Potential Remobilization of ¹³⁷Cs, ⁶⁰Co, ⁹⁹Tc, and ⁹⁰Sr from Contaminated Mayak Sediments in River and Estuary Environments

Abstract

Following 50 years of nuclear production at Mayak PA, sediments in storage reservoirs are significantly contaminated. Dam failure or flooding could potentially transport large amounts of sediments, via rivers, to the Ob estuary and Kara Sea. The objectives of this work were to investigate fresh and seawater remobilization of 137Cs, 50Co, 99Tc, and 90Sr from contaminated Reservoir 10 sediments. Sediments were extracted sequentially using synthetic Techa freshwater, seawater, and chemical reagents with increasing dissolution powers. 137Cs and 90Sr freshwater distribution coefficients (apparent Kd) agreed quite well with published values; values for 99Tc were higher and values for 60Co were lower than expected. In seawater, mean apparent Kd values decreased by 94, 77, 48, and 73% (137Cs, 60Co, 99Tc, and 90Sr, respectively), indicating increased radionuclide mobility. Remobilization in seawater was 5, 15, 1, and 23% of total activities (i.e., releases of 165, 11, 0.3, and 170 kBq kg(-1) d.w.) for 137Cs, 60Co, 99Tc, and 90Sr, respectively. 137Cs and 99Tc were strongly bound to sediments (60% and 80%, respectively). 60Co and 90Sr were more mobile (70% reversibly bound). In conclusion, Mayak Reservoir sediments could potentially contaminate the Ob estuary due to remobilization of sediment-held radionuclides upon contact with seawater.

Redox interactions of technetium with iron-bearing minerals

“…In its oxidized form, Tc is present as pertechnetate (Tc(VII)O 4 contaminant at nuclear sites (Fredrickson et al, 2004;Morris et al, 2000;Skomurski et al, 2010;Standring et al, 2002). By contrast, under reducing conditions, poorly soluble Tc(IV) species dominate, with hydrous TcO 2 -like precipitates forming at concentrations greater thañ 5610 À9 mol l À1 (Meyer et al, 1991), Tc(IV) sorption and retention to sediments observed at very low concentrations (<10 À12 mol l…”

Geochemical reconnaissance survey and environmental assessment for stream sediments of Wadi Um Gier, Southeastern Desert, Egypt

“…This is concordant with the opinions of Davis and Leckie (1978) who suggested that trace element accumulation in sediments is often dominated by adsorption on the finer fraction of sediments, sorption, precipitation and/or coprecipitation of Al, Fe and Mn oxy-hydroxides and complexation with organic matter. Additionally, Horowitz (1991) and Standring et al (2002) suggest that sediment characteristics (e.g., clay fraction, Fe, Mn and TOC) affect the trace metal-sediment interaction represented by a fast surface sorption process that takes place during a relatively short period followed by redistribution between different binding sites until equilibrium is reached.…”

The potential impact of climate on human exposure to contaminants in the Arctic

“…Models predict that discharge from Arctic rivers such as the Mackenzie and the Ob may increase up to 20% (of the pre-Industrial Period level) by the middle of the 21 st century and by up to 40% or more in a few centuries (46). This will be of particular concern in industrialized regions of the North such as some areas of Russia where, due to industrial and agricultural practices, rivers are already a major source of metals (47), pesticides (48) and radionuclicides (49). Increased runoff and river discharge will increase the loading of these contaminants into the eastern Arctic Basin, ultimately leading to higher contaminant concentrations in marine mammal species that are important components of a traditional diet.…”