This diary is the latest in a series that aim to understand what the likely impact of Fukushima sourced radionuclides will be on ecosystem and human health on the North American west coast. Herein, I report on a newly published, open-access study by Smith et al. (2014) in the Journal of Environmental Protection who studied the levels of Fukushima radionuclides in air, rainwater and food resulting from atmospheric fallout in the San Francisco Bay area. Monitoring of the fallout isotopes 90-Sr (in rainwater) 131-I, 132-I, 132-Te, 134-Cs, 136-Cs and 137-Cs began shortly after the disaster on March 11, 2011 and continued through the end of 2012. The results of the study are compared to similar measurements made in the aftermath of the Chernobyl disaster in 1986. Peak fallout activities of radionuclides from Chernobyl in 1986 in the Bay area were 10 times greater than the levels measured from Fukushima in 2011.
As in previous diaries it is important to understand that scientists use a variety of units to measure radioactivity. A commonly used unit is the Becquerel (Bq for short) which represents an amount of radioactive material where one atom decays per second and has units of inverse time (per second). Another unit commonly used is disintegrations per minute (dpm) where the number of atoms undergoing radioactive decay in one minute are counted (so 1 Bq = 60 dpm).
All of the measurements reported in the study were made at the Low Background Facility at the Lawrence Berkeley National Laboratory in California. Beginning on March 14, 2011 (international pi day for those who are interested in such things http://www.piday.org/) an air sampler was operated at the facility to track the arrival of gamma emitting radionuclides transported in the atmosphere from Fukushima to the San Francisco Bay area. Measurements at LBNL are ongoing but the paper reports measurements made until the end of 2012. Radionuclides in aerosols >0.3 microns were collected on HEPA filters and counted using sensitive gamma radiation spectrometers. Activities of Fukushima radionuclides in air 137-Cs, 131-I, 132-Te tied to the presence of short-lived 134-Cs (t1/2 = 2.06 years) are presented in Bq/m3 in the figure below:
The investigators also measured for Fukushima fallout radionuclides in rainwater in Oroville, CA and found peak activities of 131-I of 16 Bq/L on March 24, 2011. Results for rainwater are presented below in units of Bq/L:
3:51 PM PT: Levels in food, air and water will determine the impacts on ecosystem and human health. Atmospheric transport from Fukushima, at 10-fold less than Chernobyl fallout, should have equal or less impact on the Bay Area than Chernobyl did in 1986. The cumulative effective dose from Fukushima radionuclides in foodstuffs purchased in October 2013 in the Bay Area was near to zero as no short-lived 134-Cs from Fukushima could be detected. Radwatch http://radwatch.berkeley.edu/ is a great site that reports information specific to the Bay Area and have been measuring for Fukushima radionuclides in salmon harvested from Alaska. If you live in the Bay Area you should follow that site.