Overwhelming Majority of Studies Find that Dispersants Slow Growth of Oil-Eating Microbes

As I pointed out on August 20th:

There is no clear science showing that dispersants help microbes break down oil. As Chemical and Engineering News noted in June:

Behind those teams’ assumption lie murky data. The authors of the 2005 [National Research Council] dispersant report described the results of three decades of research into dispersants’ effects on biodegradation as “mixed” with studies showing evidence for “enhancement, inhibition, and no effect.”

I noted last week:

Some experts have also said that the use of Corexit has prolonged by decades the presence of toxic crude oil, because the dispersant sinks the oil beneath the ocean surface, where it cannot be quickly broken down by sun, waves and microbes.

And the head of Lawrence Berkeley National Laboratory's Ecology Department - Terry Hazen - argues that the use of dispersants can delay recovery of ocean ecosystems by decades:

Hazen has more than 30 years experience studying the effects of oil spills. He says the oil will be damaging enough; toxic dispersants will just make it worse. He points to the 1978 Amoco Cadiz Spill off the coast of Normandy as an example. He says areas where dispersants were used still have not fully recovered, while areas where there was no human intervention are now fine.

As Hazen has noted:

"The untreated coastal areas were fully recovered within five years of the Amoco Cadiz spill," says Hazen. "As for the treated areas, ecological studies show that 30 years later, those areas still have not recovered."

Admittedly, chemicals other than Corexit were used in the Amoco Cadiz spill. But the precautionary tale still holds: chemicals should not be applied to oil spills unless scientists are positive that they will provide a net long-term benefit.

Disturbingly, Corexit is apparently still being sprayed in the Gulf. See this, this and this.

The Los Angeles Times noted yesterday:

Scientists say they still don't know whether dispersants truly enable bacteria to digest spilled oil more quickly or whether dispersed oil is safer for marine life than untreated slicks.

***

Mervin Fingas, a retired scientist with the Canadian government, said that of roughly 40 biodegradability studies he surveyed between 1997 and 2008, about 60% said dispersant retarded growth of oil-eating microbes and 15% reported no effect. The remaining 25% noted a positive effect.

But positive findings are open to interpretation. At a 1999 oil spill conference, researchers reported that microbial populations dining on oil treated with the dispersant Corexit 9500 (used by BP in the gulf) grew more than seven times as large as those eating oil dispersed physically, suggesting the bacteria were helping.

Yet a comprehensive 2005 review of dispersants by the National Research Council concluded that the healthy bacterial growth in such studies could easily be due to microbes feeding on dispersant, not oil. "There is no conclusive evidence demonstrating either the enhancement or the inhibition of microbial biodegradation when dispersants are used," the 12 authors wrote.

PhD toxicologist Chris Pincetich told me last week that scientists have no idea what compounds will be formed when Corexit dispersant and oil interact under the high pressures or temperatures present at BP's deepwater spill site.

The above-linked L.A. Times article gives specifics on pressure and temperature involed:

[Scientists] can't say whether it was a help or hindrance that BP decided to spray much of the dispersant not onto the water surface, as is more common, but over oil pouring out of the leaking wellhead 5,000 feet under the sea. Both the high pressure (151 times greater than at the surface) and the oil's temperature (100 degrees Celsius, or 212 degrees Fahrenheit) could have affected dispersant action, either for better or worse.

Dr. Pincetich also told me that the tests used for the toxicity of dispersants, crude oil, and dispersant-oil mixtures are wholly inadequate.

Similarly, the Los Angeles Times reports:

But the concern is that dispersed oil may do more harm to marine life than oil left alone. And on this point, findings vary widely, in part because lab tests have limitations, said Andrew Nyman, a Louisiana State University professor. In small containers, dispersed oil can't dilute. Studies look at large, quick effects, such as death or deformity. Results depend on the oil type, whether it's fresh, the dispersant, the animal being studied and its life stage.

***

This jumble of findings has led to disagreement among experts that might be resolved by careful analysis of real-life cleanups, which hardly ever happens, said Larry McKinney, executive director of Texas A&M University's Harte Research Institute for Gulf of Mexico Studies in Corpus Christi, Texas.