Towards a tiered framework for an ecotoxicological hazard assessment of fluvial sediments - presentation and early tests

Sediments are an essential component of fluvial ecosystems. They are also quite often a cause of disturbance for fluvial works, such as dams or locks. In order to manage these disturbances without causing adverse impacts downstream, managers should have in hand an efficient assessment framework. The DIESE project (tools for sediment ecotoxicity assessment) aimed to elaborate and test a tiered assessment framework for freshwater sediment sites. We present hereafter the proposed framework, and a pilot test on 17 sites. Basically, the framework intends to provide answers to 2 questions, namely (a) does the sediment contamination present a hazard to benthic invertebrates, and (b) if bioaccumulative/biomagnified contaminants are present, is their concentration worrying? The assessment process can end at any tier, provided the data are conclusive. Sediment quality benchmarks or contamination indices were used to interpret chemical analyses; this assessment was then compared to the results of ecotoxicity tests. Overall, the framework appears consistent; this test also helped selecting the best options for interpretation. Nevertheless, the test included only 17 sites, with a limited array of contaminants; complementary tests including more organic contaminants at a wider range of concentrations would help to demonstrate the validity of this assessment framework.