Investigations of Metal Pollution in Road Dust of Steel Industrial Area and Application of Magnetic Separation

Pollution characteristics and ecological risks for metals in non-magnetic and magnetic road dust from steel industrial areas were investigated by applying a magnetic separation method. Metal (except for Al, Li, Ti, As, and Sb) concentrations in the magnetic road dust were 1.2 (Sn) to 7.8 (Fe) times higher than those in the non-magnetic road dust. For the magnetic road dust, the geo-accumulation index revealed a strongly to extremely polluted status for Cr, Zn, Cd, and Sb, a strongly polluted status for Mn, Cu, and Pb, and a moderately to strongly polluted status for Fe, Ni, Mo, and Hg. This result indicates that the dominant metal pollution sources of road dust in industrial areas were the traffic activities of heavy-duty vehicles. The mean content of magnetic particles accounted for 44.7% of the total road dust. The metal loadings in the magnetic road dust were 86% (Fe), 77% (Cr), 67% (Mn), 86% (Ni), 76% (Cu), 72% (Zn), 64% (Mo), and 62% (Cd), respectively. Removal of the magnetic fraction from road dust using magnetic separation techniques not only reduces metal contamination but can also improve effective road cleaning strategies or reduce waste generation.

The Content and Sources of Potentially Toxic Elements in the Road Dust of Surgut (Russia)

The chemical and particle size composition of road dust in Surgut, which is a rapidly developing city in Western Siberia, was studied for the first time. Contents of major and trace elements were determined using ICP-MS and ICP-AES, respectively. It was found that the road dust had an alkaline pH (from 7.54 to 9.38) and that the particle size composition was dominated by the 100–250-μm fraction. The contamination assessment based on calculations of the enrichment factor (EF) showed that the road dust was significantly enriched in Sb and Cu and moderately enriched in Zn, Pb, Mo, Ni and W. The sources of these elements are probably associated with the abrasion of car tires and brake pads. Based on calculations of global pollution index (PIr) and total enrichment factor (Ze), the road dust of Surgut was characterized by a generally low level of potential ecological risk, except for stretches of road subject to regular traffic jams, where a moderate ecological risk level was identified. In comparison to the other Russian cities (Moscow, Chelyabinsk, Tyumen, etc.) where studies of road dust composition have been carried out, Surgut had similar contents of Cr and Cu and relatively lower contents of Sb, Cd, As and Pb.

Size-Segregated Elemental Profile and Associated Heath Risk Assessment of Road Dust along Major Traffic Corridors in Kolkata Mega City

Particle size distribution (PSD) of road dust has significant repercussions on atmospheric pollution by road dust resuspension. The PSD of road dust at a few major commercial, traffic, and residential sites in Kolkata mega city was analyzed in the size range of <28–2000 µm. Predominance of the coarse size range (212–600 µm followed by 106–212 µm) was observed. In size-segregated road dust, Fe (4.02–31.2 g kg−1) dominated other elements and was followed by Mg (2.13–10.9 g kg−1), Mn (79.2–601 mg kg−1), Li (395.8–506.8 mg kg−1), and others. Fine particles (<28 μm) had higher elemental concentrations than coarser ones. Cd and Li showed the highest degree of enrichment compared to the Earth’s crust, but only Cd posed significant ecological risk due to its high ecological toxicity. Individual elements did not post significant non-cancer health risks, except for Li in children. However, the cumulative non-cancer risk from all toxic elements for children was almost four times higher than the acceptable level. Lifetime exposure to carcinogenic elements at the current level may pose 5 to 6 times higher cancer risk in the adult population than the acceptable risk of one in a million.

Source Apportionment and Source-specific Health Risk of Heavy Metals in Urban Road Dust of Jinan City, East China

For a better regional and source-risk-based control of heavy metals in urban environments, this study provides a source-specific health risk assessment by combining the models of United States Environmental Protection Agency health risk assessment and positive matrix factorization (PMF). The calculated data were optimized by the geochemical speciation of target 10 potentially toxic heavy metals. The results demonstrated that the mean concentrations of most heavy metals in urban dust of Jinan City exceeded their corresponding background values, especially that of cadmium (Cd) and zinc (Zn) exhibiting a mean of 12.9 and 7.84 times those of their backgrounds. Cd, Zn, copper, lead and manganese in road dust existed mainly in extractable forms, exhibiting higher bio-availability. The PMF receptor model determined four sources of heavy metals in urban road dust, namely industrial discharges (41.1%), natural and coal combustion sources (27.8%), traffic emissions (22.8%), and building material and manufacturing sources (8.3%). All the studied heavy metals presented low or negligible non-carcinogenic risk (non-CR) for adults and children, while the lifetime carcinogenic risk (CR) of Cd was in an acceptable level. Regarding source-specific health risks, the highest non-CR was derived from industrial discharges, while CR from traffic emissions, which were mainly associated with the higher content and bio-availability of Pb and Cd in the dust. Moreover, the risk contributions of industrial discharges and traffic emissions were 35.9% and 60.6% for non-CR and CR, respectively, presenting a significant difference with the apportioned source characteristics, thus deep-revealing the potentially source-based risks of heavy metal in urban environment.

Quantification and Characterization of Metals in Ultrafine Road Dust Particles

Road dust is an important source of resuspended particulate matter (PM) but information is lacking on the chemical composition of the ultrafine particle fraction (UFP; <0.1 µm). This study investigated metal concentrations in UFP isolated from the “dust box” of sweepings collected by the City of Toronto, Canada, using regenerative-air-street sweepers. Dust box samples from expressway, arterial and local roads were aerosolized in the laboratory and were separated into thirteen particle size fractions ranging from 10 nm to 10 µm (PM10). The UFP fraction accounted for about 2% of the total mass of resuspended PM10 (range 0.23–8.36%). Elemental analysis using ICP-MS and ICP-OES revealed a marked enrichment in Cd, Cr, Zn and V concentration in UFP compared to the dust box material (nano to dust box ratio ≥ 2). UFP from arterial roads contained two times more Cd, Zn and V and nine times more Cr than UFP from local roads. The highest median concentration of Zn was observed for the municipal expressway, attributed to greater volumes of traffic, including light to heavy duty vehicles, and higher speeds. The observed elevated concentrations of transition metals in UFP are a human health concern, given their potential to cause oxidative stress in lung cells.