Applicability of sediment quality standard derived using standardized equilibrium partitioning method for the assessment of water bodies' status

International audienceIn the implementation of the Water Framework Directive, quality standards (QS) may be derived in the most appropriate matrix, including sediment for e.g. hydrophobic substances which are barely detected in water. The EU Technical Guidance Document on EQS (TGD) recommends in certain circumstances to apply the equilibrium partitioning (EqP) method to derive a standard in sediment based on the standard derived in water. The TGD provides default values, in particular for Total Organic Carbon (TOC) content. This method is generally believed to be rather protective, except for highly hydrophobic compounds for which an additional factor has to be applied. This method was applied at national level in order to allow the derivation of QSsed for a large number of chemical to be investigated in an exceptional survey in which 85 chemicals were analyzed at about 110 sampling points together with TOC. The selection of chemicals to be investigated in sediment took place within a larger priorisation exercise among 2400 compounds considered as potential candidate substances; of which more than 400 are pharmaceuticals and associated metabolites, and about 70 are chemicals used in personal care and household products. The rest are mainly pesticides, biocides and industrial chemicals. The results of the monitoring campaign contributed to the selection of substances to be integrated in the monitoring programmes of the water agencies in the various river basins. Substances for which a risk of degradation of the quality of the water body was identified were prioritised. This risk was calculated using EqP method with both default and site specific values for TOC. The results show that for a significant number of stations, the estimation of the risk may be different depending of the use of default or site specific TOC. This result is substance-dependant. In addition, for those sampling sites with a TOC profile which differ significantly from the default EU sediment, the overall estimated risk is evidently more impacted. It is also to be noted that default values proposed in the TGD for the application of the EqP method at EU level are not protective in a majority of the stations investigated in this campaign. In order to increase the understanding of in situ toxicity, TOC as an indication of bioavailability is used to interpret the differences observed between the so-called chemical status and biological status based on biological indicators determined on the same sampling sites