Single and joint effects of Zn and Cd on Porcellio scaber (Crustacea, Isopoda) exposed to artificially contaminated food

This study aimed at determining effects of Zn, Cd and their equitoxic mixtures on metal assimilation and food consumption of the terrestrial isopod Porcellio scaber, in relation to metal availability in the food. Cd was four times less water-extractable than Zn. Cd or Zn extractability was affected neither by metal concentration nor by the presence of the other metal. In single metal exposures, assimilation efficiency (AE) was up to five times higher for Cd than for Zn. In a mixture, AE of Cd significantly increased at low mixture concentrations and decreased at high mixture concentrations. AE of Zn significantly increased at intermediate mixture concentrations. Effects of the Zn and Cd mixture on food consumption were additive (28-day EC_50,total=1.10 TU; EC_{50,water-extractable}=1.18 TU) when based on total and water-extractable concentrations but antagonistic when related to internal metal concentrations in the isopods (EC_50,internal=1.40 TU).     

Metal-metal interactions of dietary cadmium, copper and zinc in rainbow trout, Oncorhynchus mykiss

The influence of metal-metal interactions on uptake, accumulation, plasma transport and chronic toxicity of dietary Cu, Cd and Zn in rainbow trout (Oncorhynchus mykiss) was explored. Juvenile rainbow trout were fed diets supplemented with (μg/g) 500 Cu, 1000 Zn and 500 Cd singly and as a ternary mixture at 2.5% body weight daily ration for 28 days. Complex interactions among the metals dependent on the tissue/organ, metals ratios and duration of exposure were observed. While Zn did not accumulate, whole-body Cd and Cu concentrations increased following linear and saturation patterns, respectively. Early enhanced whole-body Cu accumulation in fish exposed to the metals mixture was correlated with reduced Cd concentration whereas late enhancement of Cd accumulation corresponded with elevated Cd concentration. This suggests early mutual antagonism and late cooperation between Cd and Cu probably due to interactions at temporally variable metal accumulation sites. At the level of uptake, Cd and Cu were either antagonistic or mutually increased the concentrations of each other depending on the duration of exposure and section of the gut. At the level of transport, enhanced Cd accumulation in plasma was closely correlated with reduced concentrations of both Zn and Cu indicating competitive binding to plasma proteins and/or antagonism at uptake sites. Compared to the Cu alone exposure, Cu concentrations were either lower (gills and carcasses) or higher (liver and kidney) in fish exposed to the metals mixture. On the other hand, Cd accumulation was enhanced in livers and carcasses of fish exposed to the mixture compared to those exposed to Cd alone, while Zn stimulated Cu accumulation in gills. Chronic toxicity was demonstrated by elevated malondialdehyde levels in livers and reduced concentrations of Zn and Cu in plasma. Overall, interactions of Cd, Cu and Zn are not always consistent with the isomorphous competitive binding theory.     

Metal accumulation and biomarker responses in Daphnia magna following cadmium and zinc exposure

Metal accumulation (quantified as body burden) and the responses of two biomarkers (metallothionein [MT] induction and superoxide dismutase [SOD] activity) in a freshwater cladoceran Daphnia magna were quantified after being exposed to different concentrations of Cd and Zn for 3 d. The Cd and Zn body burdens increased with increasing exposure concentrations. The responses of biomarkers were metal-specific and concentration-dependent. As a detoxification mechanism, MT was induced by exposure to Cd or Zn or Cd + Zn and was dependent on the exposure concentrations. Low concentrations of Cd or Zn exposure increased the SOD activity, which was, however, inhibited at higher metal exposure concentrations. Metallothionein concentrations in daphnids were significantly related to the metal body burden. The SOD activity was inversely related to Cd body burden, while it was independent of the Zn body burden. Survivorship of D. magna was high at lower Cd/MT ratios in the animals but then decreased linearly when the ratio exceeded six. In contrast, the relationship between survivorship and Zn/MT ratio was different due to the essentiality of Zn. Overall, MT induction was a useful indicator of metal pollution in cladocerans.     

Contribution of soil,water and food consumption to metal exposure of children from geological enriched environments in the coastal zone of Lake Victoria,Kenya

Geologically enriched environments may contain high concentrations of some metals. In areas where industrial exposures remain superficial, children may be exposed to these geological metals through soil, drinking water and consumption of food locally grown. The aim of this study was to assess the contribution of soil, water and food consumption to cadmium (Cd), chromium (Cr), copper (Cu), zinc (Zn), cobalt (Co) and titanium (Ti) body burden of children in the geologically metal rich coastal zone of Lake Victoria, Kenya. We evaluated the relationship between the metal body burden of children by analyzing the hair samples and the estimated metal intake through exposure to soil, drinking water, and food consumption. The body burdens of all metals in children at the exposed sites were high, suggesting environmental exposure. Most of the foods consumed resulted in metal intake below the maximum recommended daily intake. However, the net contribution of all food items jointly exceeded the recommended maximum daily intake at some of the exposure sites. Our results further demonstrated that the highest intake of metals occurred via ingestion of high quantities of the cyprinid fish Rastrineobola argentea. Positive linear relationships between the metal body burden in children and estimated daily intake were observed for Cd, Cr, Ti in children consuming high quantity of R. argentea; for Zn and Co in children highly exposed to soils and consuming high quantity of Brassica oleraceae, while Co burden in the body was associated with high consumption of maize meal. This study demonstrated that exposure to soil and consumption of higher quantities of some foods contributed to the increased metal body burdens of children in a geologically exposed region.     

Alteration of dissolved cadmium and zinc uptake kinetics by metal pre-exposure in the Black Sea bream (Acanthopagrus schlegeli)

We first examined the uptake kinetics of Cd and Zn in the juvenile marine black sea bream (Acanthopagrus schlegeli) over a wide range of ambient Cd and Zn concentrations, and the relationships with metal accumulation (uptake rate and amount of nonexchangeable surface binding) were established for different fish tissues. Both Cd and Zn accumulation in the body increased linearly with exposure time after the initial metal surface binding. The dissolved Cd and Zn uptake rate constants were 2.64 and 6.50 L/kg/d, respectively, and the kinetics followed a first-order process. No evidence of biphasic transport was found, in contrast to the situation in freshwater fish. Viscera were the most important sites of metal uptake, and gills were the second most important sites. The black sea breams were then acclimated at different Cd or Zn concentrations from either waterborne or dietary source for one week, and the alteration of metal uptake kinetics or subcellular distribution and metallothionein (MT) induction were further quantified. The Cd body burden was enhanced up to 8.6- and 49-fold after waterborne and dietary Cd pre-exposure, respectively. Cadmium pre-exposure also altered the tissue-specific subcellular Cd distribution and significantly elevated tissue MT levels. In contrast, the black sea breams were able to regulate Zn accumulation, and waterborne or dietary Zn pre-exposure had only weak influences on Zn body burden and redistribution. Both Cd and Zn pre-exposures enhanced the metal uptake rate constants, whereas the nonexchangeable surface bindings were less impacted by these pre-exposures. We demonstrated a positive relationship between the Cd uptake rate and Cd or MT concentration in the fish. Pre-exposure to metals may substantially modify the kinetics of metal uptake.     

Kinetic uptake of bioavailable cadmium,selenium, and zinc by Daphnia magna

Kinetic uptake of Cd, Se(IV), and Zn by Daphnia magna from the dissolved phase was determined using radiotracer techniques in moderately hard water. The metal influx rate and distribution in the soft tissue and the exoskeleton of the daphnids as influenced by metal concentration, inorganic ligands including pH, Ca2+ and SO4(2-), and body size were quantified. When the metal concentrations were <180 nM for Cd and <769 nM for Zn, the concentration factor in daphnids increased linearly within the 12 h of exposure. At a higher concentration, apparent steady state was reached after 3 h of exposure. Cadmium and Zn distribution in the soft tissues was not affected by the total ambient concentrations, whereas Se distribution in the soft tissue decreased by 7 to 10% with increasing Se concentration from 16 to 643 nM. A linear positive power relationship was found between the influx rates of the metals and the ambient concentrations. The concentration factor for Se, however, decreased significantly with increasing Se concentration in water. The influx rate of metals was inversely related to the body size in a power function. When the pH in ambient water increased from 5.0 to 7.0, the influx rate of Cd, Se, and Zn increased by 2.9, 16.6, and 4.1 times, respectively. The influx rates of Cd, Se, and Zn decreased by 6.9, 8.7, and 4.4 times, respectively, with an increase in Ca2+ concentration from 0.6 to 5.1 mM. In contrast, the uptake rates of all three metals were not significantly affected by the SO4(2-) concentration. The majority of accumulated Se was distributed in the soft tissues after 12 h of exposure, whereas Cd and Zn were about evenly distributed in the soft tissue and exoskeleton. Any changes in pH, Ca2+, and SO4(2-) concentrations did not apparently affect their distributions in the daphnids. Our study provides important kinetic data necessary for delineating the exposure routes and for further development of the biotic ligand model in Daphnia. Using a bioenergetic-based kinetic model, we showed that the dissolved uptake is dominant for Zn accumulation (>50%). For Cd and Se, dietary exposure is dominant when the bioconcentration factors of these metals in phytoplankton are at the high end.     

Effect of humic acid during concurrent chronic waterborne exposure of rainbow trout (Oncorhynchus mykiss) to copper, cadmium and zinc

The effects of commercial dissolved organic carbon (DOC) in moderating accumulation, biochemical responses and toxicity of a waterborne mixture of copper (Cu), cadmium (Cd) and zinc (Zn) were investigated during a chronic exposure. Juvenile rainbow trout (Oncorhynchus mykiss) were exposed to a ternary metals mixture containing (nominal concentrations in μg/l): Cu 30, Cd 15, and Zn 150 in hard water (260 mg/l as CaCO₃) with and without addition of 5 mg/l DOC as Aldrich humic acid (HA) for 28 days. Mortality, growth, metals accumulation, ionoregulatory impairment, and oxidative stress response were measured. While growth was unaffected, 19% mortality occurred during the first week of the exposure in fish exposed to the metals mixture without added HA. The early mortality was associated with transitory whole-body sodium (Na) loss and inhibition of branchial Na⁺, K⁺-ATPase activity. Although these ionoregulatory responses mechanistically suggested that Cu was the more potent toxicant than either Cd or Zn, they were not correlated uniquely with elevated tissue Cu concentrations. The effects of HA on accumulation were metal-specific and depended on the organ examined and exposure duration. Specifically, Zn accumulation occurred only in the gill early in the exposure and HA reversed it, while protection against accumulation was absent or complete for Cu and absent or partial for Cd, dependent on tissue and exposure duration. The computed ambient free metal ion activities could explain the Cd but not the Cu and Zn accumulation indicating the involvement of physiological regulatory mechanisms in defining accumulation of essential metals. Surprisingly, the metals mixture (with and without added HA) reduced the concentrations of malondialdehyde (MDA) in gill suggesting induction of reductive rather than oxidative stress. Overall these data indicate that the free metal ion activity alone is not universally a good predictor of metals mixture accumulation and chronic effects nor does consideration of the mechanisms of toxicity unambiguously identify the more potently toxic metal in a mixture.     

Zinc and Cadmium Regulation Efficiency in Three Ant Species Originating from a Metal Pollution Gradient

Highly efficient accumulation of trace metals is often reported in ants, but their metal regulation strategies are poorly understood. This study examined the relationships between Zn and Cd total (tot) and water soluble (ws) concentrations in soil and in workers of three ant species collected along a metal-pollution gradient: Formica cunicularia, Lasius flavus and Myrmica rubra. Regression line comparisons showed the body loads of metals to depend strongly on the metal and the species. M. rubra showed the most efficient regulation of Zn, as its average Zn concentration and the regression slope were several times lower than for the other species. Although the species differed in their Cd levels, the slopes of the relationships between Cd concentration in soil and in ants did not differ between species (tot: p = 0.71, ws: p = 0.31). The very weak relationship for Cd found for all species suggests at least some active Cd regulation. These results can be explained in the context of tissue-specific metal accumulation. High Zn accumulation in mandibles and ovarioles may explain its high accumulation in F. cunicularia and L. flavus.     

Distribution of heavy metals and their age-related changes in the eastern great white egret,Egretta alba modesta,in Korea

Organ and tissue distribution of eight metals (Fe, Mn, Zn, Cu, Pb, Ni, Cd, Hg) and their age-related changes were investigated in the chick and adult eastern great white egret,Egretta alba modesta, collected in Korea. High concentrations of the metals were found in the liver, kidney, feathers, bone, and skin; low values were found in the muscle and brain. A majority of the metal burdens in the chick and adult egrets existed in the muscle, bone, and feathers; about 50% of the Hg was in the feathers. The concentrations of Fe, Mn, Zn, and Cu in organs and tissues of the chicks characteristically changed with age, and their accumulations depended upon the metabolic turnover. In contrast, the concentrations of Pb, Ni, Cd, and Hg increased with age, suggesting that age or exposure time is a dominant factor. However, the younger stage of the downy chicks showed a rapid accumulation plateau of Pb, Ni, Cd, and Hg, and a dilution effect of these metal concentrations by increased body weight with age also was observed. Furthermore, rapid decreases of the body burden of Mn, Cu, Ni, Pb, Cd, and Hg were found in the fledgling birds, indicating that the metals were excreted via the feathers by moulting. These results indicate that consideration of the growth stage of organs and tissues is necessary for understanding the bioaccumulation processes and the toxicological criteria of the metals.     

Bioaccumulation of cadmium,lead, copper,and zinc in successive developmental stages of Lymantria dispar L. (Lymantriidae,Lepid)—a life cycle study

The forest pest insect Lymantria dispar L. (gypsy moth) was reared on an artificial diet contaminated independently with four metals at two different concentrations (2 and 10 g/g Cd, 4 and 20 g/g Pb, 10 and 50 g/g Cu, 100 and 500 gg Zn). Whole body metal concentrations were determined in each larval stage, pupae, imagoes, and F1 generation first instars and also of the corresponding exuviae, headcapsules, and faeces. The pattern of metal accumulation in successive developmental stages was metal and concentration (Cu, Zn) specific. Pb was barely assimilated by the larvae (concentration factor <0.4), whereas the concentration factors for the other metals were generally above 1 (the highest concentration factors determined for instars were: 3.5 (Zn), 4 (Cd), 5 (Cu)). All metals were eliminated via the meconium to a certain extent. In all groups, metal content was positively correlated with L. dispar larval weight. These relationships were also concentration dependent. F1-generation first instar larvae showed significantly higher metal contamination than controls, reflecting the metal burdens of the parental generation.     

Comparison of the Metal Concentrations in Organs of Two Bird Species from Western of Iran

This study was conducted to measure the concentration of several elements (Cd, Pb, Cu, and Zn) in organs of Coot, Fulica atra, and Mallard, Anas platyrhynchos, in order to: (1) determine the significant between metal concentrations in different organs (kidney, liver, pectoral muscle, and feather), (2) to evaluate species differences in metal exposure and accumulation, and (3) to study gender-related trends in metal accumulation. The metal concentrations in organs of F. atra and A. platyrhynchos decreased in the following order: Zn > Cu > Pb > Cd. These results revealed that there were no significant differences between males and females except for Cu in liver and feather, and Pb in kidney.     

Metals in Two Species of Fish in Karasu River

In this study, cadmium (Cd), copper (Cu), iron (Fe), nickel (Ni), lead (Pb) and zinc (Zn) levels were determined in the tissues (muscle, liver and gills) of two fish species, Capoeta capoeta umbla and Chalcalburnus mosullensis, collected from three stations of the Karasu River. The lowest metal accumulation was detected in the muscle tissues. Moreover there was some variability in the metal concentrations measured in the same tissues from samples obtained from the three different stations. A positive correlation was observed for the concentration of metal pairs Fe–Cu, Fe–Zn, Ni–Pb, Pb–Zn. These findings were also compared with national and international food standards, and Pb and Cd concentrations were determined to be above the level set by the standards. In conclusion, it was supposed that excessive consumption of these two fish species, which already occurs in this region, might pose a public health risk.     

Trace Metals in the Brown Mussel <Emphasis Type="Italic">Perna perna</Emphasis> from the Coastal Waters Off Yemen (Gulf of Aden): How Concentrations Are Affected by Weight,Sex, and Seasonal Cycle

The effects of seasonal cycle, sex of individuals, and changes of soft tissues weight on accumulated trace metal concentrations (Cd, Cu, Fe, Mn, Pb, Zn) were examined in the brown mussel Perna perna collected monthly from a natural rocky habitat in the coastal waters off Yemen, the Gulf of Aden, for a period of ten months. Basic hydrological parameters were recorded simultaneously. All metals analyzed displayed seasonal fluctuations with different temporal patterns and variable amplitudes. Similar seasonal cycles were observed for Cu, Mn, and Pb with an increase in accumulated concentration during the rainy period (NE monsoon), and a decrease thereafter. The concentrations of Cu, Mn, and partially Pb appeared to be related to environmental changes, the concentration of Pb possibly also being related to changes in body weight. Accumulated concentrations of Cu and Mn thus seem to reflect actual metal bioavailability in the ecosystem quite efficiently. The tissue levels of Fe and Cd changed inversely to fluctuations in body weight with additional variation due to monsoon-related environmental changes. The behaviors of Fe and Cd are therefore driven by seasonally changing body weight with a considerable contribution of external factors including fluctuations in hydrological conditions and metal exposure. The Zn concentrations tended to increase gradually throughout most of the year regardless of its concentration in the environment. Zinc is considered to be mainly regulated by physiological mechanisms in the mussel, making its accumulated metal concentration independent to some degree of environmental levels. Significant differences in trace metal concentrations between sexes (in favour of females) might have resulted from more intense formation of reproductive tissues and metal accumulation in sexual products of females during the prespawning and spawning periods.     

Tissue distribution of heavy metals and their variations with age,sex, and habitat in Japanese serows (Capricornis crispus)

Baseline data on heavy metal accumulations (Fe, Mn, Zn, Cu, Co, Ni, Pb, Cd, and Hg) in organs and tissues, and their variations with age, sex, and habitat in free-ranging Japanese serows were determined. The metal concentrations were high in liver and kidney and low in brain and muscle. Also, high accumulations of Mn and Ni in gastrointestinal organs may be due to an undeveloped excretory system for these metals by bile. About 40% of the Hg burden in the whole body was in the fleece, indicating that a major portion of Hg body burden is excreted by moulting. The metal concentrations varied widely with metal species and also with growth stage or age, especially during the fetal, fawn and puberty periods. Metal burdens of the fetus were very low compared with those of their mothers, so parturition did not change the whole-body burdens/concentrations of metals in the mothers. Iron in the muscle and liver, and Cu in the liver showed significantly higher concentrations in the males than in the females. A significant difference of Cd concentrations was found between habitats of the serow.     

Allometry of heavy metal bioconcentration in the echinoid Paracentrotus lividus

The relationships between concentration and size in Paracentrotus lividus were studied for seven metals (Zn, Pb, Cd, Fe, Cr, Cu, and Ti). In the calcified body compartment, Zn concentrations showed inverse power relationships, while concentrations of Pb, Cd, and Cr increased as power functions of echinoid size; Fe, Cu, and Ti concentrations did not vary significantly with echinoid size. In the non-calcified body compartment of the echinoid, the concentrations of Zn, Pb, Fe, Cu, and Ti showed inverse power relationships, Cd concentrations increased linearly, and Cr concentrations did not show any significant relationship with echinoid body size. Most relationships were rather weak, except in the cases of Pb and Fe in the non-calcified compartment and Cd in the calcified compartment. The allometric relationships were affected by seasonal factor in the non-calcified compartment only. The results indicate that biomonitoring programs using P. lividus as an indicator of metal contamination must take into account both echinoid size and season as source of metal concentration variations.     

Relationships between physiological characteristics and trace metal body burdens of banded garden spiders Argiope trifasciata (Araneae, Araneidae)

Banded garden spiders (Argiope trifasciata) were collected at the Ballona Wetlands, a metal contaminated salt marsh. The relationship between spider body size and individual metal loads was investigated. Biochemical markers were identified in spider fecal material and found to correlate to body metal levels. Body metal dry weight concentrations of Cd, Cr, Cu, Zn and total metals in female A. trifasciata exhibited distinct patterns of spatial and annual variation during 2006 and 2007. Spider body size was homogeneous across sites in both years, while increased Cd and Cr concentrations were sometimes associated with a reduction in spider size, though the influence of Cr was quite minor. Spiders with higher body Cu levels showed a reduction in peak area for hypoxanthine and an un-identified component in fecal material chromatograms. Spatial and annual differences in metal bioaccumulation are likely mediated by variation in site-specific environmental parameters and rainfall, while the negative relationships between body size and metal levels are presumably a consequence of a spider's expenditure of energy for metal tolerance mechanisms vs. foraging and growth. Finally, correlating body metal levels with excreta products constitutes a novel method to non-invasively predict metal levels in spiders.     

Effect of zinc deficiency on the accumulation of metallothionein and cadmium in the rat liver and kidney

The effects of zinc (Zn) deficiency and repeated exposure to cadmium (Cd) on the accumulation and distribution of metallothionein (MT), Cd and Zn in the liver and kidney were studied. Male Sprague-Dawley rats were fed either a Zn-deficient (1 ppm) or a Zn-adequate (40 ppm) diet during the experiment, and the rats were injected subcutaneously with a cadmium chloride solution (1.0 mg Cd/kg of body weight, 5 days a week) for 4 weeks. Cadmium, Zn, and Cd-induced MT concentrations in the liver and kidney were lower in the Zn-deficient rats (–Zn + Cd) than in the Zn-adequate rats (+ Zn + Cd), while the content of Cd bound to high molecular weight proteins (HMWP) was greater in the Zn-deficient rats (–Zn + Cd). The Zn bound to Cd-induced MT was reduced to 30% in the liver and to 60% in the kidney of the Zn-deficient rats (–Zn + Cd) as compared with that of the Zn-adequate rats (+ Zn + Cd). In the kidney of Zn-deficient rats, exposure to Cd caused a decrease in essential Zn associated with HMWP as compared with that of Zn-adequate rats (+ Zn + Cd). Thus, Zn-deficiency affected the distribution of Cd in tissues, MT and HMWP and accelerated substantially Cd-induced Zn-deficiency in the kidney. Although the renal Cd concentration was lower in the Zn-deficient rats (–Zn + Cd) than in the Zn-adequate rats (+ Zn + Cd), exposure to Cd for four weeks resulted in glucosuria and an increase in liver and kidney weights in the Zn-deficient rats (–Zn + Cd), but not in the Zn-adequate rats (+ Zn + Cd). These results suggest that development of Cd toxicity is related to the Zn status of the body, to the accumulation of Cd in HMWP and to the amount of essential Zn associated with HMWP.     

Cadmium Accumulation and Antioxidant Responses in <Emphasis Type="Italic">Sparus aurata</Emphasis> Exposed to Waterborne Cadmium

Cadmium (Cd), a nonessential trace element, is rapidly accumulated by most living organisms and subsequently exerts its toxicity at different molecular levels. This study exposed gilthead sea bream (Sparus aurata) to waterborne 0.1 mg/l Cd for 11 days and investigated the Cd accumulation pattern, lipid oxidation, and response of antioxidant defences. At the end of the experiment, mean Cd concentrations in gills and liver, the organs most prone to metal accumulation, were 209.4 and 371.7 ng/g ww, respectively. Muscle did not show any Cd retention during the 11 days of exposure. In liver, the cytosolic fraction of the metal was chelated into the nontoxic form by metallothionein (MT), a specific Cd-inducible protein. Zn and Cu concentrations were not influenced by Cd exposure. Glutathione (GSH) concentrations and the antioxidant enzyme activities of GSH reductase and GSH peroxidase showed an overall decreasing trend. In addition, lipid and aqueous hydroperoxide levels did not show any significant variation. Oxidative stress indirectly generated by Cd seems to be compensated for by the different biochemical systems tailored to decrease cellular damage. In particular, the negative effects of Cd accumulation in tissues were probably counteracted by the induction of MT.     

Differential Patterns of Accumulation and Retention of Dietary Trace Elements Associated With Coal Ash During Larval Development and Metamorphosis of an Amphibian

We performed an experiment in which larval gray tree frogs (Hyla chrysoscelis) were raised through metamorphosis on diets increased with a suite of elements associated with coal combustion residues (silver [Ag], arsenic [As], cadmium [Cd], chromium [Cr], copper [Cu], mercury [Hg], lead [Pb], selenium [Se], vanadium [V], and zinc [Zn]) at “low” and “high” concentrations. We quantified accumulation of metals at three life stages (mid-larval development, initiation of metamorphosis, and completion of metamorphosis) as well as effects on survival, metabolic rate, size at metamorphosis, and duration and loss of weight during metamorphosis. Most elements were accumulated in a dose-dependent pattern by some or all life stages, although this was not the case for Hg. For most elements, larval body burdens exceeded those of later life stages in some or all treatments (control, low, or high). However for Se, As, and Hg, body burdens in control and low concentrations were increased in later compared with earlier life stages. A lack of dose-dependent accumulation of Hg suggests that the presence of high concentrations of other elements (possibly Se) either inhibited accumulation or increased depuration of Hg. The duration of metamorphosis (forelimb emergence through tail resorption) was lengthened in individuals exposed to the highest concentrations of elements, but there were no other statistically significant biological effects. This study shows that patterns of accumulation and possibly depuration of metals and trace elements are complex in animals possessing complex life cycles. Further study is required to determine specific interactions affecting these patterns, in particular which elements may be responsible for affecting accumulation or retention of Hg when organisms are exposed to complex mixtures of elements.