The EPA and Press makes it sound like we are all doomed from Iodine 131. They talk about levels 10,000 times the legal limit and amounts of I-131 (Iodine 131) in amounts of fractional picocuries per liter. The highest level of Iodine 131 in the US found in rainwater was .2 picoCuries per liter of water. What is a picocurie? It is not much at all, it is a measure of activity. To start with each radioactive substance has its own level of Specific Activity, or how many particles are released when it decays. The Curie is equal to 37 billion disintegrations per second. This number was arrived at when Radium 226 (Madam Marie Curie's discovery) was studied. As a tribute to Marie Curie they named the measurement the Curie. Radium although radioactive does not decay as fast as fast as many Radioactive materials, it has a halflife of 1,620 years. So 1 gram of radium decays at a rate of 1 Curie, or 37,000,000,000 disintegrations per second. Elements and Isotopes with shorter halflives decay faster, for Example, 1 gram of Iodine 131 has a halflife of 8 days, so it decays at a rate of 124,000 Curies. This leads us to the question of what a picoCurie is, it is 1/1,000,000,000 of a Curie. Is it a dangerous amount? Well one Liter of water weighs 1 kilogram, or 1,000 grams, the Iodine 131 in that rainwater rainwater only weighs .000000000000000000161 grams, or 1.61 X 10-18 grams. No scale can measure amounts that low. If you use a little chemistry and molar equations it works out to about 7,399 atoms (Thank D. Emer). That is out of the trillions of atoms in a Kilogram of rainwater. Half of those atoms of Iodine 131 will not be there after 8 days as well.
Some of you may still be worried, however I 131 does exist in nature. It is formed when uranium atoms spontaneously split, and in high energy collisions of cosmic rays in our upper atmosphere. My best guess, we have nothing to worry about. We should celebrate the fact that we can measure quantities of a substance that are that small!
Here are my much larger numbers:
Not worried in Yukon, OK. Don't dink the Iodine!
PM1703m = 7 uR/hr; Geiger Counter Wristwatch = .04 uSv hour.