Accumulation and potential sources of heavy metals in soils of the Hetao area, Inner Mongolia, China

Abstract

Soil contamination by heavy metals is a problem in agricultural irrigation systems. To assess the accumulation and sources of heavy metals in the Yongji irrigation district of the Hetao area, Inner Mongolia, China, 195 soil samples from 39 sites (0–100 cm) were collected, and Zn, Cu, Pb, Cr, and Cd concentrations were analyzed. The mean concentrations were 107.17, 32.48, 12.31, 53.53, and 0.22 mg kg−1, respectively, with no significant differences between soil depths (P > 0.05). Concentrations of Zn, Cu, and Cd were higher than the background levels, with moderate accumulation; the contamination factor (CF) values were 1.9, 1.7, and 1.9, respectively, and the geoaccumulation index (Igeo) was > 0. Concentrations of Pb and Cr were lower than, or close to, the background levels (CF < 1, Igeo < 0), indicating that they originated from a natural source. The monomial potential ecological risk index (Eir) for Zn, Cu, Pb, and Cr was low; Eir for Cd was 55.73, implying a moderate risk. The grade of potential ecological risk index of the five heavy metals (RI) was low, declining from south to north. The studied soils were contaminated with Zn, Cu, and Cd; principal component (PC) analysis implicated the enrichment of Cd and partial Cu (high loading in PC 2) was related to agricultural activities; Zn and partial Cu, closely associated with PC 3, may have originated from irrigation water from the Yellow River. Future agricultural development should focus on fertilizer and pesticide application and the quality of irrigation water.