The largest doses and risks of radionuclides in the Arctic are from natural radionuclides, predominantly 210Po (Polonium), 21OPb (Lead), 228Th (Thorium), and 232Th. Among the radionuclides derived from anthropogenic sources, 137Cs (Cesium) is the major contributor to dose but represents only 2% to 3% of the total dose and derives from land-mammal consumption.

Anthropogenic radionuclides of interest and concern in the Arctic environment are:

137Cesium (Cs): This Cs isotope is produced during fissioning (splitting of atoms) of uranium and plutonium fuels. It is long lived (radiation half-life of 30 years) and is found in the environment as a result of worldwide fallout from atmospheric weapons tests and nuclear power production. It is used in industry as a sealed gamma source for measuring the thickness of materials and in medicine as a sealed source for therapy and as a tracer substance.

9OSr: Strontium has 6 radioisotopes which are direct fission products of uranium. 9OSr is the most important of these because of its long radiation half-life of 29 years. In medicine, it is used to treat cutaneous lesions that are only a few millimeters in depth. In industry, it is used in thickness gauges, as a source for static dust elimination by air ionization, a compact heat source, and a thermoelectric source in devices where a long-lived, independent power source is needed. 9OSr is found in the environment as a result of nuclear fallout during atmospheric weapons tests. It accumulates in bones and teeth.

Measurable levels of some radionuclides still remain in temperate and Arctic ecosystems after the weapons testing era (1952-1981). In northern ecosystems, higher levels of the longer-lived fission products (137CS (half-life 30.2 years) and 9OSr) are still present due to slower turnover rates in a cold and dry climate. The 1986 Chernobyl accident released additional 137Cs into the atmosphere, and increased loading in boreal Canada by approximately 5% (Paliouris et al. 1995). They are also transported by ocean currents from industrialized countries of Europe.

131I: Radioactive iodines, especially, 131I, 132I, and 129I, are fission products from nuclear weapons tests and nuclear reactors. Once released to the atmosphere, radioactive iodine may return via precipitation to land used for pasture, thereby contaminating vegetation and, ultimately, the food and milk supply. Radioiodine is important in terms of its selective irradiation of the thyroid.

239Pu: Plutonium is a man-made element used as fuel in nuclear power reactors and as an explosive in nuclear weapons . 239Pu has a radiation half-life of 24,390 years. Nuclear weapons testing programs have placed more than 5,000 kilograms of plutonium, mostly as insoluble particles of oxide, into the stratosphere, which has resulted in worldwide deposition. Actual concentrations in the environment are extremely low.

222Rn: Radon results from the radioactive decay of radium, a ubiquitous element in rock and soil derived from the decay of uranium. Radon gas seeps from soil into buildings primarily through sump holes, dirt floors, floor drains, cinder-block walls, and cracks in foundations and concrete floors. When trapped indoors, it can accumulate to significant levels.

Tritium (3H2): Tritium is a hydrogen atom with a nucleus containing two neutrons. It has a radiation half-life of 12.5 years. Tritiated water (3H20) is the most familiar form of tritium. It is formed when heavy water (2H20) absorbs neutrons during the process of moderating nuclear fission in a reactor. Tritiated water has also been produced in the atmosphere as a result of the release of tritium gas from nuclear reactors. By far, the greatest part of the tritium found in the environment is due to atmospheric nuclear weapons tests conducted prior to 1963.

238U: Naturally occurring uranium consists of 238U (99.27%), 235U (0.72%), and 234U (0.0054%).

235U is extracted or concentrated from natural uranium for use in nuclear power reactors or nuclear weapons. The uranium remaining after 235U has been removed is referred to as "depleted uranium," which continues to be a radiation as well as a chemical hazard. In general, chemical damage is more important than radiological effects. High levels of uranium have been detected in well water in various parts of Canada.

Human Health

Chronic low level exposures are of most concern in cases of exposure to environmental levels of radiation. Early injuries result from acute external radiation exposure with consequent damage to tissues which have a rapid turnover, such as bone marrow and the gastrointestinal mucosa. Late or delayed effects of ionizing radiation may not appear for several decades after exposure and can result either from massive doses that have caused early effects or from relatively low exposures received over an extended period of time.

The health effects caused by exposure to ionizing radiation may appear as either hereditary or somatic effects. Hereditary effects result from exposure of the reproductive organs, which may induce mutations in the genetic material of an exposed individual. The results of these mutations may appear in the offspring of the persons exposed and may range from minor disorders to serious defects. No conclusive effects, attributable to exposure from either natural or artificial radiation, have been found in human offspring. Somatic effects are the most common consequence of radiation exposure. Early somatic effects appear in the individual within days or weeks after a significant external exposure and may include nausea, loss of hair, sore throat, hemorrhage, and diarrhea. The main late somatic hazards from exposure to environmental levels of radiation are the development of leukemia and other cancers, for example, in the bone, thyroid, or lung, as well as cataracts of the eye. The probability that a malignant disease will develop following exposure is dependent on the radiation dose received. The severity of the disease is independent of the exposure, and radiation-induced cancers are indistinguishable from those that occur from other reasons.

Some radionuclides have a tendency to concentrate in certain tissues as a result of their interaction with normal physiologic processes. For example, cesium and strontium isotopes tend to congregate in bone, whereas the thyroid gland selectively concentrates iodine and radioiodine.