The release of two types of cancer-causing compounds during the burning of oil released from the BP Macondo well in the Gulf of Mexico poses little long-term risk of cancer to cleanup workers, onshore residents or fish consumers, according to two new peer-reviewed scientific papers released today by the federal Environmental Protection Agency.
But the conclusions in one of the reports are based on a single composite sample taken from numerous smoke plumes over four days in mid-July.
The reports represent the two types of information needed by scientists to determine the risk of cancer chemicals released during the burning of oil: the amount of chemicals released and how the chemicals might reach the public.
The first report estimated the amount of the most toxic constituents of the burning of oil. The second study determined how much of the chemicals might be delivered to people by prevailing winds along the Gulf Coast, and how much was deposited in Gulf waters and then ingested by fish, which in turn might be eaten by the public.
EPA officials were unavailable for comment on the sampling issue on Friday.
The risk study found that based on the single sample, as well as information about how the smoke traveled through the air and was deposited in the water, the increased lifetime risk of cancer is only 6 additional cases in 100 million among workers who inhaled the fumes.
For onshore residents who inhaled the fumes, the risk is 6 additional cases for every 1 trillion people. For most people eating fish exposed to the fumes, the risk is an additional 6 cases for every 100 million. For children, where the amount of fish they eat represents a greater percentage of their body weight, and for Gulf Coast residents considered to be "subsistence populations" eating as much as 9/10 of a pound of fish a day, the risk of cancer increases, but generally to no more than 2 additional cases in 10 million.
The study concluded that even using the most conservative estimates of fish consumption, the increased cancer risk has not exceeded 1 additional case in a million. The EPA generally doesn't consider taking additional regulatory actions until the increased cancer risk ranges from 1 in 10,000 to 1 in a million, the study said.
"For all scenarios, the risk estimates represent upper bounds and actual risks would be expected to be less," said the authors of the cancer risk paper, which include officials with EPA's Office of Research and Development and the National Oceanic and Atmospheric Administration's Air Resources Laboratory.
But even the scientists writing that paper expressed concerns about the adequacy of the sampling. Ironically, they said one reason no additional samples were taken was that the Macondo well was finally capped on July 15. The last burn occurred on July 19.
The scientists measured the release of two families of toxic chemicals -- polychlorinated dibenzodioxins and polychlorinated dibenzofurans -- by collecting samples with a battery-operated instrument package suspended in the plumes of 27 surface oil fires between July 13 and July 16.
The offshore in-situ burns were credited with destroying between 220,000 and 310,000 barrels of oil from April 28 to July 19. The EPA has found that exposure to even the tiniest amounts of the chemicals can cause cancer in humans in some circumstances. The chemicals are created in the burning of oil and other carbon-containing substances.
Despite the fact that scientists believed the single sample did not contain enough carbon for their complex testing, which normally requires three samples, the study still concluded that the testing results were an accurate measure of the emissions of the two chemicals, within a factor of two. Based on that finding, they estimated that the total amount of the toxic chemicals released during the burning operations was between 1/1000 of a pound to 3/1000 of a pound.
That compares to an EPA estimate of 2.9 pounds of dioxin or furan compounds released from all sources in the country each year.
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Mark Schleifstein can be reached at firstname.lastname@example.org or 504.826.3327.