Quantification of compositional changes of petroleum hydrocarbons by GC/FID and CC/MS during a long-term bioremediation experiment

Samples from a long-term bioremediation experiment contaminated with two cr ude oils, Arabian Heavy and Gullfax, was used to analyze the compositional change of petroleum hydrocarbons. A time course of five different homologou s series of petroleum hydrocarbons were analysed by GC/FID and GC/MS. The h omologous series were n-alkanes, acyclic isoprenoids, alkylated naphthalene s, alkylated phenanthrenes, and alkylated dibenzothiophenes. Several biomar ker compounds were monitored during the experiment to evaluate the possible use as conserved reference compounds for the quantification of other oil c ompounds, that is, nor-hopanes, hopanes, methyl-hopanes, steranes, mono- og triaromatic steranes. The 17 alpha (H),21 beta (H)-hopane was found to be stable toward biodegradation and was used as reference compound The interna l standard quantification method was used to quantify changes of the homolo gous series of oil compounds, and a graphic presentation was used to compar e the decrease of the individual compounds. This was found to be an easy wa y of comparing relative changes in oil. The disappearance of the compounds was extensive and in 6 to 7 months less than 6% remained. The decrease of the n-alkanes (>C15) and acyclic isopreno ids was almost uniform within each homologous series and thus independent o f physical-chemical characteristics. Evaporation affected compounds with bo iling points lower than n-C15. The alkylated aromatic and sulfur-aromatic c ompounds decreased according to the degree of alkylation and the decrease s howed to be delayed by 10 to 20% by each additional alkyl group. The lack o f isomeric-specific degradation of most of the aromatic and sulfur-aromatic compounds, until extensive decrease in concentration had occurred, suggest s these compounds have to be dissolved, before any biodegradation occurs.