Chemical forms of Pb, Cd and Cu in crops
Xu Jialin, Bao Ziping, Yang Jurong and Liu Hong (Institute of Environmental Sciences, Beijing Normal University, Beijing 100875), Song Wenchang (Institute of Crop Breeding and Cultivation, Chinese Academy of Agricultural Sciences, Beijing 100081).
In order to study the chemical forms of heavy metals in crops growing on polluted soil, sequential extraction method has been applied to analyze the roots and leaves of both wheat and rice growing in pots. The results revealed that acetic acid extractable Pb and HCl extractable Pb are the main forms in roots whereas the latter is the main form in leaves as well. Moreover, NaCl extractable Cd predominates in both crops, whereas ethanol extractable Cu and water extractable Cu predominates in roots and leaves respectively. Chemical forms significantly influence the characteristics of migration and accumulation as well as the degree of toxicity of these elements in plants. Pb is generally concentrated and fixed in roots which results in relatively weak accumulation in grains and insignificant retardation effect on the growth of plants. Cd may combine with protein and disturb the activity of enzymes. The existence of low molecular organic complex of Cu results in relatively high accumulation in grain and retardation effect on plant growth when the content is high.