Ecology And Environment

Factors involved in oil dispersant toxicity



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There are four major problems with attempting to identify or to confirm toxicity in oil dispersants that are being used in the BP oil spill of 2010: Ability to prove whether it is the dispersant or the oil that is toxic; proprietary commercial secrecy about the actual chemicals that are in dispersants; the incredible amounts of dispersants and oil that are entering the water every day; and the ability of dispersants to rapidly spread oil in multiple directions and over very large areas.

While invertebrates and vertibrates are definitely affected by the oil/dispersant mix, it is difficult, if not impossible to determine exactly which component of the complicated mix is causing the effects. The oil components could be in the form of toxic gas vapors, solids that suffocate, changes to the temperature and pH levels of the water, the chemicals within the solid oil mass and a host of other physical factors.

The type and amount of exposure could be a factor. A short term exposure, repeated and intermittent exposure or longer term continuous exposure will have different results.

With animals and humans, testimony about symptoms, tests of biological systems and biopsies, or even physical testing for the presence of chemicals in the living cells is problematic. Again, the problem is in determining whether it is the dispersant, the oil, or whether it is something new that comes from mixing the two substances.

The only way to develop a comparative toxcity of chemical dispersants is to have the complete list of each and every chemical component of the dispersant recipe and to analyze those components in terms of their known effect on living things. There has to be a study to determine if the unique situation of the BP oil spill creates conditions that were previously unknown.

The typical oil dispersant behaves like detergent. There are surfactants and solvents that break up the surface tension that holds the oil slick and the water together at the surface of the water. The dispersant breakdown is more likely to allow the gaseous components to vent off rapidly and the remaining solids to sink, either to float at depth or to form into balls that sink to the floor of the body of water. If the oil was not dispersed, for example, would the venting of gaseous components from natural weathering be a sustained process or would the venting be retarded in colder waters?

Today's oil dispersants are said to be less toxic than the dispersants of the past, but the current BP response to the BP oil spill is to admit over 37,000 gallons of dispersant per day since the initiation of the spill and into the indeterminate future. This is a quantity that, while the Gulf of Mexico is a vast place, is unheard of. As a result, sheer volume and sustained introduction over time is added in as a toxcity factor.

There are natural seeps of oil from the ocean floor and there are microbes that thrive on the seeping oil. But a massive ejection of oil presents too much oil. This saps the oxygen, alters the pH level and can even affect the temperature of the water that oil eating bacteria need to survive. It is known that the dispersants break the oil down much faster than natural weathering, but it is unknown whether the dispersants themselves present problems for both natural and biologically modified oil eating bacteria.

The current dispersant that is being used by BP is Nalco Holding Company's "Corexit" brand of dispersant. In a Nalco company test report, silverside fish were exposed to pure oil, to pure Corexit, and to a combination of the two. 

This link to "Toxipedia" has the current Material Safety Data Sheet that lists the toxic substances in Corexit 9500.

A mixture of one part Corexit to 10 parts oil killed half of the silverside fish over 96 hours of continuous exposure.  For oil alone, it took 10.72 ppm to kill half of the fish. For Corexit, it took 25.2 ppm for the same result. 

Current estimates are that the Corexit will kill half the fish in a 4 mile area that extends to the ocean floor. By reducing the volume of Corexit by a factor of 10, the estimates are that only 5 percent of fish over 40 square miles would be killed.

An estimated 800,000 gallons of Corexit were dispensed by June 3, 2010. EPA recommendations call for a ratio of one gallon of Corexit to 10-50 gallons of oil. If the estimates of 21 million gallons leaked by June 3 are correct, then the true ratio has actually been one gallon of Corexit to about 26 gallons of oil, which is well within the range recommended by the EPA.

The problem is that no one truly knows the amount of oil that is being emitted and therefore cannot determine the ratio of oil to dispersant. Additionally, the continuous use of dispersant into the unknown future is cancelling the life cycle of the dispersant which is estimated to be 16 days.

However, Corexit and other dispersants are agreed upon by proponents and opponents to help land and shoreline life by not allowing the oil to remain on the surface. Marine, or ocean life lives at the surface, supposedly making the Corexit/oil mix more toxic to marine life and helpful and less toxic to land life.

But the unprecedented magnitude and duration of the BP oil disaster will continue to challenge all known and conventional knowledge about oil, dispersants and toxcity to all forms of life.

References and additional information:

http://news.sciencemag.org/scienceinsider/2010/05/toxicity-aside-dispersants-could.html

http://www.commondreams.org/headline/2010/06/15-8

http://toxipedia.org/display/toxipedia/Oil+Dispersant


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