TRANSURANIC ELEMENTS IN ARCTIC TUNDRA ECOSYSTEMS 449 



about one-tenth the Thule values. This difference could be due to the short residence 

 time of ■^"'^Pu in the upper 5 cm of soil at both the Alaska and Greenland sites. 

 Plutonium inventories in surface soil at Anaktuvuk Pass decreased between 1975 and 

 1976 sampling periods at an effective half-time of 0.4 to 0.5 yr. A tentative application of 

 these values to the Greenland situation suggests that the decline in Thule soils is of a 

 similar rate. 



Radionuclides in Lichen Communities 



The ability of lichens to retain and recycle fallout radionuclides has been observed by 

 several northern investigators. The radiological health aspects of the lichen— caribou— man 

 food web have been the dominant theme of the studies carried out in European nations. 

 Similarly, the ecosystem studies at Thule, Greenland, were mainly oriented toward 

 defining the consequences of the accidentally released plutonium in the marine food webs 

 of that area which were of importance to the local Eskimos (Aarkrog, 1971a; 1971b; 

 1977). Most of the plutonium contamination (~30 Ci) resulting from the accident was 

 associated with the sea ice and other Bylot Sound marine components. Approximately 1 

 to 5 Ci of plutonium was estimated to have been contained in the cloud of smoke and 

 debris that drifted west-southwesterly from the crash site and deposited in uncertain 

 amounts on the sea ice and landscape of the area (Langham, 1970). This uncertainty was 

 enhanced by the discontinuous distribution of lichens in the Thule region, the arid 

 climate and light character of the soils, and the appreciable winds that redistributed the 

 plutonium particles that originated from worldwide fallout from nuclear weapons tests, 

 the April 1964 burnup of the SNAP-9A satellite power source, and the aircraft accident. 



Lichen samples collected from several Thule locations during 1968 (Hanson, 1972) 

 and 1974 (Table 4) illustrated the highly variable nature of plutonium concentrations 

 compared with more uniform ' ^ ''Cs concentrations in the lichen communities exposed to 

 the 1968 accident debris. During 1968 most lichen samples from uncontaminated areas 

 contained a mean 239,240p^^j concentration of 0.25 ± 0.07 (SE) pCi/g (standard dry 

 weight) and a total inventory of 0.21 nCi/m^ ; comparable values during 1974 were 

 0.33 ±0.09 pCi/g and 0.25 nCi/m^ which presumably included the 0.016 nCi of 

 2 3 9,2 4 0pjjyj^2 ^j.|^^ Yi^^ been deposited on Thule landscapes in the 6-yr interval between 

 collections. Those two sets of data were not significantly different (t value, -1.47; df. 12; 

 P<0.1 to 0.2) nor were the "^Pu/^^^-^'^^Pu ratios of the uncontaminated 1974 lichen 

 samples (last eight values in Table 4) significantly different from those which contained 

 appreciably greater amounts of 2 3 9,2 4 0p|j ^j^^^ apparently originated from the 1968 

 accident. However, the ^^^'■^'**^Pu/^ ^ ^Cs ratios of uncontaminated samples varied over 

 a 200-fold range and showed coefficients of variation (CV = standard deviation ^mean) 

 that averaged >2.0. By comparison, the ■^^^•^'*°Pu/' ■^ ^Cs ratios in uncontaminated 

 lichen samples were relatively stable at 0.02 ± 0.01. This greater variation in radionuclide 

 ratios in lichen samples collected near the accident site suggests that the rigorous climatic 

 and edaphic factors of the Thule region probably had a major influence on the 

 redistribution of radionuclides and led to a balancing of concentrations in lichens and 

 soil. 



The ^^^Cs inventory in the Ciadonia-Cetraria lichen carpet at Anaktuvuk Pass 

 increased steadily from 6.2 nCi/m^ in the initial sampling in 1962 to maximum values of 

 about 50 nCi/m^ in 1965 and has subsequently fluctuated near 35 nCi/m^ (Table 5). The 

 estimated ' ^ ^Cs deposition and the amount in the lichen carpet were in close agreement, 

 althougli the lichens had also been exposed to an undetermined amount of fallout during 



