Polycyclic Aromatic Hydrocarbons in Soils of the Background Catena in the South of the Valdai Hills

Abstract In terrestrial ecosystems, soil is the primary medium that accumulates polycyclic aromatic hydrocarbons (PAHs). In this study, the distribution of PAHs in soils of landscapes remote from major pollution sources is examined. A loamy soil-geochemical catena was studied on the territory of the Central Forest Reserve, in the southern part of the Valdai Hills. Soil pH, organic carbon content, CaCO3, particle-size distribution, and concentrations of 12 PAHs: naphthalene, fluorene, phenanthrene, anthracene, fluoranthene, pyrene, benz[a]anthracene, benzo[b]fluoranthene, benzo[k]fluoranthene, benzo[a]pyrene, dibenz[ah]anthracene, benzo[ghi]perylene were determined. The summit and upper slope positions of the catena are covered with coniferous-broadleaf forests on Retisols. The footslope position is covered by spruce forest on Stagnosol. The total concentration of 12 PAHs is comparable to that of forest soils of Central Europe and northern European Russia. The leading factors in the vertical distribution of PAHs in soil profile are the organic matter content, particle size, and acidity. The PAH concentration is highest in the topsoils (1354–2686 ng/g), where low molecular weight PAHs associated with organic matter predominate. In the Bt horizon, low molecular weight PAHs are predominantly sorbed by solid particles smaller than 10 μm in diameter. A decrease in the organic matter content, accompanied by an increase in pH, contributes to a decrease in the PAH concentration in the soil profile with depth. The total PAHs concentration in topsoil is higher in the subordinate positions due to slower decomposition of coniferous litter saturated with resinous substances and higher stability of PAHs under anaerobic conditions.