| The carcinogenic risks associated with ingesting naturally occurring radioactive materials (NORM) in drinking water were predicted using both the International Committee on Radiological Protection (ICRP) and newer Federal Guidance Report 13 (FGR13) risk estimation approaches. Predicted cancer risks were then compared to actual cancers within county populations characterized by their NORM ingestion exposures utilizing an ecological type of epidemiological comparison method. Information on groundwater concentrations for 238 U, 234U, 228Ra, 226Ra, 224Ra 222Rn 210Pb, and 210Po was obtained from both published and Internet accessible public water utility records. The effort to gather cancer rate, demographic, and geological information also relied primarily on computer resources, such as the Internet and mapping programs, that were not available for assemblage of such data at a national scale until recently.; Predicted excess lifetime risks exceeded 10-3 to 10 -4 when the concentrations within a drinking water supply were one or more orders of magnitude greater than regulatory acceptable maximum contaminant levels (MCL). The annual risks predicted for elevated ingestion exposures based upon private well measurements suggested some agreement between FGR13 predicted rates and actual rates, particularly for kidney cancers, but the association could not be statistically confirmed. In general, the comparisons between age-adjusted annual cancer rates and predicted annual risks did not show any correlations for counties with likely NORM exposure at or below federal MCLs. The exception was for leukemia, which consistently showed a small positive association between actual rates and predictions that relied on radium isotope ingestion.; The results of this study indicate that demonstrating any correspondence in epidemiological data for such low levels of predicted risk may not be possible, even when radiological and toxicological models indicate that there exists a small risk. The lack of associations between predicted and actual rates among humans for chronic low level ingestion exposure to NORM agrees with the lack of toxicological information indicating adverse effects from similar exposures and should provide reassurance that federal regulatory levels are established at very protective levels. |
