Metal distributions in Tigriopus brevicornis (Crustacea,Copepoda) exposed to copper,zinc, nickel,cadmium, silver,and mercury,and implication for subsequent transfer in the food web

The marine copepod Tigriopus brevicornis is a benthic microcrustacean inhabiting splashed rock pools in the intertidal zone. The genus has a worldwide distribution, and some species play an important role as a link in trophic webs. It is well established that many crustaceans are able to survive in contaminated environments by storing metallic pollutants in detoxified form, and thus, they may represent a source of contaminants for their predators. The present study was designed to determine the distribution of bioaccumulated metals, both essential and nonessential, with a view to assessing their availability to the next trophic level. Groups of 1000–1500 adult copepods were exposed for 1–14 days to Ag, Cd, Cu, Hg, Ni, and Zn in water. Three concentrations, chosen to be realistic in comparison with those encountered in polluted environments, were tested for each metal. Copepods were homogenized and metals were analyzed in supernatants (i.e., metals stored in soluble form in soft tissues or easily remobilized from the exoskeleton) and pellets (including metal‐rich detoxificatory granules or with cellular debris) recovered after centrifugation. Another experiment, consisting of desorption tests, was designed to evaluate the fraction of metals loosely bound onto the exoskeleton. The bioaccumulation ability is highly variable, as shown by the ratios between the concentrations reached in T. brevicornis experimentally exposed to different metals (at higher dose and at day 14) and those in controls (7, 12, 18, 26, 53, and 99, respectively, for Zn, Cu, Ni, Cd, Ag, and Hg). Cu, Zn, and Ni concentrations in copepods increased linearly with time over the whole range of exposure concentrations, whereas a plateau body metal concentration was reached with time particularly at the highest exposure concentrations for Cd, Ag, and Hg. Metals bound onto the exoskeleton were remobilized to different extents, the percentages of desorption being 11, 14, 16, 19, 31, and 32, respectively, for Zn, Cd, Cu, Ni, Ag, and Hg. Metals mainly present in the supernatant (Cd, Ni, Zn) are probably more able to be transferred along a food chain than those which were equally distributed between soluble and insoluble fractions (Ag, Cu, and Hg). © 2009 Wiley Periodicals, Inc. Environ Toxicol 25: 350–360, 2010.     

The neurotoxic effects of heavy metal exposure on GABAergic nervous system in nematode Caenorhabditis elegans

The number of cell body or synapse made by Caenorhabditis elegans GABAergic neurons is constant during development. The neurotoxic effects of metal (Pb, Hg, Cu, Cd, Cr, and Mn) exposure on GABAergic motor neurons were investigated in C. elegans. Exposure to examined metals could not alter the position of GABA neurons, whereas exposure to high concentrations (75 μM and 200 μM) of metals caused noticeable axonal degeneration and neuronal loss in nerve cords, suggesting neurodegeneration will be induced by metal exposure to different degrees. In addition, exposure to Pb, Hg, Cu, and Cd at the low concentration (2.5 μM) could also induce obviously neuronal loss. Moreover, exposure to high concentrations (75 μM and/or 200 μM) of most of examined metals significantly reduced the relative size and fluorescent intensities of AVL, RMEs, and RIS neurons. Therefore, the neurodegeneration and abnormal structures may be formed in GABAergic motor neurons after metal exposure, and the endpoint of neuronal loss will be useful for the neurotoxicity assessment from trace metal exposure.     

市售灵芝孢子粉7种重金属元素含量测定及膳食暴露风险评估

目的 测定市售灵芝孢子粉中铅、镉、砷、汞、铜、铬、镍7种重金属元素的残留量并评估其膳食暴露的健康风险。方法 收集市售灵芝孢子粉(包含中药饮片、保健食品、食品和农产品等不同产品类型)40批次,对7种重金属元素进行检测,采用点评估方法对灵芝孢子粉中7种重金属元素的膳食暴露量进行评估。结果 40批灵芝孢子粉中7种重金属元素检出率均为100%,有8批样品重金属元素超出拟定的限度。重金属元素膳食暴露评估显示消费者食用灵芝孢子粉摄入铬的量存在一定的膳食暴露健康风险。结论 灵芝孢子粉中铅、镉、砷、汞、铜、镍6种重金属元素膳食暴露低于暂定可耐受摄入量,对人体健康产生危害的风险可接受;铬元素膳食暴露的最大值和第95百分位数(P95)值超过暂定可耐受摄入量,存在一定的健康风险。     

Combined toxicity of dissolved mercury with copper, lead and cadmium on embryogenesis and early larval growth of the Paracentrotus lividus sea-urchin

The individual and combined toxicity of dissolved mercury, copper, lead and cadmium has been investigated by using the Paracentrotus lividus sea-urchin embryo-larval bioassay. Embryogenesis success and early larval growth have been recorded after incubation of fertilised eggs in seawater, both with single metals and binary combinations of Hg with every other metal. For individual metals the ranking of toxicity was Hg > Cu > Pb > Cd, with EC₅₀ values of 21.9, 66.8, 509 and 9240g/l, respectively. Lowest observed effect concentrations (LOEC) for early larval growth were approximately three times lower than the EC₅₀ values for Hg, Cu and Pb, and more than two orders of magnitude lower for Cd, emphasizing the danger of underestimating toxicity when only lethal effects are recorded. Marking & Dawson's additive indices ranged from 0.10 to 0.19, indicating additive effects with a slight trend to synergism, which was statistically significant for the Hg–Pb combination only. Hayes' additive indices were within the margins considered acceptable to describe additive interactions.     

Heavy metal (Pb,Cu, Zn,and Cd) concentrations in the water and muscle of common carp (Cyprinus carpio) fish and associated non-carcinogenic risk assessment: Alagol wetland in the Golestan,Iran

Short- and long-term exposure to heavy metals can be dangerous for human health. One of the main routes of exposure to heavy metals is intake of seafood such as fish. In this study, lead (Pb), copper (Cu), zinc (Zn), and cadmium (Cd) concentration in the water and muscle of C. Carpio fish was measured and non-carcinogenic risk of these heavy metals was estimated. The mean (range) concentrations of Cu, Zn, Pb, and Cd were 7.92?±?7.99 (1.22–39.43?mg/kg), 120.90?±?106.25 (1.15–477?mg/kg), 5.84?±?5.22 (ND-21.86?mg/kg), and 0.027?±?0.043 (ND-0.14). Except Cd, the concentrations of Cu, Zn, and Pb were significantly more than Food and Agricultural Organization United Nations (FAOUN) maximum guidelines (p??Cu?>?Pb?>?Cd in the water and muscle tissue of C. carpio fish. Lowest and highest target hazard quotient (THQ) for adults was related to Cd (0.005) and Pb (0.252) and for children, Cd (0.003) and Pb (0.168), respectively. The rank order of THQ for adults and children are Pb?>?Zn?>?Cu?>?Cd. Since THQ and hazard index (HI) for both adults and children were significantly lower than 1 (p?C. Carpio fish consumption.     

Potential health risks due to heavy metal uptake via consumption of Thunnus thynnus from the northern Levantine Sea

The potential human health risks of copper (Cu), zinc (Zn), arsenic (As), cadmium (Cd), mercury (Hg) and lead (Pb) in Thunnus thynnus from the northern Levantine Sea were assessed. The mean concentrations (mg/kg) of metals were found as 0.819 for Cu, 8.344 for Zn, 2.102 for As, 0.002 for Cd, 0.001 for Hg and 0.115 for Pb. Even though these values were below the permitted levels, 11% of the samples contained Pb above the limits. Estimated weekly intakes were conspicuously lower than the PTWI values. The target hazard quotients (THQs) of each metal and total THQ of combined metals remained well below 1, showing no public health risk for an average consumer.     

Valve movement response of the mussel Mytilus galloprovincialis to metals (Cu, Hg, Cd and Zn) and phosphate industry effluents from Moroccan Atlantic coast

Valve activity was measured in the Mediterranean mussel Mytilus galloprovincialis in response to sublethal concentrations of four metals (Hg, Cu, Zn and Cd) and two phosphate industry effluents from the Atlantic coast of Morocco. Valve movements were monitored using a proximity inductive sensor which could display all activity figures from full closure to wide opening of the shell valves. In a 1 h exposure experiments, all metals induced a decrease in the time of normal opening and the appearance of sequences of stress behaviour, including enhanced valve adductions and complete closure at high concentrations. Mercury (tested from 5 to 75 μg Hg l⁻¹) was the most toxic to the valve activity, with a threshold effective concentration at 10 μg Hg l⁻¹ and full valve closure occurring at 50 μg Hg l⁻¹. Copper (15–150 μg Cu l⁻¹) showed a toxic effect starting at threshold concentration of 20 μg Cu l⁻¹ and induced full valve closure at 150 μg Cu l⁻¹. Zinc (100–500 μg Zn l⁻¹) was effective in reducing the time of normal opening (threshold concentration at 100 μg Zn l⁻¹) but no complete closure was recorded in any of the tested concentrations. For cadmium (1000–5000 μg Cd l⁻¹), the valve activity was insensitive for exposures under 2000 μg Cd l⁻¹. Results for the testing of several samplings of the phosphate industry effluents (Safi and Jorf Lasfar) showed that their toxicity varied over the time. The effluent of the Jorf Lasfar plant (2–9.4%) was, however, more toxic than that of Safi (1–25%). In the light of these results, the sensitivity of the valve activity of Mytilus galloprovincialis to pollutants and its usefulness for in situ monitoring of coastal pollution in Morocco are discussed.     

Accumulation of Trace Elements by <Emphasis Type="Italic">Pistia stratiotes</Emphasis>: Implications for phytoremediation

The toxicity of eight potentially toxic trace elements (Ag, Cd, Cr, Cu, Hg, Ni, Pb and Zn) to Pistia stratiotes was examined to determine if this plant showed sufficient tolerance and metal accumulation to be used to phytoremediate waste water and/or natural water bodies polluted with these heavy metals. Young plants of equal size were grown hydroponically and amended with 0, 0.1, 0.3, 0.5, 1.0, 3.0 and 5.0 mM of each heavy metal individually for 21 days. Root elongation as well as emergence of new roots decreased significantly with increase in metal concentrations. The plant had the lowest and the highest tolerance indices for Hg and Zn respectively. The study indicated reduction in the rate of leaf expansion relative to metal type, their concentrations and the duration of exposure. A significant reduction in biomass production was observed in metal treated plants compared with the control plants. The relative growth rate of P. stratiotes was retarded by heavy metals under study. All trace elements accumulated to higher concentrations in root tissue rather than in shoot. Trace element accumulation in tissues and the bioconcentration factors were proportional to the initial concentration of individual metals in the growth medium and the duration of exposure. In terms of trace element removal, P. stratiotes presented differential accumulation and tolerance levels for different metals at similar treatment conditions. The implications of these results for phytoremediation are discussed.     

Neurobehavioral changes in metallothionein-null mice prenatally exposed to mercury vapor

We studied the neurobehavioral effects of prenatal exposure of MT-null and wild-type mice to elemental mercury vapor (Hg0). Pregnant mice of both strains were repeatedly exposed to Hg0 vapor at 0.50 and 0.56 mg/m3 for 6 h/day until the 18th day of gestation. The behavioral effects were evaluated with locomotor activity in the open field, learning ability in the passive avoidance response and spatial learning ability in the Morris water maze at 12 weeks of age. Hg0-exposed MT-null mice showed a significant decrease in total locomotor activity in males, and a learning disability in the passive avoidance response and a retarded acquisition in the Morris water maze in females as compared with the control. In contrast, Hg0-exposed wild-type mice did not differ from controls in the three behavioral measurements. The results indicate that MT-null mice would be more susceptible than wild-type mice to the behavioral neurotoxicity of prenatal Hg0 exposure. Mercury concentrations in the brain of both strains were slightly higher in the exposed group than in the control group, indicating the retention of residual mercury even 12 weeks after the cessation of the exposure. Brain concentrations of mercury were also significantly higher in the exposed-females than exposed-males in either strain. From these results, we suggest that the increased susceptibility of MT-null females to behavioral changes caused by prenatal Hg0 exposure is due to a greater retention of mercury and lack of MT-I,-II in the brain.     

Prolonged effects of the insecticide dimethoate on locomotor behaviour in the woodlouse,Porcellio scaber Latr. (isopoda)

Beneficial invertebrates living in hedgerows and woodland adjacent to arable land, are almost inevitably exposed to small doses of pesticides. This can present a threat to these invertebrates even at sublethal levels. Locomotor behaviour is intrinsic to many more complex behavioural responses such as predator avoidance, migration, mate seeking, etc., but is also closely related to the physiological status of the animal. Further, locomotor activity is quantifiable with the aid of modern video and computer technology. In the present study, the effect of a 48 h exposure of the woodlouse Porcellio scaber to soil contaminated with one-tenth of the LD₂₀ (96 h) dimethoate dose was quantified using computer-automated video tracking. Dimethoate-exposed woodlice were recorded for one night prior to dimethoate exposure and for two nights on contaminated soil. After a recovery period of 21 days, the woodlice were recorded for a further night. Control animals were recorded in parallel on soil treated with water. Over the 48 h of exposure, dimethoate induced a gradually increasing hyperactivity in terms of time spent in activity, mean velocity and path length and a suppression of turning rate when compared with controls. No recovery was seen after the 21 days on uncontaminated soil. These effects were statistically significant only in male woodlice.     

The interplay between chemical speciation and physiology determines the bioaccumulation and toxicity of Cu(II) and Cd(II) to Caenorhabditis elegans

Using the well‐documented model organism Caenorhabditis elegans, a combined analysis of metal speciation in the exposure medium and body burdens of metals (Zn, Cu and Cd) was performed, and factors that are predictive of toxicological endpoints in single metal and mixed metal exposures were identified. Cu, and to a lesser extent Cd, is found to associate with Escherichia coli in the exposure medium (the food source for C. elegans) as evidenced by the observed decrease in both their dissolved and free metal ion concentrations. Together with a critical analysis of literature data, our results suggest that free metal ion concentrations and thus aqueous uptake routes are the best predictor of internal concentrations under all conditions considered, and of metal toxicity in single metal exposures. Additional factors are involved in determining the toxicity of metal mixtures. In general, the eventual adverse effects of metals on biota are expected to be a consequence of the interplay between chemical speciation in the exposure medium, timescale of exposure, exposure route as well as the nature and timescale of the biotic handling pathways.     

Prediction and risk assessment of five heavy metals in maize and peanut: A case study of Guangxi,China

To assess the contamination levels and health risk of cadmium (Cd), copper (Cu), mercury (Hg), lead (Pb), and zinc (Zn) to human beings, the concentrations of these heavy metals in soil were surveyed and the concentrations in maize and peanut grains were estimated by models. The geo-accumulation index (I _geo) was calculated, and chronic daily intake (CDI), hazard quotient (HQ) and hazard index (HI) were estimated. Results indicated that the concentrations of Cd, Cu, Hg, Pb, and Zn in the soil samples exceeded the limit set by authorities in China. However, the concentrations in maize and peanut grains were rarely higher than the allowable concentrations suggested by the Ministry of Health of China (MHC). In accordance with geo-accumulation, these heavy metals in soil samples were polluted to different extents. Prediction models were developed to effectively assess the health risk of using TOC, Mn, pH, and CaO to human beings. Therefore, the concentrations of these heavy metals in the grains could be decreased by changing their levels in soil. The CDI, HQ, and HI were estimated by estimating concentrations of Cd, Cu, Pb, and Zn in maize grains, indicating that these metals exhibited a slight health risk to adult residents.     

Cadmium and mercury accumulation in rat hepatocytes: interactions with other metal ions.

The uptake of essential metals, such as calcium, copper (Cu), iron (Fe), and zinc (Zn), occurs through processes that include energy-independent carrier mechanisms as well as ion channels. Since cadmium (Cd) and mercury (Hg) inhibit the uptake of these metals, this study examined whether the essential metals in turn affect Cd and Hg accumulation. The uptake of 3 microM Cd was inhibited by Cu, Fe, Zn, and Hg, with 100 microM Zn having the greatest effect. Kinetic analysis indicated that these metals inhibited Cd accumulation in a competitive manner. In comparison, neither the essential metals nor Cd had any significant effect on Hg accumulation. At 4 degrees C the accumulation of Cd was reduced to 20% of that at 37 degrees C, while Hg uptake remained unaffected. The efflux of Cd from the hepatocytes was biphasic, energy-independent, and not affected by Zn, Cu, or Fe. Thus the essential metals decreased Cd accumulation by inhibiting its uptake. On the other hand, Hg decreased Cd accumulation by both inhibiting its uptake and enhancing its efflux. As determined by the organic SH blockers, nearly two-thirds of the Cd entered the hepatocytes through processes involving the SH ligands. The uptake of Hg, however, was not affected by the SH blockers. Furthermore, the fraction of membrane-bound Hg at 3 microM concentration was 2.5 times greater than Cd, indicating that Hg is associated with additional binding sites not utilized by Cd. These results suggest that in hepatocytes Cd uptake occurs mainly through the SH-containing transport processes associated with the uptake of Zn and, to a smaller extent, Cu and Fe. Hg can inhibit Cd uptake by binding to these sites; however, its own uptake occurs via other processes that remain to be elucidated.     

A review of the effects of heavy metals on freshwater mussels

The widespread recent decline in the species diversity and population density of freshwater mussels in North America may be partly related to chronic, low-level exposure to toxic metals. As benthic filter-feeding organisms, freshwater mussels are exposed to metals that are dissolved in water, associated with suspended particles and deposited in bottom sediments. Thus, freshwater mussels can bioaccumulate certain metals to concentrations that greatly exceed those dissolved in water. In adult mussels, the most common site of metal uptake is the gill, followed by the mantle and the kidney. The toxic effects of metals on freshwater mussels have been examined in a few acute toxicity tests, but the sublethal effects of long-term exposure to low environmental concentrations are little understood. Sublethal exposure to metals can alter growth, filtration efficiency, enzyme activity and behaviour. Sublethal effects are frequently observed at concentrations that are only half the lethal concentrations. However, few toxicity tests have used environmentally realistic exposure concentrations. Total concentrations of Cd, Cu, Hg and Zn in many oxic surface waters are in the ngl^-1 range, yet many toxicity studies have exposed mussels to concentrations in the gl^-1 or even the mgl^-1 range. An understanding of the processes by which metals affect freshwater mussels would provide insights on the ecotoxicological significance of metal contamination to natural mussel populations and aid in the development of water-quality criteria that adequately protect mussels.     

Effects of various trace metals on the binding of cadmium to rat hepatic metallothionein determined by the Cd/hemoglobin affinity assay

The Cd/hemoglobin affinity assay is finding increasing use as an indicator of metallothionein in a variety of biological tissues. Because the assay relies on the ability of heat-stable proteins to bind Cd, it is important to know the relative affinities of different trace metals to bind to such proteins, relative to Cd. This study examines the ability of 15 trace metals to prevent the binding of Cd to metallothionein using the Cd/hemoglobin affinity assay for metallothionein. Cd, Cu, Hg, and Ag were the only metals tested which significantly inhibited the binding of a fixed concentration (2 microM) of 109Cd to a crude preparation of rat hepatic metallothionein. As, Co, Cr, Fe, Mn, Mo, Ni, Pb, Sn, Th, and Zn had no inhibitory effect at the highest concentrations tested. However, As, Sn, Th, and Zn prevented the precipitation of hemoglobin at relatively low concentrations and, thus, could not be fully tested for inhibitory potency. Cu was the most potent inhibitor, producing more than 90% inhibition at 5 microM, followed by Ag, Hg, and Cd, which produced 76, 72, and 65% inhibition of cadmium binding at 5 microM, respectively. These results suggest that caution should be taken in interpreting metallothionein concentrations obtained by the Cd/hemoglobin affinity assay in tissues which contain relatively a high concentration of Cu, Ag, or Hg, relative to that of Cd.     

Translational responses and oxidative stress of mussels experimentally exposed to Hg, Cu and Cd: one pattern does not fit at all

Certain metals, like Hg, Cu and Cd, are capable of down-regulating protein synthesis in several marine organisms, including Mytilus galloprovincialis. Nevertheless, due to the complexity of the environmental stress, it is difficult to evaluate the influence of individual metals on protein synthesis via field studies. To bypass this difficulty, experimental studies were carried out on M. galloprovincialis exposed in aquarium for 15 days to one of three selected metal salts, HgCl(2), CuCl(2) and CdCl(2). Polysome profile was determined in digestive gland extracts of the exposed mussels as a way of measuring the functional status of ribosomes, superoxide radical production and lipid peroxidation as indicators of oxidative stress, metallothionein content as a metal detoxification index, and superoxide dismutase activity as a free radicals-scavenging index. Exposure of mussels to Hg(2+) or Cu(2+) resulted in a concentration- and time-dependent decrease in the polysome content of digestive gland cells, which at 15th day of exposure and at the highest metal concentrations tested, was 32% and 19% of the control, respectively. Both metals, at the concentrations used (<40 μg/L), did not significantly influence the oxidative stress biomarkers. By contrast, Cd(2+) treatment significantly induced superoxide radical production and lipid peroxidation in digestive gland cells, hinting that mussels suffered from oxidative stress. Polysome levels in Cd(2+)-exposed mussels were initially decreased by day 5 in digestive gland cells and then elevated to reach nearly the control levels by 15 days of exposure. Elevated protein synthesis was associated with significantly increased production of metallothioneins, whereas such increase was not recorded in Hg(2+)- or Cu(2+)-exposed mussels. Interestingly, the ribosome efficiency at initiating protein synthesis followed a similar pattern of polysome alterations, a fact suggesting that regulation of protein synthesis mainly occurred at the initiation phase of translation. Overall, these results suggest that the effect of each metal on protein synthesis is idiosyncratic and depends on its ability to induce specific cellular defense mechanisms against oxidative stress.     

Inducibility of metallothionein biosynthesis in the whole soft tissue of zebra mussels Dreissena polymorpha exposed to cadmium,copper, and pentachlorophenol

Freshwater mussels Dreissena polymorpha (Pallas, 1771) were exposed to the elevated concentrations of Cd (10, 50, 100, and 500 μg/L), Cu (10, 30, 50, and 80 μg/L), and an organochlorinated pesticide, pentachlorophenol (PCP) (1, 10, and 100 μg/L). Induced synthesis of biomarker metallothionein (MT) and changes in concentrations of cytosolic Cd, Cu, and Zn in the whole soft tissue of mussels were monitored after a 7‐day laboratory exposure to the contaminants. A clear dose‐dependent elevation in the MT concentration was observed after exposure to Cd at doses of 10–100 μg/L, and this increase of MT content was accompanied with a linear increase of cytosolic Cd. Cd concentration of 500 μg/L caused no additional increase of MT and Cd in mussel cytosol, suggesting possible toxic effects due to exceeding cellular inducible/defense capacity. Cu exposure resulted with variable changes in MT concentrations, with no clear linear relationship between MT and Cu concentrations in water, although a progressive dose‐dependent accumulation of Cu in the soluble fraction of mussel tissues was recorded. A decrease of cytosolic Zn was evident at higher exposure concentrations of both metals used. PCP in concentrations applied was unable to induce MT synthesis, but the higher concentrations of PCP influenced the cytosolic metal concentrations. In conclusion, the results obtained confirm the specificity of MT induction in D. polymorpha as an biological response on metal stimulation, especially by cadmium, being more closely correlated to MT than copper within the ecologically relevant concentration range. The strong induction potential of cadmium as well as an absence of MT induction following exposure to PCP as an organic chemical contaminant are supporting evidences for usage of zebra mussel MT as a specific biomarker of Cd exposure in biomonitoring programs. © 2009 Wiley Periodicals, Inc. Environ Toxicol, 2010.     

Subcellular interactions of dietary cadmium, copper and zinc in rainbow trout (Oncorhynchus mykiss)

Interactions of Cu, Cd and Zn were studied at the subcellular level in juvenile rainbow trout (Oncorhynchus mykiss) fed diets containing (μg/g) 500 Cu, 1000 Zn and 500 Cd singly and as a ternary mixture for 28 days. Livers were harvested and submitted to differential centrifugation to isolate components of metabolically active metal pool (MAP: heat-denaturable proteins (HDP), organelles, nuclei) and metabolically detoxified metal pool (MDP: heat stable proteins (HSP), NaOH-resistant granules). Results indicated that Cd accumulation was enhanced in all the subcellular compartments, albeit at different time points, in fish exposed to the metals mixture relative to those exposed to Cd alone, whereas Cu alone exposure increased Cd partitioning. Exposure to the metals mixture reduced (HDP) and enhanced (HSP, nuclei and granules) Cu accumulation while exposure to Zn alone enhanced Cu concentration in all the fractions analyzed without altering proportional distribution in MAP and MDP. Although subcellular Zn accumulation was less pronounced than that of either Cu or Cd, concentrations of Zn were enhanced in HDP, nuclei and granules from fish exposed to the metals mixture relative to those exposed to Zn alone. Cadmium alone exposure mobilized Zn and Cu from the nuclei and increased Zn accumulation in organelles and Cu in granules, while Cu alone exposure stimulated Zn accumulation in HSP, HDP and organelles. Interestingly, Cd alone exposure increased the partitioning of the three metals in MDP indicative of enhanced detoxification. Generally the accumulated metals were predominantly metabolically active: Cd, 67-83%; Cu, 68-79% and Zn, 60-76%. Taken together these results show both competitive and cooperative interactions dependent on the subcellular fraction, metal, exposure duration and relative metal exposure concentrations. Competitive interactions likely result from ionic mimicry with the metals displacing each other from common binding sites, whereas cooperative interactions suggest increased abundance of metal binding sites and/or existence of metal-specific non-interacting binding sites in some of the fractions. Moreover, the changes in subcellular distribution of the biometals Cu and Zn due to Cd exposure together with the shifts of the metals between MAP and MDP observed may have toxicological consequences.