Laboratory and field studies of oil biodegradation in natural seawater

Data from 21 laboratory and field studies of petroleum oil biodegradation in natural seawater (SW) were compared in this study. The studies were performed in SW from temperate and Arctic regions over a period over nearly 30 years. Six crude oils and an ultra-low sulphur fuel oil were included, while both local (Trondheimsfjord, Norway) and non-local (Northern Norway, Svalbard and Western Greenland) seawaters were used as microbial inocula. Different experimental systems were included in the studies, and saturated (C10-C36) and aromatic (monoaromatic and 2- to 5-ring polyaromatic carbons) oil compound groups and target analytes quantified by gas chromatographic analyses. Biodegradation rates and degradation half-life times were determined by first-order rate calculations. The effects of several variables on biodegradation rates were compared, including SW temperatures, oils, experimental laboratory systems, and differences between laboratory and field data. Significant differences were shown between degradation rates of targeted analytes, but not between oil compound groups, when dispersed oil and water-accommodated fractions, and dispersed and immobilized oils, were compared. Despite differences in oil properties, biodegradation rates were comparable between the oils. Impacts of SW temperatures were more pronounced in laboratory than in field experiments. The compiled data from all these studies emphasized the need for performing biodegradation studies at ambient seawater temperatures.