Natural Radioactivity in Southwest France and Its Possible Genetic Consequences for Mammals

Areas of very high natural radioactivity have been found in the Southwest France where in certain places dose rates from external terrestrial sources exceed $100\ {\rm rad}\ {\rm yr}^{-1}$. The ionizing radiation, in this region, originates mainly from the two natural uranium isotopes. The ability of natural radioactivity to produce chromosome aberrations in mammalian somatic cells was studied in lymphocytes from laboratory rabbits maintained, during one year, in an area where the dose rate of γ irradiation was about $8\ {\rm mrad}\ {\rm hr}^{-1}$. The γ dose was determined by individual lithium fluoride dosimeter placed around the neck of the rabbits. Induction of chromosome aberrations in male germ cells was studied in mice maintained for a three-month period (dose ± 10 rad) in the same area. A small, but significant, increase of chromosome aberrations such as dicentrics was observed in the lymphocytes of rabbits receiving up to $70\ {\rm rad}\ {\rm yr}^{-1}$ γ rays but no effect was seen in the germ cells of the male mice exposed or of their offspring. The lymphocytes of the rabbits were, however, possibly also exposed to α rays from the respiratory tracts (>600 rad) whereas such an exposure did not occur for the mouse male germ cells. Our data thus indicate that high natural radioactivity can produce chromosome aberrations in mammals. Taking into account our present findings, the human data from Hiroshima and Nagasaki as well as theoretical considerations, we doubt seriously that significant increases in the yield of chromosome aberrations could even be detected in man living in areas of high natural radioactivity at dose rates as low as 3 rad/yr.