Final Report Summary - BIOSCROBE (Biodynamic modelling of compartmentalised bioaccumulation of toxic metals by the clam Scrobicularia plana in European estuaries)
The biological explanation of the ecotoxicity of metals in estuarine sediments
The central objective of the BIOSCROBE project was to provide a scientific basis for the prediction of the ecotoxicity of toxic metals to local biodiversity in sediments of European estuaries subject to anthropogenic contamination. Estuarine sediments are sinks for toxic metals and other contaminants en route to the marine environment from rivers draining industrialised catchments. When these sediments are ingested by deposit feeding invertebrates, toxic metals associated with the sediments have the potential to be assimilated and taken up into the body of the invertebrate concerned. Such an invertebrate is the widespread intertidal estuarine clam Scrobicularia plana, often described as a keystone species given its importance in the ecology of European estuaries. Not only do sediment-associated metals offer a potential ecotoxicological threat to the clam itself, but toxic metals accumulated by the clam have the potential to be passed onto its predators such as estuarine fish or wading birds for which estuaries are prime feeding grounds. This trophic transfer of the metals up food chains offers a further potential ecotoxicological threat to such vertebrate consumers so important from the viewpoints of ecology, fisheries and biodiversity conservation. It is important then to understand how the uptake of toxic metals and their subsequent accumulation by the clam are linked to their ecotoxicity, in the knowledge that invertebrates like S. plana can store bioaccumulated metals in detoxified form without apparent toxic effect. Therefore, this project focused on the use of biodynamics to model the bioaccumulation of the non-detoxified component of accumulated toxic metals by the infaunal benthic invertebrate Scrobicularia plana, in an attempt to explain the links between trace metal uptake, accumulation and ecotoxicity in such an important estuarine species.
The biodynamic model was successfully used to determine the relative importance of uptake routes of Ag, As and Zn, and to predict accumulated concentrations of these metals in populations of S. plana living in selected metal-contaminated UK estuaries. The model also showed that both water and sediment are significant routes of exposure for the three metals, their relative importance varying with the specific dissolved and sediment concentrations of the metals at each site and with local water and sediment geochemistries.
It is becoming more generally accepted that toxicity cannot be directly linked to a critical total body accumulated metal concentration. Toxicity can occur at any total body concentration if the rate of uptake of the trace metal is faster than the rate of its excretion and detoxification combined. In this case the metal builds up in the metabolically available component and results in toxicity. Clams exposed to toxic field-collected sediments in the laboratory showed a tendency to accumulate As, Cu and Zn over the exposure period, these metals being those primarily responsible for ecotoxicity in the estuarine sediments selected. An aim of the project was to describe the partitioning of accumulated As, Cu and Zn into the subcellular fractions within the body. The results showed a continuous increase of Cu bioaccumulation with time in the non-detoxified fraction (including organelles, enzymes and cellular debris), suggesting that the rate of Cu uptake was so high from particular Cu-contaminated sediments that the newly entering Cu could not be sequestered by metallothioneins and metal-rich granules (the detoxified compartment) with the subsequent likelihood for toxic effects in the clam. Results also showed how other trace metals were taken up from metal-rich sediments and accumulated by the clams over time with different proportions in different subcellular fractions, with different consequences for the trophic availability of these bioaccumulated metals to vertebrate predators.
The European Community has a strong interest in modelling trace metal accumulation and the subsequent adverse effects on aquatic organisms that need to be considered in metal risk assessment. This IEF project provides a new mechanism-based model of the monitoring the onset of ecotoxicity, and thereby contributes to the application of scientific principles to the toxic metal risk assessment of metal-contaminated estuarine sediments.
The central objective of the BIOSCROBE project was to provide a scientific basis for the prediction of the ecotoxicity of toxic metals to local biodiversity in sediments of European estuaries subject to anthropogenic contamination. Estuarine sediments are sinks for toxic metals and other contaminants en route to the marine environment from rivers draining industrialised catchments. When these sediments are ingested by deposit feeding invertebrates, toxic metals associated with the sediments have the potential to be assimilated and taken up into the body of the invertebrate concerned. Such an invertebrate is the widespread intertidal estuarine clam Scrobicularia plana, often described as a keystone species given its importance in the ecology of European estuaries. Not only do sediment-associated metals offer a potential ecotoxicological threat to the clam itself, but toxic metals accumulated by the clam have the potential to be passed onto its predators such as estuarine fish or wading birds for which estuaries are prime feeding grounds. This trophic transfer of the metals up food chains offers a further potential ecotoxicological threat to such vertebrate consumers so important from the viewpoints of ecology, fisheries and biodiversity conservation. It is important then to understand how the uptake of toxic metals and their subsequent accumulation by the clam are linked to their ecotoxicity, in the knowledge that invertebrates like S. plana can store bioaccumulated metals in detoxified form without apparent toxic effect. Therefore, this project focused on the use of biodynamics to model the bioaccumulation of the non-detoxified component of accumulated toxic metals by the infaunal benthic invertebrate Scrobicularia plana, in an attempt to explain the links between trace metal uptake, accumulation and ecotoxicity in such an important estuarine species.
The biodynamic model was successfully used to determine the relative importance of uptake routes of Ag, As and Zn, and to predict accumulated concentrations of these metals in populations of S. plana living in selected metal-contaminated UK estuaries. The model also showed that both water and sediment are significant routes of exposure for the three metals, their relative importance varying with the specific dissolved and sediment concentrations of the metals at each site and with local water and sediment geochemistries.
It is becoming more generally accepted that toxicity cannot be directly linked to a critical total body accumulated metal concentration. Toxicity can occur at any total body concentration if the rate of uptake of the trace metal is faster than the rate of its excretion and detoxification combined. In this case the metal builds up in the metabolically available component and results in toxicity. Clams exposed to toxic field-collected sediments in the laboratory showed a tendency to accumulate As, Cu and Zn over the exposure period, these metals being those primarily responsible for ecotoxicity in the estuarine sediments selected. An aim of the project was to describe the partitioning of accumulated As, Cu and Zn into the subcellular fractions within the body. The results showed a continuous increase of Cu bioaccumulation with time in the non-detoxified fraction (including organelles, enzymes and cellular debris), suggesting that the rate of Cu uptake was so high from particular Cu-contaminated sediments that the newly entering Cu could not be sequestered by metallothioneins and metal-rich granules (the detoxified compartment) with the subsequent likelihood for toxic effects in the clam. Results also showed how other trace metals were taken up from metal-rich sediments and accumulated by the clams over time with different proportions in different subcellular fractions, with different consequences for the trophic availability of these bioaccumulated metals to vertebrate predators.
The European Community has a strong interest in modelling trace metal accumulation and the subsequent adverse effects on aquatic organisms that need to be considered in metal risk assessment. This IEF project provides a new mechanism-based model of the monitoring the onset of ecotoxicity, and thereby contributes to the application of scientific principles to the toxic metal risk assessment of metal-contaminated estuarine sediments.