Nitrate Addition Has Minimal Effect on Anaerobic Biodegradation of Benzene in Coastal Saline (salt), Brackish and Freshwater Marsh Sediments

In response to the 2010 British Petroleum (BP) Deepwater Horizon Macondo well oil spill, saline (salt), brackish and freshwater marsh sediments were used to study whether nitrate addition could stimulate petroleum biodegradation. Benzene was selected as a model petroleum hydrocarbon, and its biodegradation was assumed to follow first-order kinetics. The results show that the intrinsic benzene degradation activities in the marsh sediments were inversely correlated (R (2) = 0.83, n = 9) with the sediment salinity, with following order of benzene degradation rate regardless of nitrate treatments, freshwater > brackish > salt (P < 0.05). Addition of nitrate shows a minimal potential to stimulate the benzene degradation. Increase of redox potentials by addition of nitrate even shows a slight inhibition effect on benzene degradation in these coastal marsh sediments without a clear mechanism. Excessive loading of nitrate has been causing frequent occurrence of coastal eutrophication and hypoxia in the Gulf of Mexico. Therefore, application of additional nitrate to the coastal marsh sediments for the remediation of the 2010 BP oil spill is not recommended.