U.S. Experienced Low Levels Of Radioactive Material From Fukushima

After an earthquake and tsunami struck Japan’s Fukushima Daiichi nuclear power plant last March, the plant released radioactive gases and particulates that circled the globe. Now scientists estimate the material boosted soil radioactivity in the U.S. by on average 3 to 10% (Environ. Sci. Technol., DOI: 10.1021/es203217u).

U.S. Geological Survey researchers analyzed data collected from March 8 to April 5, 2011, by the National Atmospheric Deposition Program, a network of government and private organizations that monitors rainfall chemistry at hundreds of sites. The network used gamma-ray spectroscopy to detect ¹³¹I, ¹³⁴Cs, and ¹³⁷Cs in rain water at 35 of the 167 sampled locations. The USGS scientists then estimated average soil radiation levels based on these rainfall concentrations.

The highest level of radioactivity—5,100 becquerels per m²—was in rainwater near Portland, Ore., says Greg Wetherbee, a study author. According to historical data, baseline soil radioactivity in the sampled regions is between 240 and 2,400 becquerels per m². Concentrations decreased steadily from west to east, he says, reflecting the loss of material to fallout as the isotopes traveled with winds away from the stricken plant. Also radioactive decay played a role in the diminishing levels, especially for ¹³¹I, which has a much shorter half-life than the other isotopes do.

Wetherbee notes that the Environmental Protection Agency has stated that such small increases in radioactivity should not affect public health.