Iodine-131 in Drinking Water

As a result of the Fukushima Daiichi nuclear power reactor accidents in Japan in March of 2011, the airborne transport of iodine-131 and other fission products to the mainland U.S., and subsequent rain-out of I-131 in the Commonwealth of Pennsylvania on March 23rd, the PA DEP began a program to closely monitor raw surface water and finished drinking supplies for I-131 across the state. Prior to the rain-out, the PA DEP had also prioritize all the routine environmental surveillance sampling and analysis around our five nuclear power plant sites in order to monitor any potential detection of radioactive material from Japan. The U.S. EPA’s RadNet historical and recent air, water and milk data in PA was also re-evaluated and closely monitored during this period. Interestingly, the EPA RadNet data showed the Philadelphia drinking water had routine I-131 values above their lower limit of detection (LLD), with a few samples over the years above the 3 pCi/L [derived] maximum contaminant level (MCL). This presentation will describe the ongoing investigation of sources of I-131, raw and finished drinking water data, and conclusion that the source of I-131 is medical patient excreta. There appears to be a potential conflict between the NRC and Agreement States patient release criteria with administered I-131 and the EPA’s [possibly] overly conservative 3 pCi/L MCL in low flow watersheds, as well as a gap in the EPA’s screening methods for beta / photon emitters.