Application of the biotic ligand model to predicting zinc toxicity to rainbow trout,fathead minnow,and Daphnia magna

The Biotic Ligand Model has been previously developed to explain and predict the effects of water chemistry on the toxicity of copper, silver, and cadmium. In this paper, we describe the development and application of a biotic ligand model for zinc (Zn BLM). The data used in the development of the Zn BLM includes acute zinc LC50 data for several aquatic organisms including rainbow trout, fathead minnow, and Daphnia magna. Important chemical effects were observed that influenced the measured zinc toxicity for these organisms including the effects of hardness and pH. A significant amount of the historical toxicity data for zinc includes concentrations that exceeded zinc solubility. These data exhibited very different responses to chemical adjustment than data that were within solubility limits. Toxicity data that were within solubility limits showed evidence of both zinc complexation, and zinc-proton competition and could be well described by a chemical equilibrium approach such as that used by the Zn BLM.     

Importance of Clean Techniques and Speciation in Assessing Water Quality for Metals

Trace metals in aquatic and soil systems exist in a number of different soluble and particulate forms that impact the effect of the metals on these ecosystems. Appropriate methods of sampling and analysis are required to accurately determine the low concentrations present. Although assessment of metals in many regulatory programs is based on data for total metal concentrations, such values rarely correlate with effects. Consequently, other means are needed for the prediction of risk. Bioavailability of metals depends on their speciation, whose importance was first established for copper in aquatic systems where the toxicity of metals is related to the activity of the free metal ion. Small concentrations of natural organic matter strongly complex metals ameliorating toxicity. Several electroanalytical techniques are available that allow the assessment of metal species. Recently, a modeling approach, the Biotic Ligand Model (BLM), has been applied to the prediction of acute toxicity. The model accounts for the effects of natural organic matter, pH, and hardness and is able to predict toxicity over several orders of magnitude of soluble metal concentration using only easily determined site parameters. Total metal concentrations in sediment cover several orders of magnitude with no distinction of sediments that cause effects and those that do not except at low total metal concentrations. Relating the metal concentration to the concentrations of sulfide and organic matter binding sites enables the sediments containing higher concentrations of metals to be divided into those that do and those that do not have adverse effects. It is essential that metal speciation be considered to realistically evaluate the potential of metals to pose risk.     

The biotic ligand model and a cellular approach to class B metal aquatic toxicity

The biotic ligand model (BLM) and a cellular molecular mechanism approach represent two approaches to the correlation of metal speciation with observed toxicity to aquatic organisms. The two approaches are examined in some detail with particular reference to class B, or soft metals. Kinetic arguments are presented to suggest situations that can arise where the BLM criterion of equilibrium between all metal species in the bulk solution and the biotic ligand may not be satisfied and what might the consequences be to BLM predictive capability. Molecular mechanisms of toxicity are discussed in terms of how a class B metal might enter a cell, how it is distributed in a cell, and how the cell might respond to the unwanted metal. Specific examples are given for copper as an organism trace essential metal, which is toxic in excess, and for silver, a non-essential metal. As class B metals all bind strongly to sulfur, regulation of these metals requires that all S(II-) species be accounted for in aquatic systems, even under oxic conditions.     

A new model for predicting time course toxicity of heavy metals based on Biotic Ligand Model (BLM)

A new model for predicting time course toxicity of heavy metals was developed by extending the effective ratio of biotic ligand binding with toxic heavy metals to the total biotic ligand for 50% of test organisms (f₅₀) derived by the Biotic Ligand Model (BLM). BLM has been well-known as a useful model for prediction of heavy metal toxicity. BLM can consider the effect of exposure conditions such as pH and Ca²⁺ on heavy metal toxicity. In addition to the exposure conditions, heavy metal toxicity is strongly dependent on exposure time. In this study, BLM is extended to predict time dependency of heavy metal toxicity by connecting with the concept of primary reaction. The model developed in this study also generates the estimation of the 50% effect concentration (EC₅₀) for toxicologically unknown organisms and heavy metals. Two toxicological and kinetic constants, f_50,0 and k, were derived from the initial value of f₅₀ (f_50,0) and a time constant (k) independent of time. The model developed in this study enables us to acquire information on the toxicity of heavy metals such as Cu, Cd and Co easily.     

Modelling Bioaccumulation and Toxicity of Metal Mixtures

Bioaccumulation of metals in mixtures may demonstrate competitive, anticompetitive, or non-competitive inhibition, as well as various combinations of these and/or enhancement of metal uptake. These can be distinguished by plotting (metal in water)/(metal in tissue) against metal in water and comparison to equivalent plots for single-metal exposure. For the special case of pure competitive inhibition where only one site of uptake is involved, inhibition of metal accumulation in any metal mixture can be predicted from bioaccumulation of the metals when present singly. This is consistent with the commonly used Biotic Ligand Model (BLM) but does not explain bioaccumulation of metals in Hyalella azteca. Options for modelling toxicity of metal mixtures include concentration or response addition based on metal concentrations in either water or tissues. If the site of toxic action is on the surface of the organism, if this is the same as the site of metal interaction for bioaccumulation, if there is only one such type of site, and if metal bioaccumulation interactions are purely competitive (as in the BLM), then metal toxicity should be concentration additive and predictable from metal concentrations in either water or tissues. This is the simplest toxicity interaction to model but represents only one of many possibilities. The BLM should, therefore, be used with caution when attempting to model metal interactions, and other possibilities must also be considered.     

Sodium turnover rate determines sensitivity to acute copper and silver exposure in freshwater animals

The mechanisms of acute copper and silver toxicity in freshwater organisms appear similar. Both result in inhibition of branchial sodium (and chloride) uptake initiating a cascade of effects leading to mortality. The inhibition of the branchial Na/K-ATPase in the basolateral membrane is generally accepted as the key component responsible for the reduced sodium uptake. We propose that branchial carbonic anhydrase and the apical sodium channel may also be important targets for both copper and silver exposure. Several attempts have been made to predict metal sensitivity. A prominent example is the geochemical-biotic ligand model. The geochemical-biotic ligand modeling approach has been successful in explaining variations in tolerance to metal exposure for specific groups of animals exposed at different water chemistries. This approach, however, cannot explain the large observed variation in tolerance to these metals amongst different groups of freshwater animals (i.e. Daphnia vs. fish). Based on the detailed knowledge of physiological responses to acute metal exposure, the present review offers an explanation for the observed variation in tolerance. Smaller animals are more sensitive than large animals because they exhibit higher sodium turnover rates. The same relative inhibition of sodium uptake results in faster depletion of internal sodium in animals with higher sodium turnover. We present a way to improve predictions of acute metal sensitivity, noting that sodium turnover rate is the key predictor for variation in acute copper and silver toxicity amongst groups of freshwater animals. We suggest that the presented sodium turnover model is used in conjunction with the Biotic Ligand Model for risk management decisions.     

Extension of the biotic ligand model of acute toxicity to a physiologically-based model of the survival time of rainbow trout (Oncorhynchus mykiss) exposed to silver

Chemical speciation controls the bioavailability and toxicity of metals in aquatic systems and regulatory agencies are recognizing this as they develop updated water quality criteria (WQC) for metals. The factors that affect bioavailability may be quantitatively evaluated with the biotic ligand model (BLM). Within the context of the BLM framework, the 'biotic ligand' is the site where metal binding results in the manifestation of a toxic effect. While the BLM does account for the speciation and complexation of dissolved metal in solution, and competition among the free metal ion and other cations for binding sites at the biotic ligand, it does not explicitly consider either the physiological effects of metals on aquatic organisms, or the direct effect of water chemistry parameters such as pH, Ca(2+)and Na(+) on the physiological state of the organism. Here, a physiologically-based model of survival time is described. In addition to incorporating the effects of water chemistry on metal availability to the organism, via the BLM, it also considers the interaction of water chemistry on the physiological condition of the organism, independent of its effect on metal availability. At the same time it explicitly considers the degree of interaction of these factors with the organism and how this affects the rate at which cumulative damage occurs. An example application of the model to toxicity data for rainbow trout exposed to silver is presented to illustrate how this framework may be used to predict survival time for alternative exposure durations. The sodium balance model (SBM) that is described herein, a specific application of a more generic ion balance model (IBM) framework, adds a new physiological dimension to the previously developed BLM. As such it also necessarily adds another layer of complexity to this already useful predictive framework. While the demonstrated capability of the SBM to predict effects in relation to exposure duration is a useful feature of this mechanistically-based framework, it is envisioned that, with suitable refinements, it may also have utility in other areas of toxicological and regulatory interest. Such areas include the analysis of time variable exposure conditions, residual after-effects of exposure to metals, acclimation, chronic toxicity and species and genus sensitivity. Each of these is of potential utility to longer-term ongoing efforts to develop and refine WQC for metals.     

Effects of Chronic Waterborne and Dietary Metal Exposures on Gill Metal-Binding: Implications for the Biotic Ligand Model

The biotic ligand modeling (BLM) approach has gained recent widespread interest among the scientific and regulatory communities because of its potential for developing ambient water quality criteria (AWQC), which are site-specific, and in performing aquatic risk assessment for metals. Currently, BLMs are used for predicting acute toxicity (96?h LC50 for fish) in any defined water chemistry. The conceptual framework of the BLM has a strong physiological basis because it considers that toxicity of metals occurs due to the binding of free metal ions at the physiologically active sites of action (biotic ligand, e.g., fish gill) on the aquatic organism, which can be characterized by conditional binding constants (log K) and densities (B_max). At present, these models assume that only water chemistry variables such as competing cations (e.g., Na⁺, Ca²⁺, Mg²⁺, and H⁺), inorganic ligands (e.g., hydroxides, chlorides, carbonates), and organic ligands (dissolved organic matter) can influence the bioavailability of free metal ions and thereby the acute toxicity of metals. Current BLMs do not consider the effects of chronic history of the fish in modifying gill-metal binding characteristics and acute toxicity. Here, for Cu, Cd, and Zn, we review a number of recent studies on the rainbow trout that describe significant modifying effects of chronic acclimation to waterborne factors (hardness and chronic metal exposure) and dietary composition (metal and essential ion content) on gill metalbinding characteristics (on both log K and B_max) and on acute toxicity. We conclude that the properties of gill-metal interaction and toxicological sensitivity appear to be dynamic rather than fixed, with important implications for further development of both acute and chronic BLMs. Now that the initial framework of the BLM has been established, future research needs a more integrative approach with additional emphasis on the dynamic properties of the biotic ligand to make it a successful tool for ecological risk assessment of metals in the natural environment.     

Physiological effects of chronic silver exposure in Daphnia magna

Daphnia magna were exposed to a total concentration of 5.0+/-0.04 microg Ag/l, added as AgNO(3) (dissolved concentration, as defined by 0.45 microm filtration = 2.0+/-0.01 microg Ag/l) in moderately hard synthetic water under static conditions (total organic carbon = 4.80+/-1.32 mg/l) with daily feeding and water renewal, for 21 days. There was no mortality in control daphnids and 20% mortality in silver-exposed animals. Silver exposure caused a small but significant reduction of reproductive performance manifested as a 13.7% decrease in the number of neonates produced per adult per reproduction day over the 21-day exposure. However, silver exposed daphnids also exhibited a much more marked ionoregulatory disturbance, which was characterized by a 65% decrease in whole body Na(+) concentration, and an 81% inhibition of unidirectional whole body Na(+) uptake. Previous work on the acute toxicity of Ag(+) to daphnids has shown that Na(+) uptake inhibition is directly related to inhibition of Na(+),K(+)-ATPase activity. Therefore, we suggest that the Na(+) uptake inhibition seen in response to chronic silver exposure was explained by an inhibition of the Na(+) channels at the apical 'gill' membrane, since a 60% increase in whole body Na(+),K(+)-ATPase activity was observed in the chronically silver-exposed daphnids. Our findings demonstrate that, in broad view, the key mechanism involved in chronic silver toxicity in D. magna, the most acutely sensitive freshwater organism tested up to now, resembles that described for acute toxicity-i.e. ionoregulatory disturbance associated with inhibition of active Na(+) uptake, though the fine details may differ. Our results provide encouragement for future extension of the current acute version of the Biotic Ligand Model (BLM) to one that predicts chronic silver toxicity for environmental regulation and risk assessment. The results strongly suggest that Na(+) uptake inhibition is the best endpoint to determine sensitivity to both acute and chronic toxicity in the scope of future versions of the BLM for silver.     

Models of Cadmium Accumulation and Toxicity to Hyalella azteca during 7- and 28-Day Exposures

The inhibition of Cd accumulation by Ca in the amphipod Hyalella azteca in short-term (7-d) exposures appears to follow anti-competitive, rather than competitive, inhibition. Increasing Ca reduces Cd accumulation more at high than at low Cd concentrations. Cadmium accumulation and toxicity in chronic exposures can be predicted using the 7-d model to which the effects of acclimation, Cd inhibition of acclimation, and growth dilution are added. The resultant model is complex and species-specific, making it unwieldy for direct application in water quality guideline or criteria development. However, it does demonstrate that a mechanistic explanation of the relationship between short- and long-term accumulation and toxicity is possible, as well as suggest why the acute-to-chronic ratio changes with water chemistry. It is not, therefore, appropriate to estimate chronic Cd toxicity to H. azteca from acute toxicity assuming a constant acute-to-chronic ratio. The standard Biotic Ligand Model (BLM) can also be fit to the chronic bioaccumulation and toxicity data. This may be a more practical approach to guideline or criteria development, provided it is understood that this is an empirical fit of the model and that the underlying mechanisms are far more complex than those invoked in the standard BLM.     

Development of an electrostatic model predicting copper toxicity to plants

The focus of the present study was to investigate the mechanisms for the alleviation of Cu toxicity in plants by coexistent cations (e.g. Al(3+), Mn(2+), Ca(2+), Mg(2+), H(+), Na(+), and K(+)) and the development of an electrostatic model to predict 50% effect activities (EA50s) accurately. The alleviation of Cu(2+) toxicity was evaluated in several plants in terms of (i) the electrical potential at the outer surface of the plasma membrane (PM) (Ψ(0)(°)) and (ii) competition between cations for sites at the PM involved in the uptake or toxicity of Cu(2+), the latter of which is invoked by the Biotic Ligand Model (BLM) as the sole explanation for the alleviation of toxicity. The addition of coexistent cations into the bulk-phase medium reduces the negativity of Ψ(0)(°) and hence decreases the activity of Cu(2+) at the PM surface. Our analyses suggest that the alleviation of toxicity results primarily from electrostatic effects (i.e. changes in both the Cu(2+) activity at the PM surface and the electrical driving force across the PM), and that BLM-type competitive effects may be of lesser importance in plants. Although this does not exclude the possibility of competition, the data highlight the importance of electrostatic effects. An electrostatic model was developed to predict Cu(2+) toxicity thresholds (EA50s), and the quality of its predictive capacity suggests its potential utility in risk assessment of copper in natural waters and soils.     

The biotic ligand model: a historical overview

During recent years, the biotic ligand model (BLM) has been proposed as a tool to evaluate quantitatively the manner in which water chemistry affects the speciation and biological availability of metals in aquatic systems. This is an important consideration because it is the bioavailability and bioreactivity of metals that control their potential to cause adverse effects. The BLM approach has gained widespread interest amongst the scientific, regulated and regulatory communities because of its potential for use in developing water quality criteria (WQC) and in performing aquatic risk assessments for metals. Specifically, the BLM does this in a way that considers the important influences of site-specific water quality. This journal issue includes papers that describe recent advances with regard to the development of the BLM approach. Here, the current status of the BLM development effort is described in the context of the longer-term history of advances in the understanding of metal interactions in the environment upon which the BLM is based. Early developments in the aquatic chemistry of metals, the physiology of aquatic organisms and aquatic toxicology are reviewed first, and the degree to which each of these disciplines influenced the development of water quality regulations is discussed. The early scientific advances that took place in each of these fields were not well coordinated, making it difficult for regulatory authorities to take full advantage of the potential utility of what had been learned. However, this has now changed, with the BLM serving as a useful interface amongst these scientific disciplines, and within the regulatory arena as well. The more recent events that have led to the present situation are reviewed, and consideration is given to some of the future needs and developments related to the BLM that are envisioned. The research results that are described in the papers found in this journal issue represent a distinct milestone in the ongoing evolution of the BLM approach and, more generally, of approaches to performing ecological assessments for metals in aquatic systems. These papers also establish a benchmark to which future scientific and regulatory developments can be compared. Finally, they demonstrate the importance and usefulness of the concept of bioavailability and of evaluative tools such as the BLM.     

A novel approach for predicting the uptake and toxicity of metallic and metalloid ions

Electrostatic nature of plant plasma membrane (PM) plays significant roles in the ion uptake and toxicity. Electrical potential at the PM exterior surface (ψ₀^o) influences ion distribution at the PM exterior surface, and the depolarization of ψ₀^o negativity increases the electrical driving force for cation transport, but decreases the driving force for anion transport across the PMs. Assessing environmental risks of toxic ions has been a difficult task because the ion concentration (activity) in medium is not directly corrected to its potential effects. Medium characteristics like the content of major cations have important influences on the bioavailability and toxicity of ions in natural waters and soils. Models such as the Free Ion Activity Model (FIAM) and the Biotic Ligand Model (BLM), as usually employed, neglect the ψ₀^o and hence often lead to false conclusions about interaction mechanisms between toxic ions and major cations for biology. The neglect of ψ₀^o is not inconsistent with its importance, and possibly reflects the difficulty in the measurement of ψ₀^o. Based on the dual effects of the ψ₀^o, electrostatic models were developed to better predict the uptake and toxicity of metallic and metalloid ions. These results suggest that the electrostatic models provides a more robust mechanistic framework to assess metal(loid) ecotoxicity and predict critical metal(loid) concentrations linked to a biological effect, indicating its potential utility in risk assessment of metal(loid)s in water and terrestrial ecosystems.Key words: electrostatic models, plasma membrane, surface electric potential, ion uptake, toxicity, risk assessment     

Effects of Zn-complexes on zinc uptake by wheat (Triticum aestivum) roots: a comprehensive consideration of physical, chemical and biological processes on biouptake

Commonly used equilibrium models for metal biouptake, such as the Free Ion Activity Model (FIAM) and the Biotic Ligand Model (BLM), are limited to the cases in which mass diffusive transport is not the flux-determining step. In analyses of metal biouptake from a complexing medium, all the physical (diffusion), chemical (dissociation kinetics of metal complexes), and biological (transport and internalization) processes have to be taken into account. A short-term zinc uptake by wheat (Triticum aestivum) roots from culture solutions in the absence or presence of synthetic ligands (NTA, nitrilotriacetic acid, and EDTA, ethylenediaminetetraacetate) was studied. At the same free Zn²⁺ concentration $\left( {\left\{ {{\text{Zn}}^{{\text{2 + }}} } \right\} = 1.5 \times 10^{ - 8} {\text{M}}} \right)$ , the uptake of Zn was significantly enhanced in the presence of ligands and was larger when Zn complexes have a quicker dissociation rate. The diffusional fluxes in the same culture solution were determined with the differential pulse anodic stripping voltammetry (DPASV) method, and the diffusive gels in thin film (DGT) technique. The contribution from Zn complexes to root Zn uptake was in better agreement with the degree of Zn complex labilities measured with DPASV than with DGT. The diffusion of free Zn²⁺ ion to the root surface is a rate-controlling step for Zinc biouptake when the free Zn²⁺ concentration is low. Based on the comprehensive consideration of the diffusion and dissociation processes of Zn²⁺ ion and Zn complexes and the existence of high- and low-affinity uptake systems in the root surface, a two-pathway Zn uptake model was developed to predict the resulting Zn uptake fluxes into roots in the overall range of exposure.     

Metal bioavailability to phytoplankton--applicability of the biotic ligand model

To elicit a biological response from a target organism and/or to accumulate within this organism, a metal must first interact with a cell membrane. For hydrophilic metal species, this interaction with the cell surface can be represented in terms of the formation of M-X-cell surface complexes, e.g. M(z+)+(-)X-cell<-->M-X-cell, where -X-cell is a cellular ligand present at the cell surface. According to the free-ion model, or its derivative the biotic ligand model (BLM), the biological response elicited by the metal will be proportional to [M-X-cell]. In this paper, using freshwater algae as our test species, we examine some of the key assumptions that underlie the BLM, namely that metal internalization is slow relative to the other steps involved in metal uptake (i.e. the M-X-cell complex is in equilibrium with metal species in solution), that internalization occurs via cation transport, and that internalization must occur for toxicity to appear. Recent experiments with freshwater algae are described, demonstrating anomalously high metal accumulation and/or toxicity in the presence of a common low molecular weight metabolite (alanine), or in the presence of an assimilable inorganic anion (thiosulfate). The possible implications of these findings for the application of the BLM to higher organisms are discussed.     

Freshwater ecotoxicity characterization factors for aluminum

Purpose

Aluminum (Al) is an abundant, non-essential element with complex geochemistry and aquatic toxicity. Considering its complex environmental behavior is critical for providing a reasonable estimate of its potential freshwater aquatic ecotoxicity in the context of Life Cycle Impact Assessment (LCIA).

Methods

Al characterization factors (CFs) are calculated using the following: (1) USEtox^? model version 2.1 for environmental fate, (2) MINEQL+ to estimate the distribution of Al between the solid phase precipitate and total dissolved Al, (3) WHAM 7 for Al speciation within the total dissolved phase, and (4) Biotic Ligand Model (BLM) and Free Ion Activity Model (FIAM) for ecotoxicity estimation for seven freshwater archetypes and default landscape properties for the European continent. The sensitivity of the CFs to aquatic chemistry parameters is calculated. New CFs are compared with Dong et al. (Chemosphere 112:26–33, 2014) and default CF calculated by USEtox 2.1.

Results and discussion

Al CFs vary over 5 orders of magnitude between the seven archetypes, with an arithmetic average CF_ave of 0.04 eq 1,4-DCB (recommended for use), geometric mean CF_geo of 0.0014 eq 1,4-DCB, and weighted average CF_wt of 0.026 eq 1,4-DCB. These values are lower (less toxic) than those for Cu, Ni, Zn, and Pb (with one exception). The effect factor (EF) contributed most to this variability followed by the bioavailability factor (BF), varying over 8 and 4 orders of magnitude, respectively. These revised CFs are 2–6 orders of magnitude lower than those presented by Dong et al. (Chemosphere 112:26–33, 2014) mainly because of consideration of Al precipitation.

Conclusions

Freshwater archetype-specific Al CFs for freshwater ecotoxicity that address the effect of Al speciation on bioavailability (BF) and ecotoxicity (EF) have been calculated, and a CF of 0.04 eq 1,4-DCB is recommended for use in generic LCA. For site-specific LCA, the choice of water chemistry and, in particular, pH, and consideration of metal precipitation could significantly influence results.

Practical implications

Incorporating estimates of metal speciation and its effect on aquatic toxicity is essential when conducting LCIA. Along with metal speciation estimates, the values derived from the definition of water chemistry parameters must also be included into LCIA. For site-generic assessments, we recommend using the arithmetic average of metal CFs. We also recommend using FIAM as a suitable alternative to BLM to estimate EF if the latter is not available. Consideration of metal speciation is essential for providing more realistic estimates of Al freshwater ecotoxicity in the context of LCIA.

     

Derivation of a toxicity-based model to predict how water chemistry influences silver toxicity to invertebrates

The effect of altering water chemistry on acute silver toxicity to three invertebrate species, two Daphnids, Daphnia magna and Daphnia pulex, as well as an amphipod Gammarus pulex was assessed. In addition, the physiological basis of Ag(I) toxicity to G. pulex was examined. Daphnia magna and D. pulex were more sensitive than G. pulex and 48 h LC(50) values in synthetic ion poor water were 0.47, 0.65 and 2.1 microg Ag(I) l(-1), respectively. Increasing water [Cl(-)] reduced Ag(I) toxicity in all species, and increasing water [Ca(2+)] from 50 to 1,500 microM reduced Ag(I) toxicity in G. pulex. Whole body Na(+) content, but not K(+) or Ca(2+) was significantly reduced in G. pulex exposed to 6 microg Ag(I) l(-1) for 24 h, but there was no inhibition of whole body Na(+)/K(+)-ATPase activity. Both increasing water [Cl(-)] and [Ca(2+)] reduced this Ag(I)-induced Na(+) loss. For D. magna, the presence of 10 mg l(-1) humic acid or 0.5 microM 3-mercaptoproprionic acid (3-MPA) increased the 48 h LC(50) values by 5.9 and 58.5-fold, respectively, and for D. pulex the presence of 1 microM thiosulfate increased the 48 h LC(50) value by four-fold. The D. magna toxicity data generated from this study were used to derive a Daphnia biotic ligand model (BLM). Analysis of the measured LC(50) values vs. the predicted LC(50) values for toxicity data from the present and published results where water Cl(-), Ca(2+), Na(+) or humic acid were varied showed that 91% of the measured toxicity data fell within a factor of two of the predicted LC(50) values. However, the daphnid BLM could not accurately predict G. pulex toxicity. Additionally, the Daphnia BLM was under-protective in the presence of the organic thiols 3-MPA or thiosulphate and predicted an increase in the LC(50) value of 114- and 74-fold, respectively. The Daphnia toxicity based BLM derived from the present data set is successful in predicting Daphnia toxicity in laboratory data sets in the absence of sulfur containing compounds, but shows its limitations when applied to waters containing organic thiols or thiosulphate.     

Copper-Impaired Chemosensory Function and Behavior in Aquatic Animals

Chemosensation is one of the oldest and most important sensory modalities utilized by aquatic animals to provide information about the location of predators, location of prey, sexual status of potential mates, genetic relatedness of kin, and migratory routes, among many other essential processes. The impressive sophistication of chemical communication systems among aquatic animals probably evolved because of the selective pressures exerted by water as a “universal solvent.” Impairment of chemosensation by toxicants at the molecular or cellular level can potentially lead to major perturbations at higher levels of biological organization. We have examined the consequences of metal-impaired chemosensory function in a range of aquatic animals that represents several levels of a typical aquatic ecosystem. In each case, low, environmentally relevant metal concentrations were sufficient to cause chemosensory dysfunction. Because the underlying molecular signal transduction machinery of chemosensory systems demonstrates a high degree of phylogenetic conservation, we speculate that metal-impaired chemosensation among phylogenetically disparate animal groups probably results from a common mechanism of impairment. We propose developing a chronic chemosensory-based biotic ligand model (BLM) that maintains the advantages of the current BLM approach, while simultaneously overcoming known difficulties of the current gill-based approach and increasing the ecological relevance of current BLM predictions.     

土壤重金属生物毒性研究进展

世界范围内土壤重金属污染不断加重,由污染所带来的问题以及如何治理污染已经受到人们越来越多的关注.土壤重金属将对土壤生物产生影响,而土壤生物在重金属的胁迫下也会产生不同的响应.综述了国内外近年来土壤重金属生物毒性的研究进展,介绍了土壤重金属污染对陆地生态系统中植物、动物和微生物生长的影响;土壤重金属生物毒性的影响因素;土壤重金属生物毒性的研究方法;土壤重金属生物毒性的预测模型,最后提出了问题和展望.