Chemical availability of fallout radionuclides in cryoconite

Abstract

Atmospheric deposition on glaciers is a major source of legacy fallout radionuclides (FRNs) accumulating in cryoconite, a dark granular material with surface properties that efficiently bind FRN contaminants (specifically ¹³⁷Cs; ²¹⁰Pb; ²⁴¹Am). Cryoconite-bound FRNs in glaciers can be released when they interact with and are transported by glacial meltwater, resulting in the discharge of amassed particulate contaminants into aquatic and terrestrial environments downstream. The environmental consequences of FRN release from the cryosphere are poorly understood, including impacts of cryoconite-sourced FRNs for alpine food chains. Consequently, there is limited understanding of potential health risks to humans and animals associated with the consumption of radiologically-contaminated meltwater. To assess the chemical availability of cryoconite-adsorbed FRNs we used a three-stage sequential chemical extraction method, applied to cryoconite samples from glaciers in Sweden and Iceland, with original FRN activity concentrations up to 3300 Bq kg^-1 for ¹³⁷Cs, 10,950 Bq kg^-1 for unsupported ²¹⁰Pb (²¹⁰Pb_un) and 24.1 Bq kg^-1 for ²⁴¹Am, and orders of magnitude above regional backgrounds. Our results demonstrate that FRNs attached to cryoconite are solubilized to different degrees, resulting in a stage-wise release of ²¹⁰Pb_un involving significant stepwise solubilization, while ¹³⁷Cs and ²⁴¹Am tend to be retained more in the particulate phase. This work provides an insight into the vulnerability of pristine glacial environments to the mobilization of FRN-contaminated particles released during glacier melting, and their potential impact on glacial-dependent ecology.

Keywords: Chemical availability; Contaminant mobility; Cryoconite; Fallout radionuclides; Glaciers; Sequential extractions.