Heavy metal pollution characteristics of urban road runoff in Xi´an city

Urban road runoff caused by 29 storm events were collected at South Second Ring Road in Xi´an city using self-made volume proportional collecting device from Mar. to Sep 2009. Event mean concentration (EMC) of SS, total and dissolved Pb, Zn were tested. Pollution intensity, as well as mode of occurrence, relationship and concentration influence factors of heavy metal in runoff were explored. Results showed that EMC of total and dissolved Pb, Zn varied greatly and the median EMC of Pb, Zn and dissolved Zn were 0.042 mg.L^-1, 0.223 mg.L^-1 and 0.111 mg.L^-1 respectively. The coefficient of variation was 0.47-0.74. EMC of Zn and dissolved Zn were greater than the limit standards for runoff polution control of USEPA. The occurance of Pb was mainly granular state and 46.2% of Zn was dissolved. The correlations of Pb and Zn with SS were significant at 0.01 level and correlation coefficients were 0.825 and 0.893, which showed that particulate matters were carrier for heavy metal. Rainfall, monthly cumulative rainfall, maximum rainfall intensity and rainfall duration were negatively correlated with EMC of heavy metal. Antecedent dry period(ADP) had significant positive corelation with EMC of dissolved Zn, but the corelations with other pollutants were not obvious.