Partitioning and Speciation of Metals in Storm Water Runoff from Commercial Infrastructures

Since 2005, a monitoring program was carried out to characterize stormwater runoff quality in port industry and airport areas in the Liguria Region of Italy. The instrumented catchments were monitored for hydrology, chemistry and particulate loads. Results demonstrate the importance of the pollutant load from paved surfaces of commercial ports and airports when compared with other urban land use areas: total concentration of zinc, copper and lead may reach the order of magnitude of 1 mg/L, higher than concentrations documented for highway runoff. In particular, the study aims at assessing the potential toxicity of metals on the aquatic ecosystems in order to evaluate the most effective BMPs to integrate in the stormwater drainage systems. Therefore the partitioning of metals between the dissolved and particulate-bound fractions and the speciation of their dissolved fraction in storm runoff are examined in this paper. The dissolved metal fraction fd and the equilibrium partitioning coefficient kd are evaluated for various monitored events. The thermodynamic equilibrium model MINTEQ is used to determine the distribution between the various species and its evolution during the rainfall-runoff event, thus relating the hydrological aspects and the specific environmental conditions to the dominant species of zinc, copper and lead.