skip to main content

→ Top Stories:
Clean Power plan
Safe Chemicals

Regan Nelson’s Blog

Chemical Dispersants: The Lesser of Two Evils?

Regan Nelson

Posted May 4, 2010

, , , , , ,
Share | | |

I landed in New Orleans at noon yesterday, and by 2 p.m. was on my way to Venice, Louisiana, nicknamed “the end of the world” for being the last community accessible by automobile down the Mississippi River.  Venice is now famous for another reason, of course.  This tiny community, which has only recently rebuilt from Hurricane Katrina, has become one of the staging areas for the cleanup effort in the Gulf.  Usually a quiet industrial town, Venice is teeming with people, cameras, National Guard trucks, official vehicles, and, yesterday, for a brief moment, President Obama.

As perhaps the newest face in Venice, I got a barrage of questions yesterday.  As the oil slick sits just offshore, people want to know what damage it’s doing out there, and specifically, folks wanted to know what we knew about the chemical dispersants that BP has been spraying over the surface of the slick, and which they are now spraying directly onto the leaks at deep ocean depths. 

To paraphrase a Bush Administration Cabinet Member:  “There are known unknowns. That is to say, there are things that we know we don’t know. But there are also unknown unknowns. These are things we do not know we don’t know.”  And that basically sums up the story about chemical dispersants.

The important thing to remember about chemical dispersants is that they do not reduce the total amount of oil entering the environment.  There is a perception that chemical dispersants are like an industrial soap that somehow cleans the water of oil, and that is fundamentally untrue. 

Chemical dispersants change the chemical and physical properties of oil, essentially breaking up oil that is congealed at the surface, and sending oil droplets down into the water column.  (By dispersing oil into deeper waters, away from human eyes, dispersants can also have the welcome public relations effect of making the spill appear smaller).  The primary objective of chemical dispersants is to avoid sending oil slicks into the nearshore marine environment.  We know from years of studies following the Exxon Valdez disaster that oil can persist in sediments for decades and can lead to long-term impacts to generations and generations of fish, shrimp, and crabs that rely on coastal habitat, so it makes sense that we do our best to keep oil from reaching the nearshore environment.  Additional goals include reducing impacts to mammals and birds that are vulnerable to floating oil slicks and encouraging bacteria to degrade the oil.    

That being said, the use of chemical dispersants is a trade-off.  It is an explicit decision to weigh impacts to mammals, birds, and coastal habitat over impacts to fish and invertebrates, and possibly bottom organisms. In other words, it may be the lesser of two evils in some circumstances.

Known Unknowns and Unknown Unknowns

The National Academy of Sciences published a report outlining the major gaps in knowledge regarding the efficacy and effects of chemical dispersants.  Here are some of the things we know we don’t know:

  • Toxicity level and effects from chemically dispersed oil (chemically dispersed oil may be more toxic than naturally dispersed oil)
  • The fate and effects of dispersed oil in areas with high suspended solids and areas of low flushing rates (e.g. Louisiana marshes)
  • The short-term and long-term effects of chemical dispersants and chemically dispersed oil to marine organisms in the water column

Chemical dispersants have the effect of mixing oil throughout the water column.  During this mixing, the oil forms an oil-water emulsion, which is toxic (though not well studied).  Because the emulsion is mixed with water, it has the effect of doubling the volume of the contaminated area.  The hope is that this leads to increased exposure to bacteria that break-down the oil before it comes ashore.  But this process takes on the order of weeks to months. It is during this temporary phase when the toxic cloud of oil and water droplets gets carried by the currents that people are most concerned; it undoubtedly harms the marine life it encounters. 

The type and extent of these impacts are the true unknown unknown in this story.  Right now we just don't know that much about the effects of dispersants and we aren't putting enough resources into studying it. There are a lot of important, unanswered questions about them, including how they affect the water below the surface, the toxicity from exposure, how dispersed oil passes through the food chain. And research funds in the United States to support oil spill response options in general are extremely limited and declining.            

But there are others, too.  Skeptics argue that the dispersants often do not achieve their primary objective of effectively dispersing the oil.   Improper application or unfavorable environmental conditions can hinder the necessary mixing with oil.  Effectiveness – which is not well studied - is influenced by many factors including oil composition, turbulence of the ocean, temperature, and salinity.  Sometimes the dispersants appear to work but relief workers find the oil has simply reassembled elsewhere.   In these cases, coastal habitats are not spared the suffocating effects of the oil slick, and further undesirable chemicals have been released to the environment.  In addition, some studies indicate that chemical dispersants suppress bacterial degradation of oil. 

So what should we do? This lack of knowledge leaves experts with inadequate information to be able to confidently support a decision to apply dispersants. Despite the problems and unknowns, many experts reluctantly turn to the use of dispersants because there are no good, reliable options once the oil is spilled.  Response technologies are consistently oversold by the oil industry; the truth is there is nothing that really completely undoes the harm of spilled oil.

Gulf of Mexico

Photo credit: Rocky Kistner / NRDC

Share | | |


EricMay 4 2010 01:16 PM

Great write up. Thank you so much for the information.

Bill S.May 4 2010 02:44 PM

Great post! The media, government and BP all seem to be touting dispersants as a silver bullet that makes the oil go "away," with "away" being defined as not a beach where an oiled bird can be photographed.

I have read postings elsewhere that say that the ingredients of many of the dispersants are proprietary trade-secrets. So we don't even know what they are dumping into the Gulf of Mexico. Is this true? If so, it certainly makes it difficult to monitor on-going impacts.

DMay 6 2010 03:16 PM

See this video about mats of hair that soak the may lead to innovation approaches to clean up in a non-toxic way...what if we submerge these products in the oil areas?

Jasmine MinbashianMay 6 2010 07:35 PM


Your blogs are very informative! Thanks for taking the time to write them and helping those of us who can't be there with you to feel like we are getting a more realistic portrayal of what is going on in the Gulf.

And I don't think we should use dispersants. There are too many unknowns (known and unknown). It's like turning on the vacuum cleaner so we don't have to hear the leaky faucet.

Mr. CoolMay 8 2010 10:37 AM

I have yet to read a news article that explores what will happen if they are unable to stop the flow of oil, (including the use of relief wells). What would happen if the oil just kept coming up until the reservoir beneath the ground ran out? Would the face of the earth heat up as a result of the heat trapping oil on the surface of the ocean? Would the normal evaporation processes that produce the majority of our rain water be hindered? What other effect might be caused if there turns out to be no way to stop the flow?

Comments are closed for this post.


Switchboard is the staff blog of the Natural Resources Defense Council, the nation’s most effective environmental group. For more about our work, including in-depth policy documents, action alerts and ways you can contribute, visit

Feeds: Stay Plugged In