Levels, Sources and Hazard of Polycyclic Aromatic Hydrocarbons Accumulation in the Soil Cover of Ulan-Ude City
摘要
The soil cover pollution with polycyclic aromatic hydrocarbons (PAHs) was studied for the first time in Ulan-Ude City, the capital of Buryat Republic. The study is based on the data of geochemical soil survey in Ulan-Ude in summer 2022. The analysis of the content of 17 individual PAHs in 220 samples showed their accumulation levels in the upper (0–10 cm) soil layers in soils of different land uses in the city. The average sum of PAHs in the Ulan-Ude soil cover was equal to 801 ng/g, which exceeds the background concentration by more than 8.5 times. According to the total PAH content, the land use zones form a series: railway transport (2250 ng/g) > industrial, motor traffic (873) > residential single-storey (860) > residential multi-storey (530) > recreational (444). Medium- (43%) and high-molecular-weight (46%) compounds predominate among the polyarenes. Using the PCA/APCS-MLR model, three components controlling the accumulation of polyarenes in urban soils have been identified. The first explains 76.8% of the total variance and includes all high-molecular-weight PAHs, as well as 4-nuclear benz(a)anthracene and chrysene formed upon the combustion of wood and coal in private housing, combustion of coal at thermal power plants, industrial combustion of oil and also PAHs contained in emissions from motor and rail transport. The contribution of the second component is equal to 13.7%; it is due to low-molecular-weight 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 formed during combustion of wood, coal and diesel fuel. The assessed ecological hazard of all studied PAHs expressed through benzo(a)pyrene equivalents, showed the MPC excess for benzo(a)pyrene in their sum at 63% of the city’s territory; the excess factor varied from 1.1 to 63.9 in soils with an average value of 5.7.