Use of sediment quality guidelines in ecological risk assessment of dredged materials: Preliminary reflections

Ecological risk assessment appears as an useful approach for dredged materials. It is often proposed in the form of a tiered approach, the first tier relying upon a chemical characterisation of sediments, and a simplified risk assessment based on sediment quality guidelines. A recently proposed tiered framework, relying upon published sediment quality guidelines and a mean quotient approach at the first tier, is tested against two databases: one including bioassays results and chemicals concentrations of contaminated and non-contaminated sediments; and the second chemical concentrations in sediments from two French regions. The selected sediment quality guidelines seem reliable, as the incidence of type I and type II errors remain in accordance with their definitions. However, the relevance of this statement is somewhat limited by the size of the database used. Moreover, geochemistry may play a confusing role for some metals like Ni and Cr. The cut-off values initially proposed for the first tier appear questionable: the lower boundary allows discarding of a low proportion of sediment samples in the chemicals only database, and toxicity may be observed below this value. Conversely, the upper boundary value may be considered as too low, as a significant proportion of non-toxic samples may be observed above this value, and as a large number of sites in the chemicals only database would enter higher tiers of the framework. Further tests and development are needed with an extended database.