Erroneous Info in UCB Milk Sampling Results (and probably elsewhere on this site)

To the UCB faculty and students who have created this site and who are providing commentary on contamination levels in air, water, and food:

On http://www.nuc.berkeley.edu/node/2174
(and probably elsewhere on your site), your commentary reiterates an often paraphrased, but unfortunately incorrect comparison between external and internal radiation. You wrote: "The number in parentheses is the number of liters of milk that one would need to consume to equal the radiation exposure of a single round trip flight from San Francisco to Washington D.C. (0.05 mSv)."

Internal radiation exposure cannot be considered to be equivalent to external exposure. External radiation exposure is an exposure that is averaged across the whole body and stops as soon as a person moves away from the source of radiation. Unfortunately, people can't move away from internal exposure. Once radioactive elements are consumed, they get absorbed and remain in the body for long periods of time, continuously irradiating nearby tissues, until the body eventually eliminates the radiation or eventually dies (not necessarily as a result of the radiation). In the case of Cs137 the biological half life is 110 days. i.e. half of what was ingested gets excreted in 110 days, while the remainder takes longer than 110 days to excrete. All that time, the ingested particles constantly irradiate nearby tissues. The constant radiation over time, of tissues in proximity to the ingested radioactive particles has the potential to cause damage to cells and DNA, and this is what makes internal radiation a much greater concern than an "equivalent" dose of external radiation received across a person's entire body.

I urge you to read the BIER VII report summary at http://dels-old.nas.edu/dels/rpt_briefs/beir_vii_final.pdf This report, by the National Academy of Sciences, makes it very clear that there is no linear threshold that represents a "safe" level of radiation. Every increase in radiation, no matter how seemingly small, does appear to equate to an increased statistical probability that an adverse biologal impact (e.g. cancer) will occur. A statistical increase, however small, still represents an increased risk. Practically speaking, the risks to any single individual may be small when they are considered as part of a large population. However, within that large population, some people WILL be effected. For them, the risks become all too real.

I recognize the time and energy that everyone in the UCB Department of Nuclear Engineering has invested in this web site. You have provided valuable information that has not been available elsewhere, and this service has been and is very much appreciated! I hope you will continue your good work.

In the mean time, please consider that as part of a highly regarded university, you are viewed by most visitors as being an authoritative source on this topic. I encourage you to correct the misleading dosage comparison(s) that you have on your web site and to find a more accurate way to put dosages into context.