Image via Wikimedia Commons
Tritium is a hydrogen atom with a short half-life (12.3 years) that is used in thermonuclear (fusion) weapons; large quantities are also used to maintain the United States' sizable nuclear weapon stock. It is also commonly found in self-luminescent objects like exit signs, watches, and gauges.
It emits a weak beta particle but only poses a health risk when found in large concentrations in water. (Tritium occurs naturally in the environment, in the form of tritiated water, but in extremely low concentrations.) Tritium in exit signs can be hazardous if improperly (and illegally) disposed of in municipal landfills; when it reacts with oxygen, tritium readily forms water and can seep into the ground, contaminating groundwater, or go into water ways. It can also be harmful if inhaled in its gaseous form or if absorbed through the skin.
Wal-Mart's disclosure (it lost 15,000 signs) prompted NRC action, but the company is not alone in using the now ubiquitous glowing exit signs: Other organizations cited in the notices include the Smithsonian Institution, the West Point Military Academy, and the Department of the Navy.
Though the NRC says that the signs pose "little or no threat to the public health and safety and do not constitute a security risk," David Lochbaum, the director of the Nuclear Safety Project at the Union of Concerned Scientists, told Guevara that he's not so sure:
Fifteen thousand missing tritium exit signs at 20 trillion picocuries each means that 300 quadrillion picocuries of tritium could be making its way into people's drinking water," warns David Lochbaum, director of the Nuclear Safety Project at the Union of Concerned Scientists. "Or, nearly four million gallons of water could be contaminated above the EPA's drinking water standards. And what if 15,000 missing tritium exit signs is a low estimate?
Indeed, it was only a few years ago that the Pennsylvania Department of Environmental Protection told the NRC that over half of its water measurements downstream of landfills indicated tritium concentrations above the EPA's safety drinking water limit. The only possible source of such a large contamination? "Improperly disposed-of exit signs," according to DEP officials.
Fortunately, as more and more organizations have come to appreciate the health risks posed by tritium, many, including Wal-Mart, have begun switching over to LED and phosphorescent models. Non-radioactive photoluminescent signs like the ones produced by ecoglo are the way to go.
First image via akeg
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