PU Gang1, MENG Li2,3, TAN Lin4, NING Mohuan4, DUAN Jiahui4, DENG Shuai1, CHEN Ji-xing1, QI Xiao-bing1, XIE Tao-yuan1, LIU Yi-zhang5, *

（1. No. 205 Geological Team, Chongqing Bureau of Geology and Minerals Exploration, Chongqing 401120, China;
2. Chongqing Institute of Geology and Mineral Resources, 401120 Chongqing, China;
3. College of Environment and Ecology, Chongqing University, 401331 Chongqing, China;
4. Chongqing Institute of Geological Survey, Chongqing 401120, China;
5. State Key Laboratory of Environmental Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550081, China）

Abstract： Heavy metal pollution is one of the most important environmental issues in China. Southwest China is a typical region with the high geochemical background, where environmental problems result from enrichment of heavy metals in soil was widely concerned. In previous studies, abnormal enrichment of heavy metals in soils was observed in the northeast region of Chongqing City. However, the spatial distribution and pollution risks of heavy metals on a regional scale are not well documented. Therefore, in this study, the southern area of Chengkou-Bashan fault zone was selected as the study area, to investigate the geochemical composition and spatial distribution of heavy metals in soils, and to evaluate the pollution risks of heavy metals in main agricultural products. The results show that the study area is a typical region with high geochemical background, where Cd, As and other heavy metals are enriched in local soils. Cd presents the highest risk among the heavy metals in soils and about 54.4% of soil samples have Cd concentrations exceeding the risk screening values for soil contamination of agricultural land in China. The geochemical composition of parent rocks is the major factor that controls Cd distribution in collected soils, which present high enrichment in some regions with black shale. High pH and TOC favor enrichment of Cd in soils. However, geochemical heterogeneity of bedrocks makes enrichment mechanisms of Cd in local soils slightly different from the typical carbonate regions. Although Cd is enriched in soils, the concentrations of Cd in main agricultural products are relatively low. Only 5.97% of collected food crops exceed the safety threshold of foodstuff, Cd in walnut and sweet potato are lower than the threshold, a low percentage of potato and a relatively high percentage of maize exceed the threshold. These results indicated that Cd in soils of the study area presents a characteristic of high concentration but low pollution risks. The findings of this study provide guidelines for pollution prevention and control of heavy metals in local soils.

Key words：high geochemical background; cadmium; soil; food crops; black shale

EARTH AND ENVIRONMENT Vol.51, No.3, Tot No.353, 2023, Page 299