Bioaccumulation of total mercury in the earthworm Eisenia andrei

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.

Evaluation of the hydrogen-rich water alleviation potential on mercury toxicity in earthworms using ATR-FTIR and LC-ESI-MS/MS spectroscopy

The toxic effects of mercury in earthworms and the potential alleviation effect of hydrogen-rich water (HRW) using ATR-FTIR and LC-MS analysis methods were investigated. Different concentrations of mercury chloride (H1: 5 µg/mL, H2: 10 µg/mL, H3: 20 µg/mL, H4: 40 µg/mL, and C1: control) and mercury chloride prepared in hydrogen-rich water (H5: 5 µg/mL, H6: 10 µg/mL, H7: 20 µg/mL, H8: 40 µg/mL, and C2: control) were injected into earthworms. The changes and reductions in some bands representing proteins, lipids, and polysaccharides (3280 cm^-1, 2922 cm^-1, 2855 cm^-1, 1170 cm^-1, and 1047 cm^-1) showed that protective effects could occur in groups prepared with hydrogen-rich water. In the FTIR results, it was found that these bands in the H3 group were more affected and decreased by the influence of mercury on earthworms than the H7 group prepared with hydrogen. LC-MS analysis showed that the changes in some ions of the highest dose groups (H4 and H8) were different, and mercury caused oxidative DNA damage in earthworms. When the high-level application groups of mercury, i.e., H4 and H8 were compared with the controls, the ion exchange ([M + H] + ; m/z 283.1) representing the 8-Oxo-dG level in earthworms was higher in the H4 group than the H8 group. This reveals that HRW exhibited the potential ability to alleviate the toxic effects of mercury; however, a longer period of HRW treatment may be necessary to distinguish an obvious effect. The ATR-FTIR spectroscopy provided a rapid and precise method for monitoring the changes in biological tissues caused by a toxic compound at the molecular level.

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.

Investigating the effects of vermicomposting process using Eisenia Fetida earthworms on the reduction of parasites population

Purpose

The existence of parasite agents in natural organic fertilizers can lead to health problems and infection transmission. The aim of the present study was to survey the parasites' population reduction during the vermicomposting of the mixtures of municipal sewage sludge (SS) and cow dung (CD) using E. fetida earthworms.

Methods

The vermicomposting process was performed by using earthworms of E. fetida species. The composting process was conducted in 27 pilots for 3 months. The identification and counting of the parasites' population were carried out by Mac Master Slide, according to Bailenger method.

Results

The results indicated that the type and number of parasite elements decreased with increasing vermicomposting time. The cumulative removal percent of parasites for sewage sludge (96.10%) was more than the SS + CD (93.65%) and CD (92.93%) treatments. The results showed that after 90 days of vermicomposting, the highest cumulative reduction in the number of parasites was obtained for the treatments with 40 earthworms (98.48%), while the corresponding value for the treatments without earthworms was (88.66%). The statistical analysis indicated that in terms of the parasite's population, a significant difference was observed for the three kinds of compostable materials (P < 0.05), however, this difference was not significant for the three levels of the earthworms (P > 0.05).

Conclusion

The results showed that the mixture of sewage sludge and cow dung in combination with sawdust could lead to greater and faster reduction in the parasite's population. In addition, the bio-transformed product can be used as useful manure.

The impact of cow dung augmentation on soil restoration and bio-accumulation of metals (Lead and Cadmium) in Pheretima posthuma (Annelida: Clitellata)

To investigate the role of cow dung in soil reclamation and bio assimilation along with bio accumulation of heavy metals in earthworm (P. posthuma) (N=900) earthworms were used and treatment groups of CD-soil mixture of different proportion of cow dung were designed. Nonlethal doses of lead acetate and cadmium chloride were added in treatment groups. Mature P. posthuma were released in each experimental pot maintaining the favorable conditions. The pH, carbon, nitrogen, phosphorus, exchangeable cations, and heavy metal level of each mixture was evaluated. The results indicated that bio-assimilation of Pb and Cd by P. posthuma were significantly (P ˂ 0.01) higher in different soil-CD treatments compared to control. Highest bio-assimilation of both metals was observed in T1 of both groups (Pb = 563.8 mg/kg and Cd = 42.95 mg/kg). The contents of both metals were significantly (P ˂ 0.05) lowered in casting. The nutrient concentration in the final castings of all soil-CD treatments were also equally transformed from less or insoluble to more soluble and available for plants, except for carbon level which increased with CD proportion. It is concluded that cow dung as organic matter has a positive effect on soil reclamation and bio-assimilation of metals by P. posthuma.

Applying the diffusive gradient in thin films method to assess soil mercury bioavailability to the earthworm Eisenia fetida

This study assessed the critical soil characteristics affecting mercury (Hg) bioavailability to the earthworm Eisenia fetida using the diffusive gradient in thin films (DGT) method. The soil samples were collected from a tributary of the Hyeongsan River contaminated with industrial waste and landfill leachates called Gumu Creek. The Hg concentration in the soil had a range of 0.33-170 μg g^-1 (average 33 ± 56 μg g^-1), and the Hg concentration of earthworms incubated in the soils was 0.83-11 μg g^-1 (average 2.9 ± 3.2 μg g^-1). When correlation analysis was used to detect the key variables among the soil properties related to Hg accumulation in the soils, earthworms, and resins, the water-holding capacity, which is covaried with the organic matter content, was determined to be a primary factor in increasing Hg accumulation in the soils, earthworms, and resins. However, the experimentally determined earthworm bioaccumulation factor and the DGT accumulation factor were negatively affected by the water-holding capacity. Therefore, the water-holding capacity played a dual role in the Gumu Creek deposits: increasing the soil Hg concentration and decreasing Hg bioavailability and leachability. Further, the DGT-Hg flux was positively correlated with the Hg concentration in earthworms (r = 0.93). Although the earthworm accumulation of Hg is not processed by passive diffusion, this study proves that the DGT method is promising for predicting soil Hg bioavailability to the earthworm E. fetida, and the water-holding capacity simultaneously regulates Hg availability to the DGT and the earthworms.

Histopathological effects and biomarker response of earthworms, Eisenia fetida, after exposure to crude oil contaminated soils

Earthworms are the most abundant invertebrates in the soils and are permanently in close contact with soil particles. Therefore, they are significantly affected by the pollutants that reach the soil system. The study was aimed at evaluating the effect of exposure to crude oil contaminated soil on Eisenia fetida using cellular antioxidant enzymes and tissue organization as biomarkers. E. fetida were exposed to different concentrations of crude oil contamination of 1 mL, 2 mL. and 3 mL (0.25, 0.50 and 0.75%) for 14 days. The antioxidant/oxidant parameters were analysed in the muscle and liver tissues. The results showed that only the reduced glutathione (GSH) of earthworms exposed to 1 mL were not significant (p>0.05) from the control, while the other concentrations (2 mL – 0.50% and 3 mL – 0.75%) were significantly different (p<0.05) from the control. The activity of catalase (CAT) with respect to the total protein content was highest in the liver of earthworms exposed to 1 mL (0.25% conc.) on day 7 (51.84 μmol/mg pro) while the least CAT activity with respect to the total protein content was reported in the liver of control earthworms after 14 days (19.51 μmol/mL/min). A significant increase in the activity of superoxide dismutase at all the concentrations (0.25, 0.50 and 0.75%) after 14 days were also observed. Significant histopathological alterations were observed in E. fetida from the three concentrations. Severe disruptions in the arrangement of their body wall muscle layers, distorted internal viscera, as well as cellular degeneration, pigments, moderate to severe areas of lesion, and distortion of the shape of circular and longitudinal muscles, eroding of internal and external tissues leading to total destruction of body wall were observed. In conclusion, the study revealed that crude oil even at lower concentration induced biomarker responses in E. fetida such as higher levels of Malondialdehyde in E. fetida after exposure crude oil due its toxicity. Histopathological alterations such as cellular degeneration, moderate to severe areas of necrosis, areas of inflammation, inclusion bodies, pigments, and distortion of the shapes of circular and longitudinal muscles also showed the adverse impacts of crude oil pollution in the soils.

Metal induced non-metallothionein protein in earthworm: A new pathway for cadmium detoxification in chloragogenous tissue

Earthworms neutralize toxic metals by a small (∼13 kDa) cysteine rich metal binding protein, metallothionein (MT). Although the rate of metal accumulation and MT expression does not correlate well, the reason behind such inconsistency has not yet been deciphered. The present investigation clearly demonstrates that expression of some non-MT metal induced proteins is responsible for such incongruity. Applying selective protein isolation techniques in fluorescence tagged cadmium exposed (135 mg/kg) earthworms we were able to purify a 150 kDa metal induced protein (MIP) among others. After 60 days of exposure cadmium accumulation in earthworm intestines was significant. Immunofluorescence staining followed by confocal microscopy exhibited that MIP accumulates ingested cadmium in the intestinal region and eventually deposits the metal in the chloragogenous tissue. We determined the N-terminal sequence of 15 amino acid residues and after bioinformatics analysis, it was concluded that MIP is most probably a glutamic acid rich, novel cadmium binding protein. To further validate the binding mechanism, we conducted paper chromatography and continuous variation experiments which evidenced that cadmium readily binds to glutamic acid. The present finding is the first in-vivo evidence of a non-metallothionein cadmium binding protein induced in the intestines of earthworm exposed to a cadmium rich environment.

Evaluation of gene expression of different molecular biomarkers of stress response as an effect of copper exposure on the earthworm EIsenia Andrei

The paper reports the results of a laboratory test on the bioaccumulation and toxicological effects of sub-lethal soil concentration of copper, a widely used fungicide in organic farming, on DNA damage, a critical marker increasingly used in ecotoxicology in the earthworm Eisenia andrei. In the same experimental setting we evaluated gene expression of classical biomarker of stress induced by xenobiotic. [Heat Shock Protein 70 (HSP70) and Metallothionein (MET)], as well as genes coding for enzymes involved in detoxification of reactive oxygen species [Superoxide dismutase (SOD) and catalase (CAT)]. Additionally, expression of genes involved in the immune response were investigated: a Toll-like receptor (TLR), a receptor with cytolytic activity named Cytolytic Factor (CCF) and two antimicrobial peptides, fetidin (FET) and lysenin (LYS). Results showed significant time-dependent bioaccumulation of Cu and DNA damage at concentrations remarkably lower than those found in most agricultural soils worldwide. MET was increased as was FET and TLR. The present work gives new insights into the mechanisms of sub-lethal toxicity of copper as an environmental pollutant and in the identification of novel sub-lethal biomarkers of cellular response to the stressor such as immune response genes.

Mercury, Lead and Cadmium Concentrations in Talpa occidentalis and in Their Digeneans of the Genus Ityogonimus

INTRODUCTION

Many parasites living in aquatic ecosystems are useful indicators of environmental health. On the other hand, information is scarcer with respect to the use of helminth parasites of vertebrates living in terrestrial ecosystems as monitoring tools for toxic element environmental pollution. The present study evaluates the suitability of the model Talpa occidentalis/Ityogonimus spp. as a bioindicator system for mercury (Hg), lead (Pb) and cadmium (Cd) contamination in agricultural soils from Asturias (Spain).

METHODS

Kidney and liver samples collected from T. occidentalis specimens (n = 36) and Ityogonimus spp. samples collected from 14 infected hosts were analyzed by ICP-MS.

RESULTS

The highest mean levels of Hg and Pb were found in Ityogonimus individuals (20.9 and 12.4 µg g^-1 wet weight, respectively). Considering renal and hepatic concentrations in T. occidentalis, bioaccumulation factors of Ityogonimus for Hg were 83.7 and 58.6, respectively, whereas concerning Pb bioaccumulation factors were 38.2 and 82.9, respectively. No bioaccumulation was detected in Ityogonimus in the case of Cd.

CONCLUSIONS

More studies involving digenean parasites of small mammals are needed, especially when biomonitoring environmental toxic element pollution in terrestrial ecosystems. The present results support the above-mentioned model as a suitable biomonitoring system to evaluate environmental Hg and Pb contamination in terrestrial non-urban Iberian habitats. Similar models involving other species (Talpa spp./Ityogonimus spp.) might be used in a much wider geographical range.

Bioavailability and chronic toxicity of bismuth citrate to earthworm Eisenia andrei exposed to natural sandy soil

The present study describes bioavailability and chronic effects of bismuth to earthworms Eisenia andrei using OECD reproduction test. Adult earthworms were exposed to natural sandy soil contaminated artificially by bismuth citrate. Average total concentrations of bismuth in soil recovered by HNO₃ digestion ranged from 75 to 289mg/kg. Results indicate that bismuth decreased significantly all reproduction parameters of Eisenia andrei at concentrations ≥ 116mg/kg. However, number of hatched cocoons and number of juveniles seem to be more sensitive than total number of cocoons, as determined by IC₅₀; i.e., 182, 123 and > 289mg/kg, respectively. Bismuth did not affect Eisenia andrei growth and survival, and had little effect on phagocytic efficiency of coelomocytes. The low immunotoxicity effect might be explained by the involvement of other mechanisms i.e. bismuth sequestered by metal-binding compounds. After 28 days of exposure bismuth concentrations in earthworms tissue increased with increasing bismuth concentrations in soil reaching a stationary state of 21.37mg/kg dry tissue for 243mg Bi/kg dry soil total content. Data indicate also that after 56 days of incubation the average fractions of bismuth available extracted by KNO₃ aqueous solution in soil without earthworms varied from 0.0051 to 0.0229mg/kg, while in soil with earthworms bismuth concentration ranged between 0.310-1.347mg/kg dry soil. We presume that mucus and chelating agents produced by earthworms and by soil or/and earthworm gut microorganisms could explain this enhancement, as well as the role of dermal and ingestion routes of earthworms uptake to soil contaminant.

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.