by: EPA

General Information about Dispersants

What do we know about the biodegradation rate of non-dispersed oil?
Extensive laboratory and field research has been done on the biodegradation of crude oil. The South Louisiana crude in the Gulf spill is considered a "light" crude oil and is known to degrade at a faster rate than heavier weight oils from other locations such as Alaska. Some studies suggest that the half-life for Louisiana crude is 12-70 days in seawater.

What do we know about the biodegradation rate of chemically-dispersed oil?
Chemical dispersants are designed to form smaller droplets when mixed with oil. These smaller droplets are more readily available to be biodegraded by micro-organisms. EPA has published research on the biodegradation of dispersed oil which suggests that the dispersant speeds the biodegradation of oil. Based upon this research, the rate of biodegradation increases almost 50% in the presence of COREXIT 9500 vs. oil without dispersant.

What do we know about the biodegradation rate of the dispersant itself?
We are currently unaware of published scientific information in the peer reviewed literature about the biodegradation of the dispersant itself. We do have information about the individual components (ingredients) of the dispersant, provided by the manufacturer's Material Safety Data Sheets (MSDS). The available peer-reviewed literature indicates that the components biodegrade fairly rapidly.

Have dispersants ever been used this much before?
While dispersants have been used in previous oil spills, this is the largest application of dispersants at an oil spill response in the United States. Since the spill occurred, EPA and its federal partners have closely monitored any potential impacts of the dispersant including air quality monitoring by both planes and through mobile and fixed locations.

Thus far, preliminary results of EPA's initial air monitoring efforts have not shown risks to human health from dispersants. We have also developed a plan to monitor the surface and subsea use of dispersants. That plan is evolving and we will continue to update the website.

What are the future plans for use of dispersants for oil spills? Will the industry and federal government look to continue their use?
Generally, the use of dispersants is restricted under the National Oil and Hazardous Substances Pollution Contingency Plan (NCP). Dispersants must be on the US EPA Product List, and federal and state agencies have agreements establishing areas where rapid decisions on dispersants may be made by the Federal On-Scene Coordinators.

Some History of Dispersant Use:

•In the US, dispersants have been applied to much smaller spills off the coast of Louisiana and Texas over the last 15 years.
•At the IXTOC-I Well Blowout near Vera Cruz, Mexico in 1979, between 1 million and 2.5 million gallons of mostly Corexit dispersant products were applied over a five-month period on the oil discharge.
•In Australia last year, 50,000 gallons of dispersants were used on the 9 million gallon West Atlas oil platform spill in the northern Timor Sea.
•In the United Kingdom, dispersants are considered the first line of defense because of high seas and rugged coastlines. In 1996, 118,000 gallons of dispersants were used on the 20 million gallon Sea Empress oil spill in Wales.