Accumulation of metals and metalloids in soil cover, road dust, and their PM10 fraction in Ulan-Ude: Spatial variation and source apportionment

Abstract

Coal-fired thermal power plants remain one of the primary sources of electricity generation in the Asian part of Russia. However, coal combustion leads to severe environmental pollution. This study attempts to assess this impact in a large city in Eastern Siberia, Ulan-Ude, the capital of Buryatia, where coal is widely used in thermal power plants and for stove heating. The accumulation of trace metals (MMs) in the upper soil horizons, road dust, and their fine PM₁₀ fraction was evaluated. The coal, ash, soil and road dust samples were analyzed using inductively coupled plasma-mass spectrometry (ICP-MS/AES) to determine concentrations of As, Bi, Cd, Co, Cr, Cu, Mo, Ni, Pb, Sb, Sr, V, W, and Zn. The coal was enriched only in Sr compared to world coals, while the ash was depleted in all these MMs. Concentrations of all MMs were higher than the local natural soil background values, with priority pollutants in Ulan-Ude's soils identified as Cu, Pb, Sb, Cd, Zn, and W. For the first time, the primary sources of MMs were quantitatively assessed using the PMF receptor model. It was established that most MMs (As, Ni, Cr, Sr, V, Co, Bi) originated from mixed sources, including natural sources and emissions from coal combustion. Its contribution accounted for 32.6 % for the bulk soils and 25.4 % for the PM₁₀ fraction. The contribution of exhaust and non-exhaust emissions was estimated as 19.2 % and 22.4 % for bulk soils and the PM₁₀ fraction, respectively. The spatial distribution of the Total Pollution Index (TPI) for soils indicated that the pollution degree was highest in private residential areas (mean TPI = 24), suggesting an influence of coal combustion conditions (including temperature) on contamination levels. The PM₁₀ fraction of soil was most polluted in the railway transport zone (mean TPI = 46). Approximately 8 % of Ulan-Ude's territory displayed maximum, extremely hazardous levels of pollution in soils and their PM₁₀ fraction, posing a risk to human health. Road dust was enriched in Sr, Sb and Pb compared to the continental upper crust values. Bulk road dust exhibited a low level of pollution, while the Total Pollution Index for its PM₁₀ fraction reached an extremely hazardous level (TPI > 128). The highest pollution levels in road dust and its PM₁₀ fraction were observed on main roads. In large industrial cities, pollution from coal combustion occurs alongside other significant sources, including vehicular emissions, contributing to the diversity of total pollutant emissions.