Internal metal sequestration and its ecotoxicological relevance: a review

Reduced copper uptake and efflux by the mussel Mytilus coruscus after Cu exposure: Implication for biomonitoring

The hard-shell mussels Mytilus coruscus have been extensively employed in pollution biomonitoring. Earlier studies indicated that metal concentrations in Mytilus coruscus may not accurately reflect the true metal contamination levels in the sampling areas, possibly due to their modified metal uptake and efflux. Given the likelihood of mussels in the field being exposed to intermittent metal contaminants, this study investigated whether different Cu pre-exposures significantly affected its uptake and efflux upon Cu exposure. We found significant reduction in Cu uptake rate constant (ku) and efflux rate constant (ke) in the mussels with varying Cu pre-exposure regimes. Specifically, the ku decreased from 1.55 ± 0.37 L g-1 d-1 in the control group to 0.65 ± 0.19 after 5 days and 0.53 ± 0.28 after 15 days of exposure to 20 μg L-1 Cu, respectively, and then was further reduced to as low as 0.096 ± 0.046 L g-1 d-1 following a 5-day exposure at 50 μg L-1 Cu. Similarly, the ke decreased from 0.18 ± 0.020 to 0.15 ± 0.015 d-1 following 5-15 days of exposure to 20 μg L-1 Cu, and further decreased to 0.081 ± 0.023 d-1 after a 5-day exposure at 50 μg L-1 Cu. Our subcellular distribution analysis underscored the critical role of the metallothionein-like protein (MTLP) fraction in modifying both Cu ku and ke during the rapid-depuration phase (ke1), whereas the metal-rich granule (MRG) fraction influenced the ke during the second depuration phase (ke2). This study demonstrated that environmental assessments utilizing biomonitoring species should consider the exposure of these organisms to ensure accurate interpretations of metal contamination in marine ecosystems and enhance the effectiveness of these species in environmental monitoring. This crucial factor is often overlooked, potentially skewing data and leading to misinterpretations of environmental health and pollution levels.

Metaphire guillelmi exhibited predominant capacity of arsenic efflux

Earthworm could regulate their body concentration of arsenic via storage or excretion, and the ability of As efflux among different earthworms is not consistent. Here, whole and semi As exposure patterns with 0-10-30-60-100 mg kg-1 exposure concentrations were set to characterize the As efflux in geophagous earthworm, Metaphire guillelmi. Cast As (As-C) and earthworms' antioxidative responses were monitored to explore the efflux mechanisms under 30 mg kg-1 As-spiked soil (As30), besides, As concentration in earthworm tissue after egestion and dissection depurations were compared. In the whole exposure pattern, As concentration in gut content (As-G, 19.2-120.3 mg kg-1) surpassed that in the tissue (As-T, 17.2-53.2 mg kg-1), and they both increased with exposure concentrations. With the prolong time, they firstly increased and kept stable between day 10-15, then As-G increased while As-T decreased between day 15-20. In the semi-exposure pattern, both As-G and As-T decreased when M. guillelmi was transferred to clean soil for 5 days. During the 42-day incubation in As30, the antioxidative responses including reactive oxygen species (ROS), glutathione (GSH) and glutathione-S-transferase (GST) were firstly increased and then decreased, and As-C (13.9-43.9 mg kg-1) kept higher than As-G (14.2-35.1 mg kg-1). Significantly positive correlations were found between As-T and GSH, As-C and GST. Moreover, tissue As after dissection (11.6-22.9 mg kg-1) was obviously lower than that after egestion (11.4-26.4 mg kg-1), but significantly related to ROS and GSH. Taken together, M. guillelmi exhibited excellent capacity of As efflux, and GSH explained tissue As accumulation while GST facilitated the As elimination via cast. Besides, dissection instead of egestion revealed the As efflux in M. guillelmi more accurately. These findings contributed to a better understanding of how geophagous earthworm M. guillelmi regulated tissue As accumulation for As stress tolerance, and recommended an optimal depuration mode to characterize As accumulation.

Metallothionein: A Comprehensive Review of Its Classification, Structure, Biological Functions, and Applications

Metallothionein is a cysteine-rich protein with a high metal content that is widely found in nature. In addition to heavy metal detoxification, metallothionein is well known as a potent antioxidant. The high sulfhydryl content of metallothionein confers excellent antioxidant activity, enabling it to effectively scavenge free radicals and mitigate oxidative stress damage. In addition, metallothionein can play a neuroprotective role by alleviating oxidative damage in nerve cells, have an anticancer effect by enhancing the ability of normal cells to resist unfavorable conditions through its antioxidant function, and reduce inflammation by scavenging reactive oxygen species. Due to its diverse biological functions, metallothionein has a broad potential for application in alleviating environmental heavy metal pollution, predicting and diagnosing diseases, and developing skin care products and health foods. This review summarizes the recent advances in the classification, structure, biological functions, and applications of metallothionein, focusing on its powerful antioxidant effects and related functions.

Addressing lanthanum toxicity in plants: Sources, uptake, accumulation, and mitigation strategies

Lanthanum (La), the second most abundant rare earth element (REE) is emerging as an environmental issue, with the potential to impact ecosystems and human health. Major sources of soil contamination by La include agricultural, and industrial activities. Lanthanum is non-essential for plant growth but accumulates in various plant parts. The uptake of La by plants is intricately influenced by various factors such as soil pH, redox potential, cation exchange capacity, presence of organic acids and rhizosphere composition. These factors significantly impact the availability and absorption of La ions. Lanthanum impact on plants depends on soil characteristics, cultivated species, developmental stage, La concentration, treatment period, and growth conditions. Excessive La concentrations affect cell division, DNA structure, nutrient uptake, and photosynthesis and induce toxicity symptoms. Plants employ detoxification mechanisms like vacuolar sequestration, osmolyte synthesis, and antioxidant defense system. However, higher concentrations of La can overwhelm these defense mechanisms, leading to adverse effects on plant growth and development. Further, accumulation of La in plants increases the risk for human exposure. Strategies to mitigate La toxicity are, therefore, vital for ecosystem protection. The application of phytoremediation, supplementation, chelation, amendments, and biosorption techniques contributes to the mitigation of La toxicity. This review provides insights into La sources, uptake, toxicity, and alleviation strategies in plants. Identifying research gaps and discussing advancements aims to foster a holistic understanding and develop effective strategies for protecting plant health and ecosystem resilience against La contamination.

Microbial assisted multifaceted amelioration processes of heavy-metal remediation: a clean perspective toward sustainable and greener future

Rapidly increasing heavy metal waste has adversely affected the environment and the Earth's health. The lack of appropriate remediation technologies has worsened the issue globally, especially in developing countries. Heavy-metals contaminants have severely impacted the environment and led to devastating conditions owing to their abundance and reactivity. As they are nondegradable, the potential risk increases even at a low concentration. However, heavy-metal remediation has increased with the up-gradation of technologies and integration of new approaches. Also, of all the treatment methodologies, microbial-assisted multifaceted approach for ameliorating heavy metals is a promising strategy for propagating the idea of a green and sustainable environment with minimal waste aggregation. Microbial remediation combined with different biotechniques could aid in unraveling new methods for eradicating heavy metals. Thus, the present review focuses on various microbial remediation approaches and their affecting factors, enabling recapitulation of the interplay between heavy-metals ions and microorganisms. Additionally, heavy-metals remediation mechanisms adapted by microorganisms, the role of genetically modified (GM) microorganisms, life cycle assessment (LCA), techno-economic assessment (TEA) limitations, and prospects of microbial-assisted amelioration of heavy-metals have been elaborated in the current review with focus toward "sustainable and greener future."

Site- and species-specific metal concentrations, mobility, and bioavailability in sediment, flora, and fauna of a southeastern United States salt marsh

Salt marshes are highly productive and valuable coastal ecosystems that act as filters for nutrients and pollutants at the land-sea interface. The salt marshes of the mid-Atlantic United States often exhibit geochemical behavior that varies significantly from other estuaries around the world, but our understanding of metal mobility and bioavailability remains incomplete for these systems. We sampled abiotic (water and sediment) and native biotic (three halophyte and two bivalve species) compartments of a southeastern United States salt marsh to understand the site- and species-specific metal concentrations, fractionation, and bioavailability for 16 metals and metalloids, including two naturally occurring radionuclides. Location on the marsh platform greatly influenced metal concentrations in sediment and metal bioaccumulation in halophytes, with sites above the mean high-water mark (i.e., high marsh zone) having lower concentrations in sediment but plants exhibiting greater biota sediment accumulation factors (BSAFs). Transition metal concentrations in the sediment were an average of 6× higher in the low marsh zone compared to the high marsh zone and heavy metals were on average 2× higher. Tissue- and species-specific preferential accumulation in bivalves provide opportunities for tailored biomonitoring programs. For example, mussel byssal threads accumulated ten of the sixteen studied elements to significantly greater concentrations compared to soft tissues and oysters had remarkably high soft tissue zinc concentrations (~5000 mg/kg) compared to all other species and element combinations studied. Additionally, some of our results have important implications for understanding metal mobility and implementing effective remediation (specifically phytoremediation) strategies, including observations that (1) heavy metals exhibit distinct concentration spatial distributions and metal fractionation patterns which vary from the transition metals and (2) sediment organic matter fraction appears to play an important role in controlling sediment metal concentrations, fractionation, and plant bioavailability.

Effects of wollastonite and phosphate treatments on cadmium bioaccessibility in pak choi (Brassica rapa L. ssp. chinensis) grown in contaminated soils

Cadmium (Cd) contamination of soil can strongly impact human health through the food chain due to uptake by crop plants. Inorganic immobilizing agents such as silicates and phosphates have been shown to effectively reduce Cd transfer from the soil to cereal crops. However, the effects of such agents on total Cd and its bioaccessibility in leafy vegetables are not yet known. Pak choi (Brassica rapa L. ssp. chinensis) was here selected as a representative leafy vegetable to be tested in pots to reveal the effects of silicate-phosphate amendments on soil Cd chemical fractions, total plant Cd levels, and plant bioaccessibility. The collected Cd contaminated soil was mixed with control soil at 1:0, 1:1, 1:4, 0:1 with a view to Cd high/moderate/mild/control soil samples. Three heavy metal-immobilizing agents: wollastonite (W), potassium tripolyphosphate (KTPP), and sodium hexametaphosphate (SHMP) were added to the soil in order to get four different treatment groups, i.e., control (CK), application of wollastonite alone (W), wollastonite co-applied with KTPP (WKTPP), application of wollastonite co-applied with SHMP (WSHMP) for remediation of soils with different levels of Cd contamination. All three treatments increased the effective bio-Cd concentration in the soils with varying levels of contamination, except for W under moderate and heavy Cd contamination. The total Cd concentration in pak choi plants grown in mildly Cd-contaminated soil was elevated by 86.2% after WKTPP treatment compared to the control treatment could function as a phytoremediation aid for mildly Cd-contaminated soil. Using an in vitro digestion method (physiologically based extraction test) combined with transmission electron microscopy, silicate and phosphorus agents were found to reduce the bioaccessibility of Cd in pak choi by up to 66.13% with WSHMP treatment. Application of silicate alone reduced soil bio-Cd concentration through the formation of insoluble complexes and silanol groups with Cd, but the addition of phosphate may have facilitated Cd translocation into pak choi by first co-precipitating with Ca in wollastonite while simultaneously altering soil pH. Meanwhile, wollastonite and phosphate treatments may cause Cd to be firmly enclosed in the cell wall in an insoluble form, reducing its translocation to edible parts and decreasing the bioaccessibility of Cd in pak choi. This study contributes to the mitigation of Cd bioaccessibility in pak choi by reducing soil Cd concentration through in situ remediation and will help us to extend the effects of wollastonite and phosphate on Cd bioaccessibility to other common vegetables. Therefore, this study thus reveals effective strategies for the remediation of soil Cd and the reduction of Cd bioaccessibility in crops based on two indicators: total Cd and Cd bioaccessibility. Our findings contribute to the development of methods for safer cultivation of commonly consumed leafy vegetables and for soil remediation.

Trophic Transfer of Cd, Cu, Pb, Zn, P and Se in Dutch Storage Water Reservoirs

Heavy metals are naturally omnipresent in aquatic systems. Excess amounts of heavy metals can accumulate in organisms of pollution impacted systems and transfer across a food web. Analysing the food web structure and metal contents of the organisms can help unravel the pathways of biomagnification or biodilution and gain insight in trophic linkages. We measured heavy metals and other elements in mussel bank detritus and organisms of the Biesbosch reservoirs (the Netherlands) and linked those to stable isotopic signatures. The heavy metal contents (cadmium, copper, lead, and zinc) were often lowest in benthivorous, omnivorous and piscivorous species (mainly fish); whereas, phosphorus contents were lower in the autotrophs. Mussel bank detritus contained the highest amounts of heavy metals. The heavy metals were negatively correlated with δ15N values. For selenium no clear trend was observed. Furthermore, there was a negative correlation between fish length and some heavy metals. Based on all 20 analysed elemental contents, similarities between species became apparent, related to niche or habitat. This study confirms that elemental contents of species can differ between feeding guilds and/or species, which can be attributed to metabolic and physiological processes. The organisms in higher trophic levels have adaptations preventing metal accumulation, resulting in lower contents. Within the fish species biodilution occurs, as most metal contents were lowest in bigger fish. Overall, the metals did not seem to biomagnify, but biodilute in the food web. Metal analyses combined with isotopic signatures could thus provide insights in metal transfer and possible trophic linkages within a system.

Cytosolic distribution of copper in the gills of field-collected oysters with different copper bioaccumulation

Oysters can hyper-accumulate copper (Cu) without apparent toxicity, but the mechanism of sequestering excessive cytosolic Cu in oysters remains unclear. We here investigated the Cu distribution in the cytosolic proteins (CPs) in the gills of oysters (Crassostrea hongkongensis) through size-exclusion chromatography coupled to inductively coupled plasma mass spectrometry (SEC-ICP-MS). Oysters collected from the southern coast of China contained a gradient of gill Cu concentrations ranging from 132 to 3540 μg g-1 (dry weight), with 7-41 % of Cu distributed in the CPs fraction. The CPs-Cu concentrations were 8.6 times higher in oysters with high Cu concentrations compared to low concentrations. In the CPs, Cu was dispersed with a broad range of molecular weight, suggesting the involvement of various cytosolic proteins in Cu binding. Among the 10 major Cu peaks, peaks 2 (>600 kDa) and peak 8 (18 kDa) contained substantial Cu and showed obvious differences in response to the variation of CPs-Cu levels. Peak 8 contained metallothionein-like proteins that decreased their role in Cu binding as CPs-Cu concentrations increased. LC-MS/MS analysis revealed that peak 2 contained macromolecular protein complexes (MPCs), which played a critical role in binding excess Cu. The comparison with other bivalve species further suggested that sequestering excess CPs-Cu in MPCs was a special strategy employed by oysters in response to high Cu accumulation. This study provides valuable insights into the mechanism of hyper-accumulation and sequestration of Cu in oysters and helps to better understand Cu biomonitoring by oysters.

The effects of temperature on nickel bioaccumulation and toxicity in the freshwater snail Lymnaea stagnalis

It is well known that temperature can have important effects on the toxicity of metals (and other contaminants) to aquatic organisms. To date, research has mostly focused on thermal effects on acute metal toxicity, and there is a data gap on thermal effects on chronic metal toxicity to sensitive organisms that are particularly relevant to environmental risk assessment. This latter research is especially needed in the context of increased global temperature and heat waves frequency associated with climate change. We investigated temperature effects on chronic nickel (Ni) bioaccumulation and toxicity to the metal-sensitive freshwater snail Lymnaea stagnalis. In the laboratory, we conducted a series of experiments with juvenile snails that were pre-acclimated to different temperatures since their embryonic stage. We found that temperature and nickel separately had strong effects on juvenile growth rate and survival. Rising temperature from 18 to 26 °C had no noticeable effect on Ni-induced growth inhibition and Ni bioaccumulation in juvenile L. stagnalis exposed over 40 days to 0, 30 and 60 μg L-1 of dissolved Ni. These results agreed with estimates of Ni uptake and elimination rates (ku and ke), which were either unaffected by temperature or increased by similar factors from 18 to 26 °C. On the other hand, a temperature increase from 18 to 26 °C appeared to exacerbate Ni lethality to juvenile snails in the 40-day toxicity test. This exacerbation might have been due to a combination of factors, including detrimental changes in metabolically available Ni pools and/or to sensitization of the organism under sub-optimal temperatures. Overall, our study shows that thermal effects on metal chronic toxicity are complex, with effects that can be response-specific and not directly related to metal toxicokinetic.

Characterization and chemical fractionation of potentially toxic elements in soils of a pre-mining mineralized area; an evaluation of mobility and environmental risk

The environmental geochemical characterization of mineralized areas prior to mining does not receive adequate attention. This study shows trace element distribution in soils of two unexploited porphyry copper deposits located in Darreh-Zereshk and Ali-Abad in central Iran. The study was carried out using a compositional data analysis (CoDa) approach and combination of multivariate statistics and clustering techniques, which made it possible to identify the geochemical associations representing the different areas of the mineral deposits. The results of the chemical analyses, performed by ICP-MS, revealed high concentrations of those elements typically associated with porphyry deposits (As, Co, Cu, Mo, Ni, Pb, and Zn). The typical zonal pattern with an anomaly of Cu in central parts of the system and the prevalence of epithermal elements (Ag, Cd, Pb, and Zn) toward the peripheral propylitic alteration zone were recognized. The XRD analysis of selected soil samples allowed us to determine the distribution of elements within the different carrier minerals. Afterward, geochemical speciation patterns were investigated by a four-step sequential extraction procedure based on BCR protocol. The residual fraction consisting of primary resistant minerals was found to be the main host for As (73-93.4%), Cr (65.1-79.6%), Cu (54.3-81.4%), Ni (58.9-80.6%), V (75.9-88%), and Zn (56.5-60.5%) in the studied soils. Even though these elements are not readily leachable, their behavior and distribution could be largely affected by the mining operation and consequent changes in the physicochemical properties of the soil. The soluble-exchangeable phase was only less than 15% of the total extractions for all elements, except for Cd. With respect to the mobility factor (MF), Cd was the most mobile element followed by Sb and Pb. The measured risk assessment code (RAC) presented the following risk order: Cd > Sb > Ni > Co > Pb > Cr > As > Zn > Cu > V. This study reveals that the acquisition of pre-mining geo-environmental data of trace elements is very important to establish pre-mining backgrounds and baselines for evaluating post-mining or post-reclamation geochemical signatures.

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

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

Influence of the exposure concentration of dissolved cadmium on its organotropism, toxicokinetic and fate in Gammarus fossarum

Information on the relationship between the exposure concentrations of metals and their biodistribution among organs remained scarce in invertebrates. The objective of this study was to investigate the effects of Cd concentration on the organotropism, toxico-kinetic and fate of this metal in different organs of gammarids exposed to dissolved radioisotope ¹⁰⁹Cd. Gammarids male were exposed for 7 days to three environmental Cd concentrations (i.e. 4, 52 and 350 ng.L^-1) before being placed in depuration conditions (i.e. uncontaminated water). At several sampling times, Cd concentrations were determined by ¹⁰⁹Cd γ-counting in water, caeca, cephalon, gills, intestine and remaining tissues. Bioconcentration Factors (BCF) and Cd relative proportions in organs were calculated to assess the exposure concentration effect on the bioaccumulation capacities. The dependance of the organ-specific kinetic parameters to Cd water concentrations were estimated by fitting nested one-compartment toxico-kinetic (TK) models to both the accumulation and depuration data, by Bayesian inference. Then, for each Cd concentrations, the metal exchanges among organs over time were formalized by a multi-compartments TK model fitted to all organ data simultaneously. Our results highlighted that, at the end of the exposure phase, BCF and Cd relative proportions, in each organ, were not significantly modulated by water concentrations. Kinetically, Cd accumulation rates in all organs (except intestines) were depended on the exposure concentration, but not the elimination rates. The in vivo management of Cd (i.e. metal exchanges among organs) remained qualitatively unchanged according to exposure concentration. All these results also highlighted key role of that organs in the management of Cd: bioconcentration by caeca, storage by gills and main entry pathway by intestine. This study shows the interest of implementing TK approaches to test the effect of environmental factors on bioaccumulation, inter-organ exchanges and fate of contaminants in invertebrate body to enhance the understanding of the toxicity risk.

Subcellular localization and compartment-specific toxicokinetics of cadmium, arsenic, and zinc in brandling worm Eisenia fetida

Awareness of toxicokinetics at the subcellular level is crucial to deciphering the underlying intoxication processes of metal(loid)s, although this information is often lacking. Here, the toxicokinetics of two non-essential metal(loid)s (Cd and As) and one essential metal (Zn) in both the whole body and subcellular fractions of earthworm (Eisenia fetida) were assessed. Earthworms were exposed to natural soils originating from a gradient of metal(loid) pollution for 14 days followed by a 14-day elimination phase in clean soil. Clearly distinct toxicokinetic patterns were found in the earthworms according to the metal(loid) considered. An obvious concentration-dependent increase was observed in earthworms or subcellular compartments where no equilibrium was reached (with slow or no elimination) for Cd and As throughout the experiment. As for Zn, the earthworms were able to retain a steady-state concentration of Zn in its body or each fraction without a clear intake behavior via the dynamic trade-off between uptake and elimination at different pollution levels. These differences in toxicokinetics at the subcellular level supported the observed differences in bioaccumulation patterns and were indicative of the strategy by which non-essential and essential elements are handled by earthworms. Notably, the concentration of Cd and As in subcellular compartments showed the same pattern as for Zn in the order of cellular cytosol > cellular debris > metal-rich granules, which might be associated with the binding of non-essential/essential elements with metallothionein enriched in the cytosol. Our findings enhance the understanding of the underlying mechanisms for metal(loid) accumulation kinetics in earthworms from the perspective of subcellular partitioning, and will be beneficial for accurate risk assessment of Cd, As, and Zn.

Organ-specific accumulation of cadmium and zinc in Gammarus fossarum exposed to environmentally relevant metal concentrations

One of the best approaches for improving the assessment of metal toxicity in aquatic organisms is to study their organotropism (i.e., the distribution of metals among organs) through a dynamical approach (i.e., via kinetic experiments of metal bioaccumulation), to identify the tissues/organs that play a key role in metal regulation (e.g., storage or excretion). This study aims at comparing the organ-specific metal accumulation of a non-essential (Cd) and an essential metal (Zn), at their environmentally relevant exposure concentrations, in the gammarid Gammarus fossarum. Gammarids were exposed for 7 days to ¹⁰⁹Cd- or ⁶⁵Zn-radiolabeled water at a concentration of 52.1 and 416 ng.L^-1 (stable equivalent), respectively, and then placed in clean water for 21 days. At different time intervals, the target organs (i.e., caeca, cephalons, intestines, gills, and remaining tissues) were collected and ¹⁰⁹Cd or ⁶⁵Zn contents were quantified by gamma-spectrometry. A one-compartment toxicokinetic (TK) model was fitted by Bayesian inference to each organ/metal dataset in order to establish TK parameters. Our results indicate: i) a contrasting distribution pattern of concentrations at the end of the accumulation phase (7^th day): gills > caeca ≈ intestines > cephalons > remaining tissues for Cd and intestines > caeca > gills > cephalons > remaining tissues for Zn; ii) a slower elimination of Cd than of Zn by all organs, especially in the gills in which the Cd concentration remained constant during the 21-day depuration phase, whereas Zn concentrations decreased sharply in all organs after 24 h in the depuration phase; iii) a major role of intestines in the uptake of waterborne Cd and Zn at environmentally relevant concentrations.

Photosynthetic, antioxidative, and metabolic adjustments of a crop plant to elevated levels of La and Ce exposure

Rare earth elements (REEs) have been widely applied as fertilizers in farmland of China for decades to improve the yield and quality of crops. Unfortunately, adverse effects on plants have been observed due to overdosing with REEs. Until now, the toxicology of REEs was mainly evaluated based on phenotypic responses, but knowledge gaps still exist concerning their metabolic effects. Here, the physiological responses and nontargeted metabolomics studies were combined to systematically explore the potential effects of La and Ce on a crop plant, wheat Triticum aestivum. It was observed that REEs accumulated in the shoots of wheat, with significant reduction of the shoot biomass at higher exposure doses. The disturbance of photosynthesis and induced oxidative stress were identified by analyzing indicators of the photosynthetic (chlorophyll a/b, carotenoid and rubisco) and antioxidant systems (POD, CAT, SOD, GSH and MDA). Furthermore, the global metabolic profiles of REEs treatment groups and the non-exposed control group were screened and compared, and the metabolomic disturbance of REEs was dose-dependent. A high overlap of significantly changed metabolites and matched disturbed biological pathways was found between La and Ce treatments, indicating similarity of their toxicity mechanism in wheat shoots. Generally, the perturbed metabolomic pathways were mainly related to carbohydrate, amino acid and nucleotide/side metabolism, suggesting a disturbance of carbon and nitrogen metabolism, which finally affected the growth of wheat. We thus proved the potential adverse effect of inappropriate application of REEs in crop plants and postulated metabolomics as a feasible tool to identify the underlying toxicological mechanisms.

Toxicokinetics of metals in the soil invertebrate Enchytraeus crypticus exposed to field-contaminated soils from a mining area

Toxicokinetics may help assessing the risk of metal-contaminated soils by quantifying the development of internal metal concentrations in organisms over time. This study assessed the toxicokinetics in Enchytraeus crypticus of non-essential (Pb and Cd) and essential elements (Zn and Cu) in metal-contaminated field soils from a mining area, containing 3.49-24.3 mg Cd/kg dry soil, 433-1416 mg Pb/kg dry soil, 15.7-44.9 mg Cu/kg dry soil and 1718-6050 mg Zn/kg dry soil. Three different uptake-elimination patterns in E. crypticus were found. Both essential elements (Zn and Cu) showed fast increasing internal concentrations reaching equilibrium within 2 d in the uptake phase, without hardly any elimination after transfer to clean soil. The non-essential Cd showed a slow linear accumulation and excretion with body concentrations not reaching steady state within 21 d. Internal Pb concentrations, however, reached equilibrium within 7 d in the uptake phase. Longer exposure times in ecotoxicological tests, therefore, are required for elements like Cd. Porewater pH and dissolved organic carbon (DOC) levels were the dominant factors controlling Cd uptake from the test soils. The 21-d body Cd and Pb concentrations were best explained from 0.01 M CaCl₂-extractable soil concentrations. Steady-state Cu and Zn body concentrations were independent of soil exposure concentrations. Bioaccumulation factors (BAF) were low for Pb (<0.1 kg_soil/kg_worm), but high for Cd at 1.78-24.3 kg_soil/kg_worm, suggesting a potential risk of Cd biomagnification in the terrestrial food chain of the mining area ecosystem.

Subcellular metal partitioning as a novel tool in ecotoxicological elasmobranch assessments: The case of lesser numbfish (Narcine brasiliensis) affected by the Mariana dam disaster in Southeastern Brazil

This study comprises a novel report on subcellular metal partitioning and metallothionein (MT) metal detoxification efforts in lesser numbfish (Narcine brasiliensis) electric ray specimens, as well as the first assessment on MT contents in any ray electric organ. Individuals sampled from an area in Southeastern Brazil affected by the Mariana dam rupture disaster were assessed concerning subcellular metal partitioning and MT metal-detoxification in the liver, gonads, electric organ and muscle of both adults and embryos. Yolk was also assessed when available. Relative total and heat-stable (bioavailable) metal and metalloid comparisons between adults and embryos in different developmental stages demonstrates maternal transfer of both total and bioavailable metals and significant MT associations demonstrate the detoxification of As, Ag, Mn, Ni, Cd, Co, Cu, Se and V through this biochemical pathway. Our findings expand the lacking ecotoxicological assessments for this near-threatened species and indicates significant ecological concerns, warranting further biomonitoring efforts.

Weakened Cd toxicity to fungi under coexistence of Pb in solution

The coexistence of heavy metals in aquatic systems causes complex toxicity in microorganisms. In this study, we explored the influences of Pb²⁺ addition on Cd²⁺ toxicity in Rhodotorula mucilaginosa (Rho). Cd toxicity alone was tested with up to 200 mg/L Cd²⁺ to induce stress. Cell counts and Cd²⁺ removal rates declined to a minimum when the Cd²⁺ concentration reached 150 mg/L, confirming strong Cd-induced toxicity. Then, co-existence of Pb²⁺ and Cd²⁺ was established as Pb-CdH (Pb/Cd = 1, molar ratio), Pb-CdM (Pb/Cd = 10), and Pb-CdL (Pb/Cd = 100). The Pb-CdL and Pb-CdM treatments showed clear similarities in terms of their effects on cell counts, polysaccharide concentrations, and cell morphology. There was also no significant difference in their gene expression profiles. The competition between the two types of cations caused preferential extra/intracellular sorption of less toxic Pb²⁺. Moreover, the expression of genes related to glycolysis, the TCA cycle, and oxidative phosphorylation was significantly enhanced in the cells with Pb-CdH treatment, suggesting that these cells were functional. Furthermore, the excitability-caused increase in the cell count after Pb-CdH treatment (Cd²⁺ = 112.4 mg/L) was 30% higher than that of the 100 mg/L Cd²⁺ treatment. These results proved that the addition of Pb²⁺ in solution significantly weakened the toxicity of Cd²⁺.

Assessing the contamination level, sources and risk of potentially toxic elements in urban soil and dust of Iranian cities using secondary data of published literature

Research in urban geochemistry has been expanding globally in recent years, following the trend of the ever-increasing human population living in cities. Environmental problems caused by non-degradable pollutants such as metals and metalloids are of particular interest considering the potential to affect the health of current and future urban residents. In comparison with the extensive global research on urban geochemistry, Iranian cities have not received sufficient study. However, rapid and often uncontrolled urban expansion in Iran over recent years has contributed to an increasing number of studies concerning contamination of urban soil and dust. The present work is based on a comprehensive nationwide evaluation and intercomparison of published quantitative datasets to determine the contamination levels of Iranian cities with respect to potentially toxic elements (PTEs) and assess health risks for urban population. Calculation of geoaccumulation, pollution, and integrated pollution indices facilitated the identification of the elements of most concern in the cities, while both carcinogenic and non-carcinogenic risks have been assessed using a widely accepted health-risk model. The analysis of secondary, literature data revealed a trend of contamination, particularly in old and industrial cities with some alarming levels of health risks. Among the elements of concern, As, Cd, Cu, and Pb were found to be most enriched in soils and dusts of the studied cities based on the calculated geochemical indices. The necessity of designing strategic plans to mitigate possible adverse effects of elevated PTE concentrations in urban environments is emphasized considering the role of long-term exposure in the occurrence of chronic carcinogenic and non-carcinogenic health problems.

Delineation of the exposure-response causality chain of chronic copper toxicity to the zebra mussel, Dreissena polymorpha, with a TK-TD model based on concepts of biotic ligand model and subcellular metal partitioning model

A toxicokinetic-toxicodynamic model was constructed to delineate the exposure-response causality. The model could be used: to predict metal accumulation considering the influence of water chemistry and biotic ligand characteristics; to simulate the dynamics of subcellular partitioning considering metabolism, detoxification, and elimination; and to predict chronic toxicity as represented by biomarker responses from the concentration of metals in the fraction of potentially toxic metal. The model was calibrated with data generated from an experiment in which the Zebra mussel Dreissena polymorpha was exposed to Cu at nominal concentrations of 25 and 50 μg/L and with varied Na⁺ concentrations in water up to 4.0 mmol/L for 24 days. Data used in the calibration included physicochemical conditions of the exposure environment, Cu concentrations in subcellular fractions, and oxidative stress-induced responses, i.e. glutathione-S-transferase activity and lipid peroxidation. The model explained the dynamics of subcellular Cu partitioning and the effect mechanism reasonably well. With a low affinity constant for Na ⁺ binding to Cu²⁺ uptake sites, Na ⁺ had limited influence on Cu²⁺ uptake at low Na⁺ concentrations in water. Copper was taken up into the metabolically available pool (MAP) at a largely higher rate than into the cellular debris. Similar Cu concentrations were found in these two fractions at low exposure levels, which could be attributed to sequestration pathways (metabolism, detoxification, and elimination) in the MAP. However, such sequestration was inefficient as shown by similar Cu concentrations in detoxified fractions with increasing exposure level accompanied by the increasing Cu concentration in the MAP.

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

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

Metabolomics as a tool for in situ study of chronic metal exposure in estuarine invertebrates

Estuaries are subject to intense human use globally, with impacts from multiple stressors, such as metal contaminants. A key challenge is extending beyond traditional monitoring approaches to understand effects to biota and system function. To explore the metabolic effects of complex metal contaminants to sediment dwelling (benthic) fauna, we apply a multiple-lines-of-evidence approach, coupling environmental monitoring, benthic sampling, total metals analysis and targeted metabolomics. We characterise metabolic signatures of metal exposure in three benthic invertebrate taxa, which differed in distribution across sites and severity of metal exposure: sipunculid (very high), amphipod (high), maldanid polychaete (moderate). We observed sediment and tissue metal loads far exceeding sediment guidelines where toxicity-related adverse effects may be expected, for metals including, As, Cd, Pb, Zn and Hg. Change in site- and taxa-specific metabolite profiles was highly correlated with natural environmental drivers (sediment total organic carbon and water temperature). At the most metal influenced sites, metabolite variation was also correlated with sediment metal loads. Using supervised multivariate regression, taxa-specific metabolic signatures of increased exposure and possibility of toxic effects were characterised against multiple reference sites. Metabolic signatures varied according to each taxon and degree of metal exposure, but primarily indicated altered cysteine and methionine metabolism, metal-binding and elimination (lysosomal) activity, coupled to change in complex biosynthesis pathways, responses to oxidative stress, and cellular damage. This novel multiple-lines-of-evidence approach combining metabolomics with traditional environmental monitoring, enabled detection and characterisation of chronic metal exposure effects in situ in multiple invertebrate taxa. With capacity for application to rapid and effective monitoring of non-model species in complex environments, these approaches are critical for improved assessment and management of systems that are increasingly subject to anthropogenic drivers of change.

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

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

Development of a toxicokinetic-toxicodynamic model simulating chronic copper toxicity to the Zebra mussel based on subcellular fractionation

A toxicokinetic-toxicodynamic model based on subcellular metal partitioning is presented for simulating chronic toxicity of copper (Cu) from the estimated concentration in the fraction of potentially toxic metal (PTM). As such, the model allows for considering the significance of different pathways of metal sequestration in predicting metal toxicity. In the metabolically available pool (MAP), excess metals above the metabolic requirements and the detoxification and elimination capacity form the PTM fraction. The reversibly and irreversibly detoxified fractions were distinguished in the biologically detoxified compartment, while responses of organisms were related to Cu accumulation in the PTM fraction. The model was calibrated using the data on Cu concentrations in subcellular fractions and physiological responses measured by the glutathione S-transferase activity and the lipid peroxidation level during 24-day exposure of the Zebra mussel to Cu at concentrations of 25 and 50 µg/L and varying Na⁺ concentrations up to 4.0 mmol/L. The model was capable of explaining dynamics in the subcellular Cu partitioning, e.g. the trade-off between elimination and detoxification as well as the dependence of net accumulation, elimination, detoxification, and metabolism on the exposure level. Increases in the net accumulation rate in the MAP contributed to increased concentrations of Cu in this fraction. Moreover, these results are indicative of ineffective detoxification at high exposure levels and spill-over effects of detoxification.

First insight in trace element distribution in the intestinal cytosol of two freshwater fish species challenged with moderate environmental contamination

Cytosolic distribution of six essential elements and nonessential Cd among biomolecules of different molecular masses was investigated in the intestine of brown trout (Salmo trutta) from the karst Krka River and Prussian carp (Carassius gibelio) from the lowland Ilova River. Fish were sampled at two locations (reference and contaminated) and in two seasons (autumn and spring). Analyses were conducted by size exclusion high performance liquid chromatography and high resolution inductively coupled plasma mass spectrometry. Although studied salmonid and cyprinid fish have different biological characteristics, obtained profiles often showed mostly similar patterns in both species. Specifically, Cd and Cu were dominantly bound to metallothioneins in both species, but the same association was not observed for Zn, whereas Mo distribution was similar in the intestine of both fish species with two well shaped and clear peaks in HMM (100-400 kDa) and VLMM (2-8 kDa) range. In brown trout, Se was mostly associated with biomolecules of very low molecular masses (VLMM, <10 kDa), whereas significant additional elution in HMM region (30-303 kDa) was observed only in Prussian carp. Iron binding to VLMM biomolecules (1.8-14 kDa) was observed only in brown trouts, and of Zn in Prussian carps. Cobalt was mostly bound to HMM biomolecules (85-235 kDa) in brown trout and to VLMM biomolecules (0.7-18 kDa) in Prussian carp. Comparison of intestinal profiles with previously published data on liver and gills revealed some similarities in distribution, but also organ-specific differences due to the different function and composition of each organ. As so far there is no published data on intestinal trace metal distribution, the obtained results represent the novel findings, and the key point for the exact identification of specific metal-binding biomolecules which could eventually be used as biomarkers of metal exposure or effects.

Effects of waterborne cadmium exposure on Spinibarbus sinensis hepatopancreas and kidney: Mitochondrial cadmium accumulation and respiratory metabolism

To examine the relationship between heavy metal accumulation in mitochondria and their respiration function in fish during in vivo exposure, juvenile Spinibarbus sinensis were exposed to different waterborne cadmium (Cd) concentrations for up to 28 days. We measured the state III respiration rate and cytochrome c oxidase (CCO) activity of mitochondria in hepatopancreas and kidney and the accumulated Cd concentrations in mitochondria and heat-stable protein (HSP) fractions. Dose- and time-dependent Cd accumulation occurred at different levels in both organs, but was lower in hepatopancreas. When hepatopancreas mitochondrial Cd concentrations in Cd-exposed groups were > 5.5 μg/g dwt, their state III respiration rates were significantly lower than the control. CCO activity of hepatopancreas mitochondria exhibited decreasing dose- and time-dependent trends. However, kidney mitochondria respiratory activities were not affected significantly by Cd exposure. Cd concentrations in kidney HSP fraction were 2-5 times higher than in hepatopancreas under all exposure conditions, and were mainly present as non-deleterious metallothionein (MT)-Cd complexes. These results suggest that Cd accumulation occurred in hepatopancreas and kidney mitochondria of S. sinensis following waterborne Cd exposure, which significantly inhibited the respiration function of hepatopancreas mitochondria but did not have a deleterious effect on kidney mitochondria. The inhibitory pattern of hepatopancreas mitochondrial Cd concentrations related to function exhibited threshold and saturation effects, suggesting the capacity of S. sinensis to manage Cd toxicity. The difference in the relative proportion of Cd occurring as MT-Cd complexes in organs likely causes the organ-specific effects of Cd on hepatopancreas and kidney mitochondrial function.

Acute Cd Toxicity, Metal Accumulation, and Ion Loss in Southern Catfish (Silurus meridionalis Chen)

The amounts of cadmium in multiple organs and the amounts of Na⁺ and Ca²⁺ in the carcass were measured in dead and surviving southern catfish exposed to different concentrations of Cd. The 96 h median lethal concentration was 6.85 mg/L. The Cd content and Cd accumulation rate were positively correlated with Cd exposure concentrations, and there were significant differences between dead and surviving individuals, indicating that both Cd content in tissues and Cd accumulation rates were correlated with mortality. Cd levels in the liver of dead fish were saturated. A lethal threshold for Cd concentration in the whole fish was obtained. Bioconcentration factors for Cd did not decrease with increasing exposure. Acute exposure to waterborne Cd caused a significant decrease in the ion content of the fish carcass. There was a significant difference between the Na⁺ content of the carcass of dead fish (34.54 μmol/g wet weight) and surviving fish (59.34 μmol/g wet weight), which was not the case with the Ca²⁺ content, indicating that the lethal toxicity of Cd was probably related to the decrease in Na⁺ content. Collectively, these results suggest that whole-fish Cd concentration and carcass Na⁺ content can be useful indicators of fish acutely exposed to Cd.

Kinetic mechanisms by which nickel alters the calcium (Ca2+) transport in intact rat liver

In the present work, the multiple-indicator dilution (MID) technique was used to investigate the kinetic mechanisms by which nickel (Ni²⁺) affects the calcium (Ca²⁺) transport in intact rat liver. ⁴⁵Ca²⁺ and extra- and intracellular space indicators were injected in livers perfused with 1 mM Ni²⁺, and the outflow profiles were analyzed by a mathematical model. For comparative purposes, the effects of norepinephrine were measured. The influence of Ni²⁺ on the cytosolic Ca²⁺ concentration ([Ca²⁺]_c) in human hepatoma Huh7 cells and on liver glycogen catabolism, a biological response sensitive to cellular Ca²⁺, was also evaluated. The estimated transfer coefficients of ⁴⁵Ca²⁺ transport indicated two mechanisms by which Ni²⁺ increases the [Ca²⁺]_c in liver under steady-state conditions: (1) an increase in the net efflux of Ca²⁺ from intracellular Ca²⁺ stores due to a stimulus of Ca²⁺ efflux to the cytosolic space along with a diminution of Ca²⁺ re-entry into the cellular Ca²⁺ stores; (2) a decrease in Ca²⁺ efflux from the cytosolic space to vascular space, minimizing Ca²⁺ loss. Glycogen catabolism activated by Ni²⁺ was transient contrasting with the sustained activation induced by norepinephrine. Ni²⁺ caused a partial reduction in the norepinephrine-induced stimulation in the [Ca²⁺]_c in Huh7 cells. Our data revealed that the kinetic parameters of Ca²⁺ transport modified by Ni²⁺ in intact liver are similar to those modified by norepinephrine in its first minutes of action, but the membrane receptors or Ca²⁺ transporters affected by Ni²⁺ seem to be distinct from those known to be modulated by norepinephrine.

The transfer of trace metals in the soil-plant-arthropod system

Essential and non-essential trace metals are capable of causing toxicity to organisms above a threshold concentration. Extensive research has assessed the behaviour of trace metals in biological and ecological systems, but has typically focused on single organisms within a trophic level and not on multi-trophic transfer through terrestrial food chains. This reinforces the notion of metal toxicity as a closed system, failing to consider one trophic level as a pollution source to another; therefore, obscuring the full extent of ecosystem effects. Given the relatively few studies on trophic transfer of metals, this review has taken a compartment-based approach, where transfer of metals through trophic pathways is considered as a series of linked compartments (soil-plant-arthropod herbivore-arthropod predator). In particular, we consider the mechanisms by which trace metals are taken up by organisms, the forms and transformations that can occur within the organism and the consequences for trace metal availability to the next trophic level. The review focuses on four of the most prevalent metal cations in soil which are labile in terrestrial food chains: Cd, Cu, Zn and Ni. Current knowledge of the processes and mechanisms by which these metals are transformed and moved within and between trophic levels in the soil-plant-arthropod system are evaluated. We demonstrate that the key factors controlling the transfer of trace metals through the soil-plant-arthropod system are the form and location in which the metal occurs in the lower trophic level and the physiological mechanisms of each organism in regulating uptake, transformation, detoxification and transfer. The magnitude of transfer varies considerably depending on the trace metal concerned, as does its toxicity, and we conclude that biomagnification is not a general property of plant-arthropod and arthropod-arthropod systems. To deliver a more holistic assessment of ecosystem toxicity, integrated studies across ecosystem compartments are needed to identify critical pathways that can result in secondary toxicity across terrestrial food-chains.

Selenium toxicity, bioaccumulation, and distribution in earthworms (Eisenia fetida) exposed to different substrates

Selenium (Se) is an essential microelement for human or animal health. At high concentrations, it can cause Se poisoning. Human activities (such as coal burning and mining) threaten soil biota by mobilizing high levels of Se. We used the earthworm Eisenia fetida as a bio-indicator of environmental pollutants to investigate Se acute toxicity, enrichment, and distribution through exposure tests using filter paper, artificial soil and cow manure. The 24 h- and 48 h-LC₅₀ for the filter paper contact test were 2.7 and 1.52 μg/cm². In artificial soil test, the 14 d-LC₅₀ and 14 d-biomass inhibition concentration (IC₂₀) were 63.86 and 59.81 mg/kg, respectively. The cow manure resulted in a 2.2- and 2.6-fold higher LC₅₀ and IC₂₀ than artificial soil results, respectively. Earthworms accumulated the largest Se load (89.47 mg/kg) in artificial soil containing 80 mg Se/kg and only accumulated 90.3 mg/kg in cow manure containing 160 mg Se/kg; 46.6-60.59% of the total Se was distributed in the tail of E. fetida. The Se enrichment rate (SER_Se) and bioaccumulation factor (BAF_Se) scored higher in artificial soil than in cow manure with the same Se concentration exposure, and the highest SER_Se was 6.21 and 6.31 mg Se/kg earthworm/d, respectively. The highest BAF_Se was 1.49 in artificial soil and 0.75 in cow manure. Our results demonstrate that selenite is more toxic to earthworms living in artificial soil than in cow manure. E. fetida possesses certain Se detoxification mechanisms by distributing Se in the tail.

Soil invertebrate toxicity and bioaccumulation of nano copper oxide and copper sulphate in soils, with and without biosolids amendment

The fate, toxicity and bioaccumulation of copper oxide nanoparticles (nCuO) was investigated in soil, with and without biosolids amendment, through chronic exposures using the earthworm, Eisenia andrei, and the collembolan, Folsomia candida. The effects of copper sulphate (CuSO₄) were included so as to compare the behavior of nCuO to a readily soluble counterpart. The fate of nCuO was evaluated through characterization of dissolved and nano-particulate fractions (via single particle ICP-MS) as well as extractable Cu²⁺ throughout the duration of select tests. Neither Cu form was particularly toxic to F. candida, but effects on E. andrei reproduction were significant in all treatments (IC50 range: 98 - 149 mg Cu kg^-1 dry soil). There were no significant differences in toxicity between the Cu forms, nor in extractable Cu²⁺ activities, indicative that particle dissolution within the soil and, subsequent activity of Cu²⁺ was likely the primary mode of toxicity in the nCuO exposures. The presence of biosolids did not significantly alter toxicity of nCuO, but did affect Cu²⁺ activity over time. Bioaccumulation of total Cu in E. andrei when exposed to nCuO (kinetic bioaccumulation factor (BAF_k): 0.80 with biosolids and 0.81 without) was lower than exposure to CuSO₄ (BAF_k: 2.31 with biosolids and 1.12 without). Enhanced dark-field hyperspectral imaging showed accumulation of nCuO along the epidermis and gut of E. andrei, with trace amounts observed in muscle and chloragogenous tissue, providing evidence of nCuO translocation within the organism. The present study demonstrates that the current risk assessment approach for trace metals in the environment, based on substance solubility and bioavailability of the dissolved free ion, are applicable for nCuO exposure to soil invertebrates, but that the rate of particle dissolution in different soil environments is an important factor for consideration.

Ecotoxicological assessment of Uruguay River and affluents pre- and post-pesticides' application using Caenorhabditis elegans for biomonitoring

Uruguay River is the most important river in western Rio Grande do Sul, separating Brazil from Argentina and Uruguay. However, its pollution is of great concern due to agricultural activities in the region and the extensive use of pesticides. In a long term, this practice leads to environmental pollution, especially to the aquatic system. The objective of this study was to analyze the physicochemical characteristics, metals and pesticides levels in water samples obtained before and after the planting and pesticides' application season from three sites: Uruguay River and two minor affluents, Mezomo Dam and Salso Stream. For biomonitoring, the free-living nematode Caenorhabditis elegans was used, which were exposed for 24 h. We did not find any significant alteration in physicochemical parameters. In the pre- and post-pesticides' samples we observed a residual presence of three pesticides (tebuconazole, imazethapyr, and clomazone) and metals which levels were above the recommended (As, Hg, Fe, and Mn). Exposure to both pre- and post-pesticides' samples impaired C. elegans reproduction and post-pesticides samples reduced worms' survival rate and lifespan. PCA analysis indicated that the presence of metals and pesticides are important variables that impacted C. elegans biological endpoints. Our data demonstrates that Uruguay River and two affluents are contaminated independent whether before or after pesticides' application season. In addition, it reinforces the usefulness of biological indicators, since simple physicochemical analyses are not sufficient to attest water quality and ecological safety.

Medium-term effects of Ag supplied directly or via sewage sludge to an agricultural soil on Eisenia fetida earthworm and soil microbial communities

The widespread use of silver nanoparticles (AgNPs) in consumer products that release Ag throughout their life cycle has raised potential environmental concerns. AgNPs primarily accumulate in soil through the spreading of sewage sludge (SS). In this study, the effects of direct exposure to AgNPs or indirect exposure via SS contaminated with AgNPs on the earthworm Eisenia fetida and soil microbial communities were compared, through 3 scenarios offering increasing exposure concentrations. The effects of Ag speciation were analyzed by spiking SS with AgNPs or AgNO₃ before application to soil. SS treatment strongly impacted Ag speciation due to the formation of Ag₂S species that remained sulfided after mixing in the soil. The life traits and expression of lysenin, superoxide dismutase, cd-metallothionein genes in earthworms were not impacted by Ag after 5 weeks of exposure, but direct exposure to Ag without SS led to bioaccumulation of Ag, suggesting transfer in the food chain. Ag exposure led to a decrease in potential carbon respiration only when directly added to the soil. The addition of SS had a greater effect on soil microbial diversity than the form of Ag, and the formation of Ag sulfides in SS reduced the impact of AgNPs on E. fetida and soil microorganisms compared with direct addition.

Effect of aluminum stress on the quality of Enteromorpha prolifera based on SEM-EDX and FT-IR

To clarify the effect of aluminum stress on the quality of Enteromorpha prolifera (E. prolifera) and to explore the mechanism of the combination of aluminum and E. prolifera, we analyzed changes in the nutrients, micromorphology, element distribution, and spectrum of E. prolifera treated with different concentrations of aluminum (0, 0.2, 2.0, and 20.0 μmol·L–1) using scanning electron microscopy-energy dispersive spectroscopy (SEM-EDX) and Fourier-transform infrared spectroscopy (FT-IR). The biomass, protein, dietary fiber, and ash contents of E. prolifera initially increased and then subsequently decreased with an increasing concentration of aluminum. Meanwhile, the total amount of amino acids decreased. Scanning the surface of E. prolifera by SEM-EDX revealed that a high concentration of aluminum damaged the cells of E. prolifera. Additionally, the content of aluminum on the surface of E. prolifera cells increased and the absorption of other elements was also affected. The FT-IR analysis showed that aluminum might combine with the functional groups at the 3408 cm–1, 2928 cm–1, and 1072 cm–1 peaks in E. prolifera and alter the characteristic of the different absorption peaks.

"Nanosize effect" in the metal-handling strategy of the bivalve Scrobicularia plana exposed to CuO nanoparticles and copper ions in whole-sediment toxicity tests

To date, the occurrence, fate and toxicity of metal-based NPs in the environment is under investigated. Their unique physicochemical, biological and optical properties, responsible for their advantageous application, make them intrinsically different from their bulk counterpart, raising the issue of their potential toxic specificity or "nanosize effect". The aim of this study was to investigate copper bioaccumulation, subcellular distribution and toxic effect in the marine benthic species Scrobicularia plana exposed to two forms of sediment-associated copper, as nanoparticles (CuO NPs) and as soluble ions (CuCl₂). Results showed that the exposure to different copper forms activated specific organism's metal handling strategies. Clams bioaccumulated soluble copper at higher concentrations than those exposed to sediment spiked with CuO NPs. Moreover, CuO NPs exposure elicited a stronger detoxification response mediated by a prompt mobilization of CuO NPs to metal-containing granules as well as a delayed induction of MT-like proteins, which conversely, sequestered soluble copper since the beginning of the exposure at levels significantly different from the control. Eventually, exposure to high concentrations of either copper form led to the same acute toxic effect (100% mortality) but the outcome was delayed in bivalves exposed to CuO NPs suggesting that the mechanisms underlying toxicity were copper form-specific. Indeed, while most of soluble copper was associated to the mitochondrial fraction suggesting an impairment of the ATP synthesis capacity at mitochondrial level, CuO NPs toxicity was most likely caused by the oxidative stress mediated by their bioaccumulation in the enzymatic and mitochondrial metabolically available fractions.

Rhizospheric pore-water content predicts the biochar-attenuated accumulation, translocation, and toxicity of cadmium to lettuce

Metal bioavailability controls its behaviors in soil-plant system, especially involved in biochar amendment. This study compared a rhizospheric pore-water extraction against a BCR sequential extraction method to understand cadmium (Cd) bioavailability in two typical Chinese soils. Soils were spiked with five levels of Cd (CdCl2) and remediated with 3% corn-straw derived biochar. After 60 days of lettuce growth, Cd accumulation and enzyme activities in tissues were analyzed. Results showed that biochar increased soil properties (pH, CEC and SOM) compared to un-amended soils, but decreased contents of bioavailable Cd in soil pore-water (Cdpore-water) and BCR extracted Cd (CdFi+Fii). Contents of Cdpore-water were lower in yellow-brown soils than that in red soils. Pearson analysis showed that bioavailable Cd is negatively correlated with soil pH and CEC (p < 0.05). Cd accumulation in lettuce roots and leaves both were decreased by biochar addition, and the established linear equations proved that soil Cdpore-water is the best predictor for Cd accumulation in lettuce roots (r2 = 0.964) and in leaves (r2 = 0.953), followed by CdFi+Fii. Transfer factor (TF) values of Cd from roots to leaves were lower than 1, and slightly better correlated with soil Cdpore-water (r = -0.674, p < 0.01) than CdFi+Fii (r = -0.615, p < 0.01). Aggregated boosted tree (ABT) analyses indicated that soil properties together with Cdpore-water contribute more than 50% to root enzyme activities. Collectively, soil Cdpore-water is a promising predictor of Cd bioavailability, accumulation and toxicity in soil-plant system with biochar addition.

Accumulation, speciation and localization of silver nanoparticles in the earthworm Eisenia fetida

The use of silver nanoparticles (AgNPs) in agriculture and many consumer products has led to a significant release of Ag in the environment. Although Ag toxicity in terrestrial organisms has been studied extensively, very little is known about the accumulation capacity and coping mechanisms of organisms in Ag-contaminated soil. In this context, we exposed Eisenia fetida earthworms to artificial OECD soil spiked with a range of concentrations of Ag (AgNPs or AgNO₃). The main aims were to (1) identify the location and form of accumulation of Ag in the exposed earthworms and (2) better understand the physiological mechanisms involved in Ag detoxification. The results showed that similar doses of AgNPs or AgNO₃ did not have the same effect on E. fetida survival. The two forms of Ag added to soil exhibited substantial differences in speciation at the end of exposure, but the Ag speciation and content of Ag in earthworms were similar, suggesting that biotransformation of Ag occurred. Finally, 3D images of intact earthworms obtained by X-ray micro-computed tomography revealed that Ag accumulated preferentially in the chloragogen tissue, coelomocytes, and nephridial epithelium. Thus, E. fetida bioaccumulates Ag, but a regulation mechanism limits its impact in a very efficient manner. The location of Ag in the organism, the competition between Ag and Cu, and the speciation of internal Ag suggest a link between Ag and the thiol-rich proteins that are widely present in these tissues, most probably metallothioneins, which are key proteins in the sequestration and detoxification of metals.

Bioremediation potential of Cd by transgenic yeast expressing a metallothionein gene from Populus trichocarpa

Cadmium (Cd) is an extremely toxic environmental pollutant with high mobility in soils, which can contaminate groundwater, increasing its risk of entering the food chain. Yeast biosorption can be a low-cost and effective method for removing Cd from contaminated aqueous solutions. We transformed wild-type Saccharomyces cerevisiae (WT) with two versions of a Populus trichocarpa gene (PtMT2b) coding for a metallothionein: one with the original sequence (PtMT2b 'C') and the other with a mutated sequence, with an amino acid substitution (C3Y, named here: PtMT2b 'Y'). WT and both transformed yeasts were grown under Cd stress, in agar (0; 10; 20; 50 μM Cd) and liquid medium (0; 10; 20 μM Cd). Yeast growth was assessed visually and by spectrometry OD₆₀₀. Cd removal from contaminated media and intracellular accumulation were also quantified. PtMT2b 'Y' was also inserted into mutant strains: fet3fet4, zrt1zrt2 and smf1, and grown under Fe-, Zn- and Mn-deficient media, respectively. Yeast strains had similar growth under 0 μM, but differed under 20 μM Cd, the order of tolerance was: WT < PtMT2b 'C' < PtMT2b 'Y', the latter presenting 37% higher growth than the strain with PtMT2b 'C'. It also extracted ~80% of the Cd in solution, and had higher intracellular Cd than WT. Mutant yeasts carrying PtMT2b 'Y' had slightly higher growth in Mn- and Fe-deficient media than their non-transgenic counterparts, suggesting the transgenic protein may chelate these metals. S. cerevisiae carrying the altered poplar gene offers potential for bioremediation of Cd from wastewaters or other contaminated liquids.

Aluminium accumulation in excess and related anti-oxidation responses in C4 weed (Amaranthus viridis L.)

C₄ species, Amaranthus viridis L. exhibited a significant bioaccumulation of aluminium (Al) through the duration of 3- and 5-days exposure. As compared to control, Amaranthus appeared as excess-accumulator with maximum 5.85-fold bioaccumulation of Al in root. Cellular responses to Al tolerance initially scored tissue specific distribution of metal through cortical layers revealed by electron microscopy. The affected cells changed an oxidative status as read by histochemical stains, particularly, for hydrogen peroxide. Osmotic stress and its stability were scored by maximum proline and free amino acids accumulation with 1.53 and 1.59-fold increase over control. The accumulation of phenolics and flavonoids were over expressed in the ranges of 2.48-2.50-fold and 2.00-1.5-fold at 3- and 5-days respectively against control. Anti-oxidation to detoxify Al stress was facilitated by variants of peroxidases. For exclusion mechanism of metal, esterase activity significantly over expressed with maximum value of 1.80-fold at 5-days. The polymorphism of esterase exhibited few significant over produced bands, varied in numbers as detected by densitometric scanning. Moreover, plant extract was satisfactorily potential under in vitro anti-oxidation systems through assay of 1,1-diphenyl-2-picrylhydrazyl (DPPH), 2,2'-azino-bis-3-ethylbenzthiazoline-6-sulphonic acid (ABTS), ferric chelation activity etc. Therefore, weeds like Amaranthus would be a bioprospecting in role likely involved in phytoremediation of metal.

Breaking down insect stoichiometry into chitin-based and internal elemental traits: Patterns and correlates of continent-wide intraspecific variation in the largest European saproxylic beetle

Stoichiometric, trophic and ecotoxicological data have traditionally been acquired from patterns of variation in elemental traits of whole invertebrate bodies, whereas the critical issue of the extracellular origin of some portion of elements, such as those present in ingested food and internal organs, has been ignored. Here we investigated an unexplored, yet crucial, question relating to whether, and to what degree, metals from two major body fractions: exoskeleton (elytra) and internal (body organs with gut material present in abdomens), are correlated with each other in wild populations of the largest European saproxylic insect, the Stag Beetle Lucanus cervus, and how metals from these two fractions vary with insect size and local habitat conditions. We examined the continent-wide variation in the concentrations of 12 chemical elements (Ca, Mg, K, Na, Mn, Fe, Zn, Cu, As, Cd, Pb and Ni) measured in the elytra and abdomen of specimens from 28 populations inhabiting an urban-woodland habitat gradient across the species' entire distributional range from Spain to Russia. Across populations, elemental concentrations (except Ni and Pb) were 2-13 times higher in abdominal samples than in elytra, and the magnitude of these differences was related to both insect size and local habitat conditions. Smaller individuals from both woodland and urban habitat tended to have higher concentrations of trace elements (Zn, As, Cd, Pb and Ni). The concentration of only six elements (Mg, K, Na, Mn, Cd and Ni) was correlated in the elytra and abdomen at the individual and population levels, implying a limitation to the broader applicability of elytra as a surrogate for internal elemental pools. We highlight that in non-feeding adult saproxylic beetles, minerals, acquired during the larval stage, may be concentrated in the large quantities of residual body fat.

Trophic transfer and biotransformation of selenium in the mosquito (Aedes albopictus) and interactive effects with hexavalent chromium

As an essential micronutrient for animals with a narrow range between essentiality and toxicity, selenium (Se) usually coexists with chromium (Cr) in contaminated aquatic environments. This study investigated effects of three diets (Microcystis aeruginosa, Chlorella vulgaris and biofilms) exposed to Se or/and Cr on Aedes albopictus as a vector for the aquatic-terrestrial transfer of Se and Cr. Se(IV)-exposed mosquitoes concentrated Se up to 66-fold faster than Se(VI)-exposed ones, corresponding to the greater Se enrichment in Se(IV)-treated diets. Analysis using synchrotron-based X-ray absorption spectroscopy (XAS) showed that Se(0) (61.9-74.6%) dominated Se(VI)-exposed mosquitoes except for the C. vulgaris-fed larvae (organo-Se, 94.0%), while organo-Se accounted for 93.3-100.0% in Se(IV)-exposed mosquitoes. Cr accumulation in larvae (56.40-87.24 μg Cr/g DW) or adults (19.41-50.77 μg Cr/g DW) was not significantly different among all Cr(VI) treatments, despite varying diet Cr levels. With Cr(0) being dominant (57.7-94.0%), Cr(VI)-exposed mosquitoes posed little threat to predators. Although mosquitoes exposed to Se or Cr had shorter wings, adults supplied with C. vulgaris or biofilms co-exposed to Se(VI) and Cr(VI) had wings significantly (1.1-1.2 fold) longer than Se(VI) only exposed ones. Overall, our study reveals the role of Ae. albopictus in transferring waterborne Se and Cr from the contaminated aquatic ecosystem to the terrestrial ecosystem with the resulting eco-risks to wildlife in both ecosystems.

Do toxicokinetic and toxicodynamic processes hold the same for light and heavy rare earth elements in terrestrial organism Enchytraeus crypticus?

The widespread use of rare earth elements (REEs) in numerous sectors have resulted in their release into the environment. Existing knowledge about the effects of REEs were acquired mainly based on toxicity tests with aquatic organisms and a fixed exposure time, Here, the dynamic accumulation and toxicity of REEs (La, Ce, and Gd) in soil organism Enchytraeus crypticus were determined and modeled by a first-order one-compartment model and a time-toxicity logistic model, respectively. Generally, the accumulation and toxicity of REEs were both exposure level- and time-dependent. The overall uptake rate constants were 2.97, 2.48, and 2.38 L kg^-1d^-1 for La, Ce, and Gd, respectively. The corresponding elimination rate constants were 0.99, 0.78, and 0.56 d^-1, respectively. The worms exhibited faster uptake and elimination ability for light REEs (La and Ce) than for heavy REEs (Gd). For all three REEs, the LC50 values based on exposure concentrations decreased with time and reached ultimate values after approximately 10 d exposure. The estimated ultimate LC50 values (LC50∞) were 279, 334, and 358 mg L^-1 for Ce, Gd, and La, respectively. When expressed as body concentration, the LC50_inter value was almost constant with time, demonstrating that internal body concentration could be a better indicator of dynamic toxicity of REEs than external dose. This study highlights that specific REE and exposure time should be taken into account in accurately assessing risk of REEs.

Impacts of metallic trace elements on an earthworm community in an urban wasteland: Emphasis on the bioaccumulation and genetic characteristics in Lumbricus castaneus

Metallic trace elements (MTEs) soil pollution has become a worldwide concern, particularly regarding its impact on earthworms. Earthworms, which constitute the dominant taxon of soil macrofauna in temperate regions and are crucial ecosystem engineers, are in direct contact with MTEs. The impacts of MTE exposure on earthworms, however, vary by species, with some able to cope with high levels of contamination. We combined different approaches to study the effects of MTEs at different levels of biological organisation of an earthworm community, in a contaminated urban wasteland. Our work is based on field collection of soil and earthworm samples, with a total of 891 adult earthworms from 8 species collected, over 87 quadrats across the study plot. We found that MTE concentrations are highly structured at the plot scale and that some elements, such as Pb, Zn, and Cu, are highly correlated. Comparing species assemblage to MTE concentrations, we found that the juvenile and adult abundances, and community composition, were significantly affected by pollution. Along the pollution gradient, as species richness decreased, Lumbricus castaneus became more dominant. We thus investigated the physiological response of this species to a set of specific elements (Pb, Zn, Cu, and Cd) and studied the impacts of MTE concentrations at the plot scale on its population genetic. These analyses revealed that L. castaneus is able to bioaccumulate high quantities of Cd and Zn, but not of Cu and Pb. The population genetic analysis, based on the genotyping of 175 individuals using 8 microsatellite markers, provided no evidence of the role of the heterogeneity in MTE concentrations as a barrier to gene flow. The multidisciplinary approach we used enabled us to reveal the comparatively high tolerance of L. castaneus to MTE concentrations, suggesting that this is a promising model to study the molecular bases of MTE tolerance.

Panagrolaimus superbus tolerates hypoxia within Gallium metal cage: implications for the understanding of the phenomenon of anhydrobiosis

Panagrolaimus superbus nematodes are able to tolerate desiccation by entering into a peculiar state of suspended animation known as anhydrobiosis. When desiccated, anhydrobiotic organisms are also able to tolerate other physical stresses, as high and low levels of temperature and pressure. Here, we decided to investigate the tolerance of desiccated P. superbus to an unprecedented double stress - hypoxia within 99.99% Gallium (Ga) metal cage. The authors observed that regardless of the external relative humidity, desiccated P. superbus tolerated 7 d confined within the metal cage, displaying no negative effects on its survival and population growth rates over 40 d. The results evidence that anhydrobiosis also renders nematodes tolerant to otherwise lethal concentrations of Ga, in an oxygen-poor environment; thus, expanding its polyextremotolerance profile.

Panagrolaimus superbus nematodes are able to tolerate desiccation by entering into a peculiar state of suspended animation known as anhydrobiosis. When desiccated, anhydrobiotic organisms are also able to tolerate other physical stresses, as high and low levels of temperature and pressure. Here, we decided to investigate the tolerance of desiccated P. superbus to an unprecedented double stress – hypoxia within 99.99% Gallium (Ga) metal cage. The authors observed that regardless of the external relative humidity, desiccated P. superbus tolerated 7 d confined within the metal cage, displaying no negative effects on its survival and population growth rates over 40 d. The results evidence that anhydrobiosis also renders nematodes tolerant to otherwise lethal concentrations of Ga, in an oxygen-poor environment; thus, expanding its polyextremotolerance profile.

Comparative assessment of biomarker response to tissue metal concentrations in urban populations of the land snail Helix pomatia (Pulmonata: Helicidae)

The traffic pressure is increasing, resulting in the emission of atmospheric pollution. Soil organisms will need to respond to pollution stressors. Among them, land snails are valuable indicators of ecosystem disturbance. In this study, land snails Helix pomatia were sampled from three city localities with different traffic intensity. Oxidative stress biomarkers catalase (CAT), glutathione peroxidase (GPX), glutathione reductase (GR) and glutathione-S-transferase (GST) in the foot muscle (FM) and hepatopancreas (HP) tissue were determined. Also, five heavy metal (Cd, Cu, Ni, Pb, and Zn) concentrations were quantified in soil and tissue samples. According to the results, the highway induces the strongest contamination on the surrounding environment, with the highest metal concentrations measured in soil and snails. At the most polluted locality, only Cd exceeded some soil guidelines authorities that we referred to in this study. In addition, tissue Cd concentrations exceeded the United States Environmental Protection Agency (USEPA) value (1 mg kg^-1) for soil invertebrate toxicity at all localities making it likely responsible for generating adverse effects in snails. Regarding HP, the CAT and GST are the most sensitive parameters that could be useful as oxidative stress biomarkers in snails exposed to the actual metals in the environment. On the other hand, in FM tissue, the most pronounced changes were recorded for GPX and GR. Based on tissue-specific enzyme responses, three urban populations were clearly separated. Therefore land snails are the promising candidates for quick field-based biomarker studies after showing a tissue-specific concentration-dependent induction of certain enzymes to heavy metals.

Subcellular partitioning of cadmium and lead in Eisenia fetida and their effects to sperm count, morphology and apoptosis

Earthworms and their biomarkers are considered good indicators for assessing the effects of toxic chemicals. Therefore, in this study, we exposed Eisenia fetida to lethal and sub-lethal concentrations of Cd and Pb nitrate in artificial soil for 14 and 28 days to evaluate the impact on subcellular partitioning, lethal toxicity (LC₅₀), growth, sperm count, morphology and apoptosis (using TUNEL assay). The soluble internal pools of both metals were good predictors of the responses of biomarkers. We found sperm deformation, TUNEL positive sperms and weight loss positively and sperm count negatively correlated with the concentrations of Cd and Pb in the total internal and cytosolic fraction (p < 0.01) and to a lesser extent with Pb concentrations in the granular fraction (p < 0.05). Fourteen days LC₅₀ for Cd and Pb were 2169 ± 322 and 6387 ± 904 μg/g, respectively. Cadmium and Pb caused a significant depression in sperm count after 14 (Cd: up to 46.9%; Pb: up to 36.24%) and 28 (Cd: up to 72.47%; Pb: up to 43.12%) days of exposure relative to the control (p < 0.05). Cadmium induced higher abnormality in sperm heads than Pb. For both metals, TUNEL positive sperms significantly increased after 14 (Cd: up to 14.17%; Pb: up to 16.33%) and 28 (Cd: up to 16.33%; Pb: up to 11.67%) days of exposure compared with the control (p < 0.05). The findings of this study, illustrate the importance of considering sperm parameters as a rapid, easy and sensitive biomarker for the evaluation of metal toxicity.

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

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

Strategies for cadmium detoxification in the white shrimp Palaemon argentinus from clean and polluted field locations

In this study, we investigated the metal handling capacity of non-tolerant and tolerant populations of Palaemon argentinus to cadmium (Cd), through evaluating of the main mechanisms of metal detoxification, metallothioneins (MT) and metal-rich granules (MRG), to probe that the presence of MRG in the second population is responsible of that condition. The tolerant population were exposed to 3.06 and 12.26 μg Cd·L^-1, while the non-tolerant shrimp were exposed to 3.06 μg Cd·L^-1. Each experiment involved the exposure during 3, 7, 10 and 15 days and, the depuration during 7, 14, 21 and 28 days, for which shrimp were transferred to clean water. The range values of MT concentrations for non-tolerant shrimp were: 12.24-23.91 μg g (w.w), while for tolerant shrimp were: 8.75-16.85 μg g (w.w); MRG levels were: 0.12-0.57 μg g (w.w) and 0.3-2.1 μg g (w.w), respectively. The results showed different strategies for Cd detoxification: the induction of MT was the main pathway in the non-tolerant population, while the formation of Cd-MRG was the main mechanism for tolerant shrimp. These differences could be related to the environmental history and the health status of each populations.

Inter-species difference of copper accumulation in three species of marine mussels: Implication for biomonitoring

Marine mussels have been used widely as biomonitors of coastal contamination in many countries. Due to the restrain of their geographical distributions, it is often necessary to employ more than one species of mussels within a large-scale biomonitoring program. In the present study, we compared the differences of copper (Cu) bioaccumulation in three species of marine mussels (green mussel Perna viridis, blue mussel Mytilus edulis, and hard-shelled mussel Mytilus coruscus) widely distributing along the Chinese coastal waters, under identical Cu exposure conditions. Over the 21-days exposure to dissolved Cu, the green mussels and blue mussels exhibited comparable newly accumulated Cu concentrations, possibly due to their comparable Cu uptake rate constant k_u (blue mussel, 0.573 L g^-1 d^-1; green mussel, 0.530 L g^-1 d^-1) and efflux rate constant k_e (blue mussel, 0.053 d^-1; green mussel, 0.065 d^-1). In contrast, there was no net Cu accumulation in the hard-shell mussels, which may be accounted by the lower k_u (0.394 L g^-1 d^-1) but higher k_e (0.081 d^-1) than the other two mussel species. Further subcellular distribution analyses showed that the cellular debris and metallothionein-like protein (MTLP) fraction were the key binding sites for Cu, and the MTLP fraction may act as a main contributor in Cu regulation and elimination in the blue mussels and hard-shell mussels. There was no strong evidence that the subcellular partitioning and dynamics of Cu in the mussels were responsible for the difference underlying the Cu accumulation in the three species of mussels. Our comparative study thereby suggested that it may be feasible to directly compare the Cu bioavailability in the green mussels and blue mussels based on their Cu biomonitoring data. Cu biomonitoring data from the hard-shell mussels may underestimate the actual Cu bioavailability of the sampling area given its much stronger regulation of Cu bioaccumulation as compared to the other two mussel species.