6 tary which might cause genetic effects, have averaged between one snd five thousandths of one roentgen per year in the United tates during the last three or four years. This figure should be compared with a normal dosage of 150 chousandths of one roentgen per year from cosmic rays and natural radion active materials in the environment. In other words, the external fallout radiation has been from 0.7 percent "to about three percent of the natural radiation exposure. As another example, in certain countries of the vorld a brick house might. easily have enough natural radio~ active material in the walls to Bive up to “1,0 thousandths of a roentgen more exposure per year than a wooden house and a concrete block house gives about 100 thousandths of. a roentgen more annually. These dosages range between 8 and 100 times the dosage due to test fallout. Obviously, the genetic effect of fallout radiation must be very small compared with the genetic effect of natural radiation. ; As you pointed out in your statement, vadicrctiv~ ity from tests which already Lave tean held is ‘present in wne stretosphnere, from which it will descend for years to core. The radioactivity of this material constantly is decreasing through normal radicactive deca“Ys The tiny radioactive pavticles fall so slowly fron the stratospnere that the continuiog Fallout in the United States: gust about compensates for the radioactive decay of the rediostiontiun already deposited. Therefore, the present level of rediostrontivum in the soil is about as inuch as we shall ever have from tests already fired. Continued testing would not increase radicactivity on a stiaight acditive basis, since an equilibrium would be established votvecn the added radisoactivity end radicactive deoey. If tests were to comtinve until 1663 at the rate of “.e past five ycars, levels ja the United States “ould be exX- yected to reach ebuut four tines their present values. Levels abeut six tines the preccnt ones vould be reached by the year 2011 if testing were to continue for that leng a Dies , (:,ore)