BIODEGRADATION RATES OF CRUDE-OIL IN SEAWATER

Measurements of the rate of biodegradation of crude oil in seawater in laboratory, mesocosm, and field systems from 16 published reports were reviewed and compared. Volumetric biodegradation rates range widely from approximately 0.01 to 1 000 gC/m(3)-d. Laboratory studies report rates at the higher end of this range, while field and mesocosm studies, of which there are fewer, suggest much lower rates ranging from 0.01 to 0.3 gC/m(3)-d. Possible explanations for the discrepancy between measurements made at different scales are differences in oil concentration and in mixing energy. When temperature-scaled degradation rates from all systems are plotted versus initial oil concentration on a log-log scale, the data are approximately linear (r(2) = 0.86) over several orders of magnitude. The slope of the regressed line is near 1, indicating that the process can be interpreted as first order with respect to oil concentration. The half-life for biodegradation is estimated to be approximately two months at 20 degrees C. This analysis suggests that crude oil biodegradation in seawater is relatively slow and indicates that further research is required to bridge the gap between laboratory and field systems.