Figure 172 also shows that the concentration of om 187Cs in the dict closely parallels the course of fallout rate, but is delayed essentially one year in reaching its maximum level. This delay is due to the lag a wu = uo = = L. % 3 K aa ™, 7 eae uF t 4 oe rE . a - ‘ Adult Diet oL between the growth and actual marketing of many 100 - - | x 2 a 01k a log [ b 5 - 5 - 3 Accumulated Deposition 100} Z a Women a | La 4 E - 4 = S . = | 5 E Ld z 2 E 4 a. Wr c L Deposition Rate ~q 4 7 4 4 7 a | 1 —|96|—+--1962—--1963+-1964-+— 1965+ 966+1 967+1968 +1969 YEAR Fic. 172—""Cs in the Chicago area 1961-1969; deposition rate, accumulated deposition, concentration in diet, internal food items. Throughout the time interval considered, the accumulated deposition of #27Cs is either increasing or remaining at a nearly constant maximum level. The primary dependence of the '7Cs in the diet upon fallout rate rather than accumulated radioactivity is clearly evident, and reflects the fact that foliar and stem uptake far outweighs root uptake in the case of 7Cs under most circumstances. It should be pointed out, however, that recent work in Florida‘? has shown fairly constant dietary levels of '’Cs, presumably due to root uptake caused by local soil char- acteristics. The effective half-time for 7Cs in the Chicago diet shown in Figure 172 is about 18 months, and the halftime in manis closely the same, as illustrated by the internal dose curve. The slight increases in deposition rate, diet 137Cs, and resultant dose in the last two years is attributed to the input of new nuclear debris from Chinese and Frenchtesting. Most of the foodstuffs in the diet considered are terrestrially produced; hence we may presumethat the relatively rapid decrease in *"Cs concentration ob- dose to man. I ] ] T T logco Tl Properly modified, such models may also be useful in assessing the dosimetric aspects of other modes of environmental release of "Cs and Sr, and by extension may be applied to other contaminants. Fairly extensive measurements of 1°7Cs in air, soil, food, and man have been made routinely at Argonne for a number of years. These data allow the observation of temporal trends and indicate something of the transport through, the environment of this particular substance. Indeed, it is the transport and environmental persistence of 17Cs which justifies activity coinciding with high precipitation. From 1963 through 1967 the deposition rate decreased with a half-time of about 12 months, which is in accord with the observed half-residence time for fallout 137s in the stratosphere. 4 Se ~ = —_ E = o i= oO © a 100 uJ Oo Lroiiiil = oo Deposition Rate L a maximum in 1963 and has a half-width of ~4 years. The fine structure of annual deposition is characterized by maximal deposition rates in the spring and early summer due to the higher levels of airborne 7 100 Trl] Figure 172, where the deposition rate is shown to reach x TTT nuclear weapons testing in 1961-1962 serves as an illustration. The duration of this pulse is indicated in % 1000 TF continuation of these studies. The pulse of 1*Cs generated by the large scale Accumulated Deposition CONCENTRATION IN FISH CpCi/kg wet wt J & ee | 1964196519661967-119681969— YEAR Fic. 173—'"Cs in the Red Lakes, Minnesota area 1964-1969; deposition rate, accumulated deposition, concentration in perch, northern pike, and walleye.