Sources and reservoirs of anthropogenic iodine-129 in western New York

Abstract

Large quantities of iodine-129 have been released during nuclear weapons testing, and from nuclear power and fuel reprocessing plants. The distribution of this isotope was investigated in 110 surface water and soil samples from western New York (where several potential point sources are located) and other areas of North America, to evaluate its sources, transport pathways, and reservoirs. Elevated 129I concentrations associated with a former reprocessing facility at West Valley, NY, can be tracked to Lakes Erie and Ontario via site drainage, and for over 200 km via atmospheric transport, while only a negligible signal is associated with active power plants in the area. The results point to local reprocessing as the major source of 129I in western New York, while bomb fallout constitutes less than 0.5% of the signal. Surface soil is the dominant reservoir for anthropogenic 129I in this region. Across North America, 129I concentrations are lower than in western New York, although still significantly higher than expected weapons fallout. Reprocessing releases are currently seen to be the major source for elevated 129I concentrations on a global scale, in contrast to previous suggestions that most anthropogenic 129I was still derived from weapons fallout. Concentrations of 129I and iodine in surface reservoirs are generally found to be uncorrelated, implying that natural iodine and anthropogenic 129I are not yet in equilibrium. The results suggest that anthropogenic 129I is cycled between the atmosphere-soil-vegetation systems more rapidly than natural, pre-anthropogenic iodine.