The relationship between metal toxicity and biotic ligand binding affinities in aquatic and soil organisms: a review

Derivation of ecotoxicologically acceptable Cu concentrations in soil from different land uses in South Korea

This study aimed to establish ecotoxicologically acceptable Cu concentrations for soil-residing species by integrating the biotic ligand model and the species sensitivity distribution. Statistical analyses were performed on 35 soil solution samples collected from four distinct land use sites: residential, agricultural, forested, and industrial regions. The environmental parameters of these samples, including pH, dissolved organic carbon (DOC), Ca2⁺, Mg2⁺, K⁺, and Na⁺ concentrations, exhibited wide variations across the four regions. Specifically, pH and the concentrations of Mg2⁺, K⁺, and Na⁺ showed significant variability. Additionally, a strong correlation was observed between pH and Ca2⁺, as well as between the DOC concentration and Mg2⁺ and Na⁺. Using the biotic ligand model, we derived the half-maximal effective activities of Cu (EC50{Cu2+}) for 10 soil organisms based on the chemical compositions of the soil solution samples. Additionally, a species sensitivity distribution approach was employed to determine the 5% hazardous concentration (HC5) for soil biota, which was closely associated with DOC and Na⁺ concentrations, with Mg2⁺ playing a secondary role. We attributed these relationships to the formation of DOC complexes that mitigate Cu toxicity, along with competitive interactions with cations. Notably, HC5 values did not differ significantly across sampling sites (p = 0.523). Clustering based on environmental factors grouped the samples into four clusters, each containing soils from different land use types. However, the third cluster included an outlier from agricultural soil due to its unusually high pH and DOC levels. These findings suggest that it is crucial to consider site-specific soil characteristics when determining ecotoxicologically acceptable Cu concentrations, and soil solution characteristics do not always align with specific land use patterns.

Predicting soil ecological criteria of 17 metal(loid)s in China based on quantitative ion character-activity relationship - Species sensitivity distribution (QICAR-SSD) coupled model

Soil pollution caused by metal(loid)s is increasingly serious and poses unexpected risks to terrestrial organisms. Establishing soil quality standards is essential for assessing ecological risks of metal(loid)s and protecting soil ecosystems. However, the limited availability of metal(loid) ecotoxicological data has hampered the development of soil quality standards due to financial and practical constraints on toxicity testing. This study collected 77 normalization equations and 58 cross-species extrapolation equations to calculate the normalized EC10 (the added concentration causing a 10 % inhibition effect) of metal(loid)s under a representative scenario. A set of quantitative ion character-activity relationship (QICAR) models were then constructed using normalized EC10 and nine critical ionic characters (AR, AR/AW, BP, MP, Z/r2, Z/r, Xm, σp, and |Log(KOH)|). Subsequently, these QICAR models were employed to predict ecotoxicological EC10 of 17 metal(loid)s to 12 soil species and coupled with species sensitivity distribution (SSD) to determine Predicted No Effect Concentration (PNEC). The results demonstrated the coupled QICAR-SSD model could effectively derive terrestrial PNEC for data-poor metal(loid)s, with errors between the predicted PNEC and reported soil standards (excluding soil background levels) from different countries mostly <0.3 orders of magnitude. Finally, soil ecological criteria (SEC) for 17 metal(loid)s were calculated using an added risk approach based on PNEC and national soil background concentration. Overall, the coupled model proposed here can provide a valuable supplement to the development of soil quality standards for numerous metal(loid)s in soil components.

Ecotoxicological evaluation of surface waters in Northern Namibia

The increasing pressure on freshwater systems due to intensive anthropogenic use is a big challenge in central-northern Namibia and its catchment areas, the Kunene and the Kavango Rivers, and the Cuvelai-Etosha Basin, that provide water for more than 1 million people. So far, there is no comprehensive knowledge about the ecological status and only few knowledge about the water quality. Therefore, it is crucial to learn about the state of the ecosystem and the ecological effects of pollutants to ensure the safe use of these resources. The surface waters of the three systems were sampled, and three bioassays were applied on three trophic levels: algae, daphnia, and zebrafish embryos. Additionally, in vitro assays were performed to analyze mutagenicity (Ames fluctuation), dioxin-like potential (micro-EROD), and estrogenicity (YES) by mechanism-specific effects. The results show that acute toxicity to fish embryos and daphnia has mainly been detected at all sites in the three catchment areas. The systems differ significantly from each other, with the sites in the Iishana system showing the highest acute toxicity. At the cellular level, only weak effects were identified, although these were stronger in the Iishana system than in the two perennial systems. Algae growth was not inhibited, and no cytotoxic effects could be detected in any of the samples. Mutagenic effects and an estrogenic potential were detected at three sites in the Iishana system. These findings are critical in water resource management as the effects can adversely impact the health of aquatic ecosystems and the organisms within them.

Impacts of biochar materials on copper speciation, bioavailability, and toxicity in chromated copper arsenate polluted soil

Trace element polluted soils pose risks to human and environmental health. Biochar can decrease trace element bioavailability in soils, but their resulting ability to reduce soil toxicity may vary significantly depending on feedstocks used, pyrolysis conditions, and the target pollutants. Chromated copper arsenate (CCA) polluted sites are common, but only very few types of biochar have been tested for these sites. Hence, we tested fourteen well-characterized biochar materials for their ability to bind Cu and reduce toxicity in a CCA polluted soil in a 56-day experiment. Biochar (1%, wt/wt) increased plant (wheat, Triticum aestivum L.) shoot and root growth by 6-58% and 0-73%, reduced soil toxicity to Arthrobacter globiformis by 7-55%, decreased bioavailable Cu (Pseudomonas fluorescens bioreporter) by 5-65%, and decreased free Cu2+ ion activities by 27-89%. The A. globiformis solid-contact test constituted a sensitive ecotoxicological endpoint and deserves further attention for assessment of soil quality. Oil seed rape straw biochar generally performed better than other tested biochar materials. Biochar performance was positively correlated with its high cation exchange capacity, multiple surface functional groups, and high nitrogen and phosphorus content. Our results pave the way for future selection of feedstocks for creation of modified biochar materials with optimal performance in CCA polluted soil.

A modelling framework to assess multiple metals impacts on marine food webs: Relevance for assessing the ecological implications of deep-sea mining based on a systematic review

Industrial deep-sea mining will release plumes containing metals that may disperse over long distances; however, there is no general understanding of metal effects on marine ecosystems. Thus, we conducted a systematic review in search of models of metal effects on aquatic biota with the future perspective to support Environmental Risk Assessment (ERA) of deep-sea mining. According to results, the use of models to study metal effects is strongly biased towards freshwater species (83% freshwater versus 14% marine); Cu, Hg, Al, Ni, Pb, Cd and Zn are the best-studied metals, and most studies target few species rather than entire food webs. We argue that these limitations restrain ERA on marine ecosystems. To overcome this gap of knowledge, we suggest future research directions and propose a modelling framework to predict the effects of metals on marine food webs, which in our view is relevant for ERA of deep-sea mining.

Amelioration of cadmium cytotoxicity to human cells by nutrient cation contents and the building of a biotic ligand model

A variety of important major and trace elements may competitively inhibit cadmium (Cd) absorption in human cells and reduce Cd toxicity. However, the impact of essential elements on the cytotoxicity of metals can be difficult to quantify and anticipate. Cd acute toxicity to Caco-2 cell viability was studied in culture solutions and modeled by a biotic ligand model (BLM). The individual effects of the cations potassium (K⁺), calcium (Ca²⁺), magnesium (Mg²⁺), ferrous ion(Fe²⁺), zinc (Zn²⁺) and manganese (Mn²⁺) on Cd toxicity were also investigated. The results indicated that the toxicity of Cd in culture solutions to cell viability declined with increasing concentrations of Zn²⁺ and Mn²⁺ in the solutions, while K⁺, Ca^{2 +}, Mg^{2 +} and Fe²⁺ had no significant effect. Using the BLM, the stability constants for the binding of Cd^{2 +}, Zn²⁺, and Mn²⁺ to biotic ligands were determined to be logK_CdBL = 5.76, logK_ZnBL = 4.39 and logK_MnBL = 5.31, respectively. Moreover, it was calculated that 51% occupancy of the biotic ligand sites for Cd by Cd was required to cause a 50% reduction in Caco-2 cell viability. A BLM was successfully established using the estimated constants to predict the Cd cytotoxicity to Caco-2 cell viability as a function of solution characteristics, so that the effective concentrations that reduced cell viability by 50% (EC50) could be predicted by the BLM within 1.6 fold changes of the observed EC50. The application's viability and precision for foretelling Cd toxicity in Caco-2 cells are discussed.

Effect of dissolved organic matter on the bioavailability and toxicity of cadmium in zebrafish larvae: Determination based on toxicokinetic-toxicodynamic processes

The presence of dissolved organic matter (DOM) strongly influences the bioavailability of metals in aquatic environments; however, the association between the binding activities and the concentrations of DOM compositions is not well documented, leading to uncertainties in metal toxicity assessment. We creatively quantify the mitigation and acceleration effects of DOM compositions on cadmium (Cd) bioaccumulation and toxicity in zebrafish larvae using abiotic ligand (ABLs) and biotic ligand (BLs) in a toxicokinetic-toxicodynamic (TK-TD) model. The BL-TK-TD model could accurately predict the protective effect of fulvic acid while overestimating the complexing capacity of citric acid. The model also could successfully simulate the protective effects of native DOM in most cases from 32 natural water bodies in China. The observed LC50 values of Cd showed a peak effect for the native DOM fraction comprising hydrophilic acidic contents (3.55 ± 0.44 mg L ^- 1) in natural water from 32 sites. The BL-TK-TD model provides practically useful information to identify the effect of different DOM compositions on metal bioavailability and toxicity in aquatic environments and guides future water management policies aimed at controlling aquatic heavy metal pollution.

How to Implement User-Friendly BLMs in the Absence of DOC Monitoring Data: A Case Study on Bulgarian Surface Waters

The metal bioavailability concept is implemented in the Water Framework Directive (WFD) compliance assessment. The bioavailability assessment is usually performed by the application of user-friendly Biotic Ligand Models (BLMs), which require dissolved metal concentrations to be used with the “matching” data of the supporting physicochemical parameters of dissolved organic carbon (DOC), pH and Cadissolved. Many national surface water monitoring networks do not have sufficient matching data records, especially for DOC. In this study, different approaches for dealing with the missing DOC data are presented: substitution using historical data; the appropriate percentile of DOC concentrations; and combinations of the two. The applicability of the three following proposed substitution approaches is verified by comparison with the available matching data: (i) calculations from available TOC data; (ii) the 25th percentile of the joint Bulgarian monitoring network DOC data (measured and calculated by TOC); and (iii) the 25th percentile of the calculated DOC from the matching TOC data for the investigated surface water body (SWB). The application of user-friendly BLMs (BIO-MET, M-BAT and PNEC Pro) to 13 surface water bodies (3 reservoirs and 10 rivers) in the Bulgarian surface waters monitoring network outlines that the suitability of the substitution approaches decreases in order: DOC calculated by TOC > the use of the 25th percentile of the data for respective SWB > the use of the 25th percentile of the Bulgarian monitoring network data. Additionally, BIO-MET is the most appropriate tool for the bioavailability assessment of Cu, Zn and Pb in Bulgarian surface water bodies.

Cu, Ni, and Zn effects on basic physiological and stress parameters of Raphidocelis subcapitata algae

The submitted work observed Cu, Ni, and Zn effects on selected physiological and stress parameters of the alga Raphidocelis (Pseudokirchneriella) subcapitata. In 96-h experiments, EC50 values for algal specific growth rates (SGR) inhibition in Cu, Ni, and Zn presence were estimated as 0.15, 0.50, and 0.20 mg l^-1. In addition to growth inhibition, the effect of metals at various concentrations on algal SGR was also monitored. While these experiments confirmed approximately the same toxicity of Zn and Cu on SGR, Ni toxicity on this parameter was observed as the lowest. In terms of the effect of metals on the level of selected photosynthetic pigments, chlorophyll a, chlorophyll b, and carotenoids, the following inhibition orders can be established: Zn > Cu > Ni, Ni > Cu > Zn, and Ni > Cu ≥ Zn, respectively. As a novelty of our research, we included monitoring and evaluation of the intensity of stress, which was the response of algal cells to the presence of Cu, Ni, and Zn, and its correlation with respect to production factors and metal accumulation in algal cells. As stress factors, thiol (-SH) group and TBARS (thiobarbituric acid reactive substances) as significant indicators of lipid level peroxidation were determined. The content of -SH groups depended on the concentration of metal, and its level was the most stimulated by Zn, less by Cu and Ni. The TBARS content was 2 to 5 times higher in Cu than in Zn or Ni presence. In the presence of Zn and Ni, TBARS content reached approximately the same levels. For this parameter, the following rank order can be arranged: Cu >> Ni ≥ Zn. While Cu and Ni accumulation in R. subcapitata was confirmed, Zn accumulation was not determined or was below the detectable limit. Regression analyses revealed significant positive correlation between Cu accumulation and TBARS while carotenoids as possible antioxidants confirmed with TBARS mostly negative correlations.

In search for potential biomarkers of copper stress in aquatic plants

Over the last few decades, the use of pesticides and discharge of industrial and domestic wastewater on water surfaces have increased. Especially, Copper (Cu) pollution in aquatic ecosystems could constitute a major health problem, not only for flora and fauna but also for humans. To cope with this challenge, environmental monitoring studies have sought to find Cu-specific biomarkers in terrestrial and aquatic flora and/or fauna. This review discusses the toxic effects caused by Cu on the growth and development of plants, with a special focus on aquatic plants. While copper is considered as an essential metal involved in vital mechanisms for plants, when in excess it becomes toxic and causes alterations on biomarkers: biochemical (oxidative stress, pigment content, phytochelatins, polyamines), physiological (photosynthesis, respiration, osmotic potential), and morphological. In addition, Cu has a detrimental effect on DNA and hormonal balance. An overview of Cu toxicity and detoxification in plants is provided, along with information regarding Cu bioaccumulation and transport. Awareness of the potential use of these reactions as specific biomarkers for copper contamination has indeed become essential.

Comparative embryo/larval sensitivity of Australian marine bivalves to ten metals: A disjunct between physiology and phylogeny

Metal contamination within the urbanized coastal zon is one threat linked to a decline in the abundance, distribution and/or species diversity of wild marine bivalve populations. This study determined the 48-h embryo/larval sensitivity (no-effect concentration (NEC) and median-effect concentration (EC50)) of ten marine bivalve species (nine endemic to Australia) to aluminium (Al), cadmium (Cd), chromium (Cr), cobalt (Co), copper (Cu), iron (Fe), lead (Pb), manganese (Mn), nickel (Ni) and zinc (Zn), key metal contaminants impacting urbanized coastal zones in south-eastern Australia, in natural seawater (20-22 °C, 30‰ salinity, pH 7.8-7.9, 1.2 mg/L dissolved organic carbon). For all metals, except Fe, the order of sensitivity was oysters > mussels ≥ scallops ≥ cockles ≥ clams, where the economically-important oysters, Magallana gigas and Saccostrea glomerata, were 2.6 (Al) to 4.2 (Cd) times more sensitive than the least sensitive clam species. For all bivalve species, the order of metal sensitivity was Cu > Pb > Zn = Ni > Co > Cd > Al > Cr(VI) > Mn ≥ Fe(III), where Cu was eight times more toxic than Zn or Ni, 28 times more toxic than Cd, 220 times more toxic than Cr(VI) and 570 times more toxic than Fe(III). Iron, unlike the other nine soluble metals, occurred as particulate Fe(III) oxyhydroxide, where EC50 values decreased with increasing exposure time as the larval (D-veliger) stage. There was no significant (p > 0.05) effect of embryo/larval mass, or surface area/volume, on metal sensitivity. Further, there was no significant (p > 0.05) relationship between metal sensitivity and phylogeny (genetic distance). Divalent metal sensitivity was positively related (r2 = 0.87) to cell surface metal-binding affinity. The current Australian marine water quality guideline for Ni is not protective of the ten bivalve species (NECs were 2-6-fold below the guideline), while the guideline for Zn is not protective of oysters.

Assessment of Soil Contamination with Potentially Toxic Elements and Soil Ecotoxicity of Botanical Garden in Brno, Czech Republic: Are Urban Botanical Gardens More Polluted Than Urban Parks?

Though botanical gardens are an important and widely visited component of urban green spaces (UGS) worldwide, their pollution is rarely studied. The aim of this study was to assess botanical garden soil contamination and ecotoxicity and to evaluate whether urban botanical gardens are more contaminated than urban parks. Soil assessments showed serious contamination with Cd, Pb and Zn, emitted predominantly by traffic, agrochemicals and past construction and demolition waste. The discovery of hazardous historical ecological burden in the UGS calls for the necessity of detailed surveys of such areas. Despite prevailing moderate-to-heavy contamination, the soil was only slightly ecotoxic. Maximum immobilisation inhibition of Daphnia magna reached 15%. Growth of Sinapis alba L. was predominantly stimulated (73%), and Desmodesmus subspicatus Chodat was exclusively stimulated, possibly due to soil alkalinity and fertiliser-related nutrients. The hypothesis of a higher contamination of urban botanical gardens compared to urban parks was confirmed. However, urban parks can face a greater risk of soil ecotoxicity, hypothetically due to decreased activity of soil organisms resulting from adverse soil conditions caused by active recreation. The results highlight the need for an increased focus on botanical and ornamental gardens when assessing and managing UGS as areas potentially more burdened with contamination.

Role of Toxicokinetic and Toxicodynamic Parameters in Explaining the Sensitivity of Zebrafish Larvae to Four Metals

Given the persistence and toxic potencies of metal contaminants in ecosystems, animals, and human beings, they are considered to be hazardous global pollutants. While the lethality of metal toxicities (e.g., LC₅₀) can significantly vary, even within the same species, the underlying mechanisms are less well-understood. In this study, we developed a subcellular two-compartment toxicokinetic-toxicodynamic (TK-TD) model for zebrafish larvae when exposed to four metals (cadmium, lead, copper, and zinc) to reveal whether differences in metal toxicity (LC₅₀ values) were dominated by the TK or TD processes. Results showed that the subcellular TK and TD parameters of the four metals were significantly different, and the bioconcentration factor (BCF) value of copper was higher than those of the other metals. We also found that the TD parameter internal threshold concentration (C_IT) was significantly positively correlated to the LC₅₀ values (R² = 0.7), suggesting a dominant role of TD processes in metal toxicity. Furthermore, the combined parameter C_IT/BCF for a metal-sensitive fraction (BCF_MSF), which linked exposure to effects through the TK-TD approach, explained up to 89% of the variation in toxicity to the four metals. The present study suggests that the observed variation in toxicity of these four metals was mainly determined by TD processes but that TK processes should not be ignored, especially for copper.

Ecotoxicity profile of heavily contaminated surface water of two rivers in Tunisia

Persistent organic and inorganic contaminants generated by industrial effluent wastes poses a threat to the maintenance of aquatic ecosystems and public health. The Khniss and Hamdoun rivers, located in the central-east of Tunisia, receive regularly domestic and textile wastewater load. The present study aimed to survey the water quality of these rivers using physicochemical, analytical and toxicological approaches. In the physicochemical analysis, the recorded levels of COD and TSS in both samples exceed the Tunisian standards. Using the analytical approach, several metals and some textile dyes were detected. Indeed, 17 metals were detected in both samples in varying concentrations, which do not exceed the Tunisian standards. The sources of metals pollution can be of natural and anthropogenic origin. Three textile disperse dyes were detected with high levels compared to other studies: the disperse orange 37 was detected in the Khniss river with a concentration of 6.438 μg/L and the disperse red 1 and the disperse yellow 3 were detected in the Hamdoun river with concentrations of 3.873 μg/L and 1895 μg/L, respectively. Textile activities were the major sources of disperse dyes. For both samples, acute and chronic ecotoxicity was observed in all the studied organisms, however, no genotoxic activity was detected. The presence of metals and textile disperse dyes could be associated with the ecotoxicological effects observed in the river waters, in particular due to the industrial activity, a fact that could deteriorate the ecosystem and therefore threaten the human health of the population living in the study areas. Combining chemical and biological approaches, allowed the detection of water ecotoxicity in testing organisms and the identification of possible contributors to the toxicity observed in these multi-stressed water reservoirs.

Making the Biotic Ligand Model kinetic, easier to develop, and more flexible for deriving water quality criteria

In aquatic environments, the ecological risks posed by metals are greatly affected by water chemistry, thereby creating challenges for water quality management. Biotic ligand models (BLMs) have become the most widely used tools to interpret and predict water chemistry effects. Traditional BLM development methods require a large number of toxicity tests and organisms, and model predictions are limited to certain toxicity statistics (e.g., 48-h median effective concentration, 48-h EC₅₀), to which the models were calibrated. To address these limitations, we propose a new method to develop BLMs by integrating them into the toxicokinetic-toxicodynamic (TK-TD) framework. Metal bioaccumulation was predicted from metal exposure and water chemistry using the BLM-type toxicokinetics, whilst metal toxicity was predicted from metal bioaccumulation using the toxicodynamics. Using the new method, we developed a kinetic BLM of cadmium for Daphnia magna with only six toxicity tests and 1540 daphnids; this represents a 60-80% reduction compared to the traditional methods. The model was validated in the presence of commercial dissolved organic matter (DOM) and in natural waters sampled from 12 lakes. The kinetic BLM was able to accurately simulate the protective effects of the commercial DOM by employing the Stockholm humic model, whilst the complexation capabilities of some natural DOM were overestimated. We further used the model to predict Cd EC₅₀ and no-effect concentrations for different waters, generating predictions close to the effect concentrations reported in the literature. Overall, our method requires fewer resources and presents an easier approach to develop BLMs; the kinetic BLM is more flexible and can serve as a useful tool for developing water quality criteria.

Evaluation of diffusive gradients in thin films (DGT) technique for speciation of trace metals in estuarine waters - A multimethodological approach

Understanding the potential bioavailability of trace metals (TM) in marine systems is of prime importance to implement adapted regulations and efficiently protect our coastal and estuarine waters. In this study Diffusive Gradients in Thin films (DGT) technique with two different pore size was used to evaluate the potentially bioavailable fractions (DGT-labile) of Cd, Co, Cu, Ni, Pb and Zn at various depths of a highly stratified estuary (the Krka River estuary, Croatia) both in winter and summer. DGT-labile concentrations were compared to (1) total dissolved concentrations, (2) concentrations of labile species measured by anodic stripping voltammetry (ASV-labile) for Cu and (3) concentrations derived by chemical speciation modelling. High correlation between dissolved and DGT-labile concentrations was found for all metals, except for Zn where contamination problems prevented reliable conclusions. Percentages of DGT-labile fractions over total dissolved concentrations were (AVG ± SD): 92 ± 3%, 64 ± 2%, 23 ± 5%, 61 ± 3% and 57 ± 6% for Cd, Pb, Cu, Ni and Co, respectively. No significant difference was found between trace metal concentrations measured with an open pore and restricted pore devices, implying the predominance of kinetically labile metal complexes smaller than 1 nm. For Cu, ASV-labile and DGT labile concentrations were highly correlated (0.97) with ASV-labile concentration being around 35% lower than that of the DGT-labile. Modelling of chemical speciation reliably predicted dynamic (free, inorganic and part of organic complexes) concentration of Cd, whereas dynamic concentrations of Cu and Pb were underestimated by 32% and 65%, respectively. In view of the relative simplicity of DGT devices, they are well suited for the monitoring effort of coastal waters, informing on potentially bioavailable concentrations of TM and thereby, helping to achieve good environmental status of coastal waters, as stipulated within the EU Water Framework Directive.

The vital function of humic acid with different molecular weight in controlling Cd and Pb bioavailability and toxicity to earthworm (Eisenia fetida) in soil

Humic acid (HA) plays vital roles in regulating the environmental behaviors of metals and thus their toxicity to biota. However, the inner relation between metal bioavailability to soil organisms and the presence of HA with different molecular weight (Mw) is not well documented. In this study, we separated HAs into four fractions with Mw range of 5-30k Da, and discussed their ability to alleviating the toxicity of Cd and Pb to earthworm. The bioaccumulation capacities (C_max) increased in order of: UF1<UF2<UF3<UF4, which is in line with the variations of bioavailable concentrations of Cd and Pb in soil. Variations of Mw and binding capacities of HA determine the accumulation behavior in soil solution. The unsatisfactory of biotic ligand model fitting and the differences in fractions of the total biotic ligand sites (f) in earthworm bound by Cd and Pb suggested that only free species of Cd could be considered as biological available to earthworm, while the Pb-HAs complexes have potential ability to interact with earthworm membrane. Antioxidant enzymes are effective biomarkers, and HA with lower Mw play more important roles in restricting the toxicity of soil Cd and Pb to earthworm. These results reveal the different mechanism for HA controlling metal bioavailability between Cd and Pb in soil environment.

Extension of biotic ligand model to account for the effects of pH and phosphate in accurate prediction of arsenate toxicity

Biotic ligand model (BLM) was extended to predict the toxicity of inorganic arsenate (iAs(V)) to the luminescent bacteria, Aliivibrio fischeri. As the pH increased from 5 to 9, the HAsO₄^2- form predominated more than the H₂AsO₄^- form did, and the EC₅₀[As]_T (50% effective iAs(V) concentration) decreased drastically from 3554 ± 393 to 39 ± 6 μM; thus, the HAsO₄^2- form was more toxic to A. fischeri than H₂AsO₄^-. As the HPO₄^2- activity increased from 0 to 0.44 mM, the EC₅₀{HAsO₄^2-} values (50% effective HAsO₄^2- activity) increased from 31 ± 6 to 859 ± 128 μM, indicating that the toxicity of iAs(V) decreased, owing to the competition caused by the structural similarity between iAs(V) and phosphate ions. However, activities of Ca²⁺, Mg²⁺, K⁺, SO₄^2-, NO₃^-, and HCO₃^- did not significantly affect the EC₅₀{HAsO₄^2-} values. The BLM was reconstructed to take into account the effects of pH and phosphate, and the conditional binding constants for H₂PO₄^-, HPO₄^2-, H₂AsO₄^-, and HAsO₄^2- to the active binding sites of A. fischeri were obtained; 3.424 for logK_XH2PO4, 4.588 for logK_XHPO4, 3.067 for logK_XH2AsO4, and 4.802 for logK_XHAsO4. The fraction of active binding sites occupied by iAs(V) to induce 50% toxicity (f_mix^50%) was found to be 0.616.

Effective Modeling Framework for Quantifying the Potential Impacts of Coexisting Anions on the Toxicity of Arsenate, Selenite, and Vanadate

Hardly any study has focused on the quantitative modeling of the toxicity of anionic metal(loid)s and their mixtures in the presence of potentially competing anions. Here, we designed a univariate experiment (420 treatments) to investigate the influence of various anions (phosphate, sulfate, carbonate, and OH^-) on the toxicity of single anionic metal(loid)s (arsenate, selenite, and vanadate) and a full factorial mixture experiment (196 treatments) to examine the interactions and toxicity of As-Se mixtures at 4 phosphate levels. Standard root elongation tests with wheat (Triticum aestivum) were performed. A modeling framework, resembling the biotic ligand model (BLM) for cationic metals, was developed, extended, and applied to explain anion competitions and mixture effects. Carbonate significantly alleviated the toxicity of all three metal(loid)s. The toxicity of As was significantly mitigated by phosphate, while V toxicity was significantly relieved by OH^-. The BLM-like model successfully explained more than 93% of the observed variance in toxicity. With the parameters derived from single-metal(loid) exposures, the developed BLM-toxic unit model reached an overall prediction performance of 78% in modeling the toxicity of As-Se mixtures at varying phosphate levels, validating the effectiveness of the model framework. It is concluded that by taking possible anion competitions and interactions into account, the BLM-type approaches can serve as promising tools for the risk assessment of single and mixed metal(loid)s contamination.

Development of a coupled model of quantitative ion character-activity relationships-biotic ligand model (QICARs-BLM) for predicting toxicity for data poor metals

The biotic ligand model (BLM) is proposed as a tool to quantitatively evaluate biological toxicity of metals considering both metal speciation and the influence of environmental conditions. The model assumes that biological sites bind to metals as biotic ligands (BLs) and obtains a series of BLM parameters including conditional binding constants (K). However, developing a BLM for each metal and biology takes a lot of experimentation. In the present study, relationships between metal ionic characters and BLM parameter K were respectively investigated for three terrestrial organisms. The results showed that ionization potential was the most strongly related to log K for barley (R2 = 0.845, p <  0.01) and earthworm (R2 = 0.881, p <  0.01), and electronegativity index most significantly related to log K for lettuce (R2 = 0.835, p <  0.01). Based on these relationships, a set of quantitative ion character-activity relationships (QICARs) were developed for predicting log K of metals. Then the QICAR were coupled with BLM and a novel QICAR-BLM was constructed. Finally, the QICAR-BLM was applied to predict EC50 of other unknown-toxicity metals for selected species, and compensate for the lack of toxicity data for a large number of metals in soil.

Using the Biotic Ligand Model framework to investigate binary metal interactions on the uptake of Ag, Cd, Cu, Ni, Pb and Zn in the freshwater snail Lymnaea stagnalis

There is growing interest in the development of mechanistically-based models, such as the Biotic Ligand Model (BLM), for assessing the environmental risk of metal mixtures. However, the derivation of such models requires insights into the mechanisms of multimetal interactions that are often lacking for aquatic organisms. In the present study, we investigated how binary mixtures of six metals (Ag, Cd, Cu, Ni, Pb and Zn) interact for uptake in the great pond snail Lymnaea stagnalis, a freshwater species particularly sensitive to metals in chronic exposure. For each metal, short-term (2-3 h) uptake experiments on juvenile snails were performed with the metal alone and in combination with a second metal, at concentrations encompassing the chronic toxicity concentration range. These experiments showed significant binary metal interactions for 7 out of 15 mixtures. Most interactions were inhibitory in nature, not reciprocal and caused by either Ag or Cu. They led to relative changes of uptake that did not exceed 50% within the range of metal chronic toxicity. The BLM proved to be successful at explaining most of the interactions, via competitive inhibition. This study is in support of using bioavailability-based models, such as the BLM, to model metal mixture interactions in L. stagnalis.

Effect of pH on Cr(III) accumulation, biomass production, and phenolic profile in 2 Salvinia species

We analyzed the effect of pH on Cr(III) accumulation, biomass production, and phenolic profile of Salvinia rotundifolia and Salvinia minima plants grown in the presence of increasing concentrations of CrCl₃ . Biomass accumulation, metal tolerance index, and photosynthetic pigment contents indicate that Salvinia rotundifolia seems to be more tolerant of Cr(III) than S. minima at different pHs. Increased metal accumulation by Salvinia species under increasing pH could be explained by changes of the protonation status of cell wall functional groups because both the highest and the lowest pH values used in the present study were outside of the levels at which Cr(III) species start to precipitate. The metal translocation factor indicates that in buffered conditions S. rotundifolia tend to retain more Cr(III) in lacinias than S. minima, probably through the involvement of insoluble phenolics. The results of the present study could be useful to the management of solution pH to maximize the removal of Cr(III) by aquatic plants. Environ Toxicol Chem 2019;38:167-176. © 2018 SETAC.

Extrapolation of imidacloprid toxicity between soils by exposing Folsomia candida in soil pore water

Soil properties like organic matter (OM) content show great variation, making it hard to predict the fate and effects of a chemical in different soils. We therefore addressed the question: can we remove the complexity of the soil matrix and yet accurately predict soil toxicity from porewater exposures? Folsomia candida was exposed to imidacloprid in natural (LUFA 2.2 [4.02% OM], Grassland [12.6% OM]) and artificial soils (OECD 5 [6.61% OM], OECD 10 [10.8% OM]), in pore water extracted from spiked LUFA 2.2 soil and in water. Toxicity decreased with increasing OM content except for Grassland soil, which had the highest OM content but the lowest clay content, suggesting a role of clay minerals in the binding of imidacloprid. Distribution coefficients for imidacloprid based on toxicity (Toxicity-K_d) were derived by comparing effect concentrations in LUFA 2.2 soil and in water. Using these Toxicity-K_ds to recalculate soil LC₅₀s/EC₅₀s to porewater concentrations, the differences in LC₅₀/EC₅₀s almost disappeared. The recalculated porewater LC₅₀s did not differ by more than a factor of 0.55-1.43 from the LC₅₀ obtained upon water exposure. This similarity suggests that the toxicity in the soil is dependent on porewater concentrations and can be obtained from water exposure. The porewater test and the corresponding "pore-water extrapolation concept" developed in this study may be used to predict the toxicity of chemicals in the soil and extrapolate among different soils.

Influence of soil porewater properties on the fate and toxicity of silver nanoparticles to Caenorhabditis elegans

Engineered nanoparticles (NPs) entering the environment are subject to various transformations that in turn influence how particles are presented to, and taken up by, organisms. To understand the effect of soil properties on the toxicity of nanosilver to Caenorhabditis elegans, toxicity assays were performed in porewater extracts from natural soils with varying organic matter content and pH using 3-8 nm unfunctionalized silver (Ag 3-8Unf), 52-nm polyvinylpyrrolidone (PVP)-coated Ag NPs (Ag 52PVP), and AgNO₃ as ionic Ag. Effects on NP agglomeration and stability were investigated using ultraviolet-visible (UV-vis) spectroscopy and asymmetric flow field-flow fractionation (AF4); Ag⁺ showed greater overall toxicity than nanosilver, with little difference between the NP types. Increasing soil organic matter content significantly decreased the toxicity of Ag 3-8Unf, whereas it increased that of AgNO₃ . The toxicity of all Ag treatments significantly decreased with increasing porewater pH. Dissolution of both NPs in the porewater extracts was too low to have contributed to their observed toxic effects. The UV-vis spectroscopy revealed low levels of agglomeration/aggregation independent of soil properties for Ag 3-8Unf, whereas higher organic matter as well as low pH appeared to stabilize Ag 52PVP. Overall, both soil organic matter content and pH affected NP fate as well as toxicity to C. elegans; however, there appears to be no clear connection between the measured particle characteristics and their effect. Environ Toxicol Chem 2018;37:2609-2618. © 2018 SETAC.

Sensitivity of the glochidia (larvae) of freshwater mussels (Bivalvia: Unionida: Hyriidae) to cadmium, cobalt, copper, lead, nickel and zinc: Differences between metals, species and exposure time

Freshwater mussels (Bivalvia: Unionida) are among the most threatened freshwater faunal groups worldwide. Metal contamination is one threat that has been linked to declining mussel population distribution and abundance. This study determined the sensitivity (valve closure) of the glochidia (larvae) of six species of Australian freshwater mussels to cadmium (Cd), cobalt (Co), copper (Cu), lead (Pb), nickel (Ni) and zinc (Zn), key metal contaminants impacting urbanized coastal rivers in south-eastern Australia (home to ~50% of the population), in a soft reconstituted freshwater (hardness 42mgCaCO₃L^-1; alkalinity 22mgCaCO₃L^-1 and pH7.0) over 72h. The sensitivity of each mussel species to each metal increased 2.5-fold with increasing exposure time from 24 to 72h. The most sensitive mussel species (Cucumerunio novaehollandiae), across all metals and exposure times, was ~60% more sensitive than the least sensitive species (Velesunio ambiguus). The relative sensitivity of glochidia to the six selected metals, across all mussel species and exposure times, was: Cu>Cd>Pb>Co=Ni>Zn. Glochidia were most sensitive to Cu and least sensitive to Zn. Quantitatively, the toxicity of Cu was 3-fold more than Cd, 8-fold more than Pb, 14-fold more than Co or Ni and 16-fold more than Zn. The cell surface binding affinities (conditional log K values) of Cd (range 6.65-6.94), Co (6.04-6.29), Cu (7.17-7.46), Ni (6.02-6.29), Pb (6.24-6.53) or Zn (5.96-6.23), pooled for all mussel species after 72h exposure, were positively related to metal sensitivity. The chronic no effect concentrations (NECs) of Cu, Ni and Zn were below (i.e. glochidia were more sensitive than) their national freshwater guideline values, indicating that freshwater mussels may not be adequately protected for these metals in urbanized coastal rivers within south-eastern Australia.

Development and validation of abiotic ligand model for nickel toxicity to wheat (Triticum aestivum)

A terrestrial biotic ligand model (t-BLM) was developed to predict nickel toxicity to wheat (Triticum aestivum) root elongation in hydroponic solutions. The competitive effects of five major cations (Ca²⁺, Mg²⁺, Na⁺, K⁺ and H⁺) on Ni toxicity were investigated and Mg²⁺was found to be a strong competitor, while H⁺ showed less competing effect. Besides free Ni²⁺, the toxicity induced by the species NiHCO₃⁺ was non-neglect able at pH>7 because NiHCO₃⁺ occupied a significant fraction of total Ni under such condition. Thus, a t-BLM including Ni²⁺, NiHCO₃⁺, Mg²⁺, and H⁺ could successfully predict the nickel toxicity to wheat root elongation and it performed better prediction than the conventional free ion activity model. In addition, the model was examined with two sets of independent experiments, which contained multiple cations and low-molecular-weight organic acids to mimic the rhizosphere condition. The developed t-BLM well predicted nickel toxicity in both experiments since it can account in both complexation and competition effects, suggesting its potential to be used in a complicated matrix like soil solution. This study provides direct evidence that the t-BLM is a reliable method for the risk assessment of nickel in terrestrial system.

Modeling acute toxicity of metal mixtures to wheat (Triticum aestivum L.) using the biotic ligand model-based toxic units method

The combined toxic effects of copper (Cu) and cobalt (Co) were predicted using the biotic ligand model (BLM) for different concentrations of magnesium (Mg²⁺) and pH levels, with parameters derived from Cu-only and Co-only toxicity data. The BLM-based toxic unit (TU) approach was used for prediction. Higher activities of Mg²⁺ linearly increased the EC₅₀ of Cu and Co, supporting the concept of competitive binding of Mg²⁺ and metal ions in toxic action. The effects of pH on Cu and Co toxicity were related not only to free Cu²⁺ and Co²⁺ activity, respectively, but also to inorganic metal complexes. Stability constants for the binding of Cu²⁺, CuHCO₃⁺, CuCO₃(aq), CuOH⁺, Mg²⁺, Co²⁺, CoHCO₃⁺ and Mg²⁺ with biotic ligands were logK_CuBL 5.87, \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\mathrm{log}\,{K}_{{{\rm{CuHCO}}}_{3}{\rm{BL}}}$$\end{document}logKCuHCO3BL 5.67, \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\mathrm{log}\,{K}_{{{\rm{CuCO}}}_{3}{\rm{BL}}}$$\end{document}logKCuCO3BL 5.44, logK_CuOHBL 5.07, logK_MgBL 2.93, logK_CoBL 4.72, \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\mathrm{log}\,{K}_{{{\rm{CoHCO}}}_{3}{\rm{BL}}}$$\end{document}logKCoHCO3BL 5.81 and logK_MgBL 3.84, respectively. The combinations of Cu and Co showed additive effects under different conditions. When compared with the FIAM-based TU model (root mean square error [RMSE = 16.31, R² = 0.84]), the BLM-based TU model fitted the observed effects better (RMSE = 6.70, R² = 0.97). The present study supports the BLM principles, which indicate that metal speciation and major cations competition need to be accounted for when predicting toxicity of both single metals and mixtures of metals.

Limitations of experiments performed in artificially made OECD standard soils for predicting cadmium, lead and zinc toxicity towards organisms living in natural soils

Development of comparative toxicity potentials of cationic metals in soils for applications in hazard ranking and toxic impact assessment is currently jeopardized by the availability of experimental effect data. To compensate for this deficiency, data retrieved from experiments carried out in standardized artificial soils, like OECD soils, could potentially be tapped as a source of effect data. It is, however, unknown whether such data are applicable to natural soils where the variability in pore water concentrations of dissolved base cations is large, and where mass transfer limitations of metal uptake can occur. Here, free ion activity models (FIAM) and empirical regression models (ERM, with pH as a predictor) were derived from total metal EC50 values (concentration with effects in 50% of individuals) using speciation for experiments performed in artificial OECD soils measuring ecotoxicological endpoints for terrestrial earthworms, potworms, and springtails. The models were validated by predicting total metal based EC50 values using backward speciation employing an independent set of natural soils with missing information about ionic composition of pore water, as retrieved from a literature review. ERMs performed better than FIAMs. Pearson's r for log₁₀-transformed total metal based EC50s values (ERM) ranged from 0.25 to 0.74, suggesting a general correlation between predicted and measured values. Yet, root-mean-square-error (RMSE) ranged from 0.16 to 0.87 and was either smaller or comparable with the variability of measured EC50 values, suggesting modest performance. This modest performance was mainly due to the omission of pore water concentrations of base cations during model development and their validation, as verified by comparisons with predictions of published terrestrial biotic ligand models. Thus, the usefulness of data from artificial OECD soils for global-scale assessment of terrestrial ecotoxic impacts of Cd, Pb and Zn in soils is limited due to relatively small variability of pore water concentrations of dissolved base cations in OECD soils, preventing their inclusion in development of predictive models. Our findings stress the importance of considering differences in ionic composition of soil pore water when characterizing terrestrial ecotoxicity of cationic metals in natural soils.

Parameterizing the binding properties of dissolved organic matter with default values skews the prediction of copper solution speciation and ecotoxicity in soil

Parameterizing speciation models by setting the percentage of dissolved organic matter (DOM) that is reactive (% r-DOM) toward metal cations at a single 65% default value is very common in predictive ecotoxicology. The authors tested this practice by comparing the free copper activity (pCu²⁺  = -log₁₀ [Cu²⁺ ]) measured in 55 soil sample solutions with pCu²⁺ predicted with the Windermere humic aqueous model (WHAM) parameterized by default. Predictions of Cu toxicity to soil organisms based on measured or predicted pCu²⁺ were also compared. Default WHAM parameterization substantially skewed the prediction of measured pCu²⁺ by up to 2.7 pCu²⁺ units (root mean square residual = 0.75-1.3) and subsequently the prediction of Cu toxicity for microbial functions, invertebrates, and plants by up to 36%, 45%, and 59% (root mean square residuals ≤9 %, 11%, and 17%), respectively. Reparametrizing WHAM by optimizing the 2 DOM binding properties (i.e., % r-DOM and the Cu complexation constant) within a physically realistic value range much improved the prediction of measured pCu²⁺ (root mean square residual = 0.14-0.25). Accordingly, this WHAM parameterization successfully predicted Cu toxicity for microbial functions, invertebrates, and plants (root mean square residual ≤3.4%, 4.4%, and 5.8%, respectively). Thus, it is essential to account for the real heterogeneity in DOM binding properties for relatively accurate prediction of Cu speciation in soil solution and Cu toxic effects on soil organisms. Environ Toxicol Chem 2017;36:898-905. © 2016 SETAC.

Influences of size-fractionated humic acids on arsenite and arsenate complexation and toxicity to Daphnia magna

The intrinsic physicochemical properties of dissolved organic matter (DOM) may affect the mobility and toxicity of arsenic in aquatic environments. In the present study, the humic acid (HA) was ultra-filtered into five fractions according to molecular weight, and their physicochemical properties were characterized. Complexation of HA fractions with arsenite and arsenate was first determined by differential pulse polarography (DPP). The influences of HA fractions on arsenic toxicity were then examined using Daphnia magna as a model organism. As(V) had a higher affinity with HA than As(III), and their complexation was dependent on the total acidity and fluorescence characteristics of DOM. We demonstrated that the acidity and fluorescence also better explained the As toxicity to daphnids than UV absorbance and hydraulic diameter. Arsenic speciation determined by DPP significantly affected the toxicity of arsenite and arsenate. The results extended the free-ion activity model application to the case of arsenic. The present study clearly indicated that DOM with different molecular weights has distinct physicochemical properties, and could influence the speciation and toxicity of As to different extent.

Oxidative stress responses and insights into the sensitivity of the earthworms Metaphire guillelmi and Eisenia fetida to soil cadmium

Soil toxicological tests are commonly performed using Eisenia fetida as the standard earthworm species, but it is tolerant to a wide range of pollutants. Therefore, the inclusion of susceptible species is crucial for the accurate estimation of soil contamination. In this study, we examined the sensitivity to soil cadmium (Cd) of anecic Metaphire guillelmi and epigeic E. fetida by measuring multiple indexes of oxidative stress. Using subcellular partitioning analysis, we further elucidated the inherent mechanism underlying the species-specific sensitivity of the two earthworm species. Among the battery of biochemical indexes, reactive oxygen species and protein carbonyl groups served as sensitive biomarkers. According to their respective response thresholds, M. guillelmi was more sensitive than E. fetida and they differed in their dose-response relationships. In E. fetida, the activities of three antioxidant enzymes, superoxide dismutase (SOD), catalase (CAT) and glutathione S-transferase (GST), exhibited a hormesis-like U-shaped dose-response relationship, while in M. guillelmi SOD, glutathione peroxidase (an analogue of CAT) and GST showed an inverted U-shaped relationship. The concentrations of Cd in the subcellular fractions and whole body of the earthworms well fit (R²>0.9) a saturation model versus bioavailable Cd concentrations determined by the diffusive gradients in thin films technique. Despite the lower accumulation capacity of M. guillelmi, the Cd-binding capacity (C_max) of its subcellular heat-stable protein fraction, the so-called biologically detoxified metal pool, was 2.7 times lower than that of E. fetida, whereas the Cd binding affinity (logK) of its heat-denatured protein fraction, i.e. the metal-sensitive fraction, was 3.0 times higher, which accounted for the high susceptibility of M. guillelmi to soil Cd. Our results suggest that because of their sensitivity, as exemplified by M. guillelmi, native earthworm species should be taken into account in soil risk assessments to avoid underestimation of the toxicity of various pollutants.

Mercury alters the bacterial community structure and diversity in soil even at concentrations lower than the guideline values

This study evaluated the effect of inorganic mercury (Hg) on bacterial community and diversity in different soils. Three soils-neutral, alkaline and acidic-were spiked with six different concentrations of Hg ranging from 0 to 200 mg kg^-1 and aged for 90 days. At the end of the ageing period, 18 samples from three different soils were investigated for bacterial community structure and soil physicochemical properties. Illumina MiSeq-based 16s ribosomal RNA (rRNA) amplicon sequencing revealed the alteration in the bacterial community between un-spiked control soils and Hg-spiked soils. Among the bacterial groups, Actinobacteria (22.65%) were the most abundant phyla in all samples followed by Proteobacteria (21.95%), Bacteroidetes (4.15%), Firmicutes (2.9%) and Acidobacteria (2.04%). However, the largest group showing increased abundance with higher Hg doses was the unclassified group (45.86%), followed by Proteobacteria. Mercury had a considerable negative impact on key soil functional bacteria such as ammonium oxidizers and nitrifiers. Canonical correspondence analysis (CCA) indicated that among the measured soil properties, Hg had a major influence on bacterial community structure. Furthermore, nonlinear regression analysis confirmed that Hg significantly decreased soil bacterial alpha diversity in lower organic carbon containing neutral and alkaline soils, whereas in acidic soil with higher organic carbon there was no significant correlation. EC₂₀ values obtained by a nonlinear regression analysis indicated that Hg significantly decreased soil bacterial diversity in concentrations lower than several guideline values.

Active biomonitoring for assessing effects of metal polluted sediment resuspension on gammarid amphipods during fluvial traffic

The resuspension of polluted sediments by boat traffic could release substantial amounts of metals to the water column, affecting at the same time their bioavailability. In order to characterize the impact of sediment resuspensions on biota, caged amphipods have been deployed on three different channelized watercourses in Northern France. Firstly, the biological responses of transplanted freshwater gammarid amphipods, Gammarus fossarum, described by trace metal accumulation, feeding and reproduction activities were quite similar for the three water courses despite the differences of metal contamination and navigability. Secondly, the concentrations of metals accumulated in gammarids never exceeded the contamination thresholds previously defined for Co, Cu, Cr and Zn. Values were in the same order of magnitude whatever the studied site despite: (i) large differences noticed in the sediment quality and (ii) some concentrations in the overlying waters exceeding the Environmental Quality Standards (EQS) defined by the Water Framework Directive. Conversely, Pb was highly bioaccumulated with values systematically exceeding the threshold value whatever the site. Therefore, the impact of navigation cannot be proved and the difference between the 3 monitoring periods is rather attributed to environmental variability, probably linked to the seasonality. Moreover, this study also confirms that organisms sampled from a local population in the vicinity of the three studied watercourses could be used as test organisms, leading to similar results than the ones obtained with reference gammarids initially used for developing all the biological responses. This would simplify and then promote the development of studies based on gammarid amphipod, G. fossarum, as bioindicators.

Sorption and pH determine the long-term partitioning of cadmium in natural soils

The bioavailability of metals in soil is a dynamic process. For a proper extrapolation to the field of laboratory studies on fate and effects, it is important to understand the dynamics of metal bioavailability and the way it is influenced by soil properties. The aim of this study was to assess the parallel (concurrent) effect of pH and aging time on the partitioning of cadmium in natural LUFA 2.2 soil. Cadmium nitrate-spiked pH-amended LUFA 2.2 soils were incubated under laboratory conditions for up to 30 weeks. Measured pHpw was lower after 3 weeks and decreased only slightly toward the end of the test. Cadmium concentrations in the pore water increased with time for all soil pH levels, while they decreased with increasing pH. Freundlich kf values ranged between 4.26 and 934 L kg(-1) (n = 0.79 to 1.36) and were highest at the highest pH tested (pH = 6.5). Multiple linear regression analysis, based on a soil ligand modeling approach, resulted in affinity constants of 2.61 for Ca(2+) (log KCa-SL) and 5.05 for H(+) (log KH-SL) for their binding to the active sites on the soil surface. The results showed that pH and aging time are two important factors which together affect cadmium partitioning and mobility in spiked natural soils.

Absorption and translocation of copper and arsenic in an aquatic macrophyte Myriophyllum alterniflorum DC. in oligotrophic and eutrophic conditions

The aim of this study is to evaluate copper and arsenic accumulation and translocation at a concentration of 100 μg/L of a submersed macrophyte Myriophyllum alterniflorum. The trophic level (eutrophic and oligotrophic conditions) of the medium was also considered. To achieve this goal, plants were incubated for 21 days in the presence of 100 μg/L of Cu or AsV. The heavy metal transfers from the contaminated medium to plants and into plant tissues was discussed in terms of the bioconcentration factor (BCF) and the translocation factor (TF). Malondialdehyde (MDA) content in tissues was analyzed in order to study the toxicity of these two contaminants. Our results show that copper was more accumulated in shoots, than roots, whereas the opposite trend was observed for arsenic. In addition, the two contaminants were more accumulated in oligotrophic than eutrophic medium. The BCF of copper in shoots was 1356 in oligotrophic condition, while that of arsenic was higher in roots about 620 in the same condition. The TF was less than 1 for arsenic, and higher than 1 for copper, indicating that watermilfoil restrains the translocation of arsenic to shoots, while it has a low capacity to control the translocation of an essential micronutrient like copper. An increase in MDA content was observed under Cu and As stress. On the basis of this experiment, M. alterniflorum has a higher accumulation potential of copper and arsenic, and therefore, it can be a good candidate for the phytofiltration of these two contaminants from water.

Ecotoxicity of sediments in rivers: Invertebrate community, toxicity bioassays and the toxic unit approach as complementary assessment tools

The determination of the real toxicity of sediments in aquatic ecosystems is challenging and necessary for an appropriate risk assessment. Different approaches have been developed and applied over the last several decades. Currently, the joint implementation of chemical, ecological and toxicological tools is recommended for an appropriate and successful toxicity risk assessment. We chose the combination of the toxic unit approach with acute pore water tests (Vibrio fischeri, Pseudokirchneriella subcapitata and Daphnia magna) and whole-sediment exposure tests (V. fischeri, Chironomus riparius), together with invertebrate community composition (multivariate analyses) to detect short and long-term responses of the organisms in four rivers of the Iberian Peninsula. High toxicity was detected in three sites (the downstream sites of the Llobregat and the Júcar, and the most upstream site of the Ebro). We identified organophosphate insecticides and metals as the main variables responsible for this toxicity, particularly in the whole-sediment tests. In particular, chlorpyrifos was mostly responsible for the toxicity (TUs) of D. magna, coinciding with the C. riparius mortality (long-term toxicity) in the mentioned sites, and copper was the main pollutant responsible for the short-term toxicity of P. subcapitata. The combination of the different approaches allowed us to detect ecotoxicological effects in organisms and identify the main contributors to the toxicity in these multi-stressed rivers.

Mercury Inhibits Soil Enzyme Activity in a Lower Concentration than the Guideline Value

Three soil types - neutral, alkaline and acidic were experimentally contaminated with nine different concentrations of inorganic mercury (0, 5, 10, 50, 100, 150, 200, 250, 300 mg/kg) to derive effective concentrations of mercury that exert toxicity on soil quality. Bioavailability of mercury in terms of water solubility was lower in acidic soil with higher organic carbon. Dehydrogenase enzyme activity and nitrification rate were chosen as indicators to assess soil quality. Inorganic mercury significantly inhibited (p < 0.001) microbial activities in the soils. The critical mercury contents (EC10) were found to be less than the available safe limits for inorganic mercury which demonstrated inadequacy of existing guideline values.

Biotic ligand modeling approach: Synthesis of the effect of major cations on the toxicity of metals to soil and aquatic organisms

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 Ca(2+) , Mg(2+) , 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.