Geochemical status of non-reclaimed ash dumps subjected to long-term self-overgrowing: Evidence from the Tyumen, Russia

Establishing the geochemical state of ash dumps of solid fuel thermal power plants in the absence of reclamation is extremely important in urban conditions. The current study was performed to assess the level, spatial distribution, soil pollution and risk of potentially toxic elements (PTEs) and polycyclic aromatic hydrocarbons (PAHs) in soils of abandoned ash dumps from the city of Tyumen, Russia. In general, the soils of as dumps had elevated levels of PTEs and PAHs compared to the crustal abundance and global soil background. A number of metals, namely Sr, Ni, Cu, Cr, Zn, and V, were concentrated in the soils of ash dumps (2-6 times), while As, Co, and Pb slightly exceeded the citywide average (up to 1.5 times). Naphthalene (NAP) was the only representative of the studied PAHs, the concentrations of which in the soils of ash dumps significantly exceeded the median content in urban soils of Tyumen. Elevated levels of NAP are likely a consequence of frequent fires occurring in grassy areas. Spatial patterns of pollutants are mainly controlled by the initial heterogeneity of technogenic substrates, rather than the post-depositional processes including vegetation and soil cover development. Low and moderate pollution and human health risks of PTEs and PAHs were revealed in topsoils of the studied sites. Although elevated levels of pollutants in coal ash dump soils are due to peat combustion, they pose less of an environmental risk than the more common coal ash dumps and are potentially suitable for a wider variety of management practices.