USA TODAY US Edition
Thyroid cancer risk raised by tainted water
Drinking Tokyo’s radioactive tap water could lead to a slight increase in thyroid cancer risk over the course of a lifetime, especially in young girls, according to a preliminary assessment by a leading risk analyst.
The analysis found that the amount of radioactivity found in Tokyo’s tap water could cause approximately six excess thyroid cancers for every 10,000 1-year-old girls and one for every 10,000 boys of the same age, says Owen Hoffman, of the consulting firm SENES Oak Ridge, which has evaluated the cancer risk of fallout from Cold War nuclear tests for the National Cancer Institute.
Scientists say the cancer risk is so low that it would likely be impossible to distinguish in future decades between radiation-induced cancers and those unrelated to radiation.
Still, in exposed children, the small increased risk of thyroid cancer would persist for decades, if not for life. It would take at least four or five years for any radiationinduced cancers to occur.
“At these dose levels, the vast majority of thyroid cancers would be spontaneous and not due to this exposure,” says Fred Mettler, leader of the team that assessed the health effects of the Chernobyl meltdown in 1986, who reviewed Hoffman’s calculations. “That’s not to say one should drink contaminated water when you don’t have to.”
David Brenner, a Columbia University radiation expert, pegged the average risk of developing thyroid cancer as even lower, with a risk of dying from drinking the irradi- ated water at “virtually zero,” not least because thyroid cancer is more than 90% curable.
The Japanese government this week advised parents in Tokyo to avoid giving babies tap water — alone or mixed with infant formula — because it carries 200 bequerels of radiation per liter. A bequerel is a measure of radioactive decay per second.
Japan also has called a halt to consumption of dairy products and produce from the area around the Fukushima reactors after tests revealed contamination with radioactive iodine and cesium.
The U.S. government has restricted dairy and vegetable imports from Japan.
Those restrictions also reduce the risk of cancer, Hoffman says.
For adults consuming 2 liters of tap water a day, the risk would be much smaller, roughly three excess thyroid cancers for every 100,000 adult men and 20 for every 100,000 women, Hoffman says. “These risks are small fractions of the usual risk in an unexposed population,” he says.
The risk shrinks even more with every day that passes, because radioactive iodine disintegrates quickly, losing half of its radiation every eight days, a measure scientists call its “half life.”
“Within about 80 days, there’s almost a complete decay of radioactive iodine,” Mettler says.
“Because of its short half life and volatility, a lot of the iodine that was initially in the reactors has already come out and is decaying,” he says. “Unless there’s a new source of radioactive iodine fromthe plant, the iodine should go away.”