Polycyclic aromatic hydrocarbons (PAHs) and their derivatives in soils developing on coal waste dumps from the Upper Silesia, Poland

In southern Poland, the mining industry led to the creation of diverse post-mining waste deposited in dumps. Therefore, it is essential to study and monitor the condition of soils developing there. The soil samples have been collected from the coal waste dump at the Ziemowit Coal Mine in Upper Silesia, Poland. The aim of the research was to determine the extent of soil contamination by polycyclic aromatic hydrocarbons (PAHs) and their derivatives within the soil profile on the dump that was not subjected to thermal phenomena (self-heating).

Soil samples were taken at depths of 0, 20, and 40 cm. Powdered samples (ca. 10 g) were extracted using a dichloromethane (DCM)/methanol mixture (1:1 v:v) with an accelerated Dionex ASE 350 solvent extractor. The samples were analysed using GC–MS carried out with an Agilent Technologies 7890A gas chromatograph and Agilent 5975C Network mass spectrometer.

The PAHs detected included phenanthrene, anthracene, fluoranthene, pyrene, benz[a]anthracene, chrysene, benzo[b+k]fluoranthene, benzo[j]fluoranthene, benzo[a]fluoranthene, benzo[a]pyrene, benzo[e]pyrene, perylene, indeno[1,2,3-cd]pyrene, benzo[ghi]perylene, dibenzoanthracenes, and coronene together with their alkyl derivatives in the range of C1-C4. Concentrations of highly carcinogenic PAHs such as benzo[a]pyrene (ca. 0.95 µg/g), benzofluoranthenes (ca. 0.17-3.34 µg/g), and benzo[a]anthracene (ca. 1.70 µg/g) have been determined in all samples. Due to the combined effects of weathering and leaching by waters penetrating the highly permeable dump lighter PAHs were partially or totally removed, among them naphthalene and alkyl naphthalenes up to C3, fluorene, acenaphthene, and acenaphthylene. There are significant differences in compounds absence with sampling depth, i.e. the least leached soils were sampled deepest and closest to the coal waste level, where even C2 naphthalenes were preserved. In PAHs distribution predominate 4- to 5-rings compounds, however also heavier 6-rings PAHs were found.

The results show that coal waste dump soil, even there where self-heating is absent, can contain significant amounts of PAHs making it a potential source of contamination spreading, particularly during dry seasons when soil dusting occurs or due to leaching by rain water to nearby water reservoirs.