For this study, we collected a total of 77 topsoil samples from urban, suburban, and rural gradients in the Urumqi city area in northwest China and analyzed their concentrations of seven trace elements: Arsenic (As), cadmium (Cd), nickel (Ni), lead (Pb), mercury (Hg), copper (Cu), and Zinc (Zn). To assess and compare the contamination levels and the potential health risk of trace elements in topsoil along an urbanization gradient, we employed the pollution index and the health risk assessment model introduced by the US Environmental Protection Agency; we also used geostatistical analysis to analyze the spatial distribution patterns. The results we obtained indicate that the contamination levels of trace elements in soil decreased in the order of urban > rural > suburban gradients. We found a similar spatial distribution pattern of contamination levels of Ni, Zn, Cd, and Pb elements, with a zonal distribution pattern, while the spatial distribution patterns of As, Cu, and Hg elements show high concentration patches in many of the areas investigated in this study. Furthermore, based on the identified concentrations, the topsoil is heavily contaminated by Hg and slightly contaminated by Pb, As, and Zn in the urban gradient, whereas it is heavily contaminated by Hg in suburban and rural gradients and slightly contaminated by As in the suburban gradient. The total non-carcinogenic risk index of the analyzed trace elements for adults and children decrease in the order of urban > suburban > rural gradients, whereas the total carcinogenic risk index of the analyzed elements for adults and children decreased in the order of suburban > urban > rural gradients. However, the contamination of topsoil in all gradients is more harmful to children’s health than to that of adults. Overall, urbanization has had obvious effects on the accumulation of trace elements in soil, and As is the main carcinogenic and non-carcinogenic risk factor among the investigated elements in topsoil in all urbanization gradients.

The hazardous element (HE) pollution of urban surface dust is a serious environmental issue, due to its toxicity and potential hazardous effects. Surface dust samples were collected from core urban, urban, and suburban gradients in the city of Urumqi in arid northwestern China, and the concentrations of six HEs, such as arsenic (As), cadmium (Cd), nickel (Ni), lead (Pb), mercury (Hg), and chromium (Cr) were determined. The pollution load index (PLI) and the US EPA health risk assessment model were applied, to assess and compare the pollution levels and the potential health risk of HEs in the surface dust in different urbanization gradients. The results indicated that the average concentrations of Hg, Cd, and Ni in the surface dust decreased in the order of core urban > urban > suburban, whereas the average concentrations of As, Cr, and Pb decreased in the order of urban > core urban > suburban. The PLI of HEs in surface dust decreased in the order of core urban > urban > suburban. The concentrations of HEs in the core urban and urban gradients were relatively higher than those in the suburban gradient. Furthermore, the total non-carcinogenic and carcinogenic risk index of the investigated HEs in surface dust decreased in the order of urban > core urban > suburban, for both adults and children. In addition, the pollution of surface dust by HEs in all urbanization gradients was more harmful to children’s health than to adults’. Overall, the potential non-carcinogenic and carcinogenic health risk of the investigated HEs, instigated primarily via the oral ingestion of surface dust, was found to be within the acceptable range. However, urbanization has effected the accumulation of HEs in surface dust, and Cr was the main non-carcinogenic risk factor, whereas Cd was the main carcinogenic risk factor, among the analyzed HEs in surface dust in three urban gradients in the study area.

Pollution of urban surface dust with hazardous elements (HEs) is a serious environmental issue due to its toxicity and potential hazardous effects. Surface dust samples were collected from core urban, urban, and suburban gradients in the Urumqi city of the arid NW China, and the concentrations of six HEs, such as arsenic (As), cadmium (Cd), nickel (Ni), lead (Pb), mercury (Hg), and chromium (Cr), were determined. The pollution load index (PLI) and the US EPA health risk assessment model were applied to analyze and compare the pollution levels and potential health risk of HEs in surface dusts in different urbanization gradients. The obtained results indicate that the average concentrations of Hg, Cd, and Ni in surface dust decrease in the order of core urban > urban > suburban, whereas the average concentrations of As, Cr, and Pb decrease in the order of urban > core urban > suburban. The PLI of HEs in surface dust decreased in the order of core urban > urban > suburban. The concentrations of HEs in the core urban and urban gradients are relatively higher than in the suburban gradient. Furthermore, the total non-carcinogenic and carcinogenic risk index of investigated HEs in surface dust decrease in order of urban > core urban > suburban, for both adults and children. In addition, the pollution of surface dust with HEs in all urbanization gradients is more harmful to the children's health than to the adults. Overall, the potential non-carcinogenic and carcinogenic health risks of the investigated HEs, instigated primarily by oral ingestion of surface dust, are found to be within the acceptable range. However, urbanization can effects the accumulation of HEs in surface dust, and Cr is the main non-carcinogenic risk factor, whereas Cd is the main carcinogenic risk factor among the analyzed HEs in surface dust in all urbanization gradients.