Comptes rendus de l’Acade'mie bulgare des Sciences, Vol 70, No2, pp.243-252
Biomarkers Composition and Polycyclic Aromatic Hydrocarbons (PAHs) Characteristic of Bulgarian Coals with Different Rank and Origin
Denitsa Apostolova, Achim Bechtel, Kalinka Markova, Irena Kostova
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.
Key words: organic geochemistry, biomarkers, PAHs