Levels, sources and hazard of accumulation of polycyclic aromatic hydrocarbons in the soil cover of Ulan-Ude

For the first time, the contamination of the soil cover of Ulan-Ude, the capital of the Republic of Buryatia, with polycyclic aromatic hydrocarbons (PAHs) was studied. The work is based on the materials of the soil-geochemical survey of Ulan-Ude in the summer of 2022. Analysis of the content of 17 individual PAHs in 220 samples showed the levels of their accumulation in the upper (0–10 cm) soil horizons of different land use zones of the city. The average amount of PAHs in the soil cover of Ulan-Ude was 801 ng/g, exceeding the background concentration by more than 8.5 times. In terms of total PAH content, the land use zones form a series: transport railway (2250 ng/g) > industrial, motor transport (873) > residential single-story (860) > residential multi-story (530) > recreational (444). The composition of polyarenes is dominated by medium- (43%) and high-molecular (46%) compounds. Among polyarenes, medium- (43%) and high-molecular (46%) compounds dominate. Using the PCA/ APCS-MLR model, three components were identified that control the accumulation of PAHs in the city soils. The first explains 76.8% of the total variance and includes all high-molecular PAHs, as well as 4-nuclear benz(a)anthracene and chrysene, formed during the combustion of wood and coal in private buildings, coal at thermal power plants, industrial combustion of oil and contained in emissions from motor and rail transport. The contribution of the second component is 13.7%, it is due to low-molecular PAHs and reflects the contribution of forest fires and petrogenic sources, including coal dust. The third component is associated with the accumulation of phenanthrene, fluoranthene, pyrene and chrysene, resulting from the combustion of wood, coal and diesel fuel. An assessment of the environmental hazard of the studied PAHs, expressed in terms of benz(a)pyrene equivalents, showed that the MPC for benz(a)pyrene was exceeded in their sum on 63% of the city’s territory; the excess factor in soils varied from 1.1 to 63.9 with an average value of 5.7.