Answer to Question #639 Submitted to "Ask the Experts"

Q

I have recently moved to Plainfield, Illinois. I understand that our water supply has an increased level of radium (7-13 picocuries per liter). I have researched your site and understand that this level should not pose a concern for my family. Why then has the EPA decided to keep the MCL at 5 pCi/L?

A

The EPA recently proposed that the maximum contaminant level (MCL) for radium (²²⁶Ra and ²²⁸Ra combined) in drinking water remain at the level that has been in effect since 1977—5 pCi/L. This level is consistent with the Safe Drinking Water Act of 1996 requirement that, except in special circumstances, any revisions to existing regulations should not reduce their current level of protection. The EPA calculates the cancer mortality risk to a member of the general public from a lifetime intake of radium in drinking water at the MCL to be 2X10^-4 or less. As a public health policy, the EPA generally considers an acceptable risk range to be 10^-6 to 10^-4 (i.e., between 1 in 1,000,000 and 1 in 10,000). Sometimes other considerations lead to acceptable risks above the maximum in that range. In the case of radium, by virtue of the high cost of compliance with a lower level and the minimal public health benefits to be gained by going lower, the EPA chose to retain the combined radium MCL of 5 pCi/L.