BSAFs for freshwater fish and derivation of a sediment quality guideline for PCBs in the Rhone basin, France

International audiencePurpose Since 2005, freshwater fish contamination by polychlorobiphenyls (PCBs), polychlorodibenzodioxins, and polychlorodibenzofurans has been assessed in the Rhone River basin (France). A large database of surface sediment contamination by PCBs is also available, opening the way to the study of biota-to-sediment accumulation factor (BSAF) distribution throughout this basin. The ultimate goal of the study was to determine a sediment quality guideline (SQG) corresponding to the regulatory fish consumption limit. Materials and methods A bootstrapping procedure for determining BSAFs was applied to a data set matching the available databases of sediment and fish contamination by PCBs in the Rhone River basin. The SQG was obtained by combining the current tissue-based regulatory threshold with a characteristic BSAF value, for a species particularly prone to accumulating these compounds. As the current regulatory threshold refers to dioxins and related com- pounds, while most available sediment data deal with non- dioxin-like PCBs, a set of correlations was used to derive an SQG for the sum of seven indicator PCBs. To assess the reliability of these SQG pairs, actual fish and sediment concentrations were classified into four categories, accord- ing to a comparison with the regulatory threshold for fish data and the calculated SQG. Results and discussion BSAFs were determined for 11 species. The barbel and European eel had the highest BSAFs. The common carp, a benthic species, had surpris- ingly low BSAFs, as low as pelagic and omnivorous species such as chub. The data set was also split into two parts, one comprising fish samples at or above the regulatory limit and the other samples below this threshold. Sediment concentrations and BSAFs were higher in the former group. An SQG was derived on the basis of the 75th percentile of barbel's BSAF, equaling 26.6 ng g−1 dry weight (range 15.6-38.6 ng g−1) for the sum of seven indicator PCBs. When tested against the same database, this SQG displayed an overall efficiency of about 60% resulting from the limited reliability of sediment data and the factors influencing PCB bioavailability. Conclusions From the perspective of regulatory frame- works such as the European Water Framework Directive, a tiered monitoring strategy combining sediments (first tier) and biota (second tier) could be more relevant than a single- compartment approach. In this context, an SQG such as the one determined herein would trigger the second tier