Fractionation Of Heavy Metals In The Main Vegetable Soils In Guangdong Province

The total amount of heavy metal in soils is to determine the pollution levels and environmental capacity of the important indexes, but heavy metals in soils have different forms of existence which may produce different environmental effects, and directly affect its biological effectiveness, toxicity, mobility and in the circle of nature. At present, alone and successive extraction has been widely used in evaluation of soil heavy metal activity and biological effectiveness.Pearl river delta region in China has became the most developed and populous area, but also with ecological environment changes, and environmental pollution is severe in this region, especially for heavy metal pollution.In this paper, the main vegetable soils and vegetables in Guangdong province were the research objects. Based on field investigation and laboratory analysis,8extractants of0.1mol·L-1HCl,0.5mol·L-1HCl,0.05mol·L-1EDTA-2Na,0.005mol·L-1DTPA,1mol·L-1NH4OAC,0.1mol·L-1CaCl2,0.5mol·L-1NaH2PO4,0.03%TGA-1/15mol·L-1Na2HPO4were studied to select the suitable extraction on the basic of the correlations between the available heavy metals and the concentrations in corresponding vegetables and the extraction efficiency. In addition, the fractionation and bioavailability of lead (Pb) and cadium (Cd) in the main vegetable soils were extracted by modified BCR sequential extraction procedure in order to understand the forms of heavy metals in soils and the biological effectiveness, and help to an objective evaluation of soil heavy metal pollution condition and the vegetable production safety risk. The results showed:(1) Cd pollution was serious in the main vegetable soils in Guangdong province, and the rate of pollution reached44.5%. Followed by Hg pollution, which accounted for22.5%;(2) The best extractants for available heavy metals of Pb、Cd、As、Hg were0.005mol·L-1DTPA、0.005mol·L-1DTPA,0.5mol·L-1NaH2PO4,0.03%TGA-1/15mol·L-1Na2HPO4respectively;(3) The greatest proportion of Pb in soils was the reducible fraction, which accounted for67.48%of total Pb, followed by the residual, oxidizable, acid-soluble;(4) Cd was dominated in the acid-soluble and reducible fractions and they accounted for46.77%and34.68%of the total amounts respectively, and followed by the order of acid-soluble, reducible, oxidizable, residual. It has a big potential ecological risk; (5) The bioavailable form of heavy metals is a fast and precise method in evaluating the bioavailability of heavy metals rather than the total content of heavy metal;(6) The modified BCR method has a more precise and comprehensive on assessment of heavy metal on biological effectiveness in soils.