EPA says dioxin risk from burning BP/Deepwater Horizon oil is low - but what's the context?

by Elizabeth Grossman

On November 30th, the Louisiana Bucket Brigade (LABB) released a bulletin reporting on the accidental release of sulfur dioxide at the Murphy Oil refinery in Meraux, Louisiana. The Bucket Brigade tracks these releases as part of its work to reduce refinery accidents, and they explain that the November 30th release is "just one of several refinery-related incidents in St. Bernard's Parish" reported around Thanksgiving weekend. On November 24th, the Louisiana Department of Environmental Quality recorded "spikes" of sulfur dioxide in Chalmette, LA and on the 25th, there was a "hydrocarbon" release to a canal near the Murphy Oil refinery, reports the Bucket Brigade. According to a new report, just released by LABB, United Steelworkers, Environmental Working Group, and five local community groups, between 2005 and 2009 the state's refineries had, on average, ten accidents a week - making the release of petroleum-related contaminants a chronic problem for the surrounding communities, many of whose residents also work in these plants.

At this year's American Public Health Association meeting in Denver, Louisiana Bucket Brigade Program Director Anna Hrybyk gave a presentation on this chronic pollution and what it means for Gulf Coast residents in light of the BP/Deepwater Horizon oil disaster. Of particular concern is what the potential health effects of this pollution mean for the region's industrial fence-line communities and for local residents who participated in the BP/Deepwater Horizon clean-up. In Louisiana, over 200,000 people live within two miles of a refinery. When I spoke to Hrybyk shortly after LABB reported on the latest Murphy Oil refinery incident, she stressed what she pointed out in Denver, that when it comes to assessing ongoing potential health effects for clean-up workers who live in these communities, "background levels of exposure are not known."

While the Louisiana Department of Environmental Quality conducts ongoing ambient air monitoring and industrial facilities have chemical release reporting requirements, these measurements do not provide a comprehensive picture of the potential cumulative chemical exposures experienced by community residents or workers. Louisiana refineries report emissions of up to 80 different chemicals, according to the new LABB report. But each contaminant is measured separately, and the releases from different sources aren't addressed cumulatively. And as Hrybyk pointed out, given the combination of ongoing industrial pollution and the chronic accidental releases, the community residents LABB works with came into the BP/Deepwater Horizon event with a higher likelihood of hazardous chemical exposure than those who don't live near - or work in - refineries and chemical plants.

Hrybyk's comments came to mind as I read the EPA's recently released reports on dioxins emitted by the controlled burns of oil released by the BP/Deepwater Horizon spill. Between April 28 and July 19, 411 such "in situ" burns that set fire to between 9.3 and 13.1 million gallons of oil were conducted. Controlled burns have been used previously to combat oil spills, but never to the extent they were used here.

"The Darth Vader of toxic chemicals"
These burns raise the possibility of multiple hazardous chemical emissions. Among these are dioxins, a class of chemical formed during combustion as well as by some industrial processes like chlorine-bleaching of paper pulp and the production of the herbicide known as Agent Orange. Dioxins are of particular concern because they're not only extremely toxic, they're also persistent and tend to accumulate in fat tissue. Dioxins can last for years, bioaccumulate, and climb the food web. They are carcinogenic and associated with numerous adverse health impacts, including to the cardiovascular, developmental, immune, metabolic, and reproductive systems. Given their persistence, fat solubility, toxicity, and ability to produce effects at low doses, any potential dioxin exposure is of serious concern. Epidemiologist Richard Clapp has called dioxin "the Darth Vader of toxic chemicals."

The EPA researchers examined airborne emissions from the controlled burns in the Gulf and also considered potential human exposure via seafood that might absorb dioxins emitted by these burns. "The reports," writes the EPA, "found that while small amounts of dioxins were created by the burns, the levels that workers and residents would have been exposed to were below the EPA's levels of concern." That is a risk of less than 1 in 1,000,000. The EPA's Toxics Release Inventory reporting threshold for dioxins is 0.1 gram.

But given the Gulf Coast's industrial landscape, I asked if the EPA or any other federal agency would be considering other exposure sources when assessing potential impacts from the controlled burns, especially for response-workers who live in Gulf Coast fence-line communities. Responding to this question, the EPA replied:

EPA's study of dioxin emissions as a result of in situ burning in the Gulf during the BP Deepwater Horizon oil spill indicate that only a small amount of dioxin was released and that the additional risk to workers in the Gulf and residents on shore were below levels of concern. EPA has shared the results of these analyses with other agencies, including those involved in health surveillance. Because the additional risks from the measured emissions are below levels of concern, no specific follow-up studies are planned concerning the release of dioxin from the in situ oil burns.

I also asked if dioxin emissions from the burns would be considered in combination with any other possible chemical exposures, and was told that the "EPA is generally concerned about human health effects associated with the cumulative exposure to chemicals in the environment. However, no specific studies are planned to look at the combined risks of dioxin and other chemicals." The EPA also explained that its determination of the risk from the controlled burns' dioxin emissions was based on exposure to this source alone and did not take into consideration potential risks from other sources. Given their widespread nature and persistence, most people have some low-level exposure to dioxins, and "over 90% of exposure to dioxins is through dietary sources," notes the EPA.

But also worth noting is the fact that while the EPA considers any exposure to dioxin that results in a cancer risk of greater than 1 in 1,000,000 to be significant, what's considered significant occupationally is a risk of greater than 1 in 1,000. (OSHA's permissible exposure limits don't cover dioxin.) At the same time, the EPA's current safety standard for dioxin-contaminated soil at residential sites is 1,000 parts per trillion (ppt) and for industrial and commercial sites, 5,000 - 20,000 ppt. (The Obama administration has recently proposed lowering those levels to 72 ppt for residential sites and 950 for commercial and industrial sites.) So what's considered safe at a work-site might not be considered safe at home.

Ideally, the emissions from the BP/Deepwater Horizon controlled burns will prove as low-risk as the EPA estimates. But they are far from the only sources of dioxins - or other persistent bioaccumulative chemical emissions - on the Gulf Coast. Which brings me back to the questions the Louisiana Bucket Brigade has been asking: What information is needed to issue a clean bill of environmental health for Gulf Coast communities - including oil spill response-workers - given the multiple ongoing potential sources of chemical exposure? How do we know that a particular additional toxic exposure is an insignificant risk if we're not considering it in context?

Elizabeth Grossman is the author of Chasing Molecules: Poisonous Products, Human Health, and the Promise of Green Chemistry, High Tech Trash: Digital Devices, Hidden Toxics, and Human Health, and other books. Her work has appeared in a variety of publications including Scientific American, Salon, The Washington Post, The Nation, Mother Jones, Grist, and the Huffington Post. Chasing Molecules was chosen by Booklist as one of the Top 10 Science & Technology Books of 2009 and won a 2010 Gold Nautilus Award for investigative journalism.