Spatial Distributions, Sources, Potential Risks of Multi-Trace Metal/Metalloids in Street Dusts from Barbican Downtown Embracing by Xi’an Ancient City Wall (NW, China)

Abstract

A total of 116 dust samples in downtown within the city wall were collected, and the spatial occurrence, source and health risk status of 19 trace metal/metalloids bound in street dusts (SDs) were systematically investigated. Geochemical maps, associations, risk models and indices were calculated to define levels of distribution, possible natural or anthropogenic sources, ecological and human health risks. It was found that the wide variations of these 19 trace metals would be observed in spatial maps, which indicated strongly anthropogenic activities inputs. Compared to the calculations of the potential ecological risk index of toxic trace metals, Pb (Eri = 20.32) ranked at the level of considerable ecological risk. The non-carcinogenic and carcinogenic risk from most trace metals exposed to children and adults were no significant health risks, except for the non-carcinogenic risk of Cr and As to children, and the carcinogenic risk of Cr to adults. The unacceptable risk locations were observed at traffic conjunctions, which should be given attention. The source apportionment results indicated that the trace metals/metalloids Co, Ga, Nb, As, Ni, and Y, coupled with main elements Al, K, Mg, Ca and Si, would possibly originate from “Soil Re-suspension”, whereas Fe, Cu, Rb, La, Ba, Mn, Ti, Ce and Zr were possibly derived from “Brake Wear”. As regards the Na, no valid assumption was formulated about the presence of this element in brake wear, while Cr, Sr, Zn were possibly associated with “Tire Wear”. Comparatively, V would be suggested as a representative source of fuel consumption, and Pb could possibly belong to “Traffic Pigment”. It was noted that the barbican city, surrounded by the Xi’an Ancient City Wall at 12 m high, would trap the trace metal emissions, and consequently increase the health risk for local residents.

Geochemical, Mineralogical and Morphological Characterisation of Road Dust and Associated Health Risks

“…However, this element is used in fuel additives, aluminium based alloys offering a high corrosion resistance and formability, vehicle applications, such as inner panels, and heater and radiator tubes. Iron, with higher concentrations in fraction F1 (max = 39,895 mg kg −1 ), showed comparable results to those obtained for road dusts in Xi'an [34], Shanghai [35], Hong Kong [35], Beijing [35], Delhi [36] and Madrid [37], suggesting a significant geogenic contribution, which is confirmed by EI < 3. Elements such as Al, Fe, Ti, Zr and Na have a potential source in soil resuspended dusts and marine spray (EI < 3).…”

Geochemical, Mineralogical and Morphological Characterisation of Road Dust and Associated Health Risks

“…On the asphalt paved street (S2), a much lower PM10 emission factor was obtained (49 mg Iron, with higher concentrations in fraction F1 (max = 39,895 mg kg -1 ), showed comparable results to those obtained for road dusts in Xi'an [34], Shanghai [35], Hong Kong [35], Beijing [35], Delhi [36] and Madrid [37], suggesting a significant geogenic contribution, which is with Cu, in urban areas [45]. Zn is also used as engine oil additive.…”

Release of Nanoparticles in the Environment and Catalytic Converters Ageing

“…The melting point of α-C is 1470 • C, while the catalyst reactions occur at an operating temperature between 300 and 1000 • C [9]. The overcomes from chemical, thermal and mechanical stress conditions degrade the active catalytic washcoat [10].…”