Biomarker composition and polycyclic aromatic hydrocarbons (PAHs)
concentrations of three coal samples from Bulgarian deposits of different rank
are presented. The coal samples were taken from Stanyantsi, Bourgas and Dobroudja coal basins. Gas chromatography–mass spectrometry (GC-MS) was
applied to assess organic matter source and to identify and quantify PAHs in
the studied samples. Coal rank was determined on the basis of vitrinite reflectance, Ro %.
The alkane patterns of the three samples are dominated by long chain
n-alkanes (C27-C31), usually found in higher terrestrial plants rich in cuticular waxes. With increasing rank, the odd over even predominance is significantly reduced and short-chain n-alkanes are present in higher quantities.
Increased pristane/phytane ratios in the Dobroudja coals are attributed to the
influence of coal rank on this parameter. Based on terpenoid biomarker composition, angiosperm-dominated vegetation is concluded for the Bourgas coal
whereas conifers dominated the peat-forming vegetation at Stanyantsi. Low
terpenoid biomarker concentration and high contents of alkylated naphthalenes
and phenanthrenes in the bituminous coal reflect the diagenetic conversion of
the plant-derived terpenoid hydrocarbons to alkylated PAHs. Highest PAHs
concentration was recorded in samples of higher rank (bituminous coal), and the lowest concentration was found in lignite samples. The examination of the
PAHs composition revealed that 3 and 4 ring unsubstituted PAHs are dominant in the lignite and bituminous coal samples, whereas 4 and 5 ring PAHs
predominate in subbituminous coal. We assume that the composition of PAHs
in the extractable portion of coals is irrespective of the coal-forming vegetation.