These values do not include the contribution of radium-226 from tap water. However, the radium-226 content of the water is low and would not materially increase the daily intake estimate. New York City San Francisco 0.011 pCi/liter 0.015 pCi/liter Comparison of the two surveys in Tables 1 and 2 shows that although individual food types may vary by more than a factor of 2, the average daily intake for each city varies by less than 20% or within expected experimental error. It should also be noted that both the 1966 and 1968 food samplings were collected at mid-year so that possible seasonal variation was not studied. [It seems unlikely that a significant seasonal variation in dietary radium-226 would exist for a given location. The California State Department of Health has estimated the daily radium-226 intake of individuals receiving a hospital diet. The average daily radium-226 intake for Berkeley, California hospital diets from November 1967 to June 1968 was 0.4 pCi/day. (4) Similar diets collected from April to December 1968 in San Francisco averaged 1.3 pCi/day. (5,6,7) The radium-226 content of human bone from New York City and San Francisco is 0.036 pCi/g Ca and 0.031 pCi/g Ca, respectively, Since the dietary radium-226 levels for these cities are different by about a factor of two, it would be expected that the bone levels would reflect this difference. We suggest that a particular dietary component or a combination of a few components may control the radium-226 level in man. Little is known about the availability of radium-226 from foodstuffs, but there is indication that it is quite variable. We are initiating a few studies to attempt to correlate radium-226 bone levels with particular dietary components. ~ Pr a T —_ 3 a3 a" a eee ee ee me