Chemical Speciation, Contamination, Human Health Risk Assessment, and Source Identification of Heavy Metals in Soils Composted with Swine Manure

Heavy metal accumulation in the swine manure composting vegetable soil continues to attract attention for the reason that heavy metals are often added to animal feeds as growth promoters. The seven heavy metals (Cr, Ni, Cu, Zn, As, Cd, and Pb) concentration and chemical speciation in soil samples from 15 swine manure composting vegetable fields of Jiangxi Province were analyzed. The results showed that the average concentration of Cr, Ni Cu, Zn, As, Cd, and Pb was 48.46 ± 5.58 mg/kg, 29.06 ± 1.80 mg/kg, 48.16 ± 9.69 mg/kg, 142.32 ± 38.71 mg/kg, 10.62 ± 2.76 mg/kg, 0.13 ± 0.04 mg/kg, and 15.75 ± 2.36 mg/kg, respectively. The average concentration of Ni, Cu, Zn, and Cd was 1.12, 1.89, 1.77, and 1.17 times greater than their background values, whereas the average concentration of Cr, As, and Pb was lower than their background values. The chemical speciation analysis indicated that these heavy metals were dominated by residual fractions and have low mobility and bioavailability. The Geo-accumulation index (Igeo) indicated that the soils were unpolluted with Cr, Ni, As, Cd, and Pb, while unpolluted to moderately polluted with Cu and Zn. The Nemerow comprehensive pollution index suggested that the soils were lightly polluted with heavy metals. They posed a considerable potential ecological risk to the soils. Based on the risk assessment code (RAC), these heavy metals exhibited no to medium risks. There was little non-carcinogenic risk and acceptable carcinogenic risk to humans from the heavy metals. Principal component analysis (PCA) indicated that Ni, Cu, Zn, and Cd originated from the use of a large quantity of swine manure; Pb and As mainly derived from atmospheric deposition; Cr was mainly from natural sources.