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07 November 2009

Answer to Question #184 Submitted to "Ask the Experts"

Category: Environmental and Background Radiation — Water

The following question was answered by an expert in the appropriate field:

Is it possible to develop bleeding ulcers from drinking water that has exceeded the MCL for ²²⁶Ra and ²²⁸Ra? Our annual running average varies between an MCL of 5.0 to 6.0 pCi L^-1.

Rubin and Casarett reported on the pathophysiological effects of ionizing radiation on tissues after therapeutic exposures [P. Rubin and G.W. Casarett. "Concepts of Clinical Radiation Pathology," pp. 160-189 in Medical Radiation Biology, G.V. Dalrymple, et al., editors. W.B. Saunders Co., Philadelphia,1973 and P. Rubin and G.Casarett, Frontiers of Radiation Therapy and Oncology, 6:1-16 (1972)]. Their observations are for therapeutic exposures given at the rate of 200 rad per fraction, 5 fractions per week. They estimated for an exposure of 100 cm2 of the stomach, the risk of developing ulcers or perforation of the stomach within five years of exposure is 5 percent after a dose of 4500 rad and 50 percent after a dose of 5500 rad. In the ICRP model for radium, the dose rate to the stomach wall for ²²⁶Ra is 1.21E-10 rad/hr/pCi, low-LET, and 1.11E- 9 rad/hr/pCi, high-LET, for infants; 1.04E-11 rad/hr/pCi, low-LET, and 8.16E-11 rad/hr/pCi, high-LET, for adults. Committed doses to the stomach wall would be 1.66E-8 rad/pCi, low-LET, 9.89E-8 rad/pCi, high-LET, for infants. In adults the corresponding estimates for adults are 2.43E-9 rad/pCi, low-LET, and 4.48E-9 rad/pCi, high-LET. Lifetime intake of drinking water is about 3.053E+4 [Cancer Risk Coefficients for Environmental Exposure to Radionuclides, Federal Guidance Report No.13. EPA402-R-99-001, U.S. EPA, Washington,DC, September 1999].So, it would take water concentrations of 3,000 pCi/liter to get a committed dose of even 1 rad to the stomach wall. Concentrations of 5 to 6 pCi per liter of ²²⁶Ra would not cause bleeding ulcers.

Neal Nelson
Radiation Biologist

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