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Saturday, April 16, 2011

Geiger counters ineffective for checking food, water

Radiation factors hard to gauge; experts say rely on official data


Geiger counters are probably ineffective for consumers in detecting hazardous levels of radiation in food and water at home, scientists, professors and device makers said.

Large samples should be tested in laboratory-like settings to obtain results, said Joseph Rotunda, who heads the radiation measurement division at toolmaker Thermo Fisher Scientific Inc. Determining whether food, water or milk is safe also requires expert knowledge and more sophisticated equipment than the typical devices sold online, said Atsushi Katayama, a member of the Japan Society for Analytical Chemistry.

"Just pointing a measuring device at your food before dinner is pretty much meaningless," said Katayama, who has a doctorate in analytical chemistry from Hokkaido University. "Tap water and fish, for example, require special handling, isolation and concentration to get meaningful readings."

Geiger counters offered as far away as Germany have sold out after the March 11 disaster that crippled the Tohoku region and led to the world's worst nuclear crisis since Chernobyl. Tokyo Electric Power Co. has said its Fukushima No. 1 plant, which has withstood hundreds of aftershocks since the magnitude 9.0 earthquake and tsunami, may spew more radiation than the 1986 incident before the crisis is contained.

A sample for emergency testing should be at least 5 kg or 5 liters, according to instructions from the Health, Labor and Welfare Ministry. The manual advises against using Geiger-Muller devices, known as Geiger counters, for measurements in food and drink because of their low sensitivity to gamma radiation.

The ministry recommends using tools known as scintillation counters to detect iodine-131 in milk and vegetables, while devices called "inductively coupled plasma mass spectrometers" should be used to trace uranium. Detecting the radioactive material strontium requires nitric acid and dehydrated samples that are turned to ash over a 24-hour period in temperatures exceeding 400 degrees Celsius, according to the manual.

"Various types of radiation require different kinds of equipment," said Katayama. "It's safe to rely on government data" because the findings are closely watched by the international community, he said.

Supermarkets and convenience stores across Tokyo struggled to fill shelves with supplies in the initial weeks of the crisis after the detection of elevated iodine levels in water and food triggered bulk buying even as the government said the health risks are minimal. Companies including Morgan Stanley began shipping water to their Tokyo offices from Hong Kong.

Since March 23, water radiation readings in Tokyo have fallen below levels considered unsafe, even for infants, according to the city's Bureau of Waterworks. In the past month, the metro government ordered plants to step up filtering efforts and handed out about 240,000 bottles of water.

Seafood can require up to two years of monitoring because radioactive materials can take longer to reach larger fish such as sea bass, Katayama said. Even with the proper equipment and environment, making sense of the readings involves calculating the dosage per measure over time, he said.

"Just to know what the radiation levels are in your home, it's relatively straightforward, but when you get to measuring it in food, milk and soil it gets much more complicated," Rotunda said. "That I don't recommend at all."

The devastating temblor and tsunami disabled cooling systems at the Fukushima plant, and the buildup of pressure caused hydrogen explosions that damaged at least three reactors, leaking radiation. U.S. Nuclear Regulatory Commission Chairman Gregory Jaczko said at a Senate hearing Thursday that the nuclear station has yet to stabilize.

Readings in Tokyo soared more than 20-fold and reached 0.809 microsieverts per hour March 15, compared with 0.0338 microsieverts before the catastrophe, according to the Tokyo Metropolitan Institute of Public Health. The highest level was still below a hundredth of the radiation dose from a single chest X-ray.

German Geiger counter suppliers, including Conrad Electronic SE and Graetz Strahlungsmesstechnik GmbH, sold out of the devices in the week following the earthquake. Conrad is selling Geiger counters for $299 (about ¥36,000) to $499 (about ¥60,000) while the devices cost as much as $3,000 (about ¥ 360,000) at Graetz.

People looking to measure air pollution in their homes and neighborhoods should expect to spend about $400 (¥33,400) for a Geiger counter, said Wade Allison, a physics professor at Oxford University and author of "Radiation and Reason."

"People need genuine reassurance," said Allison. "They should note that no harmful effects, including cancer, have been confirmed for doses below 100 millisieverts."

Buyers should chose an instrument that comes with clear instructions for interpreting results and is sensitive enough to measure background radiation, or about 0.01 microsieverts, Allison and Katayama said. Geiger counters with a digital display and ability to save a log of the results are easier to use and preferable to devices featuring analog screens with moving needles, they said.

Before taking measurements, users should shield the instrument in plastic to prevent contamination and determine background radiation levels, said Motoko Koyama, a spokeswoman at the Tokyo Metropolitan Industrial Technology Research Institute.

Poor ventilation, concrete walls in underground locations and proximity to granite and mobile phones can distort readings, Koyama and Katayama said. Measurements are best taken at a distance of 1 cm, moving the device about 2 to 3 cm per second, Koyama said.

"With so many Internet sites offering up-to-date radiation readings, does it really make sense to spend all that money?" Katayama said. "You can buy a ¥100,000 device, but I doubt you will get the price's worth without expert knowledge."

Geiger counters are probably ineffective for consumers in detecting hazardous levels of radiation in food and water at home, scientists, professors and device makers said.

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