rubbish. when the radioactive cloud blew across western europe it brought with it increased future rates of down syndrome, leukemia and thyroid cancer.
That is because it contained radioactive isotopes that have a half life of thousands in some cases millions of years. They fell on the land in rain. They got into the grass that got eaten by cows and put out in milk and into my friends thyroid. They got into the ground water. They got into the crops. You cannot get it out and it goes on causing cancer, mutations and death for longer than recorded human history.
and here are some facts about how increased rates of cancer are caused by radiation but yet are not counted in the stats (because nobody measured them)
Cancer is the uncontrolled replication of cells. It is caused by damage to the p53 gene, which regulates cellular replication in differentiated stem cells.
There is an extremely minute probability that a beta decay emission will damage a specific p53 gene in such a way as to cause cancer, but there are trillions of targets in the human body and even a picocurie is .37 shots per second, or 30,000 a day.
All it takes is one cell to have its p53 gene damaged so as to replicate uncontrollably, and you've got cancer that will spread through the entire body. The progression is geometric: two cells, four, eight, a million, a billion, a tumor, metastasis, death. In how cancer can spread from just one cell to an entire body, it's like a match in a forest.
Suppose a million people each ingest a liter of water with a radioactivity of 3 million Bq (= approximately 8 million picocuries), every day for a year. That would be 106 x 3 x 106 x 3 x 107 = 9 x 1019 opportunities for beta particle emission to damage a p53 gene.
How many cancers would that cause?
I don't know. Do you? Then why are you asserting that it's safe?
The point is, an insignificant dose for one person becomes statistically significant for a large population. If the odds of dying from a glass of contaminated water are one in a million, and a million people each drink such a glass, the odds are that someone is going to die.
TL;DR: Because of the effect of cumulative probability, an 'insignificant' dose for one person is a health concern when millions of people are exposed to that same dosage.