Transport Of 60Co Research Articles

Protection of non-human biota against radiation in freshwater—Effect of time dependence in tiered exposure assessment

The ERICA's European framework that have been proposed to assess the exposure of biota to radionuclides is based on tiered approach: the Tier 1 assessment is based on equilibrium assumptions (constant radioactive releases over time, equilibrium at the interfaces water-suspended matter and water-biota); the Tier 2 assessment allows to use time-dependent and site-specific data to perform a more precise evaluation. The objective of this paper was to compare these two tiers in the context of routine releases from nuclear power plants in freshwater ecosystem. The Loire River where 14 nuclear power plants (NPPs) operate was chosen as a case study and the transport of 60Co in the river, its partition between water and suspended particles and its bioaccumulation was calculated under equilibrium and time-dependent assumptions respectively. Using this case study allowed to quantify the overpredictions linked to conservatisms assumed in Tier 1. Recommendations were identified on when a Tier 2 approach is actually needed.

Navigated control in dental implantology

Monitoring and restoration activities at low-level radioactive waste disposal sites have identified complicated mixtures of inorganic and organic contaminants in soil and groundwater. Metallic contaminants are generally complexed with various chelating agents and organic acids which alter the geochemical behavior of the contaminants in subsurface media. The objective of this study was to provide an improved understanding of the geochemical processes controlling the subsurface transport of radioactive 60Co complexed with ethylenediaminetetraacetic acid (EDTA). Specifically, we investigated the kinetics and mechanisms of Co(II) EDTA2− oxidation to Co(III)EDTA− by the soil mineral pyrolusite (β-MnO2). A column displacement technique was utilized to investigate Co(II)EDTA2− reactivity and oxidation rates through packed beds of pyrolusite-coated SiO2. The interaction of Co(II)EDTA2− with the porous media was characterized by a MnO2-induced oxidation of the Co (II)EDTA2− to Co(III)EDTA−. The oxidation of Co(II)EDTA2− appeared to involve the reduction of Mn (IV) to both an aqueous Mn2+ species and a theorized Mn(III)-oxide solid phase. The redox reaction was catalytic since the reduction products were gradually reoxidized in the presence of dissolved O2 to form a Mn(IV)-oxide phase. Oxidation of surface-bound Mn2+ and the theorized Mn(III)-oxide was slow relative to Co(II)EDTA2− oxidation, and a reversible loss in the oxidative ability of the β-MnO2 occurred when exposed to CO(II)EDTA2−. The reduction in catalytic activity of the MnO2 was not the result of direct surface poisoning by Mn2+ but rather was believed to result from the formation of an intermediate Mn(III)-oxide solid phase whose oxidative potential was significantly less than MnO2. Thus, the kinetics of Co(II)EDTA2− oxidation to Co(III)EDTA− by MnO2 was dependent on the rate of MnO2 surface regeneration. The environmental implications of this redox reaction are pronounced, since any Co(III)EDTA− produced is extremely stable, and this enhances the persistence and transport of 60Co in subsurface environments.

Kinetics and mechanisms of Co(II) EDTA oxidation by pyrolusite

Monitoring and restoration activities at low-level radioactive waste disposal sites have identified complicated mixtures of inorganic and organic contaminants in soil and groundwater. Metallic contaminants are generally complexed with various chelating agents and organic acids which alter the geochemical behavior of the contaminants in subsurface media. The objective of this study was to provide an improved understanding of the geochemical processes controlling the subsurface transport of radioactive 60Co complexed with ethylenediaminetetraacetic acid (EDTA). Specifically, we investigated the kinetics and mechanisms of Co(II) EDTA 2− oxidation to Co(III)EDTA − by the soil mineral pyrolusite (β-MnO 2). A column displacement technique was utilized to investigate Co(II)EDTA 2− reactivity and oxidation rates through packed beds of pyrolusite-coated SiO 2. The interaction of Co(II)EDTA 2− with the porous media was characterized by a MnO 2-induced oxidation of the Co (II)EDTA 2− to Co(III)EDTA −. The oxidation of Co(II)EDTA 2− appeared to involve the reduction of Mn (IV) to both an aqueous Mn 2+ species and a theorized Mn(III)-oxide solid phase. The redox reaction was catalytic since the reduction products were gradually reoxidized in the presence of dissolved O 2 to form a Mn(IV)-oxide phase. Oxidation of surface-bound Mn 2+ and the theorized Mn(III)-oxide was slow relative to Co(II)EDTA 2− oxidation, and a reversible loss in the oxidative ability of the β-MnO 2 occurred when exposed to CO(II)EDTA 2−. The reduction in catalytic activity of the MnO 2 was not the result of direct surface poisoning by Mn 2+ but rather was believed to result from the formation of an intermediate Mn(III)-oxide solid phase whose oxidative potential was significantly less than MnO 2. Thus, the kinetics of Co(II)EDTA 2− oxidation to Co(III)EDTA − by MnO 2 was dependent on the rate of MnO 2 surface regeneration. The environmental implications of this redox reaction are pronounced, since any Co(III)EDTA − produced is extremely stable, and this enhances the persistence and transport of 60Co in subsurface environments.

Transfer of60Co from midwater squid to sperm whales

Sperm whales are notable squid-eaters. They feed mainly on medium to large-sized cephalopods at midwater levels and defecate near the surface. This suggests the existence of an upward transport of60Co by sperm whales from the mesopelagic zone (150–1,200 m). To elucidate this squid-whale route for this artificial radionuclide,60Co content was determined in squid and in predator whales captured by commercial whaling. In the Cephalopoda livers60Co levels of 30–500 mBq kg−1 wet were found and in the viscera of Odontoceti (toothed whales) 15–40 mBq kg−1 wet. About 0.3% of80Co ingested was estimated to be retained in a 23-year-old male sperm whale. In the livers of Bryde's whales,60Co levels of 40–80 mBq kg−1 wet were detected, but not in euphausiids and sardines, their possible prey. The level of Co in sperm whales was nearly the same as in Bryde's whales. Specific radioactivity60Co/59Co in mBq µg−1 was several times higher in sperm whale (1.1–1.6) than in cephalopods (0.19–0.77). Eating prey with a high content of60Co in the 1960's may have contributed to the present body burden in sperm whales with a long-life span. However, the origin of60Co in Bryde's whales is unknown.