Pollutants in Hong Kong Soil: As, Cd, Cr, Cu, Hg, Pb and Zn

Six heavy metals (Hg, Cu, Cd, Cr, Pb, Zn) and 1 metalloid (As) in surface soils of Hong Kong were investigated in 10 land use categories (urban park, greening area, country park, rural area, restored landfill, agricultural farmland, orchard farm, crematorium, industrial and near highway area). Edaphic Hg concentration in Hong Kong was firstly reported here. Clustering of land uses was observed based on total pollutants concentrations (sum of 7 metals). The most polluted cluster consisted of industrial and highway areas (median: 617 to 833 mg kg-1) and the runner-up cluster included urban park, greening area and restored landfill (median: 400 to 500 mg kg-1). However, this general finding was not observed for Hg, where higher concentration was found in agricultural farmland (median 109 μg kg-1). The use of low quality fertilizers, together with the contribution from exhausts and wearable parts from automobiles were believed to be the major sources of Cr, Cu and Zn in Hong Kong, while the application of Hg-containing agrochemicals maybe the main mechanism of Hg contamination in agricultural soil. Based on the daily intake assumption of 0.2 g d-1 of soil particles by USEPA, direct ingestion of Hg-containing soils is not a major exposure pathway for population in Hong Kong. When comparing the edaphic heavy metal concentrations with Dutch soil quality guidelines demonstrated that Hg, Cd and Pb were not in level of health concerns, while Cu, Cr and Zn in less than 6% of total samples were found to exceed the Dutch intervention values sporadically. In contrast, suburban soils from northern and northeastern Hong Kong were mostly contaminated with As (10% of total samples) at concentration that could be potentially causing adverse health impacts to the nearby population.