Studies on the uptake of cadmium by the crab Carcinus maenas in the laboratory. I. Accumulation from seawater and a food source

The crab Carcinus maenas (L.) was exposed to radioactively labelled cadmium dissolved in seawater at concentrations of 0.1, 1 and 10 ppm, the latter concentration being toxic to the crabs (50% mortality after 12.3 days). Net accumulation of cadmium from solution was proportional to the level and time period of cadmium exposure. Total absorbed cadmium levels reached 0.0043 and 0.0412 mg Cd g^-1 dry weight after 40 days exposure to 0.1 and 1 ppm Cd, respectively, and 0.1115 mg Cd g^-1 dry weight after 12.3 days average exposure to 10 ppm Cd. The highest tissue concentration was found in the midgut gland, reaching 0.786 mg Cd g^-1 dry weight after 12.3 days average exposure to 10 ppm Cd. The midgut gland only contained about 10% of the total cadmium absorbed from solution, while the exoskeleton contained the bulk of obsorbed cadmium (59 to 80%) probably passively adsorbed onto the surface. When cadmium was absorbed by the crabs from a food source, the midgut gland contained 16.9% of the total absorbed cadmium whereas the exoskeleton now contained only 22.2%. Ten percent of the cadmium available in the food source (Artemia salina) was accumulated by the crabs. When placed in cadmium-free seawater, crabs that had accumulated cadmium from solution lost 69% of the absorbed cadmium in 10 days, mostly from the exoskeleton which lost 78% of its original absorbed cadmium concentration.     

Effect of total cadmium and organic complexing on the uptake of cadmium by the brine shrimp,Artemia franciscana

The effect of total cadmium and organic complexing on the rate of cadmium uptake by the brine shrimp, Artemia franciscana has been studied in chemically defined saltwater solutions. The uptake of cadmium from solution by the laboratory-reared brine shrimp displays saturable uptake kinetics. Uptake of cadmium is linear in time up to a total cadmium concentration of 200 moll^-1 and saturates above 800 moll^-1. Complexation of cadmium with organic ligands decreases the uptake of the metal by the brine shrimp. This is in agreement with the view that the availability of cadmium to aquatic organisms is related to the activity of the free cadmium ion in the solution. There is no evidence that the direct uptake of cadmium complexes is important in determining uptake of cadmium. Cadmium uptake is not, however, a mere function of the free cadmium ion activity in the solution, i.e., cadmium uptake rates may differ by an order of magnitude for the same free cadmium ion activity depending on the complexation conditions. In addition to controlling the free cadmium ion activity, the role of organic ligands in metal ion buffering and metal ion masking appear important factors in determining the availability of the metal to the organism.     

Flux of different forms of 106Ru through a marine zooplankter

The dynamics of accumulation and loss of different physico-chemical forms of ¹⁰⁶Ru were measured in the euphausiid Meganyctiphanes norvegica. The accumulation of ¹⁰⁶Ru was directly related to the concentration of the radioisotope in solution, as evidenced by similar concentration factors for euphausiids in the low and high activity ¹⁰⁶Ru chloride solutions. The chemical form of the radioisotope in solution had a pronounced effect on the uptake, with ¹⁰⁶Ru chloride fractions being accumulated at a faster rate than ¹⁰⁶Ru nitrosyl-nitrato complexes. Euphausiids lost ¹⁰⁶Ru, previously accumulated from the ¹⁰⁶Ru chloride complexes, at a faster rate than ¹⁰⁶Ru which had been accumulated from ¹⁰⁶Ru nitrosyl-nitrato forms. Also, in the case of the ¹⁰⁶Ru chloride complexes, the loss rate was inversely proportional to the time allowed for isotope accumulation. The process of molting greatly accelerated the loss of ¹⁰⁶Ru from euphausiids, with first molts shed during the loss phase accounting for 70 to 80% of the total ¹⁰⁶Ru body burden. When euphausiids accumulated ¹⁰⁶Ru from the food chain, the initial-loss rate was rapid due to large amounts of the radioisotope associated with fecal pellets; however, no relationship was found between loss rate and the number of food rations received. Molts from these individuals did not contain ¹⁰⁶Ru, thus, loss from euphausiids obtaining this radioisotope through the food chain is mainly due to fecal pellet deposition and other excretion or exchange processes.     

Crassostrea virginica as an indicator of cadmium pollution

As much as 89, 176 and 292 g Cd g^-1 dry weight were accumulated by adult Crassostrea virginica after treatment for 40 wk with 5, 10 and 15 g Cd kg^-1, respectively, in flowing seawater at ambient salinity and temperature without mortalities. Cadmium accumulation increased with increased concentration of cadmium in seawater; greater amounts were accumulated during the summer months. Uptake patterns measured as cadmium content were similar among the total soft parts, gill, mantle and visceral mass. A continuous increase of cadmium concentration in the visceral mass was observed. This differed from the uptake patterns observed as cadmium concentration in gill, mantle and total soft parts. Although cadmium accumulation in the total soft parts and the tissues was curvilinear over the entire study period, significant linear relations between cadmium concentration and time indicated a general increasing trend. At seawater temperatures below 6°C, when oysters were not actively feeding, cadmium concentrations in the total soft parts varied significantly between treatments, but not within treatments. In the tissues, the rate of uptake expressed as cadmium concentrations was visceral mass>gillmantle. Cadmium concentration in the total soft parts varied inversely with dry weight, whereas cadmium concentration in the total soft parts increased, whereas the content decreased. Cadmium concentration decreased in mantle and gill but increased in the visceral mass during spawning, whereas cadmium content decreased in all tissues. Regression analyses indicated that during spawning dry weight decreased at the same rate in gill and mantle, but they lost less weight and lost it more slowly than visceral mass. Also, during spawning, cadmium content decreased in mantle and gill at the same rate but more slowly than in the visceral mass. In mid-August, Cd concentration decreased despite the continuous addition of cadmium to the seawater; however, Cd content increased, suggesting that organism weight was responsible for fluctuations in cadmium concentrations.     

Flux of cadmium through euphausiids

Flux of the heavy metal cadmium through the euphausiid Meganyctiphanes norvegica was examined. Radiotracer experiments showed that cadmium can be accumulated either directly from water or through the food chain. When comparing equilibrium cadmium concentration factors based on stable element measurements with those obtained from radiotracer experiments, it is evident that exchange between cadmium in the water and that in euphausiid tissue is a relatively slow process, indicating that, in the long term, ingestion of cadmium will probably be the more important route for the accumulation of this metal. Approximately 10% of cadmium ingested by euphausiids was incorporated into internal tissues when the food source was radioactive Artemia. After 1 month cadmium, accumulated directly from water, was found to be most concentrated in the viscera with lesser amounts in eyes, exoskeleton and muscle, respectively. Use of a simple model, based on the assumption that cadmium taken in by the organism must equal cadmium released plus that accumulated in tissue, allowed assessment of the relative importance of various metabolic parameters in controlling the cadmium flux through euphausiids. Fecal pellets, due to their relatively high rate of production and high cadmium content, accounted for 84% of the total cadmium flux through M. norvegica. Comparisons of stable cadmium concentrations in natural euphausiid food and the organism's resultant fecal pellets indicate that the cadmium concentration in ingested material was increased nearly 5-fold during its passage through the euphausiid. From comparisons of all routes by which cadmium can be released from M. norvegica to the water column, it is concluded that fecal pellet deposition represents the principal mechanism effecting the downward vertical transport of cadmium by this species.     

Accumulation of arsenic from water and food by Littorina littoralis and Nucella lapillus

The mechanism, and factors influencing the process of arsenic accumulation and elimination in a food chain [Fucus spiralis (L.) Littorina littoralis (L.) Nucella lapillus (L.)] were examined using the radioisotope ⁷⁴As. Organisms were collected during 1978 from the estuary of Restronguet. Creek in southwest England. Arsenate uptake by L. littoralis increased linearly with increasing external arsenate concentration up to ca. 500 g 1^-1 but was independent at higher arsenate concentrations. Arsenic uptake by L. littoralis was suppressed by metabolic inhibition (potassium cyanide) and lowered salinity. At 26°C, arsenic uptake was twice that at 10°C. L. littoralis accumulated 1o times more arsenic from solution than N. lapillus. Approximately 91% of ⁷⁴As accumulated from water by L. littoralis was found in the soft tissues, especially the digestive gland and gonads, but in N. lapillus 85% was associated with the shell. Arsenate uptake was twice that of arsenite in L. littoralis. Phosphate at normal environmental levels (2.4 M) did not influence the accumulation of arsenic by L. littoralis, although concentration-dependent inhibition of arsenic uptake was found between 8 and 17 M. Compared with macroalgae, the marine snails exhibit a much greater ability for eliminating arsenic. In L. littoralis the elimination of ⁷⁴As absorbed from sea water occurred in three stages, each contining equal amounts of the initial ⁷⁴As pool, with biological half-lives of 4, 13 and 47 d. A biphasic pattern of elimination was found for food-labelled snails (L. littoralis and N. lapillus). The rapid compartment, contributing a third of the arsenic, had a half-life of 4 d, while that of the slow compartment was 12 to 13 d. Fed snails eliminated arsenic more rapidly and extensively than starved individuals. All arsenic in the tissues of the snails studied was available for exchange with that in the environment. The diet is by far the major source of arsenic in L. littoralis and N. lapillus, which appear equally efficient at assimilating arsenic from food.     

Accumulation of cadmium from contaminated water and sediment by the shrimp Callianassa australiensis

The burrowing marine shrimp Callianassa australiensis (Dana) was collected from an uncontaminated area in Western Port, Victoria, Australia in 1977. The shrimp were exposed to cadmium-contaminated water and sediment for 8 wk. The concentrations ranged from 0.5 to 63 g Cd 1^-1 for water and 0.5 to 63 g Cd g^-1 for sediment. The shrimp accumulated cadmium from water at a rate commensurate with increases in the concentration of cadmium in water and the duration of the experiment. Although the cadmium concentration in the sediments was 10³ times higher than that in water, it hat no effect on cadmium uptake by the shrimp. The concentration factors decreased with increasing concentration of cadmium in water but increased as the duration of exposure increased. The shrimp dry weight decreased with increasing concentration of cadmium in water and duration of exposure. As was the case with cadmium uptake by the shrimp, these two factors acted interactively on the shrimp dry weight, but the third factor, concentration of cadmium in sediment, had no effect.     

Metal interaction during accumulation by the mussel Mytilus edulis planulatus

Mytilus edulis planulatus (Lamarck) were collected from Howden, South-east Tasmania in autumn 1981. Interaction effects of cadmium, copper and zinc during accumulation by mussels exposed for ten days to all three metals simultaneously were examined in a series of experiments in which each metal was tested at three concentrations. In general, interaction effects were most evident at the highest concentrations tested (20 g l^-1 Cd; 20 g l^-1 Cu; 200 g l^-1 Zn) and led to a reduction in the accumulation of cadmium and an increase in that of copper and zinc. More specifically, high levels of zinc caused a decrease in cadmium uptake and an increase in copper accumulation. The presence of copper resulted in depressed cadmium accumulation while zinc accumulation increased. Cadmium tended to enhance zinc accumulation, but copper accumulation was only affected to any great extent when zinc was also present.     

Flux of radioactive cadmium through the sea-skater Halobates (Heteroptera: Gerridae)

Uptake of ¹⁰⁹Cd in freshly caught sea-skaters Halobates nereis and H. flaviventris was measured under the influence of abiotic parameters as salinity and stable Cd concentration. After 6 d of accumulation a concentration factor of 8 over the seawater level was reached with no indication for an equilibration. The calculated biological half-life of ¹⁰⁹Cd amounted to 9.3 d. Cadmium uptake from food (wingless Drosophila sp. flies reared on cadmium enriched agar) can be considerable. A large pond-skater Limnogonus fossarum, measured for comparative purposes, accumulated cadmium, but at a much lower rate. The results are discussed with respect to observed natural cadmium concentrations in open ocean sea-skater populations.     

Kinetics of zinc uptake from solution,accumulation and excretion by the decapod crustacean<Emphasis Type="Italic"> Penaeus indicus</Emphasis>

Juveniles of the dendrobranchiate decapod Penaeus indicus take up radiolabelled zinc from solution at all exposure concentrations studied from 5.6 to 100 g l^–1, with an uptake rate constant of 0.045 l g^–1 day^–1 at 15 salinity and 25°C. Over the first 10 days of zinc exposure, the new zinc taken up is added to the existing zinc content of the prawn with no significant excretion; over this period the rate of accumulation of radiolabelled zinc is a measure of the absolute zinc uptake rate from solution. Over the next 10 days of zinc exposure to 10 g Zn l^–1, however, zinc is excreted at about half the rate of uptake resulting in a raised body concentration of zinc. Moulting had no significant effect on the accumulation of zinc. Newly accumulated zinc is distributed to all organs with the highest proportions of body content being found in the exoskeleton, followed by the muscle, the hepatopancreas and the antennal organs. Radiolabelled zinc is subsequently lost from all organs. Unlike caridean shrimps or prawns (pleocyemate decapods), therefore, penaeids (dendrobranchiate decapods) do not show regulation of zinc body concentrations to a constant level over a range of dissolved zinc bioavailabilities by matching zinc excretion to zinc uptake. Nevertheless, unlike amphipod crustaceans, P. indicus does excrete some of the zinc newly accumulated from solution after a time delay. Unlike their caridean counterparts, penaeid prawns inhabiting anthropogenically contaminated coastal waters with raised zinc bioavailabilities can be expected to contain raised body concentrations of zinc.Communicated by J.P. Thorpe, Port Erin     

Sterol production and phytosterol bioconversion in two species of heterotrophic protists, Oxyrrhis marina and Gyrodinium dominans

The kinetics and efficiency of sterol production and bioconversion of phytosterols in two heterotrophic protists Oxyrrhis marina and Gyrodinium dominans were examined by feeding them two different algal species (Rhodomonas salina and Dunaliella tertiolecta) differing in sterol profiles. R. salina contains predominantly brassicasterol (≅99%) and <2% cholesterol. The major sterols in D. tertiolecta are ergosterol (45–49%), 7-dehydroporiferasterol (29–31%) and fungisterol (21–26%). O. marina fed R. salina metabolized dietary brassicasterol to produce 22-dehydrocholesterol and cholesterol. O. marina fed D. tertiolecta metabolized dietary sterols to produce cholesterol, 22-dehydrocholesterol, brassicasterol and stigmasterol. G. dominans fed either R. salina or D. tertiolecta metabolized dietary sterols to make cholesterol, brassicasterol and a series of unknown sterols. When protists were fed R. salina, which contains cholesterol, the levels of cholesterol were increased to a magnitude of nearly 5- to 30-fold at the phytoplankton-heterotrophic protist interface, equivalent to a production of 172.5 ± 16.2 and 987.7 ± 377.7 ng cholesterol per mg R. salina carbon consumed by O. marina and G. dominans, respectively. When protists were fed D. tertiolecta, which contains no cholesterol, a net production of cholesterol by the protists ranged from 123.2 ± 30.6 to 871.8 ± 130.8 ng per mg algal C consumed. Cholesterol is not only the dominant sterol, but a critical precursor for many physiologically functional biochemicals in higher animal. As intermediates, these heterotrophic protists increase the amount of cholesterol at the phytoplankton–zooplankton interface available to higher trophic levels relative to zooplankton feeding on algae directly.     

Field and experimental studies on cadmium in the edible crab Cancer pagurus

The distribution of cadmium within captive crabs (Cancer pagurus) exposed experimentally to cadmium-contaminated food and water is described and illustrated by triangular diagrams. Crabs from the Orkney Islands (Scotland) are known to contain relatively high levels of cadmium (up to 62 g g^-1 wet wt) in the hepatopancreas. The distribution of cadmium between the hepatopancreas, gonad, gill, carapace, claw muscle, heart, and haemolymph, is described in crabs collected during 1978, and compared with similar data from crabs exposed to cadmium for ca. 300 d (September 1978 – June 1979) experimentally. It is concluded that the dominant uptake route of cadmium to Orkney crabs is through their diet.     

Influence of temperature and salinity on the uptake,distribution and depuration of mercury,cadmium and lead by the black-lip oyster Saccostrea echinata

Saccostrea echinata (Quoy and Gaimard) were exposed to 10 g 1^-1 of either mercury, cadmium or lead at 30 °C, 36S; 30 °C, 20S; 20°C, 36S and 20°C, 20S for 30 d and were then transferred to clean seawater for a further 30 d to depurate. Specimens were removed at regular intervals during the exposure and depuration periods, dissected into gills, mantle, visceral mass and adductor, and analysed for the appropriate metal by atomic absorption spectroscopy. Mercury was concentrated more than the other metals in all tissues under all conditions. Cadmium uptake was greater than lead in all tissue in the high-temperature experiments, whereas both metals were concentrated to similar extents at low temperature. The gill tissue generally accumulated the greatest amount of all 3 metals, whilst the adductor concentrated the least amount. At both salinities, mercury and cadmium accumulation by all tissues was significantly greater at the higher temperature whereas lead uptake was only marginally increased. The accumulation rates of mercury at high temperature were significantly greater in all tissues at low compared with high salinity, whereas at low temperature, differences were not significant. Accumulation rates of cadmium and lead in the majority of tissues examined were significantly greater in lowsalinity water at both temperatures. In general, lead was lost the most rapidly from oyster tissues, followed by mercury and then cadmium. The residence times for mercury and cadmium differed significantly between tissues, with the gills showing the highest turnover rate. In contrast, residence times for lead were similar between tissues. Losses of all 3 metals from oyster tissues were not obviously influenced by temperature and only mercury losses differed significantly between salinities.     

Kinetics of trace metal accumulation and excretion in the polychaete <Emphasis Type="Italic">Nereis diversicolor</Emphasis>

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.     

Characteristics of arsenic accumulation by the seaweeds Fucus spiralis and Ascophyllum nodosum

This study examines the accumulation of ⁷⁴As-arsenic in the seaweeds Fucus spiralis (L.) and Ascophyllum nodosum (L.) collected from Restronguet Creek in southwest England during 1978. Also, the influence of environmental factors (valence state of arsenic, pH, salinity, temperature, phosphate concentration) and metabolic inhibitors on the uptake of arsenic by F. spiralis is examined. Most of the arsenic in the seaweeds was non-exchangeable with labelled arsenic in the medium. The accumulation of ⁷⁴As reached a steady state in 1 to 8 d, depending on the species and external arsenic concentration. At steady state the accumulated arsenic is proportional to external arsenate concentration. F. spiralis accumulated 4 times more arsenate than arsenite. The short-term uptake of arsenic increased in proportion to the external arsenic concentration up to a level of 1000 g l^-1; it then remained constant at higher levels of arsenic. Arsenic uptake increased in direct proportion to increasing temperature. Variation of pH or salinity had no effect on arsenic incorporation. The accumulation of arsenic occurred only in living tissue and was inhibited by KCN in a concentration-dependent manner. The uptake of arsenic by F. spiralis in the presence of photo-synthetic inhibitors (DCMU or CMU) or in the dark was greater than in the light controls. Thus, it was concluded that energy is required for arsenic uptake and this is derived from respiration rather than photosynthesis. There was no evidence for a common mechanism of phosphate and arsenate uptake by macroalgae, although high concentrations of phosphate (40 to 400 M) initially inhibited arsenate uptake.     

Variability in dry weight and vertical distributions of decapod larvae in the Irish Sea and North Sea during the spring

Accumulation of waterborne cadmium in Littorina littorea, Mytilus edulis and Carcinus maenas (collected in 1988 and 1989 around the island of Funen, Denmark) was investigated in a matrix of salinities (10 to 30) and calcium concentrations (2.9 to 8.9 mM Ca⁺⁺). Cadmium accumulation rates in soft parts of L. littorina, soft parts and shells of M. edulis and whole bodies and exoskeletons of C. maenas decreased with increasing salinity. Changes in the calcium concentrations accounted for 72% of the salinity effect on cadmium accumulation rates in L. littorina, whereas calcium concentrations had little or no effect on cadmium accumulation in M. edulis. Cadmium accumulation in the whole body of C. maenas was affected equally by calcium concentrations and total salinity, whereas accumulation in the exoskeleton was mainly affected by changes in total salinity. Individual variability in cadmium accumulation in the organs of C. maenas was greater than the variation attributable either to changes in ambient calcium concentrations or total salinity. An appreciable amount of the inter-individual variability in the cadmium accumulation in all three species was correlated with wet:dry weight ratios of the tissues and size of the organisms.     

Modelling the kinetics and equilibrium properties of cadmium biosorption by river green alga and water hyacinth weed

Cadmium biosorption properties of non-living, dried river green alga from a river source, and water hyacinth weed, Eichhornia crassipes from a lake in Zimbabwe have been investigated. The cadmium uptake was found to depend on initial pH, uptake being apparently minimal at low pH values and increasing with an increase in pH. Cadmium biosorption kinetics by both samples is fast, with 80% of total uptake occurring within 60?min. The effect of initial solution pH and initial cadmium concentration on cadmium biosorption from a cadmium solution has been studied. The data for algal biomass fitted the Langmuir monolayer adsorption isotherm, while the biosorption of the metal by water hyacinth weed fitted the Freundlich adsorption isotherm with 1/n values all less than 1. Maximum metal uptake capacities were recorded using 0.35?g of biomass and a 250?mg?L^?1 cadmium solution at pH 6.5 and at 25°C and these were about 85 and 50?mg?L^?1 for water hyacinth weed and green alga, respectively, showing that water hyacinth weed offered a greater potential for cadmium uptake. The absorption was described by pseudo-second order rate model and the rate constant and equilibrium sorption capacity are reported.     

Uptake of cadmium by the eelgrassZostera marina

The uptake of cadmium by the shoots ofZostera marina L. (eelgrass) was examined in the laboratory. Experiments were carried out in experimental chambers which allowed the separation of the leaves from the root-rhizome portions of intact shoots. Cadmium uptake by the root-rhizome portions over 24 h was directly related to substrate cadmium concentration (1.0, 5.0 and 10.0 g Cd ml^-1) and varied from 6.5 to 30.0 g Cd g^-1. Cadmium uptake by the root-rhizomes and the leaves in a substrate concentration of 1 g Cd ml^-1 was also related to exposure times (24, 48 and 72 h). Maximum uptake by the root-rhizomes and the leaves was observed after 72 h at a substrate concentration of 1 g Cd ml^-1 and was equivalent to 48 and 94 g Cd g^-1, respectively. Translocation of cadmium from the leaves to the root-rhizomes was observed after 24 h, and at the end of 72 h was equivalent to 27% of the total leaf uptake. No cadmium movement from the root-rhizomes to the leaves was detected.     

Cadmium kinetics in oysters — a comparative study of Crassostrea gigas and Ostrea edulis

The accumulation of cadmium was investigated in two species of oysters [Crassostrea gigas (L.) and Ostrea edulis (L.)] from the same environment and in oysters of the same species (O. edulis) from two different environments (contaminated and uncontaminated), under controlled laboratory conditions (33‰ salinity, 10°C, 100 μg Cd l^-1) for up to 111 d in 1982. C. gigas accumulated cadmium twice as fast as O. edulis (1.07 vs 0.52 μg Cd g^-1 wet wt d^-1). Furthermore, O. edulis from an uncontaminated environment accumulated cadmium faster than O. edulis from a metal-contaminated environment (0.52 vs 0.34 μg Cd g^-1 wet wt d^-1). There was no effect of cadmium exposure on total soft-tissue copper and zinc concentrations. Investigation of cytosolic metal-binding using Sephadex G-75 gel-permeation chromatography indicated that binding to very low molecular weight ligands (MW<1000) accounted for>70% of the cytosolic zinc in all oysters and>40% of the cytosolic cadmium in all oysters except O. edulis from Conwy at 83 d. In copper-contaminated oysters, excess copper was also associated with very low molecular weight ligands. Intermediate molecular weight cadmium/copper-binding proteins (similar to metallothionein in molecular weight) were observed in the cytosol and were shown to differ between species in terms of their behavior on Sephadex G-75. Finally, the distribution of accumulated cytosolic cadmium in O. edulis from the contaminated environment was shown to have a unique distribution, i.e., there was no cadmium associated with high molecular weight cytosolic macromolecules. The data indicate that both genetic and environmental factors influence cadmium accumulation in oysters.     

Experimental study on vanadium transfer in the benthic fish Gobius minutus

The radiotracer vanadium-48 was used to examine accumulation, assimilation, tissue distribution and elimination of vanadium in the benthic fish Gobius minutus (Pallas). After 3 wk exposure to ⁴⁸V in sea water, mean whole-body concentration factors were low (0.8). The tissue distribution of ⁴⁸V indicated that ⁴⁸V accumulated from water penetrates little into internal tissues, muscle or liver, and is preferentially fixed in tissues in direct contact with the sea water. Concentrations of stable vanadium in fishes collected during summer 1988 from the littoral zone near Monaco displayed the same trends. Vanadium accumulated directly from water is rapidly lost, as evidenced by a 19 d biological half-life of ⁴⁸V. Likewise, assimilation of vanadium through the food-chain is low; only 2 to 3% of ⁴⁸V ingested with prey is retained in the tissues of the goby. The results suggest that the relatively low vanadium toxicity observed in benthic fish by other investigators is a consequence of the low degree of uptake of this metal from food or water. The relative importance of uptake from food and from water to the vanadium levels in benthic fish is discussed in the light of the ⁴⁸V distribution recorded in experimental individuals and the distribution of stable vanadium in similar samples from the natural environment.