Kinetics of cadmium uptake and subcellular partitioning in the earthworm Eisenia fetida exposed to cadmium-contaminated soil

Combined effects of cadmium and sulfamethoxazole on Eisenia fetida: Insights into accumulation, subcellular partitioning, biomarkers and toxicological responses

Cadmium (Cd) and sulfamethoxazole (SMX) frequently coexist in farmlands, yet their synergistic toxicological impacts on terrestrial invertebrates remain unexplored. In this study, earthworms were exposed to artificial soils percolated with Cd (5 mg/kg), SMX (5 mg/kg) or combination of them for 7 days, followed by a 12-day elimination phase in uncontaminated soil. The uptake of Cd and SMX by the earthworms, along with their subcellular distribution, was meticulously analyzed. Additionally, a suite of biomarkers-including superoxide dismutase (SOD), catalase (CAT), malondialdehyde (MDA), and weight loss-were evaluated to assess the health status of the earthworms and the toxicological effects of the Cd and SMX mixture. Notably, the cotreatment with Cd and SMX resulted in a significantly higher weight loss in Eisenia fetida (41.25 %) compared to exposure to Cd alone (26.84 %). Moreover, the cotreatment group exhibited substantially higher concentrations of Cd in the total internal body, fraction C (cytosol), and fraction E (tissue fragments and cell membranes) in Eisenia fetida compared to Cd alone counterparts. The combined exposure also significantly elevated the SMX levels in the total body and fraction C compared with the SMX-only treated earthworms. Additionally, Eisenia fetida subjected to the combined treatment showed markedly increased activities of SOD, CAT, and MDA compared to those treated with Cd alone. The effect addition indices (EAIs), ranging from 1.00 to 2.23, unequivocally demonstrated a synergistic effect of the combined treatments. Interestingly, relocating the earthworms to clean soil did not mitigate the observed adverse effects. These findings underscore the increased risk posed by the Cd-SMX complex to terrestrial invertebrates in agricultural areas.

A refined toxicokinetic model for quantifying the interaction between Cd and Cu in zebrafish larvae

The interaction between metals is ubiquitous, but there is still a lack of quantitative models considering the interaction between metals, which leads to the deviations in predicting the joint toxicity of metals. The present study estimated the uptake rate constants (kin) and elimination rate constants (kout) and elucidated how the presence of one metal (Cu or Cd) affects the absorption and excretion of another metal (Cd or Cu) in zebrafish larvae. The results showed that Cd and Cu inhibited each other in the process of absorption and excretion by comparing separately kin and kout of Cd or Cu with the other metal Cu or Cd mixed concentrations increased, thereby affecting the Cd and Cu bioaccumulation in the zebrafish larvae. Then the interactions between Cd and Cu in the uptake and elimination processes were quantified to obtain a refined toxicokinetic model. Verification with independent experiment data showed that the refined toxicokinetic model could significantly improve the prediction of the Cd or Cu bioaccumulation in the zebrafish larvae. This study contributes to understand the toxicokinetic process of the Cd-Cu mixture in the zebrafish larvae, and the developed model could be used to predict the toxicity of the metal mixtures.

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.

From speciation to toxicity: Using a "Two-in-One" whole-cell bioreporter approach to assess harmful effects of Cd and Pb

Due to the sheer number of contaminated sites, bioavailability-based measurement and modeling of toxicity is used to triage response; despite advances, both remain relatively cumbersome. Cadmium (Cd) and lead (Pb) are two of the most toxic and globally prevalent pollutants, disproportionately impacting disadvantaged communities. Here we demonstrate the use of high throughput lights-on bioreporter technology to measure both speciation and toxicity. The organism's response is fit-for-purpose to parameterize the Biotic Ligand Model used in risk assessment of aquatic ecotoxicity and setting environmental Water Quality Criteria. Toxicity endpoints for analogous Cd and Pb models reported in literature average 71st and 44th rank-percentile sensitivity of Genus Mean Acute Values for acute toxicity (i.e., insensitive) in comparison to the bioreporter, the unique dual-mode measurement ability of which can predict toxicity endpoints from below the 5th percentile up to the 50th rank-percentile. These results are extensible to other reporters, paving the way to cost-efficient environmental risk assessment of aquatic ecotoxicity for a wide range of priority toxic pollutants.

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.

Dynamic interaction processes of rare earth metal mixtures in terrestrial organisms interpreted by toxicokinetic and toxicodynamic model

Despite the progress in explanation of mixture toxicity of rare earth elements (REEs), a large knowledge gap still exists in interpreting their mixed effects from a dynamic perspective. Here, we investigated the effects of La-Ce mixtures in Enchytraeus crypticus at different exposure times. The single and mixture toxicity of La and Ce increased with time, as reflected by the reduced LC50/MT50 values. With concentration addition as the reference model, the interactions between La and Ce were quantified by MIXTOX modelling tool, showing a time-dependent pattern with antagonistic effect after 1 and 2 d but additive effects afterwards. The dynamic accumulation and toxicity of La/Ce in organisms exposed to REE mixtures was fitted using a process-based toxicokinetic and toxicodynamic (TK-TD) model to unravel how the elements interacted. Generally, the estimated uptake, elimination, and damage rate constants of La/Ce declined with increasing level of each other, suggesting inhibited uptake and subsequently reduced toxicity of La/Ce due to competition effect. The interplay of La and Ce in TK and TD processes seemed responsible for the observed antagonism. Our study showed that mixture toxicity and interaction of REEs are time-dependent processes and application of TK-TD model may provide more insight into this dynamic effect.

The accumulation and effect of rare earth element neodymium on the root of rice seedlings

Neodymium (Nd) potentially threatens ecological equilibrium for its wide usage in industries. In this study, the accumulation and effect of Nd on roots were investigated in the rice seedlings (Oryza sativa L.) exposed to different concentrations of Nd (0, 1, 10, 100, and 1000 μM). The toxic effect of Nd on rice growth was observed at the higher concentration, but the positive effects were found at the lower concentration. The accumulation of Nd was present in six different chemical forms, and the insoluble phosphate and oxalate Nd were the major forms of Nd in the roots. In addition, Nd was accumulated in the soluble fractions, organelles, and cell walls of rice seedlings, and the root cell wall was a major Nd sink site. The result of Fourier transform infrared spectrometer spectral analysis indicated that the functional groups of -OH and C-OH were the major binding sites of Nd in the cell wall of roots. Moreover, the level of reactive oxygen species (ROS) and the activity of catalase (CAT), superoxide dismutase (SOD), and peroxidase (POD) were significantly increased with the increase of Nd concentration. The enhanced antioxidant capacity also played an important role in Nd detoxification of rice seedlings. In all, the results indicated that forming of inactive oxalate or phosphate and efficient sequestration into the root cell wall was a key process in Nd accumulation and detoxification of rice seedlings.

Gadolinium accumulation, distribution, chemical forms, and influence on the growth of rice seedlings

The content of gadolinium (Gd) is continuously increased in environment, which potentially threatens human health and ecological equilibrium. However, the phytotoxicity of Gd on plants remains unknown until now. In this study, the accumulation, distribution, and chemical forms of Gd as well as its influence on growth and nutrient balance were systematically studied in rice seedlings after the treatments of different concentrations of Gd (0, 1, 10, 100, and 1000 μM) for 10 days. The results showed that most Gd was accumulated in the roots and only a little percentage of Gd was transported to shoots. The accumulation of Gd was increased in a dose-dependent manner in various chemical forms and subcellular fractions. More than 80% of Gd was in the forms of insoluble oxalates and phosphates. Gd was mainly compartmentalized in the cell wall, and the content of Gd was increased with increasing concentrations of Gd. In addition, hormetic effects of Gd were found on rice growth. The growth of rice was induced by the lower concentration of Gd, but inhibited by the higher concentration of Gd. The results indicated that rice seedlings could cope with Gd toxicity through cell wall compartmentalization as well as forming of precipitates with oxalate and phosphate.

Different dynamic accumulation and toxicity of ZnO nanoparticles and ionic Zn in the soil sentinel organism Enchytraeus crypticus

There is still no consensus over the specific effects of metal-based nanoparticles when compared with the conventional metal salts. Here, the accumulation and toxicity of ZnO-NPs and ZnCl₂ in Enchytraeus crypticus over time (1-14 d) were investigated using a sand-solution exposure medium and applying a toxicokinetics and toxicodynamics approach. For both Zn forms, body Zn concentration in the organisms was dependent on both the exposure concentration and exposure time, with equilibrium being reached after 7-14 days of exposure. Generally, the uptake and elimination rate constants (K_u and K_e1) were smaller for ZnO-NPs (5.74-12.6 mg kg^-1d^-1 and 0.17-0.39 d^-1) than for ZnCl₂ (8.32-40.1 mg kg^-1d^-1 and 0.31-2.05 d^-1), suggesting that ionic Zn was more accessible for E. crypticus than nanoparticulate Zn. Based on external exposure concentrations, LC50s for ZnO-NPs and ZnCl₂ decreased with time from 123 to 67 Zn mg L^-1 and from 86 to 62 Zn mg L^-1, reaching an almost similar ultimate value within 14 d. LC50s based on body Zn concentrations were almost constant over time (except for 1 d) for both ZnO-NPs and ZnCl₂, with overall LC50_body of Zn being 1720 and 1306 mg kg^-1 dry body weight, respectively. Body Zn concentration, which considers all available pathways, was a good predictor of dynamic toxicity of ZnCl₂, but not for ZnO-NPs. This may be attributed to the specific internal distribution and detoxification mechanisms of ZnO-NPs. The particles from ZnO-NPs dominated the accumulation (>75%) and toxicity (∼100%). Our results suggest that dynamic aspects should be taken into account when assessing and comparing NPs and metals uptake and consequent patterns of toxicity.

Earthworms, Rice Straw, and Plant Interactions Change the Organic Connections in Soil and Promote the Decontamination of Cadmium in Soil

The joint effects of earthworms and crop straw on toxic metal speciation are not clear, and very limited information is available regarding the effects of their interaction on Cd mobility in Cd contaminated soil or in remediation processes involving plants. This study evaluated their impacts on Cd mobile form changes in soil and their effects on Cd uptake by plants. Treatments included both planted and unplanted-Cd-contaminated soil with or without rice straw and/or earthworms. The results revealed that earthworms, rice straw, and plant interactions change the Cd mobile forms in soil. The order of Cd concentration of different chemical forms was as follows: exchangeable > residual > bound to Fe-Mn oxide > bound to organic matter for earthworms, and exchangeable > bound to organic matter > residual > bound to Fe-Mn oxide for rice straw treatment, with a recovery rate of 96 ± 3%. The accumulation of Cd in plants increased in the presence of earthworms and decreased in the presence of rice straw. FT-IR spectra indicated that the degradation of rice straw increases C⁻O, C⁻O⁻H, C⁻H, and O⁻H functional groups which could complex with Cd ions. These findings highlighted that earthworms' activities and crop straw can modify soil properties and structure and promote the remediation of heavy metal. This study suggests that the ecological context of remediation instead of being limiting on soil-earthworms-plant interaction, should integrate the natural resources forsaken which can provide a positive influence on both plant health and the remediation of heavy metal in contaminated soil.

Phenanthrene Mitigates Cadmium Toxicity in Earthworms Eisenia fetida (Epigeic Specie) and Aporrectodea caliginosa (Endogeic Specie) in Soil

In classical toxicology studies, the interaction of combined doses of chemicals with dissimilar modes of toxic action in soil is complex and depending on the end point investigated and the experimental protocol employed. This study was used to examine the interactive effect of phenanthrene and Cadmium on two ecologically different species of earthworms; Eisenia. fetida and Aporrectodea. caliginosa. This interactive effect was scrutinized by using the acute toxicity test with the concentrations of 2.51 mg kg⁻¹ and 3.74 mg kg⁻¹, respectively, being lethal for 50% of E. fetida and A. caliginosa. The results showed that in the mixture treatment, phenanthrene at 5, 10, 15 and 20 mg kg⁻¹ significantly mitigated both earthworms species mortality and body-mass loss. Moreover, the factor of Cd accumulated in E. fetida and A. caliginosa tissues was significantly decreased by about 12% and 16%, respectively. Linear regression correlation coefficient revealed that the reduction of both earthworm species mortality was negatively and significantly correlated (r² = 0.98 ± 0.40 and 1 ± 3.9 p < 0.001) with phenanthrene concentration in soil. However, over 20 mg kg⁻¹ of phenanthrene, both organisms mortality rate increased again, as was the Bioaccumulation factor of phenanthrene. Thus, this study proposes that the antagonistical effect of phenanthrene on Cd at a degree of concentration can be used to mitigate Cd effect on soil living organisms. However, as an implication of these results, the interpretation of standardized toxicity bioassays, including whole effluent toxicity tests and single-compound toxicity tests, should be performed with caution. In addition, risk assessment protocols for environment pollution by a mixture of metals and polycyclic aromatic hydrocarbons should include robust methods that can detect possible interactive effects between contaminants to optimize environmental protection.

Effects of benzotriazole on copper accumulation and toxicity in earthworm (Eisenia fetida)

Triazole contaminants in water and soil environments can form complexes with metal ions, and therefore affect the bioavailability and toxicity of some heavy metals. In present study, significant increase of copper (Cu) uptake by earthworm (Eisenia fetida) was observed when combined pollution of benzotriazole (BTR) presented in soil. For instance, Cu accumulation in earthworms increased 55% approximately when BTR presented at the BTR/Cu molar ratio of 1:2.5. While the single Cu exposure (at 32 mg kg^-1 in soil) resulted in increased malondialdehyde (MDA) content in earthworms from 0.319 to 0.668 nmol mg protein^-1, joint exposure to BTR at BTR/Cu molar ratio of 1:10 significantly decreased the MDA content to 0.405 nmol mg protein^-1. This indicates a potential detoxification effect of BTR to Cu induced oxidative damage in earthworms. Varied Cu subcellular distribution can be observed in earthworms of the single and combined exposure treatments. With the combined exposure of BTR, the proportion of Cu associated with granular fraction, the toxically inert fraction in earthworms, increased from 25% to 39%. This phenomenon can be used to explain the protective effects of BTR against oxidative damage.

Effect of cadmium bioavailability in food on its compartmentalisation in carabids

Metals assimilated by organisms are sequestered in various compartments and some forms are more stable than others. Sequestration mechanisms used by invertebrates to detoxify metals and prevent interaction with important biomolecules include metal binding to proteins and other ligands, and storage in inorganic granules. The rate and extent at which metal concentrations in different compartments respond to metal concentrations in food and food characteristics has not received much attention, despite being of great relevance. We performed an experiment on the carabid beetle Pterostichus oblongopunctatus exposed to Cd via food made of ground mealworm (Tenebrio molitor) larvae, either reared on Cd contaminated medium or artificially spiked after grinding with CdCl₂ solution. Thus, in both cases we used the same type of food, differing only in the soluble Cd pool available to the predators, represented by P. oblongopunctatus. Subcellular compartmentalisation of Cd into organelles, heat-sensitive and heat-stable proteins (the first supernatant, S1 fraction), cellular debris (the second supernatant, S2 fraction) and metal-rich granules (G fraction) was checked a few times during the contamination (90 d) and decontamination (24 d) phases in a toxicokinetic experiment by using different centrifugation steps. The results showed no effect of the type of food (naturally, Cd-N, vs. artificially contaminated with Cd, Cd-A) on Cd sequestration kinetics in P. oblongopunctatus, but the amount of Cd sequestered in the S1 and G fractions were in general higher in the Cd-A than the Cd-N treatment, indicating that Cd transfer in the food web depends on the speciation of the metal in the food. The proportional distribution of Cd over different fractions was, however, similar in beetles fed both food types. Most of the accumulated Cd in the beetles existed as fraction S1 (ca. 35%), which is important for the transfer of metals to higher trophic levels in a food web.

Toxicokinetics of zinc-oxide nanoparticles and zinc ions in the earthworm Eisenia andrei

The toxicokinetics of zinc in the earthworm Eisenia andrei was investigated following exposure for 21 days to ionic zinc (ZnCl₂) or zinc oxide nanoparticles (ZnO-NPs) in Lufa 2.2 soil, followed by 21 days elimination in clean soil. Two concentrations were tested for both ZnCl₂ (250 and 500μg Zn g^-1) and ZnO-NPs (500 and 1000μg Zn g^-1), corresponding to EC₂₅ and EC₅₀ for effects on reproduction. Based on the measured internal Zn concentrations in the earthworms over time of exposure, the kinetics parameters k_a - assimilation rate constant (g_soil g^-1_{body weight} day^-1) and k_e - elimination rate constant (day^-1) were estimated using a one-compartment model for either total Zn concentrations in the soil or porewater Zn concentrations. In the ZnCl₂ treatments, k_a was higher for total Zn concentrations in soil, whereas in the ZnO-NP treatments, k_a was higher for porewater Zn concentrations. The value of k_e did not differ between the two Zn forms (ZnCl₂ vs ZnO-NPs) for either EC₅₀ or EC₂₅ when related to total Zn concentrations in soil, but for EC₅₀, k_e related to porewater Zn concentrations was significantly higher for ZnCl₂ than for ZnO-NPs. It is concluded that differences in kinetic parameters between treatments were connected with exposure concentrations rather than with the form of Zn. Zinc was efficiently regulated by the earthworms in all treatments: a 2-fold increase in exposure concentration resulted in a less than 2-fold increase in internal concentration, and after transfer to uncontaminated soil the internal Zn concentrations in the earthworms returned to ca 111μgg^-1 dw in all treatments.

Integration of cerium chemical forms and subcellular distribution to understand cerium tolerance mechanism in the rice seedlings

Rare earth elements (REEs) accumulate in the soil and ecosystem. Cerium (Ce) is one of the main additives in REE-containing fertilizers. However, little information is available on Ce distribution patterns and chemical forms in rice. The subcellular distribution and chemical forms of Ce were investigated in the rice seedlings (Oryza sativa L., cv. Zhonghua 11) exposed to 0, 10, 20, 40, 80, and 160 μM Ce. The elongation of root and shoot was significantly inhibited by 20, 40, 80, and 160 μM Ce. Cerium was significantly accumulated in the cell walls, cell organelles, and soluble fractions of the roots and shoots with the increase of Ce concentrations. The concentrations of Ce in roots were significantly higher than shoots, and a large amount of Ce was stored in cell walls. In addition, Ce existed in the different chemical forms in the rice seedlings, and there were most insoluble oxalate or phosphate forms in roots. The subcellular distribution and chemical forms of Ce were closely associated with the metal tolerance and detoxification of rice.

Toxicokinetics and toxicodynamics of lead in the soil invertebrate Enchytraeus crypticus

The aim of the present study was to link Pb toxicokinetics to toxicodynamics in Enchytraeus crypticus. The enchytraeids were exposed for 14 d to different Pb concentrations (uptake phase) in natural Lufa 2.2 soil, followed by a 14-d elimination phase in clean soil. Pb accumulation and enchytraeid mortality were determined at different time intervals. At each exposure concentration, internal Pb concentration increased with exposure time and achieved equilibrium in approximately 7 d. Median lethal concentration (LC50) based on total Pb concentration in soil decreased with exposure time, but did not reach a steady-state level. Pb toxicity, therefore, showed a delay compared to accumulation in E. crypticus. LC50s based on internal Pb concentrations in the surviving animals did reach steady state in approx.14 d, suggesting that linking toxicokinetics to toxicodynamics may reduce the effects of time. This study highlighted that exposure time, as an important factor in metal uptake and toxicity, should be taken into account in ecotoxicological tests for risk assessment.

Life cycle toxicity assessment of earthworms exposed to cadmium-contaminated soils

Cadmium (Cd) is of great concern in the soil environment and it can damage terrestrial organisms. The purpose of this study was to employ a toxicokinetic/toxicodynamic (TK/TD) approach to investigate the effects of toxicologically relevant Cd accumulation on the life cycle growth of earthworms (Lumbricus rubellus and Eisenia fetida) and to assess potential terrestrial ecosystem risk. We reanalyzed growth toxicity and whole body and pellet accumulation data linked with TK/TD and life cycle growth models to estimate key rate constants. The growth risk of earthworms exposed to Cd was also assessed. This study found that the estimated whole body killing rate constant (0.114 g d μg^-1) was much lower than that of pellet (0.248 g d μg^-1). The recovery rate constant for whole body (6.02 d^-1) was much higher than that of pellet (2.91 d^-1). We also employed a life cycle-based probabilistic risk assessment model to estimate the growth inhibition risk for earthworms in response to environmentally relevant concentrations of Cd in Taiwan. Results showed that earthworms had a 90% growth inhibition probability risk of body weight, which was lower than 872.33 mg based on assessment of toxicologically relevant Cd accumulation. This study suggests that toxicologically relevant Cd accumulation could accurately reflect the capacity of Cd toxicity to earthworms. The integrated life cycle toxicity of earthworms exposed to Cd in this study provides a robust and applicable tool for the management of ecological risk assessment of Cd-contaminated soil.

Combined effects of chlorpyriphos, copper and temperature on acetylcholinesterase activity and toxicokinetics of the chemicals in the earthworm Eisenia fetida

In polluted environments organisms are commonly exposed to a combination of chemicals with different modes of action, and their effects can be additionally modified by natural abiotic conditions. One possible mechanism for interactions in mixtures is via toxicokinetics, as chemicals may alter the uptake, distribution, biotransformation and/or elimination of each other, and all these processes can be affected by temperature. In this study, the effect of temperature (T) on the toxicokinetics of copper (Cu) and chlorpyriphos (CHP), applied either singly or in binary mixtures, was studied in the earthworm Eisenia fetida. The experiments were conducted at 10 or 20 °C and the earthworms were exposed to environmentally realistic concentrations of Cu and/or CHP for 16 d, followed by a depuration period of 4 d in uncontaminated soil. The earthworms were sampled for body Cu and/or CHP concentrations and acetylcholinesterase (AChE) activity measurements. The CHP degradation rate in the soil was substantially higher at 20 °C and in soil treated with Cu. The significant (p < 0.05) inhibition of AChE activity in the earthworms exposed to CHP was found. The effect of Cu was significant only at p < 0.1. No synergistic effect of the parallel CHP and Cu exposure was found. Four days after transferring the earthworms to uncontaminated soil, the AChE activity recovered to the level observed in control animals. The temperature effect on the toxicokinetic parameters was more pronounced for CHP than for Cu. In the case of CHP, the assimilation rate constant (k_A) was significantly higher at 20 °C than at 10 °C, both in CHP-only and CHP + Cu treatments. A similar trend was found for the elimination rate constant (k_E), but the difference was statistically significant only for non-Cu treatments. In the case of Cu, the general trend of higher k_A and k_E at 20 °C and in the absence of CHP was observed.

Subcellular partitioning of cadmium and zinc in mealworm beetle (Tenebrio molitor) larvae exposed to metal-contaminated flour

By studying the internal compartmentalization of metals in different subcellular fractions we are able to better understand the mechanisms of metal accumulation in organisms and the transfer of metals through trophic chains. We investigated the internal compartmentalization of cadmium (Cd) and zinc (Zn) in mealworm beetle (Tenebrio molitor) larvae by breeding them in flour contaminated with either Cd at 100, 300 and 600mgkg(-1), or Zn at 1000 and 2000mgkg(-1). We separated the cellular components of the larvae into 3 fractions: the S1 or cytosolic fraction containing organelles, heat-sensitive and heat-stable proteins, the S2 or cellular debris fraction and the G or metal-rich granule fraction. The concentration of Cd and Zn in each fraction was measured at 0, 7, 14 and 21 days of being fed the flour. The concentration of Cd in the flour affected the concentration of Cd measured in each larval subcellular fraction (p≤0.0001), while the concentration of Zn in the flour only affected the Zn concentration in the S2 and G fractions (p≤0.02). Both Cd and Zn concentrations in mealworms remained relatively constant during the exposure (days 7, 14 and 21) in all three fractions, but the Cd concentrations were much higher than those found in larvae before the exposure (day 0). The concentration of Cd in the flour, however, did not affect the percentage of Cd in the S1 fraction. The contribution of Cd in the G fraction to the total Cd amount was similar (30-40%) in all Cd treatments. The percentage of Zn in all three fractions was not affected by the concentration of Zn in the flour and the relative contributions of each subcellular fraction to the total burden of Zn remained generally constant for both control and treated larvae. In general, larvae sequestered approximately 30% of Cd and Zn in the S1 fraction, which is important for the transport of metals to higher trophic levels in a food web.

Diverse impacts of a step and repeated BDE209-Pb exposures on accumulation and metabolism of BDE209 in earthworms

Decabromodiphenyl ether (BDE209) and lead (Pb) are the two common contaminants at e-waste recycling sites (EWRSs). A laboratory incubation study was conducted to explore the impacts of a step and repeated BDE209-Pb exposures on accumulation and metabolism of BDE209 in earthworms Eisenia fetida for the first time. The results indicated that BDE209 concentrations in repetitively-polluted soils were clearly higher. And the existence of high-level Pb could promote the bioaccumulation of BDE209 in earthworms along the exposure time. The post-clitellum contents of BDE209 were more than the pre-clitellum during the entire incubation. Additionally, GC/MS analysis results demonstrated that BDE206, BDE208, BDE153, BDE99, BDE47 and BDE28 could be detected in Eisenia fetida throughout 28-d experiment, and BDE206 and BDE208 were predominant metabolic products. A step exposure decreased the capability to metabolize BDE209 in the presence of Pb. Average bioaccumulation factor (BAF) for a step treatment was 0.525, as well as it was more than 1.1 times that of repeated exposure (BAF = 0.48). SEM observations suggested that a step exposure mode aggravated the damage in earthworms than repeated exposure. The results and related findings will establish a useful scientific basis for soil ecological risk assessment at EWRSs.

Characterizations of bio-accumulations, subcellular distribution and chemical forms of cesium in Brassica juncea, and Vicia faba

We aim to investigate the tolerance and enrichment mechanism of cesium (Cs) in hyperaccumulation plants. In this study, Brassica juncea and Vicia faba were subjected to varying doses of Cs for 21 days to investigate the differences in bio-accumulations, subcellular distribution and chemical forms of Cs in two cultivars by differential centrifugation, and extraction of Cs in different chemical forms, respectively. The results showed that 49.87%-61.08% of the Cs were in the leaf of B. juncea, while in V. faba, 1.58%-79.29% of the Cs was in the root. The translocation factor (TF) arrived 2.79 to 3.71 in B. juncea, while it only reached 0.26 to 0.62 in V. faba. Cs subcellular distribution of the two plants was in sequence as follows: soluble fraction > cell wall >> organelles. Cs was more easily distributed to metal-sensitive fractions of V. faba. The inorganic Cs (F-ethanol), and water-soluble Cs (F-dH2O) are the main existing types of Cs in the two plants. In B. juncea, the relative content of inorganic Cs, and organic acids/CsH2PO4 (F-dH2O) were higher than that of V. faba in the stem. This suggests that Cs may induce related transporter gene expression (such as phosphate transporter, organic cation, high affinity nitrate transporter, amino acid permease, etc.) to help the transport of Cs between root to shoot.

Concentration dependent toxicokinetics of copper in the red flour beetle Tribolium castaneum (Coleoptera: Tenebrionidae)

To predict internal metal concentrations in animals under specific environmental exposures, the relationship between the exposure concentrations and values of toxicokinetic parameters must be known. At high exposure levels, the availability of carriers transporting metal ions through cellular membranes may become limited, thereby decreasing the assimilation rates (k A ). Furthermore, increased metal concentrations in food may result in greater damage to the gut and reduce the assimilation efficiency and/or increase the elimination rate (k E ). Therefore, k A should decrease and k E should increase with increasing metal concentrations. In fact, our study on Tribolium castaneum exposed to Cu at 500, 1000, 2000 and 4000 mg kg(-1) of dry flour showed that with increasing Cu concentrations, k A decreased from 0.0042 day(-1) at 500 mg kg(-1) to 0.0026 day(-1) at 4000 mg kg(-1) in females and from 0.0029 to 0.001 day(-1) in males and k E increased from 0.027 to 0.064 day(-1) and from 0.018 to 0.04 day(-1) in females and males, respectively. Significant differences in k A between the sexes were observed at 2000 and 4000 mg kg(-1), whereas significant differences between treatments were found for k A in males. Copper was efficiently regulated by T. castaneum: an eightfold increase in exposure concentrations resulted in only a ca. twofold increase in the internal concentration. No Cu effect on the respiratory metabolism of T. castaneum was found.

Regulation of body metal concentrations: Toxicokinetics of cadmium and zinc in crickets

Previous studies indicated that essential and xenobiotic metals differ substantially in terms of their toxicokinetics. Whether these differences are due to different assimilation rates, different elimination rates, or both, and whether all metals are regulated in a similar manner but with different efficiency remains unclear. To compare the mechanisms responsible for the regulation of different metals, parameters for toxicokinetic models have to be tested under exposures to the identical molar concentration of those metals. In this study, the cricket Gryllus assimilis was exposed to Zn or Cd at 2.5, 10, and 40mMkg(-1) dry food. The body concentrations of the metals were not perfectly regulated by the crickets. For Zn, a clear increase in the body concentration was found only at the highest treatment; whereas at the lowest treatment, the internal concentration remained unchanged throughout the experiment. At the lowest Zn concentration, the assimilation (kA) [day(-1)] and elimination (kE) [day(-1)] rate constants were balanced (kA=0.024, kE=0.024). When increasing the Zn exposure, kA decreased to 0.018 at 10mMkg(-1) and 0.01 at 40mMkg(-1), and kE increased to 0.05 and 0.07, respectively. Therefore, the body concentration of Zn was regulated by simultaneously changing the assimilation and elimination rate. By contrast, even at the lowest treatment, a significant increase in Cd concentration was observed in the crickets. The equilibrium Cd concentration resulted almost exclusively from increasing kE from 0.17, through 0.28 to 0.61 at 2.5, 10 and 40mMkg(-1). The kA for Cd did not reveal any clear trend. Zn was more efficiently regulated by crickets than was Cd: a 16-fold increase in exposure concentration (from 2.5 to 40mM Znkg(-1)) resulted only in a twofold increase of internal concentration, whereas the identical increase in Cd exposure concentration resulted in almost a sevenfold increase in internal concentration of this metal.

Genotoxic and oxidative responses in coelomocytes of Eisenia fetida and Hediste diversicolor exposed to lipid-coated CdSe/ZnS quantum dots and CdCl2

The emerging of Quantum Dots utilization in industrial or medicinal fields involved a potentially increase of these nanoparticles in environment. In this work, the genotoxic (comet assay) and oxidative effects (SOD activity, TBARS) of functionalized-QDs and cadmium chloride were investigated on Hediste diversicolor and Eisenia fetida coelomocytes. Results demonstrated that functionalized-QDs (QDNs) and cadmium chloride induced DNA damages through different mechanisms that depended on the nano- or ionic nature of Cd. The minimal genotoxic concentrations for H. diversicolor (<0.001ng/g for QDNs and CdCl2 ) were lower than for E. fetida (between 0.01 and 0.1 ng/g for QDNs, and between 0.001 and 0.01 ng/g for CdCl2 ). These results showed that H. diversicolor was more sensitive than E. fetida. The two contaminants had a low impact on the oxidative stress markers.

Uptake and elimination kinetics of metals in soil invertebrates: a review

Uptake and elimination kinetics of metals in soil invertebrates are a function of both soil and organism properties. This study critically reviewed metal toxicokinetics in soil invertebrates and its potential use for assessing bioavailability. Uptake and elimination rate constants of different metals are summarized. Invertebrates have different strategies for essential and non-essential metals. As a consequence, different types of models must be applied to describe metal uptake and elimination kinetics. We discuss model parameters for each metal separately and show how they are influenced by exposure concentrations and by physiological properties of the organisms. Soil pH, cation exchange capacity, clay and organic matter content significantly affect uptake rates of non-essential metals in soil invertebrates. For essential metals, kinetics is hardly influenced by soil properties, but rather prone to physiological regulation mechanisms of the organisms. Our analysis illustrates that toxicokinetics can be a valuable measurement to assess bioavailability of soil-bound metals.

Influence of the activity of Allobophora molleri in microbial activity and metal availability of arsenic-polluted soils

We investigate the use of Allolobophora molleri as a biomarker of arsenic (As)-polluted soils and study the influence of A. molleri on the metabolic activity and microbial biodiversity of soil polluted with As. Because there are no experimental data available regarding the effect of the pollutant rate of As on A. molleri, we determined the LC₅₀ that was 143.5 mg As kg(-1). Sodium arsenite was added at two rates, equivalent to 143.5 and 71.8 mg As kg(-1) soil, to a soil that was then maintained with and without worms for 120 days. In addition, a nonpolluted soil without and with earthworms was used as the control. The As concentration in the soil was measured after 7 and 120 and the worm weight and As concentration after 120 days of exposure. Soil enzymatic activities and the structure of the soil microbial community, by analysis of phospholipid fatty acids, were determined. At the end of the experiment, the highest earthworm As contents were found in soils polluted with the highest rate of As. Earthworm weights significantly decreased in soil polluted with 143.5 or 71.8 mg As kg(-1), by 49.9 and 29.8% of initial weight, because the worm consumption rate decreased. These results suggest that A. molleri can be used as a good biomarker of the As toxicity. The As available fraction decreased in polluted soil with worms because the metal was accumulated in worm tissues. However, this assimilation was lower than other worms such as L. rubbellus or L. terrestris. Soil enzymatic activities were decreased in As-polluted soils but were increased significantly by the presence of earthworms. The earthworms modified the soil microbial diversity. In this respect, A. molleri significantly increased (p < 0.05) the bacterial and fungal populations. Soil As pollution decreased microbial biodiversity but to a lesser extent in the presence of A. molleri.

Toxicokinetics and toxicodynamics of nickel in Enchytraeus crypticus

Metal toxicity is usually determined at a fixed time point, which may bias the assessment of risks associated with varied exposure time. Time-dependent accumulation and toxicity of nickel in the potworm Enchytraeus crypticus were investigated in solutions embedded in an inert quartz sand matrix. Internal Ni concentration and mortality were determined at 7 different time intervals and interpreted from the perspective of toxicokinetics and toxicodynamics. A 1-compartment model was used to describe the uptake and elimination kinetics of Ni. At each exposure concentration, Ni concentration in the organisms increased with increasing exposure time, reaching equilibrium after approximately 14 d. Median lethal concentration (LC50) decreased with time and reached an ultimate value of 0.182 mg/L. The LC50 values expressed as internal Ni concentrations (LC50inter) were almost constant (16.7 mg/kg body dry wt) at each exposure time. The LC50inter was independent of exposure time, suggesting that internal concentration was a better indicator of Ni toxicity than external concentration. The uptake rate constant was 11.9 L/kg/d, and elimination rate constants were 0.325/d (based on internal concentration) and 0.070/d (based on survival), indicating that not all internal Ni contributes to toxicity. The present study highlights the importance of taking time into account in future toxicity testing and risk assessment practices.

Subcellular accumulation of different concentrations of cadmium, nickel, and copper in Indian mustard and application of a sigmoidal model

Certain plant species can tolerate and even detoxify metallic elements. This detoxification ability has been shown to depend on how plants distribute the metallic elements in their tissues. In turn, this distribution may have an important impact on phytoremediation. Here, we investigated the effects of different single-metal concentrations (10, 50, 100, and 300 μmol L) of cadmium (Cd), nickel (Ni), and copper (Cu) on their subcellular distribution in L. var. (Indian mustard). At the applied concentration of 300 μmol L, 98% of the Cu and 79% of Cd were retained in the roots, while Ni was distributed between leaves (32%), stems (29%), and roots (39%). The cell wall and soluble fractions were the dominant storage compartments for Cd and Cu in the stems and leaves, whereas the soluble fraction was the dominant storage compartment for Ni in stems and leaves. Scanning electron microscopy (SEM) X-ray micrographs showed a breakdown of epidermal, palisade, and spongy parenchyma cells following the 300 μmol L Cd, Ni, and Cu treatment. A sigmoidal model is a powerful tool to describe the subcellular accumulation and tissue concentrations of Cd, Ni, and Cu following exposure to various concentrations of metals. The coefficients of determination () values for the description of the accumulation were high, although the membrane subcellular fraction did not fit the equation. Both the maximum accumulation capacity and the critical concentrations of metals were well described by the model. The results indicate that the use of a sigmoidal model is a promising method that could improve the understanding of metal accumulation at the subcellular level in Indian mustard.

Does glyphosate impact on Cu uptake by, and toxicity to, the earthworm Eisenia fetida?

Glyphosate (GPS) is a wildly-used pesticide throughout the world. It affects metal behaviors in soil-water system as its functional groups such as amine, carboxylate and phosphonate can react with metal ions to form metal complexes. The reaction will result in the decreasing of heavy metal bioavailability. A laboratory experiment was conducted to investigate the interactions between GPS and copper (Cu) on the acute toxicity of soil invertebrate earthworm (Eisenia fetida), which was exposed to aqueous solutions for 48 h with different mixing concentrations of Cu and GPS (technical-grade Gly acid). The mortality rates, Cu uptake by earthworm, and some biomarkers such as superoxide dismutase (SOD) activity, glutathione (GSH) content, and acetylcholinesterase (AchE) activity were measured. The mortality rates and whole-worm metal burdens increased significantly with the increasing Cu concentration in solution. However, toxicity of GPS to earthworms was not observed in this study. Furthermore, the presence of GPS could significantly reduce the acute toxicity of Cu to earthworms. The mortality rates decreased sharply and the uptake of Cu was nearly halted in the presence of GPS. In addition, the SOD activity, GSH content, and AchE activity almost declined to the levels of the control. These results demonstrate that GPS could control the toxicity as well as the bioavailability of heavy metals in soil solutions where both GPS and heavy metals often coexist.

Subcellular partitioning links BLM-based toxicokinetics for assessing cadmium toxicity to rainbow trout

The purpose of this article was to develop an integrated-scale toxicological model to investigate the impact of cadmium (Cd) toxicity on rainbow trout (Oncorhynchus mykiss) based on recent published experimental data. This model was generated from three different types of functional relationship: biotic ligand model (BLM), damage assessment model (DAM), and subcellular partitioning model (SPM), both of key toxicological determinants involved and of functional connections between them. Toxicokinetic parameters of uptake rate constant (k(1)) and elimination rate constant (k(2)) in gill, liver, and subcellular fractions were derived. A negative correlation between gill binding fraction of Cd and bioaccumulation factor was found. Detoxifying ability (% detoxified in liver metabolically detoxified pool (MDP)) and k(2) were negatively correlated, indicating that increasing % detoxified in MDP can compensate for lower k(2). This finding suggests a potential tradeoff between the abilities of elimination and detoxification for Cd. Yet, compensation between the ability to eliminate Cd and the ability to recover Cd-induced damage was not found. However, changes in k(2) and recovery rate constant (k(r)) can shift the dynamics of Cd susceptibility probability. This analysis implicates that once k(2) is determined experimentally, the values of k(r) and % detoxified in MDP can be predicted by the proposed k(2)-k(r) and k(2)-% detoxified relationships. This study suggests that the mechanistic linking of BLM-based DAM and SPM can incorporate the organ- and cell-scale exposure experimental data to investigate the mechanisms of ecophysiological response for aquatic organisms exposed to metal stressors.

Effect of complexation on the accumulation and elimination kinetics of cadmium and ciprofloxacin in the earthworm Eisenia fetida

Land application of solid wastes leads to the accumulation of both metals and antimicrobials in soils. To understand the effects of metal and antibiotic interaction on their accumulation by the earthworm Eisenia fetida, uptake and elimination kinetics and subcellular distribution of cadmium (Cd) and ciprofloxacin (CIP) were determined. The kinetics was accurately described by a one-compartment first-order kinetic model. Bioaccumulation kinetics and subcellular distribution of CIP were not affected by Cd addition. However, Cd exhibited different metabolic and subcellular distribution patterns. With CIP, Cd uptake flux and elimination rate constants were about 2.2 and 9.8 times, respectively, those without CIP. In the presence of CIP, Cd redistributed from fractions D (associated with granules) and E (associated with tissue fragments and cell membranes) to fraction C (associated with cytosol). Without CIP, Cd in fraction C could not be excreted, whereas with CIP, Cd in fraction C was significantly excreted, and the excretion rate constant was consistent with that of CIP. A good relationship was found between CIP and Cd in earthworms during uptake and elimination periods (p < 0.01). Our results indicated that the Cd-CIP complex may be taken up, stored, and eliminated by earthworms.