Assessing the chemical availability and environmental fate of fallout radionuclides in cryoconite

Glaciers are stores for contaminants, both local and further afield in origin, that are released into the environment through anthropogenic processes. Cryoconite, a heterogenous granular material commonly found on glacier surfaces, is now known to be an efficient accumulator of contaminants such as fallout radionuclides (FRNs) and potentially toxic elements, with multiple regional studies reporting notable concentrations of radioactivity in cryoconite that far exceeds that which is found in other environmental matrices. Indeed, concentrations of FRNs in cryoconite can be as much as three orders of magnitude higher than those found in nearby proglacial sediments. While we now understand that this ‘hyper-accumulation’ of FRNs is commonplace on glaciers around the world, our understanding of the extent to which release of contaminants stored in cryoconite poses an environmental downstream risk is in its infancy. To assess both the activity concentrations and chemical availability of FRNs within cryoconite, we conducted novel sequential chemical extractions twinned with gamma spectrometry for cryoconite samples from glaciers in Arctic Sweden and Iceland. Major and minor elemental composition of cryoconite was also analysed with Wavelength Dispersive X-ray Fluorescence (WD-XRF) spectrometry. The results of these experiments demonstrate that different cryoconite-bound FRNs undergo varying degrees of solubilization, with consequences for increased contaminant mobilization under higher melt scenarios. Our work identifies a clear requirement for further research in this field in order to improve understanding of downstream environmental risk from the secondary release of legacy contaminants under continued glacier retreat.