EPA Report Adds To Dispersant Toxicity Data

A new Environmental Protection Agency study of eight commercial oil spill dispersants concludes that none of them appears to cause endocrine disruption, as had been feared. In addition, the dispersants share similar cytotoxicities (Env. Sci. & Tech.; DOI: 10.1021/es102150z).

The report adds to another EPA report released last week, which showed the same eight dispersants were similarly nontoxic to small fish and mysid shrimp (C&EN, DOI: 10.1021/cen062910120805).

Researchers have been rushing to study the environmental effects of dispersants, as the oil company BP continues to apply millions of gallons of the Nalco dispersant Corexit 9500 to the oil-contaminated Gulf of Mexico. The April 20 explosion on BP's Deepwater Horizon rig in the Gulf killed 11 workers, setting off the worst oil spill disaster in U.S. history.

The most recent EPA study was spurred partly by concerns that some of the dispersants—whose formulas remain proprietary—contain nonylphenol ethoxylates (NPEs). NPEs can degrade to nonylphenol, which is an endocrine disrupter.

Richard S. Judson at EPA in Research Triangle Park, N.C., and colleagues used in vitro high-throughput assays to test not only the ability of the dispersants to bind to estrogen and androgen receptors, but also their ability to kill cells.

In addition to Corexit 9500, the group analyzed U.S. Polychemical's Dispersit SPC 1000, Mar-Len Supply's Nokomis 3-F4 and Nokomis 3-AA, Z.I. Chemical's ZI-400, Alabaster Corp.'s Sea Brat #4, Saf-Ron International's SAF-RON GOLD, and Globemark Resource's JD 2000.

The results show no androgen disruption due to any of the dispersants and only weak estrogen disruption due to two dispersants, Nokomis 3-F4 and ZI-400. Corexit 9500 does not contain NPEs.

In addition, six of the dispersants had similar levels of cytotoxicity, while JD2000 and SAF-RON GOLD were markedly less cytotoxic than the others.

The issues surrounding the potential harm of dispersants remain complicated. EPA originally ordered BP to find a substitute for Corexit 9500. However, BP continues to use it, claiming that alternatives suggested by EPA, such as Sea Brat #4, could contain NPEs.

Carys Mitchelmore, environmental sciences professor at the University of Maryland, notes that although the dispersants themselves may not be inherently toxic, they cause the oil to be distributed much more widely and potentially more available for uptake by marine organisms. It is this dispersed oil that is toxic and will affect marine organisms.