Metal toxicity in a sediment-dwelling polychaete: threshold body concentrations or overwhelming accumulation rates?

eDNA metabarcoding reveals shifts in sediment eukaryote communities in a metal contaminated estuary

Metal contamination is a global issue impacting biodiversity in urbanised estuaries. Traditional methods to assess biodiversity are time consuming, costly and often exclude small or cryptic organisms due to difficulties with morphological identification. Metabarcoding approaches have been increasingly recognised for their utility in monitoring, however studies have focused on freshwater and marine systems despite the ecological significance of estuaries. We targeted estuarine eukaryote communities within the sediments of Australia's largest urbanised estuary, where a history of industrial activity has resulted in a metal contamination gradient. We identified specific eukaryote families with significant correlations with bioavailable metal concentrations, indicating sensitivity or tolerance to specific metals. While polychaete families Terebellidae and Syllidae demonstrated tolerance to the contamination gradient, members of the meio- and microfaunal communities including diatoms, dinoflagellates and nematodes displayed sensitivities. These may have high value as indicators but are frequently missed in traditional surveys due to sampling limitations.

The relationship between population attributes of the mud snail Amphibola crenata and sediment contamination: A multi-estuary assessment

This study assessed the potential of the New Zealand mud snail Amphibola crenata to act as a bioindicator of contaminated estuarine sediment. Seventeen sites with varying contaminant burdens were identified within six New Zealand regions. Attributes (population density, individual length distribution and individual dry weight condition index) were measured for field-collected A. crenata, and related to measurements of sediment trace metals and nutrients. Population density of the mud snail was relatively high in sites with elevated nutrients and organic matter. The length distribution of A. crenata showed significant regional and site-specific variations. Minimum, mean, and median shell length of A. crenata were positively correlated with sediment cadmium and zinc concentration. Overall, the sites were able to be distinguished by A. crenata population attributes and the sediment metal and nutrient content. These results suggest that A. crenata population information has potential value for assessing estuarine sediment metal and nutrient contamination.

Effects and bioaccumulation of Cr(III), Cr(VI) and their mixture in the freshwater mussel Corbicula fluminea

Chromium has two main oxidation states, Cr(III) and Cr(VI), that can occur simultaneously in natural waters. Current consensus holds that Cr(VI) is of high ecotoxicological concern, but regards Cr(III) as poorly bioavailable and relatively non-toxic. In this work, the effects and bioaccumulation of Cr(III), Cr(VI) and their mixture were studied using the freshwater clam Corbicula fluminea as a model organism. Mixture exposures were carried out using solutions isotopically enriched in ⁵⁰Cr(III) or ⁵³Cr(VI), allowing to quantify the contribution of each redox form to total Cr accumulation in the clams. Following exposure to individual redox forms, Cr(III) accumulated preferentially in the digestive glands and Cr(VI) in the gills of C. fluminea. In mixture exposures, both redox forms accumulated mainly in the gills; the concentration of Cr(III) in the digestive glands being much lowered compared with individual exposures. Both oxidation states affected the expression of biomarkers related to energy reserves, cellular damage and mitochondrial functioning, as well as the expression of mRNA for detoxification genes. The observed effects differed between gills and digestive glands. The present study suggests that Cr(III) is a bioavailable and biologically active elemental species deserving more consideration by the ecotoxicological community.

Vanadium Toxicity Monitored by Fertilization Outcomes and Metal Related Proteolytic Activities in Paracentrotus lividus Embryos

Metal pharmaceutical residues often represent emerging toxic pollutants of the aquatic environment, as wastewater treatment plants do not sufficiently remove these compounds. Recently, vanadium (V) derivatives have been considered as potential therapeutic factors in several diseases, however, only limited information is available about their impact on aquatic environments. This study used sea urchin embryos (Paracentrotus lividus) to test V toxicity, as it is known they are sensitive to V doses from environmentally relevant to very cytotoxic levels (50 nM; 100 nM; 500 nM; 1 µM; 50 µM; 100 µM; 500 µM; and 1 mM). We used two approaches: The fertilization test (FT) and a protease detection assay after 36 h of exposure. V affected the fertilization percentage and increased morphological abnormalities of both egg and fertilization envelope, in a dose-dependent manner. Moreover, a total of nine gelatinases (with apparent molecular masses ranging from 309 to 22 kDa) were detected, and their proteolytic activity depended on the V concentration. Biochemical characterization shows that some of them could be aspartate proteases, whereas substrate specificity and the Ca²⁺/Zn²⁺ requirement suggest that others are similar to mammalian matrix metalloproteinases (MMPs).

Delineation of the exposure-response causality chain of chronic copper toxicity to the zebra mussel, Dreissena polymorpha, with a TK-TD model based on concepts of biotic ligand model and subcellular metal partitioning model

A toxicokinetic-toxicodynamic model was constructed to delineate the exposure-response causality. The model could be used: to predict metal accumulation considering the influence of water chemistry and biotic ligand characteristics; to simulate the dynamics of subcellular partitioning considering metabolism, detoxification, and elimination; and to predict chronic toxicity as represented by biomarker responses from the concentration of metals in the fraction of potentially toxic metal. The model was calibrated with data generated from an experiment in which the Zebra mussel Dreissena polymorpha was exposed to Cu at nominal concentrations of 25 and 50 μg/L and with varied Na⁺ concentrations in water up to 4.0 mmol/L for 24 days. Data used in the calibration included physicochemical conditions of the exposure environment, Cu concentrations in subcellular fractions, and oxidative stress-induced responses, i.e. glutathione-S-transferase activity and lipid peroxidation. The model explained the dynamics of subcellular Cu partitioning and the effect mechanism reasonably well. With a low affinity constant for Na ⁺ binding to Cu²⁺ uptake sites, Na ⁺ had limited influence on Cu²⁺ uptake at low Na⁺ concentrations in water. Copper was taken up into the metabolically available pool (MAP) at a largely higher rate than into the cellular debris. Similar Cu concentrations were found in these two fractions at low exposure levels, which could be attributed to sequestration pathways (metabolism, detoxification, and elimination) in the MAP. However, such sequestration was inefficient as shown by similar Cu concentrations in detoxified fractions with increasing exposure level accompanied by the increasing Cu concentration in the MAP.

Current understanding and research needs for ecological risk assessments of naturally occurring radioactive materials (NORM) in subsea oil and gas pipelines

Thousands of offshore oil and gas facilities are coming to the end of their life in jurisdictions worldwide and will require decommissioning. In-situ decommissioning, where the subsea components of that infrastructure are left in the marine environment following the end of its productive life, has been proposed as an option that delivers net benefits, including from: ecological benefits from the establishment of artificial reefs, economic benefits from associated fisheries, reduced costs and improved human safety outcomes for operators. However, potential negative impacts, such as the ecological risk of residual contaminants, are not well understood. Naturally occurring radioactive materials (NORM) are a class of contaminants found in some oil and gas infrastructure (e.g. pipelines) and includes radionuclides of uranium, thorium, radium, radon, lead, and polonium. NORM are ubiquitous in oil and gas reservoirs around the world and may form contamination products including scales and sludges in subsea infrastructure due to their chemistries and the physical processes of oil and gas extraction. The risk that NORM from these sources pose to marine ecosystems is not yet understood meaning that decisions made about decommissioning may not deliver the best outcomes for environments. In this review, we consider the life of NORM-contamination products in oil and gas systems, their expected exposure pathways in the marine environment, and possible ecological impacts following release. These are accompanied by the key research priorities that need to better describe risk associated with decommissioning options.

Development of a toxicokinetic-toxicodynamic model simulating chronic copper toxicity to the Zebra mussel based on subcellular fractionation

A toxicokinetic-toxicodynamic model based on subcellular metal partitioning is presented for simulating chronic toxicity of copper (Cu) from the estimated concentration in the fraction of potentially toxic metal (PTM). As such, the model allows for considering the significance of different pathways of metal sequestration in predicting metal toxicity. In the metabolically available pool (MAP), excess metals above the metabolic requirements and the detoxification and elimination capacity form the PTM fraction. The reversibly and irreversibly detoxified fractions were distinguished in the biologically detoxified compartment, while responses of organisms were related to Cu accumulation in the PTM fraction. The model was calibrated using the data on Cu concentrations in subcellular fractions and physiological responses measured by the glutathione S-transferase activity and the lipid peroxidation level during 24-day exposure of the Zebra mussel to Cu at concentrations of 25 and 50 µg/L and varying Na⁺ concentrations up to 4.0 mmol/L. The model was capable of explaining dynamics in the subcellular Cu partitioning, e.g. the trade-off between elimination and detoxification as well as the dependence of net accumulation, elimination, detoxification, and metabolism on the exposure level. Increases in the net accumulation rate in the MAP contributed to increased concentrations of Cu in this fraction. Moreover, these results are indicative of ineffective detoxification at high exposure levels and spill-over effects of detoxification.

Copper transformation, speciation, and detoxification in anoxic and suboxic freshwater sediments

The complex chemistry of copper (Cu) in freshwater sediments at low concentrations is not well understood. We evaluated the transformation processes of Cu added to freshwater sediments under suboxic and anoxic conditions. Freshwater sediments from three sources in Michigan with different characteristics (Spring Creek, River Raisin, and Maple Lake) were spiked with 30 or 60 mg kg^-1 Cu and incubated under a nitrogen atmosphere. After 28-d, each treatment subset was amended with organic matter (OM) to promote anoxic conditions and evaluate its effects on Cu speciation. OM addition triggered a shift from suboxic to anoxic conditions, and sequential extractions showed that Cu accordingly shifted from acid-soluble to oxidizable fractions. Extended X-ray absorption fine-structure (EXAFS) spectroscopy revealed that Cu sulfides dominated all anoxic samples except for Spring Creek 30 mg kg^-1, where Cu(I) was predominantly complexed to thiol groups of OM. Covellite and chalcopyrite (CuFeS₂) were the predominant Cu species in nearly all anoxic samples, as determined by Raman spectroscopy, scanning electron microscopy, and X-ray absorption near-edge structure (XANES) spectroscopy. Copper reduction also occurred under suboxic conditions: for two of three sediments, around 80% had been reduced to Cu(I), while the remaining 20% persisted as Cu(II) complexed to OM. However, in the third coarsest (i.e., Spring Creek), around 50% of the Cu had been reduced, forming Cu(I)-OM complexes, while the remainder was Cu(II)-OM complexes. Toxicity tests showed that survival of H. azteca and D. magna were significantly lower in suboxic treatments. Anoxic sediments triggered a near-complete transformation of Cu to sulfide minerals, reducing its toxicity.

Proposal of integrative scores and biomonitor selection for metal bioaccumulation risk assessment in mine-impacted rivers

Development of sound criteria for metal and metalloid bioaccumulation risk assessment in river basins affected by mining activities is a necessary tool to protect the aquatic communities. The aim of this study is to propose integrative scores for tissue residues that are suitable for surveillance programs and readily interpreted in terms of risk assessment in mining impacted rivers. Tissue residues of 7 trace metals and 2 metalloids were measured in ten macroinvertebrate taxa from the Nalón River basin (Spain), affected by Hg, Cu and Au mining activities. Compared with reference sites, biomonitor taxa from Hg and Au mining districts showed the highest bioaccumulation. However, low or non-significant bioaccumulation was found in sites influenced by historical Cu mining. Multivariate analyses (ANOSIM) performed on individual taxa revealed significant differences in tissue residues between sites classified according to their ecological status. The bioaccumulation risk assessment was based on the average ratio of the actual metal tissue residues in each macroinvertebrate taxon to the corresponding Ecological Threshold tissue concentration (Tissue residue Ratio to Threshold, TRT). The suitability of the biomonitors was evaluated using linear regression models fitted to the relationships between TRT scores and site sediment pollution or ecological status scores. Biomonitor selection also considered differences in invertebrate functional traits, which can influence metal and metalloid bioavailability. Site bioaccumulation risk was assessed on an Integrated Tissue concentration score (INTISS), calculated over a selection of the most relevant chemicals (As, Cu and Hg) and 3 biomonitor taxa (Baetidae, Hydropsychidae, Microdrile oligochaetes) comprising a set of feeding styles. Based on INTISS, it was possible to predict community alteration scores, using linear regression models. A comparison of site bioaccumulation and ecological status assessments based on the departure from reference conditions showed that operational monitoring programs in basins impaired by mining can be optimized by combining both approaches.

Risk assessment for sediment associated heavy metals using sediment quality guidelines modified by sediment properties

Sediment quality guidelines (SQGs) are a fundamental component of sediment quality assessment framework, frequently used in the first tier of assessment to predict the potential risks of contaminants in sediment. A recognized weakness of SQGs concerns the bioavailability of sediment contaminants, which may vary considerably with different physical-chemical properties. To better evaluate the ecological risks and predict the toxicity of the heavy metals (Cd, Cu, Ni, Pb, Zn) in the sediments of Haihe River of China, the risk quotients derived from total metal concentrations and SQG values were modified using multiple linear regressions with sediment properties, i.e. total organic carbon (TOC), acid-volatile sulfide (AVS), and particle size distribution (PSD). Then, the sediment toxicity was tested with the benthic organisms of chironomids and tubificids, and the relationships between the observed toxicity with the modified risk quotients were investigated. We found that the risk quotient modified with TOC and AVS displayed significantly improved relationship with the toxicity (p < 0.001) compared to the original risk quotient without modification (p = 0.062-0.074 > 0.05). Risk assessment indicated that although the heavy metals in the sediments of Haihe River of China are at a relatively low level, potential ecological risks caused by Ni and Zn still exist in some area, especially in the lower reaches along the estuary. The results indicated that the risk quotient and SQG values modified with sediment properties are promising for risk assessment of the metal contaminants in sediments.

"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.

Biomonitoring of Heavy Metals: The Unexplored Role of Marine Sessile Taxa

Coastal areas are known to receive significant anthropogenic inputs, mainly deriving from metropolitan areas, industries, and activities related to tourism. Among these inputs, some trace elements are listed as priority pollutants in the European Water Framework Directive, due to their ability to bioaccumulate in organisms. Many studies have been conducted on heavy metals (HMs) accumulation and on their possible effects on different edible marine species. While the most studied sessile organisms are bivalves, in the current review, we focus our attention on other sessile taxa (sponges, cnidarians, bryozoans, polychaetes, cirripeds, and tunicates), proposed as bioindicators in coastal shallow waters. Although their potential as bioindicator tools has been repeatedly highlighted in the literature, these organisms are still poorly investigated and considered for monitoring. In this context, we analyze the available literature about this topic, in order to summarize the current knowledge and identify possible applications of these organisms in a bioremediation scenario.

A biological characteristic extrapolation of compound toxicity for different developmental stage species with toxicokinetic-toxicodynamic model

Intraspecific difference in toxicity brings uncertainty to ecological risk assessment (ERA) and water quality criteria (WQC) of chemicals. Here, we compared intraspecies sensitivity to toxicants for Mesocyclops leuckarti of which toxicity data was obtained from published literatures, and zebrafish Danio rerio of which toxicity data was done in this study). Due to the internal concentration of chemicals not measured, simplified toxicokinetic-toxicodynamic (TK-TD) models were used, and we investigated whether TK-TD parameters estimated by Bayesian method might represent the differences in sensitivity between life-stages of 2 species. The results demonstrated that the difference in TK-TD parameters (background mortality m₀, no effect concentration NEC, the killing rate k_s, and the dominant rate k_d) could represent the toxicity difference between life-stages of individual species. The TK-TD model could predict toxicity in individual species (Cyprinus carpio L., Enchytraeus crypticus, Folsomia candida, Hyalella Azteca) exposed to different chemical concentrations and successfully extrapolate toxicity between different life stages of Mesocyclops leuckarti and Danio rerio by scaling several TK-TD parameters. The modified TK-TD model on the extrapolation toxicity of chemicals between life stages for species could be useful for the ERA and for deriving and revising WQC for chemicals.

The Impact of Metal-Rich Sediments Derived from Mining on Freshwater Stream Life

Metal-rich sediments have the potential to impair life in freshwater streams and rivers and, thereby, to inhibit recovery of ecological conditions after any remediation of mine water discharges. Sediments remain metal-rich over long time periods and have long-term potential ecotoxicological interactions with local biota, unless the sediments themselves are physically removed or replaced by less metal-rich sediment. Laboratory-derived environmental quality standards are difficult to apply to the field situation, as many complicating factors exist in the real world. Therefore, there is a strong case to consider other, field-relevant, measures of toxic effects as alternatives to laboratory-derived standards and to seek better biological tools to detect, diagnose and ideally predict community-level ecotoxicological impairment. Hence, this review concentrated on field measures of toxic effects of metal-rich sediment in freshwater streams, with less emphasis on laboratory-based toxicity testing approaches. To this end, this review provides an overview of the impact of metal-rich sediments on freshwater stream life, focusing on biological impacts linked to metal contamination.

Chromium bioavailability in aquatic systems impacted by tannery wastewaters. Part 2: New insights from laboratory and in situ testing with Chironomus riparius Meigen (Diptera, Chironomidae)

Chromium is widely used as a tanning agent and can become a contaminant of concern in aquatic ecosystems receiving discharges from industrial or artisanal tanning activities. In a companion study, we showed that Cr discharged by tanneries was bioavailable to indigenous chironomids with accumulation via sediment ingestion likely to represent the predominant exposure route. However, Cr accumulation by chironomids did not directly reflect the degree of sediment contamination and the potential adverse effects of Cr accumulation on chironomids were not evaluated. In the present study, chironomids were exposed to homogenised, field-collected sediments in the laboratory and to intact sediments in situ using a customized caging system. Chromium concentrations were assessed in sediments, exposed larvae of laboratory-reared Chironomus riparius and overlying waters of in situ cages. Experimental results of Cr bioaccumulation were compared with expected Cr body burden in chironomids calculated using biodynamic modelling. Our data provided strong support to the hypothesis that Cr bioaccumulation in the field is specifically controlled by the deposition of contaminated suspended particulate matter (SPM) containing a pool of Cr readily bioavailable to surface deposit feeders. Considering freshly deposited SPM as an additional route of exposure for surface deposit feeders leads to a good agreement between the modelling and experimental results. Additionally, a Cr body burden of about 77 μg g^-1 d.w. was identified as a tentative threshold above which effects on the growth of C. riparius may appear. While both laboratory and in situ experiments provide evidence for the availability of Cr in aquatic system impacted by tannery wastewaters, standard laboratory exposure conditions may miss additional exposure routes in the field and underestimate possible adverse effects on benthic organisms.

Lumbriculus variegatus (Annelida) biological responses and sediment sequential extractions indicate ecotoxicity of lake sediments contaminated by biomining

We assessed potential ecotoxicity of lake sediments affected by biomining effluents in northeastern Finland. Growth, reproduction and behavior of the sediment-dwelling oligochaete Lumbriculus variegatus (Müller 1774) were used as ecotoxicity endpoints. Standardized chronic bioassays were used for growth and reproduction, and acute and chronic tests with Multispecies Freshwater Biomonitor (MFB) for behavior assessments. Sequential extractions were used to characterize metal bioavailability and exposure conditions in the sediments, which indicated mining-induced contamination gradients of S, Cu, Ni and U and also bioavailability gradients of S and Ni. Among the ecotoxicity endpoints, growth and reproduction responses of the standard bioassays appeared more sensitive than the behavioral responses at 21 d. In the two most mining-affected test sediments, mean number of worms and dry biomass decreased 35-42% and 46-51% in comparison to the reference sediment, respectively. The behavioral changes of worms, i.e. peristaltic and overall locomotory activity, decreased on average 20-70% and 2-61% at 21 d in the same sediments. However, these behavioral changes were observed at the onset of exposure indicating MFB technique is a suitable and rapid screening level ecotoxicity assessment tool.

Chronic exposure to copper and zinc induces DNA damage in the polychaete Alitta virens and the implications for future toxicity of coastal sites

Copper and zinc are metals that have been traditionally thought of as past contamination legacies. However, their industrial use is still extensive and current applications (e.g. nanoparticles and antifouling paints) have become additional marine environment delivery routes. Determining a pollutant's genotoxicity is an ecotoxicological priority, but in marine benthic systems putative substances responsible for sediment genotoxicity have rarely been identified. Studies that use sediment as the delivery matrix combined with exposures over life-history relevant timescales are also missing for metals. Here we assess copper and zinc's genotoxicity by exposing the ecologically important polychaete Alitta virens to sediment spiked with environmentally relevant concentrations for 9 months. Target bioavailable sediment and subsequent porewater concentrations reflect the global contamination range for coasts, whilst tissue concentrations, although elevated, were comparable with other polychaetes. Survival generally reduced as concentrations increased, but monthly analyses show that growth was not significantly different between treatments. The differential treatment mortality may have enabled the surviving worms in the high concentration treatments to capture more food thus removing any concentration treatment effects for biomass. Using the alkaline comet assay we confirm that both metals via the sediment are genotoxic at concentrations routinely found in coastal regions and this is supported by elevated DNA damage in worms from field sites. However, combined with the growth data it also highlights the tolerance of A. virens to DNA damage. Finally, using long term (decadal) monitoring data we show stable or increasing sediment concentrations of these metals for many areas. This will potentially mean coastal sediment is a significant mutagenic hazard to the benthic community for decades to come. An urgent reappraisal of the current input sources for these 'old pollutants' is, therefore, required.

Bioaccumulation kinetics of copper in Ruditapes philippinarum exposed to increasing, continuous and pulsed exposure: Implications for growth

Metal bioaccumulation and toxicity to aquatic organisms depends on factors such as magnitude, duration and frequency of the exposure. The type of the exposure affects the toxicokinetic processes in the organisms. In this study, we carried out 30-day toxicity tests on juveniles of Ruditapes philippinarum exposed to increasing, continuous and pulsed exposure. Organisms were exposed to copper-spiked sediments followed by a 10-day recovery period. We assessed the interaction between the kinetics of subcellular copper partitioning and the growth response. Results showed that the growth rate of the bivalve was inversely correlated to the bioaccumulation rate and that sublethal copper concentrations stimulated the detoxification mechanisms inside the organism regardless the type of the exposure. However, a large stimulatory effect on growth was observed during the recovery period, associated with significant negative accumulation rate values and dependent on the type of antecedent exposure. This suggested that on individual and short-term basis pulsed exposures have a more adverse effect compared to increasing or continuous exposure scenarios.

Heavy metals in five Sabellidae species (Annelida, Polychaeta): ecological implications

The present work analyzed three hard-bottom and two soft-bottom species of sabellid polychaetes to determine the content of several heavy metals in their branchial crown and body. The highest concentrations of heavy metals were recorded in the hard-bottom species Branchiomma bairdi, a recent Mediterranean introduction. Differences in the metal concentrations were most notable in the high trace metal levels of the branchial crown for all the studied species. Statistical analysis showed that the Mediterranean hard-bottom species were similar each other in their heavy metal content in the body as well as in the branchial crown and appeared separated from all the other species. Arsenic and vanadium hyperaccumulation in the branchial crowns of the considered sabellid species probably acts as a deterrent for predation. The observed differences among the examined species were discussed not only at the light of habitat colonization but also in terms of the phylogeny.

Cadmium Bioaccumulation in Aquatic Oligochaetes Using a Biodynamic Model: A Review of Values of Physiological Parameters and Model Validation Using Laboratory and Field Bioaccumulation Data

This study reviews certain physiological digestive parameters in the literature that could be used to predict tissue residues in aquatic oligochaetes using the biodynamic model. Predictions were evaluated with independently measured Cd bioaccumulation data in sediment bioassays and field oligochaetes. The parameter review focused on three species commonly used in ecotoxicity testing and bioaccumulation studies: Tubifex tubifex (Tt), Limnodrilus hoffmeisteri (Lh) and Lumbriculus variegatus (Lv). Median Ingestion rates (g g^-1 d^-1, dw) at unpolluted conditions were 7.8 (Tt), 24.5 (Lh) and 11.5 (Lv), while results were lower (1.7-2.4) at polluted conditions. Assimilation efficiencies ranged from 3.4-19.6% (Tt), 2.7-16.1% (Lh), and 10.9-25.6% (Lv). The biodynamic model accurately predicted Cd tissue concentration in T. tubifex exposed to spiked sediments in laboratory bioassays. Comparisons of predicted vs. measured Cd tissue concentration in bioassays or field aquatic oligochaetes suggest that the biodynamic model can predict Cd tissue concentration within a factor of five in 81.3% of cases, across a range of measured tissue concentrations from 0.1 to 100 μg Cd g^-1 dw. Predictions can be refined by using physiological parameter values that have been measured under varying environmental conditions (e.g. temperature, dissolved oxygen). The model can underestimate tissue concentration by up to one order of magnitude when worms are exposed to highly contaminated sediments. Contrarily, predictions overestimate tissue concentration by up to two orders of magnitude when the measured Cd < 0.1 μg g^-1 dw, although in most cases these predictions do not fail bioaccumulation-based risk assessments, using a tissue threshold value of 1.5 μg Cd g^-1 dw.

The mismatch of bioaccumulated trace metals (Cu, Pb and Zn) in field and transplanted oysters (Saccostrea glomerata) to ambient surficial sediments and suspended particulate matter in a highly urbanised estuary (Sydney estuary, Australia)

A significant correlation between sedimentary metals, particularly the 'bio-available' fraction, and bioaccumulated metal concentrations in the native Sydney rock oyster (Saccostrea glomerata) tissues has been successfully demonstrated previously for Cu and Zn in a number of estuaries in New South Wales, Australia. However, this relationship has been difficult to establish in a highly modified estuary (Sydney estuary, Australia) where metal contamination is of greatest concern and where a significant relationship would be most useful for environmental monitoring. The use of the Sydney rock oyster as a biomonitoring tool for metal contamination was assessed in the present study by investigating relationships between metals attached to sediments and suspended particulate matter (SPM) to bioaccumulated concentrations in oyster tissues. Surficial sediments (both total and fine-fraction), SPM and wild oysters were collected over 3 years from three embayments (Chowder Bay, Mosman Bay and Iron Cove) with each embayment representing a different physiographic region of Sydney estuary. In addition, a transplant experiment of farmed oysters was conducted in the same embayments for 3 months. No relationship was observed between sediments or SPM metals (Cu, Pb and Zn) to tissue of wild oysters; however, significant relationship was observed against transplanted oysters. The mismatch between wild and farmed, transplanted oysters is perplexing and indicates that wild oysters are unsuitable to be used as a biomonitoring tool due to the involvement of unknown complex factors while transplanted oysters hold strong potential.

Metal bioavailability and bioaccumulation in the polychaete Nereis (Alitta) virens (Sars): The effects of site-specific sediment characteristics

The present study investigates the relationships between copper (Cu) and zinc (Zn) concentrations in sediment, pore water and their bioaccumulation in the polychaete Nereis (Alitta) virens, as well as the importance of site-specific sediment characteristics in that process. Sediment, pore water and N. virens were sampled from seven sites with different pollution histories along the English Channel coast. Results showed that site-specific metal levels and sediment characteristics were important in determining the bioavailability of metals to worms. Significant correlations were found between Cu in the sediment and in the pore water and between Zn in the pore water and in N. virens. Zn from the pore water was thus more readily available from a dissolved source to N. virens than Cu. Data also showed that metal concentrations in N. virens were lower than those found in other closely related polychaetes, indicating that it may regulate tissue concentrations of Cu and Zn.

Metal accumulation and toxicity: the critical accumulated concentration of metabolically available zinc in an oyster model

Invertebrates typically carry out detoxification of accumulated metals. There is, therefore, no threshold total body concentration of accumulated metal initiating toxicity, the onset of toxic effects rather being related to a critical concentration of metabolically available (MA) accumulated metal. The challenge remains as to whether any particular combination of subcellular fractions of accumulated metal can be identified to represent this theoretical MA component. One candidate combined fraction is the so-termed metal sensitive fraction (MSF), consisting of metal bound to organelles and non-detoxificatory soluble proteins. In this study, we used laboratory zinc accumulation and toxicity data for four populations of the oyster Crassostrea hongkongensis with different histories of zinc exposure in the field to address the challenge. We conclude that in a 'control' population of the oyster, the MSF does approximate to the theoretical metabolically available zinc concentration. In populations with a history of field exposure to raised zinc bioavailabilities, however, the MSF would include more zinc detoxified in the lysosome component of organelle-bound metal, and the MSF in such populations would deviate more from the theoretical MA metal concentration.

Toxicity and the fractional distribution of trace metals accumulated from contaminated sediments by the clam Scrobicularia plana exposed in the laboratory and the field

The relationship between the subcellular distribution of accumulated toxic metals into five operational fractions (subsequently combined into presumed detoxified and non-detoxified components) and toxicity in the clam Scrobicularia plana was investigated under different laboratory exposures. Clams were exposed to metal contaminated media (water and diet) and analysed for the partitioning of accumulated As, Cu and Zn into subcellular fractions. In general, metallothionein-like proteins, metal-rich granules and cellular debris in different proportions acted as main storage sites of accumulated metals in the clam soft tissues for these three metals. No significant differences were noted in the accumulation rates of As, Cu and Zn of groups of individuals with or without apparent signs of toxicity after up to 30 days of exposure to naturally contaminated sediment mixtures. There was, however, an increased proportional accumulation of Cu in the non-detoxified fraction with increased Cu accumulation rate in the clams, suggesting that the Cu uptake rate from contaminated sediments exceeded the combined rates of elimination and detoxification of Cu, with the subsequent likelihood for toxic effects in the clams.

Importance of subcellular metal partitioning and kinetics to predicting sublethal effects of copper in two deposit-feeding organisms

The role of subcellular partitioning of copper on the sublethal effects to two deposit-feeding organisms (41-day growth in the bivalve Tellina deltoidalis and 11-day reproduction in the amphipod Melita plumulosa) was assessed for copper-spiked sediments with different geochemical properties. Large differences in bioaccumulation and detoxification strategies were observed. The bivalve accumulated copper faster than the amphipod, and can be considered a relatively strong net bioaccumulator. The bivalve, however, appears to regulate the metabolically available fraction (MAF) of the total metal pool by increasing the net accumulation rate of copper in the biologically detoxified metal pool (BDM), where most of the copper is stored. In the amphipod, BDM concentration remained constant with increasing copper exposures and it can be considered a very weak net bioaccumulator of copper. This regulation of copper, with relatively little stored in detoxified forms, appears to best describe the strategy applied by the amphipod to minimize the potential toxic effects of copper. When the EC50 values for growth and reproduction are expressed based on the MAF of copper, the sensitivity of the two species appears similar, however when expressed based on the net accumulation rate of copper in the metabolically available fraction (MAFrate), the bivalve appears more sensitive to copper. These results indicate that describing the causality of metal effects in terms of kinetics of uptake, detoxification, and excretion rather than threshold metal body concentrations is more effective in predicting the toxic effects of copper. Although the expression of metal toxicity in terms of the rate at which the metal is bioaccumulated into metabolically available forms may not be feasible for routine assessments, a deeper understanding of uptake rates from all exposure routes may improve our ability to assess the risk posed by metal-contaminated sediments.

Sediment toxicity and bioaccumulation assessment in abandoned copper and mercury mining areas of the Nalón River basin (Spain)

Sediment toxicity and metal bioaccumulation were assessed at sites affected by historical copper (Cu) and mercury (Hg) mining activities in the Nalón River basin, Asturias, Spain. Toxicity assessment of stream sediments was based on a 28-day oligochaete Tubifex tubifex sediment bioassay, which allowed the classification of sites into three levels of toxicity: 11 sites were classified as nontoxic (including Cu mine sites), three sites as potentially toxic, and seven sites as toxic (all located in Hg mine districts). The greatest levels of arsenic (As), chromium, Hg, lead (Pb), and zinc (Zn) in T. tubifex were measured at sites affected by Hg mining and the highest Cu levels in tissues at Cu mining sites. Chronic toxicity responses were best explained by As and Hg sediment concentrations and by As, Pb, and Zn tissue residues. Residue levels of As, Hg, Zn, and Pb were successfully used to predict sediment chronic toxicity and estimate effective tissue residues.

Biodynamic modelling of the bioaccumulation of trace metals (Ag, As and Zn) by an infaunal estuarine invertebrate, the clam Scrobicularia plana

Biodynamic modelling was used to investigate the uptake and accumulation of three trace metals (Ag, As, Zn) by the deposit feeding estuarine bivalve mollusc Scrobicularia plana. Radioactive labelling techniques were used to quantify the rates of trace metal uptake (and subsequent elimination) from water and sediment diet. The uptake rate constant from solution (±SE) was greatest for Ag (3.954±0.375 l g(-1) d(-1)) followed by As (0.807±0.129 l g(-1) d(-1)) and Zn (0.103±0.016 l g(-1) d(-1)). Assimilation efficiencies from ingested sediment were 40.2±1.3% (Ag), 31.7±1.0% (Zn) and 25.3±0.9% (As). Efflux rate constants after exposure to metals in the solution or sediment fell in the range of 0.014-0.060 d(-1). By incorporating these physiological parameters into biodynamic models, our results showed that dissolved metal is the predominant source of accumulated Ag, As and Zn in S. plana, accounting for 66-99%, 50-97% and 52-98% of total accumulation of Ag, As and Zn, respectively, under different field exposure conditions. In general, model-predicted steady state concentrations of Ag, As and Zn matched well with those observed in clams collected in SW England estuaries. Our findings highlight the potential of biodynamic modelling to predict Ag, As and Zn accumulation in S. plana, taking into account specific dissolved and sediment concentrations of the metals at a particular field site, together with local water and sediment geochemistries.

Metal pollution in a contaminated bay: relationship between metal geochemical fractionation in sediments and accumulation in a polychaete

Jinzhou Bay in Northern China has been seriously contaminated with metals due to the impacts of smelting activities. In this study, we investigated the relationship between metal accumulation in a deposit-feeding polychaete Neanthes japonica and metal concentration and geochemical fractionation (Cd, Cu, Pb, Zn and Ni) in sediments of Jinzhou Bay. Compared with the historical data, metals in the more mobile geochemical fraction (exchangeable and carbonate fractions) were gradually partitioned into the more stable fraction (Fe-Mn oxides) over time. Metal concentration and geochemical fractionation in sediment significantly affected metal bioavailability and accumulation in polychaetes, except for Ni. Metal accumulation in polychaetes was significantly influenced by Fe or Mn content, and to a lesser degree by organic matter. Prediction of metal bioaccumulation in polychaetes was greatly improved by normalizing metal concentrations to Mn content in sediment. The geochemical fractionation of metals in sediments including the exchangeable, organic matter and Fe-Mn oxides were important in controlling the sediment metal bioavailability to polychaetes.

Dissolved and particulate copper exposure induces differing gene expression profiles and mechanisms of toxicity in the deposit feeding amphipod Melita plumulosa

Uptake of metals via ingestion is an important route of exposure for many invertebrates, and it has been suggested that the toxic response to metals accumulated via food differs from that of metals accumulated via the dissolved phase. To test this hypothesis, the deposit-feeding epibenthic amphipod Melita plumulosa was exposed to nontoxic or reproductively toxic concentrations of copper via the overlying water, via ingestion of sediment, or via a combination of the two. Rates of copper uptake from the two exposure routes were predicted using a biokinetic model. Gene expression profiles were measured via microarray analysis and confirmed via quantitative polymerase chain reaction. Differences in expression profiles were related to the exposure route more than to individual or combined rates of copper uptake. Chitinase and digestive protease transcript expression levels correlated to the copper uptake rate from sediment, rather than from the dissolved phase or combined total uptake rate. Overall, this study supports the hypothesis that metals accumulated via ingestion have a different mode of toxic action than metals taken up from water. Consequently, guidelines that only consider dissolved metal exposure, including equilibrium-partitioning-based guidelines, may underestimate the potential effects from deposited or resuspended metal-contaminated sediments.

An integrated use of multiple biomarkers to investigate the individual and combined effect of copper and cadmium on the marine green mussel (Perna viridis)

The present study documents individual and combined sub-lethal effect of one redox active (copper) and one non-redox active (cadmium) metal on green mussel (Perna viridis). The mussels were exposed to 60 μg L(-1) of Cu and 150 μg L(-1) of Cd (individually and in combination) for 21 days. Histopathological and ultrastructural studies revealed significant metal induced alterations such as vacuolization, fusion of gill lamellae, enhance mucous deposition, hyperplasia and necrosis in gills. Antioxidant enzyme assays revealed significant increase in superoxide dismutase (SOD), glutathione S-transferase (GST) and glutathione peroxidase (GPx) activity. Similarly, single exposure to Cd and Cu caused significant induction in Malate dehydrogenase (MDH) activity. However, combined Cu+Cd exposure modulated suppression in MDH activity. Unlike MDH, Cu and Cd individual exposure resulted in a decrease in esterase (EST) activity, but their combined exposure caused an induction. Non-enzymatic biomarkers such as lipid peroxidation (LPO) and metallothionein (MT) levels showed no significant change in response to Cu exposure, whereas, individual Cd exposure or Cd exposure in combination with Cu caused significant changes in their levels. Comet assay revealed a significant increase in DNA damage upon metal exposure. These results indicate that Cu (redox active) and Cd (non-redox active) can induce measurable physiological, biochemical as well as genotoxic perturbations in mussels even at sub-lethal concentrations. A monitoring programme based on the biomarkers discussed here would be useful to study the effect of metal pollutants reaching the coastal waters.

Toxicity and critical body residues of Cd, Cu and Cr in the aquatic oligochaete Tubifex tubifex (Müller) based on lethal and sublethal effects

The aim of the present study was to estimate critical body residues (CBRs) of three metals [cadmium (Cd), copper (Cu), chromium (Cr)] in the aquatic oligochaete Tubifex tubifex based on lethal (LBR) and sublethal effects (CBR), and to discuss the relevance of the exposure to sediment for deriving CBR. Toxicity parameters (LC50, EC50, LBR50 and CBR50) were estimated for each metal by means of data on survival and on several sublethal variables measured in short-term (4 days), water-only exposures and in long-term, chronic (14 and 28 days) exposures using metal-spiked sediment. Sublethal endpoints included autotomy in short-term exposure, as well as reproduction and growth in chronic bioassays. LBR50 and CBR50 were 3-6 times higher in sediment than in water-only exposure to Cd and about 2-11 times higher for Cu, depending on the measured endpoint; however, for Cr these parameters varied only by a factor of 1.2. Cu and Cr LBR50 and CBR50 values in 96 h water-only exposure were very similar (survival 2.39 μmol Cu g(-1) dw, 2.73 μmol Cr g(-1) dw; autotomy 0.53 μmol Cu g(-1) dw, 0.78 μmol Cr g(-1) dw). However, in metal-spiked sediments, 28 d CBR50 values for autotomy, reproduction and growth ranged 6.76-29.54 μmol g(-1) dw for Cd, 3.88-6.23 μmol g(-1) dw for Cu, 0.65 μmol g(-1) dw for Cr (calculated only on total number of young). Exposure conditions (time and presence/absence of sediment) seem to be influential in deriving metal CBR values of Cd and Cu, while appear to be irrelevant for Cr. Thus, CBR approach for metals is complex and tissue residue-toxicity relationship is not directly applicable so far.

Incorporating bioavailability into management limits for copper in sediments contaminated by antifouling paint used in aquaculture

Although now well embedded within many risk-based sediment quality guideline (SQG) frameworks, contaminant bioavailability is still often overlooked in assessment and management of contaminated sediments. To optimise management limits for metal contaminated sediments, we assess the appropriateness of a range methods for modifying SQGs based on bioavailability considerations. The impairment of reproduction of the amphipod, Melita plumulosa, and harpacticoid copepod, Nitocra spinipes, was assessed for sediments contaminated with copper from antifouling paint, located below aquaculture cages. The measurement of dilute acid-extractable copper (AE-Cu) was found to provide the most useful means for monitoring the risks posed by sediment copper and setting management limits. Acid-volatile sulfide was found to be ineffective as a SQG-modifying factor as these organisms live mostly at the more oxidised sediment water interface. SQGs normalised to %-silt/organic carbon were effective, but the benefits gained were too small to justify this approach. The effectiveness of SQGs based on AE-Cu was attributed to a small portion of the total copper being present in potentially bioavailable forms (typically<10% of the total). Much of the non-bioavailable form of copper was likely present as paint flakes in the form of copper (I) oxide, the active ingredient of the antifoulant formulation. While the concentrations of paint-associated copper are very high in some sediments, as the transformation of this form of copper to AE-Cu appears slow, monitoring and management limits should assess the more bioavailable AE-Cu forms, and further efforts be made to limit the release of paint particles into the environment.

Demonstrating the appropriateness of developing sediment quality guidelines based on sediment geochemical properties

The pool of bioavailable metals in sediments is typically much smaller than the total metal concentration and is strongly influenced by metal-binding with acid-volatile sulfide (AVS), particulate organic carbon (OC), and iron and manganese oxide solid phases. We have investigated how the properties of relatively oxidized sediments influence the exposure and effects of copper on the survival and growth rate of the deposit-feeding benthic bivalve Tellina deltoidalis. Growth rate was a much more sensitive end point than survival. Toxic effects to growth were consistently observed in sediment where both pore water and overlying water copper concentrations were below the effect threshold for dissolved copper. Decreases in growth of the bivalve were largely attributable to dietary exposure to sediment-bound copper, as the organism was observed to actively feed on fine materials from the sediment surface. For sediments with the same total copper concentrations, effects were less for sediments with greater concentrations of fine particles (<63 μm sediment) or particulate organic carbon (OC). Based on the concentration-response relationship, a no-effect value of 5.5 mg <63 μm Cu g(-1) OC for growth of T. deltoidalis was calculated. The results confirm the appropriateness of using OC-normalized copper concentration in the <63 μm sediment fraction to develop sediment quality guidelines (SQGs) that vary with sediment properties. For sediments where the amount of AVS is not sufficient to bind metals in non bioavailable forms, the metal-binding capacity provided by OC and iron and manganese oxyhydroxides associated with the fine sediments considerably reduced metal bioavailability. These sediment properties should be considered when assessing the risks posed by metal-contaminated sediments.

Inter-site differences of zinc susceptibility of the oyster Crassostrea hongkongensis

Understanding the underlying mechanisms governing metal toxicity is crucial for predicting the risks and effects of metal pollutants. We hypothesized that metal toxicity is related to a threshold concentration of metabolically available metal but not to the total body metal concentration. Following a two-month laboratory Zn exposure, we characterized mortality and Zn bioaccumulation and subcellular partitioning in the oyster Crassostrea hongkongensis sampled from three sites with contrasting histories of Zn exposure and one multiple-metal contaminated site. Large differences in Zn sensitivity, lethal body concentration, and detoxification capability between sites were observed. Specifically, the oysters from the highly Zn-contaminated site were more tolerant to Zn exposure than those from the relatively clean ones, and the former accumulated and detoxified more Zn and had a significantly higher lethal body Zn concentration. The accumulation of Zn in the metabolically available pool (operationally defined as the metal-sensitive fraction) in the oysters from the multiple-metal contaminated site was relatively fast, and correspondingly they were highly sensitive to Zn exposure. The lethal threshold concentration of total body Zn varied significantly within the four sites, and thus total body Zn concentration could not serve as a suitable toxicity indicator. Importantly, Zn accumulation within the operationally defined metabolically available pool better explained variances in mortality than Zn accumulation in the whole body. Our results suggested that Zn toxicity is governed by its accumulation in the metabolically available pool, not the total accumulated Zn concentration.

Two-compartment toxicokinetic-toxicodynamic model to predict metal toxicity in Daphnia magna

Relating the toxicity of metals to their internal concentration is difficult due to complicated detoxification processes within organisms. Only the metabolically available metals are potentially toxic to organisms, while metals in the detoxified form are toxicologically irrelevant. Accordingly, we developed a two-compartment toxicokinetic-toxicodynamic model for metals in a freshwater cladoceran, Daphnia magna. The toxicokinetics simulated the bioaccumulation processes, while the toxicodynamics quantitatively described the corresponding processes of toxicity development. Model parameters were estimated for D. magna and three metals, i.e., cadmium, zinc, and mercury, by fitting the literature data on metal bioaccumulation and toxicity. A range of crucial information for toxicity prediction can be readily derived from the model, including detoxification rate, no-effect concentration, threshold influx rate for toxicity, and maximum duration without toxicity. This process-based model is flexible and can help improve ecological risk assessments for metals.

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.

Sub-lethal effects of copper to benthic invertebrates explained by sediment properties and dietary exposure

The next generation of sediment quality guidelines (SQGs) requires better established causal links between the chronic exposure and effects of metals from both dissolved and dietary sources. The potential for dietary exposure from sediment metals to cause toxic effects to benthic invertebrates is strongly influenced by the metal-binding properties of the sediments. For relatively oxidized sediments, sublethal effects of copper to the epibenthic deposit-feeding amphipod, Melita plumulosa, and the benthic harpacticoid copepod, Nitocra spinipes, were investigated. Effects on reproduction were strongly influenced by the properties of the sediments and sediment-bound copper was found to be the major contribution to the toxicity. For sediments with the same total copper concentrations, effects were less for sediments with greater concentrations of fine particles (<63 μm sediment) or particulate organic carbon (OC). The OC-normalized copper concentration in the <63 μm sediment fraction provided a single effects threshold for all sediment types. For M. plumulosa and N. spinipes, the 10% effect concentrations (EC10s) were 5.2 and 4.8 mg <63 μm Cu g(-1) OC. These chronic EC10s indicate that a SQG of 3.5 mg <63 μm Cu g(-1) OC, that was previously proposed based on a species sensitivity distribution of acute no effects thresholds data for 12 benthic organisms, will be protective for these species. The study confirms the appropriateness of using SQGs that vary with sediment properties and that SQGs of this form provide adequate protection for metal exposure via both dissolved and dietary exposure pathways.

The impact of increased oxygen conditions on metal-contaminated sediments part II: effects on metal accumulation and toxicity in aquatic invertebrates

The present study evaluated the effect of increasing oxygen concentrations in overlying surface water on the accumulation and toxicity of sediment-bound metals in the aquatic invertebrates Lumbriculus variegatus, Asellus aquaticus and Daphnia magna. A 54 days experiment using three experimental treatments (90% O(2) in overlying surface water, 40% O(2) and a non-polluted control) was conducted. At 6 different time points (after 0, 2, 5, 12, 32 and 54 days) acid volatile sulfides (AVS), simultaneously extracted metals (SEM) and total organic carbon (TOC) were measured in the superficial sediment layer (0-1 cm). At each time point, accumulated metal levels as well as the available energy stores were measured in L. variegatus and A. aquaticus and each time D. magna was exposed to surface water in a 24 h toxicity test. Additionally metallothionein-like protein (MTLP) induction was quantified in L. variegatus. Oxygen induced changes in sediment AVS resulted in faster accumulation of metals from contaminated sediments in A. aquaticus, while no differences in toxicity in this species were observed. Ag, Cr, As and Co accumulation as well as toxicity in water exposed D. magna were clearly enhanced after 54 days, caused by oxidation of metal-sulfide complexes. Due to their feeding and burrowing behaviour, metal accumulation and toxicity in L. variegatus was not influenced by geochemical characteristics. Nevertheless, a rapid induction of MTLP was observed in both the 90% O(2) and the 40% O(2) treatment. The present study showed that elevated oxygen concentrations in overlying surface water can directly enhance metal accumulation and toxicity in aquatic invertebrates, however this is highly dependent on the organisms ecology and most dominant metal exposure route (water vs. sediment).

Arsenic toxicity in a sediment-dwelling polychaete: detoxification and arsenic metabolism

The accumulation, subcellular distribution and speciation of arsenic in the polychaete Arenicola marina were investigated under different laboratory exposure conditions representing a range of metal bioavailabilities, to gain an insight into the physiological mechanisms of how A. marina handles bioaccumulated arsenic and to improve our understanding of the potential ecotoxicological significance of bioaccumulated arsenic in this deposit-feeder. The exposure conditions included exposure to sublethal concentrations of dissolved arsenate, exposure to sublethal concentrations of sediment-bound metal mining mixtures, and exposure to lethal concentrations of sediment-bound metal mining mixtures and arsenic- and multiple metal-spiked sediments. The sub-lethal exposures indicate that arsenic bioaccumulated by the deposit-feeding polychaete A. marina is stored in the cytosol as heat stable proteins (~50%) including metallothioneins, possibly as As (III)-thiol complexes. The remaining arsenic is mainly accumulated in the fraction containing cellular debris (~20%), with decreasing proportions accumulated in the metal-rich granules, organelles and heat-sensitive proteins fractions. A biological detoxified metal compartment including heat stable proteins and the fraction containing metal-rich granules is capable of binding arsenic coming into the cells at a constant rate under sublethal arsenic bioavailabilities. The remaining arsenic entering the cell is bound loosely into the cellular debris fraction, which can be subsequently released and diverted to an expanding detoxified pool. Our results suggest that a metal sensitive compartment comprising the cellular debris, enzymes and organelles fractions may be more representative of the toxic effects observed.

Bioaccumulation and effects of metals bound to sediments collected from Gulf of Cádiz (SW Spain) using the polychaete Arenicola marina

A short-term whole-sediment test using the polychaete Arenicola marina was conducted under laboratory conditions to assess the bioavailability of metals bound to sediments collected from 12 sites of the Gulf of Cádiz. To achieve this objective, the rate of increase of metal bioaccumulation and the induction of a typical biomarker, metallothioneinlike proteins (MTLPs) were determined. Results of the multivariate analysis showed associated metal-rich sediments, increased rate of Cu and Zn accumulations, but lower toxicity with an increased MTLP induction, whereas sedimentary Ni and Co concentrations were related to higher toxicity to lugworms, although it might be caused by other contaminants present in these sediments. The linear kinetic approach was shown to be valid in certain circumstances, but more validation studies of this parameter are required before it can be recommended for use in evaluating metal bioavailability in sediments.

Guidelines for copper in sediments with varying properties

A major weakness of sediment quality guidelines (SQGs) is their poor ability to predict how toxicity thresholds change for different sediment types. Using species sensitivity distributions (SSDs) of copper effects data, new guidelines were derived for copper in non-sulfidic marine sediments in which organic carbon (OC) and particle size strongly influence copper bioavailability. The derived SQGs varied in a predictable manner with changes in sediment particle size and organic carbon (OC), and were shown to offer a significant improvement on the existing 'single value' SQG. Adequate protection for all benthic organisms is expected to be achieved for a OC-normalised copper concentration of 3.5 mg Cu g(-1) OC in the <63 μm sediment fraction. For short-term exposures, the equivalent acute guideline is 11 mg<63 μm Cu g(-1) OC. The new SQGs incorporate a high degree of conservatism owing to the use of copper-spiked sediments and laboratory-based bioassays that were expected to result in greater metal exposure of organisms to bioavailable copper than would be expected for field-contaminated sediments with similar total copper concentrations. SQGs that vary with sediment properties were prepared in an easily referenced tabular format.

Metal toxicity, uptake and bioaccumulation in aquatic invertebrates--modelling zinc in crustaceans

We use published data on the different patterns of the bioaccumulation of zinc by three crustaceans, the caridean decapod Palaemon elegans, the amphipod Orchestia gammarellus and the barnacle Amphibalanus amphitrite, to construct comparative biodynamic models of the bioaccumulation of zinc into metabolically available and detoxified components of accumulated zinc in each crustacean under both field and laboratory toxicity test conditions. We then link these bioaccumulation models to the onset of toxic effects on exposure of the crustaceans to high dissolved zinc bioavailabilities, using the tenets that toxicity effects are related to the total uptake rate of the toxic metal, and that toxicity is not usually dependent on the total accumulated metal concentration but always on the concentration of accumulated metal that is metabolically available. We dismiss the general concept that there is a critical accumulated body concentration of a metal in an invertebrate at which toxicity ensues, except under specific circumstances involving a rare lack of storage detoxification of accumulated metal. We thus propose a theoretical framework that can be extended to other metals and other aquatic invertebrates (indeed other animals) to explain the variation in the relationship between bioaccumulated body concentrations and toxicity, and subsequently to predict this relationship in many other species for which we have bioaccumulation modelling data.

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.