COMPARISON OF OIL COMPOSITION CHANGES DUE TO BIODEGRADATION AND PHYSICAL-WEATHERING IN DIFFERENT OILS

The well-characterized Alberta Sweet Mixed Blend oil and several other oils which are commonly transported in Canada were physically weather ed and then incubated with a defined microbial inoculum. The purpose w as to produce quantitative data on oil components and component groups which are more susceptible or resistant to biodegradation, and to det ermine how oils rank in relation to each other in terms of biodegradat ion potential. The biodegraded oils were characterized by quantitative determination of changes in important hydrocarbon groups including th e total petroleum hydrocarbons, total saturates and aromatics, and als o by quantitation of more than 100 individual target aliphatic, aromat ic and biomarker components. The study reveals a pattern of distinct o il composition changes due to biodegradation, which is significantly d ifferent from the pattern due to physical or short-term weathering. It is important to be able to distinguish between these two forms of los s, so that loss due to weathering is not interpreted as loss due to bi odegradation in the laboratory or in the field. Based on these finding s, the oil composition changes due to biodegradation can be readily di fferentiated fi om those due to physical weathering. To rank the teste d oils with respect to biodegradability, losses in total petroleum hyd rocarbons and aromatics were used to calculate biodegradation potentia l indices, employing equations proposed by Environment Canada and the US National Oceanic and Atmospheric Administration. The different meth ods produced very similar biodegradation trends, confirming that patte rns of oil biodegradability do exist. (C) 1998 Elsevier Science B.V. A ll rights reserved.