Heavy metal pollution in roadside urban parks and gardens in Hong Kong.

An ecological survey was conducted on metal contamination (including Cd, Pb, Ni, Zn, Cu, Mn and Fe) of vegetation (leaf of Bauhina variegata), surface soil (0-1 cm) and dust (from road curbs) collected at 13 urban parks near busy roads (with heavy traffic volume) in Hong Kong. Samples from roadside parks had significantly higher metal contents than the control site (away from automobile traffic). A close correlation was found between traffic volume and metal contents of leaf, soil and dust. Washing of leaf samples reduced the levels of Cu, Mn, Zn and Fe contamination and suggested that the source of heavy metal pollution was mainly due to aerial deposition from motor vehicles.