Heavy Metal Pollution Characteristics and Influencing Factors in Baoji Arban Soils

Abstract

In order to analyze the sources and factors influencing heavy metal pollution in industrial cities, 62 surface layer (0-20 cm) soil samples were collected in Baoji City for analysis using inductively coupled plasma mass spectrometry (ICP-MS). Cd, As, Cu, Pb, Zn, Cr, Mn, and Ni were detected in the samples. Based on geostatistical methods and geo-detector models, the soil heavy metal pollution load index (PLI) was selected as the best indicator of factors affecting heavy metal pollution. The Unmix 6.0 receptor model was also used to analyze the heavy metal source. The results showed that:① The average concentrations of Cd, Pb, Cu, Zn, As, Cr, Mn, and Ni in the surface soils of Baoji City were 0.77 mg·kg-1, 16.75 mg·kg-1, 40.52 mg·kg-1, 261 mg·kg-1, 17.03 mg·kg-1, 49.18 mg·kg-1, 331 mg·kg-1, and 30.52 mg·kg-1, respectively. These values exceeded the national secondary standard for Cd and Zn, which were 8.2 and 3.8 times more abundant, respectively, than in the background soils of Shaanxi Province, indicating that urban soils are seriously polluted with Cd and Zn. The average concentrations of Cu, As, and Ni also exceeded the background levels; ② The total pollution load index (PLIzone) for heavy metals in the surface soils of Baoji City was 1.36, which indicated mild levels of pollution, as analyzed using a geo-detector. Soil texture and distance to the city's railway had the strongest explanatory power for the distribution of pollutants (PD, H=0.040 and 0.026, respectively, with a combined explanatory power of 0.099); ③ Cd, Cu, and As mainly derive from "artificial sources" associated with industrial and agricultural activities, and Zn and Ni derive from traffic emissions. Cr, Pb, and Mn mainly derive from "mixed sources". Overall, the main source of heavy metals in the surface soils of the study area was classified as "mixed source" and soils were classified as having a mild level of pollution. These results provide scientific support for the prevention and control of heavy metal pollution in the soils of Baoji City.