Richard Denison, Ph.D., is a Senior Scientist.
EPA held a press call today to discuss the initial results of its own testing of oil spill dispersants. The testing by EPA was initiated after BP resisted complying with an EPA-Coast Guard Directive issued May 20 that directed the company to identify and switch to dispersants that are less toxic and more effective than the two Corexit® dispersants on which BP has exclusively relied to mitigate the effects of the oil disaster unfolding at Deepwater Horizon. In expressing disappointment with BP’s response to the Directive, EPA indicated it would initiate its own toxicity and effectiveness testing of Corexit and other dispersants. Today’s call reported on round 1 of that testing.
First let me say I applaud EPA for taking on the unglamorous task of conducting further testing and seeking to answer questions that would have been nice to have had answers to well before this mess developed. Second, I understand that testing takes time, that this is only round one and EPA says more is coming, so that at least partially compensates for the distinctly anticlimactic feeling I had listening in on today’s call.
So, what did we learn today? Not too much new.
The initial round of testing was conducted on Corexit 9500 and seven other dispersants listed on the National Contingency Plan (NCP) Product Schedule. Here are my initial takeaways:
- The testing was done on the dispersants by themselves – not in combination with oil. I posted earlier that acute toxicity increased as one progressed from dispersant by itself, to oil by itself, to the mixture of oil and dispersant. We’ll have to wait longer for EPA to release data that will shed further light on whether that conclusion holds or not.
- What is most remarkable about the data EPA released today is how similar they are to the industry-supplied data on the dispersants by themselves that were previously made available on EPA’s website. With only a few exceptions, the new toxicity values changed by a factor of 2 or 3.
- The exceptions that involved slightly larger changes are:
- JD-2000 appears to be 9-fold less acutely toxic to shrimp and at least 14-fold less toxic to fish than indicated by the previous data.
- Sea Brat #4 is about 5-fold less toxic to shrimp.
- Corexit 9500 is about 5-fold less toxic to fish, while Corexit 9500’s toxicity to shrimp is essentially unchanged.
- The before-and-after toxicity levels changed on average by a factor of 2.8 for shrimp and a factor of 3.1 for shrimp. Excluding JD-2000, the changes averaged only 2.0 for shrimp and 1.6 for fish.
On this point, EPA’s data report concludes: “Given the expected range of inter-laboratory variability, the results of the present study were consistent with test results reported in the NCP Product Schedule, with the exception of two dispersants for each test species which yielded higher LC50s (i.e., lower toxicity) than reported in the NCP.”
The new data for Corexit 9500 by itself leave unchanged its classification by EPA as “slightly toxic” to shrimp, and downgrade its classification from “slightly toxic” to “practically non-toxic” to fish.
No new testing was done on Corexit 9527, which was used initially in the response to the spill.
So, for the most part the new data largely confirm the previous data, while suggesting that one dispersant (JD-2000) is a fair bit less acutely toxic to fish and shrimp than its manufacturer’s data indicated, and that Corexit 9500 is a bit less acutely toxic to fish, and about as toxic to shrimp as indicated by the earlier data.
All of the bigger questions remain, of course, including:
- Does dispersant use increase the acute toxicity of the oil? EPA describes its next round of testing as aimed at answering this question.
- What about sublethal and longer-term effects?
- What is the ultimate fate and impact of dispersed vs. undispersed oil?