Unknown Quantity: Regulating Radionuclides in Tap Water Bob Weinhold. Environmental Health Perspectives
[Excerpted] The EPA last revisited drinking water standards for radionuclides in 2000,2 when it established a maximum contaminant level (MCL) for uranium and reaffirmed requirements established in 19763 for radium-226 and -228 combined, for gross alpha particle reactivity, and for beta particle/gamma ray radioactivity. By law, MCLs must balance information about health risks against the costs and limitations of available technologies. With the 2000 rule the EPA also established maximum contaminant level goals (MCLGs) of zero for radionuclides in drinking water. An MCLG is the concentration at which a chemical is believed to pose no adverse health risks.
The agency plans to complete a review of these standards by 2016 to determine if they need to be revised, expanded, or otherwise modified, says an EPA spokeswoman who asked to remain anonymous.4 Meanwhile, the EPA’s work on a radon standard for drinking water has been postponed since 1999,5 although in May 2012 the agency released a report to Congress laying out options for such a standard.6
The EPA has no plans to commission any particular studies prior to its next review of the radionuclide standards, according to its spokeswoman. As the agency works its way through the process of evaluating its standards—which the spokeswoman says now cover only the ingestion pathway, not inhalation or dermal routes—one starting point will be its current thresholds: 30 µg/L for uranium, 5 picocuries per liter (pCi/L) for combined radium-226 and -228, 15 pCi/L for gross alpha radioactivity, and 4 millirems per year for beta/gamma radioactivity.7
....But although major gaps in the science remain, studies and reviews since 2000 suggest the radiologic and chemical toxicity of radionuclides may be farther-reaching and more significant than thought at the time the EPA drinking water standards were established. For instance, the WHO and the U.S. National Research Council have concluded radionuclides follow a linear no-threshold model of carcinogenicity; that is, there is evidence that ionizing radiation can increase the risk of cancer at even the lowest doses.10,14
In framing adequately protective regulations, some experts believe greater attention needs to be extended to vulnerable populations such as children. “Our whole [regulatory] perspective is geared to cancer and adults,” says Arjun Makhijani, president of the Institute for Energy and Environmental Research, a Maryland-based advocacy group. “For instance, we’re not considering in utero doses at all.”
Others point to the need for more attention to noncancer effects in setting drinking water standards. Ellen Silbergeld, a professor of environmental health sciences and epidemiology at the Johns Hopkins Bloomberg School of Public Health, says there’s a critical shortage of information for all population groups on the chemical toxicity potential of most radionuclides. “I think this is a sleeper story,” she says. “A lot [of radionuclides] may possess considerable toxicity as metals. The research hasn’t really been done.”
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