Time-dependent multivariate and spectroscopic characterisation of oil residue in Niger Delta soil

Abstract

In this paper, we present a detailed evaluation of changes in the oil residue in soil following a spill using weathering indices obtained from analytical instruments such as UV, IR, GC, and ¹H NMR, and chemometrics based on the time of spill in the Niger Delta region of Nigeria. UV, IR and ¹H NMR spectra of eight (8) oil residue samples were analyzed. The PCA of the UV and IR spectrometric index showed that the first two PCs accounted for 87 and 71% of the variance of the index, respectively. The detailed results suggested that the absorption ratios A_225/256 and A_248/278 from UV were good estimators for petroleum of different weathering profiles and the presence of different types of di- and poly-aromatics, nitrogen, sulphur, and oxygen (NSO) containing compounds. Similarly, sulphoxide, aromatic, and carbonyl index obtained from IR would be more valuable in evaluating changes in oil residue over time. An 84% PC obtained for NMR indicators described for weathered crude oil was the best at explaining structural changes compared to the region defined for fresh heavy crude oil. These models showed good predictive ability for the crude-oil residue composition and could be used to provide a rapid assessment of compositional differences in crude-oil residue following a spill.