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by on June 8, 2010
From theoildrum

The BP spammers assigned here have already shared their childlike notions of bacterial remediation. This is a big topic going back decades with many thousands of peer-reviewed papers amongst the 1.3 million publications concerning bacteria at PubMed. Perhaps tell us when you post, in multiples of ten thousand, how many of these you have read.

Bacteria do not typically secrete enzymes into seawater to attack inaccessible oil molecules at droplet surfaces nor endocytose micelles no matter how small. Rather, they use membrane transporter proteins that can uptake specific oil molecular classes from seawater solution. Crude oil has many tens of thousands of different constituents even before weathering. These all dissolve in water to lesser or greater extent, the solubility constants of even the worst alkanes and polyaromatic hydrocarbons being low but not zero. In some Gulf localities we might be talking seawater + detergent, not straight seawater, as the applicable solvent. Oil might float in your glass but you wouldn’t want to drink the water under it.

Once brought inside the cell, hundreds of oil-induced enzymes go to work on the intial oxidative attack. These are being determined by metagenome transcriptome sequencing as we speak. All of these will ultimately use dissolved molecular oxygen as terminal electron acceptor and require iron or related metal as cofactor. The poster child here for most people would be Pseudomonas putida. Some types of oil molecules can be completely catabolized to CO2 for their ATP, others stall out as intermediate epoxides, peroxides, hydroxyls, aldehydes and carboxylates and are ejected back into the sea in vastly more soluble form (and possibly in vastly increased toxicity). No bacterial degradation of oil can occur in anaerobic sediments without an alternative electron acceptor (that’s in part why the reservoir is still there). The rate of degradation slows in cold water by about half for each ten degrees. They cannot innoculate the ocean with engineered or other bacterial strains.

On these giant undersea plumes so carefully mapped out down-current from the rig, the oxygen is observed sharply depleted at plume depth only (by all but the one vessel contracted to BP). Oxygen is unable to diffuse in fast enough from above or below to keep up with the rate of bacterial consumption. The oxygen levels measured to date are not yet so low as to form an avoidance zone (or dead zone) impairing the obligatory daily migration of food chain metazoa up and down the water column. Injecting dispersant here could be catastrophic if it pushed bacterial growth rates into the dead zone. Overall, it’s hard to say whether dispersants in this situation are good, bad, or irrelevent. Best I can do on this with three paragraphs.

Douglass Carmichael

Stanford MAHB, Stanford Strategy Studio, Media X
Shakespeare and Tao Consulting

Posted via email from Doug Carmichael reflections


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