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A RadNet radiation monitor is seen on the roof of the Bay Area Air Quality District offices on March 16, 2011 in San Francisco

The risks to California or any other part of the United States from a plume of low-level radioactive fallout making its way from Japan are virtually zero, medical and environmental experts in the Bay Area reaffirmed on Thursday.

At present, the level of radiation that's expected to hit the West Coast from the stricken Japanese nuclear plant will be so low that it won't even be measurable, these experts said. A radical increase in radiation releases that would result from a full meltdown at the Fukushima Daiichi power plant could change the situation, but even then it's unlikely that radiation levels here would pose a threat to public health. 

“There is no health risk from this at all, no need to worry or to change your behavior,” said Kirk Smith, epidemiologist and professor of global environmental health at UC Berkeley.

The federal Environmental Protection Agency has a system of some 100 radiation monitors, called Radnet, around the country; in the Bay Area it has monitors in Richmond, San Jose and in San Francisco. Portable monitors are being dispatched to locations closer to Japan, including Hawaii, Guam, Alaska and the Marianas islands as a precaution, said Mike Bandrowski, manager of the office of air toxics, radiation and indoor air for the EPA’s region 9, based in San Francisco.

“Of the current EPA monitors in place, which include some in Hawaii and Alaska, none are showing elevated levels of radiation,” Bandrowski said. The monitors show counts per minute of gamma and beta particles, data which can be publicly viewed in real time on the EPA website, he said.

Health concerns are centered on radioactive iodine, I-131, and Cesium-137, which are produced in a nuclear reactor and were likely released by Japan’s reactors. Radioactive iodine has a half-life of eight days; cesium’s half life is 30 years, but it is more quickly eliminated from the body than radioactive iodine, which is absorbed by the thyroid gland. That is why potassium iodide, a salt form of iodine — is used to block I 131 from the thyroid.

Although reports indicate some Bay Area pharmacies and other stores are doing a brisk business in potassium iodide among people worried about fallout arriving here, Dr. Stuart Heard, executive director of the California Poison Control System, and clinical professor of pharmacology at UCSF, said there is no reason for anyone to take potassium iodide now.