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.     

Concentrations of Mn,Fe, Cu,Zn and Cd in the mesopelagic decapod Systellaspis debilis from the East Atlantic Ocean

Specimens of the oceanic decapod Systellaspis debilis were collected from six sites in the East Atlantic Ocean between 1970 and 1984, and were analysed for Mn, Fe, Cu, Zn and Cd. The data confirm that there are small but significant differences in mean metal concentrations from some sites which showed no obvious pattern in relation to geographic location of the samples. As a result, ranges of site means are quoted as baseline levels for each metal (g g^-1 dry wt): 2.3 to 2.9 g Mn g^-1, 31.2 to 77.8 g Fe g^-1, 25.9 to 83.4 g Cu g^-1, 41.9 to 92.9 gZn g^-1, 11.1 to 31.8 g Cd g^-1. The concentration of cadmium in S. debilis from all sites was raised relative to cadmium concentrations reported for coastal decapods, perhaps as a result of dietary enrichment. Metal accumulation may provide useful information for understanding the complex feeding behaviour of many oceanic animals.     

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.     

Ultrastructural and biochemical studies of intracellular metal-binding patterns in kidney tubule cells of the scallop Placopecten magellanicus following prolonged exposure to cadmium or copper

Sea scallops Placopecten magellanicus, which had been trawl-collected in late November, 1982 off the Rhode Island, USA coast, were exposed to 20 g of Cd or Cu per liter for a period of seven weeks in a flowing seawater system. Metal analyses of kidneys from both groups indicated uptake of both metals, although the tissue concentrations of Cd declined markedly in the Cu-treated scallops. The ultrastructural appearance of tubule cells of kidneys from Cd-exposed scallops was indistinguishable from controls. In contrast, tubule cells from scallops exposed to Cu showed marked cellular degeneration with loss of concretions. These ultrastructural changes were associated with significant reductions in renal isocitrate dehydrogenase activity in the Cu-treated scallops. Elemental analyses conducted on the kidney concretions and on the cytosolic metal-binding proteins of Cd-exposed scallops showed a 6-to 7-fold increase in Cd content of both these metalsequestering compartments, with concomitant changes in Zn, Mn, and Cu content. Loss of the concretions from Cu-treated scallops precluded analysis of this compartment, but Cu sequestration within cytosolic metal-binding proteins was associated with marked reductions of Zn and Cd from these proteins, suggesting disruption of this cellular mechanism for control of divalent metal cations. These findings support the hypothesis that toxic metal perturbation of normal homeostatic mechanisms that control divalent metal cation bioavailability is important factor in mediating cell injury from these agents.     

Metallothioneins and lysosomes in metal toxicity and accumulation in marine mussels: the effect of cadmium in the presence and absence of phenanthrene

It has been confirmed that metallothioneins play an important role in the accumulation of cadmium (Cd) in the digestive gland cells of mussels (Mytilus galloprovincialis Lam.). The content of Cd in the tissue of mussels exposed for 9 d to the metal (estimated dosage of 180 g Cd mussel^-1 d^-1) was 66.2 ppm. This value is about the same as the metal content found in the digestive gland of Cd-exposed mussels kept in clean water for a recovery period of 28 d. At the end of the recovery period, however, the Cd bound to thionein had increased by approximately 250%. Our data demonstrate that the stability of lysosomes, a biological parameter adopted as a cellular stress index, is extremely low in mussels exposed to Cd for 9 d, but returns to control values in the digestive gland cells of mussels allowed to recover for 28 d in uncontaminated sea water. At this point most of the Cd present in the cytosol is bound to thionein. These data demonstrate the importance of metallothionein induction in the reduction of the cytotoxic effects exerted by high levels of Cd accumulation. The results of tests designed to clarify the reasons for the long biological half-life of Cd demonstrated that, in the digestive gland of mussels, the lysosomes are not able to eliminate Cd either bound to insoluble thionein polymers or to lipid peroxidation products such as lysosomal lipofuscin, both of which are apparently involved in the elimination of copper. The absence of these two mechanisms of metal sequestration and elimination via excretion of residual bodies (tertiary lysosomes) is in agreement with the persistence of cadmium in the digestive gland of mussels. Finally, the results also demonstrate that simultaneous exposure of mussels to Cd and phenanthrene, an established lysosomal membrane destabilizer, did not significantly alter the accumulation of Cd or the kinetics of the metal in mussels.     

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.     

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.     

HPLC analysis of nonprotein thiols in planktonic diatoms: pool size,redox state and response to copper and cadmium exposure

A sensitive method was developed to analyze low molecular weight thiols involved in metal homeostasis and detoxification in phytoplankton. The aims of this study were to (1) separate and measure all relevant thiols in a single HPLC run, (2) measure redox states of the thiols and (3) identify specific responses of thiols (pools, redox) to heavy metals by testing diatoms with different metal tolerances (Ditylum brightwellii, Phaeodactylum tricornutum, Skeletonema costatum andThalassiosira pseudonana). Copper or cadmium were dosed at a maximum tolerable, species-dependent level, to exponential phase cells growing in artificial medium (14 salinity). Loss of cell viability was monitored by the decrease of fluorescein fluorescence after a 24-h metal exposure. Thiols in extracts of exposed cells and controls were labeled with monobromobimane. Picomoles of cysteine, glutathione, -glutamylcysteine and phytochelatins (PCs) were detected and separated by reversed-phase high performance liquid chromatography. Cysteine increased in all species after metal exposure. The species with the largest glutathione pools in the control (P. tricornutum) synthesized the largest PC pools upon metal exposure, however, at a 40% loss of glutathione. A considerable increase of glutathione was observed inD. brightwellii upon metal exposure. However, it produced little PC (and only with Cu). In controls ( 3 pM Cu²⁺), PC₂ was detectable inS. costatum, P. tricornutum andT. pseudonana. Oxidized thiol fractions were recovered by the reductants DTT and TCEP, both performing identically. Compared to the other thiols, cysteine had low redox ratios. InD. brightwellii glutathione and PC redox ratios were lower than inP. tricornutum, S. costatum andT. pseudonana. It was expected that Cu-induced oxidative stress would decrease the thiol redox ratios, however, this was not observed.This is Communication No. 2172 of NIOO.     

Effects of cadmium and low magnesium on cell division and calcification in the marine coccolithophorid Cricosphaera (Hymenomonas) carterae

Cadmium (Cd) added to normal media and to magnesium (Mg)-deficient media produced inhibitory effects on cell division and cell calcification in the marine coccolithophorid alga Cricosphaera (Hymenomonas) carterae. Compared with controls in normal media (with 25 mM Mg), cell growth decreased progressively with Cd at concentrations of 5–20 M. In Mg-deficient media (with 6 mM and 0.08 mM Mg) the inhibitory effects were more pronounced with complete arrest of cell division at 20 M Cd. The greatest Cd inhibition occurred in media with the lowest Mg concentration (0.08 mM). Cadmium (5–40 M) also decreased recalcification (coccolith formation) in cells previoasly decalcified with CO₂ with complete inhibition at 40 M Cd. Inhibition of recalcification in various Cd concentrations (5–40 M) was more pronounced in low-Mg medium (with 6 mM and 0.08 mM Mg) compared with normal medium (25 mM Mg). Partial or complete reversal of the inhibitory effects of Cd and low Mg media on cell division and calcification occurred following a wash and resuspension of the cells in normal control medium (25 mM Mg).     

Mytilus edulis planulatus: an “integrator” of cadmium pollution?

Mussels, Mytilus edulis planulatus, were collected from Port Phillip Bay, Victoria, Australia, in February 1984, to test the assumption that they are integrators of cadmium pollution. Groups of mussels were subjected to the same average dose of cadmium (21 g l^-1), administered according to different dosing regimes over 4 wk (Regimes 1, 2, 3, 5); other groups received twice the average dose (42 g l^-1) in half the time (Regime 4). During each regime, the mussels were exposed to the different cadmium concentrations for one week at each concentration. Nominally, the regimes were: (1) 36 g (Wk 1) to 26 g (Wk 2) to 16 g (Wk 3) to 6 g (Wk 4) Cd l^-1; (2) 6 to 16 to 26 to 36 g Cd l^-1; (3) 21 to 21 to 21 to 21 g Cd l^-1; (4) 42 to 42 g Cd l^-1; (5) 42 to 42 g Cd l^-1 to background (<0.5 g) to background. Differences in cadmium accumulation by mussels from Regimes 1 and 4 were not statistically significant, nor were differences in accumulation between mussels from Regimes 2 and 3. However, mussels from Regimes 1 and 4 had accumulated significantly more cadmium than had mussels from Regimes 2 and 3. Accumulation by mussels from Regime 5 was not significantly different from that by mussels from any of the other regimes. These results suggest that, at least for cadmium, the assumption that mussels are integrators of pollution should be treated with caution. They also have implications with regard to the quantitative biological monitoring of pollution. For example, even in a carefully controlled monitoring program, using mussels of standard size and condition, significant differences in cadmium content between mussels need not indicate exposure to different levels of contamination. Rather, these differences could reflect differences in the regime by which the contamination was received.     

Cadmium effects on the carbon and energy balance of mudsnails

The present study examined the ability of shortterm physiological measurements to predict growth rates of a gastropod, Hydrobia ulvae, in response to pollutant exposure. Whereas growth rates of snails collected from Munkebo Harbor, Funen, Denmark in 1989 were substantially reduced by exposure to cadmium after ca. 3 wk, we could detect no change in total carbon balance measured in short-term radioisotope experiments. At 23 S, the reduction in percent growth after 3 wk was 186.4 for snails exposed to 100 g Cdl^-1 and 225.7 for snails exposed to 200 g Cdl^-1. At 13 S, the reduction in percent growth was 102.6 at 100 g Cdl^-1 and 106.4 at 200 g Cdl^-1. We found no effect of cadmium on sediment egestion rate over 18 d of exposure. Nor could we detect effects on carbon absorption efficiency or metabolic loss of absorbed carbon during the first 24 h following its ingestion. The fractional loss of ¹⁴C from uniformly-labeled snails showed a decrease in CO₂ and an increase in dissolved carbon in snails exposed to 200 g Cdl^-1. Such changes in the partitioning of carbon loss from body stores suggest a partial shift from aerobic to anaerobic metabolic pathways which could reconcile the seeming disparity between growth and carbon balance in response to cadmium exposure.     

Cadmium accumulation,LC50 and oxygen consumption in the tropical marine amphipod Elasmopus rapax

Adult Elasmopus rapax, collected from the eastern coast of Venezuela in 1990, were exposed to seawater containing various CdCl₂ concentrations ranging from 0.25 to 5.5 mol l^-1. The 48-h and 96-h LC₅₀ values obtained were 4.0 and 1.6 mol Cd l^-1, respectively. In amphipods exposed to 1 mol Cd l^-1 for up to 240 h, the apparent rate of cadmium uptake was higher in dead animals (most of which had molted during the preceding 24 to 48 h) than in those which survived throughout the treatments without molting. Thus, whole-body cadmium content reached 1.74 mol g^-1 dry weight (dw) in the former and only 0.85 mol g^-1 dw in the latter; the higher body Cd-load may have caused the increased mortality observed in molters. On exposure to cadmium levels above 0.5 mol l^-1 the oxygen consumption rate of non-molters decreased from 2.2 to about 1.5 ml O₂ g^-1 dw h^-1 over the first 24 h, remaining unchanged thereafter. The results place E. rapax among the most sensitive marine organisms yet studied concerning cadmium toxicity, and emphasize the usefulness of the Amphipoda as bioindicators and research tools for bioassays.     

Accumulation of cadmium by Artemia salina

The relative importance of accumulation of cadmium by Artemia salina (L.) directly from solution and from ingested food has been studied at 3 cadmium concentrations (0.1, 1 and 10 ppm) under controlled experimental conditions. At each cadmium concentration, A. salina were exposed to cadmium in 4 ways; in solution; in solution in the presence of latex food particles; in solution with cadmium-rich Dunaliella tertiolecta as a food source; and to cadmium-rich D. tertiolecta alone. Net accumulation of cadmium by A. salina continued throughout 5 days exposure under all 4 conditions. When the brine shrimp were removed to cadmium-free conditions, their accumulated cadmium concentrations declined and levelled off to a stabilised plateau after 10 days. From consideration of these stabilised levels it was shown that at least 30% of cadmium accumulation directly from solution occurs via uptake through the alimentary tract. The ratio of cadmium accumulated from solution to cadmium accumulated from food was found to be 1:4.9, 1:6.7 and 1:1.1 at 0.1, 1 and 10 ppm Cd exposure, respectively. At lower cadmium exposures uptake from food is the major route for cadmium accumulation, but at higher exposures the cadmium-saturated food source displaced cadmium-rich water from the gut and therefore actually inhibited cadmium accumulation. This study, therefore, concludes that the food chain will be the major source of cadmium as long as the previous trophic level has the ability to accumulate the metal to such an extent as to make it more available to the consumer than by direct uptake from seawater.     

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.     

Effect of cadmium on survival and osmoregulation of various developmental stages of the shrimp Penaeus japonicus (Crustacea: Decapoda)

The object of this study was to evaluate the acute toxicity of cadmium in different post-embryonic stages of the penaeid shrimp Penaeus japonicus (Bate, 1888) and to determine the effect of sublethal cadmium on the osmoregulatory capacity used as an indicator of physiological condition. Tolerance to cadmium increases with the developmental stage. The least tolerant stages are the nauplii (48 h LC₅₀: 124 g Cd l^-1) and the zoeae (96 h LC₅₀: 10 to 30 g Cd l^-1). The most tolerant stages are the postlarvae (96 h LC₅₀: 200 to 3500 Cd l^-1) and juveniles (96 h LC₅₀: 5500 g Cd l^-1). In juvenile shrimp, 2000 g Cd l^-1 significantly reduce hypo- and hyper-OC. The effect of cadmium on hypo- and hyper-osmoregulatory capacity illustrates a dose- and time-dependent response. Surviving shrimp recover their hypo-osmoregulatory capacity after 6 d of readaptation in cadmium-free seawater.     

Observations on shell deformities,ultrastructure, and increment formation in the bay scallop Argopecten irradians

Shell morphology and ultrastructure were examined in the bay scallop Argopecten irradians, cultured in recirculating seawater systems under various conditions of feeding, lighting, and handling. On a unialgal diet of Thalassiosira pseudonana, scallop growth ranged from 120 to 183 m d^-1 at 20°C in the laboratory, about two-thirds of the growth rate found in the field. However, shell deposited in the laboratory differed from that in the field in several ways. In the field, scallops formed costae as an unpigmented, corrugated marginal shell layer; shell deposited in the laboratory lacked this layer and was therefore darker. Also, microstructure of the exterior shell surface of field scallops was coarsely granular, while that of cultured scallops was relatively smooth. Excessive handling of scallops in the laboratory resulted in marginal thickening of valves, a deformity which was completely arrested by a change from daily to weekly handling. Scallops cultured in the same tank with oysters developed shell-thickening on the interior of the valves. It is postulated that shell abnormalities in bivalves result from disruption of complex behavioral processes associated with shell deposition and may be elicited by a variety of natural and experimental irritants. Under natural lighting regimes and optimal conditions for growth, scallops deposited exactly one shell increment per day, but under continuous lighting, deposition of growth increments often became aphasic. In one 28-d experiment, there was a strong correlation between number of growth increments formed and increase in shell height, suggesting that shell ridge formation occurred intermittently, rather than daily, when shell growth rates fell below approximately 150 m d^-1.     

The unusual metal status of the dugong Dugon dugon

Using atomic absorption spectroscopy, exceptionally high concentrations of iron (778 to 82,363 g g⁺¹ dry weight) and zinc (219 to 4,183 g g⁺¹ dry weight) were detected in the livers of Dugong dugon (Müller) from north Queensland compared with reported values for other marine mammals from other areas of the world. Levels of copper (9.1 to 608 g g⁺¹ dry weight), cadmium (<0.1 to 59 g g⁺¹ dry weight), cobalt (0.5 to 72 g g⁺¹ dry weight) and silver (0.2 to 39 g g⁺¹ dry weight) in the liver, and cadmium (0.2 to 209 g g⁺¹ dry weight) in the kidney were also relatively high in several samples, whilst concentrations of nickel, lead and chromium were consistently below the limits of detection in all tissues. Manganese concentrations, in all tissues examined, were generally comparable with those reported from other marine mammals. Tissue concentrations of a number of metals varied with the age of the dugong. Levels of iron, zinc, cadmium and cobalt in the liver zinc and cadmium in the kidney, and iron in the muscle were significantly positively correlated with age. Copper and manganese in both liver and kidney were negatively correlated with age. Large deposits of the iron-rich pigment, haemosiderin, the quantity of which also tended to increase with age, was a conspicuous feature of the livers of all the post-natal dugongs examined histologically. It seems unlikely that the unusual metal status of the dugong reflects anthropogenic activities, since many individuals were collected in remote areas far from major sites of urbanization and industrialization. Seagrasses, the major food of dugongs, were collected from various north Queensland dugong habitat-areas and analysed. Very high concentrations of iron but low levels of copper were detected. The significance of such dietary imbalances and their possible influence on the metal status of the dugong were therefore considered.     

Testing the ‘agonistic buffering’ hypothesis

Summary Data are presented from a 15-month study on triadic male-infant interactions (agonistic buffering) among wild Barbary macaques, and the agonistic buffering hypothesis reevaluated. The sociometrics of triadic interactions derived from the distribution of 535 interactions among individually known adult and subadult males showed that there were significant individual male differences in the frequency of initating and/or receiving triadic interactions, but there were no such differences between the high and low ranking male subgroups (Tables 2–4).Males did not choose each other equally for triadic encounters. Each male had a different set of three other males (out of 11 possible) that he preferred to approach for a triadic encounter; and each male received triadic approaches essentially from only three males (Tables 4 and 5). Each male showed a specific preference for which infant to select for participation in the triad, and in fact, males who preferred one another for triads also preferred to use the same infant in these encounters. These males that preferred each other and the same infant both had a special care-taking relationship with that preferred infant (Tables 6–7).Possessing an infant per se seemed to be irrelevant in whether a male would approach or be approached for a triad. In 78% of all triads, males separated immediately after termination of the triad. When the agonistic buffering hypothesis is reexamined against the data in this study, it appears that it cannot adequately accommodate the thesis that it serves to regulate dominant/subordinate relations among males. Rather males choose to participate with each other in agonistic buffering because, and by means of, a shared, common, and special care-taking relationship with the same infant. The indiscriminate use of the terminology agonistic buffering to describe multiple-male/infant interactions in this species should be dropped.     

Transport of cadmium and other metals in the blood of the bivalve mollusc Mercenaria mercenaria

The distribution of metals (Ba, Cr, Cu, Fe, Mn, Ni and Zn) in the blood plasma and the circulating hemocytes was determined for a eulamellibranch bivalve, the quahog Mercenaria mercenaria (L.), collected from a relatively clean site at Falmouth, Massachusetts, USA. Whole blood volume was an exponential function of quahog length (Y=5.71×10^-5 X^3.0678; Y=ml of whole blood; X=mm length). Of this volume, 1.2±0.3% ( ) was attributable to blood cells. Total metal content (g metal, or g metal normalized per g of whole blood) was much higher in blood plasma than in hemocytes. In quahogs exposed in the laboratory to 100 ppb ¹⁰⁹Cd, 93.0% of the total accumulated blood Cd was in the plasma rather than in the circulating hemocytes (7.0%), irrespective of the length of exposure (1 h to 31 d). Less than 5% of the plasma Cd was either Cd²⁺, small inorganic Cd complexes or bound to organic molecules with a molecular weight smaller than 1 000. Cadmium was primarily bound to high molecular weight protein(s) (>60 000 daltons) within the plasma. This plasma protein-Cd complex has a low affinity constant (approximately 10⁴ M ^-1), indicating non-specific Cd binding, although the capacity for Cd-binding in the plasma is great (as high as 200 g Cd per ml of plasma). Blood plasma may be far more important in metal transport than has previously been realized.