TRANSPORT OF METALS IN STORM WATER RUNOFF

This paper focuses on the urban environment and investigates the interactions between hydrologic processes and the production of pollutants in storm runoff. Experimental data for this study were obtained during a monitoring campaign carried out to characterise storm-water runoff quality from impervious surfaces that are subject to different land uses. The relevance of heavy metals emerges in particular for zinc, copper and lead, whose total concentration may reach the order of magnitude of 1 mg/l. In an aqueous environment, metals partition between the dissolved and particulate-bound phases and they can cause acute or chronic toxicity effects to the aquatic ecosystem depending on their associated phases. Therefore metals partition and speciation provide relevant information about their toxicity, bioavailability and mobility. The partitioning of metals between the dissolved and particulate-bound fraction 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