Ecotoxicological assessment of pollutant flux released from bottom ash reused in road construction

Two approaches have been used to assess the impact of municipal solid waste incineration bottom ash on lentic ecosystems, especially lake coastlines. One of the aims of this study was to complete the methodology for the assessment of waste ecocompatibility by assessing a scenario in which bottom ashes are reused as road embankment. A laboratory lysimeter was chosen to simulate the road embankment and produce the bottom ash leachate. The first approach was based on three bioassays. Results led to the following ranking of these bioassays based on organisms sensitivity, in descending order: algae Pseudokirchneriella subcapitata > duckweed Lemna minor > cladoceran Daphnia magna. At the same time, leachates were assessed with a 2 litre freshwater/sediment microcosm. All species were impaired. Toxicity effects increased with leachate concentration, from 1.56% to 8.0%. Comparison between bioassays and microcosm assays revealed that the representativeness is higher in the multispecies systems. Finally, bottom ashes have been assessed in a simplified risk assessment procedure. Predicted environmental concentration is close to the concentration that caused first effects in microcosms. Recommendations are made for the reuse of bottom ashes as road embankment.