Heavy metal pollution can negatively affect the survival,growth and reproduction of organisms.In the Pearl River Delta in southern China,Pb and Cd are two major contaminants found in water,soil and the biotic environment,mainly imported through human activities from densely urbanized regions.The present study detected and monitored the content of Pb and Cd in trees (leaf and branch material from 13 plantation species),water (river water in the Pearl River,and subterranean water under forest canopy),and soil in a seashore shelter forest in Nansha district,Guangzhou city in southern China.The results showed that (i) soil,rather than water or trees,had the highest concentrations of both Pband Cd; (ii) Pb content was always higher than Cd in water,soil and trees; (iii) Pb content was higher in branches than in leaves,but the reverse was true for Cd,implying possibly different mechanisms of accumulation for the two elements in plants.Soil may function as a major reservoir for extraneously derived heavy metal elements with adverse effects for organisms and the environment.The pathways,retention and removal of such elements in different components of the ecosystem,especially in industrial and urbanized regions with and without significant tree cover,are of direct concern to urban forestry management.