Variation in background concentrations and specific activities of 36Cl, 129I and U/Th-series radionuclides in surface waters

Assessment of the potential environmental impacts of nuclear fuel waste involves multiple lines of argument, one of which is an evaluation of the possible increments to background concentrations of certain radionuclides. This is especially relevant for radionuclides such as 3H, 36Cl and 129I where there is continuous cosmogenic or geogenic production. However, for 36Cl and 129I and certain U/Th-series radionuclides, data are scarce because the analysis methods are complex and costly. The present study used accelerator mass spectroscopy (AMS) to measure36Cl and 129I in river waters throughout Canada. Radiochemical methods were used for 3H and the selected U/Th-series radionuclides, and stable element concentrations were also determined. There were distinct differences in concentrations among the sites. Stable Cl and I tended to be at higher concentrations near the ocean or population centres. The 3H was high in regions with power reactors. The 226Ra, 235U and 238U concentrations were high in areas with known U mineralizations, as expected. The 36Cl and 129I concentrations were generally homogenous in mid-latitudes, but the 129I concentration was lower in the one arctic site sampled. Because the stable and radioactive isotopes of Cl and I varied in response to different factors, the resulting specific activities were especially variable. Both Cl and I are homeostatically controlled in animals, thus it follows that dose from 36Cl and 129I will depend more closely on specific activity than concentration, and therefore the environmental increments of interest are in the specific activities rather than simply concentrations.

► Accelerator mass spectroscopy for 36Cl and 129I in rivers throughout Canada.
► Radiochemical methods for 3H and selected U/Th-series radionuclides.
► Stable Cl and I at higher concentrations near ocean or population centres.
► 36Cl and 129I concentrations homogenous mid-latitude, 129I lower arctic.
► 36Cl and 129I specific activities were especially variable.