A week after a dam collapsed at the Kingston power plant in eastern Tennessee and dumped more than a billion gallons of toxic coal ash waste into the nearby community of Harriman and the Emory River, the Tennessee Valley Authority collected samples of the ash and tested them for radioactivity. The summary of results [pdf] released by the company suggested the risk was minimal, stating that the total radioactivity in the ash was "less than that found in low sodium salt available to consumers on the shelves of grocery stores."
But a new independent analysis of radiation in the ash suggests the company downplayed the real risk.
Scientists from Duke University last week announced that their tests found the ash has radiation levels higher than those found in typical coal ash. The combined content of radium-228 and radium-226 in the solid ash samples they collected from the TVA spill earlier this month measured about 8 picocuries per gram. That compares to the average 5 or 6 picocuries per gram reported by the Environmental Protection Agency in most ash samples from coal-fired power plants.
Produced when the naturally occurring uranium and thorium in coal decays, radium concentrates in the ash when coal is burned. Radium exposure is known to cause bone, liver and breast cancer in humans as well as anemia, cataracts and tooth damage.
"Preventing the formation of airborne particulate matter from the ash that was released to the environment seems essential for reducing possible health impacts," lead researcher Avner Vengosh, an associate professor of earth and ocean sciences at Duke's Nicholas School of the Environment, told Duke Today.
So how is it that Duke scientists are calling for action to reduce health impacts from radiation in the ash when the company is insisting the stuff is no more dangerous than low-sodium table salt?
Because they're comparing apples to oranges.
In its statement on radiation in the ash, TVA focuses on the radioactive element potassium-40, which represents the largest source of radiation exposure in most people. Manufacturers of low-sodium salt use potassium chloride as a substitute for some of the sodium chloride found in regular salt; because a portion of potassium is naturally radioactive, so is the light salt.
But Vengosh's team focused on radium isotopes, which are much more dangerous to human health than potassium-40.
The following table is based on data contained in the federal government's table of radionuclide carcinogenicity -- that is, the likelihood that a particular radioactive element is likely to cause cancer. The "morbidity risk coefficient" is a comparable estimate of the average total risk of experiencing a radiogenic cancer, whether or not the cancer proves fatal.
As the federal government's own data clearly shows, radium-226 and radium-228 are much more likely to cause cancer than potassium-40. Compared to drinking water contaminated with potassium-40, water contaminated with radium-226 presents more than 15 times the cancer risk, while water contaminated with radium-228 carries 42 times the cancer risk.
The difference in risk is even more dramatic when it comes to inhalation. Compared to breathing in potassium-40, inhaling radium-228 carries 500 times the risk of cancer, while inhaling radium-226 is 1,000 times riskier. As we've reported, cleanup workers at the site have not always worn protective masks while on the job.
The dramatic difference in risk among the various radionuclides contained in the coal ash was obscured by TVA's analysis, which focused on the most innocuous radionuclide present.
TVA issued a statement last week saying it would review the Duke findings.
In an effort to keep the ash from becoming airborne and being inhaled by people, the company has already sown grass over more than 200 acres of the spill and is spraying water on the ash in work areas.
(In the above photo, taken by Duke University professor Avner Vengosh, graduate student Laura Ruhl collects samples of ash from the TVA coal sludge spill.)