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

With the rapid advancement of industrialization and urbanization, the problem of heavy metal pollution has become increasingly prominent. Urban street dust, as a source and sink of heavy metals, can reflect the impact of different human activities on heavy metal pollution in the urban environment. In order to effectively control urban heavy metal pollution, this study took the ring road of Shijiazhuang city as the main line, and selected 35 sampling points in different functional areas in summer and winter to monitor the six heavy metals Pb, Cr, Cu, Mn, Cd and Zn in street dust. Through geostatistical analysis, pollution level assessment method, potential ecological risk assessment and orthogonal matrix factor model, we analyzed the spatial and temporal distribution characteristics, potential ecological risks and possible sources of heavy metals in street dust. The results showed that: (1) Except Mn in winter, the average content of other heavy metals was higher than the background value of the soil in Shijiazhuang City. The content of main pollutant Cd in summer and winter was 0.20~1.50 mgkg¹ and 0.13~1.41 mgkg¹, respectively, which was 5.89 times and 10.56 times of the background value, and the excess rate is as high as 86% in winter. Pb content in summer and winter was 27.23~504.68 mgkg¹ and 14.24~2 018.07 mgkg¹, respectively, which was 4.29 times and 8.98 times of the background value. The variation coefficient of Pb was the largest and obviously higher than that of other heavy metals. The ecological risk degree of the six heavy metals is higher in winter than in summer, among which Cd is the highest, Pb is the medium risk in winter, and the other heavy metals are slight ecological risk. (2) In different urban functional areas, the non-parametric test results showed that the heavy metal content had significant differences in summer, but little differences in winter. Based on the evaluation results of Nemero index, the overall pollution status of all functional areas in summer and winter is severe pollution, and the winter is more serious than the summer. Based on the evaluation results of the comprehensive potential risk index, the ecological risk degree of heavy metals increased in winter compared with summer. The park area is a very strong ecological risk area in winter. Compared with other cities in China, the content of Pb in street dust in Shijiazhuang city is at a higher level. (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.