Toxicity testing of dispersants may be overkill, but questions remain

"It’s always the oil you need to worry about. When people say dispersant-and-oil kills things, they’re right."

12-09-2010 // Bob Serata
Dr. Steve Gittings, NOAA
The U.S. Food & Drug Administration (FDA) recently joined the National Oceanic and Atmospheric Administration (NOAA) in announcing a new “chemical test to detect dispersants used in the Deepwater Horizon-BP oil spill in fish, oysters, crab and shrimp. Trace amounts of the chemicals used in dispersants are common, and levels for safety have been previously set.”

The new test is designed to detect dioctyl sodium sulfosuccinate, or DOSS, the pharmaceutical grade of which is a common ingredient in the manufacture of stool softeners and laxatives.

The stated purpose of the test is “to ensure consumers have total confidence in the safety of seafood being harvested from the Gulf,” according to the FDA.

But the EPA and dispersant manufacturers have been testing dispersant toxicity for the better part of 30 years. EPA scientists performed specific tests of dispersants on two Gulf aquatic species in August and September, confirming that dispersants aren’t nearly as lethal as oil.

It’s not very likely that dispersants will be found floating around in isolation –dispersants would more likely be mixed with oil, and probably in much smaller amounts than the oil itself. And while the resulting oil-dispersant mix may be toxic, that is primarily because of the oil component.

“I would challenge anybody to show me scientific literature proving the toxicity of dispersants is anything like what has been described in the media,” said Dr. Steve Gittings, chief scientist for NOAA’s Office of National Marine Sanctuaries.

“What people need to realize is whether dispersants are toxic or not, they’re nowhere near as toxic as oil. It’s always the oil you need to worry about. When people say dispersant-and-oil kills things, they’re right. When they say dispersants kill things, they’re really not right. Most studies show that they don't. Dispersants generally have a very low level of toxicity”

Michael R. Taylor, food safety expert and research professor at George Washington University’s School of Public Health and Health Services and senior advisor to the FDA commissioner, told a senate committee investigating the health impacts of the Deepwater Horizon oil spill, “The current science does not suggest that dispersants bioaccumulate in seafood.”

So maybe it’s time to look at some of the other attributes of dispersants, like their detergent and absorption actions, and dispersant effects on shallow water species, like corals.

NWF has already reported on two studies of the effects on corals and coral larvae of Corexit 9500, the primary dispersant used after the BP oil spill.

Gittings said, "There are people who worry that dispersants themselves might increase the absorption of oil across gill membranes in fish, enhancing their susceptibility. That's a legitimate area for further study.”

Maybe, for some fish species, dispersants decrease health damage caused by oil in the water.

Said Gittings, “Oil can be pretty sticky. That's a problem when it contacts the gill of a fish or a whale shark. If it sticks to the gills it reduces the ability of the fish to take in oxygen. But because dispersants reduce the viscosity of oil, they make it more slippery, so it is less prone to stick to the membranes. It's therefore entirely possible that a dispersant reduces the chance that oil will stick to the gills themselves."

Gittings main point is that a lot is known about dispersant toxicity but there are still questions about how dispersant/oil mixes (aka “chemically-dispersed oil”) act on living things once they are in the water column.

“There’s a number of really prime, really ripe research areas we need to pursue but I don’t think they’re along the lines of toxicity,” he said.

But NWF staff scientist Dr. Michael Murray, who focuses on the scientific and policy aspects of toxic chemicals, thinks the jury is still out on dispersant toxicity.

“The goal of dispersants is to have them be effective over a relatively short time then degrade so they’re not persistent,” he said. “But I’m not sure there’s a clear handle on knowing if all the components [of dispersants] are degrading relatively quickly and degrading into non-toxic products,” he added.

“There’s still a fair amount to be learned. Like testing early impacts on organisms beyond the two that EPA tested. And testing other end points, like the endocrine and reproduction systems. Then testing higher up the food web to see potential impacts on higher level organisms,” said Murray.

A broader battery of tests should be done for any chemical dispersant that’s nominated to be listed by the EPA for use during an oil spill,” he said.
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