The Geochemical Characteristics of Heavy Metals in Agricultural Soils of the Bijiang Watershed in Yunnan Province
ZHAO Xiao-qing,LI Li-jiao,YANG Hong-hui,TAN Shu-cheng School of Resource Environment and Earth Science,Yunnan University,Kunming,Yunnan 650091
The Lanping lead-zinc ore district has the largest lead-zinc reserves in China’s lead-zinc deposits.The upstream of the Bijiang River originates from the Lanping lead-zinc ore district.Therefore,the Bijiang River has been affected by mining activities of the Lanping lead-zinc ore district,and has become a river typically polluted by heavy metals.With the agricultural soils irrigated by the Bijiang River as the study object and according to the methods of field survey sampling,laboratory experiment and statistical analysis,the authors analyzed the content and the distribution of chemical constitutions of Pb,Zn,Cd,and As in the agricultural soils.Some conclusions have been reached:(1) Heavy metals have been highly concentrated in the agricultural soils of the Bijiang watershed.Examined on the basis of the National Soil Environmental Quality Standards(Class Ⅱ),the concentrations of Pb,Zn,Cd,and As have respectively exceeded the set standards by 66.667%,91.667%,100% and 16.667%,and the contamination degrees of the heavy metals are in order of Cd﹥Zn﹥Pb﹥As.(2) Pb and Cd in soils mainly occur as the water-soluble state which is easy to migrate and can directly become part of the ecological cycle,and hence their environmental risks are serious.Zn and As mainly occur as Fe-Mn oxides binding state and the residual state,which are relatively stable and reluctant to migrate under the common conditions.The concentrations of environmental available states(the total content of the water-soluble state,the ion exchangeable state,the carbonate binding state,the humic acid binding state) of Cd and Pb are relatively high.There exists great potential danger to the eco-environment of agricultural soils once acid rain or acid mine drainage occurs.(3) The content distribution and chemical states of Pb,Zn,Cd,and As in soils tend to decrease with the distance from the Lanping Pb-Zn deposit.Their distribution curves are of single-peak shape and bimodal-peak shape.The chemical states distribution of Cd,Pb and Zn are similar to their content distribution,but the humic acid binding state and residual state content distribution of As is similar to its content distribution.
【Fund】： 国家自然科学基金项目(编号:40961031);; 云南省应用基础研究面上项目(编号:2009CD022);; 云南大学“中青年骨干教师培养计划”专项项目(编号:21132014)联合资助
【CateGory Index】： X131.3
【CateGory Index】： X131.3