The fouling barnacle Amphibalanus improvisus is a cosmopolitan biomonitor of trace metal bioavailability in coastal waters of reduced salinity such as estuaries or the Baltic Sea. Bioavailability of Ag, As, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, V and Zn to A. improvisus was investigated in July 2014 at 15 sites along the Iranian coast of the understudied, yet biologically unique, Caspian Sea. In general, the bioavailability of these toxic metals in the water column, as biomonitored by the barnacle, was within the typical ranges expected from data available in the literature. Thus, there were no major environmental concerns raised. Nevertheless increased Cu and Zn were locally bioavailable at one site, perhaps associated with shrimp farming activities, and of Mn at another, probably from an industrial source. It is vital that the degree of contamination of the largest continental body of water in the world, particularly a water body with a unique biology is monitored.

The relationship between the subcellular distribution of accumulated toxic metals into five operational fractions (subsequently combined into presumed detoxified and non-detoxified components) and toxicity in the clam Scrobicularia plana was investigated under different laboratory exposures. Clams were exposed to metal contaminated media (water and diet) and analysed for the partitioning of accumulated As, Cu and Zn into subcellular fractions. In general, metallothionein-like proteins, metal-rich granules and cellular debris in different proportions acted as main storage sites of accumulated metals in the clam soft tissues for these three metals. No significant differences were noted in the accumulation rates of As, Cu and Zn of groups of individuals with or without apparent signs of toxicity after up to 30days of exposure to naturally contaminated sediment mixtures. There was, however, an increased proportional accumulation of Cu in the non-detoxified fraction with increased Cu accumulation rate in the clams, suggesting that the Cu uptake rate from contaminated sediments exceeded the combined rates of elimination and detoxification of Cu, with the subsequent likelihood for toxic effects in the clams.

Biodynamic modelling was used to investigate the uptake and accumulation of three trace metals (Ag, As, Zn) by the deposit feeding estuarine bivalve mollusc Scrobicularia plana. Radioactive labelling techniques were used to quantify the rates of trace metal uptake (and subsequent elimination) from water and sediment diet. The uptake rate constant from solution (+/- SE) was greatest for Ag (3.954 +/- 0.3751 g(-1) d(-1)) followed by As (0.807 +/- 0.1291 g(-1) d(-1)) and Zn (0.103 +/- 0.0161 g(-1) d(-1)). Assimilation efficiencies from ingested sediment were 40.2 +/- 1.3% (Ag), 31.7 +/- 1.0% (Zn) and 25.3 +/- 0.9% (As). Efflux rate constants after exposure to metals in the solution or sediment fell in the range of 0.014-0.060 d(-1). By incorporating these physiological parameters into biodynamic models, our results showed that dissolved metal is the predominant source of accumulated Ag, As and Zn in S. piano, accounting for 66-99%, 50-97% and 52-98% of total accumulation of Ag, As and Zn, respectively, under different field exposure conditions. In general, model-predicted steady state concentrations of Ag, As and Zn matched well with those observed in clams collected in SW England estuaries. Our findings highlight the potential of biodynamic modelling to predict Ag, As and Zn accumulation in S. plana, taking into account specific dissolved and sediment concentrations of the metals at a particular field site, together with local water and sediment geochemistries. (C) 2014 Elsevier B.V. All rights reserved.

The fouling barnacle Amphibalanus amphitrite is a cosmopolitan biomonitor of trace metal bioavailabilities, with an international comparative data set of body metal concentrations. Bioavailabilities of As, Cd, Cr, Cu, Fe, Mn, Pb, V and Zn to A. amphitrite were investigated at 19 sites along the Iranian coast of the understudied Persian Gulf. Commercial and fishing ports showed extremely high Cu bioavailabilities, associated with high Zn bioavailabilities, possibly from antifouling paints and procedures. V availability was raised at one port, perhaps associated with fuel leakage. Cd bioavailabilities were raised at sites near the Strait of Hormuz, perhaps affected by adjacent upwelling off Oman. The As data allow a reinterpretation of the typical range of accumulated As concentrations in A. amphitrite. The Persian Gulf data add a new region to the A. amphitrite database, confirming its importance in assessing the ecotoxicologically significant trace metal contamination of coastal waters across the world.

The accumulation, subcellular distribution and speciation of arsenic in the polychaete Arenicola marina were investigated under different laboratory exposure conditions representing a range of metal bioavailabilities, to gain an insight into the physiological mechanisms of how A. marina handles bioaccumulated arsenic and to improve our understanding of the potential ecotoxicological significance of bioaccumulated arsenic in this deposit-feeder. The exposure conditions included exposure to sublethal concentrations of dissolved arsenate, exposure to sublethal concentrations of sediment-bound metal mining mixtures, and exposure to lethal concentrations of sediment-bound metal mining mixtures and arsenic- and multiple metal-spiked sediments. The sub-lethal exposures indicate that arsenic bioaccumulated by the deposit-feeding polychaete A. marina is stored in the cytosol as heat stable proteins (~50%) including metallothioneins, possibly as As (III)-thiol complexes. The remaining arsenic is mainly accumulated in the fraction containing cellular debris (~20%), with decreasing proportions accumulated in the metal-rich granules, organelles and heat-sensitive proteins fractions. A biological detoxified metal compartment including heat stable proteins and the fraction containing metal-rich granules is capable of binding arsenic coming into the cells at a constant rate under sublethal arsenic bioavailabilities. The remaining arsenic entering the cell is bound loosely into the cellular debris fraction, which can be subsequently released and diverted to an expanding detoxified pool. Our results suggest that a metal sensitive compartment comprising the cellular debris, enzymes and organelles fractions may be more representative of the toxic effects observed.

Many estuaries of southwest England were heavily contaminated with toxic metals associated with the mining of copper and other metals, particularly between 1850 and 1900. The question remains whether the passage of time has brought remediation to these estuaries. In 2003 and 2006 we revisited sites in 5 metal-contaminated estuaries sampled in the 1970s and 1980s — Restronguet Creek, Gannel, West Looe, East Looe and Tavy. We evaluate changes in metal contamination in sediments and in metal bioavailabilities in sediments and water to local organisms employed as biomonitors. We find that the decline in contamination in these estuaries is complex. Differences in bioavailable contamination in the water column were detectable, as were significant detectable changes in at least some estuaries in bioavailable metal contamination originating from sediments. However, in the 100years since mining activities declined, bioavailable contamination has not declined to the regional baseline in any estuary affected by the mine wastes. The greatest decline in contamination occurred in the one instance (East Looe) where a previous industrial source of (Ag) contamination was considered. We used the macroalgae Fucus vesiculosus and Ascophyllum nodosum as biomonitors of dissolved metal bioavailabilities and the deposit feeders Nereis diversicolor and Scrobicularia plana as biomonitors of bioavailable metal in sediments. We found no systematic decrease in the atypically high Ag, Cu, Pb and Zn concentrations in the estuarine sediments over a 26year period. Accumulated metal (Ag, As, Cu, Pb, and Zn) concentrations in the deposit feeders are similarly still atypically high in at least one estuary for each metal, and there is no consistent evidence for general decreases in sediment metal bioavailabilities over time. We conclude that the legacy of mining in sheltered estuaries of southwest England is the ongoing presence of sediments rich in metals bioavailable to deposit feeders, while dissolved metal bioavailabilities from this historical source alone are no longer atypically high.

We test the hypothesis that accumulated metal in prey that is trophically available to one predator is not necessarily equally trophically available to another predator feeding on the same prey, given the variability between invertebrate digestive systems. We provided two predators, the neogastropod mollusc Hinia reticulata and the palaemonid decapod crustacean Palaemonetes varians, with the digestive glands and adductor muscles of four bivalves radiolabelled with Zn, Cd or Ag. The bivalves (the mussel Mytilus edulis, the clam Ruditapes philippinarum, the scallop Aequipecten opercularis, the oyster Crassostrea gigas) have different metal accumulation patterns with differential dependence on soluble and insoluble detoxification, as confirmed by fractionation of the prey tissues. We found no consistent significant difference between the AE of the two predators for the three trace metals accumulated in the same prey tissues. There were no significant correlations for either predator between percentages of metal in soluble form (or soluble form with organelle-associated metal) and percentage AE for any of the three metals, allowing the conclusion that both predators are assimilating each metal from more than the soluble and organelle-associated metal fractions. For neither predator did an increased percentage of Zn in the form of metal rich granules (MRG) affect its Zn AE, but increases in the percentages of both Cd and Ag bound to MRG decreased the AE of the relevant metal in P. varians but not H. reticulata. Thus the Cd and Ag in some Cd-rich and Ag-rich granules in the bivalve tissues are not as trophically available to P. varians as they are to H. reticulata. This interspecific difference confirms that the neogastropod has the stronger digestive and assimilative powers involving Cd and Ag bound in prey than the palaemonid decapod.

Biodynamic parameters of the ragworm Nereis diversicolor from southern Spain and south England were experimentally derived to assess the inter-population variability of physiological parameters of the bioaccumulation of Ag, Cd and Zn from water and sediment. Although there were some limited variations, these were not consistent with the local metal bioavailability nor with temperature changes. Incorporating the biodynamic parameters into a defined biodynamic model, confirmed that sediment is the predominant source of Cd and Zn accumulated by the worms, accounting in each case for 99% of the overall accumulated metals, whereas the contribution of dissolved Ag to the total accumulated by the worm increased from about 27 to about 53% with increasing dissolved Ag concentration. Standardised values of metal-specific parameters were chosen to generate a generalised model to be extended to N. diversicolor populations across a wide geographical range from western Europe to North Africa. According to the assumptions of this model, predicted steady state concentrations of Cd and Zn in N. diversicolor were overestimated, those of Ag underestimated, but still comparable to independent field measurements. We conclude that species-specific physiological metal bioaccumulation parameters are relatively constant over large geographical distances, and a single generalised biodynamic model does have potential to predict accumulated Ag, Cd and Zn concentrations in this polychaete from a single sediment metal concentration.

Arsenic bioaccumulation in the deposit-feeding polychaete Arenicola marina has been investigated using biodynamic modelling. Radiotracer techniques were used to determine the rates of uptake of As as arsenate from water and sediment and its subsequent efflux in the laboratory. Lugworms accumulated As from solution linearly at concentrations of 2–20μgl−1, with a corresponding uptake rate constant of 0.1648±0.0135lg−1d−1. 7.8±0.8% (assimilation efficiency) of the As ingested bound to sediments was retained after egestion of unassimilated metal. Elimination of As followed a two-compartment model, with mean efflux rate constants (from the slow pool) very similar for As accumulated from solution and ingested sediments (0.0449±0.0034 and 0.0478±0.0225d−1, respectively) and a corresponding biological half-time of roughly 15d. A biodynamic model was constructed and validated through the comparison of biodynamic model predictions against measured bioaccumulated concentrations in lugworms from five UK estuaries. The model accurately predicted bioaccumulated As concentrations in lugworms using mean values of relevant physiological parameters (uptake rate, efflux rate and growth rate constants), a site-specific ingestion rate (calculated according to mean worm size and sediment organic matter content and expressed as the rate of ingestion of the mass of fine sediment), a site-specific sediment concentration measured after HCl extraction, and a standard dissolved As concentration. This combination of parameters showed that sediment ingestion contributed 30–60% of the total As accumulated by lugworms at the studied sites, depending on the different geochemistry at each site. This study showed that it is difficult to predict accurately As bioaccumulation at sites with different chemistries, unless that chemistry is taken into account.

Biodynamic modelling has been used to predict bioaccumulated concentrations of Ag, Cd and Zn in the deposit-feeding polychaete Nereis diversicolor from 5 metal-contaminated estuar- ies in SW England and a relatively non-contaminated estuary in SE England. The modelling employed previously measured physiological parameters of bioaccumulation — uptake rate constant, assimilation efficiency (AE) and efflux rate constants after uptake from water and sediment inges- tion — and measured sediment metal concentrations specific for each population. AEs were consid- ered to relate to metals in the organic component of the ingested sediment and ingestion rates were therefore expressed in these terms, with the further assumption that the total sediment metal concen- tration is a proxy for the metal concentration in the sediment organic component. A range of growth rate constants was extracted from the literature, as were concentration ranges of dissolved Ag, Cd and Zn in contaminated coastal waters. The model showed that >99% Cd and >98% Zn accumulated by N. diversicolor is derived from sediment ingestion; more bioaccumulated Ag is derived from solu- tion, the percentage contribution of the dissolved source increasing from 46 to 80% with an increase in Ag dissolved concentration from low to high values for coastal waters. Bioaccumulated metal con- centrations predicted from the model generally showed excellent agreement with independently measured concentrations in field-collected worms, supporting the assumptions made in the model.

Radiotracer techniques were used to determine the rates of trace metal (Ag, Cd and Zn) uptake and elimination (33psu, 10°C) from water and sediment by the deposit-feeding polychaete Arenicola marina, proposed as a test species for estuarine-marine sediments in whole-sediment toxicity tests. Metal uptake rates from solution increase with increasing dissolved metal concentrations, with uptake rate constants (±SE) (lg−1d−1) of 1.21±0.11 (Ag), 0.026±0.002 (Zn) and 0.012±0.001 (Cd). Assimilation efficiencies from ingested sediments were measured using a pulse-chase radiotracer feeding technique in two different lugworm populations, one from a commercial supplier (Blyth, Northumberland, UK) and the other a field-collected population from the outer Thames estuary (UK). Assimilation efficiencies ranged from 2 to 20% for Zn, 1 to 6% for Cd and 1 to 9% for Ag for the Northumberland worms, and from 3 to 22% for Zn, 6 to 70% for Cd and 2 to 15% for Ag in the case of the Thames population. Elimination of accumulated metals followed a two-compartment model, with similar efflux rate constants for Zn and Ag and lower rates of elimination of Cd from the slow pool. Efflux rate constants (±SE) of Zn and Ag accumulated from the dissolved phase were 0.037±0.002 and 0.033±0.006d−1 whereas Cd was eliminated with an efflux rate constant one order of magnitude lower (0.003±0.002d−1). When metals were accumulated from ingested sediments, the efflux rate constants for the slow-exchanging compartment were of the same order of magnitude for the three metals, and of the same order of magnitude as those derived after the dissolved exposure for Zn and Ag (0.042±0.004 and 0.056±0.012d−1 for Zn and 0.044±0.012 and 0.069±0.016d−1 for Ag for the Northumberland and Thames populations, respectively). Cd accumulated from ingested sediments was eliminated with a rate constant not different from the fast-exchanging compartment after the water-only exposure (0.025±0.012 and 0.020±0.004d−1 for the Northumberland and Thames populations, respectively). A biodynamic model was used to estimate the relative importance of the dissolved phase versus ingested sediment as source of metal for the worms, showing that more than 90% of the Zn and Cd and more than 70% of Ag in lugworms is accumulated from sediment ingestion at realistic environmental concentrations. The model also shows that metal accumulation is highly dependent on the ingestion rate and assimilation efficiency.

Aquatic organisms exposed to atypically high local bioavailabilities of a toxic metal may come under selection for changes in one or more physiological processes, including the rate of metal uptake from an available source of the metal, the rate of efflux and the rate of detoxification of accumulated metal into a relatively metabolically inert form. We investigated parameters of the bioaccumulation kinetics of the toxic metals Ag, Cd and Zn in populations of the estuarine polychaete worm Nereis diversicolor from differentially metal-contaminated sediments of 5 metal-rich estuaries in SW England and a relatively non-contaminated control estuary in SE England. One population (from Restronguet Creek, Cornwall) is known to be tolerant to raised availabilities of Zn and Cu. We compared uptake rate constants from solution (K.) and assimilation efficiencies (AE) from sediment, and subsequent efflux rate constants (K,,) after uptake (from either water or ingested sediment) for each of the 3 metals among all populations. There was some limited interpopulation variation in the biodynamic parameters controlling bioaccumulation (and potential ecotoxicity) of trace metals between populations. There did not, however, appear to be consistent patterns to Such variation. The basis of Zn tolerance in the Restronguet Creek population is not due to a reduction of Zn uptake from either solution or ingested sediment, or increased efflux of Zn accumulated after uptake from either route. The most likely mechanism is, therefore, an increased capacity for storage detoxification of Zn accumulated after regulation of Zn body concentration has broken down.

The amphipod crustacean Talitrus saltator is an established, easily accessible, biomonitor of trace metal bioavailabilities in coastal waters. We have carried out a geographically widespread collection of T. saltator from European shores, stretching from the north-west Atlantic through the Baltic to the Mediterranean. A primary aim of the work was to establish a database of accumulated trace metal concentrations (Cd, Cr, Cu, Fe, Mn and Zn) in this biomonitor. Statistical analysis has shown significant geographical differences in the bioavailabilities of all the metals, the most distinct being copper, iron and manganese. It has proved possible to identify unusually high accumulated concentrations of Cd, Cr, Cu, Fe, Mn and Zn in this biomonitor, indicative of high metal bioavailability at a particular site. These may serve as reference points for future biomonitoring programmes seeking to identify metal contamination in coastal waters.

The electrical conductivity in doped semiconductors in the strongly localized variable range hopping regime is currently explained as phonon-assisted electron hopping. While investigating the non-Ohmic behavior of doped silicon at temperatures of 0.05-1 K, we found strong evidence for the existence of separate temperatures for the electron and phonon systems analogous to the hot-electron effect in metals. This behavior cannot easily be explained by phonon-assisted hopping and seems to favor instead a direct electron-electron interaction at low temperature. A hot-electron model makes definite predictions for the dependence of the electrical conductivity on the bias power, the frequency dependence of the resistance nonlinearities, and for an additional noise term. We have made a systematic investigation of these quantities, and find all of them in good agreement with the model predictions over a wide range of parameters.

Diet is an important exposure route for the uptake of trace metals by aquatic invertebrates, with trace metal trophic transfer depending on 2 stages-assimilation and subsequent accumulation by the predator. This study investigated the trophic transfer of trace metals from the sediment-dwelling polychaete worm Nereis diversicolor from metal-rich estuarine sediments in southwestern UK to 2 predators -another polychaete N. virens (Cu, Zn, Pb, Cd, Fe) and the decapod crustacean Palaemonetes varians (Cu, Zn, Pb, Cd, Fe, Ag, As, Mn). N. virens showed net accumulation of Cu, Zn, Pb and Cd from the prey; accumulation increased with increasing prey concentration, but a coefficient of trophic transfer decreased with increasing prey concentration, probably because a higher proportion of accumulated metal in the prey is bound in less trophically available (insoluble) detoxified forms. The trace metal accumulation patterns of P. varians apparently restricted significant net accumulation of metals from the diet of N. diversicolor to just Cd. There was significant mortality of the decapods fed on the diets of metal-rich worms. Metal-rich invertebrates that have accumulated metals from the rich historical store in the sediments of particular SW England estuaries can potentially pass these metals along food chains, with accumulation and total food chain transfer depending on the metal assimilation efficiencies and accumulation patterns of the animal at each trophic level. This trophic transfer may be significant enough to have ecotoxicological effects.

The chemical form of accumulated trace metal in prey is important in controlling the bioavailability of dietary metal to a predator. This study investigated the trophic transfer of radio- labelled Ag, Cd and Zn from the polychaete worm Nereis diversicolor to the decapod crustacean Palaemonetes varians. We used 2 populations of worms with different proportions of accumulated metals in different subcellular fractions as prey, and loaded the worms with radiolabelled metals either from sediment or from solution. Accumulated radiolabelled metals were fractionated into 5 components:metal-rich granules (MRG), cellular debris, organelles, metallothionein-like proteins (MTLP), and other (heat-sensitive) proteins (HSP). Assimilation efficiencies (AE) of the metals by P. varians were measured from the 4 categories of prey (i.e. 2 populations, radiolabelled from sediment or solution). There were significant differences for each metal between the AEs from the different prey categories, confirming that origin of prey and route of uptake of accumulated trace metal will cause intraspecific differences in subsequent metal assimilation. Correlations were sought between AEs and selected fractions or combinations of fractions of metals in the prey-MRG, Trophically Avail- able Metal (TAM = MTLP + HSP + organelles) and total protein (MTLP + HSP). TAM explained 28% of the variance in AEs for Ag, but no consistent relationships emerged between AEs and TAM or total protein when the metals were considered separately. AEs did, however, show significant positive regressions with both TAM and total protein when the 3 metals were considered together, explain- ing only about 21% of the variance in each case. A significant negative relationship was observed between MRG and AE for all metals combined. The predator (P. varians) can assimilate dietary metal from a range of the fractions binding metals in the prey (N. diversicolor), with different assimilation efficiencies summated across these fractions. TAM and/or total protein may represent an approxi- mate minimum for trophic availability but neither of these alone is a fully accurate predictor.

The comparative kinetics of the accumulation of the trace metals copper, zinc and cadmium have been measured in the estuarine burrowing polychaete worm Nereis (Hediste) diversicolor from two sites: (a) a metal-rich site, Restronguet Creek, Cornwall, UK, which hosts a copper- and zinc-tolerant population of worms, and (b) the Blackwater estuary, Essex, UK as a control site. A sediment transfer experiment showed that the Blackwater worms responded to the increased copper bioavailability in Restronguet Creek sediment by accumulating significantly increasing copper concentrations over 50 days. The Restronguet Creek worms showed no significant change in copper concentration over 50 days in sediment from either site or in sand. Nevertheless, electron microscopy showed that some Restronguet Creek worms do appear to excrete accumulated copper, probably in association with renewal of the cuticle over a long time scale. The Blackwater worms did not accumulate extra zinc from the zinc-rich Restronguet Creek sediment, in probable reflection of the regulation of body zinc concentration by N. diversicolor. Radiolabelled zinc and cadmium were accumulated from labelled sediment and labelled solution by worms from both sites. The rate of uptake of labelled zinc from sediment was significantly greater in the Restronguet Creek worms, as was the rate of uptake of labelled cadmium from 10 μg l−1 dissolved exposure; other rates of uptake did not differ between populations. Mucus, which is secreted by Restronguet Creek worms in response to enhanced copper exposure, adsorbed very small proportions of zinc and cadmium present in solution, indicating that the mucus does not act as an adsorption barrier against excessive metal uptake by these worms.

In a preliminary biomonitoring study, accumulated trace metal concentrations (Cu, Zn, Fe, Cd, Pb, Mn, Ni) have been measured in the mussel Mytilus trossulus and the barnacle Balanus improvisus collected in the Gulf of Gdansk, Poland in 1998. Mussels were collected from five sites in May 1998, and from one site in each of January and February 1998. Barnacles were collected simultaneously from four of the five sites in May 1998. Analysis of covariance has shown significant geographical and temporal differences in the local bioavailabilities of trace metals to mussels and barnacles, as reflected in the concentrations of accumulated trace metals. It is concluded that the mussel and barnacle are suitable biomonitors to employ in programmes designed to assess changes in metal pollution in the Gulf of Gdansk, one of the most metal polluted parts of the Baltic Sea, due to the outflow of the River Vistula.

The population of the infaunal, littoral polychaete worm Nereis (Hediste) diversicolor at the top of Restronguet Creek, England, an estuary with very high sediment concentrations of trace metals, is tolerant to copper. These worms accumulate abnormally high body copper concentrations in comparison to control worms (Blackwater Estuary, England), 68% of the accumulated copper being bound in metal-rich granules. We show that sufficient of the extra copper accumulated in Restronguet Creek N. diversicolor is trophically available to another polychaete worm, N. virens, acting as predator, and brings about high accumulated copper concentrations in the latter worm. Electron microscopy with microanalysis has shown that copper detoxified in Cu-rich granules in the Restronguet Creek worms passes through the gut of the predator without apparent change in elemental composition. The trophically available copper in the Restronguet Creek worms may be in soluble form or bound to other cellular material. Ingestion of the Restronguet Creek worms will deliver an extraordinarily high (and potentially toxic) challenge to predators, including fishes and birds, feeding on N. diversicolor.

The comparative tolerance and accumulation of the trace metals zinc, copper and cadmium in populations of the littoral polychaete worm Nereis diversicolor from three sites: (a) heavily metal-contaminated Dulas Bay in Anglesey, north Wales, (b) the Blackwater estuary, Essex, as a control site, and (c) West Thurrock, the Thames estuary as a site of intermediate metal contamination, were investigated. Worms from Dulas Bay did not show increased tolerance to any metal, but worms from West Thurrock showed significantly increased copper sensitivity compared to the worms from Dulas Bay and the Blackwater. Worms accumulated zinc and copper from sediments with raised zinc and copper concentrations, and all three metals from solution in proportion to dissolved concentration. Accumulated metal was not excreted in 21 days and field concentrations of zinc and copper in the worms differed between sites. There was no evidence for inter-populational differences in accumulation rates of zinc and cadmium from solution, but worms from Dulas Bay accumulated copper from solution at a significantly higher rate than did worms from the other two sites. Nereis diversicolor takes up and accumulates zinc and cadmium from solution at similar rates per unit molar exposure, but cadmium is taken up at a greater rate per unit free metal ion molar exposure. Although N. diversicolor from Dulas Bay is exposed to very high availabilities of zinc and copper, accumulation and detoxification mechanisms are sufficient to cope with the extra metal influx (accentuated for dissolved copper) without selection for a metal-tolerant population.