Abstract
Street dust is repeatedly raised by the wind as a secondary suspension, helping heavy metals therein to enter the human body through the respiratory system, harming human health. A detailed investigation was conducted to determine levels and sources of Cd (cadmium), Cr (chromium), Cu (copper), Pb (lead), Zn (zinc), Ni (nick), and Hg (mercury) contamination in street dust from Shijiazhuang, China. The average concentrations of these metals were: Cd, 1.86 mg·kg−1; Cr, 131.7 mg·kg−1; Ni, 40.99 mg·kg−1; Cu, 91.06 mg·kg−1; Pb, 154.78 mg·kg−1, Hg, 0.29 mg·kg−1; and Zn, 496.17 mg·kg−1—all of which were greater than the local soil reference values. The concentrations of the heavy metals were mapped for the three Shijiazhuang ring roads, with the results showing significant differences between each ring. Application of enrichment factors and geoaccumulation indexes showed that there was significant enrichment and accumulation of Cd, Pb, Zn, and Hg. Multivariate statistical analyses showed that Cd, Pb, Zn, and Hg levels were mainly controlled by human activities, while Cr, Ni, and Cu levels were associated with natural sources. Absolute principal component scores with multiple linear regression (APCS-MLR) were applied to facilitate source apportionment. The results showed that the mixed (traffic and industry) group contributed 53.55%, 59.7%, and 62.25% of the Cd, Pb, and Zn concentration, respectively, while the natural sources group contributed 58.01%, 65.09%, and 66.91% of the Cu, Ni, and Cr concentration, respectively. The burning coal group was found to be responsible for 63.38% of the Hg present in the samples. These results provide a useful theoretical basis for Shijiazhuang authorities to address heavy metal pollution management.
Highlights
Street dust is a type of urban pollution in itself, but is an important medium for the spread of other polluting substances in the urban environment
Statistical analysis results for Shijiazhuang street dust heavy metal concentration are shown in Table 2, with Hebei soil values [38] taken as reference values for this study
The maximum concentration of Cd was 82.5 mg/kg−1, which was 917 times the reference value, with these values suggesting overall that the metals came from human sources
Summary
Street dust is a type of urban pollution in itself, but is an important medium for the spread of other polluting substances in the urban environment. Due to the influence of industrial production, urban traffic, and industry emission activities, street dust contains many harmful substances, enhancing the risk it represents to human health [1,2,3,4,5]. The mean heavy metals values for samples from each ring. Skewness value and kurtosis value indicate where those heavy metal element concentrations do not obey normal distribution—and this applied to Cd, Cr, and Ni, whose kurtosis values were very high, indicating they were highly anomalous. The skewness results showed strongly that all the measured heavy metals in street dust were normally inclined towards lower concentrations, illustrated by the results showing that the median concentrations were lower than the mean concentrations [1]. We compared the heavy metal content of street dust from Chinese and other sources (Table 1), and it can be seen that the Shijiazhuang concentrations of the seven measured heavy metals were generally higher than elsewhere, including the Chinese cities of Xi’an, Beijing, Changchun, and Wuhan, and Toronto (Canada)—and that this applied with respect to Pb, Zn, Cd, and Hg.
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