How Much Radiation-Contaminated Water Will Kill You?

Radioactive substances are leaching into the water supply near and far from the quake-damaged nuclear reactors in Fukushima, Japan. After an abnormally high level of iodine 131 was detected in the water in Tokyo on March 23, a media frenzy ensued, residents were told not to let their infants drink the city supply, and stores quickly sold out of bottled water. Are fears of contaminated water justified in Japan? Is the level of contamination actually dangerous?

A 1-sievert (Sv) dose of radiation increases a person's lifetime cancer risk by 4 percent, according to health physicist and radiation safety expert Peter Caracappa of the Renssealaer Polytechnic Institute. To put that in real terms, if 1,000 people are exposed to 1 Sv of radiation, 40 more of them will develop cancer in their lifetimes than would otherwise.

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