FAQ: Dispersants and Bioremediation

Q. What's the difference between dispersants and bioremediation agents? Or is there a difference?

A. Dispersants and bioremediation agents are considered separately in oil spill response, because of two important differences between these response methods. One difference has to do with the mechanism by which they help to "clean up" oil, and the other has to do with where and how they are used.

In the dispersant category are products that are applied to the water surface in order to break up surface oil slicks and facilitate the movement of oil particles into the water column. There is evidence that dispersed oil degrades more quickly than undispersed oil, perhaps because the total surface area of an oil slick increases as dispersants break up the slick into small droplets.

Bioremediation agents are almost always applied to residual oil on shorelines, for long-term cleanup situations. Usually, heavy oil is first removed before bioremediation is undertaken. Bioremediation agents act by speeding up the microbial degradation of the petroleum molecules.

The Clean Water Act [Cornell Law School website] (33 U.S.C. s/s 1251 et seq.) mandates that products must be listed on the EPA's National Contingency Plan's Product Schedule in order to be authorized for use on oil discharges in the U.S. The Schedule groups products under several categories, including bioremediation agents, dispersants, and so on.

Q. I want to learn more about how dispersants affect oil degradation. Can you point me towards references on this subject?

A. Please see "Effect of dispersants on oil biodegradation under simulated marine conditions" by Richard Swannell and Fabien Daniel. This is a recent paper which includes a number of additional references on the topic of degradation of dispersed oil. You can find it in the Proceedings of the 1999 International Oil Spill Conference, pages 169-176.

Q. How toxic are the commercial chemical dispersants that are applied to oil slicks? One of my students would like to work with dispersants in a science project--what safety concerns should I be aware of?

A. The dispersants approved for use in the U.S. are less toxic than household dishwashing detergent, and much less toxic than some chemicals typically used in school chemistry laboratories, such as acetone. The EPA offers handling recommendations for some of the dispersants authorized for use on oil discharges in the U.S.

Q. Can you tell me where I can get some chemical dispersant to use in my science experiments for school? I need only a small quantity.

A. To our knowledge, commercial dispersants aren't available in stores and generally aren't available in small quantities. Your best bet would be to contact dispersant manufacturers directly to ask about purchasing a small amount. The EPA offers information about some of the common dispersants authorized for use on oil discharges in the U.S., including contact information for their manufacturers.

A less-expensive alternative would be to use liquid dishwashing detergent rather than a commercial dispersant in your experiments. Bird rehabilitators use dishwashing detergent to wash live birds that are oiled in oil spills, and we often use dishwashing detergent to demonstrate how dispersants work on oil. Detergent is not exactly the same as commercial dispersants, but it works in a similar way. Grease and oil on dishes binds to the detergent, and washes away in the rinse water. Likewise, dispersant binds to oil on the water surface, so that the oil can mix and disperse into the water.

You also can use dishwashing detergent to demonstrate how to wash oil off feathers.

Q. In my science project, I want to test how well chemical dispersants work for dispersing crude oil. You mentioned that I could use dish detergent instead of a chemical dispersant in my experiment, because chemical dispersants and dish detergent work in a similar manner. Just how are they similar? Is it just because they both do the same thing: that is, dish detergent disperses grease like chemical dispersants disperse crude oil?

A. Your guess is exactly right. Detergent soaps act like dispersants, in that one end of each detergent molecule binds to the oil, and the other end binds to water molecules. This binding helps overcome the natural resistance of oil to water (by breaking down surface tension). If you pour oil onto water without adding dispersants or detergent, the oil stays in a layer on top of the water surface. If you shake up the oil and water, it will mix temporarily, but it will always separate again. Dispersant and/or detergent help to keep the oil (or grease, if you're washing dishes) in suspension in the water (check our picture of how the process works).

Q. I'd like to do a science project to test whether bioremediation or chemical dispersants work best for removing spilled crude oil. But I don't know the type of bacteria used for bioremediation or the names of the commonly-used chemical dispersants. Can you tell me?

A. The EPA offers information about dispersants and bioremediation agents authorized for use on oil discharges in the U.S., along with contact information for their manufacturers. These products aren't generally available in small quantities, but you might be able to arrange with a manufacturer to make a special purchase. If you can't obtain a commercial chemical dispersant, you could try using liquid dishwashing detergent, which acts very similarly (see our answer to the preceding question).

A note about bioremediation agents: Biodegradation is the process in which oil molecules are broken down by bacteria (you can think of it as the bacteria "eating" the long hydrocarbon chains that make up oil). Biodegradation happens naturally, without our doing anything at all. You don't need to add bacteria to make biodegradation happen, because any water from the ocean, a lake, or a pond naturally contains bacteria. However, to make oil biodegrade faster, people sometimes apply bioremediation agents or techniques:

• They may add nutrients in the form of fertilizer (such as you might use in your garden).
  
• They may add bacteria designed to be especially effective at degrading oil.
  
• They may use techniques to make oxygen more available to native bacteria (e.g., adding special chemicals or tilling oiled substrate).

Project ideas: In your own experiment, if you can't obtain a commercial bioremediation agent, you might try adding different amounts and kinds of fertilizers. If you're testing cleanup of oiled soil, you also might try tilling some soil, and leaving other soil untilled.

Finally, recent research suggests that in the real-life circumstances of an oil spill, dispersion and biodegradation may complement each other--so it may not be meaningful to ask which is more effective. Once oil has been dispersed in the water, it may biodegrade faster, because the small globules of dispersed oil can more easily be attacked by bacteria. In your project, you might want to address this active research question yourself by testing three kinds of treatments: just enhancing biodegradation (e.g., by adding fertilizer as your bioremediation agent), just adding dispersants, and using both techniques together.