For the first time in nearly four decades, the EPA is taking a closer look at the safety of leaked tritium in our water, reports David Biello for Scientific American, via Salon:
Add two extra neutrons to the lightest element and hydrogen becomes radioactive, earning the name tritium. Even before the Three Mile Island accident in 1979 regulators worried that this ubiquitous by-product of nuclear reactors could pose a threat to human health. The U.S. Environmental Protection Agency (EPA) was only seven years old when it put the first rules on the books for tritium in 1977. But a lot has happened in the intervening decades, and it is not just a longer list of nuclear accidents.
The Chernobyl and Fukushima meltdowns let loose plenty of tritium, but so have a seemingly endless series of leaks at aging reactors in the U.S. and elsewhere. Such leaks have prompted the EPA to announce on February 4 plans to revisit standards for tritium that has found its way into water—so-called tritiated water, or HTO—along with risk limits for individual exposure to radiation and nuclear waste storage, among other issues surrounding nuclear power.
The agency’s recent announcement in the Federal Register notes that tritium levels as high as 3.2 million picocuries per liter (pCi/L) in ground water have been reported to the U.S. Nuclear Regulatory Commission (NRC) at some nuclear facilities. (A curie is a unit of radiation emission; a picocurie is one trillionth of a curie.) That is 160 times higher than the standard set back in 1977 by the fledgling EPA—and the NRC has made measurements even higher at some nuclear facilities. “Because of these releases to groundwater at these sites, and related investigations, the agency considers it prudent to reexamine its initial assumption in 1977 that the water pathway is not a pathway of concern,” the EPA stated in its filing.
This new evaluation is likely to prove challenging, however, as tritium is difficult to get a grip on from both a radiological and human health perspective. On the one hand, there is evidence that the risk from tritium is negligible and current standards are more than precautionary. On the other, there is also some evidence that tritium could be more harmful than originally thought.
Or, as a health physicist who has studied tritium for years observes, in the 1970s, the EPA did not rely on any health studies in setting its original standards. Instead, the EPA back-calculated acceptable levels of tritium in water from the radiation exposure delivered by already extant radionuclides from nuclear weapons testing in surface waters. “It’s not a health-based standard, it’s based on what was easily achievable,” remarks David Kocher of the Oak Ridge Center for Risk Analysis, who has evaluated health risks from tritium and spent 30 years at Oak Ridge National Laboratory. The standard of 20,000 pCi/L of drinking water made compliance easy. “No drinking water anywhere was anywhere close, so it cost nothing to meet.”
By the EPA’s calculations, the 1977 standard should result in an extra radiation dose of less than four millirems, or 40 microsieverts per year, about the amount from a chest X-ray. (A rem is a dosage unit of x-ray and gamma-ray radiation exposure; one sievert equals 100 rems.) But the standard begs the question: is tritium safe to drink?…
[continues at Scientific American, via Salon]