Biotic Ligand Research Articles

Exposure to waterborne Cu inhibits cutaneous Na+ uptake in post-hatch larval rainbow trout (Oncorhynchus mykiss)

In freshwater rainbow trout (Oncorhynchus mykiss), two common responses to acute waterborne copper (Cu) exposure are reductions in ammonia excretion and Na+ uptake at the gills, with the latter representing the likely lethal mechanism of action for Cu in adult fish. Larval fish, however, lack a functional gill following hatch and rely predominantly on cutaneous exchange, yet represent the most Cu-sensitive life stage. It is not known if Cu toxicity in larval fish occurs via the skin or gills. The present study utilized divided chambers to assess cutaneous and branchial Cu toxicity over larval development, using disruptions in ammonia excretion (Jamm) and Na+ uptake (JinNa) as toxicological endpoints. Early in development (early; 3 days post-hatch; dph), approximately 95% of Jamm and 78% of JinNa occurred cutaneously, while in the late developmental stage (late; 25dph), the gills were the dominant site of exchange (83 and 87% of Jamm and JinNa, respectively). Exposure to 50μg/l Cu led to a 49% inhibition of Jamm in the late developmental stage only, while in the early and middle developmental (mid; 17dph) stages, Cu had no effect on Jamm. JinNa, however, was significantly inhibited by Cu exposure at the early (53% reduction) and late (47% reduction) stages. Inhibition at the early stage of development was mediated by a reduction in cutaneous uptake, representing the first evidence of cutaneous metal toxicity in an intact aquatic organism. The inhibitions of both Jamm and JinNa in the late developmental stage occurred via a reduction in branchial exchange only. The differential responses of the skin and gills to Cu exposure suggest that the mechanisms of Jamm and JinNa and/or Cu toxicity differ between these tissues. Exposure to 20μg/l Cu revealed that Jamm is the more Cu-sensitive process. The results presented here have important implications in predicting metal toxicity in larval fish. The Biotic Ligand Model (BLM) is currently used to predict metal toxicity in aquatic organisms. However, for rainbow trout this is based on gill binding constants from juvenile fish. This may not be appropriate for post-hatch larval fish where the skin is the site of toxic action of Cu. Determining Cu binding constants and lethal accumulation concentrations for both skin and gills in larval fish may aid in developing a larval fish-specific BLM. Overall, the changing site of toxic action and physiology of developing larval fish present an interesting and exciting avenue for future research.

Effects of chronic waterborne nickel exposure on growth, ion homeostasis, acid-base balance, and nickel uptake in the freshwater pulmonate snail, Lymnaea stagnalis

The freshwater pulmonate snail, Lymnaea stagnalis, is the most sensitive aquatic organism tested to date for Ni. We undertook a series of experiments to investigate the underlying mechanism(s) for this observed hypersensitivity. Consistent with previous experiments, juvenile snail growth in a 21-day exposure was reduced by 48% relative to the control when exposed to 1.3μgl−1 Ni (EC20 less than the lowest concentration tested). Ca2+ homeostasis was significantly disrupted by Ni exposure as demonstrated by reductions in net Ca2+ uptake, and reductions in Ca2+ concentrations in the hemolymph and soft tissues. We also observed reduced soft tissue [Mg2+]. Snails underwent a significant alkalosis with hemolymph pH increasing from 8.1 to 8.3 and hemolymph TCO2 increasing from 19 to 22mM in control versus Ni-exposed snails, respectively. Unlike in previous studies with Co and Pb, snail feeding rates were found to be unaffected by Ni at the end of the exposure. Snails accumulated Ni in the soft tissue in a concentration-dependent manner, and Ni uptake experiments with 63Ni revealed a biphasic uptake profile – a saturable high affinity component at low exposure concentrations (36–189nM) and a linear component at the high exposure concentrations (189–1897nM). The high affinity transport system had an apparent Km of 89nM Ni2+ and Vmax of 2.4nmolg−1h−1. This equates to a logK of 7.1, significantly higher than logK's (2.6–5.2) for any other aquatic organisms evaluated to date, which will have implications for Biotic Ligand Model development. Finally, pharmacological inhibitors that block Ca2+ uptake pathways in snails did not inhibit Ni uptake, suggesting that the uptake of Ni does not occur via Ca2+ uptake pathways. As with Cu and Pb, the exact mechanism for the significant disruption in Ca2+ homeostasis and reduction in juvenile snail growth remains unknown.

Modelling uptake and toxicity of nickel in solution to Enchytraeus crypticus with biotic ligand model theory

Protons and other cations may inhibit metal uptake and alleviate metal toxicity in aquatic organisms, but less is known about these interactions in soil organisms. The present study investigated the influence of solution chemistry on uptake and toxicity of Ni in Enchytraeus crypticus after 14 days exposure. Ca2+, Mg2+ and Na+ were found to exert significant effects on both uptake and toxicity of Ni. An extended Langmuir model, which incorporated cation competition effects, well predicted Ni uptake. The LC50{Ni2+} predicted by a developed Biotic Ligand Model matched well with observed values. These suggest that cation competition needs to be taken into account when modelling uptake and effects. The binding constants of Ni2+, Mg2+ and Na+ on the uptake and toxic action sites were similar, but for Ca2+ they differed. This indicates that the effect of Ca2+ on Ni2+ toxicity cannot simply be explained by the competition for entry into organism.

Impacts of major cations (K(+), Na (+), Ca (2+), Mg (2+)) and protons on toxicity predictions of nickel and cadmium to lettuce (Lactuca sativa L.) using exposure models.

Biotic ligand models (BLM) explicitly accounting for hypothetical interactions with biotic ligands and bioavailability as dictated by water chemistry have been developed for various metals and different organisms. It is only recently that BLMs for plants have received increasing attention. Lettuce is one of the most important vegetable crops in the world. This study investigated the impacts of Ca(2+), Mg(2+), K(+), Na(+) and pH, on acute toxicity of Ni and Cd to butter-head lettuce seedlings (Lactuca sativa L.). 4-day assays with the root elongation inhibition (REI) as the endpoint were performed in hydroponic solutions. Magnesium was found to be the sole cation significantly enhancing the median inhibition concentration (IC50) of Ni(2+) with increasing concentration. By incorporating the competitive effects of Mg(2+), the Ni-toxicity prediction was improved significantly as compared to the total metal model (TMM) and the free ion activity model (FIAM). The conditional stability constants derived from the Ni-BLM were log K MgBL=2.86, log K NiBL=5.1, and f NiBL (50%) =0.57. A slight downtrend was observed in the 4-d IC50 of Cd(2+) at increasing H(+) concentrations, but this tendency was not consistent and statistically significant (p=0.07) over the whole range. The overall variations of Cd-toxicity within the tested Na(+), K(+), Ca(2+) and Mg(2+) concentration ranges were relatively small and not statistically significant. 80% of lettuce REI by Cd could be explained using both TMM and FIAM instead of BLM in the present study. Thus, the mechanistically underpinned models for soil quality guidelines should be developed on a metal-specific basis across different exposure conditions.

Modeling cadmium and nickel toxicity to earthworms with the free ion approach

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

Critical body residues, Michaelis–Menten analysis of bioaccumulation, lethality and behaviour as endpoints of waterborne Ni toxicity in two teleosts

Traditionally, water quality guidelines/criteria are based on lethality tests where results are expressed as a function of waterborne concentrations (e.g. LC50). However, there is growing interest in the use of uptake and binding relationships, such as biotic ligand models (BLM), and in bioaccumulation parameters, such as critical body residue values (e.g. CBR50), to predict metal toxicity in aquatic organisms. Nevertheless, all these approaches only protect species against physiological death (e.g. mortality, failed recruitment), and do not consider ecological death which can occur at much lower concentrations when the animal cannot perform normal behaviours essential for survival. Therefore, we investigated acute (96h) Ni toxicity in two freshwater fish species, the round goby (Neogobius melanostomus) and rainbow trout (Oncorhynchus mykiss) and compared LC, BLM, and CBR parameters for various organs, as well as behavioural responses (spontaneous activity). In general, round goby were more sensitive. Ni bioaccumulation displayed Michaelis-Menten kinetics in most tissues, and round goby gills had lower Kd (higher binding affinity) but similar Bmax (binding site density) values relative to rainbow trout gills. Round goby also accumulated more Ni than did trout in most tissues at a given exposure concentration. Organ-specific 96h acute CBR values tended to be higher in round goby but 96h acute CBR50 and CBR10 values in the gills were very similar in the two species. In contrast, LC50 and LC10 values were significantly higher in rainbow trout. With respect to BLM parameters, gill log KNiBL values for bioaccumulation were higher by 0.4-0.8 log units than the log KNiBL values for toxicity in both species, and both values were higher in goby (more sensitive). Round goby were also more sensitive with respect to the behavioural response, exhibiting a significant decline of 63-75% in movements per minute at Ni concentrations at and above only 8% of the LC50 value; trout exhibited no clear behavioural response. Across species, diverse behavioral responses may be more closely related to tissue Ni burdens than to waterborne Ni concentrations. To our knowledge, this is the first study to link Ni bioaccumulation with behavioural endpoints. In future it would be beneficial to expand these analyses to a wider range of species to determine whether Ni bioaccumulation, specifically in the gills, gut and whole fish, may be a good predictor of behavioural changes from metal exposure; which in the wild can lead to ecological death.

Predicting Cadmium Accumulation and Toxicity in a Green Alga in the Presence of Varying Essential Element Concentrations Using a Biotic Ligand Model

This study refines the Biotic Ligand Model (BLM) approach by integrating the modulating effects of various essential elements on cadmium (Cd) uptake kinetics in the freshwater alga Chlamydomonas reinhardtii. The algae were first acclimated to a low (LM) or high trace metal (HM) medium as well as to low or high free Cd(2+) and Co(2+) concentrations. The short-term Cd transport capacity and affinity were then quantified in exposure media in which essential trace metals and calcium concentrations were manipulated. The results show that after acclimation to the LM medium, exposure to high free Ca(2+) decreases the capacity of the Cd transport system. Also, acclimation to high (10(-9) M free Co(2+)) or low (10(-11) M free Co(2+)) did not significantly affect Cd uptake rates. When all essential trace metals were simultaneously increased in the acclimation (and exposure) medium, the capacity of the transport system decreased by ∼ 60%, a decrease close to that due to high [Zn(2+)] alone, suggesting that Zn is the main trace metal modulator of the Cd transporter capacity. Changes in Cd toxicity (growth inhibition) in the presence of different essential trace metal concentrations were strongly related to the steady-state concentration of intracellular cadmium, regardless of the cell's nutritional state. Our BLM incorporating the physiological effects of Ca(2+) and other trace metals predicts steady-state Cd accumulation in the presence of varying concentrations of essential elements at 7 nM free Cd(2+), but predictions over a wide range of free [Cd(2+)] proved to be more difficult.

Toxicity of Metals Associated with Sediments from the Columbia River to Early Life Stages of White Sturgeon

In the Upper Columbia River (UCR) between Trail, BC, and Grand Coulee Dam, WA, it has been hypothesized that metals associated with sediments might be contributing to poor recruitment of white sturgeon. Accordingly, the present study employed laboratory flow-through tests to characterize chronic toxicity of UCR sediments to early life stages of white sturgeon (Acipenser transmontanus). Sediments were collected from areas of the UCR known to be sturgeon spawning- and/or nursing-grounds and contained a range of concentrations of metals of primary interest, including copper (Cu), cadmium (Cd), lead (Pb), and zinc (Zn). Early life stage white sturgeon were exposed for 60 days and survival and growth were related to concentrations of metals in bulk sediment, pore water, overlying water, and water at the sediment-water interface. Based on probable effect concentrations (PECs) and excess simultaneously extracted metals (SEMX), site sediments in the present study had the potential to elicit adverse effects to sediment-dwelling organisms. In addition, the Biotic Ligand Model (BLM) was used to allow for more explicit consideration of bioavailability of metals to white sturgeon. BLM predictions indicated that concentrations of Cu in pore water slightly exceeded the threshold for effects (up to a factor of 2.2) for two of the five site sediments, while concentrations of metals in overlying water and at the sediment-water interface were below the threshold for effects. No effects were observed, however, in survival or growth of white sturgeon exposed to site sediments that were relatable to concentrations of metals. Of the methods used to characterize potential effects due to exposure to metals associated with sediments, BLM predictions corresponded best with the observed results.

Development and validation of a biotic ligand model for predicting chronic toxicity of lead to Ceriodaphnia dubia

While it is increasingly being recognized that biotic ligand models (BLMs) are valuable in the risk assessment of metals in aquatic systems, the development of chronic BLMs has been less advanced for lead than for other metals. The authors investigated the univariate effects of Ca and pH on the chronic reproductive toxicity of Pb to Ceriodaphnia dubia at 4 levels. Calcium influenced chronic Pb toxicity to C. dubia only to a relatively small extent, whereas a high pH (8.2) provided strong protection against Pb toxicity (compared with lower pH levels). Based on this data set, a chronic Pb BLM for C. dubia was developed. The effect of pH was modeled as a single biotic ligand site competition by H(+) with a log stability constant for binding of H(+) to the biotic ligand (K(HBL)) of 7.6, while no other competitive constants were needed. The developed BLM was shown, in an independent validation with 3 other data sets, to be capable of predicting chronic Pb toxicity to different clones of C. dubia by an error of less than a factor of 2 in most synthetic and natural waters considered. The results add to the growing evidence that BLM-based risk assessment or water-quality criteria for Pb are likely to be more appropriate relative to hardness-based assessments or criteria.

Predict Metal Toxicity and Water Quality Criteria of Different Types of Water Into Taihu Lake, China Using Biotic Ligand Model

The Biotic Ligand Model (BLM) is an important tool in predicting acute toxicity of metal to aquatic organisms. This study used the BLM to predict acute toxicity (LC50, the lethal concentration for 50% of test organisms) of Cu and Zn to Daphnia magna, and to predict water quality criteria (WQC) for different types of water (river water, treated and untreated sewage, and rainwater) into Taihu Lake, an important drinking water source for millions of population. Their effects of metal toxicity on Taihu Lake were also explored. The results showed that Taihu Lake water had a relatively higher LC50 (Cu) value (1.38 ± 0.60 mg/L) than other types of water except for untreated sewage (2.25 ± 2.13 mg/L). Of these types of water, predicted LC50 value of Cu followed the order of untreated sewage > rainwater > Taihu Lake > river water > sewage effluent. In addition, acute toxicity of Zn followed the order of river water > rainwater > Taihu Lake > sewage effluent > untreated sewage. Comparison of the predicted WQC values with the Chinese National Water Quality Standard of Surface waters indicated that the existing standard for copper might over-protect the aquatic organisms in Taihu Lake. The correlation analysis showed that increased DOC (dissolved organic carbon) concentration resulted in a higher LC50 value due to complexation between metal and organic matters, which reduced Cu toxicity. A significant positive relationship existed between cation concentration and predicted LC50 value, also indicating that cation concentration may reduce metaltoxicity. The work provided basic data for the study of water effect ratio (WER) and for the establishment of China’s own water quality critieria based on Chinese water environmental conditions.

Predicting the toxicity of metal mixtures

The toxicity of single and multiple metal (Cd, Cu, Pb, and Zn) solutions to trout is predicted using an approach that combines calculations of: (1) solution speciation; (2) competition and accumulation of cations (H, Ca, Mg, Na, Cd, Cu, Pb, and Zn) on low abundance, high affinity and high abundance, low affinity biotic ligand sites; (3) a toxicity function that accounts for accumulation and potency of individual toxicants; and (4) biological response. The approach is evaluated by examining water composition from single metal toxicity tests of trout at 50% mortality, results of theoretical calculations of metal accumulation on fish gills and associated mortality for single, binary, ternary, and quaternary metal solutions, and predictions for a field site impacted by acid rock drainage. These evaluations indicate that toxicity of metal mixtures depends on the relative affinity and potency of toxicants for a given aquatic organism, suites of metals in the mixture, dissolved metal concentrations and ratios, and background solution composition (temperature, pH, and concentrations of major ions and dissolved organic carbon). A composite function that incorporates solution composition, affinity and competition of cations for two types of biotic ligand sites, and potencies of hydrogen and individual metals is proposed as a tool to evaluate potential toxicity of environmental solutions to trout.

Development of a model to predict the effect of water chemistry on the acute toxicity of cadmium to Photobacterium phosphoreum

Cadmium (Cd) compounds are widely distributed toxic environmental and industrial pollutants, and they may bring danger to growth and development of aquatic organisms. The effects of Ca2+ (as CaCl2), Mg2+ (as MgSO4), K+ (as KCl), pH and complexants (EDTA, the commercial DOM, and three homemade DOMs) on Cd toxicity to Photobacterium phosphoreum were evaluated in standardized 15min acute toxicity tests. Increases in Ca2+ concentration resulted in higher EC50 values, indicating the competition between the two ions for uptake sites at the biotic ligand. Increased waterborne Mg2+ also reduced Cd toxicity, but to a slightly lesser degree compared with Ca2+. The overall decline in EC50 data with increasing K+ in test solutions suggested that Cd toxicity was enhanced at larger K+ concentration. The toxicity alleviation by H+ was observed over the tested pH range of 5.0–9.0. Additions of complexing agents into the exposure water reduced Cd bioavailability via complexation of Cd2+, and complexants from different sources displayed different protective effect. The influence of these toxicity modifying factors was finally incorporated into a model that can predict acute cadmidum toxicity for Photobacterium phosphoreum. After validation with laboratory and natural waters, the developed model could support efforts to improve the ecological relevance of presently applied risk assessment procedures.

The influence of calcium and pH on the uptake and toxicity of copper in Folsomia candida exposed to simplified soil solutions

The aim of the present study was to investigate the influence of Ca and pH on the uptake and effects of Cu in Folsomia candida (Collembola). Assuming that soil pore water is the main route of exposure, F. candida were exposed for seven days to Cu in simplified soil solutions at different Ca concentrations and different pH levels. A hormetic-type effect was seen for the effect of Cu on F. candida survival. Toxicity of Cu was slightly decreased and Cu uptake increased at the highest Ca concentrations. Cu toxicity and uptake were not significantly affected by pH. Conditional binding constants for Cu2+, Ca2+ and H+, calculated with a Langmuir isotherm, were used to relate Cu toxicity to the fraction of occupied binding sites (BL). The estimated 50% effect level (fCu-BL50) was 0.14 when all data were combined. To verify the Langmuir parameters, binding constants calculated based on internal Cu concentrations were used to estimate predicted effects and compared with the measured values. A good correlation between predicted and measured survival indicated that the principles of a biotic ligand model may be applicable to explain Cu toxicity to F. candida in simplified soil solutions.

Influence of Humic Acid on Algal Uptake and Toxicity of Ionic Silver

The biogeochemical cycle of silver has been profoundly disturbed by various anthropogenic activities. To better understand the relationship among silver speciation, bioavailability, and toxicity in freshwaters, we have studied the short-term uptake of silver by two species of green algae, Chlamydomonas reinhardtii and Pseudokirchneriella subcapitata, in the presence or absence of a well-characterized humic acid (Suwannee River Humic Acid, SRHA). The free Ag(+) concentrations in the exposure solutions were determined using an equilibrium ion-exchange technique. According to the biotic ligand model, for a given free metal ion concentration, metal uptake should remain the same in the presence or absence of humic acid. However, short-term silver uptake in the presence of SRHA was greater than anticipated on the basis of free Ag(+) concentration. Subsequent determination of silver subcellular distribution revealed that significantly more silver was present in the "cell debris" fraction (known to contain the cell wall and fragmented membranes) in the presence of SRHA than in its absence. Finally, this increase in silver uptake in the presence of humic acid did not result in decreased algal growth. These results suggest that the increase in silver uptake observed in the presence of SRHA is surface-bound, not truly internalized.

Influence of Ca and pH on the uptake and effects of Cd in Folsomia candida exposed to simplified soil solutions

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

Probabilistic approaches to accounting for data variability in the practical application of bioavailability in predicting aquatic risks from metals

The biotic ligand model (BLM) theoretically enables the derivation of environmental quality standards that are based on true bioavailable fractions of metals. Several physicochemical variables (especially pH, major cations, dissolved organic carbon, and dissolved metal concentrations) must, however, be assigned to run the BLM, but they are highly variable in time and space in natural systems. This article describes probabilistic approaches for integrating such variability during the derivation of risk indexes. To describe each variable using a probability density function (PDF), several methods were combined to 1) treat censored data (i.e., data below the limit of detection), 2) incorporate the uncertainty of the solid-to-liquid partitioning of metals, and 3) detect outliers. From a probabilistic perspective, 2 alternative approaches that are based on log-normal and Γ distributions were tested to estimate the probability of the predicted environmental concentration (PEC) exceeding the predicted non-effect concentration (PNEC), i.e., p(PEC/PNEC>1). The probabilistic approach was tested on 4 real-case studies based on Cu-related data collected from stations on the Loire and Moselle rivers. The approach described in this article is based on BLM tools that are freely available for end-users (i.e., the Bio-Met software) and on accessible statistical data treatments. This approach could be used by stakeholders who are involved in risk assessments of metals for improving site-specific studies.

Using a toxicokinetics approach to explain the effect of soil pH on cadmium bioavailability to Folsomia candida

The aim of this study was to improve our understanding of metal bioavailability in soil by linking the biotic ligand approach with toxicokinetics modelling. We determined cadmium bioaccumulation kinetics in Folsomia candida (Collembola) as a function of soil pH. Animals were exposed for 21 days to LUFA 2.2 soil at 5 or 20 μg Cd g−1 dry soil followed by 21 days elimination in clean soil. Internal cadmium concentrations were modelled using a first-order one-compartment model, relating uptake rate constants (k1) to total soil, water or 0.01 M CaCl2 extractable and porewater concentrations. Based on total soil concentrations, k1 was independent of soil pH while it strongly increased with increasing pH based on porewater concentrations explaining the reduced competition of H+ ions making cadmium more bioavailable in pore water at high pH. This shows that the principles of biotic ligand modelling are applicable to predict cadmium accumulation kinetics in soil-living invertebrates.

The biotic ligand model approach for addressing effects of exposure water chemistry on aquatic toxicity of metals: Genesis and challenges

The biotic ligand model approach for addressing effects of exposure water chemistry on aquatic toxicity of metals: Genesis and challenges

Acute waterborne copper toxicity to the euryhaline copepod Acartia tonsa at different salinities: Influence of natural freshwater and marine dissolved organic matter

The influence of natural dissolved organic matter (DOM) on acute waterborne Cu toxicity was evaluated in the euryhaline copepod Acartia tonsa at 3 different water salinities. Three sources of freshwater DOM (extracted by reverse osmosis) and 2 sources of marine DOM (extracted using a solid-phase technique) were used. Artificial salt water was used to prepare the experimental media. Different combinations of Cu concentrations and DOM sources and concentrations were tested at salinities of 5, 15, and 30 ppt. Toxicity data (48-h median lethal concentration [LC50] values) were calculated based on dissolved Cu concentrations. In a broad view, data showed that increasing salinity was protective against the acute waterborne Cu toxicity. In general, Cu toxicity was also lower in the presence than in the absence of DOM. Toxicity (48-h LC50) values from all treatments at the same salinity showed a positive linear relationship with the dissolved organic carbon (DOC). Thus, the protective effect of DOM against the acute Cu toxicity seems to be dependent mainly on the DOM concentration. However, it seems also to be dependent to some extent on the source of DOM used. In summary, findings reported in the present study clearly indicate that both salinity and DOM (source and concentration) should be taken into account in the development of an estuarine version of the biotic ligand model.

Toxicity of lead and zinc to developing mussel and sea urchin embryos: Critical tissue residues and effects of dissolved organic matter and salinity

Lead (Pb) EC50 values in the very sensitive early development phases (48–72h post-fertilization) of the mussels Mytilus galloprovincialis and Mytilus trossolus and sea urchin Strongylocentrotus purpuratus in 100% sea water were: M. trossolus — 45 (95% C.I.=22–72) μgL−1; M. galloprovincialis — 63 (36–94) μgL−1; S. purpuratus — 74 (50–101) μgL−1. Salinity thresholds for normal development varied: M. trossolus>21ppt; M. galloprovincialis>28ppt; S. purpuratus≥30ppt. Addition of two spectroscopically distinct dissolved organic matters (DOM) from fresh water (Nordic Reservoir) and sea water (Inshore) moderately decreased the toxicity of Pb to both mussels, but not in a concentration-dependent fashion, with only an approximate doubling of EC50 over the range of 1.4–11.2mgCL−1. Independent Pb binding capacity determinations for DOC explained the lack of a relationship between DOM concentration and toxicity. Salinity had no effect on Pb toxicity down to 21ppt in M. trossolus, and low salinity (21ppt) did not enhance the protective effect of DOC. Both DOMs increased the toxicity of Pb in developing sea urchin embryos, in contrast to mussels. Relative to Pb, the organisms were 6–9 fold less sensitive to Zn on a molar basis in 100% seawater with the following Zn EC50s: M. trossolus — 135 (103–170) μgL−1; M. galloprovincialis — 172 (126–227) μgL−1, S. purpuratus — 151 (129–177) μgL−1. Nordic Reservoir and Inshore DOM (2–12mgCL−1) had no significant effect on Zn toxicity to mussels, in accord with voltammetry data showing an absence of any strong ligand binding for Zn by DOMs. As with Pb, DOMs increased Zn toxicity to urchin larvae. Critical Tissue Residues (CTR) based on whole body concentrations of Pb and Zn were determined for M. galloprovincialis at 48h and S. purpuratus at 72h. The median lethal CTR values (LA50s), useful parameters for development of saltwater Biotic Ligand Models (BLMs), were approximately 4-fold higher on a molar basis for Zn than for Pb. The latter were not altered by DOM exposure, despite increased EC50 values, in accord with the tenets of the BLM.