Biophysical aspects of Am-241 and Pu-241 in the environment.

Most of plutonium released by nuclear explosions is Pu-241 which decays to Am-241. We have studied the deposition of Pu-241 and Am-241 in lichens collected since 1958 in the central part of Sweden (62.3 degrees N, 12. 4 degrees E). Comparative studies with Pu-isotopes, Pu-239 + 240 and Pu-238 were also performed. In 1972 the total accumulated deposition of Pu-241 was 8 mCi/km2 of Pu-239 + 240 1 mCi/km2 and of Am-241 0.2 mCi/km2. About 80% of the Am-241 activity has been formed in situ from decay of Pu-241. The biological mean-residence time for all Pu-isotopes were about 6 years and for Am-241 4 years. The spatial distribution of Am-241 in the lichen carpet is quite different from that of Pu-241. The activity concentrations of Am-241 and Pu-241 have been studied in reindeer liver and bone. The average concentrations found were in liver 0.6 and 40 pCi/kg, in bone 0.2 and 6 pCi per kg for Am-241 and Pu-241 respectively. The activity content of Am-241 and Pu-241 in the Lapps due to their reindeer diet was estimated to be in liver 1.0 E-4 and 1.0 E-2 pCi/kg, in bone (3-9) E-5 and 1.0 E-2 pCi/kg for Am-241 and Pu-241 respectively. The estimated values for the fractions of ingested activity retained were in liver 7 E-6 and 14 E-6, in bone 20 E-6 for Am-241 and Pu-241 respectively. The fraction of ingested activity of Pu retained in reindeer liver is about 2-3 times higher than that of Am.