Comments from EPA: New Radiation Highs in Little Rock Milk, Philadelphia Drinking Water, Forbes blog of Jeff McMahon, April 11, 2011:
… EPA lumps these gamma and beta emitters together under one collective MCL, so if you’re seeing cesium-137 in your milk or water, the MCL [Maximum Contaminant Level] is 3.0 picocuries per liter; if you’re seeing iodine-131, the MCL is 3.0; if you’re seeing cesium-137 and iodine-131, the MCL is still 3.0.
Here’s a somewhat historic EPA document that speaks directly to that issue:
Although not having a 4 mrem per year equivalent level specified in the current drinking water regulations as do tritium and strontium-90, the compliance monitoring scheme indicates that an iodine-131 level of 3 pCi/L is the MCL compliance level (presumably derived from the NBS Handbook); the ANPRM indicates that 700 pCi/L is the 4 mrem/year equivalent.
… If we lump together the three radionuclides in that Hilo, Hawaii reading, we get 61 pCi/L. …
[P]eople should not be exposed to more than 4 millirem per year. To make sense of that number we need to be able to express picocuries as millirems, but that’s what that legacy document does that I quoted above:
“the compliance monitoring scheme indicates that an iodine-131 level of 3 pCi/L is the MCL compliance level; the ANPRM indicates that 700 pCi/L is the 4 mrem/year equivalent.”
What this all means to me is that if you’re a water company, EPA will insist you keep the gamma/beta emitters in your water below 3 pCi/L in pursuit of another aim, which is to keep your customers’ annual radiation exposure below 700, or, put another way, below 4mrem, over the course of a year.
If we should not be exposed to more than 700 pCi/L per year, then anyone who drinks two liters of Boise rainwater or 13 liters of Hilo milk is in trouble. Both those scenarios may be unlikely, but they’re beginning to get closer to likely than the reassurances we’ve been receiving would seem to indicate.
Read McMahon’s comments here.
Note: It actually takes less than 12 liters of milk to reach the EPA’s MCL, not 13 as McMahon states. An annual MCL of 700 pCi/l divided by the 61 pCi/l of cesium and iodine found in Hilo’s milk equals 11.475 liters. There are 33.8 ounces in a liter, multiply that by 11.475 liters and it equals 388 ounces, or 3.03 gallons.
Published: April 11th, 2011 at 5:23 pm ET