Characteristics and Risk Evaluation of Heavy Metal Contamination in Paddy Soils in the Three Gorges Reservoir Area

Abstract

Soil Cd, Hg, Pb, As, Cr, Cu, Zn, and Ni of 12 districts in the Three Gorges Reservoir area (Chongqing section) were analyzed, and different evaluation methods were used to assess the degree of contamination, potential ecological risk, and human health risk of soil heavy metals in paddy soils. The results showed that the average values of all heavy metals except Cr in paddy soils in the Three Gorges Reservoir area exceeded the background values of soils in the Three Gorges Reservoir area, and the contents of Cd, Cu, and Ni in 12.32%, 4.35%, and 2.54% of the soil samples exceeded the screening values, respectively. The variation coefficients of the eight heavy metals were 29.08%-56.43%, which belonged to the medium and above-intensity variation levels and were influenced by anthropogenic activities. The eight heavy metals were contaminated in the soil, and 16.30%, 6.52%, and 2.90% of the soil Cd, Hg, and Pb were heavily contaminated. At the same time, the potential ecological risk of soil Hg and Cd were in the medium risk level on the whole. Wuxi County and Wushan County had relatively high pollution levels among the 12 districts, the Nemerow pollution index showed a moderate pollution level, and the comprehensive potential ecological risks were also at a moderate ecological hazard level. The results of the health risk evaluation showed that hand-mouth intake was the main exposure path of non-carcinogenic risk and carcinogenic risk. Soil heavy metals presented no non-carcinogenic risk for adults (HI<1), but 12.68% of the sites had non-carcinogenic risk for children (HI>1). As and Cr were the main influencing factors for non-carcinogenic and carcinogenic risks in the study area, and their total contributions to non-carcinogenic and carcinogenic risks were more than 75% and 95%, respectively, which was cause for concern.