Bioaccumulation of total and methyl mercury in three earthworm species (Drawida sp., Allolobophora sp., and Limnodrilus sp.)

Mercury distribution in organisms, litter, and soils of the Middle Araguaia floodplain in Brazil

Mercury (Hg) is a chemical element that, depending on its concentration, may become toxic to living organisms due to the ability of Hg to bioaccumulate in food chains. In this study, we collected samples of soil, litter, and organisms in the Middle Araguaia floodplain, Brazil. Total mercury (THg) concentrations in litter were significantly higher (p < 0.0001) than that in soil, ranging from 10.68 ± 0.55 to 48.94 ± 0.13 and 20.80 ± 1.07 to 55 .19 ± 1.59 ng g-1, respectively. Total mercury concentration levels in soil showed a linear, inversely proportional relationship with soil organic matter (SOM) contents and soil pH, consistent with the geochemical behavior of chemical elements in flooded environments. Ten orders of organisms were identified, and the average THg concentrations determined in their bodies were up to 20 times higher than those in soil and litter. We found a significant linear relationship between the levels of THg in litter and those found in soil organisms, thereby allowing the prediction of THg concentration levels in soil organisms through the analysis of litter at the sample units. The different dynamics and feeding habits of soil organisms and the concentration of THg in these organisms may be influenced by the river's course. This study provides evidence of the bioaccumulation of THg in soil organisms in the floodplain of the Middle Araguaia River, an important river basin in the Brazilian savanna.

Decoding the biological toxicity of phenanthrene on intestinal cells of Eisenia fetida: Effects, toxicity pathways and corresponding mechanisms

Phenanthrene is frequently detected and exists extensively in the soil environment, and its residues inevitably impose a significant threat to soil organisms. Exposure to and toxicity of phenanthrene on earthworms has been extensively studied before, however, the possible mechanisms and related pathways associated with phenanthrene-triggered toxicity at the intestinal cell level remain unclear. Herein, primary intestinal cells isolated from Eisenia fetida (Annelida, Oligochaeta) intestine were used as targeted receptors to probe the molecular mechanisms involved in ROS-mediated damaging effects and the potential pathways of phenanthrene-induced toxicity at cellular and sub-cellular levels. Results indicated that phenanthrene exposure induced oxidative stress by activating intracellular ROS (elevated O2-, H2O2, and OH- content) bursts in E. fetida intestinal cells, causing various oxidative damage effects, including lipid peroxidation (increased MDA content), protein oxidation (enhanced PCO levels), and DNA damage (enhanced 8-OHdG levels). The enzymatic and non-enzymatic strategies in earthworm cells were activated to mitigate these detrimental effects by regulating ROS-mediated pathways involving defense regulation. Also, phenanthrene stress destroyed the cell membrane of E. fetida intestinal cells, resulting in cellular calcium homeostasis disruption and cellular energetic alteration, ultimately causing cytotoxicity and cell apoptosis/death. More importantly, the mitochondrial dysfunction in E. fetida cells was induced by phenanthrene-caused mitochondrial membrane depolarization, which in turn caused un-controlled ROS burst and induced apoptosis through mitochondria-mediated caspase-3 activation and ROS-mediated mitochondrial-dependent pathway. Furthermore, exposure to phenanthrene activated an abnormal mRNA expression profile associated with defense regulation (e.g., Hsp70, MT, CRT, SOD, CAT, and GST genes) in E. fetida intestinal cells, resulting in various cellular dysfunctions and pathological conditions, eventually, apoptotic cell death. Taken together, this study offers valuable insights for probing the toxic effects and underlying mechanisms posed by phenanthrene at the intestinal cell level, and is of great significance to estimate the detrimental side effects of phenanthrene on soil ecological health.

Biological approaches for E-waste management: A green-go to boost circular economy

E-waste is a pressing situation on human due to its complex composition. Although E-waste on one hand has some toxic components but at the same time, it would be a promising business sector. Recycling of E-waste to mine-out valuable metals and other components has opened a chance of business and hence a way towards transformation of linear economy to circular one. Chemical, physical and traditional technologies are holding the position in E-waste recycling sector but sustainability with respect to cost and environmental issues is a major concern associated with these technologies. In order to overcome these gaps, lucrative, environment friendly and sustainable technologies need to be implied. Biological approaches could be a green and clean approach to handle E-waste through sustainable and cost-effective means by considering socio-economic and environmental aspects. This review elaborates biological approaches for E-waste management and advancements in expanse. The novelty covers the environmental and socio-economic impacts of E-waste, solution and further scope of biological approaches, further research and development need in this contour to come up with sustainable recycling process.

Health risk assessment of mercury in Nile tilapia (Oreochromis niloticus) fed housefly maggots

The bioaccumulation of total mercury (THg) and methylmercury (MeHg) by housefly maggots (HM) during the conversion of food waste (vegetables and meat (VM) and rice waste) under various waste feed ratios were investigated. Subsequently, Nile tilapia (Oreochromis niloticus) were fed with the commercial feed, commercial dried HM, dried HM, and fresh HM, followed by a human health risk assessment of Hg via fish consumption. The THg concentrations of HM fed with food waste ranged from 39.5 to 100 μg kg^-1 ww. Concentrations of MeHg in the maggots fed with 100 % vegetables and meat (VM) waste (13.7 ± 1.12 μg kg^-1 ww) was significantly higher than that fed with other mixed ratios of rice waste and VM waste (p<0.05). Concentrations of MeHg were positively correlated with the weight and lipid content of houseflies (p<0.05). THg and MeHg concentrations in tilapia fed with the converted HM (dried and fresh HM) were 22.5 ± 6.50 μg kg^-1 ww and 2.43 ± 0.36 μg kg^-1 ww, respectively. There was no significant difference in MeHg between tilapia fed the four experiment diets (p>0.05). Health risk assessment results indicated that mercury in tilapia fed the food waste-grown HM did not pose potential health risks to humans (target hazard quotient < 1). In conclusion, HM could convert food waste into high-quality and safe fish feeds for cultivating tilapia.

The effects of different temperatures in mercury toxicity to the terrestrial isopod Porcellionides pruinosus

Climate changes and metal contamination are pervasive stressors for soil ecosystems. Mercury (Hg), one of the most toxic metals, has been reported to interact with temperature. However, compared to aquatic biota, little is known about how temperature affects Hg toxicity and bioaccumulation to soil organisms. Here, toxicity and bioaccumulation experiments were replicated at 15 °C, 20 °C, and 25 °C to understand how sub-optimal temperatures affect the toxicokinetics and toxicodynamics of Hg via soil. Genotoxicity and energy reserves were also assessed to disclose potential trade-offs in life-history traits. Results underpin the complexity of temperature-Hg interactions. Survival was determined mainly by toxicokinetics, but toxicodynamics also played a significant role in defining survival probability during early stages. The processes determining survival probability were faster at 25 °C: General Unified Threshold of Survival (GUTS) model identified an earlier/steeper decline in survival, compared to 20 °C or 15 °C, but it also approached the threshold faster. Despite potentiation of Hg genotoxicity, temperature promoted faster detoxification, either increasing toxicokinetics rates or damage repair mechanisms. This metabolism-driven increase in detoxification led to higher depletion of energy reserves and likely triggered stress response pathways. This work emphasized the need for comprehensive experimental approaches that can integrate the multiple processes involved in temperature-metal interactions.

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.

Soil Contamination and Bioaccumulation of Heavy Metals by a Tropical Earthworm Species (Alma nilotica) at Informal E-Waste Recycling Sites in Douala, Cameroon

Soil contamination at electronic waste (e-waste) recycling sites is pervasive, though many locations have yet to be studied. While such contamination can present risks to soil organisms, little is known on the risks to native species. The objective of the present study was to assess soil contamination by heavy metals at e-waste recycling sites, and the potential of Alma nilotica, a native earthworm species, to bioaccumulate these metals. Soil samples collected from eight informal e-waste recycling sites and two non-e-waste sites in Douala, Cameroon, were analyzed for metal content. Metal concentrations in earthworm juveniles exposed to the soils for 21 days followed by a 14-day post-exposure period were measured weekly. Mean soil metal concentrations at e-waste sites ranked as Cu > Pb > Zn > Hg > Ni > As > Cd > Co > Cr. Based on contamination factors, soil contamination ranged from "moderate" (Cr), through "considerable" (Co and Cd), to "very high" for the rest of the metals. Based on the modified degree of contamination and risk index, all e-waste sites had "ultra-high" contamination with Ni, Pb, and Zn posing very high ecological risks and Bonaberi being the most contaminated site. There was a positive correlation between soil metal concentrations and metal accumulation (retention) by eathworms, but Hg and Co had the highest bioaccumulation factors (BAFs) despite having low soil concentrations. These results document that e-waste sites in Douala are contaminated with metals and that native earthworm species can bioaccumulate the studied metals at levels that could account for the toxic effects earlier recorded. With e-waste recycling growing worldwide, there is a need for more data, especially from understudied locations. Environ Toxicol Chem 2022;41:356-368. © 2021 SETAC.

Antifouling paint particles in soils: toxic impact that goes beyond the aquatic environment

Antifouling paint particles (APPs) originate from vessel maintenance and cleaning activities and their potentially toxic components are found at high concentrations in nearby soils, yet no studies have investigated their toxicity to soil organisms. We investigated the effects of exposure to soils containing APPs on the mortality, biomass, and reproductive performance of the earthworm Eisenia andrei. Earthworms were exposed to contaminated soil from a boatyard and non-contaminated soils treated with different concentrations of APPs (0.01, 0.14 and 1.50%, w/w) for 56 days. An ecological risk assessment using a Hazard Quotient (HQ) was also carried out. Exposure to contaminated soils reduced worm survival, biomass, and reproductive performance and these effects were concentration-dependent. The HQ was high in soil samples with APPs in both acute and chronic tests, and copper contributed the most to the HQ. Copper, zinc, and lead had the highest concentrations and exceeded the Brazilian legal limits. A principal component analysis (PCA) was performed and showed that biomass and number of juveniles parameters was associated with the metals Cu, Sn and Zn, while the mortality parameter had no association with any analyzed metal. These findings highlighted that the synergistic effects of compounds present in the APPs, such as the booster biocides DCOIT, and metal mixtures should not be overlooked. We conclude that soils contaminated with APPs are toxic to earthworms. This reveals that the ecological impact of APPs goes beyond effects on aquatic environments, compromising key organisms of edaphic ecological processes.

Ecotoxicological impact of the antihypertensive valsartan on earthworms, extracellular enzymes and soil bacterial communities

The use of reclaimed water in agriculture represents a promising alternative to relieve pressure on freshwater supplies, especially in arid or semiarid regions facing water scarcity. However, this implies introducing micropollutants such as pharmaceutical residues into the environment. The fate and the ecotoxicological impact of valsartan, an antihypertensive drug frequently detected in wastewater effluents, were evaluated in soil-earthworm microcosms. Valsartan dissipation in the soil was concomitant with valsartan acid formation. Although both valsartan and valsartan acid accumulated in earthworms, no effect was observed on biomarkers of exposure (acetylcholinesterase, glutathione S-transferase and carboxylesterase activities). The geometric mean index of soil enzyme activity increased in the soils containing earthworms, regardless of the presence of valsartan. Therefore, earthworms increased soil carboxylesterase, dehydrogenase, alkaline phosphatase, β-glucosidase, urease and protease activities. Although bacterial richness significantly decreased following valsartan exposure, this trend was enhanced in the presence of earthworms with a significant impact on both alpha and beta microbial diversity. The operational taxonomic units involved in these changes were related to four (Proteobacteria, Bacteroidetes, Actinobacteria and Firmicutes) of the eight most abundant phyla. Their relative abundances significantly increased in the valsartan-treated soils containing earthworms, suggesting the presence of potential valsartan degraders. The ecotoxicological effect of valsartan on microbes was strongly altered in the earthworm-added soils, hence the importance of considering synergistic effects of different soil organisms in the environmental risk assessment of pharmaceutical active compounds.

Significant bioaccumulation and biotransformation of methyl mercury by organisms in rice paddy ecosystems: A potential health risk to humans

Rice has been confirmed as one of the principal intake pathways for methylmercury (MeHg) in human, however, the impact of edible organisms, such as snails, loaches and eels, living in the rice-based ecosystem to the overall MeHg intake has been overlooked. Here, we conducted a cross-sectional ecological study, and the results showed that bioaccumulation of MeHg in these edible organisms was significantly higher than in paddy soils and rice roots (p < 0.001), even though rice roots and grains have significantly higher total Hg (THg) (p < 0.001). The MeHg/THg ratios were consistently and significantly higher in those edible organisms than in rice grains, suggesting a potential elevated MeHg exposure risk through consumption. Based on results of bioaccumulation factors (BAFs) for MeHg, it was clear that MeHg was bioaccumulated and biotransformed from paddy soils to earthworms and then to eels, as well as from paddy soils to snails and then to eels and loaches, potentially indicating that the consumption of eels and loaches was absolutely pernicious to people regularly feeding on them. Overall, MeHg was biomagnified along the food chain of the paddy ecosystem from soil to the organisms, and it was of potential higher risks for local residents to eat them, especially eels and loaches. Therefore, it is intensely indispensable for people fond of such diets to attenuate their consumption of rice, eels and loaches, thus mitigating their MeHg exposure risks.

Insights into the mechanisms underlying the remediation potential of earthworms in contaminated soil: A critical review of research progress and prospects

In recent years, soil pollution is a major global concern drawing worldwide attention. Earthworms can resist high concentrations of soil pollutants and play a vital role in removing them effectively. Vermiremediation, using earthworms to remove contaminants from soil or help to degrade non-recyclable chemicals, is proved to be an alternative, low-cost technology for treating contaminated soil. However, knowledge about the mechanisms and framework of the vermiremediation various organic and inorganic contaminants is still limited. Therefore, we reviewed the research progress of effects of soil contaminants on earthworms and potential of earthworm used for remediation soil contaminated with heavy metals, polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs), polycyclic aromatic hydrocarbons (PAHs), pesticides, as well as crude oil. Especially, the possible processes, mechanisms, advantages and limitations, and how to boost the efficiency of vermiremediation are well addressed in this review. Finally, future prospects of vermiremediation soil contamination are listed to promote further studies and application of vermiremediation in contaminated soils.

Synthesis of earthworm trace metal uptake and bioaccumulation data: Role of soil concentration, earthworm ecophysiology, and experimental design

Trace metals can be essential for organo-metallic structures and oxidation-reduction in metabolic processes or may cause acute or chronic toxicity at elevated concentrations. The uptake of trace metals by earthworms can cause transfer from immobilized pools in the soil to predators within terrestrial food chains. We report a synthesis and evaluation of uptake and bioaccumulation empirical data across different metals, earthworm genera, ecophysiological groups, soil properties, and experimental conditions (metal source, uptake duration, soil extraction method). Peer-reviewed datasets were extracted from manuscripts published before June 2019. The 56 studies contained 3513 soil-earthworm trace metal concentration paired data sets across 11 trace metals (As, Cd, Cr, Cu, Hg, Mn, Ni, Pb, Sb, U, Zn). Across all field and laboratory experiments studied, the median concentrations of Hg, Pb, and Cd in earthworm tissues that were above concentrations known to be hazardous for consumption by small mammals and avian predators but not for Cu, Zn, Cr, Ni, and As. Power regressions show only Hg and Cd earthworm tissue concentrations were well-correlated with soil concentrations with R² > 0.25. However, generalized linear mixed-effect models reveal that earthworm concentrations were significantly correlated with soil concentrations for log-transformed Hg, Cd, Cu, Zn, As, Sb (p < 0.05). Factors that significantly contributed to these relationships included earthworm genera, ecophysiological group, soil pH, and organic matter content. Moreover, spiking soils with metal salts, shortening the duration of exposure, and measuring exchangeable soil concentrations resulted in significantly higher trace metal uptake or greater bioaccumulation factors. Our results highlight that earthworms are able to consistently bioaccumulate toxic metals (Hg and Cd only) across field and laboratory conditions. However, future experiments should incorporate greater suites of trace metals, broader genera of earthworms, and more diverse laboratory and field settings to generate data to devise universal quantitative relationships between soil and earthworm tissue concentrations.

A tale of three cities: Mercury in urban deciduous foliage and soils across land-uses in Poughkeepsie NY, Hartford CT, and Springfield MA USA

Mercury is a global pollutant that harms human and wildlife health through chronic exposure. The role of urban forests in Hg biogeochemistry has been understudied in cities without historical mining or current coal combustion. This study aimed to quantify total Hg concentrations and pools in urban forests to determine whether adjacent land-use impacts Hg accumulation. Three cities in the northeastern United States were studied: Hartford, Connecticut; Poughkeepsie, New York; and Springfield, Massachusetts. We identified ~20 urban forests sites in a ~10 km by ~10 km grid for each city and sampled foliage and soil at each site. Foliage from Populus exhibited significantly lower Hg concentrations (15.6 ± 2.1 ng g^-1) than mean foliar Hg concentrations (23.7 ± 0.6 ng g^-1) but most deciduous genera had comparable concentrations. Average forest floor Hg concentrations (195 ± 21 ng g^-1) and Hg pools (1.9 ± 0.5 mg m^-2) were similar to previous, non-urban studies in the region. Average A horizon (182 ± 19 ng g^-1) and B horizon (125 ± 14 ng g^-1) Hg concentrations were double those of regional forest soils. Mineral soil Hg pools for the top 30 cm (49 ± 6 mg m^-2) averaged two to ten times higher than rural, montane forests in the region. Soil pH, LOI, and %clay were poorly correlated with mineral soil Hg concentrations. Instead, highest foliar and soil Hg concentrations and pools were in urban forests adjacent to high and medium intensity developed areas in Springfield and Hartford. To differentiate the impact of land-uses not captured by the National Land Cover Database (NLCD) system, we implemented new land-use categories. Industrial areas had highest foliar and soil Hg concentrations and pools of any land use. Our results show increasing land-use increases Hg accumulation in urban forests.

Mercury species in the nests and bodies of soil-feeding termites, Silvestritermes spp. (Termitidae, Syntermitinae), in French Guiana

Mercury pollution is currently a major public health concern, given the adverse effects of mercury on wildlife and humans. Soil plays an essential role in speciation of mercury and its global cycling, while being a habitat for a wide range of terrestrial fauna. Soil fauna, primarily soil-feeding taxa that are in intimate contact with soil pollutants are key contributors in the cycling of soil mercury and might provide relevant indications about soil pollution. We studied the enrichment of various mercury species in the nests and bodies of soil-feeding termites Silvestritermes spp. in French Guiana. Soil-feeding termites are the only social insects using soil as both shelter and food and are major decomposers of organic matter in neotropical forests. Nests of S. minutus were depleted in total and mobile mercury compared to nearby soil. In contrast, they were enriched 17 times in methylmercury. The highest concentrations of methylmercury were found in body of both studied termite species, with mean bioconcentration factors of 58 for S. minutus and 179 for S. holmgreni relative to the soil. The assessment of the body distribution of methylmercury in S. minutus showed concentrations of 221 ng g^-1 for the guts and even higher for the gut-free carcasses (683 ng g^-1), suggesting that methylmercury is not confined to the gut where it was likely produced, but rather stored in various tissues. This enrichment in the most toxic form of Hg in termites may be of concern on termite predators and the higher levels in the food chain that may be endangered through prey-to-predator transfers and bioaccumulation. Soil-feeding termites appear to be promising candidates as bio-indicators of mercury pollution in soils of neotropical rainforest ecosystems.

Mercury Accumulation in Millipedes (Narceus spp.) Living Adjacent to a Southern Appalachian Mountain Stream (USA)

Millipedes are among the most important processors of leaf litter in temperate forests. Through consumption of leaf litter, millipedes may be exposed to mercury that accumulates in leaf tissues prior to senescence. To investigate mercury uptake in millipedes, Narceus spp. were collected from a remote site in the southern Appalachian Mountains, an area known to receive high mercury deposition. Additionally, aquatic primary consumers (larval caddisflies and stoneflies), brook trout (Salvelinus fontinalis) and rainbow trout (Oncorhynchus mykiss) were collected from the same site for comparisons of mercury concentrations and percent methylmercury. Bioaccumulation factors for millipedes were 18.5 and 20.2 for total and methylmercury, respectively. At this site, the mean THg concentration in millipedes was ~ 10 × greater than both brook trout and rainbow trout and ~ 200 × greater than that of aquatic primary consumers. Millipede THg concentrations ranged from 222 to 1620 ng/g ww in an area where EPA fish consumption criteria (300 ng/g MeHg in fish tissue, ww) were not exceeded. The mean percent methylmercury in millipedes was 1.4%, suggesting these animals were accumulating large quantities of inorganic mercury.

Mercury accumulation from food decreases collembolans' growth

In the terrestrial environment, mercury (Hg) contamination can be originated from different inorganic and metal-organic sources, redistributed and transformed in soils. In the present study, the effects of contaminated food with environmentally relevant concentrations of Hg were evaluated in the soil-dwelling invertebrate Folsomia candida. Changes in growth rate and Hg bioaccumulation levels were observed at different concentrations of Hg in food, which can be complementary for data already available for reproduction and survival from standardized protocols. Collembolan growth was recorded every two days, and their growth rate along with a Von Bertalanffy's growth curve were derived showing that growth was dependent on Hg food concentration. Also, the final length of animals reflected the Hg concentration in food, with differences in all treatments comparing to non-exposed organisms. Toxicokinetic patterns from different Hg concentrations in food were not significantly different during the uptake phase, but differences were found in the depuration phase. Combining the two approaches, collembolans seem to invest their energy for depuration processes, neglecting other vital processes, such as growth. Also, contaminated food avoidance possibly occurred, thus decreasing their feeding and contaminant intake. Therefore, growth tests in collembolans can act as complementary tools to bioaccumulation and reproductive assays, towards a mechanistic understanding of how organisms use their energy upon contamination. Changes in growth rate, even at low and environmentally relevant concentrations, could be a warning signal when occurring in species with key roles in ecosystems. Also, this study highlights the importance of these complementary tests for a better and complete approach to risk assessment studies.

Spatial distribution characteristics of mercury in the soils and native earthworms (Bimastos parvus) of the leachate-contaminated zone around a traditional landfill

The contents and spatial distribution of mercury (Hg), including soil-Hg fractionation and Hg-containing native earthworm Bimastos parvus (B. parvus) species, were investigated in the leachate-contaminated zone of a large traditional landfill, Japan. Soil-Hg was fractionated into 5 categories: F1/water soluble Hg (Hg-w), F2/human stomach acid soluble Hg (Hg-h), F3/organic-chelated (Hg-o), F4/elemental Hg (Hg-e), and F5/mercuric sulfide (Hg-s). The total mercury (T-Hg) and methylmercury (MeHg) of native B. parvus, and the geochemical properties of soils were examined in this study. Soil T-Hg concentration ranged between 0.227 and 2.919 mg kg^-1 dry weight (dw). The T-Hg and MeHg concentrations of B. parvus species ranged from 1.242 to 6.775 mg kg^-1 dw and from 0.031 to 0.218 mg kg^-1 dw, respectively. Percentages of soil-Hg fractions were in the order of F3/Hg-o > F4/ Hg-e > F5/Hg-s > F1/Hg-w > F2/Hg-h, and the fractions of Hg-o and Hg-e were 55.50% and 35.31%, respectively. Similar distributions and close correlations between the levels of B. parvus Hg and soil Hg-o, Hg-e, and Hg-s were observed in this study. The distribution of Hg in B. parvus was associated with soil organic matter (SOM) content and particle size (sand, clay); however, it was not correlated with Hg-w or Hg-h. The results indicated that easily bioavailable and soluble Hg fractions (Hg-w, Hg-h) of the soil were not appropriate to illustrate the distribution of Hg in native B. parvus. Instead, the stable soil-Hg fractions (Hg-o, Hg-e, and Hg-s) demonstrated good relationships of spatial distribution with B. parvus Hg in leachate-contaminated soil. It is advisable to preclude the evaluation of Hg biological distribution using soluble Hg fractions only. Stable Hg fractions in leachate-contaminated soil should also be included for assessing the biological distribution of Hg in leachate-contaminated soils.

NMR-based metabolic toxicity of low-level Hg exposure to earthworms

Mercury is a globally distributed toxicant to aquatic animals and mammals. However, the potential risks of environmental relevant mercury in terrestrial systems remain largely unclear. The metabolic profiles of the earthworm Eisenia fetida after exposure to soil contaminated with mercury at 0.77 ± 0.09 mg/kg for 2 weeks were investigated using a two-dimensional nuclear magnetic resonance-based (¹H-¹³C NMR) metabolomics approach. The results revealed that traditional endpoints (e.g., mortality and weight loss) did not differ significantly after exposure. Although histological examination showed sub-lethal toxicity in the intestine as a result of soil ingestion, the underlying mechanisms were unclear. Metabolite profiles revealed significant decreases in glutamine and 2-hexyl-5-ethyl-3-furansulfonate in the exposed group and remarkable increases in glycine, alanine, glutamate, scyllo-inositol, t-methylhistidine and myo-inositol. More importantly, metabolic network analysis revealed that low mercury in the soil disrupted osmoregulation, amino acid and energy metabolisms in earthworms. A metabolic net link and schematic diagram of mercury-induced responses were proposed to predict earthworm responses after exposure to mercury at environmental relevant concentrations. These results improved the current understanding of the potential toxicity of low mercury in terrestrial systems.

Mercury bioaccumulation in arthropods from typical community habitats in a zinc-smelting area

This study assessed the enrichment of mercury in the food web from the different community habitats in a zinc-smelting area of China. We used a nitrogen stable isotope technique to analyze trophic level relationships among arthropods and found that the first trophic level consisted of plants in the different community habitats, the second trophic level consisted of herbivores such as locusts and grasshoppers (primary consumers), and the third trophic level included spiders and mantes (secondary consumers). Mercury enrichment in the primary consumers was not evident, but enrichment in arthropods of the third trophic level was significant. The average of enrichment coefficients in spiders and mantes was greater than 1. The δ¹⁵N values indicated that mercury concentrations accumulated from primary producers to top carnivorous arthropods increased. In this zinc-smelting area, the biological amplification of mercury in the food web is significant. It is reasonable to assume that humans, located at the top of the food chain, are exposed to biomagnified levels of mercury.

Differences in the bioaccumulation of selenium by two earthworm species (Pheretima guillemi and Eisenia fetida)

Information on the bioaccumulation of selenium (Se) in soil invertebrates (e.g. earthworms) is rather scarce. In the present study, bioaccumulation of Se in two eco-physiologically different earthworms, namely anecic Pheretima guillemi and epigeic Eisenia fetida, was determined after 28 days exposure to a successive doses of Se-spiked soil, specifically 0.5, 5, 50, and 200 μg Se g^-1 soil. The results showed that Se concentration in earthworms elevated with increasing exposure levels, and maximums were up to 54.6 and 83.0 μg g^-1 dry weight in Pheretima guillemi and Eisenia fetida, respectively, after 4 weeks exposure to 200 μg Se g^-1 soil. Exposure to Se caused significant inhibition on earthworm growth, with the fresh weight loss ranging from 8.9% to 80.5%. Bioaccumulation factors (BAFs), empirically-derived and non-steady state, ranged from 0.12 to 4.17 and generally declined at higher exposure levels. Moreover, BAFs of Pheretima guillemi were higher than those of Eisenia fetida in low-dose Se-spiked soils, but the opposite was true in high-dose soils, indicating there is a species-specific response to exposure of Se between different earthworms. Further research is thus needed to reveal the accumulation pattern of Se in a wider range of earthworm species other than Eisenia fetida, which allows a better risk assessment of excessive Se to soil invertebrates and higher order organisms.

Using species-specific enriched stable isotopes to study the effect of fresh mercury inputs in soil-earthworm systems

The fate of mercury (Hg) in the soil-earthworm system is still far from being fully understood, especially regarding recurrent and challenging questions about the importance of the reactivity of exogenous Hg species. Thus, to predict the potential effect of Hg inputs in terrestrial ecosystems, it is necessary to evaluate separately the reactivity of the endogenous and exogenous Hg species and, for this purpose, the use of enriched stable isotope tracers is a promising tool. In the present work, earthworms (Lumbricus terrestris) were exposed to historically Hg contaminated soils from the Almadén mining district, Spain. The soils were either non-spiked, which contain only endogenous or native Hg naturally occurring in the soil, or spiked with isotopically enriched inorganic Hg (¹⁹⁹IHg), representing exogenous or spiked Hg apart from the native one. The differential reactivity of endogenous and exogenous Hg in the soil conditioned the processes of methylation, mobilization, and assimilation of inorganic Hg by earthworms. Both endogenous and exogenous Hg species also behave distinctly regarding their bioaccumulation in earthworms, as suggested by the bioaccumulation factors, being the endogenous methylmercury (MeHg) the species more readily bioaccumulated by earthworms and in a higher extent. To the best of our knowledge, this work demonstrates for the first time the potential of enriched stable isotopes to study the effects of fresh Hg inputs in soil-earthworm systems. The findings of this work can be taken as a case study on the dynamics of Hg species in complex terrestrial systems and open a new door for future experiments.

The eco-toxic effects of pesticide and heavy metal mixtures towards earthworms in soil

Earthworms are the key soil organisms, contribute to many positive ecological services that could be degraded by pesticides and other soil pollutants such as heavy metals. Chemicals usually occur as mixtures in the environmental systems which can lead synergistic effects. The assessment and characterization of soil pollutants that effects risks are very difficult due to the complexity of soil matrix, poor understanding about the fate and effects of chemical combinations like pesticide and metal mixtures in terrestrial systems, and scarcity of toxicological data on mixtures of pollutants. In this review we summarized the current studies on individual and joint effects of pesticides and metals on earthworms and indicate the mixture that cause the synergistic interactions. The review explores the methods and models used previously to evaluate the toxicity of chemical mixtures, and suggests the perspective approaches for a better knowledge of combine effects as well as research methods The summarized report indicates that pesticide and metal mixtures at all organization levels affect the earthworms negatively. Whereas, the combined pollution generated by mixtures of pesticides and metal ions could induce the DNA damage, disruption in enzyme activities, reduction in individual survival, production and growth rate, change in individual behavior such as feeding rate, and decrease in the total earthworm community biomass and density. Among the pesticides organophosphates were identified the most toxic pesticides causing the synergistic effects. The findings indicate the scarcity of toxicological data concerning the assessment of pesticide and metal mixtures at genome level; while the mechanisms causing synergism were still not sufficiently explored.

Ecotoxicology of mercury in tropical forest soils: Impact on earthworms

Mercury (Hg) is one of the most toxic nonessential trace metals in the environment, with high persistence and bioaccumulation potential, and hence of serious concern to environmental quality and public health. Emitted to the atmosphere, this element can travel long distances, far from emission sources. Hg speciation can lead to Hg contamination of different ecosystem components, as well as biomagnification in trophic food webs. To evaluate the effects of atmospheric Hg deposition in tropical forests, we investigated Hg concentrations in earthworm tissues and soils of two Forest Conservation Units in State of Rio de Janeiro, Brazil. Next, we performed a laboratory study of the biological responses (cast analysis and behavioral, acute, chronic and bioaccumulation ecotoxicological tests) of two earthworms species (Pontoscolex corethrurus and Eisenia andrei) to Hg contamination in tropical artificial soil (TAS) and two natural forest soils (NS) spiked with increasing concentration of HgCl₂. Field results showed Hg concentrations up to 13 times higher in earthworm tissues than in forest soils, while in the laboratory Hg accumulation after 91-days of exposure was 25 times greater in spiked-soils with 128mgHgkg^-1 (dry wt) than in control (unspiked) soils. In all the toxicity tests P. corethrurus showed a higher adaptability or resistance to mercury than E. andrei. The role of earthworms as environmental bioremediators was confirmed in this study, showing their ability to greatly bioaccumulate trace metals while reducing Hg availability in feces.

Total mercury and methylmercury concentrations over a gradient of contamination in earthworms living in rice paddy soil

Mercury (Hg) deposited from emissions or from local contamination, can have serious health effects on humans and wildlife. Traditionally, Hg has been seen as a threat to aquatic wildlife, because of its conversion in suboxic conditions into bioavailable methylmercury (MeHg), but it can also threaten contaminated terrestrial ecosystems. In Asia, rice paddies in particular may be sensitive ecosystems. Earthworms are soil-dwelling organisms that have been used as indicators of Hg bioavailability; however, the MeHg concentrations they accumulate in rice paddy environments are not well known. Earthworm and soil samples were collected from rice paddies at progressive distances from abandoned mercury mines in Guizhou, China, and at control sites without a history of Hg mining. Total Hg (THg) and MeHg concentrations declined in soil and earthworms as distance increased from the mines, but the percentage of THg that was MeHg, and the bioaccumulation factors in earthworms, increased over this gradient. This escalation in methylation and the incursion of MeHg into earthworms may be influenced by more acidic soil conditions and higher organic content further from the mines. In areas where the source of Hg is deposition, especially in water-logged and acidic rice paddy soil, earthworms may biomagnify MeHg more than was previously reported. It is emphasized that rice paddy environments affected by acidifying deposition may be widely dispersed throughout Asia. Environ Toxicol Chem 2017;36:1202-1210. © 2016 SETAC.

Mercury in soil, earthworms and organs of voles Myodes glareolus and shrew Sorex araneus in the vicinity of an industrial complex in Northwest Russia (Cherepovets)

The characteristic properties of uptake and distribution of mercury in terrestrial ecosystems have received much lesser attention compared to aquatic particularly in Russia. Terrestrial ecosystems adjacent to large industrial manufactures-potential sources of mercury inflow into the environment frequently remain unstudied. This is the first report on mercury (Hg) levels in the basic elements of terrestrial ecosystems situated close to a large metallurgical complex.Mean values of mercury concentration (mg Hg/kg dry weight) in the vicinity of city of Cherepovets were the following: 0.056 ± 0.033-in the humus layer of soil; 0.556 ± 0.159-in earthworms; in the organs of voles Myodes glareolus (kidneys-0.021 ± 0.001; liver-0.014 ± 0.003; muscle-0.014 ± 0.001; brain-0.008 ± 0.002); in the organs of shrew Sorex araneus (kidneys-0.191 ± 0.016; liver-0.124 ± 0.011; muscle-0.108 ± 0.009; brain-0.065 ± 0.000). Correlation dependences between Hg content in soil and earthworms (r _s  = 0.85, p < 0.01) as well as soil and all studied shrews' organs (rs = 0.44-0.58; p ≤ 0.01) were found.The results obtained evidence for a strong trophic link in the bioaccumulation of Hg in terrestrial food webs. Despite the vicinity to a large metallurgical complex, mercury content in the studied objects was significantly lower than values of corresponding parameters in the soils and biota from industrial (polluted) areas of Great Britain, the USA, and China.

Mercury toxicity to Eisenia fetida in three different soils

Three different soils were spiked with 12 different concentrations of inorganic mercury (Hg). Sub-chronic Hg toxicity tests were carried out with Eisenia fetida in spiked soils by exposing the worms for 28 days following standard procedures. The toxicity studies revealed that Hg exerted less lethal effect on earthworms in acidic soil with higher organic carbon (S-3 soil) where water soluble Hg recovery was very low compared to the water soluble Hg fractions in soils with less organic carbon and higher pH (S-1 and S-2 soils). The concentrations of total Hg that caused 50 % lethality to E. fetida (LC₅₀) after 28 days of exposure in S-1, S-2 and S-3 soils were 152, 294 and 367 mg kg^-1, respectively. The average weight loss of E. fetida in three soils ranged from 5 to 65 %. The worms showed less weight loss in the organic carbon-rich soil (S-3) compared to less organic carbon containing soils (S-1 and S-2). The bioconcentration of Hg in E. fetida increased with increased Hg concentrations. The highest bioaccumulation took place in the acidic soil with higher organic carbon contents with estimated bioaccumulation factors ranging from 2 to 7.7. The findings of this study will be highly useful for deriving a more robust soil ecological guideline value for Hg.

Forest floor decomposition, metal exchangeability, and metal bioaccumulation by exotic earthworms: Amynthas agrestis and Lumbricus rubellus

Earthworms have the potential to reduce the retention of pollutant and plant essential metals in the forest floor (organic horizons) by decomposing organic matter and increasing exchangeability of metals. We conducted a laboratory experiment to investigate the effects of two exotic earthworms, Amynthas agrestis and Lumbricus rubellus, on forest floor decomposition, metal exchangeability, and metal bioaccumulation. Eighty-one pots containing homogenized forest floor material were incubated for 20, 40, or 80 days under three treatments: no earthworms, A. agrestis added, or L. rubellus added. For earthworm treatments, A. agrestis and L. rubellus were stocked at densities observed in previous field studies. Pots containing either A. agrestis or L. rubellus had lost more forest floor mass than the control plots after 40 and 80 days of incubation. Forest floor pots containing A. agrestis had significantly lower % C (16 ± 1.5 %) than control pots (21 ± 1.2 %) after 80 days. However, L. rubellus consumed more forest floor and C mass than A. agrestis, when evaluated on a per earthworm biomass basis. Exchangeable (0.1 M KCl + 0.01 M AcOH extractable) and stable (15 M HNO3+ 10 M HCl extractable) concentrations of Al, Ca, Cd, Cu, Mg, Mn, Pb, and Zn in forest floor material were measured. Stable concentrations and % exchangeable metals in forest floor material were similar among treatments. Although exchangeable metal concentrations varied significantly for most metals among treatments (except Mg and Zn), we conclude that earthworms did not increase or decrease the exchangeability of metals. However, earthworms bioaccumulated Cu, Cd, Zn, and Mg and had potentially hazardous tissue concentrations of Al and Pb. This was best illustrated by calculating bioaccumulation factors using exchangeable concentrations rather than total concentrations. Future research is needed to understand the effect of earthworms on metals in other soil types.

Uptake dynamics of inorganic mercury and methylmercury by the earthworm Pheretima guillemi

Mercury uptake dynamics in the earthworm Pheretima guillemi, including the dissolved uptake rate constant (ku) from pore-water and assimilation efficiencies (AEs) from mercury-contaminated soil, was quantified in this study. Dissolved uptake rate constants were 0.087 and 0.553 L g(-1) d(-1) for inorganic mercury (IHg) and methylmercury (MeHg), respectively. Assimilation efficiency of IHg in field-contaminated soil was 7.2%, lower than 15.4% of spiked soil. In contrast, MeHg exhibited comparable AEs for both field-contaminated and spiked soil (82.4-87.2%). Within the framework of biodynamic model, we further modelled the exposure pathways (dissolved exposure vs soil ingestion) to source the accumulated mercury in Pheretima guillemi. The model showed that the relative importance of soil ingestion to mercury bioaccumulation depended largely on mercury partitioning coefficients (K(d)), and was also influenced by soil ingestion rate of earthworms. In the examined field-contaminated soil, almost (>99%) accumulated IHg and MeHg was predicted to derive from soil ingestion. Therefore, soil ingestion should be carefully considered when assessing mercury exposure risk to earthworms.

Mercury in Eisenia fetida and soil in the vicinity of a natural gas treatment plant in northern Croatia

In the last two decades (1990-2012), as part of a mercury monitoring programme, earthworms and soils have been collected from four locations in the vicinity of a natural gas production and treatment plant near the village of Molve, Croatia. The aim of this study was to determine the concentration of mercury in the collected samples, monitor its changes over a longer period of time and determine the bioaccumulation of total mercury in earthworms (Eisenia fetida) from the soil. Total mercury concentrations in earthworms from the surroundings of four boreholes (Molve 9-12) ranged within 0.195-1.050, 0.129-1.0, 0.229-1.236 and 0.223-0.799 μg g^-1 dry weight, while total mercury concentrations in different soil types at the same locations within 0.055-0.350, 0.035-0.250, 0.031-0.240 and 0.071-0.475 μg Hg g^-1 of soil. The calculated mercury bioaccumulation factor ranged between 0.9 and 17.5. Mercury levels in soil and earthworms, as a tool for soil pollution assessment, suggested low mercury exposure and risks for human health in the monitored area.

Diastereomer- and enantiomer-specific accumulation, depuration, bioisomerization, and metabolism of hexabromocyclododecanes (HBCDs) in two ecologically different species of earthworms

In this study, two ecological types of earthworms were exposed to soil samples that were artificially contaminated with individual hexabromocyclododecane (HBCD) diastereomers (α-, β-, and γ-HBCDs) to investigate the bioaccumulation, depuration, enantiomer selectivity and isomerization of HBCDs in earthworms. The uptake rate constant (ku), bioaccumulation factor (BAF), biota soil accumulation factor (BSAF), and half-life (t1/2) for the α-HBCD were the highest among the three diastereomers. The bioaccumulation parameters of the three diastereoisomers differed between the two ecologically different species of earthworms. The BSAF values of α- and γ-HBCDs were substantially higher in Eisenia fetida than those in Metaphire guillelmi, with the higher lipid and protein contents in E. fetida as the primary reason for this difference. The other processes, such as uptake, depuration, metabolism and isomerization, also differed between the two species and led to a difference in the bioaccumulation of β-HBCD. The β- and γ-HBCDs were bioisomerized to α-HBCD in the earthworms, but to a greater extent in E. fetida. The highest BSAF, t1/2 of α-HBCD and the bioisomerization of β- and γ-HBCDs to α-HBCD might explain in part why α-HBCD was the dominant isomer in biota samples. Most of the enantiomer fractions (EFs) for the three HBCD diastereoisomers in the earthworms were different from those in standard samples (p<0.05), indicating that enantiomer selectivity occurred. Moreover, the trends and extent of the enantioselectivity were different between the two species. Additionally, the EFs of α-HBCD that was bioisomerized from β- or γ-isomers were also different from those in the standards (p<0.05), which likely reflect the integration of several processes, such as enantioselective isomerization and the subsequent selective metabolism of the produced α-HBCD or selective excretion of the enantiomers.

Soil geochemistry and digestive solubilization control mercury bioaccumulation in the earthworm Pheretima guillemi

Mercury presents a potential risk to soil organisms, yet our understanding of mercury bioaccumulation in soil dwelling organisms is limited. The influence of soil geochemistry and digestive processes on both methylmercury (MeHg) and total mercury (THg) bioavailability to earthworms (Pheretima guillemi) was evaluated in this study. Earthworms were exposed to six mercury-contaminated soils with geochemically contrasting properties for 36 days, and digestive fluid was concurrently collected to solubilize soil-associated mercury. Bioaccumulation factors were 7.5-31.0 and 0.2-0.6 for MeHg and THg, respectively, and MeHg accounted for 17-58% of THg in earthworm. THg and MeHg measured in soils and earthworms were negatively associated with soil total organic carbon (TOC). Earthworm THg and MeHg also increased with increasing soil pH. The proportion of MeHg and THg released into the digestive fluid (digestive solubilizable mercury, DSM) was 8.3-18.1% and 0.4-1.3%, respectively. The greater solubilization of MeHg by digestive fluid than CaCl2, together with a biokinetic model-based estimate of dietary MeHg uptake, indicated the importance of soil ingestion for MeHg bioaccumulation in earthworms.

Trace Metals and Metalloids in Forest Soils and Exotic Earthworms in Northern New England, USA

Trace metals and metalloids (TMM) in forest soils and invasive earthworms were studied at 9 uncontaminated sites in northern New England, USA. Essential (Cu, Mo, Ni, Zn, Se) and toxic (As, Cd, Pb, Hg and U) TMM concentrations (mg kg^-1) and pools (mg m^-2) were quantified for organic horizons (forest floor), mineral soils and earthworm tissues. Essential TMM tissue concentrations were greatest for mineral soil-feeding earthworm Octolasion cyaneum. Toxic TMM tissue concentrations were highest for organic horizon-feeding earthworms Dendobaena octaedra, Aporrectodea rosea and Amynthas agrestis. Most earthworm species had attained tissue concentrations of Pb, Hg and Se potentially hazardous to predators. Bioaccumulation factors were Cd > Se > Hg > Zn > Pb > U > 1.0 > Cu > As > Mo > Ni. Only Cd, Se Hg and Zn were considered strongly bioaccumulated by earthworms because their average bioaccumulation factors were significantly greater than 1.0. Differences in bioaccumulation did not appear to be caused by soil concentrations as earthworm TMM tissue concentrations were poorly correlated with TMM soil concentrations. Instead, TMM bioaccumulation appears to be species and site dependent. The invasive Amynthas agrestis had the greatest tissue TMM pools, due to its large body mass and high abundance at our stands. We observed that TMM tissue pools in earthworms were comparable or exceeded organic horizon TMM pools; earthworm tissue pools of Cd were up 12 times greater than in the organic horizon. Thus, exotic earthworms may represent an unaccounted portion and flux of TMM in forests of the northeastern US. Our results highlight the importance of earthworms in TMM cycling in northern forests and warrant more research into their impact across the region.

Fate and uptake of pharmaceuticals in soil-earthworm systems

Pharmaceuticals present a potential threat to soil organisms, yet our understanding of their fate and uptake in soil systems is limited. This study therefore investigated the fate and uptake of (14)C-labeled carbamazepine, diclofenac, fluoxetine, and orlistat in soil-earthworm systems. Sorption coefficients increased in the order of carbamazepine < diclofenac < fluoxetine < orlistat. Dissipation of (14)C varied by compound, and for orlistat, there was evidence of formation of nonextractable residues. Uptake of (14)C was seen for all compounds. Depuration studies showed complete elimination of (14)C for carbamazepine and fluoxetine treatments and partial elimination for orlistat and diclofenac, with greater than 30% of the (14)C remaining in the tissue at the end of the experiment. Pore-water-based bioconcentration factors (BCFs), based on uptake and elimination of (14)C, increased in the order carbamazepine < diclofenac < fluoxetine and orlistat. Liquid chromatography-tandem mass spectrometry and liquid chromatography-Fourier transform mass spectrometry indicated that the observed uptake in the fluoxetine and carbamazepine treatments was due to the parent compounds but that diclofenac was degraded in the test system so uptake was due to unidentifiable transformation products. Comparison of our data with outputs of quantitative structure-activity relationships for estimating BCFs in worms showed that these models tend to overestimate pharmaceutical BCFs so new models are needed.

Comparison of elemental contents in earthworm cast and soil from a mercury-contaminated site (Idrija area, Slovenia)

The aim of this paper was to test the new sampling media-earthworm casts in a highly contaminated area. The investigation was carried out at the ancient Hg ore roasting site Pšenk in the surroundings of Idrija, where extremely high Hg contents in soils and SOM were determined in previous investigations. 32 earthworm cast samples were collected in the research grid 30 × 30 m in order to compare the Hg contents and spatial distribution in earthworm casts to the values and distributions in SOM and soil (0-15 cm). Extremely elevated Hg concentrations were determined in earthworm casts from the studied area ranging from 5.4 to 4330 mg/kg with the median of 31 mg/kg. The Hg values in casts are somewhat lower than in soil (6.3-8600 mg/kg) and slightly higher compared to soil organic matter (SOM) (1.5-4200 mg/kg). Strong correlation (r²=0.75) between Hg contents in casts and soil was found, while correlation between casts and SOM was positive but weaker (r²=0.35). Spatial distribution of Hg in earthworm casts show the highest concentrations in the central part of investigated area, similar to the distribution in soil. Hg contents rapidly decrease from the center toward the margins of the studied area, where they reach values of less than 50mg/kg. It was shown that Hg contents and dispersion in casts are comparable to those in soil, which indicates that at investigated area soil contamination is strongly reflected in contamination of earthworm casts.

Earthworms and soil pollutants

Although the toxicity of metal contaminated soils has been assessed with various bioassays, more information is needed about the biochemical responses, which may help to elucidate the mechanisms involved in metal toxicity. We previously reported that the earthworm, Eisenia fetida, accumulates cadmium in its seminal vesicles. The bio-accumulative ability of earthworms is well known, and thus the earthworm could be a useful living organism for the bio-monitoring of soil pollution. In this short review, we describe recent studies concerning the relationship between earthworms and soil pollutants, and discuss the possibility of using the earthworm as a bio-monitoring organism for soil pollution.

Oxidative stress in earthworms short- and long-term exposed to highly Hg-contaminated soils

Exposure to mercury is often assessed by the measurement of molecular and biochemical antioxidant defences against an excessive production of reactive oxygen species. Here we examined some selected biomarkers of oxidative stress in the earthworm Lumbricus terrestris short- (2d) and long-term (44 d) exposed to Hg-contaminated soils (up to 1287 mg/kg dry wt). This level of Hg exposure did not cause earthworm mortality, however it yielded organisms to a situation of oxidative stress which was evidenced by the time-dependent responses of biomarkers. The reduced to oxidized glutathione ratio was a sensitive and early biomarker of Hg exposure, although the glutathione reductase activity back returned their normal physiological concentrations. Metallothioneins and total glutathione seemed to have a significant role in reducing Hg-induced oxidative stress when exposure to Hg prolonged up to 44 d. We combined biomarker responses into an integrate biomarker index which positively correlated with the Hg concentrations measured in the postmitochondrial fraction of the earthworm muscle, and with the available Hg fraction in soil. Current results suggest that glutathione redox cycle can be a complementary tool in the exposure and effect assessment of Hg-polluted soils.

Global DNA methylation in earthworms: a candidate biomarker of epigenetic risks related to the presence of metals/metalloids in terrestrial environments

In this work, possible relationships between global DNA methylation and metal/metalloid concentrations in earthworms have been explored. Direct correlation was observed between soil and tissue As, Se, Sb, Zn, Cu, Mn, Ag, Co, Hg, Pb (p< 0.05). Speciation results obtained for As and Hg hint at the capability of earthworms for conversion of inorganic element forms present in soil to methylated species. Inverse correlation was observed between the percentage of methylated DNA cytosines and total tissue As, As + Hg, As + Hg + Se + Sb (β = -0.8456, p = 0.071; β = -0.9406, p = 0.017; β = -0.9526, p = 0.012 respectively), as well as inorganic As + Hg (β = -0.8807, p = 0.049). It was concluded that earthworms would be particularly helpful as bioindicators of elements undergoing in vivo methylation and might also be used to assess the related risk of epigenetic changes in DNA methylation.

Accumulation of mercury and methylmercury by mushrooms and earthworms from forest soils

Accumulation of total and methyl-Hg by mushrooms and earthworms was studied in thirty-four natural forest soils strongly varying in soil physico-chemical characteristics. Tissue Hg concentrations of both receptors did hardly correlate with Hg concentrations in soil. Both total and methyl-Hg concentrations in tissues were species-specific and dependent on the ecological groups of receptor. Methyl-Hg was low accounting for less than 5 and 8% of total Hg in tissues of mushrooms and earthworms, respectively, but with four times higher concentrations in earthworms than mushrooms. Total Hg concentrations in mushrooms averaged 0.96 mg Hg kg(-1) dw whereas litter decomposing mushrooms showed highest total Hg and methyl-Hg concentrations. Earthworms contained similar Hg concentrations (1.04 mg Hg kg(-1) dw) whereas endogeic earthworms accumulated highest amounts of Hg and methyl-Hg.