Experimental and modelling studies to identify bioavailable contaminant concentrations and bioavailability : towards the definition of a general scale for thresholds calculation

The increasing worldwide contamination of aquatic ecosystems with thousands of industrial chemical compounds is one of the key environmental problems today. However, chemicals present in the water column or sediments are not totally bioavailable to the aquatic organisms. Chemical compounds are distributed among all phases in environmental systems and, therefore, they can be buried in a media that does not allow direct transfer to the organism. In this situation, the total concentration is normally not the right value for assessing which will be the risks of a certain pollutant. In fact, only the part of the concentration that can be taken up by the biota represents a real risk for the ecosystem and the human health. Therefore, environmental legislation should be based on the concept of bioavailability; this will provide effective health protection and avoid unnecessary economic pressures. In this report, simulated results as well as experimental campaigns have been summarized with the aim of providing a comprehensive study on bioavality for POPs and metals. A comprehensive modeling approach has been developed to assess bioconcentration factors for several families of POPs. This approach is quite general and aims at developing a scale between total concentration in the water column and bioavailable concentration as a function of physicochemical properties of a compound. However, in order to develop further the approach, the experimental data obtained from Thresholds-1 and Thresholds-2 Mediterranean campaigns should be included in the study as well as the results provided by the Thau lagoon study. With this information, validation of the model and assessment of the preliminary results obtained in this deliverable will be possible. These open questions will be explored in a companion report when the Thau modeling case study will be developed and experimental data on POPs concentrations in biota would be available. The bioavailability of dissolved trace metals in the water column depends on their speciation, which in turn depends on several physico-chemical parameters (e.g. T, pH, redox, etc.). However, up to know no general tool is available to evaluate trace metal bioavailability to aquatic organisms. We expect that the experimental measurements carried out at Thau lagoon for Cd and Hg will help in the development of such as tool.