Why would they want to use the non-toxic, effective one?
British Petroleum and government disaster-relief agencies are using a toxic chemical (Corexit 9500) to disperse oil in the Gulf of Mexico, even though a better alternative appears to be available.
[…] The decision has been a controversial one. A few scientists think dispersants are mostly useful as public relations strategy, as they make the oil slick invisible, even though oil particles continue to do damage. Others consider Corexit the lesser of two evils: It’s known to be highly toxic, adding to the harm caused by oil, but at least it will concentrate damage at sea, sparing sensitive and highly productive coastal areas. Better to sacrifice the deep sea than the shorelines.
[…] Called Dispersit, it’s manufactured by the U.S. Polychemical Corporation and has been approved for use by the Environmental Protection Agency. Both Corexit and Dispersit were tested by the EPA, and according to those results, Corexit was 54.7 percent effective at breaking down crude oil from the Gulf, and Dispersit was 100 percent effective.
Not only did Corexit do a worse job of dispersing oil, but it was three times as lethal to silverfish – used as a benchmark organism in toxicity testing — and more than twice as lethal to shrimp, another benchmark organism and an important part of Gulf fisheries.