Arsenic resistance and cycling in earthworms residing at a former gold mine in Canada

Medicinal Earthworm: Speciation and Bioaccessibility of Arsenic and Its Potential Health Risks

Arsenic in environmental health has caused public concerns all over the world. However, high levels of arsenic residues in medicinal animals have not received enough attention. Medicinal earthworms are consumed widely in China, but its arsenic potential health risks to humans are unknown. This work investigated the total concentration, bioaccessibility, and speciation of arsenic in earthworms by ICP-MS and HPLC-ICP-MS to evaluate its potential health risks to humans. Arsenic was found in all earthworms at concentrations ranging from 0.4 to 53.6 mg kg⁻¹. The bioaccessibility of arsenic (bAs) varied significantly and ranged from 12.1 to 69.1%, with inorganic arsenic (iAs, including As(III) and As(V)) as the predominant species. Furthermore, a small amount of arsenobetaine (AB) was found. The estimated daily intake dose (EDI), hazard quotient (HQ), and carcinogenic risk (CR) of arsenic in most of the samples exceeded the safe threshold level. Results from this study indicated that the potential health risks by the consumption of earthworms may not be negligible. Herein, recommendations for the use of earthworms and regulatory recommendations for arsenic limit standards were proposed. This study reminds us that more control and monitoring of arsenic in medicinal animals should be carried out.

Silver nanomaterials released from commercial textiles have minimal impacts on soil microbial communities at environmentally relevant concentrations

Silver nanomaterials (Ag NMs) have been used in a variety of commercial products to take advantage of their antimicrobial properties. However, there are concerns that these AgNMs can be released during/after use and enter wastewater streams, potentially impacting aquatic systems or accumulating in wastewater biosolids. Biosolids, which are a residual of wastewater treatment processes, have been found to contain AgNMs and are frequently used as agricultural fertilizer. Since the function of soil microbial communities is imperative to nutrient cycling and agricultural productivity, it is important to characterize and assess the effects that silver nanomaterials could have in agricultural soils. In this study agricultural soil was amended with pristine engineered (PVP-coated or uncoated AgNMs), aged silver (sulphidized or released from textiles) nanomaterials, and ionic silver to determine the fate and toxicity over the course of three months. Exposures were carried out at various environmentally relevant concentrations (1 and 10 mg Ag/kg soil) representing between 30 to over 800 years of equivalent biosolid loadings. Over thirteen different methodologies and measures were used throughout this study to assess for potential effects of the silver nanomaterials on soil, including microbial community composition, average well colour development (AWCD) and enzymatic activity. Overall, the AgNM exposures did not exhibit significant toxic effects to the soil microbial communities in terms of density, activity, function and diversity. However, the positive ionic silver treatment (100 mg Ag/kg soil) resulted in suppression to microbial activity while also resulting in significantly higher populations of Frankia alni (nitrogen-fixer) and Arenimonas malthae (phytopathogen) as compared to the negative control (p < 0.05, Tukey HSD) which warrants further investigation.

Arsenic speciation in the bracket fungus Fomitopsis betulina from contaminated and pristine sites

Uptake, distribution and speciation of arsenic (As) were determined in the bracket fungus Fomitopsis betulina (previously Piptoporus betulinus), commonly known as the birch polypore, collected from a woodland adjacent to a highly contaminated former mine in the Southwest UK and at an uncontaminated site in Quebec, Canada, with no past or present mining activity. The fruiting body was divided into cap, centre and pores representing the top, middle and underside to identify trends in the distribution and transformation of As. Total As, determined by inductively coupled plasma-mass spectrometry (ICP-MS), was approximately tenfold higher in the mushroom from the contaminated compared to the uncontaminated site. Overall, accumulation of As was low relative to values reported for some soil-dwelling species, with maximum levels of 1.6 mg/kg at the contaminated site. Arsenic speciation was performed on aqueous extracts via both anion and cation high-performance liquid chromatography-ICP-MS (HPLC-ICP-MS) and on whole dried samples using X-ray absorption near edge structure (XANES) analysis. Seven As species were detected in F. betulina from the contaminated site by HPLC-ICP-MS: arsenite (As^III), arsenate (As^V), dimethylarsinate (DMA^V), methylarsonate (MA^V), trimethylarsine oxide (TMAO), tetramethylarsonium ion (Tetra) and trace levels of arsenobetaine (AB). The same As species were observed at the uncontaminated site with the exception of TMAO and Tetra. Arsenic species were localized throughout the fruiting body at the contaminated site, with the cap and pores containing a majority of As^V, only the cap containing TMAO, and the pores containing higher concentrations of DMA^V and MA^V as well as tetra and a trace of AB. XANES analysis demonstrated that the predominant form of As at the contaminated site was inorganic As^III coordinated with sulphur or oxygen and As^V coordinated with oxygen. This is the first account of arsenic speciation in F. betulina or any fungi of the family Fomitopsidaceae.

Impact assessment of legacy wastes from ancient mining activities on current earthworm community

Mineral resource exploitation by human societies throughout history led to the deposit of mining and smelting wastes and the subsequent contamination of surrounding soils by trace metals. After several centuries, the impact of these legacy hazardous wastes may remain a cause of environmental concern, especially for indigenous soil invertebrate populations such as earthworms. Therefore, we conducted a passive biomonitoring campaign in a former metallurgical district (Vosges Mountains, eastern France). According to community descriptors, we evidenced a significant decrease of anecic and endogeic earthworm density in the former mining stations. To link these results to soil contamination and bioaccumulation levels in earthworm tissues, we propose an original modelling approach using nonlinear mixed-effects regression models. Beyond a dose-response relationship between metal internal concentrations and their levels in soils, we highlighted contrasted behaviors according to ecological groups (epianecics and endogeics most impacted). We interpreted these results in relation to some eco-physiological features without completely exclude the influence of textural characteristics of soil, especially for deep-burrowing species such as anecic strict. Nonetheless, the presence of earthworm populations currently living in highly contaminated sites and handling elevated internal concentrations raises the question of the acquisition of genetic adaptive traits and the trophic transfers of metals.

Genetic analysis in earthworm population from area contaminated with radionuclides and heavy metals

This study assessed the effects of environmental contamination by naturally occurring radionuclides and heavy metals on the genetic structure of a population of the earthworm Aporrectodea caliginosa. A. caliginosa were collected from four sites and characterized by amplified fragment length polymorphism (AFLP) analyses. No differences in genetic structure and diversity were found between sites that differed greatly in soil contamination levels of radionuclides and metals. However, when the genetic structure of the A. caliginosa population was analyzed without considering information about the sampling site, a complex intraspecific genetic structure was identified. At least three highly divergent lineages were found, in unequal proportions, of each genetically isolated group from each study site. No associations were found between the distribution of the detected genetic clusters and the geographical origin of the samples. Thus, no noticeable adaptive changes or signs of directional selection were detected, despite the long history of genotoxic waste disposal at the sampling site. These results suggest a combined effect of three factors on the genetic structure and diversity of A. caliginosa in soils: the complexity of the contaminant composition, the heterogeneous spatial distribution of the pollutants, and the complexity of the intraspecific genetic structures of A. caliginosa.

Genetic, epigenetic, and developmental toxicity of Chironomus riparius raised in metal-contaminated field sediments: A multi-generational study with arsenic as a second challenge

Ecotoxicity tests conducted under well-controlled lab conditions often do not reflect the real environmental conditions. To this end, we designed an ecotoxicity test using an aquatic midge, Chironomus riparius, raised in metal-contaminated field sediments (MCFS), which reflect the real environmental conditions, for five consecutive generations (F0-F4) followed by a toxic response to arsenic exposure (as a second challenge). The toxic responses (i.e. DNA damage, DNA methylation, stress response gene expression, and mortality) were compared to those organisms reared in lab sediments (LS). Under the MCFS condition, increased adult emergence was observed for the second and third generations (F1 and F2), while a decreased tendency was evident thereafter (F3 and F4) compared to that of F0. When comparing C. riparius raised in MCFS or LS exposed to arsenic, increased sensitivity (declined survival) was observed in the larvae from F2. However, that tendency was not present in F4 of the MCFS midges, indicating a possible physiological adaptation. Increased DNA damage was observed in the MCFS-exposed organisms (F0, F2, and F4) compared to the those exposed to LS, particularly at F0. Arsenic exposure induced hypermethylation at F0 and, in contrast, hypomethylation at the later generations (F2, F4) in the MCFS-exposed organisms. Global DNA methylation results were supported by the expression of genes involved in enzymatic methylation. Moreover, alterations in oxidative stress related to gene expression showed that significant oxidative stress and perturbation of glutathione reserves occurred under the MCFS and the subsequent arsenic exposure conditions. Overall, our results suggest that multigenerational rearing under MCFS conditions resulted in physiological adaptation of C. riparius to metal exposure, specifically at later generations, which in turn modulated its response to arsenic stress through possible genetic and epigenetic mechanisms.

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.

Genetic effects in Helix aspersa near a coal plant revealed by the micronucleus test

Coal plants can be a major source of mutagenic pollutants. In this study we used the common land snail Helix aspersa, to detect the mutagenic effect of pollution from a coal plant in central Italy applying the micronucleus test (MN) on snail's haemocytes and evaluating trace elements concentration (As Cd, Pb, Hg, and Zn) in soil and snails. Snails from a biological farm were exposed for 13 days in five locations at different distances from the plant. Wild snails collected in the same locations were also analysed. MN frequency in exposed snails was significantly higher in four locations within 10 km from to the plant, with respect to the control and the farthest location. Comparing the MN frequency between farmed and wild snails, a significantly higher frequency emerged for the exposed snails in all locations except the farthest, likely indicating adaptation or selection of the wild organisms due to chronic exposure to pollutants. In natural snails significantly higher MN frequencies with near the plant emerged as well. Trace elements analysis showed significant correlations between MN frequencies and both Zn and As concentrations in soil, for both exposed and wild snails, and Zn and Pb concentrations in exposed snails. Our results were consistent with those previously obtained when evaluating primary DNA damage in natural snails from the same area and show that the snails near the plant were affected by a permanent cytogenetic damage. Moreover, they confirm the suitability of snails for biomonitoring the presence of pollutants with mutagenic effect.

Allelopathic effects of volatile organic compounds from Eucalyptus grandis rhizosphere soil on Eisenia fetida assessed using avoidance bioassays, enzyme activity, and comet assays

Allelopathy has been identified as an underlying mechanism of detrimental environmental impacts within commercial plantations. Eucalyptus spp. are known to generate huge amounts of volatile organic compounds (VOCs) that can function as phytotoxins and thus inhibit other plants. In the present study, biochemical markers, including activities of acetylcholinesterase (AChE) and oxidative stress enzymes, such as superoxide dismutase (SOD) and glutathione S-transferase (GST), were assayed to assess changes in Eisenia fetida at the physiological level induced by different doses of VOCs as part of an acute toxicity test over 7 and 14-day exposures. In addition, the toxicities of VOCs were investigated using a soil avoidance test and comet assay. The results revealed that E. fetida exhibited significant avoidance behavior towards the highest concentrations of undecane, decane, 2,4-dimethyl heptane, and 2,2,4,6,6-pentametyl heptane. The tail DNA percentages were significantly increased for all experimental treatments relative to control. However, under the treatments of VOCs, Olive tail moment content and comet tail length also display an obvious increase compared to control, except for that of octane, undecane and decane treatments. As VOC concentrations and durations increased in the soil, activities of AChE, SOD, and GST were either stimulated or inhibited. Among the VOCs, decane, 2,4-dimethyl heptane, 2,2,4,6,6-pentamethyl heptane, and 2,4-di tert buyl phenol exerted stronger effects on enzymatic activities. In summary, VOCs in rhizosphere soils of E. grandis might exert a toxic impact on E. fetida, among which 2,4-dimethyl heptane, 2,2,4,6,6-pentamethyl heptane, and 2,4-di tert buyl phenol have the strongest effects.