At the time, a massive controversy erupted around the use of chemical oil spill dispersants, especially those of the Corexit family.
Those products were described as "highly toxic" and their effectivness cast into doubt. There were rumors that Corexit was chosen only to fill the coffers of its manufacturer and not on the basis of effectivness and safety (in fact, it also happened to be the dispersant most readily available in large amounts. Logistics is not a joke).
Now it happens that I needed to delve deeper into the world of oil spill dispersants, and I learn some interesting things. One good place to start is here: Oil Spill Dispersants: Efficacy and Effects by the National Academy of Science.
The use of dispersants is always a tradeoff, because they - and and the dispersed oil even more - are toxic to marine animals. But if an oil slick makes landfall, seabirds and coastal animals will die in droves too. Mangrove forests are very sensitive too, can be destroyed by oil spillages.
That's why professionals of the field talk about "net environmental damage" and not spillage fairies that will make the oil slick disappear.
The issue of efficacy vs. toxicity for dispersants is a rather hot one, and the wiseness of their massive use in the case of the Macondo oil spill is open to debate. It is indeed possible that the injection of dispersant at the base of the rising oil plume hampered mechanical recovery efforts on the surface, but mechanical recovery was also hampered by bad weather and, according to some professionals, poor command and control (which also affected the operations for dispersant application).
But this is not what prompted me to write this post.
In fact I decided to write something because I was disturbed by the singling out of Corexit as a particularly toxic dispersant; and its manufacturer, Nalco, as being particularly secretive about the composition of the product.
A number of dispersants' MSDS were available at this website, but now all links are dead. I have read the document, tho, and all manufacturers reveal as little as they legally can about the composition of their products. Nalco in fact revealed Corexit's composition in detail, albeit after some pressure by EPA*.
The website above also has a chart of dispersants' effectivness and toxicity for selected marine organisms. Judge for yourself, but again Corexit does not seem to be especially toxic.
And of course humans should not come into direct contact with dispersants; all use instructions stress the need to wear protective equipment and apply the dispersant in an appropriate manner.
*The composition of Corexit is already specified in the original patents filed by Exxon in the 1970's and discussed in the book by NAS.