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

In order to effectively manage urban heavy metal pollution at its source, this study conducted an analysis of the heavy metal content (Pb, Cr, Cu, Mn, Cd, Zn) in street dust from various functional districts in Shijiazhuang city during both summer and winter. This was done in conjunction with single factor pollution index, Nemero comprehensive pollution index, potential ecological risk index method and orthogonal matrix factor model. The spatial and temporal distribution characteristics, degree of pollution, ecological risk assessment and potential sources of pollution were thoroughly examined. The results showed that: 1) Except Mn in winter, the average content of other heavy metals was higher than the background value of soil in Shijiazhuang City. Among them, the average content of Cd in winter is 0.95 mg·kg⁻¹, which is 10.56 times of the background value, and the excess rate is as high as 86%. In general, the ecological risk degree of all heavy metals in winter is higher than that in summer. The single factor ecological risk index of Cd in summer and winter is 177.81 and 316.93, respectively, belonging to strong ecological risk; Pb in winter is medium ecological risk, and other heavy metals are slight ecological risk. 2) The heavy metal pollution degree of street dust in different urban functional areas is heavy pollution, Cd and Pb are the main heavy metal pollutants, and the pollution in the park area is the most serious, followed by the commercial area. The comprehensive potential ecological risk degree of heavy metals in street dust of all urban functional areas increased in winter compared with summer. Among them, the winter park area is a very strong ecological risk area. 3) Human activities are an important factor in the formation of heavy metal pollution in street dust. Based on the results of PMF model, it can be seen that traffic release, industrial emission and fuel combustion are the main sources of heavy metals in street dust in Shijiazhuang City. Traffic release, industrial emission and fuel combustion are the main sources of heavy metals Pb, Cu, Cd and Zn, while natural sources are the main contributors of Cr and Mn. Urban street dust pollution control should focus on winter park areas and areas with large traffic flow, and focus on the precise control of Cd and Pb in street dust in terms of reducing ecological risks.