Very high concentrations of naturally occurring
radionuclides are encountered in Finnish groundwaters and wells.
Radon ingested through
drinking water can cause considerable radiation to the stomach. We assessed the effect of natural
uranium and other
radionuclides in
drinking water on the risk of
stomach cancer. Subjects (n = 144,627) in the base cohort had lived outside the municipal tap water system during 1967-1980. A subcohort of 4,590 subjects was formed for use as a reference group by random sampling of the base cohort, with stratification by age and sex. Within the subcohort, 371 subjects had used
drinking water from drilled wells prior to 1981.
Stomach cancer cases within the subcohort were identified through a
cancer registry, and cases using water from drilled wells were selected. Activity concentrations of
radon,
radium-226 and natural
uranium in the
drinking water were analyzed using radiochemical and alpha spectrometric methods. The median activity concentration of
radon in well water was 130 Bq/l for both the 88
stomach cancer cases and the 274 subjects in the subcohort. Median
radium concentrations were 0.007 Bq/l for cases and 0.010 Bq/l for the subcohort, with a median
uranium concentration of 0.07 Bq/l for both groups. Risk of
stomach cancer was not associated with exposure to
radon or other
radionuclides. The hazard ratio of
stomach cancer was 0.68 for
radon (95% CI 0.29-1.59 at 100 Bq/l water), 0.69 per Bq/1 for
radium-226 (95% CI 0.33-1.47) and 0.76 per Bq/1 for
uranium (95% CI 0.48-1.21). Our results do not indicate an increased risk of
stomach cancer from ingestion of
radon or other natural
radionuclides through
drinking water at these exposure levels.