B. . Manhattan Project Workers Another study of human respiratory exposure to plutonium relates to 25 young men exposed to plutonium during the Manhattan Project. °° The latest examination of this group ' found them to be free of lung cancer although the report states, "The bronchial cells of several subjects showed moderate to marked metaplastic changes, but the significance of these changes is not clear." Such metaplastic changes are a possible indicator for detecting incipient or actual lung cancer. In one case the report indicates that the subject “was a heavy smoker (3 packs/day) and undoubtedly this contributed to the changes. Nevertheless, these findings suggest that lung cancer may become manifest in some of these subjects in the future. Indeed, one would not be surprised to find one lung cancer even in such a group of non-exposed subjects. During the latest examination of these workers, in vivo measurement of the plutonium lung burdens were conducted with these results: , An average MDA for a 2000-sec counting time is about 7 nCi if one uses the 95% confidence level.&? For the 68% confidence level and a Similar counting time, the comparabie value is about 3.5 nCi. *. 66/ Hemplemann, L.H., et al, “Manhattan Project Plutonium 67/ MDA refers Workers; A Twenty-Seven Year Tollow-Up Study of Selected Cases. to the minimum detectable amount.