Distribution characteristics, source analysis and health risk assessment of heavy metals in farmland soil in Shiquan County, Shaanxi Province

Soil heavy metal pollution can cause irreversible harm to the ecological environment and human health. A total of 678 surface soil samples and 60 crop samples were collected to study the contamination level, source of heavy metals and human health risk in agricultural soil in central Shiquan County. The results show that the arithmetic mean values of chromium, copper, zinc, arsenic, lead, nickel, cadmium, and mercury in the soils of the study area were 1.67, 2.17, 1.73, 1.25, 1.24, 1.86, 5.04 and 2.17 times of their background values, respectively. However, the risk control standards for agricultural soil pollution in China were not exceeded. The high-value areas of soil heavy metals Cr, Cu, Zn, Ni, Cd, and Hg are mainly distributed in the northwest-southwest area of the study region. The results of the geo-accumulation index (Igeo) showed that the pollution levels of heavy metals in soil were in the order of Cd (0.98) > Cu (0.40) > Hg (0.20) > Ni (0.19) > Zn (0.14) > Cr (0.06) > Pb (-0.30) > As (-0.81). In addition, the soil cadmium contamination factor (CF) was 5.04, the pollution load index (PLI) was 2.97, which were significantly higher than other metals contamination levels. It indicates that cadmium pollution reaches a high level. Correlation analysis and principal component analysis (PCA) showed that Cr, Cu, Zn, As, Ni, Cd and Hg in soil were mainly derived from industrial pollution, while Pb was derived from soil parent material. The soil environment in the study area will not cause non-carcinogenic effects on adults and children. It is necessary to pay attention to the high risk of cancer caused by Cr in local residents. The excessive rate of heavy metals in vegetable crops in the study area was significantly higher than that in paddy. The results can provide basic information for soil heavy metal control and crop planting planning in Shiquan County.