Cadmium bioaccumulation and retention kinetics in the Chilean blue mussel Mytilus chilensis: seawater and food exposure pathways.

The Chilean blue mussel (Mytilus chilensis, Hupe 1854) represents the most important bivalve exploited along the Chilean coast and is a major food source for the Chilean population. Unfortunately, local fish and shellfish farming face severe problems as a result of bioaccumulation of toxic trace metals into shellfishes. Blue mussels collected along the Chilean coasts contain levels of Cd above the regulatory limits for human consumption. In this study, we examined the bioaccumulation, depuration and organ distribution of Cd in the M. chilensis, from 109Cd-labelled bulk seawater and from feeding with 109Cd-labelled algae. The uptake of 109Cd via seawater displayed a simple exponential kinetic model suggesting that cadmium activity tends to reach an equilibrium value of 1.838+/-0.175 ng g(-1) (mean+/-asymptotic standard error, p < 0.001) after 78+/-9 days. The depuration rate for 109Cd accumulated via seawater was slow, with only 21% of the total 109Cd accumulated in the whole mussel being eliminated after 52 days. Total elimination of Cd in mussels was adequately described by a double component kinetic model, in which the biological half-life for the long-lived component represents more than 6 months. In contrast, depuration after radiolabelled food uptake was fast, reaching only 20% of retention in 10 days. This knowledge of the long half-life of cadmium accumulated via seawater as well as the non-negligible level of cadmium accumulated into the shells is relevant to the management of Cd levels in this species and the refinement of detoxification processes in order to comply with authorized Cd levels.

The barnacle Balanus amphitrite as a biomonitor for Cd: radiolabelled experiments.

Radiolabelled experiments were carried out to measure necessary parameters in the development of a biodynamic ecotoxicological simulation model of Cd accumulation in the barnacle biomonitor Balanus amphitrite. The Cd uptake rate constant from the dissolved phase, the Cd assimilation efficiency (AE) from suspended particulate matter (SPM) and the efflux rate constant were obtained using (109)Cd. A Cd uptake rate constant from the dissolved phase (k(u)) of 0.0072 Lg(-1)h(-1) was determined for the barnacle under environmentally realistic dissolved Cd concentrations (maximum of 400 ng L(-1)). Cd AE from SPM was determined from the barnacle feeding on SPM with low and high chl a concentrations, resulting in AEs of 39.0% and 48.7%, respectively, and an efflux rate of 0.0072 d(-1). The difference between the AEs resulted from differences in chl a:SPM ratios suggesting a general tendency of higher AE when SPM is enriched with chl a. These results reinforce that the accuracy of ecotoxicological models for metal accumulation in organisms depends on how representative the selected food items are of the organism's natural diet.

Comparative accumulation of (109)Cd and (75)Se from water and food by an estuarine fish (Tetractenos glaber).

Few data are available on the comparative accumulation of metal(loid)s from water and food in estuarine/marine fish. Smooth toadfish (Tetractenos glaber), commonly found in estuaries in south-eastern Australia, were separately exposed to radio-labelled seawater (14kBqL(-1) of (109)Cd and 24kBqL(-1) of (75)Se) and food (ghost shrimps; Trypaea australiensis: 875Bqg(-1)(109)Cd and 1130Bqg(-1)(75)Se) for 25 days (uptake phase), followed by exposure to radionuclide-free water or food for 30 days (loss phase). Toadfish accumulated (109)Cd predominantly from water (85%) and (75)Se predominantly from food (62%), although the latter was lower than expected. For both the water and food exposures, (109)Cd was predominantly located in the gut lining (60-75%) at the end of the uptake phase, suggesting that the gut may be the primary pathway of (109)Cd uptake. This may be attributed to toadfish drinking large volumes of water to maintain osmoregulation. By the end of the loss phase, (109)Cd had predominantly shifted to the excretory organs - the liver (81%) in toadfish exposed to radio-labelled food, and in the liver, gills and kidney (82%) of toadfish exposed to radio-labelled water. In contrast, (75)Se was predominantly located in the excretory organs (gills, kidneys and liver; 66-76%) at the end of the uptake phase, irrespective of the exposure pathway, with minimal change in percentage distribution (76-83%) after the loss phase. This study emphasises the importance of differentiating accumulation pathways to better understand metal(loid) transfer dynamics and subsequent toxicity, in aquatic biota.

Influence of food quality and salinity on dietary cadmium availability in Mytilus trossulus.

Surficial sediments (a combination of re-suspended and suspended sediments denoted as RSS) were collected from two distinct marine intertidal habitats. The two habitats differed with respect to salinity (25ppt versus 15ppt) and RSS % organic carbon content (24% versus 15%). Feeding experiments were conducted simulating the conditions in the two habitats to determine if salinity and RSS % organic carbon content affected cadmium accumulation in the pacific blue mussel Mytilus trossulus. Eleven different treatments including pure phytoplankton, collected RSS and control clay were radiolabeled with (109)Cd and pulse-fed to M. trossulus under both high (25ppt) and low salinities (15ppt). Metal uptake and accumulation was determined using the DYMBAM biodynamic metal bioaccumulation model. Although M. trossulus ingestion rates (IR) were significantly higher at 25ppt as compared to 15ppt, assimilation efficiencies (AEs) and [(109)Cd] tissue levels were significantly lower at high as compared to low salinity exposures. Of the abiotic and biotic parameters examined and in contrast to other studies, differences in salinity rather than ingestion rate or food quality (as defined by % organic carbon content) seemed to best define the observed differences in (109)Cd AE by M. trossulus.

Uptake and loss of dissolved 109Cd and 75Se in estuarine macroinvertebrates.

Semaphore crabs (Heloecius cordiformis), soldier crabs (Mictyris platycheles), ghost shrimps (Trypaea australiensis), pygmy mussels (Xenostrobus securis), and polychaetes (Eunice sp.), key benthic prey items of predatory fish commonly found in estuaries throughout southeastern Australia, were exposed to dissolved (109)Cd and (75)Se for 385 h at 30 k Bq/l (uptake phase), followed by exposure to radionuclide-free water for 189 h (loss phase). The whole body uptake rates of (75)Se by pygmy mussels, semaphore crabs and soldier crabs were 1.9, 2.4 and 4.1 times higher than (109)Cd, respectively. There were no significant (P>0.05) differences between the uptake rates of (75)Se and (109)Cd for ghost shrimps and polychaetes. The uptake rates of (109)Cd and (75)Se were highest in pygmy mussels; about six times higher than in soldier crabs for (109)Cd and in polychaetes for (75)Se - the organisms with the lowest uptake rates. The loss rates of (109)Cd and (75)Se were highest in semaphore crabs; about four times higher than in polychaetes for (109)Cd and nine times higher than in ghost shrimps for (75)Se - the organisms with the lowest loss rates. The loss of (109)Cd and (75)Se in all organisms was best described by a two (i.e. short and a longer-lived) compartment model. In the short-lived, or rapidly exchanging, compartment, the biological half-lives of (75)Se (16-39 h) were about three times greater than those of (109)Cd (5-12h). In contrast, the biological half-lives of (109)Cd in the longer-lived, or slowly exchanging compartment(s), were typically greater (1370-5950 h) than those of (75)Se (161-1500 h). Semaphore crabs had the shortest biological half-lives of both radionuclides in the long-lived compartment, whereas polychaetes had the greatest biological half-life for (109)Cd (5950 h), and ghost shrimps had the greatest biological half-life for (75)Se (1500 h). This study provides the first reported data for the biological half-lives of Se in estuarine decapod crustaceans. Moreover, it emphasises the importance of determining metal(loid) accumulation and loss kinetics in keystone prey items, which consequently influences their trophic transfer potential to higher-order predators.

Uptake and transport of radioactive nickel and cadmium into three vegetables after wet aerial contamination.

Knowledge of radionuclide or trace element retention and translocation to plants following an aerial contamination event, for example, sprinkling with contaminated water, is necessary for the evaluation of human exposure through consumption of contaminated vegetables. The fate of 63Ni and 109Cd in all plant parts of three different vegetables after wet deposition on leaves or on fruits was studied. Lettuce (Lactuca sativa L.), radish (Raphanus sativus L.), and bean (Phaseolus vulgaris L.) grown under controlled conditions in a growth chamber were contaminated with 63Ni and 109Cd either on leaves, by means of two different contamination methods (a single early contamination and a repetitive one), or on bean husks (third contamination method: a single contamination at a late stage). Spiked and nonspiked organs were harvested at maturity and radionuclide contents were measured. The fraction retained was on average 56% of the initially administered doses of 63Ni and 87% of 109Cd. The leaf-to-other organ translocation factor was considerably higher for 63Ni (on average 43% of retained radioactivity) than for 109Cd (8%). Nickel-63 migrated throughout the whole plant following foliar contamination, and mainly toward young leaves, seeds in formation, and sink organs, whereas 109Cd migrated to a much lesser extent and only to the organs that were closest to the spiked one, and not at all into fruit. After a fruit contamination event, both radionuclides were translocated into the seeds of spiked fruits. Radionuclide retention and translocation were not affected by plant species, but principally by the type of organ contaminated.

The toxicokinetics of cadmium in carp under normoxic and hypoxic conditions.

Temporal depletion of oxygen, i.e. hypoxic events, frequently occurs in natural waters. It has been suggested that accumulation of micro-pollutants increases in aquatic animals as a result of an increased ventilation rate during such occasions. The observed increased toxicity under hypoxia of micro-pollutants may support this hypothesis, but for heavy metals the available uptake studies are contradictory. The present study tests whether accumulation of cadmium in common carp, Cyprinus carpio (L.) is increased under hypoxia and if the toxicokinetics are altered. A cadmium toxicity study was performed in which the cadmium uptake rates were determined using the radiotracer 109Cd under hypoxia and normoxia. The cadmium toxicokinetics were studied with radiotracer experiments at 100% air saturation, 50%, and 25% saturation from 6.5 nmol/L Cd at 25 degrees C. We could confirm the higher sensitivity of carp to cadmium under hypoxia. Hypoxic conditions did not influence the uptake rates or the accumulation dynamics. Therefore, the increased sensitivity of carp for Cd under hypoxia cannot be explained by a higher Cd body burden, initiated by a higher uptake rate or lower elimination rate under hypoxia. Additional, possible indirect effects, such as internal anoxia due to gill damage, could play a role in Cd toxicity under hypoxia.

Effects of Zn pre-exposure on Cd and Zn bioaccumulation and metallothionein levels in two species of marine fish.

Zinc is an essential trace metal but also a potential toxicant to aquatic organisms. In this study, two juvenile marine fish species, the black sea bream Acanthopagrus schlegeli and the grunt Teraponjarbua, were pre-exposed to Zn either from waterborne (0.74-170 microg L-1) or dietary (39-5926 microg g-1) Zn for 1 or 3 weeks. The concentrations of Zn and metallothionein (MT) in the whole body of the black sea bream and in the gills, viscera and carcass of the grunt were then measured during this pre-exposure. Following the pre-exposure, both fish species were then exposed to 109Cd and 65Zn labeled food or water to quantify the dietary assimilation efficiency (AE) and the uptake rate of dissolved Cd and Zn. Zn concentrations in both fish species were enhanced after pre-exposure, but the increases were much less than the increase of ambient Zn pre-exposure concentration. Following Zn pre-exposure, MT concentrations in the viscera and carcass were significantly elevated, whereas the MT levels were not significantly elevated in the gills. Waterborne and dietary Zn exposure enhanced the uptake rates of dissolved Cd and Zn in both fish. The maximum increases of uptake rate constants of dissolved Cd and Zn were up to 1.9-2.8 and 2.1-2.6 times, respectively, in the seabream and grunt. In contrast, dietary assimilation efficiency of Cd and Zn was not significantly enhanced following Zn pre-exposure. A positive linear relationship was found between the uptake rate constants of dissolved metals and Zn or MT concentrations in the fish. The results suggested that Zn pre-exposure increased the potential of metal uptake from ambient water, but had little effect on dietary metal uptake. Furthermore, the Zn body concentration and metal uptake from the dissolved phase were significantly dependent on the fish body size.

Association between cadmium and calcium uptake and distribution during the moult cycle of female shore crabs, Carcinus maenas: an in vivo study.

Net influxes into the haemolymph and tissue distribution of 45Ca and 109Cd were studied in vivo in female Carcinus maenas at different moult stages. Net influxes of 45Ca and 109Cd from water were higher in postmoult (A and B) C. maenas than in C3- and C4-intermoult crabs and the net influx of calcium was higher in C3-intermoult crabs than in C4-intermoult crabs. The net influxes of 45Ca and 109Cd increased in postmoult C. maenas with decreasing external calcium concentrations at constant salinity. At all external calcium concentrations a significant correlation existed between 45Ca and 109Cd accumulated in the haemolymph of individual animals. In vivo exposure of postmoult C. maenas to external lanthanum decreased the 45Ca and 109Cd uptake rates to 30 and 10%, respectively, of the control values. About 30% of injected 109Cd were found in the midgut gland, 10-20% in the gills and only a few (1-2) percent was lost to the seawater 24 h after injection. No major variations in tissue distribution of 109Cd were observed between moult stages in these tissues. Premoult crabs retained more cadmium in the haemolymph 24 h after injection than other moult stages, and postmoult crabs retained more in muscle. Between 20 and 40% of the injected 45Ca were excreted to the water, while only a few percent of the injected 45Ca were found in the soft tissues 24 h after injection. Large moult stage variations, however, were observed in the tissue distribution of internalised 45Ca. This study demonstrates that cadmium and calcium uptakes are elevated in postmoult C. maenas. The results indicate that cadmium and calcium in this stage are taken up via Ca2+-channels located in the apical membrane of gill epithelium cells. When internalised, however, cadmium and calcium are metabolised in fundamentally different ways, determined by the chemical properties and biological significance of the two metals.

Cadmium in the shore crab Carcinus maenas: seasonal variation in cadmium content and uptake and elimination of cadmium after administration via food.

The uptake and assimilation efficiency of cadmium administered via the food in the shore crab Carcinus maenas were investigated together with elimination kinetics and seasonal variations in cadmium content. The majority of shore crabs assimilated between 41 and 86% of the cadmium administered in their food. More than 90% of the cadmium taken up from food was retained in midgut gland. Elimination of cadmium after uptake from one meal of radioactively labelled soft parts of blue mussels could be described by a three-compartment model (percent 109Cd-retained = 64 x e(-0.001107 x t) + 25 x e(-0.0385 x t)+11 x e(-0.888 x t)). The biological half-life for cadmium in the most slowly exchanging compartment (containing 64% of the body burden) was 626 days. Groups of male and female shore crabs were collected from an uncontaminated site in the period May till October and the concentrations of cadmium in midgut gland and gills were determined. Male crabs had higher cadmium concentrations in the midgut gland in June and August (mean 2.7 microg Cd g(-1) dry weight) than they had in May, September and October (mean 1.7 microg Cd g(-1) dry weight). Females generally had slightly lower cadmium concentrations in the midgut gland than the males, except for a relatively high concentration in May. The cadmium concentrations in gills generally ranged between 0.3 and 0.5 microg Cd g(-1) dry weight) except for male values in October (mean 1 microg Cd g(-1) dry weight). Some of the seasonal changes in cadmium content of the crabs might plausibly be explained by changes in cadmium uptake from water, i.e. changes during the moult cycle and changes in cadmium uptake rates from water brought about by changes in ambient factors such as salinity and temperature. However, uptake of cadmium from water and transfer to the midgut gland take place at a rate that is two orders of magnitude too low to account for the increase in the cadmium concentrations in midgut gland in male crabs between May and June. The distribution of cadmium among tissues in crabs collected at uncontaminated sites also corresponds better with results obtained after administration of cadmium via the food than via water, and the exposure of the crabs to cadmium via the food is large enough to explain the increase in concentration between May and June.

In vivo and in vitro cadmium accumulation during the moult cycle of the male shore crab Carcinus maenas--interaction with calcium metabolism.

The effect of moult stage on cadmium accumulation and distribution was investigated in vivo in male shore crabs Carcinus maenas exposed to 1 mg Cd l(-1) for 7 days. The accumulation of cadmium in all tissues examined was markedly higher in postmoult (A(1-2) and B(1-2)) compared to intermoult (C1, C3 and C4) and premoult (D(0-3)). In addition, elevated levels of cadmium were found in gills of late premoult (D(2-3)) animals. The total amount of cadmium accumulated in the tissues (haemolymph, gills, midgut gland and muscle) increased from 43 microg Cd in early premoult (D(0-1)) to 391 microg Cd in late postmoult (B(1-2)). Gills and midgut gland were the primary cadmium accumulating tissues in C4-intermoult and premoult (D(0-3)); in early postmoult (A(1-2)) haemolymph and midgut gland were the main cadmium containing tissues, while midgut gland dominated in late postmoult (B(1-2)) and early intermoult (C1 and C3). A detailed account of calcium distribution in haemolymph, gills, midgut gland, muscle and exoskeleton during the moult cycle is presented. Mechanistic links between cadmium and calcium uptake in posterior gills of C4-intermoult and early postmoult (A(1-2)) crabs were explored using an in vitro gill perfusion technique. Calcium and cadmium influxes were markedly higher in postmoult compared to intermoult. No differences between intermoult and postmoult effluxes were found for either calcium or cadmium. From intermoult to postmoult net influx increased from 2.4 to 29 micromol Ca2+ g(-1) ww(gill) h(-1) and from 0.24 to 25 nmol Cd2+ g(-1) ww(gill) h(-1). The results indicate that the postmoult increase in cadmium influx is due to increased active transport of cadmium, at least partly, by accidental uptake via calcium transporting proteins. The in vitro net influx rates corresponded accurately to the observed in vivo accumulation of both cadmium and calcium. Although cadmium accumulation and distribution are clearly linked to changes in calcium requirements, cadmium did not interfere with calcium accumulation or distribution at any stage during the moult cycle.

Effects of dietary calcium and cadmium on cadmium accumulation, calcium and cadmium uptake from the water, and their interactions in juvenile rainbow trout.

The objective of this study was to examine the effects of chronically elevated dietary Ca2+ (as CaCO3), alone and in combination with elevated dietary Cd, on survival, growth, and Cd and Ca2+ accumulation in several internal compartments in juvenile rainbow trout (Oncorhynchus mykiss). In addition, effects on short-term branchial uptake and internal distribution of newly accumulated waterborne Ca2+ and Cd during acute waterborne Cd exposure (50 microg/L as CdNO3 for 3 h) were monitored using radiotracers (45Ca, 65Cd). Fish were fed with four diets: 20 mg Ca2+/g food (control), 50 mg Ca2+/g food, 300 microg Cd/g food, and 50 mg Ca2+/g + 300 microg Cd/g food for 30 days. There were no significant effects on growth, mortality, or total body Ca2+ accumulation. The presence of elevated Ca2+, Cd, or Ca2+ + Cd in the diet all reduced waterborne Ca2+ uptake in a short-term experiment (3 h), though the inhibitory mechanisms appeared to differ. The effects were marked after 15 days of feeding, but attenuated by 30 days, except when the diet was elevated in both Ca2+ and Cd. The presence of elevated Ca2+ in the diet had only modest influence on Cd uptake from the water during acute Cd challenges but greatly depressed Cd uptake from the diet and accumulation in most internal tissues. None of the treatment diets prevented the decreases in waterborne Ca2+ uptake and new Ca2+ accumulation in internal tissues caused by acute exposure to waterborne Cd. In conclusion, there are complex interactions between waterborne and dietary effects of Ca2+ and Cd. Elevated dietary Ca2+ protects against both dietary and waterborne Cd uptake, whereas both waterborne and dietary Cd elevations cause reduced waterborne Ca2+ uptake.

Gastrointestinal uptake and fate of cadmium in rainbow trout acclimated to sublethal dietary cadmium.

Adult rainbow trout were pre-exposed to a sublethal concentration of dietary Cd (500 mg/kg dry wt.) for 30 days to induce acclimation. A gastrointestinal dose of radiolabeled Cd (276 microg/kg wet wt.) was infused into the stomach of non-acclimated and Cd-acclimated trout through a stomach catheter. Repetitive blood samples over 24 h and terminal tissue samples were taken to investigate the gastrointestinal uptake, plasma clearance kinetics, and tissue distribution of Cd. Only a small fraction of the infused dose (non-acclimated: 2.4%; Cd-acclimated: 6.6%) was internalized across the gut wall, while most was bound in the gut tissues (10-24%) or remained in the lumen (16-33%) or lost from the fish (approximately 50%) over 24 h. Cadmium loading during pre-exposure produced a profound increase of total Cd in the blood plasma (approximately 28-fold) and red blood cells (RBC; approximately 20-fold). The plasma Cd-time profiles consisted of an apparent rising (uptake) phase and a declining (clearance) phase with a maximum value of uptake in 4 h, suggesting that uptake of gastrointestinally infused Cd was very rapid. Acclimation to dietary Cd did not affect plasma Cd clearance (approximately 0.5 ml/min), but enhanced new Cd levels in the plasma (but not in the RBC), and resulted in a longer half-life for plasma Cd. Tissue total and new Cd levels varied in different regions of the gastrointestinal tract, and overall levels in gut tissues were much greater than in non-gut tissues, reflecting the Cd exposure route. Dietary Cd, but not the infused Cd, greatly increased total Cd levels of all gut tissues in the order posterior-intestine (640-fold) > cecae (180-fold) > mid-intestine (94-fold) > stomach (53-fold) in Cd-acclimated fish relative to naïve fish. Among non-gut tissues in the Cd-acclimated fish, the great increases of total Cd levels were observed in the liver (73-fold), kidney (39-fold), carcass (35-fold), and gills (30-fold). The results provide some clear conclusions that may be useful for environmental risk assessment of dietary Cd exposure in fish.

Possible involvement of plasma histidine in differential brain permeability to zinc and cadmium.

Zinc gets into the brain parenchyma across the blood-brain and the blood-cerebrospinal fluid barriers, while cadmium hardly gets into the brain parenchyma. Because histidine may be involved in zinc transport across the brain barrier systems, the binding to histidine was compared between zinc and cadmium to understand the difference in brain permeability to both metals. Sephadex G-10 gel filtration indicated that 109Cd, unlike 65Zn, does not bind to histidine. When the plasma incubated with 65Zn or 109Cd was dialyzed in physiological saline containing histidine (0-10 mM), 65Zn concentration in the dialysate was increased with the increase of the histidine concentration, suggesting the transfer of zinc from plasma proteins to histidine. The low affinity of zinc to plasma proteins may be important for brain permeability to this metal. On the other hand, 109Cd was not detected in the dialysate in the presence of 0.1 mM histidine, which is equal to the concentration in the plasma, suggesting no transfer of cadmium from plasma proteins to histidine. These results suggest that the avid binding of cadmium to plasma proteins is related to brain impermeability to this metal.

Accumulation of 109Cd by second-generation chironominae propagated from wild populations sampled from low-, mid-, and high-saline environments.

Our objective was to determine if second-generation (F2) chironomids propagated from adults of larvae sampled from low-, mid-, and high-saline environments differed in their ability to accumulate cadmium from their environment. Second-generation chironomids cultured from wild populations were exposed to 109Cd at 0, 0.7, and 4.3 ppt salinity for 10 days, at which time survival and amounts of 109Cd accumulated were determined. Cultures included two of Chironomus tentans from a freshwater lake (lake 78; 0 ppt), and the euryhaline C. athalassicus from a mid- (lake 71; 0.7 ppt) and high (lake 56; 4.3 ppt)-saline environment. A laboratory-reared culture of C. tentans was included as a positive control. Species-dependent accumulation of 109Cd occurred; second-generation C. athalassicus cultured from the high-salinity lake survived in the three salinities and accumulated significantly greater amounts of the radiotracer at 0 and 0.7 ppt compared to the second-generation freshwater species, C. tentans. Second-generation C. athalassicus cultured from lake 71 also survived all salinities with 109Cd accumulation tending to be greater than the freshwater species at the mid-salinity range. In contrast, the freshwater species cultured from lake 78 as well as the laboratory-reared culture did not survive the highest salinity of 4.3 ppt and accumulated less 109Cd compared to the species from the high-saline environments. Species-dependent differences in metal accumulation need to be considered in studies that assess metal concentrations in aquatic organisms across an environmental gradient, such as salinity.

Plant uptake of cadmium-109 and zinc-65 at different temperature and organic matter levels.

The uptake of 109Cd and 65Zn and their stable isotopes by ryegrass (Lolium multiflorum Lam.), grown on two different soil types, was investigated in climatically controlled growth chambers at 9 and 21 degrees C. The soils were treated with 0 and 4% organic matter (pig [Sus scrofa] manure) and spiked with 109Cd and 65Zn before sowing. The organic matter addition resulted in increased uptake of the 109Cd, Cd, and Zn by ryegrass, but the uptake of 65Zn was decreased. The latter effect was ascribed to isotopic dilution of 65Zn as the amount of stable Zn in the plant tissues increased with the organic matter addition. The effect of temperature was more pronounced than that of organic matter addition, and the uptake of both 109Cd and 65Zn and their stable isotopes was higher in ryegrass grown at 21 degrees C than that grown at 9 degrees C. Results from fractionation and speciation analysis of soil cadmium and zinc were correlated with plant uptake, and there was a good consistency between observed plant uptake and the physico-chemical forms of cadmium and zinc in soil and soil solution presumed to be plant available.

109Cd accumulation in the calcified parts of rat bones.

A recent epidemiological study showed an increased risk for bone fractures after chronic low-level cadmium exposure. This finding agrees with those of cadmium accumulation in rat bones after chronic oral exposure which reduced the mechanical strength of the bones. There are indications that ossicular cadmium uptake may be higher during growth and may contribute over proportion to life long cadmium accumulation in the skeleton. The present study investigates this hypothesis in 59 male Sprague-Dawley rats. 109Cd distribution showed no differences after intravenous (i.v.) administration of different doses (0.02-2.00 micromol 109Cd/kg body weight) and at different time points after injection (3 and 10 days). Iron-deficiency had no impact on 109Cd distribution, neither during growth nor in adult animals. Age, however, showed an impact on cadmium distribution. Hepatic 109Cd accumulation was significantly higher in adult rats while 109Cd distribution in the bones as well as 109Cd concentration in cortical and trabecular bone tissue was significantly higher during growth. No difference in 109Cd uptake was found between femur epiphysis and diaphysis after one-dose i.v. application, which is in contrast to earlier results after chronic oral cadmium administration to rats. This difference may be explained by a different saturation for cadmium uptake in these two bone sections. Cadmium exposure during growth, thus, seems to contribute considerably to cumulative ossicular cadmium accumulation over a lifetime and possibly to cadmium-derived bone fragility in advanced age.

109Cd transport in rat brain.

The brain distribution of 109CdCl2 following administration into either the tail vein, the lateral ventricle or the olfactory bulb was studied to clarify permeability of the brain barrier system to cadmium (Cd) and Cd movement in the cerebrospinal fluid (CSF) and the brain extracellular fluid. One hour after intravenous (i.v.) injection, 109Cd was largely concentrated in the choroid plexus, and 109Cd concentration in the major part of the brain parenchyma, except for the circumventricular organs such as the pineal gland and the regions around them, was low. Six days after i.v. injection, 109Cd concentration in the choroid plexus was still high, and 109Cd was also detected highly in the pineal gland and small part around the median eminence. 109Cd concentration in the major part of the brain parenchyma was decreased in parallel with that in the blood. In the case of injection of 109CdCl2 into the lateral ventricle, a large portion of 109Cd was detected in the ventricular system 6 days after injection, and 109Cd concentration in the major part of the brain parenchyma was less than the detection limit. These results suggest that Cd cannot easily get into the brain and is blocked not only by the blood- brain and the blood-CSF barriers, but also by the ependymal and pial surfaces. In the case of injection of 109CdCl2 into the olfactory bulb, a large portion of 109Cd was detected in the injected area 24 h after injection, and, the next 24 h later, 109Cd distribution in the brain was not changed appreciably. These results suggest that Cd cannot easily move in the brain extracelular space, and is taken up into the brain parenchyma.

Cadmium turnover in the hemocytes of Mercenaria mercenaria (L.) in relation to hemocyte turnover.

The turnover of cadmium (Cd) in the hemocytes of the quahog Mercenaria mercenaria L. was investigated using 109Cd radiolabeling, and compared to the rate of hemocyte turnover as estimated following [3H]thymidine incorporation. Quahogs were injected with 5 microl of 0.8 microM 109Cd, and the hemocytes sampled over a 60-day depuration period. Additional organisms were injected with 15 microl of 4.7 microM [3H]thymidine and radioactivity monitored over a 60-day period. Assuming that the loss of 3H from the hemocytes during the first 27 days of the experiment is due to hemocyte turnover, results indicate that Cd turnover rate (t 0.5 = 25.3 +/- 6.3 days) was similar to hemocyte turnover rate (t 0.5 = 28.5 +/- 14.3 days). This suggests that hemocytes retain Cd internally throughout their circulatory lifespan.

Uptake of 109Cd from natural sediments by the blue mussel Mytilus trossulus in relation to sediment nutritional and geochemical composition.

The objective of this study was to determine if trace metal bioavailability from suspended particulate matter (SPM) and recently deposited lake sediment (LS) to the filter-feeding bivalve Mytilus trossulus was dependent on the nutritional content and/or the geochemistry of the sediment. For SPM these characteristics are seasonally dependent; for LS they are dependent on lake chemistry and trophic status. To meet this objective, SPM was sampled from the Fraser River estuary, British Columbia, Canada, during Winter (March), spring (April, May), and summer (June, July) months. Deposited LS was sampled from an acidic dystrophic and a circumneutral, oligotrophic lake. Sediments were labeled with 109Cd, fed to M. trossulus and the amount of 109Cd accumulated over a 4-h feeding period assessed. Simultaneous extraction (separation of the sediment into easily reducible, reducible, and organic sediment components) of the radiolabeled sediments indicated that 109Cd associated with the inorganic, not the organic portion of sediment. The amount of 109Cd accumulated by the mussel over the 4-h feeding period was dependent on sediment %carbon (%C) and %nitrogen (%N) content (R2 = 0.75 and 0.52, respectively, for SPM and R2 = 0.76 and 0.64 for LS, respectively), and not on sediment concentrations of easily reducible manganese or reducible iron. These findings suggest that mussels obtain 109Cd from the inorganic portion of sediment as a consequence of digestive processes that are selecting for the carbon and nitrogen component of sediment. Hence, accumulation of cadmium from sediment will be dependent on sediment %C, and to a lesser extent %N content; however, amounts that the organism will be exposed to will depend on concentrations present on the inorganic component. Predictive models of metal accumulation by filter-feeding organisms need to consider the role of both sediment components for predicting amounts of metal that the organisms will bioaccumulate.