Remediation of Vegetable Oil Spills: Anaerobic Biodegradability and Toxicity of Vegetable Oil in Freshwater Sediments

The anaerobic biodegradation kinetics of vegetable oil in freshwater sediments is being investigated to evaluate the feasibility of oil sedimentation as a spill response alternative. Concern over the potential toxicity of fatty acid intermediates led to the use of a twolevel, four-factor full factorial experimental design to test the effects of several amendments on the rate and extent of oil biodegradation. Ferric hydroxide initially stimulated the rate of oil biodegradation, but it ultimately reduced the apparent extent of oil mineralization. Addition of clay reduced the extent of vegetable oil biodegradation, but had no effect on the rate of the reaction. Amendment of the sediments with calcium inhibited the rate and extent of oil biodegradation. The toxicity of intermediates formed during the anaerobic biodegradation of canola oil in freshwater sediments was investigated using the Microtox Solid-Phase Test. Toxicity data confirmed that toxic intermediates, probably long chain fatty acids, were formed transiently during the early stage of the process, but the sediment toxicity returned to a level that was similar to the unoiled sediments within five months in all microcosms except those amended with clay. The residual toxicity in the clay-amended microcosms is thought to be due to hydrogen sulfide, formed by reduction of sulfate, which was present as a contaminant in the clay.