As anticipated, routine monitoring by the Minnesota Department of Health has found trace amounts of radioactive material likely from the damaged Japanese nuclear power plants in air samples taken in March from St. Paul and two other locations. The amounts recorded are thousands of times less than normal background radiation and well below levels that would be of health concern, health officials said.
Air samples taken from a monitor in St. Paul on March 22 found concentrations of Iodine-131 that would give the average person a dose of 0.004 millirem of radiation over the course of a year. The average person is exposed to at least 365 millirem per year from background sources of radiation. Iodine-131 is a "man-made" isotope or substance that is only found as a byproduct of nuclear fission or reactions, such as those from power plants.
Results from samples taken in St. Paul on March 29 were slightly higher, at 0.011 millirem per year. Samples from near the Prairie Island nuclear power plant on March 22 yielded an estimated dose of 0.003 millirem per year. Samples from near the Monticello nuclear power plant on March 29 showed a concentration that would give a dose of 0.006 millirem per year.
MDH sampling results, including concentration levels, can be found at http://www.health.state.mn.us/divs/eh/radiation/index.html.
"The amounts of radiation we are detecting are just a very small fraction of the amount of radiation we are exposed to on a daily basis from a variety of sources," said Sherrie Flaherty, radiation control supervisor with MDH. A standard chest x-ray will give a dose of about 4-10 millirem and a transatlantic plane ride will expose the average person to about 7 millirem.
"The exposure level at which we would begin to have concerns for human health is 10,000 millirem," Flaherty said. "We are clearly well below that."
MDH's findings are consistent with those of other agencies taking samples/conducting testing in Minnesota. Air monitoring by the Environmental Protection Agency (EPA) found slightly elevated levels of iodine around March 22. Sampling of rainwater in St. Paul by the EPA found a concentration of Iodine 131 on March 22 of 32 picoCuries/liter. It would take a concentration of 1,000 picoCuries/liter to produce a dose of 50 millirem per year. Sampling by Xcel Energy from sites around its two nuclear power plants has found similar results since the incidents in Japan.
"We fully expected to see very slight increases in radiation as the result of the releases from the reactors in Japan," Flaherty said, "and that's what we're finding."
Because Minnesota is home to two nuclear power plants, one at Prairie Island and one at Monticello, MDH conducts routine sampling for radiation as part of its environmental monitoring program. Air samples are taken weekly from a unit in St. Paul and bi-weekly from units at Prairie Island and Monticello. Surface water is sampled quarterly from the Mississippi River at sites just downstream from the power plants. Samples of milk from a farm near each of the power plants are taken and tested monthly (no results from March were yet available for this news release). However, because some radioactive material has been found in milk elsewhere in the U.S., MDH has begun sampling milk weekly to verify nothing of significance is turning up on local dairy farms.
MDH may increase the frequency of other sampling if further test results indicate a need to monitor more closely.
"We are watching the reports of radiation releases from Japan's nuclear power plants carefully, and if there are no further leaks into the air, we would expect to see the current levels of Iodine-131 in Minnesota be undetectable in four to six weeks," Flaherty said.
More information on MDH's radiation control program is available on the MDH website at http://www.health.state.mn.us/ or by calling 651-201-4400.
