Pollution And Bioavailability Of Heavy Metals In Agricultural Soil Of Dongguan

The continual development of economic and human health have been seriously effectedby soil pollution.In order to study the relationships between soil contamination and humanfood chain,200soil samples,36Chinese flowering cabbage samples,13water spinach samplesand11onion samples were systemically collected from the cultivating layers offarmland.Eight kinds of heavy metals named Cd,Pb,Zn,Cu,Cr,Ni,Hg and As were evaluatedand analyzed in character content,pollution status. The relationships between soil heavymetals content, chemical speciation and crop, is the focus of this paper.The results show that:(1) The average content of Cr, Cu, Ni, Pb, Zn, Cd, Hg, As of study soil are more than thebackground value of Guangdong. From the statistics of the single factor pollution index ofsoil,the Cd contents in83%,Cu in54.5%and Hg in21%of the soil samples are beyond thelimit standard of GB15618-1995. Based on the comprehensive pollution index,3.5%soilbelongs to the moderate pollution,69%belongs to the mild,27%belongs to the warning limit,0.5%at the level of security,and no severe pollution of the soil. According to the analysis ofthe potential ecological risk index,55.5%of the soil is medium ecological risk by Cd,20.5%by Hg,and the others are slight ecological risk.(2) The ion-exchangeable fraction of Cd in soil is as high as21.82%, which causes Cd insoil very active, Water soluble, exchangeable and carbonate bound fractions account for ahigher percentage in different depth soil, which furtherly explains that the soil is moreseriously damaged by Cd. The other elements such as Cr,Cu,Ni,Pb,Zn,Hg and As are mainlyin the residual fraction.(3) Cd is the most important pollution elements in the crops,followed by Cr, Hg, Pb, Ni.Firstly,Cd contaminations of Chinese flowering cabbage exceed the standard rate of88.89%,whose single pollution times index of is1.8. Ni contents in8.33%, Cr in11.11%,Pbin11.11%and Hg in5.56%of Chinese flowering cabbage were beyond the limit standard.Secondly,Cd contaminations of water spinach exceed the standard rate of76.92%,whosesingle pollution times index of is2.2. Cr contents in7.69%and Hg in7.69%were beyond thelimit standard. Thirdly, Cd contaminations of onion exceed the standard rate of45.45%,whosesingle pollution times index of is1.2. Cr contents in9.09%was beyond the limit standard. It showed that there is a strong positive correlation among the crops contents and total massconcentration and ion exchangeable form of Cd in soil, according to the rate which exceed thelimit standard of Cd contents in vegetables was so high.