Chemical characterization of naturally weathered oil residues in arid terrestrial environment in Al-Alamein, Egypt

The main objective of this study was to investigate compositional changes i n a range of source- and weathering-dependent molecular parameters in oil r esidues in the and terrestrial environment of Al-Alamein, Egypt. The result s of aromatic hydrocarbon analysis demonstrated the stability of several ar omatic hydrocarbon ratios in oil residues over a wide range of weathering a nd hydrocarbon concentrations. The ratios of C2-dibenzothiophenes/C2-phenan threnes (C2-DBTs/C2-PHENs), C3-dibenzothiophenes/C3-phenanthrenes (C3-DBTs/ C3-PHENs), C2-chrysenes/C1-chrysenes (C2-CHRYs/C1-CHRYs), and C2-dibenzothi ophenes/C1-dibenzothiophenes (C2-DBTs/C1-DBTs) were nearly constant in oil residues of varying degrees of weathering. Biomarker ratios of hopanes and steranes were useful for source identification even for severely weathered oil residues. The data confirmed previous observations that C-29 20S/(20S 20R) and C-29 beta beta/(beta beta + alpha) sterane epimer ratios, and C-2 9/C-30, C-30 alpha beta/(alpha beta+beta alpha), C-31 22S/(22S + 22R) hopan e ratios correlate well even after extensive weathering of spilled oils, al though some exceptions were encountered for an extensively weathered surfac e sample. The data provided clear evidence of correlation between samples o f the weathered oil residues and the possible source oil. Moreover, the res ults of biomarker compositions were in good agreement with weathering class ification based on alkanes and aromatic hydrocarbons. In general, samples w ith lowest pregnane indices (PI) and tricyclic terpane indices (TriTI) show ed the lowest concentrations of n-alkanes and alkylated polycyclic aromatic hydrocarbon (PAH) homologues, the highest weathering ratios (WRs), the hig hest values of unresolved complex mixture (UCM)/total resolved peak (TRP) r atios, and the highest ratios of C-2 and C-3-alkylated CHRYs to their count erparts in the PHEN and DBT series. (C) 2001 Elsevier Science Ltd. All righ ts reserved.