Oil Spill Dispersants Shifting Ecosystem Impacts in Gulf, Scientists Warn

A seemingly feel-good story showed up this week on the nation's front pages and newscasts: The oil that befouled the Gulf of Mexico for 86 days is vanishing from the surface, leaving workers with little to clean.

But scientists warn the oil's ecological impacts are shifting, not ebbing, thanks to massive volumes of dispersants that have kept the crude beneath the waves.

"This is a management decision, to use dispersants," College of William and Mary marine science professor Robert Diaz said yesterday. "It doesn't make the oil go away, it just puts it from one part of the ecosystem to another."

That dispersed oil now hovers, diluted in the water column, posing a challenge for scientists to track and measure the subsea plumes. Mapping the long-term effects of the nearly 2 million gallons of dispersant used by BP PLC may well be equally difficult, given the array of unanswered questions that surround the products' rapid breakdown of oil droplets and their chronic toxicity.

In other words, while dispersants may have helped spare the Gulf's birds, the chemicals are likely shifting dangers to other species lower in the food chain. The National Research Council described dispersant use in 2005 as "a conscious decision" to direct hydrocarbons to one part of the marine ecosystem, "decreasing the risk to water surface and shoreline habitats while increasing the potential risk to organisms in the water column and on the seafloor."

Diaz spoke at a Capitol Hill briefing aimed at guiding future research into dispersants, which remain a politically volatile topic even as their use in the Gulf tapers off thanks to the capped Macondo wellhead. A May meeting at the University of New Hampshire's Coastal Response Research Center, planned by government scientists and oil industry representatives, yielded a consensus judgment that dispersant use "has generally been less environmentally harmful than allowing the oil to migrate on the surface into the sensitive wetlands."

Another group of scientists, however, issued a public plea (pdf) last week that decried dispersants and warned that, mixed with oil, the products "pose grave health risks to marine life and human health."

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