Bioremediation Effective in Cleanup of Exxon Valdez Spill, Company Reports

Senior staff biochemist Roger Prince told the conference on in-situ and on-site bioreclamation that along with more traditional forms of oil removal, Exxon spread 50,000 pounds of fertilizer * over 74 miles of beach to supplement naturally available nitrogen and phosphorous.

"Microbes need nitrogen to build more biomass, to grow more rapidly and eat more of the oil,"  Prince told BNA April 5.  "As they eat the oil it converts the oil into more microbes (at) a conversion rate of 50 percent.

Biodegradation is the only route, after evaporation, without human intervention for the oil to leave the environment.  It will happen, you cannot stop it," Prince said.

The question that remains is how much longer this process will take, he said, adding that "we stimulated the rate fivefold faster" through bioremediation.

Exxon used two fertilizers in the cleanup:  Customblen, a slow-release solid fertilizer that was developed by Grace Sierra Chemicals for agricultural and lawn use, and Inipol, manufactured by a subsidiary of Elf Aquitaine. *  (others experimented with)

A honey-colored liquid microemulsion, Inipol is composed mainly of oleic acid, the principal fatty acid of olive oil, according to a December 1992 Exxon report, Bioremediation for Shoreline Cleanup Following the 1989 Alaskan Oil Spill.  It is also composed of water droplets containing urea, a source of nitrogen.  These droplets are stabilized p.3169 within the oil by tri(laureth-4)phosphate, a greasy bulking agent frequently used in cosmetics, which also provides phosphorus.

"Oleic acid sticks to the oil and delivers the nitrogen close to the oil," Prince said.  Because of this, Inipol was applied on surface areas, while Customblen was used on subsurface areas.

In 1990, Exxon participated with Alaska in a two-year monitoring program to test the efficiency and safety of the fertilizer. "The state wasn't completely convinced this wasn't being done by sleight of hand," Prince said.

"There were two camps.  One said it would be completely disastrous, a complete waste of time.  The other said it would stimulate the microbes so dramatically they would make the beach anaerobic, with nasty smells, death, and destruction," Prince said.  "Fortunately, it came out in the middle."

Monitoring

In monitoring 26 sites, some of which had received bioremediation, there was a statistically significant difference in the number of microbes on fertilized versus unfertilized beaches in the month following treatments in both l989 and l990, according to Exxon's report.  Shorelines that had received fertilizer applications had almost a hundredfold more bacteria per gram of sediment than untreated sites, it said.

"Before the oil spill, microorganisms able to degrade hydrocarbons were present in the Sound but their numbers were limited by the availability of hydrocarbons," the report said.  "The spill provided these oil-degrading microorganisms with an abundant food supply and their numbers dramatically increased.

"However, as expected, once they consumed the oil, their numbers returned to pre-spill levels," the report said.

As evidence of the treated waters' safety, the report cited tests of Mysid shrimp who survived in water samples collected from treated beaches during a summer 1990 monitoring program.  Mysid shrimp were determined to be the most sensitive test organism to nitrogen and ammonia, Prince told BNA.  The shrimp were placed in beach water samples for 96 hours and had a survival rate of 90 percent.

Also, there was testing for 2-butoxyethanol, a common solvent used in Inipol as a viscosity reducer and stabilizer.  "While it is biodegradable, it is potentially harmful to mammals if a sufficient amount is absorbed through the skin.  Even though it is water soluble and volatile, there were concerns that it might persist on treated shorelines and present a hazard to wildlife," the report said.   msds

Samples were collected by wiping Inipol-sprayed cobbles from a treated beach one hour after application and again after the first, second, and fourth tides.  The amount of the solvent decreased by up to 98 percent and was undetectable after four tides.

"At the end of 48 hours, there was less than .04 percent of the initial level.  This suggested there was negligible risk of exposure to wildlife," the report maintained.

According to Prince, bioremediation "will probably be part of the toolbox to respond to any future spills." He concluded that the Prince William Sound cleanup effort provides "the firsts quantitative proof that bioremediation of oil spills really works."