Pollution Characteristics and Source Apportionment of Heavy Metals in Vegetable Field in the Three Gorges Reservoir Area (Chongqing Section)

Abstract

To explore the pollution characteristics, ecological risks, and sources of heavy metals, soil surface samples of vegetable fields in 14 typical districts of the Three Gorges Reservoir area (Chongqing section) were collected in October 2021. The contents of seven types of heavy metals (As, Cd, Cr, Cu, Ni, Pb, and Zn) were analyzed. Based on the single-factor pollution index, the Nemerow integrated pollution index and potential ecological risk coefficient of heavy metals were evaluated. Additionally, the effects of different planting years and methods (open-field and greenhouse planting) on soil heavy metal accumulation were analyzed. The results indicated that the mean concentrations of heavy metals in vegetable soils in the area were lower than the national risk screening values for soil contamination of agricultural land (GB 15618-2018) but higher than their background values in Chongqing. According to the single-factor pollution index method, Pb, Zn, Cu, and Cd showed negligible slight hazards. The Nemerow pollution index showed that the study area was at a slight hazard level, and the main factors were Ni and Cd. Heavy metal pollution was found in 91.4% of the soil samples (PN>1) with different degrees, and 9.19% of them were severely polluted. The potential ecological risk coefficient showed that the vegetable lands were polluted slightly, and 9.77% of soil samples polluted by Cd were at moderate ecological risk. According to cluster analysis, the sources of Cd-Cu-Pb-Zn and As-Cr-Ni were similar. The content of heavy metals in the open field and greenhouse showed an increasing trend with the increase in planting years, and the content of heavy metals in greenhouse soil were generally higher than that in open field soil.