Distribution and Fractionation of PotentiallyToxic Metals under Different Land-Use Patternsin Suburban Areas

To explore the geochemical effects of land-use patterns on potentially toxic metals in agricultural soils in tropical areas, soil samples were collected in Hainan Island, China. Total concentrations of chromium, copper, lead and zinc were analyzed by inductively coupled plasma mass spectrometry. The sequential extraction procedure was applied to determine the fractions of these potentially toxic metals. The results showed that the concentrations of potentially toxic metals differed among different landuse types. The concentrations of Cr, Pb and Zn revealed the following order: abandoned cropland> paddy field>vegetable land, while Cu was ordered as abandoned cropland>vegetable land>paddy field. Fractionation analysis showed that the carbonate-bound fraction was present in high proportion in abandoned croplands, the Fe-Mn oxide-bound fraction and the organic matter-bound fraction were present in high proportion in paddy fields, and the exchangeable fraction and residual fraction were present in high proportion in vegetable lands. The chemical fractionations of potentially toxic metals were correlated with pH and organic matter, resulting in the transformation of different fractions. The results of this study contribute to a better understanding of the effects of land-use patterns on potentially toxic metals in tropical areas.