Fractionation of heavy metals in pavement runoff

The transport of anthropogenic constituents by runoff from urban roadways can adversely impact the quality of adjacent receiving waters and soils. Metal elements are the most persistent constituents found in pavement runoff. A section of urban highway pavement in Cincinnati, Ohio, USA with an average daily traffic count of 150 000 vehicles was instrumented to sample lateral sheet flow from the pavement. Field samples from two diverse rainfall runoff events were analyzed to determine metal element partitioning between dissolved and particulate-bound fractions. Results indicate that dissolved metal element washoff response is a function of the degree to which a metal element is in dissolved form. Irrespective of the degree to which a metal element is dissolved, the particulate bound metal element washoff response is mainly a function of rainfall intensity. Results indicate that for both events Cu, Cd, Zn and Ni are mainly in dissolved form while Al and Fe are mainly in particulate-bound form. Cr and Pb partitioning is intermediate to these two cases. These findings can assist in the development of effective control strategies to immobilize dissolved and particulate-bound metal elements in pavement runoff.