AsianScientist (Sep. 22, 2011) – After the magnitude 9.0 earthquake and resulting tsunami in Japan on March 11 this year, Japan’s Fukushima Dai-ichi power plant was severely compromised.
While radioactive material was found in the water in many of the surrounding areas, the extent of this contamination remained unknown.
In a study published in the journal PLoS ONE, researchers report that the reactor accident fallout extended as far as the San Francisco Bay area in California, although the levels of radioactive material were very low and posed no health risk to the public.
To collect the rainwater samples, the researchers placed plastic containers outside in the Oakland and Berkeley hills and in Albany from March 16 to 26, and examined them for the presence of above-normal amounts of radioactivity, measuring levels of radioactive isotopes of cesium, iodine, and tellurium. Collection periods varied from a few to approximately 12 hours.
Following collection, each sample was gamma-ray counted using a 60 percent relative efficiency high-purity germanium detector. No chemical or physical processing of any kind was done to the rainwater samples before counting.
The first sample that showed elevated radioactivity was collected on March 18, and levels peaked on March 24 before returning to normal.
The authors stress that the results of their study show that the levels of radioactive material were very low.
“Thus the levels of fallout we have observed in San Francisco Bay area rain water pose no health risk to the public,” they wrote.
After the manuscript was submitted, the authors conducted similar gamma-ray counting measurements on samples of weeds collected in Oakland, and on vegetables and milk sold commercially in the San Francisco Bay area.
In some of these samples, the team also detected low levels of the same fission products in the weeds as previously observed in the rainwater. Likewise, they wrote that the levels detected also pose no hazard to the public.
The article can be found at: Norman EB et al. (2011) Observations of Fallout from the Fukushima Reactor Accident in San Francisco Bay Area Rainwater.
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Source: Public Library of Science.
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