NATURAL ATTENUATION OF OIL SPILLS IN PATAGONIAN SOILS. CHARACTERIZATION BY ~1H NMR SPECTROSCOPY

摘要

The natural attenuation of oil spill contaminated soils, with different exposure times, in Patagonian environment was evaluated by the use of several parameters to quantify the degree of changes in the composition. Column (CC) and gas chromatography (GC); UV-visible and ~1H NMR techniques were used to determine compositional and structural indexes. The results show that the nC_(18)/Phytane GC index, that was 1.5 for crude oil, decreased with exposure time to values between 0.97-0.17 in the residues. The percentages for the four aliphatic (H_1 - H_4) and the aromatic (H_A) proton types, determined by ~1H NMR, were: 12.9-34.4 (H_1), 43.3-60.2 (H_2), 4.24-24.2 (H_3), 1.33-17.9 (H_4), and 0.44-4.81 (H_A), in crude oil and residues, respectively. Furthermore, the characterization of significant ~1H NMR signals indicated the presence of carboxylic acid hydrogens in the polar fraction of the crude oil and of residues of two years age. The Principal Components Analysis (PCA) of the parameters determined by CC, GC and NMR showed that the first three principal components (1st, 2nd, and 3rd PC), accounted for more than 84% of variance. The 1st PC is largely influenced by H_3, H_1, H_4, H_2, and the nC_(18)/Phytane GC parameter, in the order given. The evaluation of the different parameters by PCA suggests that ~1H NMR is more useful than GC to evaluate the degree of the chemical transformations of oil spills in soils.