Abstract
Tritium of artificial origin was initially introduced to the environment from the global atmospheric fallout after nuclear weapons tests. Its level was increased in rainwaters by a factor 1000 during peak emissions in 1963 within the whole northern hemisphere. Here we demonstrate that tritium from global atmospheric fallout stored in sedimentary reservoir for decades as organically bound forms in recalcitrant organic matter while tritium released by nuclear industries in rivers escape from such storages. Additionally, we highlight that organically bound tritium concentrations in riverine sediments culminate several years after peaking emission in the atmosphere due to the transit time of organic matter from soils to river systems. These results were acquired by measuring both free and bound forms of tritium in a 70 year old sedimentary archive cored in the Loire river basin (France). Such tritium storages, assumed to be formed at the global scale, as well as the decadal time lag of tritium contamination levels between atmosphere and river systems have never been demonstrated until now. Our results bring new lights on tritium persistence and dynamics within the environment and demonstrate that sedimentary reservoir constitute both tritium sinks and potential delayed sources of mobile and bioavailable tritium for freshwaters and living organisms decades after atmospheric contamination.
Highlights
What we currently Know on Environmental Behavior of Tritium and what we Looked for Tritium is a rare isotope of hydrogen and its only radioactive form
Www.nature.com/scientificreports and river sediments collected far from the influence of releases from nuclear facilities[5,9]. Among other hypotheses such as isotopic fractionation or hypothesis dealing with tritium bioaccumulation[10], current consensual explanation for OBT/HTO disequilibrium is that tritium integrated into the organic matter (OM) would persist for the long term while the free forms rapidly exchange with the surrounding environment[1]
In the southern part of the coastal region of Fukushima prefecture (Japan), HTO concentrations measured in wells near the damaged Fukushima-Daiichi nuclear power plant (FDNPP) and in rainwater were significantly increased during several weeks after the accident[19,20,21,22] and huge volumes of tritiated water produced by the damaged FDNPP are still stored in containers close to the power plant
Summary
Acquired from our Work A well preserved 70 year old riverine sedimentary archive. Riverine sediment archives are generally viewed as a recording of past mineral and organic sedimentary fluxes and associated contaminants. Such preservation of aquatic POM could be promoted by factors either facilitating the preservation (e.g. increase of aquatic primary productivity, physical protection of labile OM by mineral matrices) or limiting its mineralization by in situ OM processes These pioneering results highlight that while tritium from atmospheric emission store in river sediments as bound forms to organic compounds originating from soils erosion in the catchment, tritium from nuclear releases in the river would escape from such storages in most cases. OBT contents in such surface sediments acquired in the upstream Loire River ranged from 8.4 ± 1.8 to 31.6 ± 2.8 Bq/L at the end of the nineties[5] (Fig. 4) Those measured within the sedimentary archive over the same time period when corrected from radioactive decay are in the lower range of those last values, i.e. 10.6 ± 1.4 Bq/L. While these mechanisms were previously hypothesized, they were never demonstrated before
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