7. VARIABILITY OF Sr?° IN MILK Monitoring of selected milk supplies indicates the seasonal variability and time trends for Sr® in milk. In addition, it is desirable to know something of the local variability independent of these time and seasonal changes. Three studies are reported here which are related to these problems. 7.1 NEW YORK STATE DEPARTMENT OF HEALTH MILK POWDERING PLANT SURVEY From the end of June 1957 through the end of August 1957, the New York State Department of Health collected three series of powdered milk samples at nine milk powdering plants in New York State. These samples were analyzed at HASL for Sr® and Sr®, and each value reported is the average of replicate analyses. The error term is one standard deviation from the mean. The data are presented in Table 68, and the sampling locations are indicated on Fig. 15. The variable Sr®9/sr% ratio may reflect the fallout from the Plumbbobtests in Nevada conducted during this time, but the Sr® figures are reasonably consistent at a given site. Although differences can be seen from one location to another, they are not large and probably reflect variable grazing conditions rather than differences in the amountof fallout. A relatively small range of Sr*® values, such as shown here for New York State milk, is expected in an area where weather conditions do not vary markedly. 7.2 VARIABILITY OF Sr*® IN POWDERED MILK DURING A ONE-DAY SPRAY-DRYING OPERATION AT COLUMBUS, WISC. On Nov. 16, 1956, Dr. L. T. Alexander visited the Borden Company’s milk powdering plant at Columbus, Wisc., to collect samples during a one-day spray-drying operation. A special run was conducted over a 15-hr period. Samples were taken at about 2-hr intervals. This was a production run, and the milk entering the processing equipment was not from a single large batch but represented several tank changes during the series. Since processing consumes about one tank per hour and one tank represents the largest blend made, the test should indi- cate the variability that might be expected in Sr® for a normal run. This variability is ex- tremely important because our normal sampling is a 5-lb can selected weekly. The results of analyses for this one-day processing period range from 3.5 to 5.5 puc/g of cesium. This relatively large variation must be taken into account when observing trends in the milk results for any graphical location as a factor of time. 7.3 VARIABILITY OF Sr® IN MILK COLLECTED AT SIX WISCONSIN FARMS Dr. Lyle T. Alexander of the Department of Agriculture collected milk from six Wisconsin farms on the same day. These farms were selected to contrast the source of drinking water for cattle, particularly as related to cesium content of the milk. The cesium data are not yet available, but the strontium concentrations in the milk do indicate a possible lowering of milk concentration when well water is the source for the cattle. 150