Cancer risks associated with naturally occurring radioactive materials in drinking water

Elevated levels of naturally occurring uranium were discovered in private wells in South Carolina, triggering concern among affected home owners about risks they face from their past consumption. Further sampling detected other naturally occurring radioactive materials (NORM) such as radon and an isotope of lead that exceeded proposed or established federal drinking water standards. The federal regulations are based upon theoretically derived carcinogenic risk estimates which incorporate radiological and toxicological observations as well as mathematical models to calculate tissue doses associated with drinking water ingestion. The details and assumptions involved with this radiological dosimetric process will be briefly described. The International Commission for Radiological Protection as well as the United States National Research Council and the Environmental Protection Agency provide dose conversion factors, nominal probability factors, and cancer risk coefficients which convert radiological activity concentrations into various types of cancer risk estimations. The magnitude of risks estimated to be associated with ingestion of drinking water from these sampled private wells were calculated as posing only small to moderate risks for the homeowners, with radon and an isotope of radium providing the majority of risk. However, issues with available dosimetric measures for radon result in a wide range of uncertainty associated with its risk estimates. The risks predicted for the private wells exposures will be presented and compared to the risks associated with regulated, average, and maximal exposures from ingestion of drinking water in the United States.