Dispersants, like Corexit 9500/9527, are a mixture of solvents, surfactants and other unknowns that are designed to make oil more soluble in water. Most of what is known about the toxicity of dispersants and dispersed oil is based on acute toxicity tests. The scientific literature suggests that acute (short-term) toxicity tests with death as the primary endpoint may not adequately assess the long-term impacts of chemically-dispersed oil. Long-term studies are needed to adequately determine delayed effects due to metabolism of chemically-dispersed oil, bioaccumulation, or photo-enhanced toxicity.Public Health ImpactsThe exact makeup of the dispersants is kept secret under competitive trade laws, however the manufacturer is required to reveal any toxic substances contained in the formula. According to datasheets submitted to EPA by the Manufucturer Nalco, Corexit 9527 contains 2-butoxyethanol. It has been documented that people exposed to higher than recommended levels of “2-butoxyethanol for several hours reported irritation of the nose and eyes, headache, a metallic taste in their mouths, and vomiting. No harmful effects were seen on their lungs or hearts. People who swallowed large amounts of cleaning agents containing 2-butoxyethanol have shown breathing problems, low blood pressure, low levels of hemoglobin (the substance in the blood that carries oxygen to organs of the body), acidic blood, and blood in the urine.” The Occupational Safety and Health Administration (OSHA) has set an exposure limit of 50 parts of 2-butoxyethanol per million parts of air (50 ppm) for an 8-hour workday, 40-hour workweek. This target was derived from a chronic inhalation exposure study on rats, though the confidence was not high because the potential for effects in humans from repeated, long-term exposures has not been investigated.According to a recent news report, over a dozen workers have reported health problems such as dizziness, headaches, chest pain, and nausea and are being treated in local medical centers. The cause of the illnesses is under investigation.Wildlife ImpactsThe scientific literature is inconclusive on the impact of dispersants to the marine environment. One long-term study did show that dispersants reduced the “persistence of oil in subtidal and intertidal sediments compared to untreated oil.” Studies have shown that early treatment with COREXIT EC9500A, helps decrease the formation of “mousse” of the spilled oil. In toxicity studies, it has been shown that COREXIT 9500A combined with fuel oil #2 is more lethal than either fuel oil #2 or the dispersant alone. Bioaccumulation could be a serious problem since sunlight has been found to increase the deleterious effect of Polycyclic Aromatic Hydrocarbons (PAH).Photosensitization can occur when PAHs bioaccumulate in the tissues of aquatic organisms and form free-radicals when these organisms are exposed to sunlight. Photosensitization can lead to longer-term impacts which differ from the initial effects of PAH toxicity. Corals are known to bioaccumulate spilled oil quickly and are not adept at filtering the toxins out. Translucent pelagic larvae and epibenthic or benthic organisms living in shallow water will be the most susceptible to photoenhanced toxicity.Photomodification occurs when the chemically-dispersed oil is exposed to sunlight and is transformed into a more toxic chemical. Studies have demonstrated that chemically dispersed oil is significantly more toxic than oil alone when exposed to sunlight.ConclusionThe general consensus of the scientific community is that the use of dispersants requires a trade-off. The choice to use dispersants means accepting 1) greater concentrations of chemically-dispersed oil in the water column, 2) a potential reduction in persistent stranded oil, and 3) increased unknowns on long-term toxicity on sediments and marine life. So far, BP has applied almost 1 million gallons of dispersant to the surface and subsea in response to the BP Horizon Drilling Disaster. The initial choice was to keep the oil out of sensitive marsh areas at the expense of deep water marine life in the hope that marine bacteria would metabolize the oil. The sheer magnitude of the amount of oil that keeps flowing into the Gulf makes any trade-off decision moot. There is just not enough dispersant to keep all the oil out of the marshes. Further, the bacteria that eat oil also metabolize oxygen in the process. This has the potential to create an enormous area in the Gulf with depleted dissolved oxygen. Essentially, BP is conducting the largest chemical experiment ever attempted in the Gulf of Mexico and the final results will not be in for another 10-20 years. National Academy of Sciences. (2005) Oil Spill Dispersants: Efficacy and Effects. National Academy of Sciences. (2005) Oil Spill Dispersants: Efficacy and Effects. National Academy of Sciences. (2005) Oil Spill Dispersants: Efficacy and Effects.NALCO Safety Data Sheet COREXIT AC9527A. Accessed at http://www.deepwaterhorizonresponse.com/posted/2931/Corexit_EC9527A_MSDS.539295.pdf on June 2, 2010. Agency for Toxic Substances and Disease Registry ToxFAQs 2-butoxyethanol Agency for Toxic Substances and Disease Registry ToxFAQs 2-butoxyethanol EPA Integrated Risk Information System. Ethylene glycol monobutyl ether (EGBE)(2-Butoxyethanol) (CASRN 111-76-2) accessed at http://www.epa.gov/NCEA/iris/subst/0500.htm on June 2, 2010. Baca, Ward, Lane, and Schuler. Net Environmental Benefit Analysis of Dispersed Oil on Nearshore Tropical Ecosystems Derived from the 20 Year TROPICS Field Study. EPA Emergency Management COREXIT EC9500A. Accessed at http://www.epa.gov/oem/content/ncp/products/corex950.htm on June 2, 2010EPA Oil Program Center. Technical Product Bulletin #D-4. COREXIT AC9500A. Accessed at http://www.epa.gov/oem/content/ncp/products/corex950.htm June 2, 2010 National Academy of Sciences. (2005) Oil Spill Dispersants: Efficacy and Effects. National Academy of Sciences. (2005) Oil Spill Dispersants: Efficacy and Effects. National Academy of Sciences. (2005) Oil Spill Dispersants: Efficacy and Effects.Casey DeMoss Roberts, MSPH is GRN’s Assistant Director of Water Resources.