129I dispersion and sources in Northwest Canada

Abstract

Radioiodine, 129I is a biophilic and mobile radionuclide, and a major contaminant of concern for long term radioactive waste disposal. Nuclear fuel reprocessing has released large amounts of anthropogenic 129I in a number of locations globally; this has led to an increase in the concentration of 129I and the 129I/127I ratio in the environment. Therefore, a detailed understanding of its movement and concentration in the environment is essential. While 129I dispersion has been examined in the vicinity of nuclear activities, little is known about its accumulation in remote regions. Accordingly, we have undertaken reconnaissance sampling in the Arctic as a location that may be affected by 129I fallout. Samples from large watersheds were collected in northern Canada on a trajectory starting in Whitehorse, Yukon Territory (60°43′00″N) and moving north to Tsiigehtchic, Northwest Territory (67°26′26″N). Results show concentrations of 129I up to 27×106atoms/L are present in Northwest Canada and 129I/I ratios up to 1.68×10−10. Annual 129I fallout ranges from 2.78×109 to 7.95×109atoms/m2/yr, calculated by normalizing the measured values to watershed area and discharge. These quantities substantially exceed literature values for waters containing only geogenic or cosmogenic production and are similar for all watersheds regardless of watershed area or discharge. Anthropogenic releases of 129I into the atmosphere or oceans are the major potential sources of 129I in the Arctic.