Chernobyl radioactivity persists in reindeer
Introduction
After radioactive fallout, reindeer contain elevated radiocaesium concentrations due to intake of contaminated lichens and other vegetation (Lidén, 1961, Hanson, 1966, Holleman et al., 1971, Gaare and Staaland, 1994, Staaland et al., 1995). Particularly, high concentrations can be observed in reindeer during the winter resulting from a combination of higher radiocaesium intake and lower radiocaesium excretion rate (e.g. Holleman et al., 1971). Contaminated lichens are generally considered to be the main source of radiocaesium intake during winter, and may be the main radiocaesium source during summer (Staaland et al., 1995). Additionally, fungi can be another important source of radiocaesium intake in the autumn (Hove et al., 1990).
Following fallout from the 1986 Chernobyl accident, individual radiocaesium activity concentrations in reindeer meat in the most affected areas in Scandinavia reached 150 kBq kg−1 (fresh weight, FW) (Strand et al., 1992) and declined with effective half-times of 3–5 years (Pedersen et al., 1993, Åhman and Åhman, 1994, Amundsen, 1995, Gaare et al., 2000, Åhman et al., 2001). In comparison, half-times of 6–9 years have been observed in northern Fennoscandia that received less Chernobyl fallout (Skuterud et al., 1999, Åhman et al., 2001, Rissanen et al., 2003). Observations of slower rates of decline in radiocaesium concentrations in several vascular plants compared to lichens (Gaare and Staaland, 1994, Gaare et al., 2000) indicated that the significant seasonal differences in radiocaesium concentrations in reindeer observed during the first years after the Chernobyl accident (e.g. Eikelmann et al., 1990, Pedersen et al., 1993, Åhman and Åhman, 1994) would be less pronounced with time (Gaare and Staaland, 1994). The point in time at which seasonal differences in radiocaesium concentrations become reduced might be dependent on the species composition of the reindeer diet, and may even vary between grazing areas.
About 58% of Norwegian territory is used as pasture by reindeer, a major part of which is used for reindeer herding (Norwegian Reindeer Husbandry Administration, 2004; Danielsen, J. Directorate for Nature Management, Trondheim, personal communication). The probability that any future 137Cs contamination event in Norway will affect reindeer grazing areas is therefore great. A thorough understanding of reindeer radioecology is therefore essential in Norwegian nuclear emergency preparedness. However, most terrestrial radioecological studies in Norway were terminated during the 1990s, with the exception of routine monitoring of 137Cs concentrations in semi-domestic reindeer in central and southern Norway where a continued requirement existed to ensure that meat complied with the national intervention limit of 3000 Bq kg−1. Furthermore, by the end of the 1990s, studies indicated that rates of decline in 137Cs concentrations in other components of the ecosystem were slower than previously reported (Jonsson et al., 1999, Smith et al., 2000). The present study was therefore initiated to obtain new data and more detailed knowledge about the long-term transfer of 137Cs in the soil–plant/lichen–reindeer food chain that could help explain the persisting elevated 137Cs concentrations in reindeer. The study was conducted during the period 2000–2003 with sampling of soil, vegetation and reindeer tissues in two of the areas in Norway that were most affected by fallout from the Chernobyl accident. Supplementary data on 137Cs in reindeer from 1986 onwards were obtained from the Norwegian Reindeer Husbandry Administration.
Section snippets
Study areas
The Vågå and Østre Namdal reindeer herding districts (Fig. 1) were selected because of the comparatively high levels of fallout received from the Chernobyl accident and the area's contrasting climates. Reindeer grazing in Vågå occurs mostly between 1000 and 1600 m above sea level (a.s.l.), whilst the Østre Namdal pasture is mainly situated between 450 and 1100 m a.s.l. Both areas lie in northern boreal and alpine vegetation zones, the low alpine zone starting at about 1200 m a.s.l. in Vågå and 750
Soil
The deposition density in individual samples varied nearly 11-fold (18–190 kBq m−2) in Vågå and 19-fold (4.2–79 kBq m−2) in Østre Namdal, and there were significant differences in deposition densities between sampling locations within each area (Fig. 1; one-way ANOVA, P < 0.001). The average deposition density at the Vågå locations was more than three times that in Østre Namdal (factor 3.5 between the geometric mean values of 52 and 15 kBq m−2; t-test, P < 0.001).
Vegetation
Activity concentrations of 137Cs in the
Long-term trends
In the analysis of long-term trends we chose to split the time period into two parts. The rationale behind this approach was that single exponential models could not satisfactorily describe the trends during the whole period (Fig. 4, Fig. 5), and that non-linear regression analyses with double exponential models returned insignificant parameters. The selection of local concentration minima as years when long-term trends changed may have emphasized the insignificance in the decline in 137Cs
Conclusions
- 1.
There has been no detectable decrease in 137Cs concentrations in reindeer in Vågå and Østre Namdal during the last few years, and seasonal differences in 137Cs concentrations in reindeer have been less pronounced than the first years after the Chernobyl fallout, probably because of persistently elevated 137Cs concentrations in fodder plants. Furthermore, 137Cs concentrations in the autumn have occasionally exceeded those in winter. The study suggests that future long-term decline in 137Cs
Acknowledgement
This work was made possible by support from the Research Council of Norway (project no. 134118/720). This support is gratefully acknowledged, and we also wish to thank Mr Jon Drefvelin (NRPA) for his efficient help in analyzing plant samples, Mr Morten Sickel (NRPA) for producing graphical presentations, Dr Justin Gwynn (NRPA) for linguistic support, and Dr Birgitta Åhman (Swedish University of Agricultural Sciences) for constructive comments on a draft of the manuscript.
References (44)
- et al.
Effect of origin of radiocaesium on the transfer from fallout to reindeer meat
Sci. Total Environ.
(2001) - et al.
Long-term studies on transfer of 137Cs from soil to vegetation and to grazing lambs in a mountain area in Northern Sweden
J. Environ. Radioact.
(2001) - et al.
Examination of a relationship between 137Cs concentrations in soils and plants from alpine pastures
J. Environ. Radioact.
(2000) - et al.
Seasonal variations in soil-to-grass transfer of fallout strontium and cesium and of potassium in North German soils
J. Environ. Radioact.
(1996) - et al.
Environmental processes affecting plant root uptake of radioactive trace elements and variability of transfer factor data: a review
J. Environ. Radioact.
(2002) - et al.
Pathways of fallout radiocaesium via reindeer to man
- et al.
Soil-to-plant transfer of fallout caesium and strontium in Austrian lowland and Alpine pastures
J. Environ. Radioact.
(2000) - et al.
Long-term consequences for Northern Norway of a hypothetical release from the Kola nuclear power plant
Sci. Total Environ.
(2004) - et al.
Soil organic horizons as a major source for radiocesium biorecycling in forest ecosystems
J. Environ. Radioact.
(2002) - et al.
An overview of the effect of organic matter on soil–radiocaesium interaction: implications in root uptake
J. Environ. Radioact.
(2002)
Feed selection and radiocesium intake by reindeer, sheep and goats grazing alpine summer habitats in southern Norway
J. Environ. Radioact.
Mobility and plant availability of radioactive Cs in natural soil in relation to stable Cs, other alkali elements and soil fertility
J. Environ. Radioact.
Radiocesium in Swedish reindeer after the Chernobyl fallout: seasonal variations and long-term decline
Health Phys.
Radiocaesium contamination in Norway
Radiat. Prot. Dosim.
Dynamics of radionuclides in forest ecosystems
Seasonal variation of cesium 134 and cesium 137 in semidomestic reindeer in Norway after the Chernobyl accident
Rangifer
Monitoring 137Cs in the Dovre–Rondane region 1997–1999
Fallout radionuclides in Alaskan food chains
Am. J. Vet. Res.
Relationship between potassium intake and radiocesium retention in the reindeer
Transfer of radiocesium from lichen to reindeer
Health Phys.
Fungi: a major source of radiocesium contamination of grazing ruminants in Norway
Health Phys.
Radioaktivt cesium i rein og beiter i Vågå etter Tsjernobylulykken (in Norwegian)
Reindriftsnytt
Cited by (43)
Steep declines in radioactive caesium after 30 years of monitoring alpine plants in mountain areas of central Norway
2024, Journal of Environmental RadioactivityTrophic food chain transfer of radiocaesium from reindeer meat to the blowfly Calliphora vicina and the parasitoid wasp Nasonia vitripennis
2023, Science of the Total EnvironmentEffective and environmental half-lives of radiocesium in game from Poland
2022, Journal of Environmental RadioactivityA review on the use of lichens as a biomonitoring tool for environmental radioactivity
2022, Journal of Environmental RadioactivityFukushima Accident: 10 Years After
2021, Fukushima Accident: 10 Years After