The UK’s Health Protection Agency has a follow-up on their monitoring of people and places potentially contaminated with the extremely dangerous alpha-emitter, Polonium-210, the weapon used to kill Russian dissident Alexander Litvinenko (see our posts here and here about Polonium-210, and here and here about the murder). Their spin is that tests “so far” show minimal risk to the general public. What surprised me is that their tests showed widespread exposure to the public. Here are the reported results:
Test result update
*596 people had results ‘below reporting level’ – below 30 millibecquerels (mBq) per day (natural levels of Po-210 in urine are typically in the range 5-15 mBq per day). It is therefore unlikely that any of these people had been exposed to Po-210
*85 people had results above 30 mBq per day in their urine, but with a dose less than 1mSv indicating no public health risk, and no health concern to the individual, but probable contact with Po-210
*35 people had results above 1 millisievert (mSv), but below 6mSv indicating no public health risk, and no health concern to the individual, but probable contact with Po-210
There are 716 results in categories 1, 2 and 3a and these are NOT [their emphasis] of health concern.
*17 people had results above 6mSv which are not significant enough to cause any illness in the short term and any increased risk in the long term is likely to be very small. (via BigMedicine)
Out of 733 people tested, 137, or almost one in five, showed probable contact with Polonium-210. Of these, 17 or one in eight of the exposed and a bit over 2% of those tested, had levels even Health Protection acknowledges increases their risk, although they characterize that risk as likely very small.
When risks are relatively low in the statistical sense, say in the 1% to 2% range, not low in a public health sense, they become difficult to estimate. Our ability to measure risks at this level is very limited, because it requires good dose information combined with relatively large numbers of people exposed and followed sufficiently long to count the cancers (usually 30 or 40 years). So we have to estimate the risks with the help of data from other circumstances (for example, the atom bomb survivors) and the help of mathematical models that extend the risks found at the high levels to the lower but never measured levels of concern. So we don’t know with confidence how low or high the risks of the Polonium-210 exposed public might be. The judgment the risks are very low is probably correct. Probably. On the other hand, this homicide, using a very tiny amount of an extremely dangerous radioactive poison, exposed 137 other people.
Those are the 137 we know about so far.