B. O. Bartlett’s scientific contributions

ONE of the main difficulties in estimating the integrated radiation dose which the population may receive from environmental contamination with strontium-90 has been to determine the average extent to which it enters food chains many years after deposition. Environmental surveys gave little information on this question in the earlier years of fallout from nuclear weapons tests as 90Sr directly retained on vegetation was then the main source of dietary contamination1. A more complete analysis was possible after 1966 when the reduced rate of fallout caused uptake from the soil to make the dominant contribution. The integrated total of 90Sr which will enter diet from a given deposition now appears to be about half that suspected a decade ago.

Results of an extensive survey in the United Kingdom of the milk Sr/sup 90/ content are considered to provide an improved basis for establishing an empirical relationship (the bone/ milk factor) between the ratio of Sr/sup 90/ and Ca in milk and that in the bones of infants. Bones of more than 500 infants who died between the ages of one week and one year were analyzed. Each bone measurement was related to the milk from the appropriate zone in the country-wide milk survey. The bone/milk factor was found to significantly increase between ages of 1 and 5 months, but no significant changes were noted between the age of six months and one year. Consideration was given to the extent to which variation in the bone/milk factor between years may be attributable to dietary factors. It was concluded that the average ratio of Sr/sup 90/ to Ca in bones of infants in the first year of life is about one-fourth that in milk. (H.M.G.)

The extent to which recently deposited Sr⁹°, aside from the ; cumulative total in the soil, is responsible for the contamination of milk was ; examined in U.K. on the basis of survey data from 1958 to 1961. Data are given ; for the estimated Sr⁹° depositions and Sr⁹° contamination of milk in ; England and Wales. Proportionality factors are derived for deposited and soil Sr/; sup 90/ and are compared with those for other parts of the world. (D.L.C.);

Alternative methods were used to estimate the relative extents to which the Sr/sup 90/ in milk produced in England and Wales was determined by the annual deposition of fall-out and the cumulative total in the soil during the years 1958 to 1960. Proportionality factors are suggested for estimating Sr/sup 90/ from measurements of the current deposit and the cumulative total estimated from the analysis of rain water. Assumptions were used which are considered to indicate the possible upper limit of the contribution of the soil. The calculations should therefore be a cautious basis for the prediction of future situations. It is emphasized, however, that only very approximate relationships can be establisherIn 1958 and 1959 the level of Sr/sup 90/ in milk was determined mainly by the direct retention of the recent deposit on vegetation, but in 1960, when the rate of fall-out had decreased, absorption from the soil may have been responsible for about four-fifths of the contamination in milk. The more thorough incorporation in the soil causes a progressive decrease in its contribution to the contamination of diet. It is emphasized that calculations made for one region are not necessarily applicable to others and that the importance of absorption from the soil will be enhanced in areas where the Ca content of the soil is particularly low. (auth)