The fate of heavy oil wastes in soil microcosms I: a performance assessment of biotransformation indices

A controlled soil microcosm study was used to evaluate the performance of selected oil biotransformation indices using samples of Nigerian crude, a blended ballast oil and No. 6 fuel oil. Biotic losses were demonstrated through loss of solvent extractable matter (SEM) and changes in class fraction distribution in weathered soil extracts relative to sterilised controls. GC-EI MS peak identification and quantification was achieved for selected (Σ) n-alkanes, the isoprenoid alkanes norpristane (iC18), pristane (iC19) and phytane (iC20), combined mono-substituted (1-, 2-, 3- and 9-) methylphenanthrenes (Σmethylphenanthrenes), combined dimethylphenanthrenes (Σdimethylphenanthrenes) and the hopane isomers 17α(H)21β(H)-hopane and 17α(H)21β(H)-30-norhopane. The [Σn-alkanes:17α(H)21β(H)-hopane] index was most sensitive to oil biotransformation and most accurately reflected depletion of oil from contaminated soils in this study. This index was found to be the most reliable for the No. 6 fuel oil saturates, dropping from 81.9 to 18.1 over the course of the 256-day microcosm study. In terms of sensitivity, and taking into account the results of an ANOVA analysis, the biotransformation indices most sensitive to oil biotransformation were (in order of decreasing sensitivity): [ΣC14–28:17α(H)21β(H)-hopane]≫[∑C14–28:Σdimethylphenanthrenes]>[C18:phytane].