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We evaluated the effects of varying water chemistry ([Ca2+]=0.2-3mM, [Mg2+]=0.05-3mM, dissolved organic matter (DOM, natural, from maple leaves)=0.3-10mg of CL-1, pH=5.0-8.5) on the acute (96-h, unfed fish) and chronic (30-d, fed fish) toxicity of waterborne Cu to juvenile rainbow trout (Oncorhynchus mykiss) exposed in flow-through conditions. Acute and chronic Biotic Ligand Models (BLMs) were developed from the obtained toxicity data-sets, using the Visual MINTEQ software. Our results indicate that Cu is predominantly an acute toxicant to rainbow trout, as there were no observable growth effects and the 96-h and 30-d LC50 values were similar, with mortality mostly occurring within the first few days of exposure. Calcium and DOM were greatly protective against both acute and chronic Cu toxicity, but Mg seemed to only protect against chronic toxicity. Additional protection by pH 5.0 in acute exposure and by pH 8.5 in chronic exposure occurred. In the range of conditions tested, the observed 96-h LC50 and 30-d LC20 values varied by a factor of 39 and 27 respectively. The newly developed acute and chronic BLMs explained these variations reasonably well (i.e. within a 2-fold error), except at pH≥8 where the high observed acute toxicity could not be explained, even by considering an equal contribution of CuOH+ and Cu2+ to the overall Cu toxicity. The 96-h LC50 values of 59% of 90 toxicity tests from 19 independent studies in the literature were reasonably well predicted by the new acute BLM. The LC20 predictions from the new chronic BLM were reasonable for 7 out of 14 toxicity tests from 6 independent chronic studies (with variable exposure durations). The observed deviations from BLM predictions may be due to uncertainties in the water chemistry in these literature studies and/or to differences in fish sensitivity. A residual pH effect was also observed for both the acute and the chronic data-sets, as the ratio of predicted vs. observed LC values generally increased with the pH. Additional mechanistic studies are required to understand the influence of pH, Na, and Mg on Cu toxicity to trout. The present study presents the first experimentally developed chronic Cu BLM for the rainbow trout. To the best of our knowledge, it also presents the first acute Cu BLM that is based on a published data-set for trout. These newly developed BLMs should contribute to improving the risk assessment of Cu to fish in freshwater.

In Pb-contaminated environments, simultaneous exposure to both waterborne and dietborne Pb is likely to occur. This study examined the potential interactive effects of these two pathways in juvenile rainbow trout that were exposed to Pb in the water alone, in the diet alone, and in combination for 7 weeks. The highest waterborne Pb concentration tested (110μgL(-1)) was approximately equivalent to the 7-week LC20 (97μgL(-1)) measured in a separate trial, while the lowest was a concentration often measured in contaminated environments (8.5μgL(-1)). The live diet (10% daily ration on a wet mass basis) consisted of oligochaete worms (Lumbriculus variegatus) pre-exposed for 28days to the same waterborne Pb concentration, and the highest dietary dosing rate to the trout was 12.6μg Pb g fish(-1)day(-1). With waterborne exposure, whole body Pb burden increased to a greater extent in the worms than in the fish. Nonetheless, in trout waterborne exposure still resulted in 20-60-fold greater Pb accumulation compared to dietborne Pb exposure. However, combined exposure to both waterborne and dietborne Pb reduced the whole body accumulation extensively at waterborne Pb>50μgL(-1), with similar antagonistic interaction in liver and carcass (but not gill or gut) at a lower threshold of 20μgL(-1). Growth effects in trout were minimal with marginal reductions in the dietborne and combined exposures seen only at 110μgL(-1). Chronic Pb exposure reduced lipid and carbohydrates level in the worms by 50% and 80% respectively, while protein was unchanged, so growth effects in trout may have been of indirect origin. After 7 weeks, Ca(2+) homeostasis in the trout was unaffected, but there were impacts on Na(+). Blood Na(+) was reduced in waterborne and dietborne exposures, while gut Na(+)/K(+) ATPase activities were reduced in waterborne and combined exposures. This study is the first, to our knowledge to examine the interaction of waterborne and dietborne Pb exposure in fish. While physiological impacts of Pb were observed in both worms and fish, higher concentrations of dietborne Pb actually protected fish from waterborne Pb bioaccumulation and these effects. The impacts of metals on diet quality should not be neglected in future dietborne toxicity studies using live prey.

We examined the mechanisms of toxicity of waterborne Cu to the freshwater pond snail Lymnaea stagnalis. The snail is one of the most sensitive species to acute Cu exposure (96 h LC50, LC20: 24.9, 18.0 μg l−1); they are not protected by the water quality criteria of the US EPA. Tissue Na and Ca were also reduced by Cu in the acute exposure. In contrast, during 28 d chronic exposures to Cu in the presence of food, which resulted in higher DOC concentrations, there was no significant mortality but an inhibition of growth, which may reflect a re-allocation of resources to detoxification. Cu detoxification was evidenced in chronic exposure by increases in metallothionein-like protein concentrations and Cu binding to metal-rich granules, decreases in thiobarbituric acid-reactive substances, and changes in the subcellular distribution in the soft tissues. Our results demonstrated that apart from external Cu bioavailability, compartmentalization of metals within the cells can alter toxicity of Cu to the snails.

Oysters can accumulate cadmium (Cd) in very high concentrations in their tissues and there is now increasing concern for the seafood safety of farmed oysters worldwide. Bioaccumulation and biokinetics of Cd (dietary assimilation, uptake from the dissolved phase, and efflux) were mea- sured in different populations of Pacific oyster Crassostrea gigas collected along the west coast of the USA in 2 different seasons. Triploid juvenile oysters were first transplanted to 5 Washington sites and 1 Oregon site for 3 mo, then transported back to the laboratory for tissue Cd measurements and bio- kinetic experiments. A second group of seed oysters was collected from California and Washington for additional analysis. Oysters from all sites had Cd concentrations lower than the food standard limit and there was spatial difference in tissue Cd concentrations. A significant fraction of Cd was associ- ated with metallothionein-like proteins, implying that the oysters can detoxify Cd by induction of metallothionein. The difference in Cd dietary assimilation (using diatoms as a food source) and efflux in oysters transplanted to different locations was not significant. The uptake rate constants for Cd from the dissolved phase, however, differed markedly among the transplanted populations, and appeared to be affected by the oysters' clearance rate, depending on the population. This uptake rate was also negatively affected by the size of oysters. Dietary assimilation of Cd was comparable at diatom food concentrations below 2 to 5 mg l -1 , and was lower with ingested sediments than with diatoms. Measurements of Cd kinetics in different populations of Pacific oysters under a variety of environmental conditions provide an insight into the Cd accumulation in this commercially important species.

Dietary toxicity of metals on fish is often studied using commercial pellet food, and there is a lack of investigation on the toxicity of metals that are biologically incorporated into the natural food from the aquatic environment. In this study, we investigated the toxicity of dietborne Cd from the oligochaete Lumbriculus variegatus to the rainbow trout Oncorhynchus mykiss. The oligochaete worms were exposed to waterborne Cd (0.1, 5, 20, and 200 microgL(-1)) for 1 week and the fish were fed this food exclusively (daily ration=3.5% body wet weight) for 1 month. Cd concentrations in the worms averaged 0.1, 0.6, 2.2, and 30.3 microgg(-1) wet weight respectively, whereas the whole fish accumulated 0.002, 0.005, 0.019, and 0.387 microg Cd g(-1) wet weight respectively, after feeding upon control or Cd-contaminated worms for 4 weeks. Highest concentrations of Cd were retained in the gut, followed by the kidney and liver of the fish, with the latter two increasing over time; however, gut tissue accounted for >80% of whole body Cd burdens at all times. The trophic transfer efficiency of Cd was low (0.9-6.4%) although higher than in previous studies using Cd-spiked commercial diets, and was only weakly correlated to the internal Cd storage in the worms. The level of Cd in the contaminated worms did not affect Cd trophic transfer efficiency, but was reduced over the dietary exposure period. Dietborne Cd did not interfere with whole body Ca uptake from the water or alter plasma [Ca], but reduced growth by 50% in the trout exposed to the highest Cd dose. Cd stored in the metallothionein-like proteins of the fish gut tissue increased while that in the heat-denaturable proteins was reduced, suggesting detoxification over time. This study suggests a higher bioavailability and toxicity of Cd from the natural diets than from the commercial diets used in previous studies.

There is increasing evidence to indicate that metal pre-exposure may mediate the subsequent metal uptake from the dietary or dissolved phase by marine invertebrates. In this study, we examined the detoxification and the effects of Ag, Cd, or Zn pre-exposure on the metal uptake of the clam Ruditapes philippinarum. The relationships between metal body burden and metal uptake of Ag, Cd, Hg, and Zn were also concurrently examined. Radiotracers 110m Ag, 109 Cd, 203 Hg, and 65 Zn were used to chase the metal uptake in the clams. The clams accumulated Ag and Cd over time, but there was not a significant Zn accumulation. Metallothionein played a role in the detoxification of Ag and Cd, but the insoluble fraction was also the detoxification pool for Cd and Zn. Generally, metal pre-exposure did not greatly affect metal uptake. Ag pre-exposure had no effect on dietary Ag uptake. Cd and Zn pre-exposure increased Zn dietary uptake by 10%. After 2 wk Ag exposure and 3 wk of Cd or Zn exposure, Cd and Hg dissolved uptake was reduced by 2 to 6 times. However, these effects mainly appeared during the earlier part of the exposure period (i.e. up to Weeks 2 or 3). The effects of metal exposure on uptake of dissolved Cd and Hg were related to the coupling relationships of dissolved metal uptake between the 2 metals and other metals (Ag and Cd or Hg; Cd and Hg; Zn and Hg). The effects on dietary and dissolved uptake of all metals were independent of Ag, Cd or Zn body burden; thus, metal body burdens may not necessarily indicate the potential metal uptake of marine clams in the environment. Our data have important implications for kinetic modeling predicting metal uptake by marine clams.

Larval experience affects early post-metamorphic performance of a range of marine invertebrates, and even brief events during the larval stage can be important. One of the important larval stresses for organisms living in urban coastal environments is exposure to toxicants. Larvae may pass through patches of toxicants in their dispersal stage with the potential to affect their post- metamorphic performance. However, most studies on embryonic or larval tolerance to pollutants end at, or before, metamorphosis, have little follow-up and almost all are done under laboratory condi- tions. In this study, we tested whether short-term larval exposure to copper has short- and long-term carry-over effects in the encrusting bryozoan Watersipora subtorquata by following settlement and metamorphosis in the laboratory, then transplanting colonies into the field, in 2 seasons and at 2 sites in SE Australia. Cu at 100 µg l -1 accelerated larval attachment in winter and summer, but inhibited metamorphosis. When transplanted to the field, juveniles survived and grew well, and effects on sur- vival and growth did not appear until several weeks or months after settlement. Larval exposure to Cu reduced survival of colonies to about 2/3 that of control colonies in summer and at 1 site, reduced survival to about 20% that of controls in winter. The fall in survivorship occurred abruptly after 3 to 5 wk in summer and 14 wk in winter. The surviving colonies grew more slowly than the controls. In general, there was little temporal variation in Cu effects, but there was spatial variation in effects on survival and growth of colonies within and between sites.

We examined the toxicity of Cd, provided in a natural diet and at an environmentally relevant concentration ( approximately 12microgg(-1) dry wt.), to the juvenile rainbow trout (Oncorhynchus mykiss). In addition, we tested the protection by elevated dietary Ca against both the accumulation and toxicity of dietary Cd from this natural diet (background Ca approximately 1mgg(-1) dry wt.). Food pellets were made from blackworms (Lumbriculus variegatus), and spiked with Cd and either no additional Ca or elevated ( approximately 60mgg(-1) dry wt.) concentrations for each of the treatment diets. Survival was unaffected for trout fed diet with 12microgg(-1) dry wt. Cd for a month, but growth was potentially reduced. Tissue burden analysis revealed that the stomach, liver and kidney accumulated the most Cd, with concentrations progressively increasing in the liver and kidney over the whole exposure period. Cd concentrations in the plasma and red blood cells were unaffected by the different treatments, but subcellular fractionation analysis indicated that a higher concentration of Cd was associated with the metal-sensitive fractions of red blood cells of the fish that were exposed to the dietborne Cd. Dietary Cd exposure also caused potential toxicity to cells of the stomach in that they bound more Cd to heat-denaturable proteins. However, detoxification appeared to take place in the Cd-exposed fish because more Cd was bound to metallothionein-like proteins by week 4 of exposure. Elevated Ca in the Cd diet generally protected against accumulation and toxicity of dietborne Cd. The protection against Cd accumulation was almost complete at the gills, robust in the stomach and whole body (or =50% reductions), but not significant in the liver, kidney, carcass, plasma, or red blood cells. Elevated dietary Ca also reduced Cd accumulation in the organelles of the fish stomach and red blood cells. In addition, dietborne Ca not only reduced the uptake of Cd by the cells, but also altered how the cells handled Cd intracellularly. In general, our results have demonstrated the need to use diets with natural compositions for dietary toxicity studies.

This study investigated the kinetics of Cd bioaccumulation, detoxification, subcellular distribution, and efflux in the nereid polychaete Perinereis aibuhitensis after Cd pre-exposure. Cd pre-exposure increased the Cd body burden in the worms, but did not affect the overall Cd uptake and efflux rates and metallothionein-like protein (MTLP) concentrations. During short-term exposure to dissolved Cd, Cd in the cytosolic fraction increased after Cd pre-exposure, and this fraction also increased during the Cd efflux period, indicating that the insoluble fraction of Cd was presumably lost at a faster rate than the loss of cytosolic Cd. Even though the MTLP concentration remained comparable after Cd pre-exposure, both the MTLP synthesis rate and the degradation rate increased, thus leading to a high MTLP turnover in the Cd-exposed worms. However, Cd uptake and efflux into different protein size fractions did not follow the patterns of MTLP synthesis and degradation, strongly suggesting that Cd kinetics is decoupled from the MTLP kinetics in the worms. Our study adds to an increasing body of evidence on the complicated relationship between metal biokinetics and MTLP kinetics in different groups of marine invertebrates which have strong contrasts in their metal handling strategies.

Metal interaction is vital for assessing the use of aquatic organisms in monitoring metal contamination. The present study examined the interactions between Ag and Cd accumulation and between Ag and Cu accumulation in the green mussel (Perna viridis). Accumulation of Ag and Cd in the whole tissue of green mussels exposed to 5 microg/L of Ag and 20 microg/L of Cd for two weeks was independent; however, interaction was observed at the subcellular level. Approximately 25% of Ag shifted from the insoluble fraction (IF) to the metallothionein-like protein in the presence of Cd, which probably resulted from the competition of Cd on IF in the Ag-Cd coexposure. On the other hand, coexposure of the mussels to Ag (5 microg/L) and Cu (30 microg/L) for two weeks increased the Ag and Cu concentrations in the tissue synergistically (two- to fivefold), but Ag and Cu subcellular distributions were similar in the coexposed and the singly exposed mussels. Exposure to Ag alone increased the dietary uptake of Ag by 30%, but the effect was reduced in the presence of Cd. No interaction, however, was observed between uptake rates of metals from the dissolved phase. To conclude, a significant interaction was observed for total Ag and Cu accumulation, but not for total Ag and Cd accumulation, in the mussels. Metal interaction is more likely to be observed at the subcellular level than at the whole-tissue level.