Metal distribution in soils of an in-service urban parking lot.

Increasing traffic is becoming one of the main sources of metal pollution in urban areas. To investigate the possible impacts of traffic-related activities on metal distribution in soils, a total of 370 soil samples were collected in a ground parking space in service for about 20 years in Chengdu, China. The concentrations of Cu, Fe, Mn, Pb, Rb, Sr, Ti, and Zn in soils were measured using portable energy-dispersive X-ray fluorescence. Soil samples exhibited various levels of metal pollution ranging from no pollution to borderline moderate pollution for Zn and Pb, with median enrichment factors following the order of Zn (2.7), Pb (2.2), Sr (1.9), Cu (1.8), Fe (1.3), Rb (1.1), and Mn (0.5). Both cluster analysis and spatial distribution mapping demonstrated that Pb, Zn, Cu, Mn, Sr, and Fe concentrations in the parking space were influenced by traffic, with strong spatial variation in different areas of the parking space. These metals shared similar spatial distribution patterns with relatively elevated concentrations in the four corners, left and right sides and entrance and rear areas, compared with the metal concentrations in the central area. Such spatial patterns revealed the influences of yellow road paint, wear and tear of vehicular parts including brakes and tires, as well as tailpipe emissions. The pollution sources in the parking space were identified as yellow road paint and vehicular emissions. This study highlights that metal pollution in the parking areas should be given more attention.