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Effect of cadmium cations and their interaction with silicon cations was determined in poplar calli and expressed as changes in callus growth, cell viability and cadmium cation accumulation. Cell viability throughout culture versus cadmium cation accumulation in cells is discussed. At the same time, the study sought appropriate methods for cadmium cation detection in callus cells and also in experiments with low plant material (e.g. protoplasts). Cadmium cations were determined by atomic absorption spectroscopy and using fluorescence microscopy with a specific cadmium cation fluorescent dye. The detection of cadmium cations in callus cells by the latter method appears suitable because the callus cells are surrounded by primary cell walls without auto-fluorescence and these values fit well with atomic absorption spectroscopy quantification. However, the visualisation method has some limits discussed below.

Consumption of periphyton is a potentially important route of metal exposure to benthic invertebrate grazers. The present study examined the bioaccumulation kinetics of dissolved and dietary Cd and Cu in five species of mayflies (class Insecta). Artificial stream water and benthic diatoms were separately labeled with enriched stable metal isotopes to determine physiological rate constants used by a biokinetic bioaccumulation model. The model was employed to simulate the effects of metal partitioning between water and food, expressed as the bioconcentration factor (BCF), as well as ingestion rate (IR) and metal assimilation efficiency of food (AE), on the relative importance of water and food to metal bioaccumulation. For all test species, the contribution of dietary uptake of Cd and Cu increased with BCF. For a given BCF, the contribution of food to the body burden increased with k(uf) , the metal uptake rate constant from food that combined variation in IR and AE. To explore the relative importance of water and diet exposure routes under field conditions, we used estimated site-specific aqueous free-ion concentrations to model Cd and Cu accumulation from aqueous exposure, exclusively. The predicted concentrations accounted for less than 5% of the observed concentrations, implying that most bioaccumulated metal was acquired from food. At least for the taxa considered in this study, we conclude that consumption of metal-contaminated periphyton can result in elevated metal body burdens and potentially increase the risk of metal toxicity., (Copyright © 2011 SETAC.)

The toxicokinetics of cadmium was determined for five populations belonging to four species of Artemia (A. salina, A. parthenogenetica, A. franciscana, and A. persimilis) using a bicompartmental model. The effects of sublethal cadmium concentration on the kinetic parameters in A. parthenogenetica were determined. The BCF values are inversely related to the concentration, as is the uptake rate (ku), whilst the elimination rate (ke) constant seems to be directly related to the exposure concentration. Values corresponding to the rate of metal influx (I) remain relatively constant (0.2477 to 0.4455 microg/g.h) in the concentration range from 0.1 to 1 mg Cd/L, and are higher (1.098 microg/g.h) at an exposure to 10 mg Cd/L. The cadmium accumulation pattern seems well conserved in the genus and is characterized by a fast elimination of the metal with Ke ranging from 0.0050 to 0.0231 h(-1). A. persimilis displays a different model to that corresponding to the other studied species exposed to the same cadmium concentration, presenting a low uptake rate constant (1.0564 mL/g. h) and a low BCF (211.3 mL/g).

Coupled respirometric and radiotracer techniques were applied to simultaneously measure the rates of oxygen and metal uptake in the green mussel Perna viridis. This was performed under different metabolic conditions by varying the ambient oxygen partial pressure (P(O2)), temperature, air exposure, and body size. When the mussels were tested under different hypoxic and anoxic conditions, Cd and Zn uptake decreased with decreasing P(O2), accompanied by a decrease in the ventilation activity of mussels. Significant reduction in metal uptake was observed at a P(O2) level of 3 kPa. Under anoxic conditions, the uptake of Cd and Zn was 1.6 to 2.7 times and 2.8 times, respectively, lower than those measured under normoxia. In contrast, both the absorption efficiencies of Cd and Zn and the oxygen extraction efficiency increased significantly with decreasing P(O2). There were significant correlations between the rates of Cd/Zn and O2 uptake by the mussels when quantified under various P(O2) levels. The uptake of Cd and Zn was temperature dependent and increased with temperature over a range of 15 to 30 degrees C. Significant correlations between the rates of Cd/Zn and O2 uptake were also found in the temperature experiments. With reimmersion of mussels after aerial exposure, the mussels experienced an apparent O2 debt. Metal uptake also increased within the first 15 min followed by gradual recovery to the control levels. Similarly, the quantified uptake rates of Zn were significantly correlated with the O2 uptake in experiments with different sizes of mussels. These results strongly suggest that Cd and Zn uptake are coupled with oxygen uptake in the mussels; thus, physiological processes need to be considered in studying metal accumulation.

The toxic effects of Cd, Cu, and Zn on four different marine phytoplankton, Dunaliella tertiolecta, Prorocentrum minimum, Synechococcus sp., and Thalassiosira weissflogii, were examined by comparing the cell-specific growth rate, pulse-amplitude-modulated (PAM) parameters (maximum photosystem II quantum yield phiM and operational quantum yield phi'M, chlorophyll a content, and cellular metal concentration, over a 96-h period. The calculated no-observed-effect concentration (NOEC) based on both cell-specific growth rate and two PAM parameters (phiM and phi'M) were mostly identical. Thus, these PAM parameters and cell-specific growth rate were comparable in their sensitivities as the biomarkers for trace metal toxicity to marine phytoplankton. The cyanobacteria Synechococcus sp. was the most sensitive species among the four algal species tested because of its higher cell surface to volume ratio. The toxicity of the three tested metals followed the order of Cd > Cu > Zn based on the cellular metal concentration of the four algae at the NOEC. The cellular metal bioaccumulation followed the same Freundlich isotherm for each metal regardless of the algal species, indicating that the metal accumulation was a nonmetabolic process under high ambient metal concentrations and that the cell surface metal binding was comparable among the different species. For all the algae examined in our study, the bioaccumulation potentials of Cu and Zn were similar to each other, while the Cd bioaccumulation was much lower under environmentally realistic metal concentration.

Previous studies have shown that metal partitioned to a subcellular compartment containing trophically available metal (TAM) is readily available to predators and may be enhanced by increased binding of metal to heat-stable proteins (HSP - e.g., metallothioneins). The aim of the current investigation was to determine the influence of TAM on the trophic transfer of Cd along an experimental, three-level food chain: Artemia franciscana (brine shrimp)-->Palaemonetes pugio (grass shrimp)-->Fundulus heteroclitus (mummichog). P. pugio were fed for 7 days on A. franciscana exposed to Cd in solution (including (109)Cd as radiotracer) and subjected to subcellular fractionation or fed to F. heteroclitus. An HSP-driven increase in the percentage of Cd associated with TAM (TAM-Cd%) in A. franciscana exposed to 1 muM Cd resulted in a bioenhancement (i.e., a greater than linear increase with respect to A. franciscana exposure) of Cd trophic transfer to P. pugio. Increased dietary Cd exposure did not affect TAM-Cd% in P. pugio nor trophic transfer to F. heteroclitus.

Short-term uptake of cadmium by a wild-type (2137) and a cell wall-less strain (CW-2) of Chlamydomonas reinhardtii was examined as a function of Cd speciation in a well-defined, aqueous medium. Internalization fluxes were determined for free cadmium concentrations ranging from 5 x 10(-10) M to 5 x 10(-4) M in the presence of ligands forming both labile and inert hydrophilic complexes. A first-order biological internalization, as predicted by the free ion activity model (FIAM), was observed for both strains. The maximum Cd internalization flux, Jmax, for the wild-type strain was 5-fold higher (1.3 x 10(-11) mol cm(-2) min(-1)) than for the CW-2 strain (2.3 x 10(-12) mol cm(-2) min(-1)) and was not influenced by the presence of competitors such as Ca in the experimental solution. The conditional stability constant for the adsorption of Cd to transport sites of the CW-2 strain was 5-fold higher (10(6.7) M(-1)) than for the wild-type strain (10(6) M(-1)). Competition experiments demonstrated that Mo, Mn, Cu, Co, Zn, Ni, Ca, and Pb inhibited, at least partially, Cd uptake, while no inhibition was observed for similar concentrations of Mg and Fe. The stability constant for the competitive binding of Ca to the Cd transport site was determined to be 10(4.5) M(-1). Cu and Zn competed with Cd uptake sites with stability constants of 10(5.6) and 10(5.2) M(-1), respectively. Protons also appeared to compete with Cd uptake sites as uptake could generally be predicted quantitatively in their presence. Finally, in the presence of low concentrations (<20 mg L(-1)) of Suwannee River fulvic acid, Cd internalization fluxes could be predicted from [Cd2+], in accordance with the FIAM.

Although aquatic mosses are widely used as metal biomonitors in rivers, there are few effective models to describe metal uptake and loss by these plants. To fill this gap, we exposed the aquatic moss Fontinalis dalecarlica for 28 d to three Cd concentrations (approximately 5-50 nM) in a flow-through laboratory system. Cadmium accumulation by F. dalecarlica was rapid during the first few days of exposure and slowed thereafter but did not reach a steady state within our 1-month long experiment. This lack of a plateau in moss concentrations suggests that, for biomonitoring purposes, the duration of moss exposure should be considered either through a model of the type that we tested or by standardizing the exposure time of mosses transplanted in the field. During the subsequent 22-d elimination phase of our experiment, Cd concentrations in mosses did not return to their initial levels. This result suggests that a two-compartment model is likely to be more effective at describing Cd losses than would a one-compartment alternative. Indeed, predictions of a two-compartment model closely fitted our experimental data, which augurs well for the wider use of this model for other moss species and metals.

In order to study Zn and Cd accumulation and depuration, a set of oysters, Crassostrea rhizophorae, were transplanted to a metal contaminated coastal lagoon and another one was harvested there and transplanted to a non-polluted site. C. rhizophorae oysters and Perna perna mussels native from both sites were collected in order to monitor variability of metal concentration in resident populations. After three months exposure, oysters transplanted to the polluted site accumulated fourfold Zn (307-1319 microgg(-1)) without reaching the concentration level of resident oysters (9770 microgg(-1)). Cadmium concentrations had a slight but significant decrease during the same period (1.25-0.54 microgg(-1)). Oysters transplanted to the non-polluted site, showed threefold Zn depuration (6727-2404 microgg(-1)), while Cd had no significant variation (0.90-1.45 microgg(-1)). Results showed that transplanted oysters do not reach heavy metal concentrations in indigenous populations suggesting transplanted organisms would be better used to evaluate bioavailability instead of environmental concentrations.

This study investigates the distribution of three trace elements (Cd, Cu and Zn) in tissues (exoskeleton, abdominal muscle and hepatopancreas) of two shrimp species (Penaeus merguiensis and Penaeus semisulcatus). Special emphasis in this study was placed on evaluating the effects of storage conditions on redistribution of the elements and moreover the potential roles of metallothionein in tissue redistribution. The specimens were collected from the northern part of Persian Gulf during September 2001 and January 2002. The concentrations of metals in the tissues were measured using an Inductively Coupled Plasma-Atomic Emission Spectrophotometer (ICP-AES) and an ICP-Mass Spectrometer (ICP-MS). Metallothionein levels were determined using Differential pulse polarography. Results show a similar hierarchy for Cd and Cu concentrations among different tissues as follows: hepatopancreas>exoskeleton>muscle; and for Zn, the hepatopancreas again contained the highest levels, though there were not any significant differences in Zn concentrations between muscle and exoskeleton. Significant differences were found between the species in the case of Cd and Zn concentrations. Cd and Zn levels in P. semisulcatus were markedly higher than in P. merguiensis. In general, there were highly significant differences among the storage conditions from accumulation the selected trace elements and metallothionein in both species point of view, but in most cases, no significant differences could be observed among the fresh, refrigerated and frozen specimens of P. semisulcatus. In regards to Zn and Cu accumulation in edible (muscle) tissues of P. merguiensis, optimum conditions for frozen storage is -30 degrees C as ice-frozen, and in terms of short-term storage, 1-day refrigeration is recommended. The redistribution of Zn and Cu during the storage period can be attributed to the role of metallothionein in their transport from organ(s) to muscle during storage. The variations in pH values measured in the muscle of P. merguiensis in different storage conditions showed a similar trend with metallothionein, Zn and Cu. In contrast, it appears that cadmium is transported from muscle to the other tissues. Exoskeleton is probably one of the recipient tissues of cadmium. The inter-elemental relationships were assessed for each species, separately. A significant positive relationship was observed between the concentrations of Zn and metallothionein in P. semisulcatus, whereas in P. merguiensis, Cd concentrations decreased significantly with increasing metallothionein. Highly significant differences between the sexes in Cu and Zn contents could be detected. The differences between the sexes in the levels of Zn and Cu were significantly greater in P. semisulcatus. Highly significant size-related differences were found in the levels of Cd, Cu and metallothionein in the selected tissues of the shrimp species. Comparison between the mean concentrations of the elements in muscle tissue and existing guidelines indicate that in nearly all cases, the concentrations were well below permissible levels for human consumption. The only exception was observed regarding mean values of Cd, which was somewhat greater than some of the recommended levels.

Laboratory microcosm experiments were conducted to investigate the influence of acid volatile sulfides (AVS) and simultaneously extracted metals (SEM) in sediments on the bioavailability and toxicity of Cd, Ni, and Zn in sediments to polychaete worms Neanthes arenaceodentata. Cohorts of juvenile N. arenaceodentata were exposed to sediments spiked with metal mixtures containing Cd, Ni, and Zn (0.5-15 micromol x g(-1) of total SEM) with Low- (approximately 1 micromol x g(-1)), Medium- (approximately 5 micromol x g(-1)), and High-AVS concentrations (approximately 10 micromol x g(-1)) for 20 days to determine mortality, growth rate, and metal bioaccumulation. Tissue Cd and Zn concentrations at the end of the exposure were significantly higher in sediments with the low-AVS concentration at a given SEM concentration due to the increased dissolved metal concentrations in overlying water (OW). However, tissue Ni concentrations were not related to dissolved Ni in the OW. AVS concentrations also influenced the toxicity of metals to the worms. Significant mortality was observed only at the highest SEM treatments at Low-AVS series. Most individuals survived at the highest SEM treatments at Medium- and High-AVS series. Similarly, the growth rates of worms were reduced in treatments having higher molar differences between SEM and AVS ([SEM-AVS]). Overall, the bioavailability and toxicity of metals in sediments was not well predicted by sediment metal concentrations only, but considering the influence of geochemical factors (AVS) on the metal bioavailability improved the prediction of toxicity. Also, the relationship between tissue metal concentration and toxicity was used to determine which contaminant was most responsible for the observed toxicity of the metal mixture.

We examined the effects of Ca, one of the major ions contributing to water hardness, on the uptake and elimination of Cd and Zn in the Asiatic clam Corbicula fluminea, a common bivalve species in the rivers and streams of Southern China. Over the wide range of dissolved Cd (4.5 to 446 nM) and Zn (15.3 to 1529 nM) concentrations, uptake of both metals increased with increasing dissolved metal concentration, showing Michaelis-Menten-type saturation kinetics. At each tested metal concentration, increased Ca concentration led to a significantly lower metal uptake. When the Ca, Cd, Zn concentrations were expressed as free-ion activities, Cd and Zn uptake data fitted the Michaelis-Menten inhibition model well. We also quantified the effects of the two Ca blockers on metal uptake by the clams. Verapamil significantly inhibited the uptake Cd and Zn, but the inhibitive effect of lanthanum on metal uptake was more evident for Cd than for Zn. Ca did not significantly affect the assimilation efficiency of either metal from ingested phytoplankton, nor did it affect the elimination of the two metals during a 1-month depuration period. Our study has shown that Ca inhibited the uptake of metals from water; such an effect could be predicted based on the free-metal ion activities. Ca did not seem to have a direct effect on metal assimilation from food or metal elimination from the bivalve.

This study examined the extent to which dissolved Cd and Zn uptake rates vary in several aquatic insect taxa commonly used as indicators of ecological health. We further attempted to explain the mechanisms underlying observed differences. By comparing dissolved Cd and Zn uptake rates in several aquatic insect species, we demonstrated that species vary widely in these processes. Dissolved uptake rates were not related to gross morphological features such as body size or gill size--features that influence water permeability and therefore have ionoregulatory importance. However, finer morphological features, specifically, the relative numbers of ionoregulatory cells (chloride cells), appeared to be related to dissolved metal uptake rates. This observation was supported by Michaelis-Menten type kinetics experiments, which showed that dissolved Cd uptake rates were driven by the numbers of Cd transporters and not by the affinities of those transporters to Cd. Calcium concentrations in exposure media similarly affected Cd and Zn uptake rates in the caddisfly Hydropsyche californica. Dissolved Cd and Zn uptake rates strongly co-varied among species, suggesting that these metals are transported by similar mechanisms.

Marine mammals and seabirds tend to exhibit high accumulations of mercury, cadmium, and selenium in their livers and kidneys. In this study, chemical forms of mercury, cadmium, and selenium accumulated in the livers and kidneys of northern fur seal (Callorhinus ursinus), Risso's dolphin (Grampus griseus), and black-footed albatross (Diomedea nigripes) were studied by extended X-ray absorption fine structure (EXAFS) spectroscopy to reveal the detoxification mechanisms of these metals. It was found that mercury and selenium exist in the form of HgSe in the liver of northern fur seal. Mercury levels were found to be higher than those of Se, based on their molar ratio, in black-footed albatross. XAFS analysis disclosed an existence of chalcogenide containing both Hg-Se and the Hg-S bonds, suggesting the existence of a solid solution Hg(Se, S) as granules in black-footed albatross. In contrast, Cd concentrations in the kidney were higher than those in the liver for northern fur seal, black-footed albatross, and Risso's dolphin. It was found that Cd was bound to sulfur, which was probably derived from the metallothionein. The Cd-O bond was observed in the tissues of northern fur seal.

The concentrations of lead, zinc, copper and cadmium accumulated by 12 emergent-rooted wetland plant species including different populations of Leersia hexandra, Juncus effusus and Equisetum ramosisti were investigated in field conditions of China. The results showed that metal accumulation by wetland plants differed among species, populations and tissues. Populations grown in substrata with elevated metals contained significantly higher metals in plants. Metals accumulated by wetland plants were mostly distributed in root tissues, suggesting that an exclusion strategy for metal tolerance widely exists in them. That some species/populations could accumulate relatively high metal concentrations (far above the toxic concentration to plants) in their shoots indicates that internal detoxification metal tolerance mechanism(s) are also included. The factors affecting metal accumulation by wetland plants include metal concentrations, pH, and nutrient status in substrata. Mostly concentrations of Pb and Cu in both aboveground and underground tissues of the plants were significantly positively related to their total and/or DTPA-extractable fractions in substrata while negatively to soil N and P, respectively. The potential use of these wetland plants in phytoremediation is also discussed.

The aim of this study was to characterize the biological treatment of heavy metal-contaminated water employing Myriophyllum species, namely M. spicatum L. and M. triphyllum. Both species were found to be capable of removing cadmium (Cd) from water; the latter significantly outperformed. Myriophyllum species were treated with 0, 2, 4, 6, 8, 16 mgl(-1) cadmium solutions for 24, 48, 72, 96 h, respectively. Cd uptake of both species was the lowest at 2 mgl(-1) and the highest at 16 mgl(-1). Concentration related cadmium stress on both species exhibit significant difference on pigment levels (8-16 mgl(-1)). These findings contribute to the fact that submerged aquatic plants can be used for the removal of heavy metals.

Parameters of environmental health, including paracellular permeability of external epithelia, functional state of lysosomes and the level of metallothioneins (MTs), were examined using fluorescent markers and vital microfluorometry in different tissues of the marine gastropod, Hexaplex trunculus, from a coal-polluted and coal-free site. Vital microfluorometrical examinations exhibited enhanced paracellular permeability of external epithelia to the anionic marker, fluorescein (FLU), lower lysosomal accumulation of neutral red (NR) as well as higher levels of MTs, when compared with epithelia of gastropods from the coal-free site. Those differences were particularly marked in the foot epithelium, which is in direct contact with the substrate. In addition, cadmium was measured by ICP-AES in the hepatopancreas of gastropods sampled from the coal-polluted site and two coal-free sites. Significantly higher levels of Cd were found in gastropod hepatopancreas from the coal-polluted site. In addition, two months feeding experiments conducted in aquaria containing: (a) coal pieces covered by barnacles; (b) natural rocks covered by barnacles; and (c) natural rocks with barnacles + bare coal pieces, demonstrated significant increase of Cd concentration in the hepatopancreas of the gastropods exposed to coal. We suggest that coal in the marine environment has detrimental effects on marine gastropods, both directly through contact with the organisms and indirectly through the food web.

To identify Cd- and Zn-accumulating plants exhibiting a high growth rate, seeds from the halophyte species Mediterranean saltbush (Atriplex halimus L.) were collected on a heavy-metal-contaminated site in southeastern Spain (Llano del Beal, Cartagena). Seedlings from this ecotype were exposed for 3 wk to 0.1 mM Cd or Zn in a nutrient solution in a fully controlled environment. All plants remained alive and no significant growth inhibition was recorded until the end of the experiment. Mean Cd and Zn accumulation in aerial parts was 830 and 440 mg kg(-1), respectively, and the rate of metal translocation even increased with the duration of stress exposure. Resistance to heavy metals in this species may be partly linked to precipitation of Cd in oxalate crystals in the stems. A Cd-induced decrease in glutathione concentration also suggests that phytochelatins overproduction may occur in these conditions. We conclude that Mediterranean saltbush, which is able to produce up to 5 Mg dry matter ha(-1) yr(-1), may be an effective species for phytoextraction and should be tested for this purpose in field conditions.

In Southeast Asia the aquatic macrophyte water spinach (Ipomoea aquatica Forsk.) is a popular vegetable that is cultivated in freshwater courses. These often serve as recipients for domestic and other sorts of wastewater that often contain a variety of pollutants, such as heavy metals. In addition, fertilizers are frequently used where water spinach is cultivated commercially for the food market. To estimate the importance of ambient nutrient concentrations for accumulation of mercury (Hg), cadmium (Cd), and lead (Pb) in water spinach, plants were exposed to nutrient solutions of different strength and with varying metal concentrations. Metal-induced toxic effects, which might possibly affect the yield of the plants, were also studied. The lower the nutrient strength in the medium was, the higher the metal concentrations that accumulated in the different plant parts and the lower the metal concentration in the medium at which metal-induced toxic effects occurred. Accordingly, internal metal concentrations in the plants were correlated to toxic effects. Plants exposed to metals retained a major proportion of the metals in the roots, which had a higher tolerance than shoots for high internal metal concentrations.

Although the differential responses of stream taxa to metal exposure have been exploited for bioassessment and monitoring, the mechanisms affecting these responses are not well understood. In this study, the subcellular partitioning of metals in operationally defined metal-sensitive and detoxified fractions were analyzed in five insect taxa. Samples were collected in two separate years along an extensive metal contamination gradient in the Clark Fork River (MT, USA) to determine if interspecific differences in the metal concentrations of metal-sensitive fractions and detoxified fractions were linked to the differences in distributions of taxa relative to the gradient. Most of the Cd, Cu, and Zn body burdens were internalized and potentially biologically active in all taxa, although all taxa appeared to detoxify metals (e.g., metal bound to cytosolic metal-binding proteins). Metal concentrations associated with metal-sensitive fractions were highest in the mayflies Epeorus albertae and Serratella tibialis, which were rare or absent from the most contaminated sites but occurred at less contaminated sites. Relatively low concentrations of Cu were common to the tolerant taxa Hydropsyche spp. and Baetis spp., which were widely distributed and dominant in the most contaminated sections of the river. This suggested that distributions of taxa along the contamination gradient were more closely related to the bioaccumulation of Cu than of other metals. Metal bioaccumulation did not appear to explain the spatial distribution of the caddisfly Arctopsyche grandis, considered to be a bioindicator of metal effects in the river. Thus, in this system the presence/ absence of most of these taxa from sites where metal exposure was elevated could be differentiated on the basis of differences in metal bioaccumulation.

For ecological risk assessment, the additive model may be used to empirically predict toxic mixture effects. Detailed toxicity tests were performed to determine whether effects of mixtures of copper-cadmium and copper-carbendazim on Caenorhabditis elegans were similar to the effects of the individual compounds. Effects on the course of reproduction, the length of the juvenile period, the length of the reproductive period, and body length were analyzed. Dose-response data were compared to the additive model and tested for four deviation patterns from additivity: No deviation, synergistic/antagonistic deviation, dose ratio-dependent deviation, dose level-dependent deviation. During the exposure, the cadmium-copper effect on reproduction changed from a synergistic, to a dose ratio-dependent deviation from additivity. More cadmium in the mixture decreased the toxicity and more copper increased the toxicity. The effect of copper-carbendazim on reproduction was synergistic at low dose levels and antagonistic at high dose levels and independent of time. Mixture effects on the juvenile and reproductive period were similar to single component effects. It was concluded that the observed time-dependence of toxic interactions was small and that interactions on the timing of reproduction were not found. The additive model underestimated mixture effects on reproduction and body length.

This paper presents, the concentrations of total Hg, Cd and Zn in edible muscle tissue, and in the liver of the fish Micropogonias furnieri and Mugil liza from the Samborombon Bay, La Plata river estuary, Argentina. The highest accumulation of the three metals was observed in liver samples, whereas in muscle tissue concentrations they were always lower, values even lower than the detection limit of the analytical method used. A marked relationship between metal contents of the studied species and their trophic and ecological habits was observed. In all cases, metal levels found in edible muscle tissue were lower than the international standards of reference for organisms directed to human consumption. Finally, the validity of using these two species as bioindicators of heavy metal pollution in the assessed ecosystem was discussed.

Metal speciation in aquatic systems is mainly determined by the type and concentration of ligands present in solution. A very important group of complexing agents is dissolved organic matter (DOM), e.g., humic and fulvic acids. According to the free-ion activity model, only the free metal ion is available to biota. Nevertheless, DOM has been reported to decrease or increase metal uptake, leading to uncertainty concerning the bioavailability of metal-DOM complexes. In this work the effect of Aldrich humic acid on cadmium accumulation by the zebra mussel, Dreissena polymorpha, was studied under laboratory conditions. Mussels, collected in a drinking water reservoir, were exposed to varying environmentally relevant concentrations of cadmium in the presence and absence of humic acid. Cadmium concentrations in the mussel tissues were analyzed, and measurements with a cadmium-ion-selective electrode were made to determine the free cadmium ion activity in the exposure waters. The uptake of humic acid by the zebra mussels was measured by the decrease of the total organic carbon (TOC) concentration in the water over time. The free cadmium ion activity in the water decreased from 51.6% to 19.9% of the total cadmium concentration in the presence of humic acid. This decrease by a factor of 2.6 resulted in a decrease in the cadmium uptake rate in the soft tissue of zebra mussels from 12.9 to 7.9 nmol/g dry wt/day, which corresponds to a decrease by a factor of 1.6. This implies that cadmium uptake rates were higher than predicted by the free-ion activity model and indicates that cadmium-humic acid complexes are partly available to zebra mussels.

The effects of metal mixture (Cd+Cu) versus single-metal exposure on total MT response and bioaccumulation were investigated in the freshwater bivalve Dreissena polymorpha. A two-month exposure period, including two levels of contamination, was chosen for each of the two metals: 5, 10 microg/L for Cu, and 2, 20 microg/L for Cd, with mixtures of, respectively, 5 microg/L Cu+2 microg/L Cd, 5 microg/L Cu+20 microg/L Cd, 10 microg/L Cu+2 microg/L Cd, and 10 microg/L Cu+20 microg/L Cd. Total MT contents were assessed by an Ag-saturation method, and metals contents were determined by atomic absorption spectrometry. Results at the whole-organism level showed a significant and early increase of total MT biosynthesis after exposure to Cd. This increase was significantly correlated with Cd bioaccumulation. By contrast, Cu did not modify total MT response, and mussels limited Cu bioaccumulation. The mixture either did not influence or only weakly influenced metal accumulation and MT response to Cu and Cd after long-term exposure. Our results suggest that the form of MT existing in D. polymorpha was not Cu-inducible. This could limit the use of MT in D. polymorpha as a biomarker of heavy metal pollution in freshwater ecosystems.

The potential for filter-feeding bivalves to accumulate metals from a wide range of food sources is an important consideration when examining trophic transfer of metals up the food chain. The objective of this study was to determine the role of Leptothrix discophora in mediating metal uptake in the filter-feeding bivalve Mytilus trossulus. The bacterium L. discophora SP-6 was cultured in the absence or presence of Mn, allowing for a naturally formed Mn oxide sheath to develop. Secondary metals (Cd and Pb) were then added to the cultures, allowing for potential Cd and Pb adsorption to the Mn oxide sheath. Resulting bacterial aggregates of known diameter were then fed to the bivalve M. trossulus using a flow-through system. Initial concentrations of both Pb and Cd on the bacterium did not differ significantly in the presence or absence of the Mn oxide; conversely both Pb (F = 7.39, p < 0.0001) and Cd (F= 33.65, p < 0.0001) were found at lower concentrations in the mussel tissue when the Mn oxide was present. To determine whether these differences in metal uptake could be attributed to sorting by the mussel based on food quality, nutritional analysis was performed. Bacterial food matrixes containing Mn oxides were found to have significantly lower levels of carbon (F = 256, p < 0.0001). Particle clearance rates for the various food matrixes were positively correlated with organic content (R2 = 0.852, p > 0.008). The results of our study suggest that metal uptake in M. trossulus was significantly decreased for Cd with a similar trend for Pb when the SP-6 sheath contained Mn oxides. The mechanism mediating this differential uptake is best explained by food quality, in that a higher quality food source enhanced metal uptake due to an increased clearance rate of organic-rich particles by M. trossulus.

The biosorption of cadmium(II) and zinc(II) ions onto dried Fontinalis antipyretica, a widely spread aquatic moss, was studied under different values of temperature, initial pH and water hardness. The equilibrium was well described by Langmuir adsorption isotherms. Maximum biosorption capacity of cadmium was independent on temperature and averaged 28.0 mg g(-1) moss, whereas for zinc, capacity increased with temperature, from 11.5 mg g(-1) moss at 5 degrees C to 14.7 mg g(-1) moss at 30 degrees C. Optimum adsorption pH value was determined as 5.0 for both metal ions. Cadmium uptake was unaffected by the presence of calcium ions, but zinc sorption was improved when water hardness increased from 101.1 to 116.3 mg CaCO(3)l(-1). Inversely, as hardness increases, the competition with calcium ions strongly reduces the affinity of the biosorbent for zinc.

Heavy metal pollution is a serious threat to ecosystem functioning. Different approaches have been developed to relate the exposure of heavy metals to their accumulation and toxicity. One approach is to relate metal toxicity to the concentrations of the metals in the whole body or a specific target tissue instead of the external exposure concentrations. To test the usefulness of this approach, the relationship between cadmium exposure, accumulation, and toxicity was investigated using an oligochaete worm and kinetic modeling. The uptake and elimination of cadmium by the aquatic oligochaete Tubifex tubifex from the aqueous phase was studied as function of time at different exposure concentrations using both radioactive and non-radioactive cadmium. A two-compartmental pharmacokinetic model was constructed and parametrized by fitting the model to the measured cadmium body concentrations during exposure to different cadmium concentrations. The uptake rate constants were dependent on the cadmium exposure concentration, and this relation could be well-described by incorporation of Michaelis-Menten type uptake kinetics. The toxicity of cadmium was analyzed by determining the lethal exposure concentration associated with a mortality of 50% (LC50) at different time points. LC50 values decreased with increasing exposure time reaching the incipient lethal level after 15 d. Critical body concentrations (CBC) associated with 50% mortality were calculated by combining the model-predicted pharmacokinetic parameters and the measured LC50 values. The predicted mean CBC (0.32 micromol/g wet weight +/- 0.02) was in good agreement with the experimentally obtained CBC for cadmium found in T. tubifex (0.37 micromol/g wet weight +/- 0.07) and appeared to be independent of exposure time and exposure concentration. Our results show that a pharmacokinetic modeling approach provides a tool to link metal exposure to availability, accumulation, and toxicity under variable exposure scenarios taking into account the kinetics of the processes.

A biosorbent was prepared by coating the fibrous network of loofa sponge (Luffa cylindrica) with a thin film of calcium alginate. Alginate-coated loofa sponge removed Cd(II) rapidly, reaching equilibrium loading of 124 mg g(-1) in 30 min. Seventy % of equilibrium uptake was achieved in 10 min. In contrast, it took 240 min for alginate beads to reach a loading equilibrium of 88 mg g(-1) under identical conditions. The biosorption behaviour followed the Langmuir adsorption isotherm and the ACLS biosorbent was shown to be highly effective in removing Cd(II) from a 10 mg l(-1) solution in a continuous flow fixed-bed column bioreactor.

The mined ecotype of Sedum alfredii Hance has been identified to be a zinc (Zn) hyperaccumulator native to China. In the present article, the characteristics of cadmium (Cd) uptake and accumulation were compared with hydroponic experiments between the mined and the nonmined ecotypes of Sedum alfredii Hance. The results indicate that the plants of the mined ecotype (ME) have higher tolerance of Cd than the plants of the nonmined ecotypes (NME) in terms of dry matter yield. The thresholds of external Cd levels for the reduction of plant growth were 100 micromolL(-1) for the NME and 400 micromolL(-1) for the ME, respectively. Kinetic study showed that the rates of Cd influx into roots (IR) and transport to shoots (TR) were higher in the ME than in the NME, with 5-fold higher for the maximum IR (Imax) and 13-fold higher for the maximum TR (Tmax) in the NME, respectively. Cadmium concentrations increased with increasing external Cd supply levels. Root Cd concentrations in the NME were higher than that in the ME, with a maximum being 5646 mg kg(-1) for the NME and 2889 mg kg(-1) for the ME at 1000 micromolL(-1) Cd. On the contrary, shoot Cd concentrations of the NME were far lower than that of the ME. Maximum shoot Cd concentrations were 533 mg kg(-1) in leaves and 935 mg kg(-1) in stems at 1000 micromol L(-1) Cd for NME, whereas, 4933 and 3874 mg kg(-1) at 400 micromol L(-1) Cd for the ME, respectively. Meanwhile, Cd concentrations in the shoots of both the NME and ME increased with advancing Cd treatment time. At 100 micromolL(-1) Cd, concentrations of Cd in leaves and stems of the NME sharply increased within initial 8 and 12 days, and those in the ME increased dramatically until D20 and D16, respectively. However, leaf and stem Cd concentrations reached their maximum values on D4 for the NME and D8 for the ME, respectively, when the plants were exposed to 1 micromol L(-1) Cd. Cadmium accumulation by plant shoots was obvious higher in the ME than in the NME at varied Cd supply levels or Cd treatment time. The maximum Cd taken up by the shoots was 1032 microg plant(-1) in concentration-dependent uptake, and 1699 microg plant(-1) in time-course uptake for the ME, with 15-fold and 18-fold higher than those for the NME, respectively. The ratios of shoot/root of Cd ranged from 12 to 39, varying with Cd supply levels, and from 13 to 24 in the varied treatment times for the ME, more than 10 times greater than those for the NME. In addition, Cd distribution in leaves, stems and roots of ME was greatly different from those of NME. The percentage of Cd distribution in shoots was more than 79 at the varied Cd supply levels, or 83 in the varied treatment time for ME, both higher than that for NME. It could be concluded that the mined ecotype of Sedum alfredii Hance has a greater ability to tolerate, transport, and accumulate Cd, as compared with the nonmined ecotype.

The cadmium (II) and copper (II) adsorption properties of chemically pretreated biomass of red marine alga Gracilaria fisheri were investigated. Batch equilibrium experiments showed that the maximum adsorption capacity values of the pretreated biomass for cadmium and copper were 0.63 and 0.72 mmol g(-1), respectively. The equilibrium data fitted well to the Langmuir isotherm model. The adsorption capacity increased as pH increased and reached a plateau at pH 4.0. The cadmium and copper uptake rates were rapid with 90% of the biosorption completed within 30 minutes. The presence of light metal ions (Na+, K+, Mg2+ and Ca2+) in solution had an insignificant effect on cadmium and copper sorption capacity. These findings indicate a positive potential for the biosorbent development with effective heavy metal removal capacity in the presence of light metal ions in waste streams by using the biomass of plentifully available red marine algae.

Bioaccumulation of cadmium, copper, and zinc was examined in common ragworms Hediste diversicolor from control (Bay of Somme, Blackwater) and metal-rich (Seine estuary, Boulogne harbor, Restronguet Creek) sites in France and the United Kingdom. The degree of exposure in the field was assessed by considering both total concentrations in superficial sediment and the quantities of metals which may be released in vitro at different pH levels. Among the three contaminated sites, release of the three metals was not detectable in Boulogne harbor, in correlation with limited enhancement of the metal concentrations in the common ragworms from this site. Even at those sites where zinc could be released in vitro from the sediment, zinc concentrations were not enhanced in common ragworms, in agreement with previous findings indicating that the body content of this metal is regulated in H. diversicolor. At all the studied sites, bioaccumulated zinc was mainly in cytosolic form. The distribution of cadmium and copper varied according to the origin of the common rag-worms, the insoluble fraction increasing with the degree of contamination (cadmium in the Restronguet Creek, copper in the Seine estuary, and even more in Restronguet Creek). In the cytosolic fraction, metals were partly linked to cytosolic heat-stable thiolic compounds (CHSTC) with molecular masses (5-6 kDa and about 12 kDa) consistent with metallothionein-like proteins (MTLP). Metal-binding to MTLP varied with the degree of contamination and with the metal studied. In contrast to many invertebrates, the presence of metal-binding CHSTC (MM about 2 kDa) other than MTLP seems to be a peculiar feature of H. diversicolor.

Biosorption of Cd by the brown seaweed Sargassum polycystum biomass was experimentally investigated and mathematically modeled at different pH and ionic strength levels. From the potentiometric titration of the biomass, three types of functional groups were identified, and the dissociation constant and the numbers of these groups were determined. The carboxyl group (pK(H) 3.70 +/- 0.09) was found to play a major role in binding protons and Cd. The background ion, Li+, could interfere with the uptake of protons and Cd by competition forthe carboxyl sites. Whereas the binding mechanism on the carboxyl group was established as an ion exchange process, the second functional group, phosphonate (pK(H) 5.41 +/- 0.31), most likely bound metals by a complexation reaction. A biosorption model was developed based upon the binding mechanisms and was successfully used for predicting the isotherm and pH edge experiments. In addition, the speciation of the binding sites as a function of the pH was simulated using the developed model in order to visualize the distribution of Cd on the binding sites.

The biofilter potential of the freshwater bivalve, Lamellidens marginalis was examined in cage experiments conducted in a river canal (Ichhapore, 24-Parganas, West Bengal, India) receiving industrial effluents from steel and metal factories as well as from an ordinance factory. Cadmium is one of the major contaminants in this river canal. Lamellidens collected from pollution free natural ponds, were sorted into three size groups (large: 59+/-3.2 g, 10+/-2.3 cm; medium: 30+/-2 g, 6+/-1.7 cm and small: 13+/-1.5 g, 4+/-1.2 cm) were held in cages at three different sites along a cadmium concentration gradient. Concentrations of cadmium were measured from water, sediment and different tissues of Lamellidens at weekly intervals using atomic absorption spectrophotometric methods. Cadmium uptake by Lamellidens in all media were highly concentration dependent in both summer and winter months. For all three size groups, cadmium uptake was maximum in the gills at the beginning of experiment, and liver at the later phase. Cadmium uptake was maximum in the small bivalves and minimum in the large bivalves groups. Cadmium uptake was 11-67% higher during summer than during the monsoon season for all tissues and size groups. Estimation of concentration factor revealed that tissues were saturated with cadmium during the 13-14th week after Lamellidens introduction during summer, but remained unsaturated during the monsoon season. It is concluded that Lamellidens might be considered as an efficient biofilter for reclamation of aquatic environment having sub-lethal concentrations of cadmium.

The two main objectives of this study were to compare cadmium and zinc fluxes from a contaminated sediment to the water column in bioturbated and unbioturbated systems and jointly to analyze accumulation kinetics of these released metals by benthic filter-feeder bivalves. The experimental approach was based on indoor microcosms containing a two-compartment biotope: natural contaminated sediment (45 +/- 5 microg Cd/g, dry wt, and 1,938 +/- 56 microg Zn/g, dry wt) and water column. Four experimental conditions were studied: no organism added to the sediment-water biotope, presence of bivalves Corbicula fluminea, presence of Hexagenia rigida nymphs (bioturbation source), and presence of C. fluminea and H. rigida simultaneously. Results reveal that bioturbation produces a significant metal release into the water column via the resuspended sediment particles. The use of C. fluminea as an indicator of transferred metals in the water column shows that the metal bioavailability is very limited, quantities of cadmium and zinc bioaccumulated in the soft bodies being less than those measured in unbioturbated systems. This experimental study demonstrates that only the dissolved fraction resulting from diffusive metal fluxes across the sediment-water interface is bioavailable for this bivalve species.

This report describes a study in which in vitro fertilization methods were used to expose medaka (Oryzias latipes) eggs to cadmium (Cd(2+)). This approach was applied to address the differential sensitivity and cumulative potential of Cd(2+) when exposure was initiated early (before fertilization and water hardening of the chorion) versus later during embryo development (i.e., well after the chorion has undergone water hardening). Following range finding exposures (2.5, 10, 20, 40 or 80 mg/l) under artificially controlled experimental procedures, results from hatching success and embryo malformations showed the earlier exposure interval more sensitive than the assay involving only the embryonated egg. Subsequent accumulation studies have shown that the exposure initiated before fertilization apparently led to more Cd(2+) deposition in the chorion compared to the exposure during embryonated stages of the eggs. Similarly, values for total Cd(2+) indicated higher concentrations in those eggs exposed prior to--and during--water hardening. Results suggest an alteration of the properties of the zona radiata in the early-stage eggs, making it more permeable to the potential exit or entrance of waterborne agents even after water hardening. Ongoing studies must now address the development of more realistic exposure conditions of the gametes by using incubation media with osmolarities similar to surface waters, and by shortening duration for gamete exposure. Also, sensitive methods to localize Cd(2+) and to delineate the transfer from the chorion to the embryo are needed.

Concentrations of cadmium (Cd), lead (Pb) and zinc (Zn) in total soft tissues (ST) and byssus (BYS) of the green-lipped mussel Perna viridis from 11 different geographical locations off the west coast of Peninsular Malaysia were determined. The metal concentrations distributed between the BYS and ST were compared. The results of this study indicated that higher levels of Cd (1.31 microg/g), Pb (38.49 microg/g) and Zn (206.52 microg/g) were accumulated in the BYS than in the total ST (Cd: 0.29 microg/g; Pb: 8.27 microg/g; Zn: 102.6 microg/g). Semi-static and short period controlled laboratory experiments were also conducted for the accumulation and depuration of Cd, Pb and Zn in the total ST and BYS of P. viridis. The ratios (BYS/ST) for Pb and Cd from the laboratory experiments showed that the total ST accumulated more metals than the BYS. Therefore, these laboratory results disagreed with those found for the field samples. However, the laboratory results for the Zn ratio (BYS/ST) agreed with those of the field samples. It was evident that when compared to the ST, the BYS was a more sensitive biomonitoring organ for Zn while it could be a complementary organ for Cd and Pb in the total ST. Since total ST of P. viridis had been reported to have regulative mechanism for Zn, its BYS can be used as a biomonitoring organ for the identification of coastal areas exposed to Zn pollution.

Estuarine and marine near-shore environments are often subjected to heavy metal pollution. We establish a bioassay using the quantitative evaluation of metallothionein (MT) transcript in the fish hepatoma cell line, RTH-149, as a tool for detecting heavy metal pollution in brackish-marine water containing other pollutants in addition to heavy metals. RT-competitive polymerase chain reaction was used for the quantitative evaluation of the transcript in absolute units. Cadmium was used as a model pollutant to optimize two parameters of the assay: exposure periods (24, 96, 144 h) and salinity (0%, 25%, 50%, 75%, 100% sea water). Results revealed that salinity at or below 25% sea water at an exposure period of 144 h are the preferable conditions for detecting MT mRNA levels for in vitro assays employed on water samples from highly polluted brackish habitats.

To elucidate the differences between the detoxification mechanisms of essential metal (Zn) and non-essential metal (Cd) in Littorina brevicula that is highly resistant to a wide range of heavy metal concentrations, Asian periwinkles were exposed to Cd (400 microg/L), Zn (3000 microg/L) and a mixture of both metals. We examined metal accumulation, elimination and subcellular distribution for binding to proteins. The metal concentration in L. brevicula increased gradually with exposure time (up to 70 days), following which accumulated levels reached saturation point. The accumulated Zn content was increased in the presence of Cd, while Cd uptake was decreased when Zn was present. During the depuration period (42 days), Cd was not removed from periwinkles, while Zn was eliminated in a rate of 2.19 microg Zn g(-1) day(-1). This elimination rate was particularly high on exposure to the metal mixture (3.80 microg Zn g(-1) day(-1)). Subcellular distribution studies on Cd and Zn revealed that most Cd (80%) was bound to cytosolic ligand, while more than 75% Zn was distributed in the membrane (insoluble) fraction. An additional difference in sequestering of metal in the cytosol was noted between Cd and Zn; most Cd in the cytosol was bound to metallothionein-like cadmium binding protein, MBP-1 (9.8 kDa), while the profile for Zn distribution revealed the presence of four Zn-binding ligand peaks, specifically, HMW (60 kDa), MBP-1 (9.8 kDa), MBP-2 (5 kDa) and LMW (<1 kDa). Our data confirm that metallothionein-like cadmium binding protein, MBP-1, has the same affinity for Zn, while MBP-2 displays comparatively higher affinity for Zn than Cd.

Experimental studies showed that brown marine algae, Sargassum vulgaris and Padina pavonia, can be used to develop an efficient biosorbent for heavy metal removal from aqueous solutions. Sargassum vulgaris exhibited high uptake capacities for cadmium (0.9 to 1.1 mmol Cd/gr) and nickel (0.85 to 1 mmol Ni/gr) that are higher than those of other types of biomass and powdered activated carbon, while P. pavonia showed a broader range of nickel and cadmium uptake capacities (0.7 to 1 mmol Ni/gr and 0.8 to 1.1 mmol Cd/gr). The metal adsorption and desorption processes were rapid, with 70% of the sorption and desorption completed within 10 minutes. The equilibrium data for both algae fit well to Langmuir and Freundlich isotherm models. More than 90% desorption of adsorbed metals from the algae was achieved by hydrochloric acid and ethylenediaminetetraacetic acid (1:1 molar ratio). After eight to nine adsorption and desorption cycles, S. vulgaris showed a 15 to 35% decrease in metal uptake capacities; P. pavonia showed a higher decrease of 50 to 60%.

An experimental study of the role of metallothioneins (MTs) in Cd and Zn depuration processes in the freshwater bivalve Corbicula fluminea was conducted after in situ exposure on the river Lot (France). Specimens of adult C. fluminea were first transplanted from a lacustrine reference site to a polymetallic polluted station (Bouillac, (B)) for a 42-days' exposure period from September to November 1996. They were then depurated after transfer to the laboratory, and were sub-sampled periodically until May 1997. During the first phase, MT concentrations measured with the Mercury-Saturation Assay were induced for a factor of 3.5 compared with time 0, whereas metal uptake showed accumulation factors of 17 and 4 for Cd and Zn, respectively. During the depuration phase, Cd and Zn concentrations decreased by 18 and 70%, respectively, giving estimated biological half-lives of 500 and 40 days. During the same period, MT concentrations decreased by 37% after transfer under unpolluted conditions, especially between 0 and 3 days, suggesting that MTs play a predominant role in Cd depuration. The quantity of Cd sequestered by the MT fraction, after size-exclusion liquid chromatography, represents on average 40% of the total Cd bioaccumulated in the soft body of the molluscs, compared with only 4-9% for total accumulated Zn. This essential metal was principally bound to low molecular weight proteins, which represented 20% of total Zn. Furthermore, it was observed that MTs had a key role in Cd remanence in the bivalves, and it was also reported that other proteins or small peptides were involved in the depuration of Zn.