ИСТИНА

Purpose : Sealed soils dominate on the territory of Moscow and other megacities, but their properties and level of pollution remain poorly studied. The purpose of this work is to determine sources, composition and distribution of PAHs in the sealed soils of eastern Moscow and to compare them with unsealed urban and background soils of the Meshchera lowland. PAH accumulation in sealed soils poses potential risk for public health since PAHs can migrate, enter the biological circulation and food chains, if asphalt is removed. Methods : In the field study a layer of asphalt and underlying soils were sampled in the overburden pits laid by the city services. The content of low- and high-molecular weight PAHs in the samples was determined by low-temperature spectrofluorimetry. Results : The main sources of PAHs in the sealed soils include industrial and vehicle emissions, particles of brake pads and tires and asphalt concrete. The greatest contribution is made by emissions from cars with a diesel engine, containing predominantly low-molecular weight PAHs. Pollutants enter the soil through cracks with precipitation. Asphalt concrete contains bitumen, which is enriched with many polyarenes. The average amount of PAHs in the asphalt concrete samples collected in the eastern Moscow is 93.5 mg/kg with a predominance of naphthalene, diphenyl, phenanthrene and fluorene (93% of the total PAHs). The sum of polyarenes in the upper part of the sealed soils averages 14.5 mg/kg, which is 142 times higher than the background and 4.5 times higher than in unsealed soils. The composition of PAHs is dominated by naphthalene (61.0% of the total PAHs) and phenanthrene (16.2%). Despite small share of high-molecular weight PAHs benzo(a)pyrene average content (0.16 mg/kg) exceeds the MPC by 8 times. The accumulation of PAHs under asphalt is due to their conservation by the soil organic matter in anaerobic conditions. It is enhanced by a low-flush water regime, which hampers leaching from the soil profile. Conclusions : The hazard of pollution with PAHs for sealed soils is caused by their high content in comparison with unsealed soils and poor ability to self-purification. It can be enhanced only via special remediation activities that involve participation of soil microbiota.