Reply #6: The "safe" limit is very likely

[quaker bill]

near the detection limit for the "ion coupled plasma" detectors used in modern labs. This type of detector is very sensitive to very tiny amounts of metals. They are 2 to 3 orders of magnitude more sensitive than the atomic absorption spectrometers they have largely replaced. In most cases this "safe limit" has little to do with actual health consequences. I don't think anyone has concluded that there is a level of Sr90 that is "safe", at least above natural background which is unavoidable. None of it is good for you. The point is that 240 times this concentration might still be a very small amount, not good for you no doubt, but perhaps still well less than lethal.

The "safe" level for most toxic heavy metals were lowered to the new detection limit when this technology became available to labs.