Objective Recent surveys of soil contamination in China show that the overall soil environmental quality is not optimistic, in that heavy metal pollution is serious in some areas and heavy metals in soil can be absorbed and enriched by various vegetables and plants, directly threatening people's health through the food chain. However, there are few reports on the investigation of heavy metals in soil in Yunnan Province. The purpose of this study is to evaluate the concentrations of soil lead (Pb), cadmium (Cd), and chromium (Cr) in Yunnan Province, assess the farmland soil environmental quality, and provide evidence for further research and policymaking.
Methods A total of 897 farmland soil samples were collected from 897 villages of 45 counties of 16 cities in Yunnan Province selected by stratified random sampling method. According to the fivepoint sampling method, for each soil sample, five subsamples were collected within 1 m2 quadrat below surface at a depth of 5-20 cm with bamboo and wood sampling tools, and then quartered and mixed to get a representative sample weighing approximately 1 000 g after removing rocks and plant roots. A total of 897 soil samples were collected. Concentrations of Pb, Cd, & Cr and pH values were detected, and the farmland soil environmental quality was assessed by both singlefactor pollution index and Nemerow comprehensive pollution index.
Results In the 897 soil samples, the concentrations of Pb, Cd, and Cr were 22.180, 0.207, and 67.000 mg/kg, respectively. The Nemerow comprehensive pollution index was 0.639, and the single-factor pollution index of Cd, Cr, and Pb in the soil samples were 0.540, 0.357, and 0.078 respectively, which were all determined as pollution grade I. The soil samples with a comprehensive pollution index of grade I and above accounted for 31.10%, and the samples with a single-factor pollution index of Cd, Cr, and Pb graded Ⅲ and above accounted for 34.34%, 9.92%, and 2.01%, respectively.
Conclusion The farmland soil in Yunnan is generally clean and safe, notwithstanding substandard soil in some areas, and Cd is the dominant pollutant. Future work should include confirming the causes and sources of pollution, as well as adopting prompt actions to control further Cd pollution in farmland soil.
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