Geographic Distribution and Source Apportionment of Heavy Metals in Soils and Vegetables in Urban Fringe

Contamination of agricultural soil by heavy metals has become a global issue concerning food security and human health risk. A total of 95 surface soil samples (bulk soil), 34 vegetable samples, 27 irrigation water samples, and 20 fertilizer samples were collected from Wuqing District, Tianjin, China. The concentrations of heavy metals (i.e., As, Cd, Cu, Cr, Ni, Pb, and Zn) in these samples were tested. After determining the metal accumulation and potential ecological risks in farmland soil, kriging interpolation and positive matrix factorization (PMF) were used to identify and quantify the sources of soil heavy metals. The results showed that (1) Cd and As were the main contaminants in the soil in the studied area, and Cd had the highest effectiveness in soil, with its average content in vegetables slightly higher than the allowable threshold (0.02 mg·kg^-1). (2) The results of the enrichment index of vegetables show that Cd and Pb were the dominant heavy metals in vegetables, and vegetables had a strong enrichment ability to Cd. (3) The spatial distribution of heavy metals in the soil showed that the contaminants were non-homogeneous, and all the heavy metals showed high-value areas in some parts of the studied area, indicating the negative effects of human activities on the soil environment of farmlands. (4) Industrial activity (for Cd), effects of pesticides, fertilizers, and plastic film mulching (for As and Pb), natural sources (for Ni, Cu, Cr, and As), Organic fertilizer (for Zn and Cu), traffic discharges (for Pb and Cd) and sewage irrigation (for Cr, Ni, and Pb) were ascertained as the potential sources based on the Positive matrix factorization (PMF) analysis results. (5) The accumulation of heavy metals in the studied area was mainly caused by industrial activities, including atmospheric deposition, the discharge of industrial waste water, the disposal of waste residue, and the emission of waste gas, and so on.