In our work with about 100 subjects resident in eastern Europe (mostly Poland) at the time of the Chernobyl reactor accident or traveling as tourists, /sup 131/I was readily detectable in the thyroid through mid-June, 1986, and was detectable in some subjects as late as early July, 9 to 10 weeks after the start of the accident. Among 42 subjects who were in eastern Europe on April 26, 1986, and in whom /sup 131/I was detectable, the median activity in the thyroid was 1.4 nCi at the time of measurement. When extrapolated back to April 26 using a single exponential retention function for the thyroid and an 8-day effective half-life, the median activity was 42 nCi. The frequency distribution resembled a lognormal distribution. The extrapolated activities lay between approximately 2 and 1200 nCi. The risk levels derived from these observations of internal radioactivity and my conservative dose projection assumptions are as much as 10 times less than the risk levels published in the lay press during the months following the accident. This underscores the importance of basing risk estimation for internal radioactivity on direct observations. 2 refs., 1 tab.
