Temporal and spatial differences of heavy metal sources and ecological risks in street dust in the city: A case of Shijiazhuang City

To effectively manage urban heavy metal pollution at its source, this study analyzed the heavy metal contents (Pb, Cr, Cu, Mn, Cd, and Zn) in street dust from various functional districts in Shijiazhuang City during summer and winter. This was performed in conjunction with the single-factor pollution index method, Nemero comprehensive pollution index method, potential ecological risk index method, and the orthogonal matrix factor model. The spatial and temporal distribution characteristics, degree of pollution, ecological risk, and potential sources of pollution were thoroughly examined. The results showed that: 1) Except Mn in winter, the average contents of other heavy metals in street dust were higher than the background values of the soil in Shijiazhuang City. Among them, the average content of Cd in winter was 0.95 mg∙kg^–1, which was 10.56 times of the background value, and the excess rate was as high as 86%. In general, the degree of ecological risk for all heavy metals was higher in winter than in summer. The single factor ecological risk index of Cd in summer and winter was 177.81 and 316.93, respectively, indicating a strong ecological risk; Pb in winter was a medium ecological risk, and other heavy metals had a slight ecological risk. 2) The degree of heavy metal pollution in street dust in different urban functional areas was heavy pollution; Cd and Pb were the main heavy metal pollutants, and pollution in the park area was the most serious, followed by the commercial area. The comprehensive potential ecological risk degree of heavy metals in the street dust of all urban functional areas increased in winter compared to summer. Winter park areas posed a very strong ecological risk. 3) Human activity was an important factor contributing to heavy metal pollution in street dust. Based on the results of the positive matrix factorization (PMF) model, traffic release, industrial emissions, and fuel combustion were the main sources of heavy metals (e.g. Pb, Cu, Cd and Zn) in street dust in Shijiazhuang, whereas natural sources were the main contributors of Cr and Mn. Urban street dust pollution control should focus on winter park areas and areas with large traffic flows and on the precise control of Cd and Pb in street dust in terms of reducing ecological risks.