Technetium-99 determination in low-volume samples from the global environment with accelerator mass spectrometry

Le résumé fourni par la source

The long-lived fission product technetium-99 ( 99 Tc, t 1/2 = (2.111± 0.012) × 10 5 years) was successfully detected in small-volume (10 L, and 1 g, respectively) environmental samples such as Pacific Ocean and river water, Antarctic snow, and peat.Its presence in the environment is almost exclusively of anthropogenic origin and the determined levels are attributed to nuclear weapons testing in the 1950s and 60s as no local contamination source is known to be present at these sampling sites.A unique capability for Accelerator Mass Spectrometry (AMS) measurements of environmental 99 Tc at unprecedented sensitivity was established, first using the Gas-filled Analysing Magnet System (GAMS, Germany) and after its shutdown, at the Heavy Ion Accelerator Facility (HIAF, Australia).New chemical extraction and measurement techniques, including improved non-isotopic normalisation, enabled detection limits as low as 0.6 femtograms (fg) per sample for Antarctic snow, and enhancement of precision from 30% (GAMS) to 16% (HIAF).The rather high concentrations of about 280 fg ( 99 Tc) per g (dry mass) measured in peat indicate Tc accumulation in this archive, which opens the possibility of studying its migration behaviour even under reducing conditions.Furthermore, it allowed deduction of an improved estimate of the global 99 Tc inventory to (120-190) TBq.The first direct detection of 99 Tc at 8 fg L -1 in river water highlights the need for further studies in urban areas to evaluate potential contributions from nuclear medicine.The achieved sensitivity allows monitoring of on-going releases, improving the risk assessment of releases from nuclear waste repositories and tracer applications in environmental sciences. Environmental signicanceData on the environmental distribution of Technetium-99 ( 99 Tc), a key radionuclide for nuclear waste management and a potential emerging contaminant from nuclear medicine, remains limited.By optimizing accelerator mass spectrometry procedures, this research established the global fallout baseline in environmental reservoirs that are not affected by direct releases and identied a 99 Tc accumulation in peatlands.The reduced sample size required for this analytical approach, supports high-resolution monitoring of environmental 99 Tc concentrations, essential for evaluating long-term environmental risks from nuclear medicine emissions or post-Fukushima contamination.Such studies will target surpluses above the established global fallout baseline and elucidate the migration behaviour of 99 Tc.

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