Answer to Question #11260 Submitted to "Ask the Experts"

What is the body burden of cesium-137 (¹³⁷Cs) in wild game (specifically elk) in Idaho? What effects do the foraging habits of the game have on the body burden (e.g., mushrooms or lichen as a major food source vs. berries or alfalfa)? Could an individual consuming a significant amount of wild game have detectable levels (through in vivo monitoring) of ¹³⁷Cs?

The presence of ¹³⁷Cs in the environment in the United States is due primarily to fallout deposited decades ago when atmospheric nuclear bomb testing was being conducted. The deposited ¹³⁷Cs has a long physical half-life of about 30 years and remains in the soil, available to some plants and to the wildlife that feed on them.

Much of the environmental monitoring that has been conducted in Idaho has been by the Idaho National Engineering and Environmental Laboratory. Past studies (in the late 1990s) have shown that burdens of ¹³⁷Cs in the muscle tissue of elk have ranged from 0.085 to 0.63 bequerels per kilogram (Bq kg^-1). A 2011 measurement showed 0.15 Bq kg^-1 of ¹³⁷Cs in elk muscle tissue.

These values are not extremely high, especially if compared to the US Food and Drug Administration's derived investigation level of 1,200 Bq kg^-1 for food (this is a decision-making level associated with contaminated food intake and represents a potential committed effective dose of 5 millisieverts [mSv], based on total diet and an assumption that 30% of the food is contaminated).

Foraging habits no doubt do affect the intakes of ¹³⁷Cs by wild animals, including elk. Elk will eat both mushrooms and lichen as part of their diets, and these foods do concentrate ¹³⁷Cs relative to the soil concentration more than do many other available foods. The mushrooms are likely the stronger concentrators with concentration factors on the order of 10,000 having been determined. I am not familiar with specific studies that have identified the relative amounts of mushrooms and lichens that are typically consumed by elk in Idaho, although neither food appears to be the overall favorite of elk. The mushrooms are eaten probably sometimes for variety as well as when other preferred foods are less abundant. The lichens seem to be eaten largely when other preferred foods are not available. Mushrooms probably are consumed more in the summer and fall months and lichen probably more in the winter months when preferred foods are not to be found, but I cannot estimate the relative amounts of these two foods consumed by the typical elk.

There have been numerous examples of elevated ¹³⁷Cs levels (compared to normal background) in human beings who have been moderate-to-heavy consumers of game meats, especially deer, and I expect the same would be true for elk consumers. Eisenbud (Environmental Radioactivity, 2^nd ed., p. 382, Academic Press, 1973) cited results from a couple of publications that claimed elevated levels of ¹³⁷Cs in individuals in the sub-Arctic region who ate large quantities of moose or caribou, as well as elevated levels in Alaskan Eskimos among those who ate moose and caribou as compared to those who ate primarily reindeer. Here are a couple internet links that also refer to the transfer of ¹³⁷Cs from game animals to man:

• International Nuclear Information System – Radiocaesium Transfer to Man from Moose and Roe Deer in Sweden
• ResearchGate – Cesium-137 Body Burdens in Norwegian Lapps, 1965-1983

In the United States, levels of ¹³⁷Cs have not been so high as to present a health concern.

George Chabot, PhD, CHP