PAHs in medium and high rank Bulgarian coals – insights from aromatic indices

The study presents analyses of aromatic components in bitumen extracts from Bulgarian medium and high rank coals. Bulk samples from Balkan, Ro = 0.96%, Dobroudzha, Ro = 1.13%, and Svoge, Ro = 5.20% coal-bearing provinces, were considered. After extensive chromatographic separation and GC-MS study of the aromatic fractions, our attention was focused on polycyclic aromatic hydrocarbons (PAHs) compositions. Aromatic indices, based on quantification of individual compounds, revealed that: (i) the highest amounts of PAHs were present in Balkan and Dobroudzha samples, 219–365 μg/g TOC, and dropped to 3.5 μg/g TOC at Svoge sample; (ii) the alkylated naphthalenes and phenantrenes prevalence confirmed published data; (iii) the relationship between aromatic indices vs. Ro, % is in agreement with the previously obtained results, indicating their decrease with thermal maturity. For some indices only weak correlation was obtained, suggesting that PAH concentrations are not solely affected by coal rank, but also by environmental conditions and vegetation.