Transport of plutonium in surface and sub-surface waters from the Arctic shelf to the North Pole via the Lomonosov Ridge

Co-transport behavior of Am(III) and natural colloids in the vadose zone sediments

Americium (III) (Am(III)) in the natural environment is considered immobile due to its low solubility, strong adsorption, and high affinity to solid surfaces. However, the presence of natural colloids may carry Am(III) transport for long distance. The individual and co-transport behaviors of Am(III) and natural colloids through the unsaturated packed columns were investigated under the influence of pH, electrolyte concentration, velocity, Am(III) concentration and natural colloids concentration. Under all experimental conditions, Am(III) individual transport construct sight breakthrough curves (BTCs, CAm/C0 < 3%), but the presence of natural colloids increased the BTCs plateau of Am(III) significantly (30% < CAm/C0 < 80%), indicating that the colloids were able to promote Am(III) transport in the unsaturated porous media. DLVO theoretical calculations reveal that the increased pH and decreased electrolyte concentration lead to a rase in electrostatic repulsion, and the natural colloids tend to be dispersed and stabilized, which facilitates elution. In addition to this, the increase of velocity and colloids concentration will lead to greater breakthrough of natural colloids. The non-equilibrium two-site model and the two-site kinetic retention model well-described the BTCs of Am(III) and natural colloids, respectively. This study provide new insights into the behavior of natural colloids carrying the Am(III) into aquifers through the vadose zone sediments.

Sources, fate and distribution of inorganic contaminants in the Svalbard area, representative of a typical Arctic critical environment-a review

Global environmental changes not only contribute to the modification of global pollution transport pathways but can also alter contaminant fate within the Arctic. Recent reports underline the importance of secondary sources of pollution, e.g. melting glaciers, thawing permafrost or increased riverine run-off. This article reviews reports on the European Arctic-we concentrate on the Svalbard region-and environmental contamination by inorganic pollutants (heavy metals and artificial radionuclides), including their transport pathways, their fate in the Arctic environment and the concentrations of individual elements in the ecosystem. This review presents in detail the secondary contaminant sources and tries to identify knowledge gaps, as well as indicate needs for further research. Concentrations of heavy metals and radionuclides in Svalbard have been studied, in various environmental elements since the beginning of the twentieth century. In the last 5 years, the highest concentrations of Cd (13 mg kg^-1) and As (28 mg kg^-1) were recorded for organic-rich soils, while levels of Pb (99 mg kg^-1), Hg (1 mg kg^-1), Zn (496 mg kg^-1) and Cu (688 mg kg^-1) were recorded for marine sediments. Increased heavy metal concentrations were also recorded in some flora and fauna species. For radionuclides in the last 5 years, the highest concentrations of ¹³⁷Cs (4500 Bq kg^-1), ²³⁸Pu (2 Bq kg^-1) and ^{239 + 240}Pu (43 Bq kg^-1) were recorded for cryoconites, and the highest concentration of ²⁴¹Am (570 Bq kg^-1) was recorded in surface sediments. However, no contamination of flora and fauna with radionuclides was observed.

Scavenged 239Pu, 240Pu, and 241Am from snowfalls in the atmosphere settling on Mt. Zugspitze in 2014, 2015 and 2016

Concentrations of ²³⁹Pu, ²⁴⁰Pu, and ²⁴¹Am, and atomic ratio of ²⁴⁰Pu/²³⁹Pu in freshly fallen snow on Mt. Zugspitze collected in 2014, 2015 and 2016 were determined by accelerator mass spectrometry (AMS). For the sub-femtogram (10⁻¹⁵ g) - level of Pu and Am analysis, a chemical separation procedure combined with AMS was improved and an excellent overall efficiency of about 10⁻⁴ was achieved. The concentration of ²³⁹Pu ranges from 75 ± 13 ag/kg to 2823 ± 84 ag/kg, of ²⁴⁰Pu from 20.6 ± 5.2 to 601 ± 21 ag/kg, and of ²⁴¹Am was found in the range of 16.7 ± 5.0–218.8 ± 8.9 ag/kg. Atomic ratios of ²⁴⁰Pu/²³⁹Pu for most samples are comparable to the fallout in middle Europe. One exceptional sample shows a higher Pu concentration. High airborne dust concentration, wind directions, high Cs concentrations and the activity ratio of ^239+240Pu/¹³⁷Cs lead to the conclusion that the sample was influenced by Pu in Saharan dust transported to Mt. Zugspitze.

Colloid-associated plutonium transport in the vadose zone sediments at Lop Nor

A framework to describe the characteristics of pore water in unsaturated media was established in order to study transport of colloid-associated (239)Pu (i.e., colloidal Pu) through the vadose sediments. Effluent concentrations and recoveries of Pu were found to decrease with increasing ionic strength. However, they would remain approximately constant at a critical value of 0.0289 M (Na(+)) though ionic strengths were further increased. Fast deposition rate coefficient (k(fast)) was thus experimentally determined. To our knowledge, this relationship between the mobility of colloidal Pu and the critical ionic strength was the first time observed. On the other hand, significant detachment of colloidal Pu once retained in the sediments was not observed during the subsequent chemical and physical perturbations. But slow release and transport could persist as long as flow continued. The threshold infiltration intensity (0.166 cm/min) revealed a nonmonotonic dependence of the cumulative amount of detached colloidal Pu on the intensity.