A performance assessment of source correlation and weathering indices for petroleum hydrocarbons in the environment

The source of petroleum contaminants in the environment and the extent to which these contaminants have weathered following deposition can often be determined through an empirical evaluation of oil n-alkanes, isoprenoids (pristane and phytane), and hopane and sterane biomarkers. Common source correlation and weathering indices have been calculated for three sets of oil samples: fresh, 25% (w/w) weathered, and 50% (w/w) physically weathered diesel standards, crude oils from different sources, and a set of representative heavy oils. For the weathered diesel oils, the C18:phytane demonstrated low specificity between the oils. C18:17α(H),21β(H)-Hopane and n-alkanes:17α(H),21β(H)-hopane differentiated between crude oils but would be expected to vary significantly during weathering due to the microbial amenability of the alkane numerators. Pristane:phytane, phytane:17α,21β-hopane and tricyclic terpanes:hopanes were considered to be the indices best able to distinguish between oils from different origins, based on these results. 17α(H),21β(H)-Hopane:17α(H),21β(H)-norhopane did not adequately distinguish between the respective crude oil samples. Finally, the relationship between heavy oil composition and the index value was investigated. Here, the values of n-alkanes:17α(H),21β(H)-hopane, phytane:17α(H),21β(H)-hopane, and tricyclic terpanes:hopanes decreased as the combined total of polar and asphaltene compounds within oil samples increased. This relationship may be useful in assessing the degradation status of petroleum wastes