Effect of origin of radiocaesium on the transfer from fallout to reindeer meat

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Data on radiocaesium contamination of reindeer from five regions in Sweden have been used, together with interpolated radiocaesium deposition data, to quantify spatial variation in transfer to reindeer meat and to consider how it changes with time in different areas. Since the regions were contaminated to different extents by global and Chernobyl fallout, it was also possible to determine the influence of the origin or age of radiocaesium fallout on the transfer to reindeer meat. The regions differed significantly with regard to transfer of radiocaesium to reindeer meat. In two regions in the North of Sweden, where there was less Chernobyl 137Cs, aggregated transfer coefficients (Tag), estimated for the main slaughter period in the first year after the Chernobyl fallout, were low (0.15 and 0.36 m 2 kg −1 in January–April). Average Tag values calculated for the winter period (January–April) in two regions in the middle of Sweden, where deposition from Chernobyl dominated (83 and 94%, respectively, of the total deposition), were 0.78 and 0.84 m 2 kg −1, respectively with a maximum Tag for an individual reindeer of 1.87 m 2 kg −1. There was a threefold increase in Tag values from early autumn to late winter reflecting the change in the reindeer diet from less contaminated vascular plants to more contaminated lichens. The decline of 137Cs in reindeer meat from 1986 to 2000 differed between regions with longer effective half-lives ( T ef) in the northerly regions (11.0 and 7.1 years, respectively) with less Chernobyl fallout, and shorter half-lives in the other three regions (3.5–3.8 years). This observation, together with a lack of a decline in early autumn in the region with least Chernobyl fallout, supports the theory of a gradual, but reversible, fixation of radiocaesium in the soil over the mid-long term. The results suggest that both the extent of transfer of 137Cs to reindeer meat, and its subsequent decline with time, are affected by the differing origins of radiocaesium and that previous contamination may substantially influence radiocaesium transfer in the event of a further accident.