Isotopic fractionation evidence of PAH migration through a soil cover over self-heating coal waste

Self-heating of coal waste is a serious problem in coal mining areas. This process involves the emission of polycyclic aromatic hydrocarbons (PAHs), which are hazardous to health. One technique for suppressing fires is to cut off the air supply by covering the heap with a barrier. This paper aims to examine in situ isotopic fractionation of PAHs migrating through the soil cover of an active self-heating coal waste landfill in Ostrava, Czech Republic. For this purpose, two profiles were sampled from a 6.5 m-thick soil stockpile deposited on burning coal wastes. The mineral and organic matter parameters of the soil and the distribution and composition of stable carbon isotopes in individual PAHs were investigated. Migration of combustion products through the soil profile, induced by water vapour, was evidenced. In these conditions, non-volatile PAHs (e.g., benzo( a )pyrene) can also migrate. The soil cover is not an effective barrier for low molecular weight (LMW) PAHs. The PAHs occurring at the highest concentrations (phenanthrene, fluoranthene, pyrene, and benzo( a )anthracene) during migration undergo isotope fractionation according to the Rayleigh equation. This results in δ 13 C depletion in individual PAHs as migration distance increases. This study represents a seminal effort in the field, as it is the first documentation of this process. The isotopic composition of the above-mentioned PAHs indicates that more than 80% of the components are retained in the over 6 m thick soil stockpile.