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S. N. Luoma

Publications and source records attributed to S. N. Luoma.

At least 37 records · Page 2Linked to original sources
USGS2007

Biological uptake of polychlorinated biphenyls by Macoma balthica from sediment amended with activated carbon

This work characterizes the efficacy of activated carbon amendment in reducing polychlorinated biphenyl (PCB) bioavailability to clams ( Macoma balthica ) from field-contaminated sediment (Hunters Point Naval Shipyard, San Francisco Bay, CA, USA). Test methods were developed for the use of clams to investigate the effects of sediment amendment on biological uptake. Sediment was mixed with activated carbon for one month. Bioaccumulation tests (28 d) were employed to assess the relationships between carbon dose and carbon particle size on observed reductions in clam biological uptake of PCBs. Extraction and cleanup protocols were developed for the clam tissue. Efficacy of activated carbon treatment was found to increase with both increasing carbon dose and decreasing carbon particle size. Average reductions in bioaccumulation of 22, 64, and 84% relative to untreated Hunters Point sediment were observed for carbon amendments of 0.34, 1.7, and 3.4%, respectively. Average bioaccumulation reductions of 41, 73, and 89% were observed for amendments (dose = 1.7% dry wt) with carbon particles of 180 to 250, 75 to 180, and 25 to 75 μm, respectively, in diameter, indicating kinetic phenomena in these tests. Additionally, a biodynamic model quantifying clam PCB uptake from water and sediment as well as loss through elimination provided a good fit of experimental data. Model predictions suggest that the sediment ingestion route contributed 80 to 95% of the PCB burdens in the clams.

Environmental Toxicology and Chemistry↗
USGS2006

Comparison of selenium bioaccumulation in the clams Corbicula fluminea and Potamocorbula amurensis: A bioenergetic modeling approach

Selenium uptake from food (assimilation efficiency) and dissolved phase (influx rate) as well as loss kinetics (efflux rate) were compared between two bivalves, Corbicula fluminea and Potamocorbula amurensis. The effects of salinity and temperature on these kinetic parameters for both clam species also were evaluated. The Asiatic clam, C. fluminea, more efficiently assimilated Se associated with algae (66-87%) than Se associated with oxic sediments (20-37%). However, no consistent difference was found between Se assimilation efficiencies from both food types (19-60%) for P. amurensis. The temperature and salinity had a minor influence on the Se assimilation from ingested food. However, the effects of temperature and salinity were more evident in the uptake from dissolved sources. The influx rate of Se(IV) increased by threefold with the increase of temperature from 5 to 21??C for C. fluminea. The increase of salinity from 4 to 20 psu decreased the uptake rate constant (ku) of Se in P. amurensis from 0.011 to 0.005 L/g/h, whereas salinity change (0-8 psu) had a negligible effect on the Se influx rate of C. fluminea. The Se influx rate of P. amurensis decreased by half with the 3.5-fold increase in tissue dry weight. The rate constant of loss was greater for P. amurensis (0.029/d at 8 psu) than for C. fluminea (0.014/d at 0 psu and 0.01/d at 8 psu). A bioenergetic model suggests that dietary uptake is the dominant pathway for Se bioaccumulation in the two clams in San Francisco Bay and that interspecies differences in Se bioaccumulation can be explained by differences in food ingestion rates. ?? 2006 SETAC.

Environmental Toxicology and Chemistry↗
USGS2006

Influence of metal exposure history on the bioaccumulation and subcellular distribution of aqueous cadmium in the insect Hydropsyche californica

The influence of metal exposure history on rates of aqueous Cd accumulation, elimination, and subcellular distribution was examined in the aquatic insect Hydropsyche californica . Specimens were obtained from a reference site and a metal‐contaminated site and returned to the laboratory where they were continuously exposed to aqueous Cd (518 ng/L, nominal) for 6 d, followed by 9 d of depuration. Rates of Cd accumulation and elimination were similar in insects from the two sites. Efflux rate constants, k e , ranged from 0.20 to 0.24/d ( t 1/2 ≈ 3 d). Immediately following exposure, the cytosol accounted for 40% of the body burden in insects from both sites; however, 89 ± 2% of the cytosolic Cd was associated with metallothionein‐like proteins (MTLP) in insects from the contaminated site, compared to 60 ± 0% in insects from the reference site. The concentration of Cd bound to non‐MTLPs (representing potentially Cd‐sensitive proteins) was significantly greater in the insects from the reference site (134 ± 7 ng/g) than in those from the contaminated site (42 ± 2 ng/g). At the end of the depuration period, 90% of the accumulated Cd body burden had been eliminated, and Cd concentrations in MTLPs and non‐MTLPs were similar between the sites. Results suggested that differences in exposure history had no influence on the bioaccumulation of Cd, but did affect the concentrations of Cd bound to MTLP during Cd exposure in these insects.

Environmental Toxicology and Chemistry↗
USGS2006

Trophic transfer of trace metals: Subcellular compartmentalization in a polychaete and assimilation by a decapod crustacean

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

Marine Ecology Progress Series↗
USGS2006

Trophic transfer of trace metals from the polychaete worm Nereis diversicolor to the polychaete N. virens and the decapod crustacean Palaemonetes varians

Diet is an important exposure route for the uptake of trace metals by aquatic invertebrates, with trace metal trophic transfer depending on 2 stages - assimilation and subsequent accumulation by the predator. This study investigated the trophic transfer of trace metals from the sediment-dwelling polychaete worm Nereis diversicolor from metal-rich estuarine sediments in southwestern UK to 2 predators - another polychaete N. virens (Cu, Zn, Pb, Cd, Fe) and the decapod crustacean Palaemonetes varians (Cu, Zn, Pb, Cd, Fe, Ag, As, Mn). N. virens showed net accumulation of Cu, Zn, Pb and Cd from the prey; accumulation increased with increasing prey concentration, but a coefficient of trophic transfer decreased with increasing prey concentration, probably because a higher proportion of accumulated metal in the prey is bound in less trophically available (insoluble) detoxified forms. The trace metal accumulation patterns of P. varians apparently restricted significant net accumulation of metals from the diet of N. diversicolor to just Cd. There was significant mortality of the decapods fed on the diets of metal-rich worms. Metal-rich invertebrates that have accumulated metals from the rich historical store in the sediments of particular SW England estuaries can potentially pass these metals along food chains, with accumulation and total food chain transfer depending on the metal assimilation efficiencies and accumulation patterns of the animal at each trophic level. This trophic transfer may be significant enough to have ecotoxicological effects. ?? Inter-Research 2006.

Marine Ecology Progress Series↗
USGS2005

Trophic transfer of metals along freshwater food webs: Evidence of cadmium biomagnification in nature

We conducted a study with cadmium (Cd) and copper (Cu) in the delta of San Francisco Bay, using nitrogen and carbon stable isotopes to identify trophic position and food web structure. Cadmium is progressively enriched among trophic levels in discrete epiphyte‐based food webs composed of macrophyte‐dwelling invertebrates (the first link being epiphytic algae) and fishes (the first link being gobies). Cadmium concentrations were biomagnified 15 times within the scope of two trophic links in both food webs. Trophic enrichment in invertebrates was twice that of fishes. No tendency toward trophic‐level enrichment was observed for Cu, regardless of whether organisms were sorted by food web or treated on a taxonomic basis within discrete food webs. The greatest toxic effects of Cd are likely to occur with increasing trophic positions, where animals are ingesting Cd‐rich prey (or food). In Franks Tract this occurs within discrete food chains composed of macrophyte‐dwelling invertebrates or fishes inhabiting submerged aquatic vegetation. Unraveling ecosystem complexity is necessary before species most exposed and at risk can be identified.

Limnology and Oceanography↗
USGS2005

Delineating copper accumulation pathways for the freshwater bivalve Corbicula using stable copper isotopes

Delineation of metal uptake routes in aquatic invertebrates is critical for characterizing bioaccumulation dynamics and assessing risks associated with metal exposure. Here we demonstrate that Cu stable isotopic ratios can be manipulated in both exposure media and algae to determine the efflux rate constant ( k e ) and to estimate Cu assimilation efficiency (AE) from ingested food in a freshwater bivalve ( Corbicula fluminea ). The Cu AE in Corbicula fed 65 Cu‐spiked Cryptomonas ozolini was 38%. Copper uptake routes had no significant influence on efflux; k e of 0.004 per day characterized the slowest component of efflux following short‐term exposures to 65 Cu in water or in both food and water. Incorporation of the physiological parameters for dietary and dissolved uptake as well as rate constants of loss into a bioaccumulation model allowed for assessing the relative contribution of water and food as Cu sources. At [ 65 Cu 2+ ] of 6.7 μg/L, Corbicula accumulated twice as much Cu from diet as from water. In most freshwater systems, the dietary pathway is likely to act as the major Cu uptake route for Corbicula . Extrapolation of our laboratory results to the San Francisco Bay—Delta (California, USA) indicated that our biodynamic model and the laboratory‐derived parameters for dietary 65 Cu uptake provided a realistic representation of the processes involved in Cu accumulation by the bivalve Corbicula .

Environmental Toxicology and Chemistry↗
USGS2004

Modeling selenium bioaccumulation through arthropod food webs in San Francisco Bay, California, USA

Trophic transfer is the main process by which upper trophic level wildlife are exposed to selenium. Transfers through lower levels of a predator's food web thus can be instrumental in determining the threat of selenium in an ecosystem. Little is known about Se transfer through pelagic, zooplankton‐based food webs in San Francisco Bay ([SFB], CA, USA), which serve as an energy source for important predators such as striped bass. A dynamic multipathway bioaccumulation model was used to model Se transfer from phytoplankton to pelagic copepods to carnivorous mysids ( Neomysis mercedis ). Uptake rates of dissolved Se, depuration rates, and assimilation efficiencies (AE) for the model were determined for copepods and mysids in the laboratory. Small (73‐250 μm) and large (250‐500 μm) herbivorous zooplankton collected from SFB ( Oithona/Limnoithona and Acartia sp.) assimilated Se with similar efficiencies (41‐52%) from phytoplankton. Mysids assimilated 73% of Se from small herbivorous zooplankton; Se AE was significantly lower (61%) than larger herbivorous zooplankton. Selenium depuration rates were high for both zooplankton and mysids (12‐25% d −1 ), especially compared to bivalves (2‐3% d −1 ). The model predicted steady state Se concentrations in mysids similar to those observed in the field. The predicted concentration range (1.5‐5.4 μg g −1 ) was lower than concentrations of 4.5 to 24 μg g −1 observed in bivalves from the bay. Differences in efflux between mysids and bivalves were the best explanation for the differences in uptake. The results suggest that the risk of selenium toxicity to predators feeding on N. mercedis would be less than the risk to predators feeding on bivalves. Management of selenium contamination should include food webs analyses to focus on the most important exposure pathways identified for a given watershed.

California↗
USGS2004

Differences in dissolved cadmium and zinc uptake among stream insects: Mechanistic explanations

This study examined the extent to which dissolved Cd and Zn uptake rates vary in several aquatic insect taxa commonly used as indicators of ecological health. We further attempted to explain the mechanisms underlying observed differences. By comparing dissolved Cd and Zn uptake rates in several aquatic insect species, we demonstrated that species vary widely in these processes. Dissolved uptake rates were not related to gross morphological features such as body size or gill size-features that influence water permeability and therefore have ionoregulatory importance. However, finer morphological features, specifically, the relative numbers of ionoregulatory cells (chloride cells), appeared to be related to dissolved metal uptake rates. This observation was supported by Michaelis-Menten type kinetics experiments, which showed that dissolved Cd uptake rates were driven by the numbers of Cd transporters and not by the affinities of those transporters to Cd. Calcium concentrations in exposure media similarly affected Cd and Zn uptake rates in the caddisfly Hydropsyche californica. Dissolved Cd and Zn uptake rates strongly co-varied among species, suggesting that these metals are transported by similar mechanisms.

Environmental Science & Technology↗
USGS2004

Stable metal isotopes reveal copper accumulation and loss dynamics in the freshwater bivalve Corbucula

Characterization of uptake and loss dynamics is critical to understanding risks associated with contaminant exposure in aquatic animals. Dynamics are especially important in addressing questions such as why coexisting species in nature accumulate different levels of a contaminant. Here we manipulated copper (Cu) stable isotopic ratios (as an alternative to radioisotopes) to describe for the first time Cu dynamics in a freshwater invertebrate, the bivalve Corbicula fluminea . In the laboratory, Corbicula uptake and loss rate constants were determined from an environmentally realistic waterborne exposure to 65 Cu (5.7 μg L - 1 ). That is, we spiked deionized water with Cu that was 99.4% 65 Cu. Net tracer uptake was detectable after 1 day and strongly evident after 4 days. Thus, short-term exposures necessary to determine uptake dynamics are feasible with stable isotopes of Cu. In Corbicula , 65 Cu depuration was biphasic. An unusually low rate constant of loss (0.0038 d - 1 ) characterized the slow component of efflux, explaining why Corbicula strongly accumulates copper in nature. We incorporated our estimates of rate constants for dissolved 65 Cu uptake and physiological efflux into a bioaccumulation model and showed that dietary exposure to Cu is likely an important bioaccumulation pathway for Corbicula .

Environmental Science & Technology↗
USGS2004

Food web pathway determines how selenium affects aquatic ecosystems: A San francisco Bay case study

Chemical contaminants disrupt ecosystems, but specific effects may be under-appreciated when poorly known processes such as uptake mechanisms, uptake via diet, food preferences, and food web dynamics are influential. Here we show that a combination of food web structure and the physiology of trace element accumulation explain why some species in San Francisco Bay are threatened by a relatively low level of selenium contamination and some are not. Bivalves and crustacean zooplankton form the base of two dominant food webs in estuaries. The dominant bivalve Potamocorbula amurensis has a 10-fold slower rate constant of loss for selenium than do common crustaceans such as copepods and the mysid Neomysis mercedis (rate constant of loss, k e = 0.025, 0.155, and 0.25 d -1 , respectively). The result is much higher selenium concentrations in the bivalve than in the crustaceans. Stable isotope analyses show that this difference is propagated up the respective food webs in San Francisco Bay. Several predators of bivalves have tissue concentrations of selenium that exceed thresholds thought to be associated with teratogenesis or reproductive failure (liver Se >15 μg g - 1 dry weight). Deformities typical of selenium-induced teratogenesis were observed in one of these species. Concentrations of selenium in tissues of predators of zooplankton are less than the thresholds. Basic physiological and ecological processes can drive wide differences in exposure and effects among species, but such processes are rarely considered in traditional evaluations of contaminant impacts.

California↗
USGS2004

Importance of equilibration time in the partitioning and toxicity of zinc in spiked sediment bioassays

The influences of spiked Zn concentrations (1–40 μmol/g) and equilibration time (˜ 95 d) on the partitioning of Zn between pore water (PW) and sediment were evaluated with estuarine sediments containing two levels (5 and 15 μmol/g) of acid volatile sulfides (AVS). Their influence on Zn bioavailability was also evaluated by a parallel, 10‐d amphipod ( Leptocheirus plumulosus ) mortality test at 5, 20, and 85 d of equilibration. During the equilibration, AVS increased (up to twofold) with spiked Zn concentration ([Zn]), whereas Zn‐simultaneously extracted metals ([SEM]; Zn with AVS) remained relatively constant. Concentrations of Zn in PW decreased most rapidly during the initial 30 d and by 11‐ to 23‐fold during the whole 95‐d equilibration period. The apparent partitioning coefficient ( K pw , ratio of [Zn] in SEM to PW) increased by 10‐ to 20‐fold with time and decreased with spiked [Zn] in sediments. The decrease of PW [Zn] could be explained by a combination of changes in AVS and redistribution of Zn into more insoluble phases as the sediment aged. Amphipod mortality decreased significantly with the equilibration time, consistent with decrease in dissolved [Zn]. The median lethal concentration (LC50) value (33 μM) in the second bioassay, conducted after 20 d of equilibration, was twofold the LC50 in the initial bioassay at 5 d of equilibration, probably because of the change of dissolved Zn speciation. Sediment bioassay protocols employing a short equilibration time and high spiked metal concentrations could accentuate partitioning of metals to the dissolved phase and shift the pathway for metal exposure toward the dissolved phase.

Environmental Toxicology and Chemistry↗
USGS2004

Uptake pathway for Ag bioaccumulation in three benthic invertebrates exposed to contaminated sediments

We exposed 3 benthic invertebrates, the clam Macoma balthica , the polychaete Neanthes arenaceodentata and the amphipod Leptocheirus plumulosus , to Ag-contaminated sediments to evaluate the relative importance of various uptake routes (sediments, porewater or overlying water, and supplementary food) for Ag bioaccumulation. Silver bioaccumulation was evaluated at 4 levels of sediment Ag (0.1, 0,3, 1,2 and 3.3 µmol Ag g -1 ) and 2 levels of acid-volatile sulfide (AVS), <0.5 or ~40 µmol g -1 , and compared among food treatments with or without Ag contamination, or with different food rations. L. plumulosus were incubated for 35 d in the Ag-contaminated sediments after 3 mo of Ag-sediment equilibration, and M. balthica and N. arenaceodentata for 19 d after 5 mo equilibration. Ag bioaccumulation in the 3 organisms was significantly correlated with 1N HCl-extractable Ag concentrations (Ag-SEM: simultaneously extracted Ag with AVS) in sediments. The Ag concentrations in porewater and overlying water were greatest in the sediments with least AVS, consistent with previous studies. Nevertheless, the amphipod and clam exposed to oxic sediments (<0.5 µmol AVS g -1 ) accumulated amounts of Ag similar to those accumulated by organisms exposed to anoxic sediments (~40 µmol AVS g -1 ), when Ag-SEM levels were comparable. The dissolved Ag source was important for bioaccumulation in the polychaete N. arenaceodentata . Amphipods fed Ag-contaminated food contained ~1.8-fold more tissue Ag concentrations than those fed uncontaminated food. As suggested in kinetic (DYMBAM) modeling studies, ingestion of contaminated sediments and food were the principle routes of Ag bioaccumulation by the benthic invertebrates during chronic exposure, but the relative importance of each uptake route differed among species.

Marine Ecology Progress Series↗
USGS2003

Metal uptake by phytoplankton during a bloom in South San Francisco Bay: Implications for metal cycling in estuaries

The 1994 spring phytoplankton bloom in South San Francisco Bay caused substantial reductions in concentrations of dissolved Cd, Ni, and Zn, but not Cu. We estimate that the equivalent of ~60% of the total annual input of Cd, Ni, and Zn from local waste‐water treatment plants is cycled through the phytoplankton in South Bay. The results suggest that processes that affect phytoplankton bloom frequency or intensity in estuaries (e.g. nutrient enrichment) may also affect metal trapping. The bloom was characterized by hydrographic surveys conducted at weekly intervals for 9 weeks. Metal samples were collected from the water column on three occasions, timed to bracket the period when the bloom was predicted. Factors that might confound observations of biological influences, such as freshwater inputs, were relatively constant during the study. Before the bloom, concentrations of dissolved Cd were 0.81 ± 0.02 nmol kg −1 , Zn concentrations were 19.8 ± 1.5 nmol kg −1 , Ni were 42 ± 1.4 nmol kg −1 , and Cu were 37 ± 1.4 nmol kg −1 . These values are elevated relative to riverine and coastal end‐members, reflecting inputs from wastewater and(or) sediments. At the height of the bloom, dissolved Zn, Cd, and Ni were reduced to 19, 50, and 75% of their prebloom concentrations, respectively. Dissolved Cu concentrations increased 20%. The mass of Cd taken up by phytoplankton was similar to the mass of Cd removed from solution if particle settling was considered, and Cd concentrations estimated in phytoplankton were higher than concentrations in suspended particulate material (SPM). Particulate concentrations of Zn and Ni during the bloom appeared to be dominated by the influence of changes in resuspension of Zn and Ni‐rich sediments.

California↗
USGS2003

Influence of microalgal biomass on absorption efficiency of Cd, Cr, and Zn by two bivalves from San Francisco Bay

The bioavailability to clams (Potamocorbula amurensis and Macoma balthica) of Cd, Cr, and Zn from suspended particulate material (SPM) collected during a phytoplankton bloom was compared to bioavailability from SPM dominated by resuspended sediments. Bioavailability was also compared among mudflat sediments amended with different levels of living benthic microalgae. Bioavailability was defined by absorption efficiencies determined using pulse-chase protocols, modified for studying natural particle assemblages. The partitioning of Cd and Zn to particles (K(d)) increased as the microalgae biomass (Chl a) increased in the particle assemblages; partitioning of Cr was less affected by the algal biomass. The clams fed particle assemblages enriched with microalgae absorbed Cd and Zn with significantly greater efficiency than did the clams fed algae-poor particles. This was partially explained by the greater occurrence of Cd and Zn in the cytosolic fraction of the particle assemblages that were microalgae enriched, as well as by the efficient absorption of cytosolic material by the clams. Among metals, Zn was most efficiently absorbed by both clams, and Cr the least. M. balthica absorbed Zn more efficiently from all types of food particles (39-82%) than did P. amurensis (13-50%). P. amurensis absorbed Cd with greater efficiency from the bloom SPM (44-48%) than did M. balthica (13-21%), but the two clams absorbed Cd similarly from benthic microalgae (26-51%). The addition of microalgae to complex natural particle assemblages clearly affected the bioavailability of associated metals, so studies using sediments (or suspended particulate material) that do not include a realistic living food component could underestimate metal bioavailability from particle ingestion.

Limnology and Oceanography↗
USGS2003

Selenium in San Francisco Bay zooplankton: Potential effects of hydrodynamics and food web interactions

The potential toxicity of elevated selenium (Se) concentrations in aquatic ecosystems has stimulated efforts to measure Se concentrations in benthos, nekton, and waterfowl in San Francisco Bay (SF Bay). In September 1998, we initiated a 14 mo field study to determine the concentration of Se in SF Bay zooplankton, which play a major role in the Bay food web, but which have not previously been studied with respect to Se. Monthly vertical plankton tows were collected at several stations throughout SF Bay, and zooplankton were separated into two operationally defined size classes for Se analyses: 73-2,000 ??m, and ???2,000 ??m. Selenium values ranged 1.02-6.07 ??g Se g-1 dry weight. No spatial differences in zooplankton Se concentrations were found. However, there were inter- and intra-annual differences. Zooplankton Se concentrations were enriched in the North Bay in Fall 1999 when compared to other seasons and locations within and outside SF Bay. The abundance and biovolume of the zooplankton community varied spatially between stations, but not seasonally within each station. Smaller herbivorous-omnivorous zooplankton had higher Se concentrations than larger omnivorous-carnivorous zooplankton. Selenium concentrations in zooplankton were negatively correlated with the proportion of total copepod biovolume comprising the large carnivorous copepod Tortanus dextrilobatus, but positively correlated with the proportion of copepod biovolume comprising smaller copepods of the family Oithonidae, suggesting an important role of trophic level and size in regulating zooplankton Se concentrations.

Estuaries↗
USGS2003

Subcellular compartmentalization of Cd and Zn in two bivalves. I. Significance of metal-sensitive fractions (MSF) and biologically detoxified metal (BDM)

Many aspects of metal accumulation in aquatic invertebrates (i.e. toxicity, tolerance and trophic transfer) can be understood by examining the subcellular partitioning of accumulated metal. In this paper, we use a compartmentalization approach to interpret the significance of metal, species and size dependence in the subcellular partitioning of Cd and Zn in the bivalves Macoma balthica and Potamocorbula amurensis . Of special interest is the compartmentalization of metal as metal-sensitive fractions (MSF) (i.e. organelles and heat-sensitive proteins, termed Œenzymes¹ hereafter) and biologically detoxified metal (BDM) (i.e. metallothioneins [MT] and metal-rich granules [MRG]). Clams from San Francisco Bay, CA, were exposed for 14 d to seawater (20” salinity) containing 3.5 µg l -1 Cd and 20.5 µg l -1 Zn, including 109 Cd and 65 Zn as radiotracers. Uptake was followed by 21 d of depuration. The subcellular partitioning of metal within clams was examined following exposure and loss. P. amurensis accumulated ~22x more Cd and ~2x more Zn than M. balthica . MT played an important role in the storage of Cd in P. amurensis , while organelles were the major site of Zn accumulation. In M. balthica , Cd and Zn partitioned similarly, although the pathway of detoxification was metal-specific (MRG for Cd; MRG and MT for Zn). Upon loss, M. balthica depurated ~40% of Cd with Zn being retained; P. amurensis retained Cd and depurated Zn (~40%). During efflux, Cd and Zn concentrations in the MSF compartment of both clams declined with metal either being lost from the animal or being transferred to the BDM compartment. Subcellular compartmentalization was also size-dependent, with the importance of BDM increasing with clam size; MSF decreased accordingly. We hypothesized that progressive retention of metal as BDM (i.e. MRG) with age may lead to size dependency of metal concentrations often observed in some populations of M. balthica .

Marine Ecology Progress Series↗