Madam, – Reports that tapwater in Tokyo contains 210 becquerels/kg of the radioactive isotope iodine-131 – which is twice the permitted “safe” level of infants – makes for scary reading indeed.
However, safe levels are set very low for infants, just as medicines are often prohibited for pregnant women even though there is no compelling evidence to do so. This is the precautionary principle in practice. The half-life of iodine-131 is just eight days, so if one bottles the tapwater and waits for eight days the radioactivity will have dropped to half, ie 105 becquerels/kg and by the ninth day it will be within the safe limit. – Yours, etc,