Heavy metal contents in vegetables and market garden soils in hong kong

Urbanization is one of the major causes of soil pollution of many market garden soils in various municipalities. The aim of this project was to monitor the heavy metal contents in market garden soils and vegetables in Hong Kong as affected by human activities. Cadmium, Zn, Cu and Pb concentrations were determined on soil and two vegetable samples, Brassica chinensis and B. parachinensis, collected from eleven different locations. The EDTA-extractable heavy metal concentrations in soil were analysed to assess their availability for plant uptake. Mean total Cd, Cu, Pb and Zn concentrations for all soil samples were (mg kg⁻¹): 1.01 (range 0.25 to 2.17), 18 (range 5 to 67), 60 (range 24 to 113) and 105 (range 20 to 232), respectively, and were all below the investigation levels for contaminated soil. The heavy metal concentrations of soils in more urbanized sites were consistently higher than some remote sites. Significant positive correlations were found between EDTA-extractable and total metal contents in soils for Cu, Pb and Zn (P < 0.05). Heavy metal concentrations in the vegetable species studied were all below the maximum permitted level except for Cd. The mean Cd concentrations in B. chinensis and B. parachinensis were respectively approaching and above the maximum permitted concentration of 0.05 mg Cd kg⁻¹ fresh weight. Sites with higher urbanization and traffic volume had higher concentrations of metals in plant tissue. The results indicate that there is a potential risk of a high daily Cd intake in consuming vegetables of Brassica sp. available in the local market.