tag:blogger.com,1999:blog-5251183560375528307.post1328911349265961001..comments2024-03-28T21:34:42.328-05:00Comments on Bit Tooth Energy: The Gulf Deepwater Oil Spill - EPA changes its mindHeading Outhttp://www.blogger.com/profile/01790783659594652657noreply@blogger.comBlogger2125tag:blogger.com,1999:blog-5251183560375528307.post-18226240041337554732010-05-25T00:02:28.539-05:002010-05-25T00:02:28.539-05:00Thanks for this background, I suspect I will refer...Thanks for this background, I suspect I will refer to it more once the emphasis shifts from killing the well to the cleanup.Heading Outhttps://www.blogger.com/profile/01790783659594652657noreply@blogger.comtag:blogger.com,1999:blog-5251183560375528307.post-61413092408862459392010-05-22T23:05:17.483-05:002010-05-22T23:05:17.483-05:00I'd like to post a comment here about dispersa...I'd like to post a comment here about dispersants, the change of mind referred to in this thread's title. And since, HO, I know a little about you, let me reciprocate with a one sentence background about me. I've spent roughly 15 years in the Canadian equivalent of EPA, another 15 as a science manager in an oceanographic institute, and 10 running a small environmental consulting company. For readers to whom the term is a new one, the LC50 figures in your quote from EPA refer to the concentration that kills 50% of the test organisms in a bioassay, a number usually calculated from a 2-day or 4-day exposure. Menidia (a small fish) and Mysidopsis (a shrimp) are two of the organisms used in bioassays as the aquatic equivalent of laboratory rats. So we have EPA calling here for a less toxic dispersant, which has an LC50 to shrimp greater than 18 ppm. <br /><br />Death (LC50) is not the only relevant endpoint. Any dispersant, will increase the biological availability of the more toxic components of oil. This enhances not only lethality but also the probability of sublethal effects. One of the issues with dispersing oil at depth in the water column is that it's much more resistant to degradation there, and in the sediment, than it is exposed to air, nutrients and mixing at the surface. It's also inaccessible to cleanup efforts until it comes ashore, as some of it it will. Trapped in the water column, the lighter fractions of the oil dissolve and it's these lighter fractions that are the most toxic to marine life, with potential for a range of reproductive, carcinogenic and mutagenic effects. <br /><br />As dispersed oil degrades, its buoyancy slowly decreases and it should eventually sink or in other ways enter the sediment, unless it comes ashore first. Once oil (dispersed or not) enters the sediment, the rate of degradation slows dramatically as an adequate oxygen and nutrient supply becomes more of a problem. Storms are quite effective at moving sediment towards and onto the shore, so 'fresh' contamination from this incident can be expected onshore, mostly likely in the Eastern GOM, for years and years and years to come.<br /><br />The main vehicles for dispersant application in this incident have been aircraft and vessels. With aircraft, obtaining adequate mixing of the dispersant with the oil isn't possible; it’s even difficult with vessel application. For the aircraft applications, natural mixing though the action of wind and breaking waves is pretty much it; calm conditions make that mixing even less efficient. If the dispersed oil sinks before it drifts ashore, see above. If it doesn't, and I've seen news video of what looks to me a lot like dispersed oil in the marshes, well we're back to enhanced toxicity. As the saying goes, you pays your money and you makes your choices, none of which are consequence-free.<br /><br />I apologise for going on at length about this, but the comments I’ve read on TOD suggest to me that most readers here will be relatively unfamiliar with the questions surrounding dispersant use. Those interested in reading more about the complexity of the decision to apply or not to apply, could look at <a href="http://www.nap.edu/catalog.php?record_id=11283" rel="nofollow"><i>Oil Spill Dispersants: Efficacy and Effects</i></a>, a 2005 publication of the National Academies, starting around page 39. In oversimplified terms, the decision is a tradeoff between protecting shoreline resources or protecting pelagic and benthic resources. In a blowout like this one, it's not a question so much of protecting the environment as it is of deciding which components of the environment you're more and less willing to see damaged. Interagency spill response groups go through periodic exercises to evaluate just what might be the preferred responses to almost every imaginable situation, allowing decisions to be made in situations like this more quickly when the time comes. And the decision is never made on the basis of science alone, no matter how much scientists like me like to argue the case.porsenahttps://www.blogger.com/profile/04362269873149438270noreply@blogger.com