Effects of metals on earthworm life cycles: a review

Current Developments in Soil Ecotoxicology

Ecotoxicology focuses on how chemicals affect organisms in the environment, with the ultimate goal of safeguarding the structure and function of ecosystems [...].

Assessment of growth, reproduction, and vermi-remediation potentials of Eisenia fetida on heavy metal exposure

Heavy metal pollution is a significant environmental concern with detrimental effects on ecosystems and human health, and traditional remediation methods may be costly, energy-intensive, or have limited effectiveness. The current study aims were to investigate the impact of heavy metal toxicity in Eisenia fetida, the growth, reproductive outcomes, and their role in soil remediation. Various concentrations (ranging from 0 to 640 mg per kg of soil) of each heavy metal were incorporated into artificially prepared soil, and vermi-remediation was conducted over a period of 60 days. The study examined the effects of heavy metals on the growth and reproductive capabilities of E. fetida, as well as their impact on the organism through techniques such as FTIR, histology, and comet assay. Atomic absorption spectrometry demonstrated a significant (P < 0.000) reduction in heavy metal concentrations in the soil as a result of E. fetida activity. The order of heavy metal accumulation by E. fetida was found to be Cr > Cd > Pb. Histological analysis revealed a consistent decline in the organism's body condition with increasing concentrations of heavy metals. However, comet assay results indicated that the tested levels of heavy metals did not induce DNA damage in E. fetida. FTIR analysis revealed various functional group peaks, including N-H and O-H groups, CH2 asymmetric stretching, amide I and amide II, C-H bend, carboxylate group, C-H stretch, C-O stretching of sulfoxides, carbohydrates/polysaccharides, disulfide groups, and nitro compounds, with minor shifts indicating the binding or accumulation of heavy metals within E. fetida. Despite heavy metal exposure, no significant detrimental effects were observed, highlighting the potential of E. fetida for sustainable soil remediation. Vermi-remediation with E. fetida represents a novel, sustainable, and cutting-edge technology in environmental cleanup. This study found that E. fetida can serve as a natural and sustainable method for remediating heavy metal-contaminated soils, promising a healthier future for soil.

Accumulation of heavy metals from single and combined olive mill wastewater and pomace in soil and bioaccumulation in tissues of two earthworm species: Endogeic (Aporrectodea trapezoides) and Epigeic (Eisenia fetida)

Soil and earthworms are threatened by anthropogenic contamination resulting from olive mill waste dumping on the soil due to their pollutant properties. While several studies have explored the effects of olive mill waste on soil properties and the accumulation of heavy metals in soil, there is currently a gap in the literature regarding the potential bioaccumulation of heavy metals from olive mill waste in earthworms. In this study, soil with earthworms from two ecological categories (endogeic: Aporrectodea trapezoides and epigeic: Eisenia fetida) was treated with increasing doses of olive mill wastewater (OMWW) and olive mill pomace (OMP), applied individually or combined, in an indoor experiment in plastic containers, under laboratory conditions. The results revealed the presence of significant concentrations of heavy metals in the two types of wastes ranging as follows: Fe˃ Zn˃ Cu˃ Cd˃ Cr for OMWW, and Fe˃ Zn˃ Cu˃ Cr for OMP (with Cd below the detection limit). The study demonstrated distinct effects of OMWW and OMP, both individually and in combination, on soil heavy metal content, ranging as follows: soil OMWW > soil Combination > soil OMP for Cd; soil Combination > soil OMWW > soil OMP for Cr and Fe; and soil Combination > soil OMP > soil OMWW for Cu and Zn. Additionally, our investigation showed that both earthworm species exhibited significant uptake of these metals into their tissues, particularly the endogeic species. Interestingly, the most significant difference between species was in the accumulation of Cu, with the epigeic species accumulating significantly lower amounts.

A multi-biomarker approach to verify chronic effects on Eisenia andrei earthworms exposed to tailings from one of the world's largest mining disasters

Mining is of great relevance to the global economy, but its activities are challenging due to socio-environmental impacts. In January 2019, an iron ore tailings dam collapsed in Brumadinho (Minas Gerais, Brazil) releasing 12 × 106 m3 of tailings, causing human losses and devastation around 3.13 × 106 m2 of a watershed. In this context, the present study aimed to investigate the potential toxic effects of tailings from the collapsed dam using earthworms Eisenia andrei as a model organism for terrestrial environments. An extensive set of tests was performed, including behavioral (avoidance), acute (mortality and biomass) and chronic tests, such as biomass, reproduction and cytotoxicity (viability and cell density and change in coelomocyte pattern). The physical-chemical characterization revealed a higher density of the tailings in relation to the control soil, which can result in physical changes, such as soil compaction and surface sealing. Aluminum, Ca, Fe, Hg, Mg, Mn, K, Na and P registered higher concentrations in the tailings compared to the control soil, while Total Nitrogen, Total Organic Carbon and Organic Matter were higher in the natural soil. Based on the avoidance test, an EC50 of 27.18 ± 2.83% was estimated. No lethality was observed in the acute exposure, nor variations in biomass in the acute and chronic assays. However, there was a tendency to reduce the number of juveniles in relation to cocoons in the proportions of 3125; 12.5 and 25%. Significant changes in viability, cell density and pattern of amebocytes and eleocytes were observed up to the 35th day of exposure. A multi-biomarker approach (Integrated Biological Response version 2) indicated concentration-dependent effects and attenuation of cellular changes over time. These are the first results of chronic effects on earthworms exposed to tailings from the B1 dam. Despite being conclusive, we highlight the possible heterogeneity of the tailings and the necessary care in extrapolating the results.

Metal pollution drives earthworm biodiversity in urban lawns

Urban soils represent hotspots of metallic trace elements (MTEs) pollution. Despite the critical impact of soil organisms on soil ecosystem services, there is limited understanding regarding the effects of MTE levels in urban soils on these organisms. This is particularly surprising considering that earthworms, key organisms for soil ecosystems, are commonly used in MTE toxicity tests. This research investigates the impact of MTE pollution on earthworm communities in lawns within the city of Paris. In this study, we sampled a comprehensive array of earthworm communities, totalling 965 individuals from 13 distinct species belonging to Lumbricus, Aporrectodea, Allolobophora and Octolasion genera. These communities were collected from three different locations within 18 parks. At these sites, we assessed the concentrations of eight metals and metalloids in the soil (As, Cd, Cr, Cu, Zn, Ni, Pb and Hg), along with selenium concentrations and eight fundamental soil parameters, to examine the association between earthworm communities and soil attributes. Median MTE concentrations exceeded recommended statutory limit values by approximately 20 % (0.6 mg/kg Cd), 30 % (36.8 mg/kg Cu), 40 % (122.0 mg/kg Zn), and up to 90 % (0.6 mg/kg Hg and 99.7 mg.kg Pb). Nevertheless, these concentrations exhibited considerable variability both between and within parks, correlating with variations in earthworm community structures. Specifically, our results highlight that Cu concentrations in the soil explain about 6 % of the variation in the assemblage of earthworm species. Our findings underscore the importance of considering MTE pollution levels to enhance our comprehension of earthworm distribution in urban environments and its effects on the ecosystem services provided by urban lawns.

Biomarker response index in earthworms following chronic exposure to leachate from a closed dumpsite: Behavioral, cytotoxicity and antioxidant system alterations

Leachate, an effluent produced during solid waste decomposition, interacts directly with soil, mainly in dumpsite areas. Studies on terrestrial animal exposure to leachate are, however, lacking. Plants are the most frequently studied organisms, while animal studies, especially earthworms, are limited. Nevertheless, ecotoxicological assessments involving earthworms are crucial due to their role in soil health and ecosystem maintenance, which are paramount in understanding potential terrestrial ecosystem leachate effects. In this context, this study aimed to evaluate behavioral effects, sublethal cytotoxicity and antioxidant system alterations in Eisenia andrei earthworms chronically exposed to leachate from a closed dumpsite. Cytotoxicity was determined by coelomocyte density, viability and cell typing, while antioxidant system alterations were assessed through superoxide dismutase (SOD), catalase (CAT), glutathione-S-transferase (GST), reduced glutathione (GSH) and metallothionein (MT) determinations. Malondialdehyde (MDA) and protein carbonylation (PTC) levels were also determined as oxidative effect markers. Finally, the Biomarker Response Index (BRI) was assessed, aiming to quantitatively integrate the results of the investigated endpoints and establish a biological health state (BHS) for each leachate concentration. Leachate exposure led to leak responses at concentrations of up to 50%, but attraction at higher concentrations. Decreased cell density (28%) was observed after 48 days and reduced viability (50%), after 14 days of leachate exposure. The observed cell typing changes indicate anti-inflammatory immune system effects. Leachate exposure led to several antioxidant system alterations, increasing SOD (2-6 %), CAT (5-35 %) and GST (5-70 %) activities and GSH (7-37%) and MT (3-67%) levels. Earthworm antioxidant defenses were, however, able to prevent lipid peroxidation, which decreased (11-37%) following leachate exposure to concentrations above 12.5%, and PTC, which increased at 42 days (26%) and reduced at 56 days (12 %). This is the first PTC assessment in leachate-exposed earthworms. The increased carbonylation levels observed after 42 days alongside MDA decreases highlight the need for further research employing oxidative effect biomarkers other than MDA. Finally, an integrated approach employing the BRI was carried out, revealing mild initial changes evolving to moderate to major effects at the highest leachate exposure concentration, with an effect attenuation detected at the end of the experiment. In this sense, this study brings forth a significant novelty, employing a biomarker previously not assessed in earthworms, demonstrating an oxidative effect, alongside the use of the BRI as an integrative tool for the endpoints applied in this assessment.

Evaluation the Toxicity of Heavy Metal Mixtures in Anecic Earthworms (Aporrectodea giardi)

Using earthworms as bioindicators of heavy metal contamination in soils is a relevant tool for environmental risk monitoring. This study examines the combined effects of four distinct concentrations mixtures (M1, M2, M3 and M4) containing Cd, Cr, Cu, Ni, Fe and Mn on Aporrectodea giardi earthworms after 12 and 24 days (12 D/24 D) of exposure via the monitoring of certain biomarkers of stress including total protein content, glutathione (GSH), metallothionein (MT), catalase and lipoxygenase (LOX) activities. The results show a decrease in the total protein level for the M3 mixture after 24 D, whereas it increases for all other treatments regardless of exposure time. Glutathione and metallothionine levels increased for M2 and M3 and decreased for M1 and M4 after 12 D; they increased after 24 D for all the mixtures. Regarding enzyme activities, catalase activity was decreased for all the treatments unless for M3 (P > 0.05). However, LOX increased for M1, M2 and M4 except for M3 after 12 D, when inhibition of this biomarker was observed. LOX activity was inhibited for all the mixtures at the end of the treatment. All the mixtures generated oxidative stress in Aporrectodea giardi, which is minimized by increasing MT levels to remove the metal ions and triggering the antioxidant system, composed primarily of GSH and LOX to restore cellular homeostasis. These findings suggest that the species Aporrectodea giardi could be an excellent candidate for ecotoxicological risk assessment of soils contaminated by metal mixtures and it can be used in bioremediation for its fitness which allows it to tolerate high concentrations of metal mixtures.

Environmental relevant concentrations of polystyrene nanoplastics and lead co-exposure triggered cellular cytotoxicity responses and underlying mechanisms in Eisenia fetida

Heavy metal pollution of soils and the widespread use of plastics have caused environmental problems worldwide. Nanoplastics (NPs) contaminants in water and soil environments can adsorb heavy metals, thereby affecting the bioavailability and toxicity of heavy metals. In this paper, the effect of co-exposure of polystyrene microspheres with 100 nm particle size and lead acetate (Pb) on the Eisenia fetida coelomocytes was investigated. The environmental concentration of NPs used was 0.01 mg/L and the concentration of Pb ranged from 0.01 to 1 mg/L, and the exposed cells were incubated at 298 k for 24 h. Our study demonstrated that exposure of cells to environmental relevant concentrations of NPs did not significantly affect the cytotoxicity of Pb exposure. It was shown that co-exposure induced cellular production of reactive oxygen species (ROS, increased to 134.4 %) disrupted the antioxidant system of earthworm body cavity cells, activated superoxide dismutase and catalase (CAT), produced reduced glutathione, and inhibited glutathione-dependent enzyme (GST) activity (Reduced to 64 %). Total antioxidant capacity (T-AOC) is first enhanced against ROS due to the stress of NPs and Pb. When the antioxidant reserves of cells are exhausted, the antioxidant capacity will decrease. The level of malondialdehyde, a biomarker of eventual lipid peroxidation, increased to 231.7 %. At the molecular level, due to co-exposure to NPs and Pb, CAT was loosely structured and the secondary structure is misfolded, which was responsible for exacerbating oxidative damage in E. fetida coelomocytes. The findings of this study have significant implications for the toxicological interaction and future risk assessment of co-contamination of NPs and Pb in the environment.

Damage on DNA and hematological parameters of two bat species due to heavy metal exposure in a nickel-mining area in central Brazil

Exposure to heavy metals in mining zones is a significant threat, which can affect ecosystem services and contribute to the decline of wild bat populations. The present study investigated the impacts caused by mining on two bat species in central Brazil, the nectarivorous Glossophaga soricina and the frugivorous Carollia perspicillata. The bats were collected from a nickel-mining zone (treatment) and a protected area (control). The leukocyte profile of each species was compiled and genotoxicity (comet assay) and mutagenicity (micronucleus test) were determined using the appropriate procedures. Glossophaga soricina presented significantly higher frequencies of eosinophils and monocytes in the mining zone in comparison with the protected area, whereas C. perspicillata presented higher frequencies of lymphocytes in the mining zone, but significantly lower frequencies of monocytes. Concomitantly, G. soricina also presented a higher frequency of DNA damage, although no variation was found in this parameter in C. perspicillata when comparing environments. We also found no significant differences between populations in terms of the frequency of micronuclei and other nuclear abnormalities. Overall, the results of the study indicate that bats are susceptible to immunological disorders and DNA damage in mining zones, with the nectarivorous G. soricina appearing to be relatively more susceptible and thus a potentially effective bioindicator of the impact of contamination in these environments.

Joint toxicity of cadmium and fenpyroximate on two earthworms: Interspecific differences, subcellular partitioning and biomarker responses

Cadmium (Cd) and fenpyroximate are common soil contaminants found together in the field, but their combined toxicity to terrestrial invertebrates has not been studied. Therefore, earthworms Aporrectodea jassyensis and E. fetida were exposed into Cd (5, 10, 50 and 100 μg/g) and fenpyroximate (0.1, 0.5, 1, and 1.5 μg/g) and their mixture, and multiple biomarker responses (mortality, catalase (CAT), superoxide dismutase (SOD), total antioxidant activity (TAC), lipid peroxidation (MDA), protein content, weight loss and subcellular partitioning) were determined to estimate health status and mixture effect. MDA, SOD, TAC, and weight loss were significantly correlated with Cd in total internal and debris (p < 0.01). Fenpyroximate altered the subcellular distribution of Cd. It appears that maintaining Cd in a non-toxic form was the earthworms' primary Cd detoxification strategy. CAT activity was inhibited by Cd, fenpyroximate, and their combined presence. BRI values for all treatments indicated a major and severe alteration in earthworm's health. The combined toxicity of Cd and fenpyroximate was greater than the toxicity of either substance alone. According to EAI, all combined treatments exhibited a clear antagonistic effect. In general, the sensitivity of A. jassyensis was greater than that of E. fetida.

How do different arsenic species affect the joint toxicity of perfluorooctanoic acid and arsenic to earthworm Eisenia fetida: A multi-biomarker approach

Perfluorooctanoic acid (PFOA) and arsenic are widely distributed pollutants and can coexist in the environment. However, no study has been reported about the effects of different arsenic species on the joint toxicity of arsenic and PFOA to soil invertebrates. In this study, four arsenic species were selected, including arsenite (As(III)), arsenate (As(V)), monomethylarsonate (MMA), and dimethylarsinate (DMA). Earthworms Eisenia fetida were exposed to soils spiked with sublethal concentrations of PFOA, different arsenic species, and their binary mixtures for 56 days. The bioaccumulation and biotransformation of pollutants, as well as eight biomarkers in organisms, were assayed. The results indicated that the coexistence of PFOA and different arsenic species in soils could enhance the bioavailability of arsenic species while reducing the bioavailability of PFOA, and inhibit the arsenic biotransformation process in earthworms. Responses of most biomarkers in joint treatments of PFOA and As(III)/As(V) showed more significant variations compared with those in single treatments, indicating higher toxicity to the earthworms. The Integrated Biomarker Response (IBR) index was used to integrate the multi-biomarker responses, and the results also exhibited enhanced toxic effects in combined treatments of inorganic arsenic and PFOA. In comparison, both the biomarker variations and IBR values were lower in joint treatments of PFOA and MMA/DMA. Then the toxic interactions in the binary mixture systems were characterized by using a combined method of IBR and Effect Addition Index. The results revealed that the toxic interactions of the PFOA/arsenic mixture in earthworms depended on the different species of arsenic. The combined exposure of PFOA with inorganic arsenic led to a synergistic interaction, while that with organic arsenic resulted in an antagonistic response. Overall, this study provides new insights into the assessment of the joint toxicity of perfluoroalkyl substances and arsenic in soil ecosystems.

Evaluation of the treatment performance and reuse potential in agriculture of organized industrial zone (OIZ) wastewater through an innovative vermifiltration approach

Vermifiltration (VF) is a natural and sustainable biofilter that has many advantages, including being energy-free, cost-effective, and allowing ease of application and maintenance. In this study, the effectiveness of a lab-scale VF system was assessed by the removal efficiency of total suspended solids, electrical conductivity, chemical oxygen demand, total nitrogen, total phosphorus, fecal coliform, and heavy metals in organized industrial zones (OIZ) and domestic wastewater (DW) for the first time. Additionally, the reuse suitability of the treated wastewater was determined by comparing different countries' and global irrigational criteria. The lab systems were built with four layers: one worm-bed and three varying filtering materials, and operated at an optimum hydraulic loading rate of 1.8-2 m³/m²/day for 45 days with Eisenia fetida as the earthworm species. The results demonstrated that removal efficiencies of total suspended solids and chemical oxygen demand were found to be 95% and 80% in OIZ wastewater and 90% and 88% in DW, respectively. Total nitrogen and total phosphorus were removed at rates of 69% and 67% in OIZ wastewater, respectively, and 84% and 74% in DW. Besides, the VF system has shown satisfactory removal performance for heavy metals ranging from 51% to 77% in OIZ wastewater that has met Turkish national wastewater discharge limits. Although the final characterization of treated wastewater was suitable, heavy metal and fecal coliform levels have not met many countries' irrigation water quality criteria. To meet global irrigation standards and to enhance the VF performance, further experimental studies should be carried out, including parameters such as bed material type in the reactor, worm type, and different operating conditions.

Revealing microcystin-LR ecotoxicity to earthworm (Eisenia fetida) at the intestinal cell level

Potential adverse effects of microcystin-LR (MC-LR) on soil invertebrates have not been studied. Here we investigated the mechanism of MC-LR toxicity to earthworm (Eisenia fetida) intestine at the individual level and at the cellular level. The results showed an inverse relationship between the bodyweight and survival rate of earthworms over exposure time- and MC-LR doses in soil. Dose-dependent intestinal lesions and disturbances of enzymatic activities (e.g., cellulase, Na⁺/K⁺-ATPase, and AChE) were observed, which resulted in intestinal dysfunction. Excessive reactive oxygen species generation led to DNA damage and lipid peroxidation of intestinal cells. The oxidative damage to DNA prolonged cell cycle arrest at the G2/M-phase transition in mitosis, thus stimulating and accelerating apoptosis in earthworm intestine. MC-LR target earthworm intestine tissue. MC-LR at low concentrations can damage earthworm intestine regardless of exposure routes (oral or contact). High toxicity of MC-LR to earthworms delineates its ecological risks to terrestrial ecosystems.

Reproductive damage and compensation of wild earthworm Metaphire californica from contaminated fields with long-term heavy metal exposure

Reproduction is a significant biological process for organisms responding to environmental stresses, however, little is known about the reproductive strategies of invertebrates under long-term exposure to contaminations. In this study, earthworm Metaphire californica (Kinberg, 1867) from contaminated fields with an increased metal gradient were collected to investigate their reproductive responses. The results showed heavy metals (Cd, Cu, Zn, and Pb) induced histological damage to earthworms' seminal vesicles, including tissue disorders and cavities, and decreases in mature spermatozoa. Sperm morphology analysis indicated deformity rates were up to13.2% (e.g. head swollen or missing) for worms from the most contaminated site, which coincided with DNA damages. Furthermore, the computer-assisted sperm analysis (CASA) system was employed for the evaluation of sperm kinetic traits. Results suggested earthworms exposed to higher contamination showed a lower sperm viability rate but faster sperm velocity after re-exposure with Cd solution (like the curvilinear velocity and straight-line velocity paraments) compared with those from relatively clean sites. The activities of lactate dehydrogenase and sorbitol dehydrogenase showed the highest 32.5% and 12.5% up-regulation respectively with the increased metal gradient. In conclusion, this study elucidated the earthworm reproductive toxicity, underlying reproductive compensation, metal stress-induced damages, and adaptive responses caused by heavy metal exposure, while also providing the possibility of sperm trait analysis (CASA) for related earthworm toxicological studies.

Complexation, retention and release pattern of arsenic from humic/fulvic acid extracted from zinc and iron enriched vermicompost

Arsenic (As) is a highly poisonous heavy metal with major environmental ramifications. Inorganic components such as zinc (Zn) and iron (Fe), as well as organic vermicompost, have been used as management solutions, with limited attempts of using them together. The current study involved preparing non-enriched vermicompost as well as six distinct Zn and Fe enriched vermicomposts and analyzing their chemical composition using the standard procedures. Organic fractions from these seven vermicompost and arsenic polluted soils of West Bengal, India were recovered and separated into humic (HA) and fulvic acid (FA) fractions. Potentiometric titrations, viscometric assays, and visible spectrophotometry were used to characterize the HA and FA samples. In aqueous phase the stability constant (log K) of the complexes formed with As indicates that stability of FA extracted from enriched vermicompost V₄ (Zn and Fe sulphate @ 10% w/w dry weight basis of composting substrates before application of vermiworms) was maximum as 10.20 with a mole ratio (x) value of 1.36. Fourier-transform infrared (FT-IR) spectroscopy and Scanning Electron Microscopy (SEM) studies confirmed the complexation of As with HA/FA. The release isotherm of As from the HA/FA complexes in the presence of competitive oxy-anions was found to follow the order of sulphate > nitrate > phosphate.

How a functional soil animal-earthworm affect arbuscular mycorrhizae-assisted phytoremediation in metals contaminated soil?

Phytoremediation is a promising and sustainable technology to remediate the risk of heavy metals (HMs) contaminated soils, however, this way is limited to some factors contributing to slow plant growth and low remediation efficiency. As soil beneficial microbe, arbuscular mycorrhizal fungi (AMF) assisted phytoremediation is an environment-friendly and high-efficiency bioremediation technology. However, AMF-symbiotic formation and their functional expression responsible for HMs-polluted remediation are significantly influenced by edaphic fauna. Earthworms as common soil fauna, may have various effects on formation of AMF symbiosis, and exhibit synergy with AMF for the combined remediation of HMs-contaminated soils. For now, AMF-assisted phytoremediation incorporating earthworm coexistence is scarcely reported. Therefore, the main focus of this review is to discuss the AMF effects under earthworm coexistence. Effects of AMF-symbiotic formation influenced by earthworms are fully reviewed. Moreover, underlying mechanisms and synergy of the two in HMs remediation, soil improvement, and plant growth were comprehensively elucidated. Phenomenon of "functional synergism" between earthworms and AMF may be a significant mechanism for HMs phytoremediation. Finally, this review analyses shortcomings and prescriptions in the practical application of the technology and provides new insights into AMF- earthworms synergistic remediation of HMs-contaminated soils.

In vitro cultivation of primary intestinal cells from Eisenia fetida as basis for ecotoxicological studies

The earthworm Eisenia fetida is a commonly used model organism for unspecific soil feeders in ecotoxicological studies. Its intestinal cells are the first to encounter possible pollutants co-ingested by the earthworm, which makes them prime candidates for studies of toxic effects of environmental pollutants on the cellular as compared to the organismic level. In this context, the aim of this study was to demonstrate the suitability of preparations of primary intestinal E. fetida cells for in vitro ecotoxicological studies. For this purpose, a suitable isolation and cultivation protocol was established. Cells were isolated directly from the intestine, maintaining >85% viability during subsequent cultivations (up to 144 h). Exposure to established pollutants and soil elutriates comprising silver nanoparticles and metal ions (Cu²⁺, Cd²⁺) induced a significant decrease in the metabolic activity of the cells. In case of microplastic particles (MP particles), namely 0.2, 0.5, 2.0, and 3.0 µm diameter polystyrene (PS) beads as well as 0.5 and 2.0 µm diameter polylactic acid (PLA) beads, no active uptake was observed. Slight positive as well as negative dose and size dependent effects on the metabolism were seen, which to some extent might correlate with effects on the organismic level.

Earthworms as candidates for remediation of potentially toxic elements contaminated soils and mitigating the environmental and human health risks: A review

Global concerns towards potentially toxic elements (PTEs) are steadily increasing due to the significant threats that PTEs pose to human health and environmental quality. This calls for immediate, effective and efficient remediation solutions. Earthworms, the 'ecosystem engineers', can modify and improve soil health and enhance plant productivity. Recently, considerable attention has been paid to the potential of earthworms, alone or combined with other soil organisms and/or soil amendments, to remediate PTEs contaminated soils. However, the use of earthworms in the remediation of PTEs contaminated soil (i.e., vermiremediation) has not been thoroughly reviewed to date. Therefore, this review discusses and provides comprehensive insights into the suitability of earthworms as potential candidates for bioremediation of PTEs contaminated soils and mitigating environmental and human health risks. Specifically, we reviewed and discussed: i) the occurrence and abundance of earthworms in PTEs contaminated soils; ii) the influence of PTEs on earthworm communities in contaminated soils; iii) factors affecting earthworm PTEs accumulation and elimination, and iv) the dynamics and fate of PTEs in earthworm amended soils. The technical feasibility, knowledge gaps, and practical challenges have been worked out and critically discussed. Therefore, this review could provide a reference and guidance for bio-restoration of PTEs contaminated soils and shall also help developing innovative and applicable solutions for controlling PTEs bioavailability for the remediation of contaminated soils and the mitigation of the environment and human risks.

Counting Enchytraeus crypticus Juveniles in Chronic Exposures: An Alternative Method for Ecotoxicity Studies Using Tropical Artificial Soil

Soil toxicity tests are commonly applied using Enchytraeus crypticus to analyze reproductive outputs. However, the traditional method for counting potworms takes a long time due to the significant number of offspring. This paper compares the conventional total counting of E. crypticus juveniles (M1) and an alternative methodology (M2). The proposed methodology (M2) uses a simple random counting method (1/4) for the partial counting of juveniles and total estimation. Chronic bioassays (21 days of exposure) were performed in tropical artificial soil (TAS) using sugarcane vinasse as a hazardous substance. Comparing the final density of juveniles recorded in M1 and M2, no statistical differences were pointed out in either one. Applying analyses based on effective concentration (EC10 and EC50), no statistical differences were identified there either. The t-test showed that there was no statistical difference between the counting methods (M1 and M2) in each treatment (control and dilutions). Moreover, we ran the Tukey test for M1 and M2 methods separately and observed that 100 % of the vinasse showed a statistical difference compared to the control treatment in both (p ≤ 0.05), affirming that independent of the counting method, the ecotoxicological outputs were similar. Therefore, the proposed alternative is a suitable method for bioassay using. E. crypticus in tropical artificial soil, decreasing to 1/4 the total time required for counting.

Outdoor disinfectant sprays for the prevention of COVID-19: Are they safe for the environment?

Due to the wide range of viability on inanimate surfaces and fomite transmission of SARS-CoV-2, hydrogen peroxide (0.5%, HP) and hypochlorite-based (0.1%, HC) disinfectants (common biocides) are proposed by World Health Organization to mitigate the spread of this virus in healthcare settings. They can be adopted and applied to outdoor environments. However, many studies have shown that these two disinfectants are toxic to fishes and aquatic non-target organisms (primary producers and macroinvertebrates). The global market of these disinfectants will increase in coming years due to COVID-19. Therefore, it is urgent to highlight the toxicities of these disinfectants. The main findings of this article allow the community to develop a new strategy to protect the environment against the hazardous effects of disinfectants. Therefore, we use the "toxicity calculated ratio (TC ratio)" that refers to the fold increase or decrease in the toxicities reported in the literature (NOEC, LOEC, LC50 and EC50) relative to the WHO-recommended dose of HP and HC. The calculated TC ratios are valuable for policy makers to formulate the regulations to prevent disinfectant exposure in the environment. Our results were collected via PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-analysis) guidelines and showed that the TC ratios are from the single digits to several thousand-fold lower than the HP and HC recommended dose, which means these disinfectants are potentially dangerous to non-target organisms. The results also showed that HP and HC are toxic to the growth and reproduction of non-target organisms. Therefore, we recommend policymakers formulate protocols for critical assessment and monitoring of the environment-especially on non-target organisms in water bodies located in and around disinfectant-exposed areas to safeguard the environment in the future.

Metallothionein dependent-detoxification of heavy metals in the agricultural field soil of industrial area: Earthworm as field experimental model system

Earthworms are known to reclaim soil contamination and maintain soil health. In the present study, the concentration of DTPA extractable heavy metals, Cd, Cu, Cr, Pb, and Zn in vermicasts and tissues of the earthworms (anecic: Lampito mauritii; epigeic: Drawida sulcata) collected from the soils of four different industrial sites, Site-I (Sago industry), Site-II (Chemplast industry), Site-III (Dairy industry) and Site-IV (Dye industry) have been studied. The heavy metals in industrial soils recorded were 0.01-326.42 mg kg^-1 with higher Cu, Cr, and Zn contents while the vermicasts showed lower heavy metal loads with improved physicochemical properties and elevated humic substances. The higher humic substances dramatically decreased the heavy metals in the soil. The bioaccumulation factors of heavy metals (mg kg^-1) are in the order: Zn (54.50) > Cu (17.43) > Cr (4.54) > Pb (2.24) > Cd (2.12). The greatest amount of metallothionein protein (nmol g^-1) was recorded in earthworms from Site-IV (386.76) followed by Site-III (322.14), Site-II (245.82), and Site-I (232.21). Drawida sulcata can produce a considerable amount of metallothionein protein than Lampito mauritii as the metallothionein production is dependent upon the presence of pollutants. The molecular docking analysis indicates a binding score of 980 for Cd, Cr and Cu, and 372 for Zn. Pb may bind with a non-metallothionein protein of earthworms and bio-accumulated in the internal chloragogenous tissues. Metallothionein neutralizes the metal toxicity and controls the ingestion of essential elements.

The chronic effects of CuO and ZnO nanoparticles on Eisenia fetida in relation to the bioavailability in aged soils

The bioavailability and bioaccumulation of metal-based engineered nanoparticles (ENPs) in soils need to be evaluated in environmentally relevant scenarios. The aim of this study was an analysis of potentially available metal-component ENPs (nano-ZnO and nano-CuO) in soils. Earthworms (Eisenia fetida) were used to examine the bioaccumulation potential of ENPs. Micro-particles (micro-ZnO and micro-CuO) and metal salts (ZnCl₂ and CuCl₂) were used to evaluate the nano-effect and the activity of dissolved ions, respectively. Zn- and Cu-compounds were added to sandy loam and silt loam at a concentration of 10 mg kg^-1. The bioavailable fractions of metals were extracted from soil using H₂O, MgCl₂ with CH₃COONa or EDTA. EDTA was the most effective extractant of Zn and Cu (10.06-11.65 mg Zn kg^-1 and 2.69-3.52 mg Cu kg^-1), whereas the H₂O-extractable metal concentration was at the lowest level (1.98-2.12 mg Zn kg^-1 and 0.54-0.82 Cu mg kg^-1). The bioavailable metal concentrations were significantly higher in silt loam than sandy loam soil, which was related to the higher pH value of silt. There were no significant differences between the Zn content in the earthworms incubated in the two soils, which may confirm the auto-regulation of the Zn content by earthworms. However, the bioaccumulation of Cu was strongly correlated with the extractable Cu concentrations. The juvenile earthworms accumulated Cu and Zn more than adults. Based on our results, aging neutralized the differences between the ionic and particulate effects of metal-compounds.

Dose-dependent effects of lead and cadmium and the influence of soil properties on their uptake by Helix aspersa: an ecotoxicity test approach

Three soil types with different physicochemical properties were selected to evaluate their effect on lead and cadmium bioavailability and toxicity in the land snail Helix aspersa. In 28-day ecotoxicity tests, H. aspersa juveniles were exposed to increasing concentrations of Pb or Cd. EC50s, concentrations reducing snail growth by 50%, differed between the soils and so did Cd and Pb uptake in the snails. For lead, EC50s were 2397-6357 mg Pb/kg dry soil, while they ranged between 327 and 910 mg Cd/kg dry soil for cadmium. Toxicity and metal uptake were highest on the soil with the lowest pH, organic matter content and Cation Exchange Capacity (CEC). Growth reduction was correlated with metal accumulation levels in the snails' soft body, and differences in toxicity between the soils decreased when EC50s were expressed on the basis of internal metal concentrations in the snails. These results confirm the effect of soil properties; pH, CEC, OM content, on the uptake and growth effect of Pb and Cd in H. aspersa, indicating the importance of properly characterizing soils when assessing the environmental risk of metal contaminated sites.

Compartmentation and effects of lead (Pb) in the collembolan, Folsomia candida

The impact of soil lead (Pb) pollution on survival, growth, and reproduction of the collembolan, Folsomia candida, and Pb compartmentation in its gut and remaining body parts were studied by exposing animals to laboratory-spiked soil. The survival, growth, and reproduction of F. candida were significantly reduced by increasing soil Pb concentration. The LC₅₀ values of survival based on total and CaCl₂-extractable Pb concentration in soil were 2562 mg kg^-1 and 351 mg kg^-1, respectively. The EC₅₀ values of reproduction were 1244 mg kg^-1 and 48 mg kg^-1, respectively. The Pb concentration in whole body, gut, and remaining body parts was significantly increased with the increase of soil Pb concentration and followed an exponential increase when the soil Pb concentration was equal to or above a threshold (1000 mg kg^-1 for whole body and remaining body part, 500 mg kg^-1 for gut). Below this threshold, these relationships were linear. The Pb concentration in the gut was higher than whole body and remaining body part of F. candida, and the threshold of internal Pb concentration at which F. candida can compensate was in the range 7-13 mg Pb kg^-1 dry animal (corresponding to soil Pb concentration 500-1000 mg Pb kg^-1 dry soil). The results indicate that reproduction of F. candida was a more sensitive indicator of lead toxicity than survival and growth. Pb was mainly accumulated in the gut of F. candida. We discuss the internal Pb concentration as an indicator of adverse effects in the risk assessment of soil Pb pollution.

Residue and toxicity of cyantraniliprole and its main metabolite J9Z38 in soil-earthworm microcosms

As part of a new generation of diamide insecticides, cyantraniliprole has broad application prospects. In the present study, a QuEChERS-UPLC-MS/MS method was established to determine the residues of cyantraniliprole and its main metabolite J9Z38 in soil and earthworms. Moreover, the accumulation and toxicity of cyantraniliprole and J9Z38 in earthworms were evaluated. The present results show that the detection method of cyantraniliprole and J9Z38 has high sensitivity and accuracy, which could be used for the accurate quantification of cyantraniliprole and J9Z38 residues in soil and earthworms. Additionally, cyantraniliprole degraded faster than its main metabolite J9Z38 in the artificial soil. Moreover, the bioenrichment efficiency of cyantraniliprole was higher than J9Z38. The toxicity test result showed that cyantraniliprole and J9Z38 could induce oxidative stress effect in earthworms from 5.0 mg/kg, finally resulting in cellular damage. Moreover, the oxidative damage degree induced by cyantraniliprole was higher than J9Z38. Combining the results of residue test and toxicity test, although cyantraniliprole degraded faster than its main metabolite J9Z38 in the artificial soil, its risk to earthworms was higher than J9Z38.

Use of integrated biomarker response for studying the resistance strategy of the earthworm Metaphire californica in Cd-contaminated field soils in Hunan Province, South China

Research was conducted to study the response and detoxification mechanisms of earthworms collected from Cd-contaminated areas in Hunan Province, South China. Metaphire californica, the dominant earthworm species in fields, referred as earthworm-A and -B that collected from low- (0.81 mg kg^-1) and high-Cd soil (13.3 mg kg^-1), respectively, for exchanging incubation in laboratory. The results showed that earthworm-A gradually accumulated higher Cd when exposed in the high-Cd soil, whereas Cd concentration of earthworm-B decreased after being transferred to low-Cd soil (albeit BAF_Cd >20). The integrated biomarker response index was calculated with the biomarkers of antioxidant systems (e.g., superoxide dismutase (SOD), peroxidase (POD), glutathione (GSH), glutathione peroxidase (GPx), glutathione-S transferase (GST), and malondialdehyde (MDA)) and energy index (e.g., protein and glycogen) in M. californica. GSH, GPx, and GST contributed the most to the integrated biomarker response (IBR) in earthworm-A when exposed in high-Cd soil for 14 d. Earthworm-B responded with higher GST and GPx activities and decreased protein content in low-Cd soil. For 28 d, the response of earthworm-A was not evident in either low- or high-Cd soil, and the inductive effect of metal stress on earthworm-B tended to be stable, except for the higher MDA content (p < 0.05) when exposed in low-Cd soil. The IBR index of earthworm-B (2.93 and 3.40) in low- and high-Cd soil, respectively, was higher than that of earthworm-A (0.89 and 1.0). Overall, earthworm-A exhibited a detoxification process to resist high-Cd toxicity from low-to high-Cd soil. Earthworm-B exhibited a physiological resilience once its habitat had changed to a normal or low-Cd soil environment, possibly owing to the cost of its resistance adaptation to the historical highly contaminated soil in fields.

Interaction effects of salinity, sewage sludge, and earthworms on the fractionations of Zn and Cu, and the metals uptake by the earthworms in a Zn- and Cu-contaminated calcareous soil

This study assessed the effects of salinity and sewage sludge on the fractionation of Zn and Cu in a soil around a lead-zinc mine as well as their uptake by earthworms (Eisenia fetida) in order to identify novel methods for employing the earthworms in waste management techniques. Eisenia fetida specimens were kept under laboratory conditions for 42 days. The first treatment involved the addition of 0%, 2%, 4%, and 8% (w/w) sewage sludge to contaminated soil. In the second treatment, NaCl was added to the soil at concentrations of 0, 1170, 2340, 3510, and 4680 mg L^-1. The results indicated that the combined application of high salinity and sewage sludge had adverse effects on the survival of the earthworms. The presence of the earthworms increased the amount of Zn and Cu bound to organic matter. The organic fraction of Zn and Cu also significantly aggregated with increasing salinity levels. The interaction of salinity and earthworm showed that the residual Cu fraction increased with the presence of earthworm and decreased with increasing salinity. The residual fraction of Cu was significantly affected by the interactions of salinity and sewage sludge, where the highest amount was seen in the EC₀ (distilled water) × SS₈ (8% sewage sludge) treatment. The Zn and Cu contents increased with the earthworms when exposed to higher levels of salinity and sewage sludge.

Assessment of the immobilization effectiveness of several amendments on a cadmium-contaminated soil using Eisenia fetida

Proper protocols for assessing the remediation effectiveness of contaminated soils are an important part of remediation projects. In the present study, the residual immobilization effectiveness of hydrated lime (L), hydroxyapatite (H), biochar (B) and organic fertilizer (F) alone and in combination was assessed by Eisenia fetida. The results showed that the application of amendments had no significant effect on the death rate and average fresh weight loss of earthworms. The earthworm Cd concentration increased with prolonged exposure time, however, the significant immobilization efficacy of amendments observed on the 7th day nearly disappeared after 28 days of exposure. The immobilization efficiencies, estimated by the earthworms internal Cd concentration, of L, H and B on the 7th day were 38.6%, 37.8% and 20.7%, respectively. These values decreased to 4.9%, 19.8% and 15.1%, respectively, on the 28th day. The detoxification effect of amendments was confirmed by the Cd subcellular fractionation in earthworms with lower proportions of Cd distributed in the metal-sensitive fractions in L, H and B treatments. The level of oxidative stress response of earthworms increased with exposure duration and amendments alleviated the oxidative damage induced by Cd to the earthworms. In addition, the pH and CaCl₂-Cd in soils were both increased due to earthworm life activities and gut-related ingestion. In summary, the assessment of immobilization effectiveness of heavy metal-contaminated soils using Eisenia fetida was time-dependent. The immobilization efficacy of L and H performed better than B and F on the 7th day, while H and B performed better than L and F on the 28th day. Accordingly, the short-term earthworm exposure experiment (7 days) was recommended to be an alternative approach to time-consuming plant bioassays in assessment of reduced phytoavailability in chemical immobilization remediation. But the impact of earthworms on the immobilization effect of amendments needs to be considered in practical remediation.

Interspecific differences in toxicological response and subcellular partitioning of cadmium and lead in three earthworm species

Earthworms are often used as test subjects in toxicological studies, due to their ubiquitousness and sensitivity to contaminant exposure. Such testing is typically conducted using Eisenia fetida as the test subject, but continued use of E. fetida (eco) toxicology is questionable. Therefore, in this study three earthworm species, Aporrectodea rosea, Aporrectodea trapezoides and E. fetida, were exposed to lethal and sublethal concentrations of cadmium (Cd) and lead (Pb) nitrate in artificial soil for 7, 14 and 28 days. A biomarker of genotoxicity (TUNEL assay), biochemical markers [malondialdehyde (MDA) and total antioxidant capacity (TAC)], weight loss, lethal toxicity (LC₅₀) and subcellular partitioning were assessed. Cadmium and Pb caused significant inhibition in TAC and growth and significant increases in DNA damage and lipid peroxidation in the earthworms. Acute toxicity rank (14 days) for both Cd and Pb were E. fetida > A. trapezoides > A. rosea. Subcellular partitioning of Cd and Pb in the earthworms were cytosol > debris > granules and debris > granules > cytosol, respectively. Comparison of biomarker responses between study species showed that E. fetida proved to be less susceptible to Cd and Pb exposure than A. rosea and A. trapezoides. Therefore, this study confirms that A. rosea and A. trapezoides are more suitable as subjects than E. fetida for the soil toxicity tests, because of both their greater susceptibility to toxicants and in their abundance in the field.

Assessment of Toxicity to Earthworm Eisenia fetida of Lead Contaminated Shooting Range Soils with Different Properties

The objective of the study was to evaluate the toxicity of trace elements to earthworms (Eisenia fetida) in recreational and military shooting range soils. The earthworms were exposed to soils; then mortality, growth, and reproduction endpoints were determined. In the recreational shooting range, the total Pb concentration was 6151 mg kg^-1 and in the soil of the impact berm of the military shooting range, it was 653 mg kg^-1. These Pb contaminated soils caused significantly higher mortality, weight loss and lower reproduction than the reference grassland soil. The most sensitive indicator was reproduction rate - a significantly lower cocoon production was found in shooting range soils than in reference soil. The soil organic matter content and bulk density also influenced survival of earthworms.

The toxicity thresholds of metal(loid)s to soil-dwelling springtail Folsomia candida-A review

Increasing concentrations of metals in soil have posed a serious threat to the soil environment. The control and evaluation of soil metal hazards demand the establishment of soil ecological criteria, which is mainly based on the obtainment of toxicity thresholds. As the most typical representative of soil-dwelling springtails, Folsomia candida performs numerous essential ecological functions in soil and has been extensively used to investigate metal toxicity effects and thresholds. This review outlined the current state of knowledge on the metal toxicity thresholds to Folsomia candida, including (1) toxicity thresholds of soil metals for the different endpoints, (2) the influence factors of metal toxicity thresholds including the test conditions, the chemical forms of metal, the soil physicochemical properties, aging time and leaching, (3) the bioavailable fractions predicting metal toxicity thresholds, (4) the internal threshold of metals. To conclude, several recommendations for future research are given to obtain the more reliable toxicity thresholds and further supplement the toxicity data of metals to Folsomia candida.

Influence of earthworm bioturbation on metals phytoavailability and human gastric bioaccessibility

At the global scale, urban agriculture is increasingly developing in cities due to demographic growth and sustainable food concerns. But, urban soils are frequently polluted with metals. In urban gardens, organic matter is also commonly added both to valorize organic household waste and to promote biophysicochemical fertility. As earthworms promote the decomposition and the recycling of soil organic matter, they can also influence the biogeochemical cycle of metals in urban polluted soils. In order to produce safe vegetables in urban areas, it is crucial to highlight the mechanisms involved in complex soil-earthworm-plant ecosystems. An experiment was set up to examine these relationships using lettuce cultivated in controlled conditions with RHIZOtest® devices. Thanks to the RHIZOtest® devices, metal transfer and bioaccessibility were for the first time compared for urban polluted soil without (1-urban soil polluted with Pb, Cd, Cu, and Zn: essential or toxic metals currently found in environment, SNB) and with bioturbation (2-this metal-polluted soil subjected to earthworm bioturbation, SB) and earthworm casts (3-earthworm casts produced in this polluted soil and naturally enriched in organic matter and microorganisms, T). Metal concentration, phytoavailability, and human gastric bioaccessibility were determined in the different samples. Results showed that earthworm bioturbation increased the phytoavailability of all the metals. For the experimental condition SB, the phytoavailability of metals was increased up to 75% compared to SNB. In addition, surprisingly, metal phytoavailability was always superior in SB compared to earthworm casts (T). Moreover, earthworms led to an increase in Zn gastric bioaccessibility up to 10% in the soils in the same way as for phytoavailability, meaning Zn bioaccessibility in SB > T > SNB, whereas it remained unchanged in the lettuces. These data are important to promote sustainable agriculture activities in urban areas; actually, databases concerning different experimental conditions are needed to develop decision support tools.

Biochemical and reproductive effects of red mud to earthworm Eisenia fetida

Red mud (RM) is the main waste of alumina production whose disposal poses a problem. The research of various possible effects of red mud on soil organisms has been scarce. We have exposed earthworms (Eisenia fetida) to red mud: artificial soil mixtures. The tested samples of red mud were of different origin: Croatian (CRRM) and Hungarian (HURM). The effects of exposure on the metabolic and oxidative status of earthworms were measured using several biochemical biomarkers (acetylcholinesterase, catalase and glutathione S-transferase activity and metallothionenin content) and reproductive success was assessed upon counting the number of hatched juveniles. The LC₅₀ value for CRRM was 40% and for HURM 62% of red mud in the growth medium on weight basis, respectively. A significant effect (p < 0.001) of the RM concentration and origin, as well as significant interactions between the origin of RM and the applied concentrations on all measured biomarkers were observed. CRRM had a higher content of different metals as well as a higher conductivity in comparison to HURM. The reproduction was inhibited after exposure to both RMs. Namely, 25% CRRM caused a 53.26% reduction in the number of juveniles, whereas 18% HURM caused a 68.84% reduction, and 50% HURM caused 97.9% reduction, respectively. Both RMs caused changes in the measured biomarkers related to an oxidative stress. Consequently, the possible adverse effects on soil organisms before the environmental application of red mud should be assessed to avoid further environmental damage.

Spatial variability and seasonal toxicity of dredged sediments from Guanabara Bay (Rio de Janeiro, Brazil): acute effects on earthworms

The toxicity of dredged sediments from Guanabara Bay (Rio de Janeiro, Brazil) was evaluated using acute bioassays with Eisenia andrei and metal determination. The sediments were collected in August 2014 (winter) and February 2015 (summer) and in five areas distributed along the Bay: Port of Rio de Janeiro, Port of Niterói, Meriti River mouth, Iguaçu River mouth, and the Environmental Protection Area (APA) of Guapimirim. The sediments were mixed with a ferralsol (a representative Brazilian tropical soil) in proportions varying between 0 (pure soil) and 30%. The acute bioassays with E. andrei followed a standard protocol (ISO 11268-2:2012). Total metal determination in the sediments was performed by ICP-OES. The medium lethal earthworm concentration (LC₅₀) was estimated through PriProbit analysis. The sediments from the APA of Guapimirim, which is a control area at the Guanabara Bay, were the only ones whose total metal concentrations were in agreement with the limits established by Brazilian law for land disposal of dredged sediments. However, the sediments collected in the APA of Guapimirim were the most toxic ones among the study areas due to very high contents of salts in these materials. Winter sediments were generally more toxic compared to the summer ones due to the increase of metal concentrations and salt precipitation to bottom sediments during the winter. The exceptions were (i) the sediments from APA of Guapimirim, where the toxicity in the summer (LC₅₀ = 3.99%) and winter (LC₅₀ = 4.60%) were relatively similar to each other, since the toxicity is linked to salt in excess; and (ii) the Iguaçu River mouth, where the presence of mangrove areas might be associated with the filtering of pollution sources (winter LC₅₀ = 12.67%; summer LC₅₀ = 11.58%). In the Port of Rio de Janeiro, LC₅₀ obtained in the winter (7.30%) was almost three times lower than that found in the summer (19.64%). The sediments from Meriti River mouth showed the highest total metal concentrations, were the most toxic sediments among the study areas (excluding the APA of Guapimirim), and its winter LC₅₀ (6.64%) was almost twice lower than that obtained in the summer (12.55%). By following the same tendency, summer LC₅₀ (17.52%) found for the sediment collected in the Port of Niterói was also higher than the value found in the winter (12.34%). Finally, the dredged sediments from Guanabara Bay were toxic to earthworms in mixtures with pure ferralsol and winter samples were generally more toxic than the summer ones, in agreement with the increase of metal and salt concentrations during the winter.

Influence of metal-contamination on distribution in subcellular fractions of the earthworm (Metaphire californica) from Hunan Province, China

Earthworms have the ability to accumulate of heavy metals, however, there was few studies that addressed the metals in earthworm at subcellular levels in fields. The distributions of metals (Cd, Cu, Zn, and Pb) in subcellular fractions (cytosol, debris, and granules) of earthworm Metaphire californica were investigated. The relationship between soil metals and earthworms were analyzed to explain its high plasticity to inhabit in situ contaminated soil of Hunan Province, south China. The concentration of Cd in subcellular compartments showed the same pattern as Cu in the order of cytosol > debris > granules. The distribution of Zn and Pb in earthworms indicated a similar propensity for different subcellular fractions that ranked as granules > debris > cytosol for Zn, and granules > cytosol > debris for Pb. The internal metal concentrations in earthworms increased with the soil metals (p<0.05). Significant positive correlations were found between soil Cd and Cd concentrations in cytosol and debris (p<0.01). Moreover, the soil Pb concentration significantly influenced the Pb concentrations in cytosol and debris (p<0.01), similar to that of Cd. The soil Cu concentrations was only associated with the Cu in granules (p<0.05). Soil Zn concentrations correlated with the Zn concentrations in each subcellular fraction (p<0.05). Our results provide insights into the variations of metals partitioning in earthworms at subcellular levels and the relationships of soil metals, which could be one of the detoxification strategies to adapt the long-term contaminated environment.

Structural equation model of the relationship between metals in contaminated soil and in earthworm (Metaphire californica) in Hunan Province, subtropical China

Earthworms have the ability to take up heavy metals in soil and partition them in different subcellular compartments. In this study, we used a structural equation model (SEM) to investigate the two-step causal relationship between environmental availability (EA) and environmental bioavailability (EB) of heavy metals (Cd, Cu, Zn, and Pb), as reflected by their levels in soil fractions and in earthworms from field-contaminated areas in Southern China. In the SEM, the correlation between EA and EB reflected the bioavailability of Cd, Zn, and Pb. For Cd, the causal relationship between the latent variables EA and EB was reflected by DTPA fractions in soil as well as by earthworm internal and subcellular cytosol fractions. The extractable and oxidizable fractions of Zn in soil influenced Zn concentrations in the cytosol and debris. The DTPA and reducible Pb fractions were bioavailable to earthworm internal Pb concentrations and those in cytosol fractions. These results implied that the DTPA, extractable, oxidizable, or reducible fractions of different metals could be the bioavailable sources to earthworm internal metals and partitioned in their subcellular compartments.

Arsenic characteristics in the terrestrial environment in the vicinity of the Shimen realgar mine, China

In this study, multiple types of samples, including soils, plants, litter and soil invertebrates, were collected from a former arsenic (As) mine in China. The total As concentrations in the soils, earthworms, litter and the aboveground portions of grass from the contaminated area followed the decreasing order of 83-2224 mg/kg, 31-430 mg/kg, 1-62 mg/kg and 2-23 mg/kg, respectively. X-ray absorption near-edge structure (XANES) analysis revealed that the predominant form of As in the soils was arsenate (As(V)), while no arsenite (As(III)) was detected. In the grass and litter of the native plant community, inorganic As species (As(V) and As(III)) were the main species, while minor amounts of DMA, MMA, AsC, and an unknown As species were also detected in the extracts analyzed with high-performance liquid chromatography inductively coupled plasma mass spectrometry (HPLC-ICP-MS). The As speciation and As concentrations varied with the plant species, and very high As levels (197-584 mg/kg) and proportions of inorganic As (>99%) were found in two As-hyperaccumulating ferns, Pteris vittata and Pteris cretica. The major As species extracted from earthworms were inorganic, with proportions of 51-53% As(III) and 38-48% As(V). AsB was the only organic species present in the earthworm samples, although at low proportions (<8.99%). The internal bioconversion of other As species is hypothesized to contribute greatly to the formation and accumulation of AsB in earthworms, although the direct external absorption of organic As from soils might be another source. This study sheds light on the potential sources of complex organoarsenicals, such as AsB, in terrestrial organisms.

Effects of soot by-product from the synthesis of engineered metallofullerene nanomaterials on terrestrial invertebrates

The synthesis of carbon-based nanomaterials is often inefficient, generating large amounts of soot with metals as waste by-product. Currently, there are no specific regulations for disposal of engineered nanomaterials or the waste by-products resulting from their synthesis, so it is presumed that by-products are disposed of in the same way as the parent (bulk) materials. We studied the terrestrial toxicity of soot from gadolinium metallofullerene nanomanufacturing on earthworms (Eisenia fetida) and isopods (Porcellio scaber). The metallofullerene soot consisted of carbon particle agglomerates in the nanometer and submicrometer ranges (1-100 and 101-999 nm, respectively), with metals used during nanomanufacturing detectable on the particles. Despite high metal concentrations (>100 000 mg/kg) in the soot, only a relatively small amount of metals leached out of a spiked field soil, suggesting only moderate mobility. Seven- and 14-d exposures in field soil demonstrated that the soot was only toxic to earthworms at high concentrations (>10 000 mg/kg); however, earthworms avoided spiked soils at lower concentrations (as low as 500 mg/kg) and at lower soil pH. The presence of soot in food and soil did not cause isopod avoidance. These data demonstrate that metallofullerene soot from nanomanufacturing may only be toxic to earthworms at high concentrations representative of improper disposal or accidental spills. However, our results indicate that terrestrial invertebrates may avoid soils contaminated with soot at sublethal concentrations. Environ Toxicol Chem 2018;9999:1-12. Published 2018 Wiley Periodicals, Inc. on behalf of SETAC. This article is a US government work, and as such, is in the public domain in the United States of America.

Protective role of metallothionein during regeneration in Eisenia andrei exposed to cadmium

Lumbricid earthworms are often exposed to simultaneous action of various environmental stressors like soil contamination, temperature fluctuation or predators' attacks, which may induce extrusion of coelomocyte-containing coelomic fluid or loss of tail segments. If the injuries are not lethal, renewal of the immune-competent cells and soluble components of coelomic fluid and/or the regeneration of tail segments occurs. The aim of our investigations was to test the hypothesis that exposure of adult earthworms Eisenia andrei to cadmium-polluted soil at room temperature (RT) and/or low temperature (6°C) have adverse effects on restoration of experimentally depleted coelomocytes or on regeneration of amputated posterior segments. Intact control earthworms and their experimental counterparts subjected to electrostimulation-induced coelomocyte depletion or surgical amputation of posterior segments were maintained either in control soil or in soil spiked with cadmium chloride (500mg/kg air-dried soil) at RT or 6°C. Four weeks after the beginning of experiments, cadmium accumulation in earthworm bodies was significantly lower at 6°C than at room temperature. The numbers of restored cells and fluorophore contents were hardly affected by temperature or cadmium. However, cocoon production was reduced by cadmium and completely abolished at 6°C and regeneration of amputated posterior segments was inhibited in cold but was enhanced by cadmium exposure at RT. Independently on the temperature, the 4-week cadmium exposure of adult earthworms was connected with significantly upregulated expression of Cd-metallothionein (but not of catalase, lysenin and phytochelatin) in coelomocytes.

Proposed modification to avoidance test with Eisenia fetida to assess metal toxicity in agricultural soils affected by mining activities

Use of avoidance tests is a quick and cost-effective method of assessing contaminants in soils. One option for assessing earthworm avoidance behavior is a two-section test, which consists of earthworms being given the choice to move between a test soil and a control substrate. For ecological relevance, tested soils should be field-contaminated soils. For practical reasons, artificial soils are commonly used as the control substrate. Interpretation of the test results compromised when the test soil and the artificial substrate differ in their physico-chemical properties other than just contaminants. In this study we identified the physico-chemical properties that influence avoidance response and evaluated the usefulness of adjusting these in the control substrate in order to isolate metal-driven avoidance of field soils by earthworms. A standardized two-section avoidance test with Eisenia fetida was performed on 52 uncontaminated and contaminated (Cu >155mgkg^-1, As >19mgkg^-1) agricultural soils from the Aconcagua River basin and the Puchuncaví Valley in Chile. Regression analysis indicated that the avoidance response was determined by soil organic matter (OM), electrical conductivity (EC) and total soil Cu. Organic matter content of the artificial substrate was altered by peat additions and EC by NaCl so that these properties matched those of the field soils. The resultant EC₈₀ for avoidance (indicative of soils of "limited habitat") was 433mg Cu kg^-1 (339 - 528mgkg^-1 95% confidence intervals). The earthworm avoidance test can be used to assess metal toxicity in field-contaminated soils by adjusting physico-chemical properties (OM and EC) of the artificial control substrate in order to mimic those of the field-collected soil.

De novo transcriptome assembly, functional annotation and differential gene expression analysis of juvenile and adult E. fetida, a model oligochaete used in ecotoxicological studies

Background

Earthworms are sensitive to toxic chemicals present in the soil and so are useful indicator organisms for soil health. Eisenia fetida are commonly used in ecotoxicological studies; therefore the assembly of a baseline transcriptome is important for subsequent analyses exploring the impact of toxin exposure on genome wide gene expression.

Results

This paper reports on the de novo transcriptome assembly of E. fetida using Trinity, a freely available software tool. Trinotate was used to carry out functional annotation of the Trinity generated transcriptome file and the transdecoder generated peptide sequence file along with BLASTX, BLASTP and HMMER searches and were loaded into a Sqlite3 database. To identify differentially expressed transcripts; each of the original sequence files were aligned to the de novo assembled transcriptome using Bowtie and then RSEM was used to estimate expression values based on the alignment. EdgeR was used to calculate differential expression between the two conditions, with an FDR corrected P value cut off of 0.001, this returned six significantly differentially expressed genes. Initial BLASTX hits of these putative genes included hits with annelid ferritin and lysozyme proteins, as well as fungal NADH cytochrome b5 reductase and senescence associated proteins. At a cut off of P = 0.01 there were a further 26 differentially expressed genes.

Conclusion

These data have been made publicly available, and to our knowledge represent the most comprehensive available transcriptome for E. fetida assembled from RNA sequencing data. This provides important groundwork for subsequent ecotoxicogenomic studies exploring the impact of the environment on global gene expression in E. fetida and other earthworm species.

Electronic supplementary material

The online version of this article (doi:10.1186/s40659-017-0114-y) contains supplementary material, which is available to authorized users.

Oxidative stress responses and insights into the sensitivity of the earthworms Metaphire guillelmi and Eisenia fetida to soil cadmium

Soil toxicological tests are commonly performed using Eisenia fetida as the standard earthworm species, but it is tolerant to a wide range of pollutants. Therefore, the inclusion of susceptible species is crucial for the accurate estimation of soil contamination. In this study, we examined the sensitivity to soil cadmium (Cd) of anecic Metaphire guillelmi and epigeic E. fetida by measuring multiple indexes of oxidative stress. Using subcellular partitioning analysis, we further elucidated the inherent mechanism underlying the species-specific sensitivity of the two earthworm species. Among the battery of biochemical indexes, reactive oxygen species and protein carbonyl groups served as sensitive biomarkers. According to their respective response thresholds, M. guillelmi was more sensitive than E. fetida and they differed in their dose-response relationships. In E. fetida, the activities of three antioxidant enzymes, superoxide dismutase (SOD), catalase (CAT) and glutathione S-transferase (GST), exhibited a hormesis-like U-shaped dose-response relationship, while in M. guillelmi SOD, glutathione peroxidase (an analogue of CAT) and GST showed an inverted U-shaped relationship. The concentrations of Cd in the subcellular fractions and whole body of the earthworms well fit (R²>0.9) a saturation model versus bioavailable Cd concentrations determined by the diffusive gradients in thin films technique. Despite the lower accumulation capacity of M. guillelmi, the Cd-binding capacity (C_max) of its subcellular heat-stable protein fraction, the so-called biologically detoxified metal pool, was 2.7 times lower than that of E. fetida, whereas the Cd binding affinity (logK) of its heat-denatured protein fraction, i.e. the metal-sensitive fraction, was 3.0 times higher, which accounted for the high susceptibility of M. guillelmi to soil Cd. Our results suggest that because of their sensitivity, as exemplified by M. guillelmi, native earthworm species should be taken into account in soil risk assessments to avoid underestimation of the toxicity of various pollutants.