Spatial distribution and sources of potentially toxic elements in road dust and its PM fraction of Moscow megacity.

For the first time, the contents of potentially toxic elements (PTEs) in road dust and in its PM fraction were studied in Moscow from June 09 to July 30, 2017 on roads with different traffic intensities, inside courtyards with parking lots, and on pedestrian walkways in parks. The contents of PTEs in road dust and PM fraction were analyzed by ICP-MS and ICP-AES. The main pollutants of road dust and its PM fraction included Sb, Zn, W, Sn, Bi, Cd, Cu, Pb, and Mo. PM was a major carrier of W, Bi, Sb, Zn, Sn (accounts for >65% of their total contents in road dust); Cu (>50%); and Cd, Pb, Mo, Co, Ni (30-50%). PM fraction was 1.2-6.4 times more polluted with PTEs than bulk samples. Resuspension of roadside soil particles accounted for 34% of the mass of PTEs in road dust and for 64% in the PM fraction. Other important sources of PTEs were non-exhaust vehicles emissions (~ 20% for dust and 14% for PM) and industrial emissions (20% and ~6%). The road dust and PM particles were most contaminated in the central part of the city due to the large number of cars and traffic congestions. Local anomalies of individual PTEs were observed near industrial zones mainly in the west, south, and southeast of Moscow. In the yards of residential buildings the total enrichment of road dust and PM with PTEs was only 1.1-1.5 times lower than that on major roads which poses a serious danger to the population spending a significant part of their lives in residential areas. The spatial pattern of the PTEs distribution in road dust and its PM fraction should assist in more efficient planning of washing and mechanical cleaning of the road surface from dust to minimize the risk to public health.