Dissolved-particulate partitioning of heavy metals in urban road runoff of Shanghai

The partitioning characteristics between the dissolved and particulate-bound fractions of heavy metals in runoff waters in roads are preliminarily investigated in this paper. 56 runoff samples were collected in two rainfall-runoff events in five different areas located in the central area of Shanghai. The results indicate that during the wash-off processes, the 25th percentile concentrations of Cr and the 90th percentile concentrations of Zn, Pb and Cd are over the fifth classified values of the National Surface Water Standards, while the pollution levels of Cu and Ni are relatively lower. The results also show the high positive correlations between the total heavy metal concentrations and the total suspended sediment (TSS) concentrations are in the order of Pb>Cu>Zn>Cd, and the correlation of Ni and TSS is not obvious. The fractions of dissolved-to-total metals are ranked by Cu and Ni of 35%, Zn and Cr of 19%~22%, and Cd and Pb of 4%~8%. With the modified dissolved-particulate partitioning (K_d) calculated method, the order of K_d is Pb>Cd>Zn>Ni>Cu>Cr. The K_d values of metals show the similar spatial distribution pattern among the different areas. The results also show that TSS concentration has the great negative influence and shows the so-called "particle concentration effect" on K_d values. When pH values of runoff belong to the interval of 6.4~7.2, it has a relatively weaker effect on K_d values.