Assessment of ecotoxicological risks related to depositing dredged materials from canals in northern France on soil.

The implementation of an ecological risk assessment framework is presented for dredged material deposits on soil close to a canal and groundwater, and tested with sediment samples from canals in northern France. This framework includes two steps: a simplified risk assessment based on contaminant concentrations and a detailed risk assessment based on toxicity bioassays and column leaching tests. The tested framework includes three related assumptions: (a) effects on plants (Lolium perenne L.), (b) effects on aquatic organisms (Escherichia coli, Pseudokirchneriella subcapitata, Ceriodaphnia dubia, and Xenopus laevis) and (c) effects on groundwater contamination. Several exposure conditions were tested using standardised bioassays. According to the specific dredged material tested, the three assumptions were more or less discriminatory, soil and groundwater pollution being the most sensitive. Several aspects of the assessment procedure must now be improved, in particular assessment endpoint design for risks to ecosystems (e.g., integration of pollutant bioaccumulation), bioassay protocols and column leaching test design.

Characterizing the risks to aquatic ecosystems: a tentative approach in the context of freshwater dredged material disposal.

The development of relevant frameworks for assessing ecological risks posed by dredged material management does not only involve an appropriate selection of assessment and measurement endpoints but also requires a sound approach to both risk characterization and the associated uncertainty. A formal methodology addressing both aspects has been developed in France for freshwater sediment deposits in water. Both exposure and effects measurements are 1st transformed into scores or classes. As far as possible, class boundaries are based on existing knowledge or expertise. Benthic organism exposure is based on a ratio of the deposit area to the burrow pit area, whereas pelagic species exposure is based on the ratio of porewater volume to water column volume. The combination of exposure and effect scores yields risk scores, or classes, which are linked to management decisions. Uncertainty is assessed with respect to a set of 4 predetermined criteria for exposure (the strength of association with the assessment endpoint, spatial and temporal representativeness, and the use of standard methods) and 4 criteria for effects (strength of association, the distinction between effect and no effect, sensitivity, and the use of standard methods). This approach was applied to 8 sediments from French canals contaminated to varying degrees.