Status, Distribution and Ecological Risk Assessment of Persistent Toxic Substances in Suburban Agricultural Soils in Hohhot City, North China

Abstract

A total of 52 soil samples of Hohhot City were collected and four heavy metals and eight organochlorine pesticides were analyzed. The results showed that Cr, Cu, Zn, and Pb in soil were in range of 20.54 -48.15 mg/kg, 40.10 -94.60 mg/kg, 35.14 -110.48 mg/kg, 38.86g -245.36 mg/kg, with a mean value of 37.24 mg/kg, 60.76 mg/kg, 80.49 mg/kg, and 145.99 mg/kg, respectively. The high degree of variation of Pb, Zn, and Cu, reflected that the heavy metals were mainly interfered by human factors. The content values of ∑DDTs ranged from 5.01 ng/g to 105.08 ng/g with a mean of 36.94 ng/g, while the ∑HCHs ranged from 6.52 ng/g to 48.65 ng/g with an average of 23.29 ng/g, indicated that DDTs were highly used than HCHs in the study area. The relatively low α-HCH/γ-HCH ratio and relatively high o,p'-DDT/p,p'-DDT ratio indicated the application of lindane and dicofol on regional agricultural soil. The mean Igeo values was Pb (2.9) > Cu (1.5) > Cr (−0.31) > Zn (−0.35), revealing that the soil in Hohhot City was not polluted by Cr and Zn (Igeo < 0), moderate polluted by Cu (1 < Igeo < 2), moderate to heavy pollution by Pb (2 < Igeo < 3). The range of potential ecological risk index of metals was from 35.02 to 132.96, indicating low to moderate potential ecological risk. HCHs in all soil samples were less than 50 ng/g, which could be considered as unpolluted, while DDTs in several samples were between 50 and 500 ng/g, which could be regarded as having low pollution.