After the magnitude 9.0 earthquake and resulting tsunami in Japan on March 11, 2011, the Fukushima Dai-ichi power plant was severely compromised and radioactive material was found in the water in many of the surrounding areas, but the extent of this contamination remained unknown.
In a study published today in the online journal PLoS ONE, researchers report that the reactor accident fallout extended as far as the San Francisco Bay area, resulting in elevated levels of radioactive material that were nonetheless very low and posed no health risk to the public.
The researchers collected rainwater samples in Berkeley, Oakland, and Albany, California from March 16th to March 26th and examined them for the presence of above-normal amounts of radioactivity, measuring levels of radioactive isotopes of cesium, iodine, and tellurium. The first sample that showed elevated radioactivity was collected on March 18th, and levels peaked on March 24th before returning to normal.
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More information: Norman EB, Angell CT, Chodash PA (2011) Observations of Fallout from the Fukushima Reactor Accident in San Francisco Bay Area Rainwater. PLoS ONE 6(9): e24330. doi:10.1371/journal.pone.0024330