[Characteristics of metals pollution in expressway stormwater runoff]

Heavy metal concentrations of Cd, Cu, Pb and Zn were monitored during 10 rainfall runoff events occurred on a representative expressway road in Nanjing. Discharge rule of metal pollution, event mean concentrations (EMC) and the effect of hydrologic characteristics were evaluated. The results indicated that the discharge characteristics were various in different types of rainfall events. The metal concentrations fluctuated in the range of comparatively high levels during the events with short duration, light rainfall and low intensity. In the events with long duration, heavy rainfall and initial high intensity, the initial metal concentrations were high and metal exhibited a pronounced first flush. Second flush effect existed in the events with short duration, medium rainfall and double intensity peaks. The EMCs of Cd, Cu, Pb and Zn were 1.43 microg x L(-1), 0.092 mg x L(-1), 38.6 microg x L(-1) and 0.51 mg x L(-1), respectively. EMCs showed that the pollution extent of Pb was serious. Pollution of Cd, Cu and Pb were similar to other domestic reports, but Pb was lower than those studies. Cu and Zn were similar to related foreign studies, but Cd and Pb were lower. Correlation analysis suggested that the influence of rainfall on the discharge of Cu and the influence of antecedent dry period on the accumulation of Zn were significant.