Many questions still unanswered on dispersants following EPA report

This week, the EPA released an additional round of research findings on the dispersant used in the Gulf Oil Spill.

The EPA has conducted acute toxicity testing of eight chemical oil dispersants - including the one used in response to the Gulf oil spill - on two aquatic test species which are found in the Gulf, a small mysid shrimp and a small fish, Menidia (neither are consumed by humans). 

The first round of EPA laboratory testing found that the dispersants were less toxic than the southern Louisiana crude itself and that they displayed similar toxicities to one another.  The second round of EPA testing found that the dispersant/oil mixtures had similar toxicities to southern Louisiana crude itself and similar toxicities to one another (with the exception of the dispersant brand Nokomis/oil mixture which was more toxic to the shrimp than oil alone).

These results represent another piece to a very complex puzzle. 

In a statement to the press about these research results, Dr. Paul Anastas said that ‘while more needs to be done, the picture is becoming clearer’ that dispersants were an ‘important tool in this response.’ 

Dr. Anastas pointed to four lines of evidence:

  1. the dispersants appeared to be helping keep oil off our shoreline (in other words, in the water)
  2. the dispersants are less toxic than the oil being released
  3. the dispersant/oil mixture has roughly the same toxicity as the oil itself  
  4. no traces of dispersant have been found ‘away’ from the well head

But while it may be tempting to conclude that the use of dispersants during this catastrophic oil spill was a good idea, we urge the federal government not to hasten this evaluation and rush to judgment.

The unprecedented and widespread application of dispersants in this oil spill was a grand experiment.  Given the scale of this spill, its position offshore, and the severe and long-lasting impacts of oil to salt marsh ecosystems, the rational was clear and defensible. 

However, as the most recent National Research Council panel on the topic concluded in 2005, much remains unknown about the efficacy and impacts of chemical dispersants.  And as a consequence, careful and thorough study of these factors is imperative. 

It would be unwise to draw conclusions about the safety of their use following these two laboratory experiments on toxicity (particularly when the results from phase II are not concordant with previous research on the topic) and field evidence that shows the dispersants were successfully dispersing the oil.

Many important pieces of the puzzle are outstanding:

  •  Where has the oil gone?  What proportion has hit land, sunk to the bottom, evaporated, or remains mixed into the water column?  This final calculus has not been conducted but is essential to understand the efficacy of the dispersants.
  • How did the chemical dispersion at 5000 feet depth differ from the physical dispersion at that depth that was happening naturally?
  • How large an area offshore is impacted?
  • What ocean organisms and ecosystems encountered the oil?  What harm has occurred and may occur long term?
  • Is the chemically dispersed oil – or the dispersants – getting into the food chain; is there the potential for it to get into the food chain?
  • What are the public health implications of exposure to dispersants by the response workers?
  • What are the public health implications for food consumption?

It is clear that the use of chemical dispersants is a tradeoff - but it’s not at all clear that we fully understand the tradeoff we made yet.  This question of tradeoffs represents a ‘500 piece’ puzzle and cannot be evaluated with four puzzle pieces.

We need federal scientists from NOAA as well as the EPA get to the bottom of the remaining questions.  It’s the follow-through that will make this catastrophe less of a disaster. 

About the Authors

Lisa Suatoni

Senior Scientist, Oceans program

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