Radioactive cesium levels continue to rise in milk from San Francisco Bay Area
April 15th, 2011
UCB Milk Sampling Results
Back to Main UCB Air and Water Sampling Page
The following are results for milk samples obtained from a Bay Area organic dairy where the farmers are encouraged to feed their cows local grass. We have detected I-131, Cs-134, and Cs-137 and are tracking their levels.
4/13/2011: Major revision note: We just performed a major revision of our preliminary milk measurements. Our activity measurements for milk with a “best by” date after 4/4/2011 were accidentally calculated for the “best by” date itself, rather than an earlier date such as the purchase date. Since milk can be on the shelves starting almost 18 days before the “best by” date, our numbers after 4/4/2011 did not accurately reflect the maximum activity that the radioisotopes could have at the time of purchase. Incidentally, our first two milk measurements were not corrected at all and therefore reflect the activity at the time of measurement. The original numbers are at the bottom of the page for reference.
In order to make a valid comparison between all milk samples, we decided to correct all milk samples to represent the activity at their time of bottling — this is 18 days before the “best by” date. This revision does not change the Cs-134 or Cs-137 numbers since they have long radioactive half-lives. The I-131 activity increases by factors of 2 to 5 because of its 8 day half-life. Please note that though all I-131 activities have increased due to this revision, the levels are still very low — one would have to consume at least 1,900 liters of milk to receive the same radiation dose as a cross-country airplane trip.