Petroleum residues as water-repellent substances in weathered nonwettable oil-contaminated soils

Some soils develop severe water repellency several years or decades followi ng oil contamination. We previously reported on the characteristics of thre e such soils. Here we report on the characteristics of putative water-repel lent substances in them. We examined the effectiveness of various polar, no npolar and amphiphilic solvents for removal of water-repellent substances i n three nonwettable soils, Only the amphiphilic solvent mixture isopropanol /14.8 M ammonia (7:3, vol/vol) (IPA/NH4OH) completely eliminated soil water repellency in all three soils. We thus define putative water-repellent sub stances as those substances whose removal from soil by IPA/NH4OH removes wa ter repellency. High-resolution CPMAS C-13-NMR spectroscopy and thermal des orption followed by conventional gas chromatography/mass spectroscopy with electron impact ionization (GC/EI/MS) and GC/MS with chemical ionization (G C/CI/MS) were used to characterize extracted putative water-repellent subst ances. We conclude that: (i) the identified representatives of these substa nces consist mostly of homologous series of long-chain and polycyclic aliph atic organic compounds; namely, n-fatty acids, n-alkanes, and cycloalkanes, and that (ii) they are of petroleum origin rather than plant or microbial origin.