90Sr in northern Sweden : Relationships and annual variations from 1961 to 1969 in lichen, reindeer and man

• The transport of fallout-90Sr has been investigated in the food-chain: Lichen-reindeer-man during 1961-1969. The maximum levels which occurred in lichen during 1963-1965 were about 13 nCi/kg dry wt. The90Sr-level in the lichen-carpet decreased to about 5 nCi/kg dry wt. in 1967-1969. The effective half-time of 90Sr in the lichen-carpet was estimated to be 2.5 ± 0.8 a. The vertical distribution of90Sr in the lichen-carpet was studied during 1966— 1969 and indicates an increased deposition of90Sr-fallout during 1968-1969. The90Sr/Ca-ratio has also been studied in reindeer-bone and muscle tissues. This ratio increased up to 1965 to about 700 pCi/g in reindeer-meat and to 1000pCi/g in bone, and then there was a decrease to about 400 pCi/g in both meat and bone in 1969. The seasonal variation of the 90Sr/Ca-ratio in reindeer-meat and bone since 1965 was evaluated from the 90Sr/Ca-ratio in lichen by using a three-compartment model for the Sr-retention in reindeer. The90Sr/Ca-ratio in the skeleton of adult Swedish Lapps was calculated from the 90Sr/Ca-ratio estimated for diet. The absorbed dose delivered by90Sr +90Y during the period 1950-1970 has been estimated to be 30 mrad to the endosteum (cells lining bone-surfaces) and 20 mrad to the active bone-marrow. Corresponding absorbed dose values for the whole period 1950-2000 were estimated to be 80 ± 15 mrad to the whole endosteum and 50 ± 10 mrad to the bone-marrow.

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