotinoid insecticides have caused environmental problems worldwide. To evaluate ecological toxicity resulting from the combined pollution of neonicotinoids and heavy metals, typical representatives of neonicotinoid insecticides (imidacloprid, thiamethoxam, dinotefuran) and heavy metals (cadmium, copper, zinc) were selected as soil pollutants; earthworms were used as test organisms. Analysis of the main and interaction effects of a combined pollution process were performed using a uniform design method. Results showed that the reactive oxygen species (ROS) content of earthworms in most treatment groups was higher during exposure than that of the control group. The malondialdehyde (MDA) and ROS content of earthworms demonstrated relatively low values on the 21st day and increased by the 28th day. The interaction between dinotefuran and Cd had significant antagonistic effects on ROS and MDA. The combined pollution adversely affected both the growth and genes of earthworms and also caused damage to the epidermis, midgut, and DNA. The interaction between imidacloprid and Cd was synergistic to ROS, weight inhibition rate, and Olive tail moment (OTM), but was antagonistic to MDA. Of all the single and combined exposures, Zn as a single chemical affected ROS and DNA damage the most, and MDA was significantly enhanced by imidacloprid. Composite pollutants may create different primary effects and interactions causing potential harm to soil organisms.

Determination of (Bio)-available mercury in soils: A review

Despite the mercury (Hg) control measures adopted by the international community, Hg still poses a significant risk to ecosystem and human health. This is primarily due to the ability of atmospheric Hg to travel intercontinentally and contaminating terrestrial and aquatic environments far from its natural and anthropogenic point sources. The issue of Hg pollution is further complicated by its unique physicochemical characteristics, most noticeably its multiple chemical forms that vary in their toxicity and environmental mobility. This meant that most of the risk evaluation protocols developed for other metal(loid)s are not suitable for Hg. Soil is a major reservoir of Hg and a key player in its global cycle. To fully assess the risks of soil Hg it is essential to estimate its bioavailability and/or availability which are closely linked to its toxicity. However, the accurate determination of the (bio)-available pools of Hg in soils is problematic, because the terms 'bioavailable' and 'available' are ill-defined. In particular, the term 'bioavailable pool', representing the fraction of Hg that is accessible to living organisms, has been consistently misused by interchanging with other intrinsically different terms e.g. mobile, labile, reactive and soluble pools. A wide array of physical, chemical, biological and isotopic exchange methods were developed to estimate the (bio)-available pools of Hg in soil in an attempt to offer a plausible assessment of its risks. Unfortunately, many of these methods do not mirror the (bio)-available pools of soil Hg and suffer from technical drawbacks. In this review, we discuss advantages and disadvantages of methods that are currently applied to quantify the (bio)-availability of Hg in soils. We recommended the most feasible methods and give suggestions how to improve the determination of (bio)-available Hg in soils.

Citric acid enhanced phytoextraction of nickel (Ni) and alleviate Mentha piperita (L.) from Ni-induced physiological and biochemical damages

Phytoremediation is considered one of the well-established and sustainable techniques for the removal of heavy metals and metalloids from contaminated sites. The metal extraction ability of the plants can be enhanced by using suitable organic materials in combination with metal-tolerant plants. This experiment was carried out to investigate the phytoextraction potential of Mentha piperita L. for nickel (Ni) with and without citric acid (CA) amendment in hydroponic experiment. The experiment was performed in controlled glass containers with continuous aeration in complete randomized design (CRD). Juvenile M. piperita plants were treated with different concentrations of Ni (100, 250, and 500 μM) alone and/or combined with CA (5 mM). After harvesting the plants, the morpho-physiological and biochemical attributes as well as Ni concentrations in different tissues of M. piperita plants were measured. Results revealed that Ni stress significantly decreased the plant agronomic traits, photosynthesis in comparison to control. Nickel stress enhanced the antioxidant enzymes activities and caused the production of reactive oxygen species (ROS) in M. piperita. The CA treatment under Ni stress significantly improved the plant morpho-physiological and biochemical characteristics when compared with Ni treatments alone. The results demonstrated that CA enhanced the Ni concentrations in roots, stems, and leaves up to 138.2%, 54.2%, and 38%, respectively, compared to Ni-only-treated plants. The improvement in plant growth with CA under Ni stress indicated that CA is beneficial for Ni phytoextraction by using tolerant plant species. Graphical abstract.

Assessment of earthworm activity on Cu, Cd, Pb and Zn bioavailability in contaminated soils using biota to soil accumulation factor and DTPA extraction

The study aims to investigate effect of earthworm activity on metal bioavailability in soils using their BSAF-metals. Based on a microcosmic laboratory experiment, epigeic species Amynthas corticis (A. corticis) and endogeic species Amynthas robustus (A. robustus) were cultured in two types of soils contaminated by Cd, Zn, Pb and Cu for 120 days. Earthworm characteristics (i.e. numbers, biomass and BSAF), soil properties (i.e. pH, organic C and N contents along with their components such as mineralization and microbial masses) and DTPA extracted metals in soil were determined. After the incubation, the biomass and survival numbers of both earthworm species decreased significantly (P < 0.05). The accumulation of Cd, Zn and Pb in earthworm tissues and BSAF-metals were earthworm species dependent. According to two-way ANOVA, BSAF-Pb clearly showed the effect of different species of earthworms while BSAF-Cu indicated an interactive effect of earthworms and soil type. Earthworms changed soil properties significantly, especially for mineralized C (C_min), dissolved N (N_dis) and pH (P < 0.05). Earthworm activity increase DTPA extracted Zn and Cu, and the effect of A. robustus were stronger than for A. corticis. Redundancy analysis (RDA) showed that BSAF-Cu and BSAF-Pb contributed for respectively 51.9% and 51.7% of soil properties and DTPA metal changes, indicating that the effects of BSAF-Cu and BSAF-Pb on soil properties and on metal bioavailability in soil were similar. BSAF-Cu, indicating the interactive effect of earthworms and soil, accounted for 38.5% and 45.1% of soil properties and soil metal bioavailability changes. BSAF-Pb, representing the effect of earthworm species, accounted for 13.3% and 6.6% of soil property and soil metal bioavailability variations. Stepwise regression indicated that earthworm might change soil properties through their activities and interactions with soil, and hence increase heavy metal bioavailability. It suggested that BSAF is an important indicator for evaluating the effect of earthworm activity on soil metal bioavailability and designing remediation strategies.