Tis BRS 112 RADIATION STANDARDS, INCLUDING FALLOUT 4. The production of milk throughout the country at all seasons permits a continuous testing program. 5. Reliable analytical methods could be devised for analysis of the isotopic content of milk. The Public Health Service, in 1957, established a raw milk sampling network composed of five milksheds. This network was expanded to 12 stations by 1959. The experience gained here led to the establishing, in 1960, of a pasteurized milk sampling program by the Division of Radiological Health and the Division of Environmental Engineering and Food Protection. This network is now composed of some 60 stations, set up to measure the radioactivity content of milk consumed by approximately 60 million Americans. The samples are weighted with respect to the contribution of the major processing plants to the total supply and represent 90 percent or more of the milk marketed in the area sampled. Samples are collected by State and local milk sanitation authorities and are analyzed quantitatively at the Division of Radiological Health’s regional laboratories at Winchester, Mass., Montgomery, Ala., and Las Vegas, Nev. The analyses are for those nuclides of largest potential health importance including iodine 131, cesium 137, barium 140, strontium 89, and strontium 90. APPEARANCE OF IODINE 131 IN MILK IN FALL OF 1961 From the initiation of the pasteurized milk sampling network in 1960 to September 1961, iodine 131 was not detectable in milk. Iodine 131 was found in milk samples obtained at Montgomery, Ala., and New Orleans, La., on September 19, 1961, and in that obtained at Atlanta, Ga., Charleston, S.C., New Orleans, La., St. Louis, Mo., and Tampa, Fla., on September 20. This was 3 weeks after the beginning of the Russian atomic test series. By September 21 the Russians had detonated at least 14 bombs with at least 3 estimated by the Atomic Energy Commission to be on the order of several megatons. While iodine 131 in fallout was first detected September 11, 1961, on air filters from Medford, Oreg., iodine 131 in milk was detected first in the milk of the Southern and Southeastern States. These iodine levels in milk were detected some 2 or 3 days after a weather phenomenon, which consisted of a hurricane off the east coast of the United States, and a ridge of high pressure over the eastern one-half of the country. This tremendous ridge of high pressure persisted over the eastern onehalf of the United States for the period September 17-20. The gross beta radioactivity in air was markedly elevated over the south and southeastern portions of the United States and the highest levels reported by the radiation surveillance network was 709 nuc/m' of air at Little Rock, Ark., on September 19, 1961. On the basis of the air sampling results, the milk sampling stations intensified their operations, and during the period of the highest iodine level 20 stations were on a daily sampling schedule, and the remaining stations were on a twice-a-week sehedule. SOURCES OF EXPOSURE TO IODINE 131 Iodine 131 produced in nuclear detonations can be carried relatively long distances depending on the tropospheric air currents. It becomes deposited on vegetation directly as well as by rain. Unwashed vegetation consumed relatively promptly following deposition of the iodine fallout could be a source of radioiodine intake by humans. Several factors reduce the likelihood of this being a significant source of intake. <Arelatively small amount of the consumption of fresh vegetables occurs rapidly enough after deposition for this te be a factor. The transit time for fresh vegetables, and certainly that for canned or frozen, is sufficient to have allowed most, if not all, of the radioiodine to decay. Furthermore, even when fresh vegetables are consumed very soon after fallout, the ordinary household preparation of washing and peeling will remove most of the jodine 131, since it is in the form of surface deposition. The sequence of events in the production and distribution of milk, however, make it a significant source of intake. Dairy cows at pasture consume iodine 131 deposited on the surface of forage crops. The idoine 181 appears in the milk. The processing and marketing of milk is designed to bring the freshest possible product to the public, and the time between cow and consumeris of the order of 2 to 4 days. Thus, only a relatively small amount of decay of the iodine 131 in the milk has taken place. In the case of other dairy products, however, the time for processing and marketing is sufficient to permit decay of the iodine 131. igsperReREAcdiAADsge