Wal-Mart Cannot Account for More than 15,000 Radioactive Exit Signs

Department store Jihad?

It began in late 2007 as a routine audit. Retail giant Wal-Mart noticed that some exit signs at the company's stores and warehouses had gone missing.

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.

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.

And what about exposure from thousands of signs dumped near a source of drinking water, or packed with explosives in the back of a truck that has been driven into a crowded building?

"I'm sure thousands of them would create a credible dirty bomb," says Norm Rubin, director of nuclear research at Energy Probe in Toronto. "Most experts think the main purpose of a dirty bomb is to cause panic, disruption and expensive cleanup rather than lots of dead bodies. A bunch of tritium, especially if oxidized in an explosion, would probably do that job fine."