Radon concentration levels in ground water from Toluca, Mexico.

Concentration levels of 222Rn have been analysed in water samples from deep wells of the aquifers around the City of Toluca, Mexico. The 222Rn source is the decay of 226Ra within the solid matrix of the aquifer. With a half life of 1600 years the 226Ra continuously releases 222Rn to the pores, from which it diffuses into the main body of water. This paper describes the methods used for sampling and measuring solubilized and 226Ra-supported 222Rn in the water samples, in order to evaluate possible health hazards due to the presence of radon in the drinking water supplies. The relationship of 222Rn with the hydrogeologic characteristics of the zone is also described. The analytical method involves laboratory extraction of 222Rn into toluene. Alpha disintegrations of 222Rn and contributions from short-lived daughters are counted by the liquid scintillation technique. The system was calibrated using a 226Ra standard solution. Results up to 11.3 Bq/l of 222Rn were obtained in the water samples.