Radiostrontium , radiocesium and stable mineral composition of bones of domestic reindeer from Vågå , Norway

Radiostrontium, radiocesium and macromineral concentrations were measured in metatarsal or metacarpal bones from 78 reindeer (59 calves and 19 adults) in the Vågå reindeer herding district in Southern Norway. Samples were collected in the period August 1988 to May 19#9. Radiocesium concentrations increased from August through the winter. Radiostrontium varied slightly around an average value 1810 Bq/kg D M . Mg concentrations decreased through the winter, the concentrations of other minerals and bone density showed only small variations. N o signs of mineral deficiencies were observed. It is concluded that radiostrontium mainly originated from the Chernobyl nuclear accident.


Introduction
After the Chernobyl accident the contamination of mountain pasture and subsequent accumulation of the radioisotopes 134 Cs and 137 Cs in reindeer have been highlighted (Skogland 1987;Jones et al 1989;Pedersen et al 1990).In addition to radiocesium the fallout also contained radiostrontium ( 90 Sr) with an activity in Fen-noscandia amounting to about 2% of radiocesium activity (Antilla 1986;Aarkrog 1988).The concentration of this isotope in products from farm animals has been below the action limit of 90 Sr and has therefore not been emphasized by health authorities to the same extent as radiocesium.Analyses of soils from high mountain areas in Valdres, Norway indicate that the 90 Sr deposition after the Chernobyl was comparable in size to the fallout after the atmospheric nuclear weapon tests (Bjørnstad et al. 1990).
The Cs isotopes are rapidly recycled within the body (Staaland et al 1990) and rapidly excreted.Contrary 90 Sr follow Ca in biological systems and is firmly bound to the bone matrix and may remain in the bones throughout the lifetime of animals. 90Sr decays to 90 Y, a ft-emitter at a much higher energy level than 90 Sr, 0.546 and 2.28 MeV respectively. 90Y has been related to damage of the bone marrow and to development of leukemia in man.It should also be mentioned that 90 Y not like Sr follow calcium in biological systems and therefore more easily can be circulated within the body.
In the arctic maximum concentrations of most fallout radionuclides are associated with the lichen-reindeer-man food chain (Hanson 1967).Most Sr is found in the reindeer bones whereas Cs accumulate in the soft tissues.The levels of both 90 Sr and 137 Cs in reindeer breeders consuming large amount of reindeer meat were only about twice that of other people living in the same areas both in Russia (Nevstrueva et al. 1967) and in Norway (Westerlund 1985).Apparently radiostrontium is more mobile in arctic lichen dominated ecosystems than radiocesium (Hanson et al. 1967).Studies from Norway (Hove and Strand 1990) and from the Faroe Islands and Greenland (Hansen and Aarkrog 1990) indicate that radiostrontium and radiocesium can persist for long periods in alpine ecosystems.This long retention has raised concern about possible genetic damage to reindeer and other parts of alpine ecosystems (Skogland 1990).
The purpose of the present study was therefore to measure bone radiostrontium and radiocesium contents and to examine possible seasonal variations in their concentrations in reindeer in an area heavily contaminated with radioactivity from the Chernobyl accident.Comparison is made to the values observed after the global fallout in the 1960 / ies.Results obtained are furthermore compared to variations in concentrations of major bone minerals.May 1989.In addition samples were taken from 19 adult reindeer of different ages.The animals were from the herd of The Vågå domestic reindeer company in Southern Norway.

Material and methods
About 8-10 cm of the middle part of the bone was used for analyses (Fig. 1).Soft tissues were removed and the bone marrow expelled.Cleaned bone samples were dried at 105°C to constant weight.The density was measured by submersion of bone specimens in glycerol of known density.
After cleaning and drying the bones were crushed in a steel mortar.One subsample was used for measurement of the two isotopes 137 Cs and 90 Sr and another for measurement of the minerals P, Ca, Mg, Na and K.

Radiometry
137 Cs was analyzed in approximately 10 g of crushed bone, using either a Canberra Ge-detector (20% efficiency and 2kev resolution at 1332 kev) or a Packard 3'' Nal Gamma counter 5000 series.
The concentration of 90 Sr in the samples were determined from analysis of 90 Y concentration, assuming radiological equilibration between 90 Sr and 90 Y (Bjørnstad et al. 1990).Following gammaspectrometry the samples were dry-ashed overnight at 600°C and dissolved in HC1.After addition of carrier, 90 Y was isolated by liquid extraction (Peppard et al 1957).The extracted 90 Y was back-extracted into 6 M NHCX The Cerenkov spectra from 90 Y were couted using a low-level liquid scintillation counter (Quantulus 1220 LKB Wallac, Finland).Chemical yields were determined by compleximetric titration.
Chemical analyses of P, Ca, Mg, Na and K were performed at the Chemical Research Laboratory of our University.Bones were ground and ashed at 500°C and the ash dissolved in aqua regia.The concentrations of the elements were determined by Inductively Coupled Plasma Spectrometry (ICP).
Statistical analyses of the data include calculation of the standard deviation of the means and the Duncan multiple range test (Ray 1982).

Result
In 5 animals chemical composition and content of the radioisotopes were measured in the two metatarsal and the two metacarpal bones.No significant differences in either chemical composition or isotope content was detected (P>0.05, Duncan test).Therefore either the metacarpal or metatarsal bone was used for the rest of the animals.
The average bone 90 Sr activity through the year was 1814 ±270 Bq/kg dry matter (DM) with no apparent seasonal trend.Also relatively to Ca 90 Sr levels (Bq 90 Sr/mmol Ca) remained stable between 0.28 and 0.31 from November to May (Fig. 2, Table 1).The concentrations of 137 Cs increased from August-September to May.Since K concentrations remained almost constant through the year, also the 137 Cs relatively to K increased through the winter (Fig. 1).
Density of the bones increased from 1.77 g/cm 3 in calves sacrificed in August to about 1.85 g/cm 3 in the winter.Also total ash content showed a similar increase from autumn to winter and spring.There were no significant differences between calves and adult animals in bone ash content (Fig. 2).The most consistent seasonal variation in bone mineral concentrations was found for Mg where a pronounced downward trend was observed from August to May in the calves.Values for adult animals were significantly lower (P<0.05),and the data indicated the same downward trend through the winter (Fig. 2).For Ca an apparent opposite trend was observed with the lowest concentrations in the autumn and higher values through the winter from December to May.Phosphorous and K were apparently only subjected to minor and usually insignificant variations in concentrations, but K was significantly higher in calves slaughtered in August and March (p<0.05,Duncan test).Also for Na no apparent seasonal trend in concentrations could be found, but values obtained from adult animals were slightly higher than for calves (p<0.05 in August and December).Concentrations of Ca, P and Na in March were unexpectedly low and K high compared to values obtained from February and April.

Discussion
Reindeer bones collected in northern Norway in 1956 and 1958 contained about 0.15 and 0.22 Bq/mmol Ca of 90 Sr (Hvinden and Lillegraven 1961), whereas values from the early 1970'ies were about 0.50 Bq/mmol (Westerlund 1985).Our value, about 0.29 Bq/mmol (i.e.1800 Bq/kg dry weight) is between these values from reindeer bones in northern Norway.The radiostrontium in these bones came from atmosphe-ric nuclear weapon tests in the 1960'ies (Fig. 3).The physical half life of 90 Sr is 28 years and the estimated biological half life in reindeer bones between 7 and 9 years based on data from Westerlund (1985, Fig. 3).Data on the deposition of radiostrontium in Vågå during the nuclear weapons tests do not exist.However beeing a relatively dry inland area levels may have been comparable to those in Finnmark.Extrapolation of radiostrontium data from Finnmark in the 1970'ies and early 1980'ies give rise to present day concentrations in reindeer bones of about 500 Bq/kg of 90 Sr (Westerlund 1985).With measured values of about 1800 Bq dry bones the conclusion is that the Chernobyl accident contributed significant quantities of 90 Sr to alpine ecosystems in addition to the well recognized radiocesium contamination.From a physiological point of view 90 Sr closely follow the seasonal trend of Ca.
In White-tailed deer Rabon (1968) observed that radiostrontium levels in bones decreased with age.Fawns aged 0-11 months had twice as  (Westerlund 1985) and present data from the Vågå reindeer herd, black dot ( much 89 Sr and 90 Sr in long bones as had animals older than 3 years.Our data suggest about equal levels in young and old animals which is also to be expected if Ca and Sr behave similarly in biological systems.In Rabon's study, which was performed on deer at the Savannah River plant in South Carolina radiostrontium ranged between 10pCi/g weight (i.e.370 Bq/kg) in old animals to about 20 pCi/g wet weight (740 Bq/kg) in young animals.
The radiocesium levels in the bones reflect dietary radiocesium intake, i.e. being high due to lichens in winter and much lower due to green vegetation in summer.Contrary to blood values from the same herd which remained constant and decreased slightly, bone values for 137 Cs apparently increased through the winter (Garmo et al. 1990).
This may indicate that accumulation into bones occurs at a slow rate compared to the rest of the body pools, accordingly that bone Cs is less readily exchanged with the environment than soft tissue radiocesium.The lower values found for radiocesium in bones from adult animals than for calves correspond to a body size effect observed by Rabon (1968) for white tailed deer.The bone content of radiocesium do not follow the K values and it is well known that K is a bad tracer for radiocesium (Oughton et al. 1991).
Very few data on bone mineral composition are available for reindeer.Mineral concentration in femurs from reindeer calves collected in the Elgå herding district in the eastern part of southern Norway showed similar seasonal trends as in the present study (Staaland and Saebø 1987).In particular a decrease in Mg concentration and an increase in K concentration was observed from fall to spring.Bjarghov et al. (1977), which examined metatarsal bones from coastal areas found no change in bone Mg from fall to spring.In an experimental study, however, Bjarghov et al. (1976) reported slightly increased K levels in plasma of reindeer calves fed a pure lichen diet through the winter and decreased Mg levels.In the Elgå material Na levels in femur bones apparently increased from fall to spring, but average values varied between only 220 and 240 mmol/kg dry bone against a mean value of about 280 mmol/kg dry matter in the present study (Table 1).In the Elgå area there is a presumed low availability of Mg and Na (Staaland and Saebø 1987).Higher values found in the Vågå reindeer could result from the use of salt licks or be an effect of higher levels of these minerals in lichens from the Vågå area (Garmo 1986;Staaland and Saebø 1987).Also in sheep (McDougall et al. 1974) Na depletion reduce bone Na levels.No signs of P or Ca deficiency were detected, the Ca values were almost identical in Vågå and Elgå and bone density values indicated adequate Ca intake because inadequate Ca in diet decrease bone density in sheep (Field et al. 1975).

Fig. 2 .
Fig. 2. Mineral concentrations (± S.D.) in metatarsal or metacarpal bones from reindeer in the Vågå reindeer herding district in southern Norway.For further explanations see Fig. 1.