Since the dawn of the nuclear age, radioactive technetium (Tc)-99 has been released into the environment from nuclear weapons testing, spent fuel reprocessing facilities, and other nuclear activities. Quantifying the measurement, effect, and risk of trace concentrations of Tc-99 is paramount to understanding the isotope’s behaviour in human-environment systems. Ground state Tc-99 decays by beta emission (Emax — 292 keV) with a half-life (t1/2= 2.11 x 105 y), while the metastable isomer Tc-99m (t1/2 = 6.0 h) decays rapidly by emitting a gamma photon. Technetium-99 is present in the environment in mobile pertechnetate (TcO4−) form. Tc-99 is used as an oceanographic tracer to investigate seawater movement and coastal pollution using seaweed as a bioindicator. The purpose of this study is to develop a sample preparation method to measure low concentrations, down to femtogram levels, of Tc-99 in environmental samples such as seaweed, water and medical Tc-99m waste using an accelerator mass spectrometer (AMS). When present in its soluble form, Tc (VII)can be reduced to Tc (IV) in the presence of a strong reducing agent such as SnCl2, then precipitated out of solution as an iron hydroxide by the addition of an iron carrier. Using AMS to measure precipitates prepared through a simple one-step co-precipitation method show high levels of isobaric interferences by Ruthenium-99 (Ru-99) and impurities by the co-precipitation of other hydroxides. A double-step co-precipitation method was determined to be efficient at reducing interferences of impurities present in the final precipitate. Using Tc-99m as a chemical tracer, the efficiencies of different oxidizing- reducing agents were compared to optimize the yield of Tc-99. The aims and objectives of the study are first: to develop a method for the separation and purification of Tc-99 from Ru-99 by ARS-II with ABEC column. Second: to develop methods for the removal of interferences and extraction of Tc-99 from iii environmental small size samples, and third: to develop a method to analyze Tc-99 by low energy AMS. Concentrations of Tc-99 were measured in seaweed samples with a newly developed oxidation-reduction method using Tc-99m as a yield tracer. The detection of Tc-99 from seaweed samples follows a two-step procedure. The first step is the oxidation of technetium from Tc (IV) to Tc (VII) oxidation state with H2O2 followed by iron hydroxide precipitation. The second step is the reduction of Technetium from Tc (VII) to the Tc (IV) oxidation state with SnCl2 followed by iron hydroxide co-precipitate. The co-precipitate contains the Tc (IV) and is dried at 80oC and then at 200oC to remove excess water, then mixed with PbF2 to produce TcF5– in the AMS ion source. The purification and separation of Ru-99 from Tc-99 is done by ARS-II with ABEC column and measure by AMS. Currently, the most sensitive practical choice for Tc-99 is ICP-MS, with typical LOD at picogram (pg.) levels. This translates to 10-100s of litres required for a seawater sample. AMS has shown potential <10 fg LOD, which translates to volume requirement of sub-litre to litres for seawater samples, this would make the AMS quantification of Tc-99 an incredibly useful and competitive alternative.

The environmental mobility of Technetium-99 is inextricably tied to its oxidation state. Under oxidizing conditions Tc-99 predominates as the Tc(VII)O4- anion. This anion has a high solubility and is precluded from sorption on most soil or mineral surfaces, giving it a high environmental mobility. Under reducing conditions, Tc-99 predominates as Tc(IV)O2 or Tc(IV)2S7. Tc(IV) species tend to be insoluble and are therefore immobile. Due to this redox dichotomy, there has been significant interest in developing reductive immobilization strategies for Tc-99, particularly in anoxic environments where Tc(IV) is conventionally assumed to be stable. However, O2 is not the only common environmental oxidant. Many high valent manganese species are environmentally prolific and well known to exist in anoxic and overall reducing environments. These powerful oxidants can create localized oxidizing conditions in otherwise reducing environments. Limited research on the oxidation of Tc(IV) species has left a knowledge gap in the true recalcitrance of such immobilization forms in environmental settings. Our work aims to bridge this knowledge gap by studying the oxidation of Tc(IV) by various, environmentally common, high valent manganese species. Mn(III)-ligand complexes in particular have been overlooked. Up until recently, aqueous Mn(III) was assumed to be absent from the environment due to its disproportionation in aqueous systems without suitable complexing ligands. More recently, Mn(III)-ligand complexes have been shown to be prolific in a variety of natural waters. We have shown that various manganese oxides and Mn(III)-ligand complexes are capable of rapidly oxidizing Tc(IV) to Tc(VII), even in the absence of oxygen, resulting in dissolution of Tc-99 and release to the aqueous phase. This thesis presents novel information on the redox interface chemistry of Tc-99, which is crucial to developing effective remediation methods.