430 TRANS URANIC ELEMENTS IN THE ENVIRONMENT 



TABLE 4 Estimated Inventories of "^Pu, ^^^^^°Pu, and '^^Csin 

 Areal Samples* of Greenland Lichen Communities During August 1974 



*Samples above dashed line are considered contaminated by 1968 accident debris, 

 t Refer to I ig. 2. 



the pre-Health and Safety Laboratory (HASL) measurement period. For example, values 

 in lichens sampled in July 1964 reached 41 ± 2.6 nCi/m^ compared to a calculated fallout 

 deposition at Anaktuvuk Pass during the period 1960 to 1964 of 26 nCi/m^ . This 

 maintenance of high '^^Cs inventory prompted the experiments on effective half-times 

 of radionuclides in lichens and the modeling of Arctic food chains which demonstrated 

 the significant differences in radionuclide behavior within lichen communities and the 

 important implications to Arctic ecosystems (Ebeihardt and Hanson. 1969; Hanson and 

 Eberhardt, 1967; Hanson, 1973). A salient feature of those data was the longer effective 

 half-time of '^"^Cs (10 yr) compared with that of ''°Sr ( 1 .0 to 1.6 yr) in lichens. This 

 was due primarily to the greater mobility and recycling of '^^Cs and the impedance of 

 ^°Sr translocation by cation-exchange phenomena (Tuominen, 1967; 1968). Similar 

 mechanisms may be operative in the relatively rapid loss (Ti^ , 6.1 yr) of ^^^'~'*'^Pu from 

 lichen carpets reported from Scandinavia (Holm and Persson, 1975). Similar results were 

 obtained from Alaskan liclien carpets at Anaktuvuk Pass (Table 6 and Fig. 3), which 

 showed (1) a general increase of both ^^^Pu and 239,240p^j jy^^^^ ,q^^g ^^ 1071 ; (2) a 

 decline during 1972 and 1973, periods of low fallout deposition; (3) a sudden increase 

 during 1974 that correlated with increased fallout deposition presumably due to the 

 Chinese nuclear weapons tests of 1973 and 1974; and (4) another decline in 1975 and 

 then an increase in 1976 samples. The lower 1975 values for plutonium are unexplained 

 but also occurred to a lesser degree in the '^^Cs values; the decrease was more 

 pronounced when compared with similar decreases that occurred in 1972. The 

 probability that this was due to either sampling or analytical error is considered to be 



