Exceptional plutonium accumulation in glacier mice and cryoconite in Icelandic glaciers

This study comprehensively surveys artificial (¹³⁷Cs, ²⁴¹Am, ²³⁸Pu, ^239+240Pu) and natural (²¹⁰Pb) radionuclides in Icelandic glacier mice and cryoconite. Samples were collected from five glaciers in Iceland - Fjallsjökull, Falljökull, Kvíárjökull, Skaftafellsjökull, and Sólheimajökull - with glacier mice found only at the first three sites. Radionuclide concentrations in both glacier mice and cryoconite were slightly higher than those previously reported in Iceland. The maximum activity concentrations measured in glacier mice were: 407 ± 30 Bq kg^-1 for ¹³⁷Cs, 2690 ± 170 Bq kg^-1 for ²¹⁰Pb, 52.6 ± 2.2 Bq kg^-1 for ^239+240Pu, 1.23 ± 0.14 Bq kg^-1 for ²³⁸Pu, and 32.4 ± 6.2 Bq kg^-1 for ²⁴¹Am. In cryoconite, the maximum activity concentrations were 244 ± 16 Bq kg^-1 for ¹³⁷Cs, 3680 ± 175 Bq kg^-1 for ²¹⁰Pb, 37.7 ± 6.6 Bq kg^-1 for ^239+240Pu, 3.17 ± 0.35 Bq kg^-1 for ²³⁸Pu, and 18.6 ± 1.8 Bq kg^-1 for ²⁴¹Am. On average, glacier mice exhibited lower radionuclide activity concentrations compared to cryoconite. The highest mean activity concentrations measured in glacier mice were 109 Bq kg^-1 for ¹³⁷Cs, 893 Bq kg^-1 for ²¹⁰Pb, 20.1 Bq kg^-1 for ^239+240Pu, 0.41 Bq kg^-1 for ²³⁸Pu, and 8.8 Bq kg^-1 for ²⁴¹Am. In cryoconite, the corresponding highest mean activity concentrations were 141 Bq kg^-1 for ¹³⁷Cs, 1827 Bq kg^-1 for ²¹⁰Pb, 21.3 Bq kg^-1 for ^239+240Pu, 0.49 Bq kg^-1 for ²³⁸Pu, and 10.5 Bq kg^-1 for ²⁴¹Am. As evidenced by the ²³⁸Pu/^239+240Pu and ²⁴¹Am/^239+240Pu activity ratios the primary source of these isotopes is global fallout. Additionally, the ²⁴⁰Pu/²³⁹Pu atom ratio further indicates the dominance of global fallout. A notable finding of this study is the elevated levels of ^239+240Pu as compared to other Icelandic samples, although the origin of this phenomenon remains unclear. These results confirm that both cryoconite and glacier mice participate in the cycling of long-range transported pollutants within glacial and proglacial ecosystems in Iceland, albeit likely on a limited scale.