[Characteristics of heavy metal contamination in street dusts along the urban-rural gradient around Beijing].

Road-deposited sediment (RDS) is an important carrier of the diffused pollution. This study analyzed the influences of the urban-suburban-rural gradient (central urban, urban village, central suburban county, rural town, and rural village areas) on the content and chemical fractions of heavy metals. The concentrations of five heavy metals (Cr, Cu, Ni, Pb, and Zn) in RDS in the central urban area were the highest, and the lowest concentrations appeared in the rural village area. The mass of RDS per unit area were opposite to the metals concentrations in distribution. The proportion of weak acid extractable Ni, Pb, and Zn in RDS was higher than that of Cr and Cu. The contribution of heavy metals in smaller grain size (32.4% - 62.4%) was greater than that in coarser grain size (22.9% - 49.6%). It will be helpful to reduce the RDS pollution for runoff and apply appropriate strategies for controlling runoff pollution from RDS according to RDS and its contribution to heavy metal pollution along the urban-rural gradient.