Development of a method for the application of solid-phase microextractionto monitor biodegradation of volatile hydrocarbons during bacterial growthon crude oil

A quantitative solid-phase microextraction, gas chromatography, flame ioniz ation detector (SPME-GC-FID) method for low-molecular-weight hydrocarbons f rom crude oil was developed and applied to live biodegradation samples. Rep eated sampling was achieved through headspace extractions at 30 degreesC fo r 45 min from flasks sealed with Teflon Mininert. Quantification without de tailed knowledge of oil-water-air partition coefficients required the prepa ration of standard curves. An inverse relationship between retention time a nd mass accumulated on the SPME fibre was noted. Hydrocarbons from C-5 to C -16 were detected and those up to C-11 were quantified. Total volatiles wer e quantified using six calibration curves. Biodegradation of volatile hydro carbons during growth on crude oil was faster and more complete with a mixe d culture than pure isolates derived therefrom. The mixed culture degraded 55% of the compounds by weight in 4 days versus 30-35% by pure cultures of Pseudomonas aeruginosa, Rhodococcus globerulus or a co-culture of the two. The initial degradation rate was threefold higher for the mixed culture, re aching 45% degradation after 48 h. For the mixed culture, the degradation r ate of individual alkanes was proportional to the initial concentration, de creasing from hexane to undecane. P. fluorescens was unable to degrade any of the low-molecular-weight hydrocarbons and methylcyclohexane was recalcit rant in all cases. Overall, the method was found to be reliable and cost-ef fective.