Factors affecting uptake and metabolism of radioactive caesium in reindeer have been well known since the 1960/1970s. After the Chernobyl accident in 1986, Norway (particularly at NMBU) and Sweden developed countermeasures and actions to reduce contamination levels in reindeer. However, it was still difficult to use this knowledge to predict contamination levels in reindeer meat, because of the vast reindeer grazing areas – often well above 1000 km2 – and the very heterogeneous deposition levels within these areas. There is still a need for control and measures in reindeer husbandry in parts of these two countries due to the Chernobyl fallout so this problem remains important. Fortunately, the development of GPS/electronic tracking technology for livestock has opened new possibilities.
In 2011, the Norwegian Radiation Protection Authority, in cooperation with the Geological Survey of Norway, carried out a detailed aerial survey of the Chernobyl fallout in some of the most Chernobyl contaminated areas in southern Norway, including the grazing area of the Vågå reindeer herding company. Some 20 reindeer in their herd are carrying GPS collars, and we are very grateful to the herders for giving us online access to their positions and position logs! By combining positions and the deposition map, we can follow the deposition levels in the areas roamed by each reindeer. An example is given for the reindeer doe Linn in figure 1.
Based on the ground deposition levels, and vegetation sampling in the area, we can estimate radiocaesium concentrations in the plants and lichens consumed by each reindeer. Furthermore, using general knowledge of the reindeer’s seasonally varying diet, we can feed our mathematical reindeer a daily caesium dose, and estimate the resulting concentrations in reindeer meat. To validate the model results we compare estimated concentrations with results of live monitoring when the herders round up their animals for slaughter every autumn and winter. Fig. 2 shows model results and measured concentrations of caesium-137 in some of the Vågå reindeer during the last years.
The measured concentrations in the individual reindeer differ more than the modelled concentrations. This shows that differences in deposition alone do not explain the differences in concentrations between the animals. But the model results are nevertheless really encouraging! They do for instance show that the concentrations increase during the autumn because the grazing area used during this season have relatively high deposition levels. Thereafter the concentrations decline while the herd is moved across a less contaminated area on their way to the winter slaughter location. Then the concentrations increase again because the winter diet and lower metabolism results in higher caesium concentration until the spring and fresh forage becomes available.
Presently the model does not account for the reindeer’s intake of wild mushrooms in late summer and autumn – that is work in progress. Autumn 2014 was very rich in mushrooms, and the Vågå herders could not slaughter the animals as planned because of the contamination levels in the deer. Anyway, the most challenging aspect with mushrooms is to know if and how abundant the mushrooms will be. Nevertheless, using detailed aerial surveys and GPS technology we are developing a tool that will help assessing consequences and the need for countermeasures in reindeer husbandry – should another accident result in fallout over Norway. Reindeer husbandry occurs in 40% of Norway’s territory, and are thus relatively likely to be affected – again.
This article was first published on forskning.no