vat yesay MUTI BARE vate TSS RADIATION STANDARDS, INCLUDING FALLOUT 119 fluctuations of radioactivity levels in a wide range of environmental sources possibly related to levels in even the nonmilk fraction of the human diet might also be expected to be reflected in the levels in milk. (2) Milk and milk products represent a significant part of the diet for all age groups and a very large proportion of the total diet in infants and children, for whom susceptibility to radiation injury is believed to be greater than in adults. For the younger age groups, the rate of deposition of bone mineral is greater than for adults, and this warrants special interest in the strontium 90 content of their diet. It has been jiogical to give attention to a dietary source which supplies much of the essential protein and most of the calcium in the diet for the age groups most susceptible to radiation injury. (3) It is convenient and relatively inexpensive to obtain representative samples of milk consumed by the population, compared with obtaining samples of the total diet. (4) Milk is produced the year around in all areas of the United States. (5) Methodology is available for the analysis of strontium 90 in samples of milk. PUBLIC HEALTH SERVICE MILK SAMPLING NETWORK For these reasons the Public Health Service in 1957 initiated steps to estimate strontium 90 along with other substances in milk consumed by the U.S. population. The first milk monitoring program used raw milk and was established to develop suitable sampling methods and radiochemical analytical proficiencies. Early in 1960 a processed (or pasteurized) milk sampling program was established to provide a sampling program more directly related to the milk consumed by large population groups. At present the Public Health Service, in cooperation with State and local agencies, maintains a processed milk monitoring network of more than 60 stations. (See fig. 1.) These stations sample milk consumed by an estimated one-third of the U.S. population. Each sample is composited in proportion to the volume of milk sold by those plunts supplying not less than 90 percent of the milk supply of the city where the sample is taken. Prior to September 15, 1961, the sample for each station was taken from 1 day’s sales per month. Since September 15 the sampling schedule has been accelerated to one sample per week, RESULTS OF MILK ANALYSES FOR STRONTIUM 90 The results of the strontium 90 analyses in the milk network are published regularly in Radiological Health Data. The data are summarized in table IV, in which annual average strontium 90 concentrations in milk have been computed for each of the stations as well as an estimated annual average for the United States. For 1962 individual monthly averages are included through March. Table IV also contains estimates of the populations served by each of the sampling stations. Table V contains the values of strontium 90 in milk from the original raw milk network. INTAKE OF STRONTIUM 90 BY THE POPULATION Some evaluation of the significance of these concentrations of strontium 90 in milk may be obtained by comparisons of estimates of total daily intake of strontium 90 derived from them with the guidance of the Federal Radiation Council. For strontium 90 the Federal Radiation Council gives the following ranges : Range 1 Range II Range III 0 to 20 mye per day. 20 to 200 auc per day. 200 to 2,000 wuc per day. The Federal Radiation Council also provides some guidance whichis useful in estimating total daily intake from milk concentrations. In giving the ranges for total daily intake expressed in wyc/day, the Council makes use of an assumption of a total daily intake of calcium of 1 gram. Since 1 liter of milk supplies about 1 gram of calcium per day, it might be appropriate to use the strontium 90 content of 1 liter of milk as an estimate of total intake of this radionuclide. Actually, a diet including other sources of calcium may have a somewhat higher Seepgs SeagateeelspalateagTDESEt tai