Bioavailability of sediment-bound metals to marine bivalve molluscs: An overview

Performance of mussel Mytilus galloprovincialis under variable environmental conditions and anthropogenic pressure: A survey of two distinct farming sites in the Adriatic Sea

Changes in natural conditions and anthropogenic pollutants, alone or in combination, pose a significant challenge to coastal bivalve populations. The susceptibility of economically important bivalves to potential stressors in their farming environment has not been sufficiently investigated, despite the increase in anthropogenic pressure along the coast and the remarkable warming of seawater in recent years. Thus, the aim of this study was to evaluate the performance of mussel (Mytilus galloprovincialis) from two important farming sites in the eastern Adriatic, namely Mali Ston Bay (MSB) and Lim Bay (LB), in relation to variations of seawater parameters, reproductive cycle dynamics and tissue content of potentially harmful pollutants. The complex seasonal and site-specific patterns of chemical pollutants were determined, with tissue levels of metals, As, PAHs and PCBs largely comparable to those previously reported for the Mediterranean region. Concentrations of organochlorinated pesticides were below the level of detection. Significantly higher Cd, As and Hg concentrations were detected in the tissues of the MSB mussels. The reproductive cycle was clearly associated with the bioaccumulation of pollutants. All biochemical response parameters varied to some extent across seasons and/or between farming sites. A very pronounced seasonality was recorded for acetylcholinesterase and glutathione S-transferase activity at both sites. Metallothionein concentration and superoxide dismutase activity were generally steady throughout the study period. The most striking difference between the two sites was recorded for lipid peroxides concentrations which were predominantly significantly higher in the MSB mussels, indicating expressed pro-oxidant conditions at this site. In particular, significant correlations were found between lipid peroxides and the potentially toxic metals (Cd, As, Hg) accumulated in the mussel tissue. Data reported here are valuable as baseline information for further studies related to stress in farmed bivalves caused by oscillations of environmental factors and increasing anthropogenic pressure along the coastline.

Quantitative determination of heavy metal contaminants in edible soft tissue of clams, mussels, and oysters

Aquatic environments are important sources of healthy and nutritious foods; however, clams, mussels, and oysters (the bivalves most consumed by humans) can pose considerable health risks to consumers if contaminated by heavy metals in polluted areas. These organisms can accumulate dangerously high concentrations of heavy metals (e.g., Cd, Hg, Pb) in their soft tissues that can then be transferred to humans following ingestion. Monitoring contaminants in clams, mussels and oysters and their environments is critically important for global human health and food security, which requires reliable measurement of heavy-metal concentrations in the soft tissues. The aim of our present paper is to provide a review of how heavy metals are quantified in clams, mussels, and oysters. We do this by evaluating sample-preparation methods (i.e., tissue digestion / extraction and analyte preconcentration) and instrumental techniques (i.e., atomic, fluorescence and mass spectrometric methods, chromatography, neutron activation analysis and electrochemical sensors) that have been applied for this purpose to date. Application of these methods, their advantages, limitations, challenges and expected future directions are discussed.

The distribution of metal and petroleum-derived contaminants within sediments around oil and gas infrastructure in the Gippsland Basin, Australia

As oil and gas infrastructure comes to the end of its working life, a decommissioning decision must be made: should the infrastructure be abandoned in situ, repurposed, partially removed, or fully removed? Environmental contaminants around oil and gas infrastructure could influence these decisions because contaminants in sediments could degrade the value of the infrastructure as habitat, enter the seafood supply if the area is re-opened for commercial and/or recreational fishing, or be made biologically available as sediment is resuspended when the structures are moved. An initial risk hypothesis, however, may postulate that these concerns are only relevant if contaminant concentrations are above screening values that predict the possibility of environmental harm or contaminant bioaccumulation. To determine whether a substantive contaminants-based risk assessment is needed for infrastructure in the Gippsland Basin (South-eastern Australia), we measured the concentration of metals and polycyclic aromatic hydrocarbons (PAHs) in benthic sediments collected around eight platforms earmarked for decommissioning. The measurements were compared to preset screening values and to background contaminant concentrations in reference sites. Lead (Pb), zinc (Zn), PAHs and other contaminants were occasionally measured at concentrations that exceeded reference values, most often within 150 m of the platforms. The exceedance of a few screening values by contaminants at some platforms indicates that these platforms require further analysis to determine the contaminant risks associated with any decommissioning option.

Evidences of metabolic alterations and cellular damage in different tissues of scallops Aequipecten tehuelchus exposed to cadmium

Scallops Aequipecten tehuelchus (Patagonia, Argentina) were exposed to 0, 2, 5 and 12 μg Cd/L for 7 and 14 days, causing in digestive gland a significant production of reactive oxygen and nitrogen species (RONS), induction of catalase (CAT) and glutathione S-transferase (GST) activities and metallothioneins (MT) synthesis. In gills, there was inhibition of GST and induction of CAT, MT and α-tocopherol (α-Toc). In muscle, a significant increment of MT was also registered and inhibition of CAT. Lipid peroxidation, measured as TBARS, was not promoted in any tissue. More significant effects were observed in digestive gland than in gills and muscle, evidencing the critical role of digestive gland in Cd accumulation and metabolisation. This research would evidence dose-dependent effects of Cd on MT, GST, CAT and α-Toc in the three organs assayed, as well as a time-dependent effect of Cd on the response of CAT, GST and TBARS in digestive gland.

Copper and lead isotope records from an electroplating activity in sediments and biota from Sepetiba Bay (southeastern Brazil)

An old electroplating plant in Sepetiba Bay discharged metal-enriched wastes into the surrounding mangroves for 30 years (from the 1960s to 1990s), resulting in a hotspot zone of legacy sediments highly concentrated in toxic trace metals. This study applies Cu and Pb isotope systems to investigate the contributions of past punctual sources relative to emerging modern diffuse sources. The electroplating activity imprinted particular isotopic signatures (average δ⁶⁵Cu_SRM-976: 0.4 ‰ and ²⁰⁶Pb/²⁰⁷Pb: 1.14) distinct from the natural baseline and urban fluvial sediments. The isotopic compositions of tidal flat sediments show intermediate isotope compositions reflecting the mixing of Cu and Pb from the hotspot zone and terrigenous materials carried by rivers. Oyster isotope fingerprints match legacy sediments, attesting that anthropogenic Cu and Pb are bioavailable to the biota. These findings confirm the interest in combining two or more metal isotope systems to discriminate between modern and past metal source emissions in coastal environments.

Bioaccumulation, release and genotoxicity of stainless steel particles in marine bivalve molluscs

During the decommissioning and removal of radioactive material in nuclear facilities, fine, tritiated dusts of stainless steel, cement or tungsten are generated that could be accidently released to the environment. However, the potential radio- and ecotoxicological effects these tritiated particles may have are unknown. In this study, stainless steel particles (SSPs) representative of those likely to be tritiated are manufactured by hydrogenation and their tissue-specific bioaccumulation, release (depuration) and subsequent genotoxic response have been studied in the marine mussel, Mytilus galloprovincialis, as a baseline for future assessments of the potential effects of tritiated SSPs. Exposure to 1000 μg L^-1 of SSPs and adopting Cr as a proxy for stainless steel revealed relatively rapid accumulation (∼5 h) in the various mussel tissues but mostly in the digestive gland. Over longer periods up to 18 days, SSPs were readily rejected and egested as faecal material. DNA strand breaks, as a measure of genotoxicity, were determined at each time point in mussel haemocytes using single cell gel electrophoresis, or the comet assay. Lack of chemical genotoxicity was attributed to the rapid processing of SSP particles and limited dissolution of elemental components of steel. Further work employing tritiated SSPs will enable radio-toxicology to be studied without the confounding effects of chemical toxicity.

Essential and Non-Essential Elements in Razor Clams (Solen marginatus, Pulteney, 1799) from the Domitio Littoral in Campania (Southwestern Tyrrhenian Sea, Italy)

The levels of essential (Cu, Cr, Co, Mn, Se, Zn) and non-essential (As, Be, Bi, Cd, Cs, Ga, Ni, Pb, Sr, Tl, U, V) trace elements were studied in razor clams (Solen marginatus) collected from the Tyrrhenian coast of Southern Italy at five selected sites along the Domitio littoral in the Campania region. The main objectives of this study were to assess the contamination status of these bivalve mollusks and to evaluate the risks to the environment and consumers due to metal contamination. The concentrations of 18 trace elements were determined after microwave-assisted mineralization and by inductively coupled plasma mass spectrometry (ICP-MS). Concentrations of the toxic elements Pb and Cd were below the maximum levels established by Commission Regulation (EC) 1881/2006, while higher average concentrations of arsenic were found at each of the five sites studied. Regarding the other trace elements, contamination levels followed the order: Zn > Sr > Mn > Cu > Se > Cr > V > Ni > Co > Ga > Cs > Be > U > Bi > Tl. No significant differences among the sites were found with regard to any of the trace elements analyzed, and element levels in razor clams did not reflect sediment contamination. The results demonstrated the substantial food safety of the razor clams in this area with respect to heavy metals but revealed a potential health risk due to arsenic contamination in all the areas sampled.

Benthic food web structures as an explanation for prolonged ecological half-life of 137Cs in flatfish species in the Fukushima coastal area

After the accident at the Fukushima Daiichi Nuclear Power Plant (FDNPP), Japan, in March 2011, ¹³⁷Cs in demersal fish had, between 2011 and 2015, a prolonged ecological half-life when compared to pelagic fish. Using stable isotope mixing models combined with gut content analysis and ¹³⁷Cs activity concentrations, this study investigated the hypothesis that an unexplored food web structure could be a contributing factor explaining the ecological half-life of ¹³⁷Cs in benthic flatfish. Benthic invertebrates and demersal fish species sampled in 2015 still showed ¹³⁷Cs activity concentrations higher than pre-accident. The mixing models of stable N and C isotopes and gut content analysis identified deposit, suspension and filter feeders to be the main flatfish food items in the benthos. There was a significant correlation between ¹³⁷Cs activity concentrations in specific flatfish species and benthos, and between ¹³⁷Cs activity concentrations in benthos and surface sediment. The results of this study partially explained the ¹³⁷Cs activity concentrations found in the analysed demersal fish, suggesting that the benthos can be a continuous source of ¹³⁷Cs for the demersal fish during this period of time. Extending monitoring programmes to include invertebrates that are not food species for humans would greatly improve our ability to understand the role of trophic transfer pathways and take appropriate management actions.

Light-trapped caddisflies to decipher the role of species traits and habitats in Hg accumulation and transfer

We present a novel meta-community approach to explore the influence of species traits, such as adult body size, larval feeding type and microhabitat, as well as larval macrohabitat (main river channel vs. floodplain water bodies) on the concentration of total Hg accumulated ([THg]) in assemblages of adult caddisflies. We analyzed [THg] in 157 light-trapped adult caddisflies in a floodplain sector of the French upper Rhône River and used a linear mixed effect model to decipher the role of species traits and habitats in Hg accumulation. Variation of [THg] between species was best explained by the larval feeding type, whereas the contributions of adult size and larval micro and macro-habitat were minor. Results showed that [THg] in species associated with floodplain macrohabitats in the larval stage was lower than in those associated with the main river channel. This difference could depend on complexation of Hg by DOM (in the floodplain) and MES (in the main channel). This research provides a first evidence of the potential of an entire caddisfly assemblage for the assessment of contamination in large alluvial rivers. The implications of the results are discussed in view of the possible role of caddisflies as vectors of Hg to riparian predators.

Comparing the concentrations of heavy metals on two bivalve species in Santos Bay, Brazil: Subsidies to understanding the assimilation dynamic of bivalve contaminants

Contaminant substances consist of chemical elements that present the potential to adversely impact the ecology of the environment, thus representing a threat to local fauna and flora. In this context, heavy metals are critical agents that, depending on the nature and level, are potentially toxic to living organisms. In order to evaluate the bioaccumulation of heavy metals in the Santos estuary and to determine the potential influence of salinity gradient on the heavy metal bioconcentration, the present study measured the concentrations of As, Cd, Pb, Cu, Cr, Fe, Ni, and Zn in two bivalve species (Crassostrea rhizophorae and Perna Perna) sampled at different sites of Santos Bay, in the southeastern region of Brazil. Throughout the study, the "sentinel species" used were effective in bioaccumulating contaminants. In oysters, based on the Brazilian legislation, critical limits were exceeded for As, Zn, Cu, and Cr. In the case of mussels, on the other hand, only for As, Zn, and Cr, the critical limits were overcome. In the present study, obtained data suggested salinity as a determinant parameter in As incorporation processes of bivalve mollusks. PRACTITIONER POINTS: The present study presents important results for the development of environmental management policies in estuarine environments. The present study points out differences between different organisms as biomonitors, providing subsidies for the decision of an effective biomonitoring program. The present study discusses values of contaminants as a danger to public health in Santos Bay, which can be extrapolated to other similar environments around the world.

"Nanosize effect" in the metal-handling strategy of the bivalve Scrobicularia plana exposed to CuO nanoparticles and copper ions in whole-sediment toxicity tests

To date, the occurrence, fate and toxicity of metal-based NPs in the environment is under investigated. Their unique physicochemical, biological and optical properties, responsible for their advantageous application, make them intrinsically different from their bulk counterpart, raising the issue of their potential toxic specificity or "nanosize effect". The aim of this study was to investigate copper bioaccumulation, subcellular distribution and toxic effect in the marine benthic species Scrobicularia plana exposed to two forms of sediment-associated copper, as nanoparticles (CuO NPs) and as soluble ions (CuCl₂). Results showed that the exposure to different copper forms activated specific organism's metal handling strategies. Clams bioaccumulated soluble copper at higher concentrations than those exposed to sediment spiked with CuO NPs. Moreover, CuO NPs exposure elicited a stronger detoxification response mediated by a prompt mobilization of CuO NPs to metal-containing granules as well as a delayed induction of MT-like proteins, which conversely, sequestered soluble copper since the beginning of the exposure at levels significantly different from the control. Eventually, exposure to high concentrations of either copper form led to the same acute toxic effect (100% mortality) but the outcome was delayed in bivalves exposed to CuO NPs suggesting that the mechanisms underlying toxicity were copper form-specific. Indeed, while most of soluble copper was associated to the mitochondrial fraction suggesting an impairment of the ATP synthesis capacity at mitochondrial level, CuO NPs toxicity was most likely caused by the oxidative stress mediated by their bioaccumulation in the enzymatic and mitochondrial metabolically available fractions.

Iron and Manganese Retention of Juvenile Zebrafish (Danio rerio) Exposed to Contaminated Dietary Zooplankton (Daphnia pulex)-a Model Experiment

In present study the effect of iron (Fe) and manganese (Mn) contamination was assessed by modeling a freshwater food web of water, zooplankton (Daphnia pulex), and zebrafish (Danio rerio) under laboratory conditions. Metals were added to the rearing media of D. pulex, and enriched zooplankton was fed to zebrafish in a feeding trial. The elemental analysis of rearing water, zooplankton, and fish revealed significant difference in the treatments compared to the control. In D. pulex the Mn level increased almost in parallel with the dose of supplementation, as well as the Fe level differed statistically. A negative influence of the supplementation on the fish growth was observed: specific growth rate (SGR%) and weight gain (WG) decreased in Fe and Mn containing treatments. The redundancy analysis (RDA) of concentration data showed strong correlation between the rearing water and D. pulex, as well as the prey organism of Fe- and Mn-enriched D. pulex and the predator organism of D. rerio. The bioconcentration factors (BCF) calculated for water to zooplankton further proved the relationship between the Fe and Mn dosage applied in the treatments and measured in D. pulex. Trophic transfer factor (TTF) results also indicate that significant retention of the metals occurred in D. rerio individuals, however, in a much lower extent than in the water to zooplankton stage. Our study suggests that Fe and Mn significantly accumulate in the lower part of the trophic chain and retention is effective through the digestive track of zebrafish, yet no biomagnification occurs. Graphical abstract.

Differences in Copper Isotope Fractionation Between Mussels (Regulators) and Oysters (Hyperaccumulators): Insights from a Ten-Year Biomonitoring Study

Copper (Cu) isotope compositions in bivalve mollusks used in marine-monitoring networks is a promising tool to monitor anthropogenic Cu contamination in coastal and marine ecosystems. To test this new biomonitoring tool, we investigated Cu isotope variations of two bivalves-the oyster Crassostrea gigas and the mussel Mytilus edulis-over 10 years (2009-2018) in a French coastal site contaminated by diffuse Cu anthropogenic sources. Each species displayed temporal concentration profiles consistent with their bioaccumulation mechanisms, that is, the Cu-regulating mussels with almost constant Cu concentrations and the Cu-hyperaccumulating oysters with variable concentrations that track Cu bioavailability trends at the sampling site. The temporal isotope profiles were analogous for both bivalve species, and an overall shift toward positive δ⁶⁵Cu values with the increase of Cu bioavailabilities was associated with anthropogenic Cu inputs. Interestingly, mussels showed wider amplitudes in the isotope variations than oysters, suggesting that each species incorporates Cu isotopes in their tissues at different rates, depending on their bioaccumulation mechanisms and physiological features. This study is the first to demonstrate the potential of Cu isotopes in bivalves to infer Cu bioavailability changes related to anthropogenic inputs of this metal into the marine environment.

Application of Biomarker Tools Using Bivalve Models Toward the Development of Adverse Outcome Pathways for Contaminants of Emerging Concern

As contaminant exposures in aquatic ecosystems continue to increase, the need for streamlining research efforts in environmental toxicology using predictive frameworks also grows. One such framework is the adverse outcome pathway (AOP). An AOP framework organizes and utilizes toxicological information to connect measurable molecular endpoints to an adverse outcome of regulatory relevance via a series of events at different levels of biological organization. Molecular endpoints or biomarkers are essential to develop AOPs and are valuable early warning signs of the toxicity of pollutants, including contaminants of emerging concern. Ecological risk-assessment approaches using tools such as biomarkers and AOPs benefit from identification of molecular targets conserved across species. Bivalve models are useful in such approaches and integral to our understanding of ecological and human health risks associated with contaminant exposures. We discuss the value of using biomarker approaches in bivalve models to meet the demands of twenty-first-century toxicology. Environ Toxicol Chem 2020;39:1472-1484. © 2020 SETAC.

The euryhaline pygmy mussel, Xenostrobus securis, is a useful biomonitor of key metal contamination in the highly urbanised Sydney Estuary, Australia

This study critically evaluated the native pygmy mussel (Xenostrobus securis) as a biomonitor of the key metal contaminants in the highly urbanised Sydney Estuary, south-eastern Australia. Five metals (Cd, Cr, Cu, Pb and Zn) were identified as key contaminants, based on their enrichment factors (EFs) in the whole soft tissue of X. securis at 24 sampling sites, relative to baseline values from near-pristine reference sites in the adjacent Hawkesbury Estuary. Inverse relationships established between mussel size (dry tissue weight) and tissue concentrations of each metal were used to reduce variance (by 4-fold) among individuals; gender and reproductive status had no significant (p > 0.05) effect on tissue metal concentrations in X. securis. Metal concentrations in three environmental matrices - filtered (<0.2 μm) surface water (operationally defined as the dissolved/colloidal phase), suspended particulate matter (SPM; >0.2 μm) and surface sediment (<2 mm particle size), which are most relevant to a suspension-feeding estuarine bivalve, were also determined at each sampling site. For each of the five metals, highly significant (p < 0.01) positive linear regressions were established between metal EFs for mussel tissue and each environmental matrix. Metals in surface sediment and SPM explained 80-91% and 81-90%, respectively, of the variability in metal concentrations in mussel tissue, with filtered surface water explaining 74-86%. Cumulative mussel tissue EFs of all five metals, when regressed against each environmental matrix, showed that surface sediment concentrations explained 93% of their variability between sites, SPM 94% and filtered surface water 87-90%. Hence, X. securis very closely reflects the metal concentrations in its aquatic environment. The study provides a quality-assured benchmark of key metal contamination in the Sydney Estuary, and an appropriate methodology that may be used to discern any changes in metal contaminant status using X. securis.

Spatial distribution, bioaccumulation profiles and risk for consumption of edible bivalves: a comparison among razor clam, Manila clam and cockles in the Venice Lagoon

Despite their ecological and economical relevance, a lack of data is still occurring about the distribution, abundance, bioaccumulation and risks for consumption of some edible bivalves. The present study has been carried out in the Venice Lagoon taking into account three bivalve species to investigate i) the possible relationship among the biological features-distribution, abundance and bioaccumulation patterns- of razor clams (Solen marginatus Pulteney, 1799), Manila clams (Ruditapes philippinarum Adams and Reeve, 1850) and lagoon cockles (Cerastoderma glaucum Poiret, 1789) and the hydrological features, namely sediment physico-chemical characteristics and contamination; ii) their specific role as bioindicators of inorganic contamination; iii) the possible risks for human health associated with the consumption of these edible bivalves. Results showed that species distribution and abundance, especially for razor clams, was mainly influenced by environmental conditions and sediment granulometric composition, above metal(loid) contamination. The contamination patterns were different among species, as Manila clam generally showed higher bioaccumulation values for most of the metal(loid)s, whilst lagoon cockles preferentially accumulated Ni. Eventually, a serious concern exists for the human consumption, for all species and investigated sites regarding As. This study will raise attention on the effects of bioaccumulation of inorganic pollutants by edible bivalves and risks for consumers' safety, especially concerning razor clams and cockles, for which a critical lack of data on metal(loid) bioaccumulation occurs from the Northern Adriatic Sea.

Trophic transfer of metals in a seagrass food web: Bioaccumulation of essential and non-essential metals

Metal concentrations are reported for a seagrass ecosystem receiving industrial inputs. δ¹³C and δ¹⁵N isotope ratios were used to establish trophic links. Copper concentrations (dry mass) ranged from <0.01 μg/g in fish species to 570 μg/g (μ = 49 ± SD = 90 μg/g) in the oyster Saccostrea glomerata. Zinc concentrations ranged from 0.6 μg/g in the seagrass Zostera capricorni to 10,800 μg/g in the mud oyster Ostrea angasi (μ = 434 ± 1390 μg/g). Cadmium concentrations ranged from <0.01 μg/g in fish species to 268 μg/g in Ostrea angasi (μ = 6 ± 25 μg/g). Lead concentrations ranged from <0.01 μg/g for most fish species to 20 μg/g in polychaetes (μ = 2 ± 3 μg/g). Biomagnification of metals did not occur. Organisms that fed on particulate organic matter and benthic microalgae had higher metal concentrations than those that fed on detritus. Species physiology also played an important role in the bioaccumulation of metals.

Trace Elements in Marine Sediment and Organisms in the Gulf of Thailand

This review summarizes the findings from studies of trace element levels in marine sediment and organisms in the Gulf of Thailand. Spatial and temporal variations in trace element concentrations were observed. Although trace element contamination levels were low, the increased urbanization and agricultural and industrial activities may adversely affect ecosystems and human health. The periodic monitoring of marine environments is recommended in order to minimize human health risks from the consumption of contaminated marine organisms.

A critical examination of the possible application of zinc stable isotope ratios in bivalve mollusks and suspended particulate matter to trace zinc pollution in a tropical estuary

The application of zinc (Zn) isotopes in bivalve tissues to identify zinc sources in estuaries was critically assessed. We determined the zinc isotope composition of mollusks (Crassostrea brasiliana and Perna perna) and suspended particulate matter (SPM) in a tropical estuary (Sepetiba Bay, Brazil) historically impacted by metallurgical activities. The zinc isotope systematics of the SPM was in line with mixing of zinc derived from fluvial material and from metallurgical activities. In contrast, source mixing alone cannot account for the isotope ratios observed in the bivalves, which are significantly lighter in the contaminated metallurgical zone (δ⁶⁶Zn_JMC = +0.49 ± 0.06‰, 2σ, n = 3) compared to sampling locations outside (δ⁶⁶Zn_JMC = +0.83 ± 0.10‰, 2σ, n = 22). This observation suggests that additional factors such as speciation, bioavailability and bioaccumulation pathways (via solution or particulate matter) influence the zinc isotope composition of bivalves.

Metal speciation in sediment and bioaccumulation in Meretrix lyrata in the Tien Estuary in Vietnam

The concentrations of seven toxic metals (cadmium (Cd), nickel (Ni), chromium (Cr), arsenic (As), lead (Pb), copper (Cu), and zinc (Zn)) were determined in sediments and the soft tissues of a bivalve species (Meretrix lyrata) collected from the Tien Estuary in Tien Giang Province, South Vietnam. The total metal concentrations in sediments (mg/kg dry weight) increased as Cd (0.06) < Cu (5.0) < Pb (13.9) < As (16.3) < Ni (24) < Cr (50) < Zn (62). Speciation analysis revealed that these metals existed mainly in the residual fraction (43-94%), followed by the Fe-Mn oxide-bound (5-35%) and organic/sulfide-bound (0.6-9.2%) fractions. The metal concentrations in M. lyrata (mg/kg dry weight) were in the ranges of 1.3-1.9 (Cd), 1.5-2.8 (Ni), 1.8-3.4 (Cr), 11-16 (As), 0.3-0.6 (Pb), 6.9-8.7 (Cu), and 95-128 (Zn), which are safe for human consumption. The order of the mean biota-sediment accumulation factor (BSAF) of the metals in the non-residual fractions of the sediment for M. lyrata was Cd > Cu > As > Zn > Cr > Ni > Pb. The Risk Assessment Codes (RACs) suggest that the highest mobility of Cd (with RAC = 37%) poses greater environmental risk to aquatic biota. Correlation analysis results show that M. lyrata can be used as a biomonitor of Cd and Cu pollution in the exchangeable, acid-soluble, and non-residual sediment fractions.

Sediment-bound trace metals in Golfe-Juan Bay, northwestern Mediterranean: Distribution, availability and toxicity

The concentration, potential mobility, cation exchange capacity and toxicity of eight sediment-bound metals in Golfe-Juan Bay, France were examined. Results revealed significant spatial gradient of metal contamination along Golfe-Juan coast. The distribution and concentration of the metals appear to be influenced by the geochemical properties of the sediment, proximity to anthropogenic sources and general water circulation in the bay. The portion of trace metals found in the exchangeable, carbonate, oxidizable and reducible fractions of the sediment constitute 31%-58% of the total sediment-bound trace metal content, suggesting significant potential for remobilization of metals into the water column. Pb and Ni content of the sediment exceed the limits of the French marine sediment quality. Whole sediment extracts showed acute toxicity to marine rotifers. This study concludes that monitoring and management of sediment-bound trace metals in Golfe-Juan Bay are important so as not to underestimate their availability and risk to the marine ecosystems.

Contaminated Marine Sediments As a Source of Cesium Radioisotopes for Benthic Fauna near Fukushima

Marine animals, seawater, and sediment near Fukushima, Japan have become contaminated with ¹³⁴Cs and ¹³⁷Cs released in March 2011 from the damaged Fukushima Dai-ichi nuclear power plant. Radiocesium concentrations in some benthic fauna declined more slowly than in pelagic fish in the same region. We tested the hypothesis that benthic fish remained more contaminated due to the bioavailability of radiocesium in sediments. Laboratory experiments demonstrated that the assimilation efficiency of ¹³⁷Cs was 16% in polychaetes ingesting Fukushima sediment, up to 55% in crabs ingesting polychaetes, and about 80% in fish ingesting worms. In addition, all animals acquired Cs directly from the aqueous phase, but this accounted for only 1.2-2.5% of their total body burden. Thus, diet accounted for nearly all of the total body burden of Cs in these animals. Rate constants of Cs loss from animal tissues were 20% d^-1 for polychaetes, 10% d^-1 for crabs, and 6% d^-1 for fish after acquisition of Cs from water; rate constants following dietary uptake were 45% d^-1, 14% d^-1, and 5% d^-1 for polychaetes, crabs, and fish, respectively. A bioaccumulation model indicated that the transfer factors of Cs from sediments and the trophic transfer factors from worms to predators were about 1. Overall, sediment-bound Cs is sufficiently bioavailable to deposit-feeding polychaetes, and macrofauna assimilate Cs from these polychaetes to account for >90% of their body burden. This helps to explain the longer retention of Cs in bottom-dwelling fish near Fukushima.

Geochemistry and bioavailability of mudflats and mangrove sediments and their effect on bioaccumulation in selected organisms within a tropical (Zuari) estuary, Goa, India

Metals are non-degradable in the aquatic environment and play a vital role in estuarine biogeochemistry but could also be detrimental to associated biota. A comparative evaluation of the trace metal concentrations (Fe, Mn, Zn, Cu, Ni, and Co) was carried out in the Zuari estuary, Goa during the post-monsoon season of 2013 at six locations, each representing three mangrove and three mudflat regions. In addition, fractionation of trace metals in sediments was performed to provide information on the mobility, distribution, bioavailability and toxicity. Special attention was paid to the marine mollusks viz. bivalves and gastropods that are extensively used as bio-indicators in coastal pollution. Considering the percentage of metals in the sequentially extracted fractions, the order of mobility from most to least bioavailable forms was Mn > Zn > Cu > Ni > Co > Fe. Mn maintained high bioavailability (average around 60%) in Fe-Mn oxide and carbonate bound forms indicating that Mn is readily available for biota uptake. The bioavailability of Fe was on an average of around 6% whereas other metals like Cu, Zn, Ni and Co were around 19% to 34%. When the bioavailable values were compared with standard Screening Quick Reference Table (SQUIRT), Zn showed higher toxicity level and bioavailability in the lower estuary. On the basis of calculated Bio Sediment Accumulation Factors (BSAF's), overall trend in bioaccumulation was in the order of Cu > Zn > Mn > Ni > Co > Fe. Metal Pollution Index (MPI) computed was higher for gastropods than bivalves.

Metal-contaminated resuspended sediment particles are a minor metal-uptake route for the Sydney rock oyster (Saccostrea glomerata)--A mesocosm study, Sydney Harbour estuary, Australia

Resuspension of surficial sediments is considered a key process influencing bioaccumulation of metals in filter-feeders in the contaminated Sydney Harbour estuary (Australia). However, previous investigations were unable to establish a significant relationship between metals in sediments or suspended particulate matter (SPM) and oyster tissue concentrations. This study used a 60-d laboratory mesocosm experiment to expose Sydney rock oysters, Saccostrea glomerata, to a natural range of SPM concentrations with different SPM-metal concentrations. Dissolved metal concentrations were low and the availability of algae provided as food was constant for all treatments. Tissue metal concentrations of Cu, Pb and Zn increased significantly, however, no relationship was determined between tissue metal concentrations in the oyster and either SPM or SPM-metal concentrations. The results indicated that exposure to resuspended contaminated sediment particles contributed little to the observed metal uptake. Dissolved or algae food sources appear to be more important for metal accumulation in these oysters.

Accumulation of trace metals in sediments in a Mediterranean Lagoon: Usefulness of metal sediment fractionation and elutriate toxicity assessment

The authors investigated sediment quality in Bizerte Lagoon (Tunisia) focusing on geochemical characteristics, metal sediment fractionation and elutriate toxicity assessment. Nickel, Cu, Zn, Pb, Cr and Cd partitioning in sediments was studied; accumulation and bioavailability were elucidated using enrichment factors, sequential extractions, redox potential, acid volatile sulfide and biotest procedures in toxicity evaluation. Results revealed an accumulation for Pb and Zn, reaching 99 and 460 mg kg(-1) respectively. In addition, the acid volatile sulfide values were high in both eastern and western lagoon areas, thus affecting metal availability. Mean enrichment factor values for Pb and Zn were 4.8 and 4.9, respectively, with these elements as the main contributors to the lagoon's moderate enrichment level. Toxicity levels were influenced by accumulation of Zn in different surface sediment areas. Core sediments were investigated in areas with the highest metal concentrations; metal fractionation and biotest confirmed that Zn contributes to sediment toxicity.

Iron assimilation by the clam Laternula elliptica: Do stable isotopes (δ⁵⁶Fe) help to decipher the sources?

Iron stable isotope signatures (δ(56)Fe) in hemolymph (bivalve blood) of the Antarctic bivalve Laternula elliptica were analyzed by Multiple Collector-Inductively Coupled Plasma-Mass Spectrometry (MC-ICP-MS) to test whether the isotopic fingerprint can be tracked back to the predominant sources of the assimilated Fe. An earlier investigation of Fe concentrations in L. elliptica hemolymph suggested that an assimilation of reactive and bioavailable Fe (oxyhydr)oxide particles (i.e. ferrihydrite), precipitated from pore water Fe around the benthic boundary, is responsible for the high Fe concentration in L. elliptica (Poigner et al., 2013 b). At two stations in Potter Cove (King George Island, Antarctica) bivalve hemolymph showed mean δ(56)Fe values of -1.19 ± 0.34‰ and -1.04 ± 0.39 ‰, respectively, which is between 0.5‰ and 0.85‰ lighter than the pool of easily reducible Fe (oxyhydr)oxides of the surface sediments (-0.3‰ to -0.6‰). This is in agreement with the enrichment of lighter Fe isotopes at higher trophic levels, resulting from the preferential assimilation of light isotopes from nutrition. Nevertheless, δ(56)Fe hemolymph values from both stations showed a high variability, ranging between -0.21‰ (value close to unaltered/primary Fe(oxyhydr)oxide minerals) and -1.91‰ (typical for pore water Fe or diagenetic Fe precipitates), which we interpret as a "mixed" δ(56)Fe signature caused by Fe assimilation from different sources with varying Fe contents and δ(56)Fe values. Furthermore, mass dependent Fe fractionation related to physiological processes within the bivalve cannot be ruled out. This is the first study addressing the potential of Fe isotopes for tracing back food sources of bivalves.

Revisiting methods for the determination of bioavailable metals in coastal sediments

A simple methodology for the determination of bioavailability of fourteen metals in coastal sediments has been developed by simulating the conditions of digestive process of marine fishes. With this aim, a representative sediment composite sample was treated with hydrochloric acid solutions at different pH values, temperatures and contact times, in the presence and absence of Pepsin and Trypsin. The addition of Pepsin and Trypsin did not affect the extraction of most elements. As a result of the present study, the digestion with a hydrochloric acid solution at pH 1, 40°C and 12h is proposed. Adjustments of the temperature and time reaction could be made according to the specific ecosystem under study. The amount of metal extracted by other methods based on acetic acid was lower than that extracted by HCl treatment proposed.

Bioavailability and toxicity of zinc from contaminated freshwater sediments: linking exposure-dose-response relationships of the freshwater bivalve Hyridella australis to zinc-spiked sediments

To evaluate the use of the freshwater bivalve Hyridella australis as a potential biomonitor for zinc contamination in freshwater sediments, the bioavailability and toxicity of zinc contaminated sediments (low 44 ± 5, medium 526 ± 41, high 961 ± 38 μg/g dry mass) were investigated in laboratory microcosms for 28 days by examining H. australis exposure-dose-response relationships. Zinc concentrations in sediments and surface waters were measured as zinc exposure. Zinc in whole organism soft body tissues and five individual tissues were measured as organism zinc dose. Sub-cellular localisation of zinc in hepatopancreas tissues was investigated to further understand the zinc handling strategies and tolerance of H. australis. Total antioxidant capacity, lipid peroxidation and lysosomal membrane stability were measured in hepatopancreas tissues as zinc induced biomarker responses. Accumulated zinc concentrations in whole body tissues of H. australis reflected the zinc exposure and exhibited exposure dependent zinc accumulation at day 28. Gills accumulated significantly higher zinc concentrations than other tissues, however, no significant differences in zinc accumulation between treatments were detected for any of the individual tissues analysed. Analysis of individual tissue zinc concentrations, therefore, may not offer any advantages for monitoring bioavailable zinc in freshwater environments with this organism. Relationships between tissue zinc and calcium concentration suggest accumulation of zinc by H. australis may have occurred as an analogue of calcium which is a major constituent in shell and granules of unionid bivalves. A high percentage of accumulated zinc in the hepatopancreas tissues was detoxified and stored in metallothionein like proteins and metal rich granules. Of the zinc accumulated in the biologically active metal pool, 59-70% was stored in the lysosome+microsome fraction. At the concentrations tested, increasing zinc exposure resulted in decreasing total antioxidant capacity and measurable increases in the sublethal effects, lipid peroxidation and lysosomal membrane destabilisation, were observed. Based on exposure-dose analysis, H. australis partially regulates zinc uptake and weakly exhibits bioavailability of zinc in freshwater environments, however, exposure-response analysis shows zinc induced toxicological effects, suggesting the potential of this organism as a biomonitor for zinc in heavily contaminated freshwater environments.

Strong correlations between metal in mollusk soft tissue and nonresistant sediment fraction: a tool for biomonitoring intertidal zone of the Persian Gulf, Iran

Cadmium (Cd) and lead (Pb) were determined in three species of mollusks and associated sediment. Samples were collected from two locations along the intertidal zone of the Persian Gulf near Bandar Abbas. The study was conducted during the spring of 2011, 10 sediment samples and 15 mollusks from each of the following species: Saccostrea cucullata, Solen brevis, and Callista umbonella, were simultaneously collected. Soft tissue, shell, and sediment were tested for metals using an atomic absorption spectrophotometer. Geochemical fractions of the sediment were examined for metals using a sequential extraction technique. Our results indicate that over half of Cd and Pb in the sediment had natural origins. Independent sample t test showed statistically significant (p < 0.05) inter-tissue differences in accumulation of Cd and Pb. Soft tissue of C. umbonella contained highest levels of Cd. Pb accumulation was highest in S. brevis shell. Significant correlations (p < 0.05) were found between Cd in the soft tissue of C. umbonella and its levels in the geochemical fractions of the sediment. Lead levels in the resistant geochemical fractions of the sediment and S. brevis shell were significantly correlated. Our results suggest that soft tissue of C. umbonella and shell of S. brevis are reliable biomonitoring tools for Cd and Pb, respectively.

Exposure-dose-response of Tellina deltoidalis to metal contaminated estuarine sediments 2. Lead spiked sediments

Lead accumulation in estuarine sediments, as a result of activities such as mining and ore smelting, and through urban runoff is a continuing problem in the increasingly developed world. Marine organisms accumulate lead, which is known to be highly toxic to biological processes and to degrade organism and ecosystem health. Here the relationship between lead exposure, dose and response was investigated in the sediment dwelling, deposit feeding, marine bivalve Tellina deltoidalis. Bivalves were exposed in the laboratory to individual lead spiked sediments at < 0.01, 100 and 300 μg/g dry mass, for 28 days and accumulated total tissue lead concentrations of 4, 96 and 430 μg/g, respectively. Subcellular fractionation indicated that around 70% of the total accumulated tissue lead was detoxified, three quarters of the detoxified lead fraction was converted into metal rich granules, with the remainder in the metallothionein like protein fraction. The majority of biologically active lead was associated with the mitochondrial fraction with up to a 128 fold increase in lead burden in exposed organisms compared to controls. This indicates lead detoxification was occurring but the organism was unable to prevent lead interacting with sensitive organelles. With increased lead exposure T. deltoidalis showed a suppression in glutathione peroxidase activity, total glutathione concentration and reduced GSH:GSSG ratios, however, these differences were not significant. Lead exposed T. deltoidalis had a significantly reduced total antioxidant capacity which corresponded with increased lipid peroxidation, lysosomal destabilisation and micronuclei frequency. The exposure-dose-response relationships demonstrated for lead exposed T. deltoidalis supports its potential for the development of sublethal endpoints in lead toxicity assessment.

Exposure-dose-response of Tellina deltoidalis to metal-contaminated estuarine sediments: 1. Cadmium spiked sediments

Cadmium is a ubiquitous environmental metal contaminant with an affinity for biological membranes; it can enter cells by facilitated transport and it binds therein to various biomolecules and affects membrane system function. The relationship between cadmium exposure, dose and response was investigated in the benthic, deposit feeding, marine bivalve Tellina deltoidalis, using 28 day microcosm spiked cadmium exposures. Tissue cadmium reached steady state with the exposure concentration. Half the accumulated cadmium was detoxified and with increased exposure more was converted into metal rich granules. Most biologically active cadmium was in the mitochondrial fraction, with up to 7320-fold cadmium increases in exposed organisms. Cadmium exposed T. deltoidalis generally had reduced glutathione peroxidase enzyme activity. An increase in total glutathione concentrations, due to a build up of oxidised glutathione, was indicated by the reduced to oxidised glutathione ratio. All cadmium exposed T. deltoidalis had reduced total antioxidant capacity that corresponded with increased lipid peroxidation, lysosomal destabilisation and micronuclei frequency. Clear exposure-dose-response relationships have been demonstrated for T. deltoidalis exposed to cadmium-spiked sediments, supporting this organism's suitability for laboratory or in situ evaluation of sediment cadmium toxicity.

Dietary bioavailability of Cu adsorbed to colloidal hydrous ferric oxide

The dietary bioavailability of copper (Cu) adsorbed to synthetic colloidal hydrous ferric oxide (HFO) was evaluated from the assimilation of (65)Cu by two benthic grazers, a gastropod and a larval mayfly. HFO was synthesized, labeled with (65)Cu to achieve a Cu/Fe ratio comparable to that determined in naturally formed HFO, and then aged. The labeled colloids were mixed with a food source (the diatom Nitzschia palea) to yield dietary (65)Cu concentrations ranging from 211 to 2204 nmol/g (dry weight). Animals were pulse fed the contaminated diet and assimilation of (65)Cu from HFO was determined following 1-3 days of depuration. Mass transfer of (65)Cu from HFO to the diatom was less than 1%, indicating that HFO was the source of (65)Cu to the grazers. Estimates of assimilation efficiency indicated that the majority of Cu ingested as HFO was assimilated (values >70%), implying that colloidal HFO potentially represents a source of dietary Cu to benthic grazers, especially where there is active formation and infiltration of these particles into benthic substrates.

Oxidation of acid-volatile sulfide in surface sediments increases the release and toxicity of copper to the benthic amphipod Melita plumulosa

Acid-volatile sulfides (AVS) are an important metal-binding phase in sediments. For sediments that contain an excess of AVS over simultaneously extracted metal (SEM) concentrations, acute or chronic effects should not result from the metals Cd, Cu, Ni, Pb and Zn. While AVS phases may exist in surface sediments, the exposure to dissolved oxygen may oxidize the AVS and release metals to more bioavailable forms. We investigated the role of oxidation of AVS, and specifically copper sulfide phases, in surface sediments, in the toxicity to juveniles of the epibenthic amphipod, Melita plumulosa. Sediments containing known amounts of copper sulfide were prepared either in situ by reacting dissolved copper with AVS that had formed in field sediments or created in sediments within the laboratory, or by addition of synthesised CuS to sediments. Regardless of the form of the copper sulfide, considerable oxidation of AVS occurred during the 10-d tests. Sediments that had a molar excess of AVS compared to SEM at the start of the tests, did not always have an excess at the end of the tests. Consistent with the AVS-SEM model, no toxicity was observed for sediments with an excess of AVS throughout the tests. However, the study highlights the need to carefully consider the changes in AVS concentrations during tests, and that measurements of AVS and SEM concentrations should carefully target the materials to which the organisms are being exposed throughout tests, which in the case of juvenile M. plumulosa is the top few mm of the sediments.

Single versus combined exposure of Hyalella azteca to zinc contaminated sediment and food

The amphipod Hyalella azteca was exposed for 28 d to different combinations of Zn contaminated sediment and food. Sediment exposure (+clean food) resulted in increased Zn body burdens, increased mortality and decreased body mass when the molar concentrations of simultaneously extracted Zn were greater than the molar concentration of Acid Volatile Sulfide (SEM(Zn)-AVS>0), suggesting that dissolved Zn was a dominant route of exposure. No adverse effect was noted in the food exposure (+clean sediment), suggesting selective feeding or regulation. Combined exposure (sediment+food) significantly increased adverse effects in comparison with sediment exposure, indicating contribution of dietary Zn to toxicity and bioaccumulation. The observed enhanced toxicity also supports the assumption on the presence of an avoidance/selective feeding reaction of the amphipods in the single sediment or food exposures. During 14 d post-exposure in clean medium, the organisms from the same combined exposure history received two feeding regimes, i.e. clean food and Zn spiked food. Elevated Zn bioaccumulation and reduced reproduction were noted in amphipods that were offered Zn spiked food compared to the respective organisms that were fed clean food. This was explained by the failure of avoidance/selective feeding behavior in the absence of an alternative food source (sediment), forcing the amphipods to take up Zn while feeding. Increasing Zn body burdens rejected the assumption that Zn uptake from food was regulated by H. azteca. Our results show that the selective feeding behavior should be accounted for when assessing ecological effects of Zn or other contaminants, especially when contaminated food is a potential exposure route.

Looking for suitable biomarkers in benthic macroinvertebrates inhabiting coastal areas with low metal contamination: comparison between the bivalve Cerastoderma edule and the Polychaete Diopatra neapolitana

Metals accumulated in marine sediments are often a threat to benthic communities. With the recognized importance and wide use of stress biochemical responses as indicators of metal contamination it becomes essential to compare these markers between different species and verify their ubiquity and accuracy. Using wild Diopatra neapolitana and Cerastoderma edule, collected at several areas differing in metal contamination, this study aimed to assess the use of these two macrobenthic species as sentinel organisms and to determine the applicability of currently used biomarkers in benthic species exposed to a range of low metal and As concentrations. Total metal accumulation and intracellular partitioning was analyzed and metal-induced alterations were assessed through the analysis of several biochemical parameters in both organisms, including stress-induced reactive oxygen species (ROS), lipid peroxidation and protein content, the activity of antioxidant enzymes catalase (CAT), superoxide dismutase (SOD) and of glutathione S-transferase (GST). Metal chelation by Metallothioneins (MTs) was also determined. Results revealed that D. neapolitana accumulated higher levels of metals when compared to C. edule, independently of the sediment concentration. Results also showed strong species-specific responses to metals and differences in the ability to sequester metals. Overall, C. edule showed to be more efficient metal chelator and precipitatior than D. neapolitana, which was less tolerant and presented oxidative stress. MTs proved to be a good predictor of metal accumulation in both species, even under low metal exposures. On the other hand, lipid peroxidation was a good indicator of oxidative damage, only observed in D. neapolitana, which was a result of higher metal retention in the soluble fraction.

Bioavailability of particulate metal to zebra mussels: biodynamic modelling shows that assimilation efficiencies are site-specific

This study investigates the ability of the biodynamic model to predict the trophic bioaccumulation of cadmium (Cd), chromium (Cr), copper (Cu), nickel (Ni) and zinc (Zn) in a freshwater bivalve. Zebra mussels were transplanted to three sites along the Seine River (France) and collected monthly for 11 months. Measurements of the metal body burdens in mussels were compared with the predictions from the biodynamic model. The exchangeable fraction of metal particles did not account for the bioavailability of particulate metals, since it did not capture the differences between sites. The assimilation efficiency (AE) parameter is necessary to take into account biotic factors influencing particulate metal bioavailability. The biodynamic model, applied with AEs from the literature, overestimated the measured concentrations in zebra mussels, the extent of overestimation being site-specific. Therefore, an original methodology was proposed for in situ AE measurements for each site and metal.

The influence of sediment particle size and organic carbon on toxicity of copper to benthic invertebrates in oxic/suboxic surface sediments

The use of sediment quality guidelines to predict the toxicity of metals in sediments is limited by an inadequate understanding of exposure pathways and by poor causal links between exposure and effects. For a 10-d exposure to Cu-spiked sediments, toxicity to the amphipod Melita plumulosa was demonstrated to occur through a combination of dissolved and dietary Cu exposure pathways, but for the bivalves Spisula trigonella and Tellina deltoidalis, toxicity occurred primarily by exposure to dissolved Cu. For relatively oxidized sediments that had moderate amounts of organic carbon (2.6-8.3% OC), silt (20-100% <63-µm particles) but low acid-volatile sulfide (AVS), acute toxicity thresholds for the three species were derived based on the OC-normalized Cu concentration of the less than 63-µm sediment fraction. For all three species, no effects were observed at concentrations below 10 µg/L dissolved Cu (in pore water and overlying water) or below 12 mg Cu/g OC (for <63 µm sediment). For sediments with silt/OC properties of 20/0.5, 50/1, or 70/4%, the particulate Cu-based threshold equated to 60, 120, or 480 mg Cu/kg, respectively. For oxic/suboxic sediments in which AVS is not limiting metal availability, sediment quality guidelines of this form will provide adequate protection against toxicity and improve the prediction of effects for sediments with varying properties.

Modeling metal bioaccumulation in a deposit-feeding polychaete from labile sediment fractions and from pore water

Estuarine sediments are often highly enriched in particle-reactive metal contaminants and because aquatic animals have often been shown to acquire metals predominantly from their diet, benthic animals feeding on deposited or resuspended sediments may also accumulate metals through this uptake pathway. Laboratory experiments were performed in which the surface deposit-feeding polychaete, Nereis succinea, was exposed to As(+5), Cd, and Cr(+3) in pore water or in estuarine sediments with and without enrichment with algal debris. These experiments generated metal uptake parameters (assimilation efficiency of ingested metal [AE], uptake rate constant of dissolved metal, efflux rate constants following dietary or aqueous metal exposures) used in a kinetic model of metal bioaccumulation. The model showed that > 97% of the body burden of these metals is accumulated through ingested sediment. The kinetic model was further modified to consider the geochemical fractionation of the metals in the sediments because metals bound to some fractions were shown to be unavailable to these polychaetes. The modified model substituted the AE term for each metal by the percentage of metal extracted in neutral and weak acid exchangeable fractions (termed "carbonex" fraction) multiplied by the slope of the regression between the metal AE and its fractionation in carbonex. The modified model generated predictions of As, Cd, and Cr body burdens in polychaetes at three different estuarine sites that matched independent field observations at these sites (r²=0.84 for sediments without organic enrichment, r²=0.87 with organic enrichment). Model predictions that relied on total metal concentrations showed weaker relationships (r²=0.11-0.50). This study adds to the evidence for the dominance of dietary uptake of metals in aquatic animals and identifies a key sedimentary fraction of metals that can account for bioavailability of sediment-bound metals.

Relating the sediment phase speciation of arsenic, cadmium, and chromium with their bioavailability for the deposit-feeding polychaete Nereis succinea

We studied the influence of sediment geochemistry on bioavailability of As, Cd, and Cr in deposit-feeding polychaetes. Metal phase speciation in sediments was determined with a sequential extraction scheme, and assimilation efficiencies (AEs) of ingested metals were determined by pulse-chase feeding experiments using γ-emitting isotopes. Worms were fed sediments collected from geochemically diverse estuaries that were labeled by sorbing dissolved radiotracers or mixing with radiolabeled algae. Uptake of sediment-bound metals was compared with that from labeled algae or goethite. Metal AEs showed a positive relationship with the exchangeable and carbonate sedimentary fractions, whereas metals in iron and manganese oxides and acid-volatile sulfides, or in pyrite and other refractory material, were inversely correlated with AEs. Arsenic was most bioavailable from algae (72%), less from sediments mixed with algae (24-70%) and least from sediments labeled directly (1-12%). Arsenic AEs in sediments labeled directly showed a positive correlation with sedimentary Mn and Al and negative correlation with Fe. Cadmium AEs were positively correlated with salinity and negatively correlated with sedimentary organic C. The AEs of Cr from sediments or algae were less than 5%, but they were 34% from pure goethite. By quantifying the relationship of metal speciation in sediments with their bioavailability for deposit-feeding polychaetes, the present study provides new insight into understanding metal bioaccumulation in benthic invertebrates.

How life history contributes to stress response in the Manila clam Ruditapes philippinarum

INTRODUCTION

Within the last decade, numerous studies have investigated the role of environmental history on tolerance to stress of many organisms. This study aims to assess if Manila clams Ruditapes philippinarum may react differently to cadmium exposure and trematode parasite infection (Himasthla elongata) depending on their origin and environmental history in Arcachon Bay (France).

MATERIALS AND METHODS

Clams were exposed to Cd (15 microg L(-1)) and parasites (25 cercariae per clam), alone or in combination, at 15 degrees C under controlled laboratory conditions for 7 days. Metal accumulation and success of parasite infestation were examined, also physiological parameters such as metallothionein response and hemocyte counts and activities (phagocytosis, oxidative burst, viability, and adhesion).

RESULTS AND DISCUSSION

Sensitivity of Manila clams to both stressors differed from one site to another, suggesting local adaptation of populations. Clams from the more parasitized site presented better resistance to trematodes than the others in terms of first line defense, i.e., avoidance of infection. On the other hand, clams that adapted to chronic Cd contamination showed better detoxification mechanisms, both in a faster transfer of metal from gills to visceral mass and in a higher metallothionein baseline, than clams which had never experienced Cd contamination. Finally, hemocyte concentration and viability differed between clam origin site, highlighting the fact that populations living in different environments may adapt their physiological and biochemical responses to environmental stressors.

CONCLUSION

It is therefore important to be cautious when extrapolating results from field studies of one species and one site, if the life history of the organisms is not taken into account.

Toxicity of metals to the bivalve Tellina deltoidalis and relationships between metal bioaccumulation and metal partitioning between seawater and marine sediments

The Australian benthic bivalve Tellina deltoidalis tolerates a wide range of sediment and water conditions, is easy to handle in the laboratory, and is a useful species for undertaking whole-sediment toxicity tests. The sensitivity of T. deltoidalis to metals was investigated in 10-day metal-spiked sediment exposures for Cd, Cu, Ni, Pb, and Zn and in water-only exposures for Cu and Zn. The survival of T. deltoidalis in 10-day exposures to metal-spiked sediments was 88-100% for Cd, Ni, Pb, and Zn concentrations of 75, 420, 1,000, and 4,000 mg/kg, respectively. The 4-day LC(50)s for dissolved Cu and Zn were 0.18 and 13 mg/L, respectively. The 8-day LC(50) for Cu was 31 (24-34) microg/L. Cu and Zn concentrations in the tissues of T. deltoidalis increase linearly with increasing dissolved exposure concentration. In the Cu-spiked sediment and water exposures, the survival was negatively correlated with the Cu concentration in both the overlying water and in the tissues of T. deltoidalis. In contrast, particulate Cu concentrations were found to be a poor predictor of Cu bioaccumulation and toxicity for Cu-spiked sediments.

Bioavailability of a natural lead-contaminated invertebrate diet to zebrafish

Dietary metals are increasingly recognized as key determinants of total metal burdens in fish, yet their ecotoxicological significance remains unclear. In this study, a pairwise experimental design was used to assess reproductive performance of zebrafish (Danio rerio) fed diets supplemented with a natural Pb-enriched polychaete, Nereis diversicolor. Zebrafish were fed 1% flake food (dry wt diet/wet wt fish/d), 1% brine shrimp, and 1% N. diversicolor collected from either Gannel estuary, Cornwall, United Kingdom (UK), an estuary with legacy Pb contamination, or Blackwater estuary, Essex, UK, a reference site with low background metal concentrations, for 63 d. Mean daily dietary doses of Pb were 0.417 and 0.1 mg/kg/d (dry wt feed:wet wt fish) for fish fed N. diversicolor from Gannel and Blackwater estuaries, respectively. With the exception of Ag, which was higher for fish fed N. diversicolor from Gannel estuary, there were no differences in daily dietary exposures to other metals (As, Cd, Cu, Fe, and Zn) between treatment groups. Fish fed Pb-enriched Gannel N. diversicolor exhibited no significant impairment to incidence of spawning, numbers of eggs per breeding pair or hatch rate of embryos compared with pre-exposure levels, when N. diversicolor was omitted from the dietary regimen. Nevertheless, metal analysis revealed significant increases in whole-body Pb burdens of male fish fed polychaetes from Gannel estuary, Ag in female fish fed Gannel worms, and Ag and Cd in male fish fed the Blackwater worms. These data demonstrate that Pb naturally incorporated in N. diversicolor is bioavailable to fish, and fish exhibit sex-dependent dietary metal accumulation patterns, but after 63 d of the experimental feeding regimen, reproductive performance was unaffected.

Geochemical and microfaunal proxies to assess environmental quality conditions during the recovery process of a heavily polluted estuary: the Bilbao estuary case (N. Spain)

This study explores the eventual environmental improvement of the Bilbao estuary (northern Spain), from 1997 to 2006, in order to assess current estuarine restoration being undertaken as part of a Revitalization Strategic Plan. The monitoring programme is based on spatial and temporal variation in the distributions of both benthic foraminiferal assemblages and heavy metals contained in surficial sediments from the polluted intertidal flats. The overall pattern shows a decreasing metal concentration; however, reversals to this trend are noticed in the middle estuary. From 2000 to 2003, a significant decrease in heavy metal concentration was observed which is most likely related to the implementation in 2001-2002 of the biological treatment at a central wastewater treatment plant. Although the metal concentration decreased by 85% for some elements, these values still remain considerably high. No significant change occurred between 2003 and 2006 in metal concentrations. During the monitoring period the estuary channel presented environmental conditions close to azoic in 3/4 of its watercourse. Only in the year 2006, the two lowermost estuarine samples exhibited an increase in microfaunal densities. These samples were dominated by pollution-resistant estuarine species. The fact that estuarine sediments quality is recovering very slowly seems to be caused mainly by the resuspension of accumulated contaminants in the sediments due to dredging and working activities in the estuary. Thus, local authorities should consider also the clean up of the pollutants stored in the sediments, not seeking only the achievement of the water quality standards, as these polluted sediments can act as source of contamination.

Effects of settling organic matter on the bioaccumulation of cadmium and BDE-99 by Baltic Sea benthic invertebrates

Settling organic matter (OM) is the major food source for heterotrophic benthic fauna. The high sorption affinity of many contaminants for OM implies that OM can influence both the distribution and bioavailability of contaminants. Here, we experimentally examine the role of settling OM of various nutritional qualities on the bioaccumulation of cadmium and the flame retardant BDE-99 by three benthic invertebrates; Macoma balthica, Monoporeia affinis and Marenzelleria sp. Contaminants were associated with three types of OM; a microalgae (Tetraselmis spp.), lignin and sediment. Bioaccumulation of Cd was proportional to OM nutritional quality for all three species, and was species-specific in the order Marenzelleria>M. balthica>M. affinis. BDE-99 bioaccumulation was highest in the treatment with the most nutritious OM (Tetraselmis). Consequently, both benthic species composition and the nutritive value of organic matter settling to the seafloor can have a substantial effect on the bioaccumulation of both metals and organic contaminants.

Biodynamic modeling of PCB uptake by Macoma balthica and Corbicula fluminea from sediment amended with activated carbon

Activated carbon amendment was assessed in the laboratory as a remediation strategy for freshwater sediment contaminated with polychlorinated biphenyls (PCBs) from the Grasse River (near Massena, NY). Three end points were evaluated: aqueous equilibrium PCB concentration, uptake into semipermeable membrane devices (SPMDs), and 28-day bioaccumulation in the clam Corbicula fluminea. PCB uptake by water, SPMDs, and clams followed similar trends, with reductions increasing as a function of carbon dose. Average percent reductions in clam tissue PCBs were 67, 86, and 95% for activated carbon doses of 0.7, 1.3, and 2.5% dry wt, respectively. A biodynamic model that incorporates sediment geochemistry and dietary and aqueous uptake routes was found to agree well with observed uptake by C. fluminea in our laboratory test systems. Results from this study were compared to 28-day bioaccumulation experiments involving PCB-contaminated sediment from Hunters Point Naval Shipyard (San Francisco Bay, CA) and the clam Macoma balthica. Due to differences in feeding strategy, M. balthica deposit-feeds whereas C. fluminea filter-feeds, the relative importance of the aqueous uptake route is predicted to be much higher for C. fluminea than for M. balthica. Whereas M. balthica takes up approximately 90% of its body burden through sediment ingestion, C. fluminea only accumulates approximately 45% via this route. In both cases, results strongly suggest that it is the mass transfer of PCBs from native sediment to added carbon particles, not merely reductions in aqueous PCB concentrations, that effectively reduces PCB bioavailability and uptake by sediment-dwelling organisms.

Exposure-effect model for calculating copper effect concentrations in sediments with varying copper binding properties: a synthesis

An exposure-effects model is described for calculating copper effect concentrations for benthic organisms in sediments with varying copper-binding properties. It is based on a bioenergetic-based kinetic model that describes the rate of assimilation of copper by benthic organisms from dissolved and particulate phases. During acute exposures, the total copper assimilated by the organisms was used as a measure of the organisms' exposure to bioavailable copper, and toxicity occurs when the copper exposure exceeds a threshold value. Exposure-effects models were developed for nine benthic organisms and were used to predict the effect of sediment-water partitioning (Kd) and copper assimilation from ingested solids on toxic effects and how these factors will influence derived sediment quality guideline (SQG) concentrations. Species sensitivity distributions were used to calculate SQG concentrations for copper for sediments of varying copper binding properties. The modeling indicated that "single value" SQG concentrations would be ineffective for predicting the toxicity of metals in sediment. It is proposed that, for all contaminants (not just metals), a better approach would be to have SQG concentrations, or ranges, that are applied to different sediment types. SQGs should account for contaminant exposure from both water-filtration and particulate-ingestion exposure routes, as can be achieved by models of sediment-water contaminant partitioning (Kd) and the contaminant assimilation efficiency (AE) of ingested particles. The study indicates that improved mechanistic models of contaminant exposure, as influenced by both organism physiology and sediment properties, are needed to predict toxic effects in sediments.