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Uptake and toxicity of Ni-Co mixtures in Enchytraeus crypticus were determined after 4 d, 7 d, 10 d, and 14 d exposure. Generally, body concentrations of Ni and Co increased with increasing exposure concentrations. Ni body concentration was significantly reduced in the presence of Co, whereas Ni only marginally affected Co uptake. When expressed as free ion activities, individual toxicity of Ni and Co increased with time, with median lethal concentrations (LC50) decreasing from 78.3 μM and 511 μM at 4 d to 40.4 μM and 393 μM at 14 d, respectively. When expressed as body concentrations, LC50BodyNi remained constant with time whereas LC50BodyCo increased during the first 7 d but remained stable afterwards. As identified by the MIXTOX model, interactions between Ni and Co were mainly antagonistic when based on free ion activities, however, no interaction was observed when based on body concentrations. A process-based model, incorporating exposure time to analyze the mechanisms underlying the dynamic mixture toxicity confirmed the differences in toxicokinetics of the 2 metals. The author's findings suggest that body concentrations, which incorporate bioaccumulation processes, are time-independent and can act as a more constant indicator of metal toxicity. The observed antagonism was mainly caused by competition between Co and Ni for binding sites and subsequent inhibition of Ni uptake. This competitive interaction occurred at the uptake level (toxicokinetics), but not at the target level (toxicodynamics). Environ Toxicol Chem 2014;9999:1-10. © 2014 SETAC [ABSTRACT FROM AUTHOR]

The present study aimed to investigate the influence of different fractions of dissolved organic carbon (DOC) on the uptake and toxicity of nickel (Ni) in the soil invertebrate Enchytraeus crypticus after different exposure times. The addition of DOC as humic acid or fulvic acid significantly reduced Ni uptake by E. crypticus in the soil-solution test system. Median lethal effect concentrations were calculated based on total dissolved Ni concentrations (LC50[Ni]), free Ni ion activity (LC50{Ni2+}), and Ni body concentrations (LC50Body-Ni). The LC50[Ni] values increased with increasing DOC levels and decreased with exposure time (4, 7, and 10 d). Humic acid exerted a greater protective effect on Ni toxicity than fulvic acid, but the protective effects decreased with prolonged exposure time. The LC50{Ni2+} values also decreased with exposure time but were almost constant with variation in DOC levels, indicating that the protective effect of DOC is mainly through complexation with free Ni ions to reduce Ni bioavailability. The LC50Body-Ni value was independent of DOC concentration and exposure time, with an estimated overall value of 22.1 µg/g dry weight. The present study shows that body concentration could serve as an effective indicator for predicting Ni toxicity with variations in the exposure environment (e.g., DOC) and exposure time. Environ Toxicol Chem 2017;36:3019-3027. © 2017 SETAC [ABSTRACT FROM AUTHOR]

The biotic ligand model (BLM) approach is used to assess metal toxicity, taking into account the competition of other cations with the free metal ions for binding to the biotic ligand sites of aquatic and soil organisms. The bioavailable fraction of metals, represented by the free metal ion, is a better measure than the total concentration for assessing their potential risk to the environment. Because BLMs are relating toxicity to the fraction of biotic ligands occupied by the metal, they can be useful for investigating factors affecting metal bioaccumulation and toxicity. In the present review, the effects of major cations on the toxicity of metals to soil and aquatic organisms were comprehensively studied by performing a meta-analysis of BLM literature data. Interactions at the binding sites were shown to be species- and metal-specific. The main factors affecting the relationships between toxicity and conditional binding constants for metal binding at the biotic ligand appeared to be Ca2+, Mg2+, and protons. Other important characteristics of the exposure medium, such as levels of dissolved organic carbon and concentrations of other cations, should also be considered to obtain a proper assessment of metal toxicity to soil and aquatic organisms. Environ Toxicol Chem 2015;34:2194-2204. © 2015 SETAC [ABSTRACT FROM AUTHOR]

Supralittoral ecosystems are among the most challenging environments for soil organisms, particularly when salinity fluctuations are involved, frequently combined with the presence of contaminants as a result of intense anthropogenic activities. Knowledge of how salinity influences the effect of contaminants in supralittoral species is crucial for determining the safety factors required when extrapolating results from optimal laboratory conditions to these natural ecosystems. The present study therefore evaluated the effects of 2 metals (copper and cadmium) and 2 organic compounds (carbendazim and 4-nonylphenol) in the absence or presence of 15‰ NaCl in the potworm Enchytraeus albidus, a model organism for ecotoxicology studies commonly found in supralittoral ecosystems, The potworms had a higher reproduction in saline soil than in control soil. Moreover, the effects of copper and carbendazim on reproduction were smaller than when they were tested in nonsaline soil. Potworms exposed to nonsaline soils also had significantly higher tissue concentrations of metals, which partly explains the effects on reproduction. The influence of salinity on effects of 4-nonylphenol was, however, less clear; effects on survival decreased in saline soil, but effects on reproduction were highest in saline soil. The latter slightly correlated with tissue concentrations of the chemical. The present study provides the first evidence that soil salinity has a significant influence on the impact of contaminants evaluated with the enchytraeid reproduction test. Environ Toxicol Chem 2015;34:2159-2166. © 2015 SETAC [ABSTRACT FROM AUTHOR]

The aim of the present study was to improve our understanding of cadmium bioavailability by linking toxicokinetics and toxicodynamics. The springtail Folsomia candida was exposed to different cadmium concentrations in solutions embedded in inert quartz sand. Survival and cadmium uptake in the animals were followed for 21 d. After 10 d, some animals were transferred to clean medium to assess cadmium elimination. Using a first-order one-compartment model, an overall uptake rate constant ( k1) of 0.18 L kganimal-1 d−1 and an elimination rate constant ( k2-TK) of 0.02 d−1 were calculated. Survival decreased with time, resulting in an estimated final median lethal concentration (LC50) of 0.51 mM. A lethal body concentration (LBC) of 4.6 µmol Cd g−1 dry body weight was estimated by multiplying the final LC50 by the bioconcentration factor ( k1/ k2-TK). The LC50animal values based on internal cadmium concentrations were between 3.56 µmol Cd g−1 and 9.91 µmol Cd g−1 dry body weight, with an overall value of 7.9 µmol Cd g−1 dry body weight (95% confidence interval [CI]: 3.8-12.0 µmol Cd g−1 dry body wt). Because the 95% CI of the LC50animal included the LBC, there was good agreement of cadmium toxicokinetics and toxicodynamics. Environ Toxicol Chem 2014;33:1570-1577. © 2014 SETAC [ABSTRACT FROM AUTHOR]

The current European legislation requires that combined effects of the active substances and any substance of concern contained in biocidal products are taken into account in environmental risk assessment. The hypothesis whether the consideration of active substances together with all formulation additives that are labeled as presenting an environmental hazard is sufficient for a reliable environmental risk assessment was tested in the present study by investigating 3 wood preservative products. Relevant single substances in the products, some of their generic mixtures, the biocidal products themselves, and aqueous eluates prepared from the products (representing potential environmental mixtures) were tested for effects on algal growth and Daphnia acute immobilization as well as reproduction. Predictions for the products and the eluates were based on the concept of concentration addition and were mostly found to provide reliable or at least protective estimates for the observed acute and chronic toxicity of the mixtures. The mixture toxicity considerations also indicated that the toxicity of each product was dominated by just 1 of the components, and that assessments based only on the dominating substance would be similarly protective as a full-mixture risk assessment. Yet, there remained uncertainty in some cases that could be related to the toxicity of transformation products, the impact of unidentified formulation additives, or synergistic interaction between active substances and formulation additives. Environ Toxicol Chem 2014;33:382-393. © 2013 SETAC [ABSTRACT FROM AUTHOR]

The use of the free ion approach to quantify the toxic effects of Cd and Ni to the earthworms Lumbricus rubellus and Aporrectodea longa exposed in soils of different types was explored. Median lethal concentration (LC50) of Cd (expressed as the total concentration in soil) varied by approximately 11-fold and 28-fold for L. rubellus and A. longa, respectively. For Ni, these values were 50-fold and 38-fold, respectively. For the 2 earthworm species, no significant influence of cations (H+, Ca2+, Mg2+, K+, and Na+) on Cd2+ toxicity was observed, while Mg2+ was found to significantly alleviate Ni2+ toxicity. The free ion activity model, which is a special case of the free ion approach with no impact of cations, sufficiently described the variability in Cd2+ toxicity across soils but failed in predicting Ni2+ toxicity. The free ion approach, in which the protective effects of Mg2+ were included, explained 89% and 84% of the variations in LC50{Ni2+} (expressed as free ion activity) for L. rubellus (log LC50{Ni2+} = 1.18log{Mg2+}−0.52) and A. longa (log LC50{Ni2+} = 0.51log{Mg2+}−2.16), respectively. Prediction error was within a factor of 2 for both Cd2+ and Ni2+ toxicity, indicating the applicability of the free ion approach for predicting toxicity of these 2 metals. Although extrapolation of the free ion approach across metals still needs more research efforts, this approach, as an alternative to the biotic ligand model, provides a feasible framework for site-specific risk assessment. Environ Toxicol Chem 2014;33:438-446. © 2013 SETAC [ABSTRACT FROM AUTHOR]

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. Environ Toxicol Chem 2013;32:1835-1841. © 2013 SETAC [ABSTRACT FROM AUTHOR]

The present study sought to quantify the components of a biotic ligand model (BLM) for the effects of Cd on Folsomia candida (Collembola). Assuming that soil porewater is the main route of exposure and to exclude the effects of soil particles on metal availability, animals were exposed for 7 d to different Cd concentrations between 0.1 mM and 100 mM in simplified soil solutions at different Ca concentrations (0.2 mM, 0.8 mM, 3.2 mM, and 12.8 mM) or at different pH (5.0, 6.0, and 7.0). Higher Ca concentrations decreased the toxicity of Cd (adult survival) in test solutions, whereas toxicity was slightly lower at pH 7 and 6 than at pH 5, suggesting a mitigating effect of Ca and to a lesser extent pH on Cd toxicity to F. candida. Internal Cd concentrations in the animals increased with increasing exposure level but were significantly reduced by increasing Ca concentrations and were not significantly affected by pH. By using Langmuir isotherms, binding constants for Cd, Ca, and protons and the fraction of binding sites occupied by Cd were calculated and used to predict effects of Cd on survival. Predicted toxicity showed a good agreement with measured responses when Ca and pH were used as separate factors or combined together. The present study shows indications of protective effects of Ca but less of protons on the toxicity and uptake of Cd in F. candida on exposure to simplified soil solutions, which can be described using the principles of a biotic ligand model. Environ Toxicol Chem 2013;32:1759-1767. © 2013 SETAC [ABSTRACT FROM AUTHOR]

A biotic ligand model (BLM) was developed to estimate Cu toxicity to lettuce ( Lactuca sativa) in terms of root elongation after 4 d of exposure. Effects of Na+, K+, Ca2+, and Mg2+ on Cu toxicity were examined. The addition of these cations resulted in a 50-fold difference in the copper median effective activity ( ${\rm EC}50_{{\rm cu}^{2 + } } $). However, these variations could not be interpreted entirely as a function of the concentrations of these cations alone. In particular, only the relationship between ${\rm EC}50_{{\rm cu}^{2 + } } $ and the activity of protons was found to be significant in the whole range of pH examined from 5.0 to 7.0. The addition of K+, Na+, Ca2+, and Mg2+ at concentrations up to 20 mM resulted in a 16-fold difference in ${\rm EC}50_{{\rm cu}^{2 + } } $ values. This difference was significant, as indicated by non-overlapping standard deviations of the negative logarithm of ${\rm EC}50_{{\rm cu}^{2 + } } $ ( ${\rm pEC}50_{{\rm cu}^{2 + } } $) obtained with (7.37 ± 0.22) and without (6.76 ± 0.22) additions of K+, Na+, Ca2+, and Mg2+. The variations were not statistically significantly related to concentrations of these cations; therefore, only protons can be integrated in the BLM predicting Cu toxicity to lettuce L. sativa with the important parameters: log KHBL = 6.27, log KCuBL = 7.40, and $f_{{\rm CuBL}}^{{\rm 50}\%} $ = 0.36 at pH = 7. The lack of significant relationships between ${\rm EC}50_{{\rm cu}^{2 + } } $ and concentrations of the cations was not in line with the main assumption of the BLM about the competition between cations for binding sites. Environ. Toxicol. Chem. 2012;31:355-359. © 2011 SETAC [ABSTRACT FROM AUTHOR]

The electrostatic nature of plant cell membrane (CM) plays significant roles in ionic interactions at the CM surface and hence in the biotic effects of metal ions. Increases in major cations (commonly Ca2+, Mg2+, H+, Na+, K+, etc.) in bulk-phase medium reduce the negativity of CM surface electrical potential (ψ0), but these slightly increase the driving force of a metal ion crossing CMs (surface-to-surface transmembrane potential difference, Em,surf). Toxicologists commonly attributes the interactions between heavy metals and common cations (e.g., H+, Ca2+, and Mg2+) to competitions for binding sites at a hypothetical CM surface ligand. The ψ0 effects are likely to be more important to metal toxicity and the alleviation of toxicity than site-specific competition. Models that do not consider ψ0, such as the biotic ligand model (BLM) and the free ion activity model (FIAM), as usually employed are likely to lead to false conclusions about competition for binding at CM surface ligands. In the present study a model incorporating ψ0 effects and site-specific competition effects was developed to evaluate metal (Cu2+, Co2+, and Ni2+) toxicities threshold (EA50, causing 50% inhibition) for higher plants. In addition, the mechanisms for the effects of common cations on toxicity of metals were also explored in terms of CM surface electrical potential. Environ. Toxicol. Chem. 2010;29:1503–1511. © 2010 SETAC [ABSTRACT FROM AUTHOR]

Total concentrations of metals in soil are poor predictors of toxicity. In the last decade, considerable effort has been made to demonstrate how metal toxicity is affected by the abiotic properties of soil. Here this information is collated and shows how these data have been used in the European Union for defining predicted-no-effect concentrations (PNECs) of Cd, Cu, Co, Ni, Pb, and Zn in soil. Bioavailability models have been calibrated using data from more than 500 new chronic toxicity tests in soils amended with soluble metal salts, in experimentally aged soils, and in field-contaminated soils. In general, soil pH was a good predictor of metal solubility but a poor predictor of metal toxicity across soils. Toxicity thresholds based on the free metal ion activity were generally more variable than those expressed on total soil metal, which can be explained, but not predicted, using the concept of the biotic ligand model. The toxicity thresholds based on total soil metal concentrations rise almost proportionally to the effective cation exchange capacity of soil. Total soil metal concentrations yielding 10% inhibition in freshly amended soils were up to 100-fold smaller (median 3.4-fold, n = 110 comparative tests) than those in corresponding aged soils or field-contaminated soils. The change in isotopically exchangeable metal in soil proved to be a conservative estimate of the change in toxicity upon aging. The PNEC values for specific soil types were calculated using this information. The corrections for aging and for modifying effects of soil properties in metal-salt-amended soils are shown to be the main factors by which PNEC values rise above the natural background range. [ABSTRACT FROM AUTHOR]

In an effort to improve the understanding and prediction of Cd uptake by soil bacteria, adsorbed and intracellular Cd were determined in unpolluted and highly polluted model soil solutions within a concentration range spanning from 10-9 to 5 × 10-5 M Cd. In parallel, the free Cd ion concentrations ([Cd2+]) were measured by a hollow fiber permeation liquid membrane. Obtained results demonstrated that Cd uptake by bacterium Sinorhizobium meliloti was related to [Cd2+] in the solution. Addition of different complexing organic substances reduced [Cd2+] in the bacterial medium and decreased both adsorbed and intracellular Cd. The adsorbed Cd was considerably reduced in the presence of 10-4 to 5 × 10-2 M [Ca] or [Mg]. No effect on Cd adsorption was observed in the presence of Zn or Mn, even at 100-fold excess. Intracellular Cd decreased in the presence of a high excess of Ca and Zn, while no significant effect was observed in the presence of Mg. An increase of dissolved Mn from 10-9 to 10-8 M resulted in a twofold decrease of the intracellular Cd, but no clear trend was observed in the presence of 10-7 to 10-6 M Mn. Based on complexation and competition studies, the stability constants, necessary for quantitative description of Cd uptake by S. meliloti and the development of the bacterial biotic ligand model for Cd, were derived and validated in the solutions containing mixtures of Cd, Zn, Ca, and Mg. Further numerical simulations of Cd uptake by S. meliloti exposed to soil pore waters demonstrated the importance of Zn competition and the insignificant influence of Ca and H on Cd uptake. [ABSTRACT FROM AUTHOR]

The effect of pH on the acute toxicity of Cu to barley (Hordeum vulgare) root elongation was investigated in solution culture. The results showed that the median effective concentrations (EC50s; i.e., the concentration that reduced root elongation by 50% based on free Cu2+ activity) were not significantly different in the low-pH range from 4.5 to 6.5, but in the high-pH range from 7.0 to 8.0, a significant effect of pH on EC50s was found. The nonlinear relationship between EC50 and H+ activity in the present study indicated that the increased toxicity with increasing pH in solution may not be caused by decreasing H+ competition. When we take account of CuOH+ activities, a good linear relationship (r² > 0.97) between the ratio of CuOH+ activity to free Cu2+ activity and acute Cu toxicity to barley root elongation was achieved, which indicated that the observed toxicity in the highpH range may be caused by CuOH+ plus free Cu2+ in solution. Linear-regression analysis suggested CuOH+ had a greater binding affinity than Cu2+ at the biotic ligand sites. The logistic dose-response curve showed that expressing the Cu dose as Cu2+ + 2.92 ∙ CuOH+ improved the data fit significantly compared to consideration of the free Cu2+ activity only. Thus, our results suggest CuOH+ was highly toxic to barley root elongation. The enhanced toxicity of CuOH+ therefore needs to be considered when modeling the effect of pH on Cu toxicity to barley for exposures having pH greater than 6.5. [ABSTRACT FROM AUTHOR]

Cobalt is widespread in the environment and excess dietary Co exposure can result in toxic effects in many organisms. However, whether the multi-biological toxicities caused by Co exposure can be transferred from parents to progeny has not been clarified. In the present study, we analyzed the multiple toxicities of Co to the nematode Caenorhabditis elegans and its progeny. Endpoints of life span, body size, vulva development, brood size, generation time, body bend, head thrash, and chemotaxis plasticity were used for toxicity testing. Our results indicate that Co induced multi-biological defects by affecting the life span, development, reproduction, behavior, and behavioral plasticity. Moreover, we found that most of these multi-biological defects could be transferred from parents to the filial generation (F1 and F2) progenies, and that this transmission could only be partially recovered. Certain specific phenotypes in the progeny exhibited even more severe defects than in the parents, such as chemotaxis plasticity. We classified the defects caused by Co exposure into four groups according to their transferable properties. Furthermore, the stress responses were investigated in embryos using a stable transgenic line, hsp16-2-gfp. Our data suggest that the multi-biological defects caused by Co exposure can be transferred from parents to progeny, and that Co toxicity might be accumulated in the eggs of nematodes. [ABSTRACT FROM AUTHOR]