As the audit spread across Wal-Mart’s U.S. operations, the mystery thickened. Stores from Arkansas to Washington began reporting missing signs. They numbered in the hundreds at first, then the thousands. Last month Wal-Mart disclosed that about 15,800 of its exit signs – a stunning 20 per cent of its total inventory – are lost, missing, or otherwise unaccounted for at 4,500 facilities in the United States and Puerto Rico.
Poor housekeeping, certainly, but what’s the big deal?
In a word: radiation.
The signs contain tritium gas, a radioactive form of hydrogen. Tritium glows when it interacts with phosphor particles, a phenomenon that has led to the creation of glow-in-the-dark emergency exit signs.
It’s estimated there are more than 2 million tritium-based exit signs in use across North America.
It turns out that Ontario-based companies SRB Technologies (Canada) Inc. of Pembroke and Shield Source Inc. of Peterborough have sold the lion’s share of these signs, which use tritium produced as a by-product from the operation of Canadian-made Candu nuclear reactors.
The health effects of tritium exposure continue to be a hot topic of debate. It’s not strong enough to penetrate the skin, and in low quantities regulators and industry groups say tritium is safe. But when inhaled or ingested it can cause permanent changes to cells and has been linked to genetic abnormalities, developmental and reproductive problems and other health issues such as cancer.
“The problem is that because it’s hydrogen it can actually become part of your body,” says Shawn-Patrick Stensil of Greenpeace Canada. “The radiation doesn’t emit far, but when it actually becomes part of your cell it’s right next to your DNA. So for a pregnant woman, for example, it can be really dangerous.”