Enrichment of road dust particles and adjacent environments with metals and metalloids in eastern Moscow

Abstract

Road dust is one of the most informative indicators of the ecological state of urban environments, as vehicles have become the major source of pollution in many cities. Road dust consists of blown out soil particles, solid particles discharged from vehicles and abrasion of the road surface. Vehicle emissions contain many heavy metals and metalloids (HMMs) in environmentally hazardous concentrations, and roadside soils can accumulate technogenic fallout from the atmosphere over many years. In Moscow, detailed studies of the chemical composition of road dust have been not performed yet, wherefore, the aim of our work was to identify the levels of HMMs accumulation in particles of road dust on roads with various traffic intensities and to analyze their dependence on the composition of roadside soils and atmospheric fallout in the winter. The contents of Ag, As, Be, Bi, Cd, Co, Cr, Cu, Fe, Mn, Mo, Ni, Pb, Sb, Sn, Sr, Ti, V, W, Zn and La in road dust and in individual particle-size fractions (PM1, PM1–10, РМ10–50, РМ>50), as well as in urban soils and in dust component of snow (atmospheric precipitation), were determined by ICP-MS and ICP-AES methods. Road dust as a whole and its fractions are enriched with technogenic Ag, Cd, Sb, Zn, Sn, Cu, Pb, W, Bi, and Mo; other elements come mainly from natural and mixed sources, both natural and technogenic. The total enrichment with HMMs is maximal in PM1 fraction and decreases with increasing particle size. With an increase in the traffic intensity, the content of the majority of HMMs increases in the PM>50 fraction; decreases in the PM10–50 and PM1–10 fractions, and virtually does not change in the PM1 fraction. On small roads, the most environmentally hazardous particles PM1 and PM1–10 concentrate up to 93% of Ag; 51–60% of Cd, Bi, As, Sb, and Sn; 31–50% of Cr, Mo, Pb, Ni, Zn, Co, and Cu; and 15–30% of W, V, Fe, Mn, Be, Ti, and Sr. On larger roads, the proportion of all elements associated with PM1 and PM1–10 fractions decreases: on the Moscow Ring Road, they account for 78% of Ag; 31–35% of Cd and Sb; 16–30% of Bi, As, Sn, Mo, Pb, Ni, Zn, Co, and Cu; 6–15% of W, Cr, V, Fe, Mn, and Be; and 2–5% of Ti and Sr. The geochemical feature of eastern Moscow is the formation of the Sb–Ag–Sn–W paragenesis common to road dust, soils, and solids in the snow and derived from motor vehicle emissions. As and Mo enter road dust and soil during winter season mainly with snow from the atmosphere. Bi, Cd, Cu, Pb, and Zn enter road dust mainly with soil particles blown out from polluted roadside soils during summer season.