See also:

Peregrine Falcons
 
Mercury and Marine Mammals
 
Organochlorines in Beluga
 
Slide Show: Status of Contaminants in the Arctic Borderlands (off site)

Arctic Borderlands Ecological Knowledge Co-op

What is happening?

• The graph shows a major decline in cesium-137 levels in the muscle of caribou from the Western Arctic (near Barrow, AK), Porcupine and the Bluenose herds between 1964 and 1995.
• The cesium is declining with an environmental half-life of about 10 years, which means that half of the cesium disappears every 10 years.
• The data show that the lowest levels of cesium-137 were found in the Western Arctic herd in 1965, when cesium levels were at a maximum throughout the North. In 1995, the levels in the Western Arctic herd were barely above detectable levels.

Why is it happening?

• Cesium-137 was produced in atmospheric nuclear weapons tested by the United States, USSR, China, Britain and France between 1946 and 1992. The cesium-137 entered the atmosphere, deposited onto lichen in precipitation and moved into the caribou when the lichen was eaten.
• The Chernobyl nuclear accident in 1986 was a significant source of cesium-137 but the levels in caribou in Canada's North did not increase much. The amount of cesium produced in the atmospheric tests during the 1960s was much greater.
• Cesium-137 only reaches high levels in caribou and reindeer. Studies done on marine mammals, small mammals and birds in Canada's North show very low levels of the radionuclide.
• Cesium levels change dramatically on a seasonal basis, with the highest levels found in the early spring after the caribou have been feeding on lichen all winter.

Why is it important?

• The cesium-137 in caribou also accumulates in the people that eat the caribou. Health Canada has done several measurements in most northern communities using a device called a "whole body counter" which measures the cesium-137 in a person. The levels of cesium-137 have also declined in people since the 1960s.
• Cesium-137 is a radionuclide that gives off energy as it decays. If the levels of cesium-137 are high enough they can produce a high radiation dose in people. A very high radiation dose can lead to cancer.
• The decrease in cesium-137 levels in caribou is good news because it shows that one man-made contaminant is declining rapidly and will disappear over the years if there are no new sources.

Technical Notes

• The graphed data are from several sources. Cesium-137 is measured in muscle using a gamma spectrometer. The Alaskan data are from Radiological Health Data and Reports from 1966, 1967 and 1968 and a paper by Todd O'Hara and co-authors on the "Radionuclide levels in caribou of Northern Alaska in 1995-96" (Arctic 1999). The data for the other two herds are from Health Canada and a paper by Macdonald and co-authors ("Regional variation in radionuclide concentrations and radiation dose in caribou [Rangifer tarandus] in the Canadian Arctic; 1992-94". Science of the Total Environment 1996). There are no data for the Western Arctic herd in 1987 and the Porcupine herd in 1995.
• Indicator text prepared by Colin Macdonald for the Co-op.