Stormwater retention basin efficiency regarding micropollutant loads and ecotoxicity

Retention basin efficiency in micropollutant removal has not been very well studied, in particular for pollutants highlighted by the European Water Framework Directive of 2000 such as pesticides, polybrominated diphenyl ethers (PBDEs) and alkylphenols. This study is based on in situ experiments carried out on a stormwater retention basin with the aim of estimating the basin efficiency in trapping and removing micropollutants from stormwater run-off from an industrial catchment drained by a separate sewer system. Along with stormwater, the basin receives some dry weather effluent flows, which are supposedly non-polluted. Ninety-four substances from five families (metals, polycyclic aromatic hydrocarbons (PAHs), PBDEs, alkylphenols and pesticides) were analyzed during 10 event campaigns in urban wet weather discharges at the inlet and outlet of the basin. The ecotoxicity of the samples was also tested. The results show high inter-event variability in both chemical and ecotoxic characteristics. They indicate good event efficiency concerning heavy metals and most PAHs. The studied pesticides, mainly found in the dissolved fraction, were not trapped. Particulate fraction study highlighted that settling is not the main process explaining micropollutant removal in a retention basin, as was noted for alkylphenols and PBDEs.