Ionising radiation is an integral part of our environment. Naturally occurring radioactive isotopes, such as lead-210, actinium-229, bismuth-214 or potassium-40 (as well as cosmic radiation), are mainly responsible for its presence on the surface of our planet. Intensive nuclear weapons testing in the mid-20th century and the Chernobyl disaster introduced a whole range of new radioactive isotopes into the atmosphere. For scientists, this is an opportunity to trace the transport and accumulation processes of radioactive contaminants in the Earth's ecosystem, the researchers remind in the Institute of Nuclear Physics PAS press release.

In a paper published in Science of the Total Environment (https://doi.org/10.1016/j.scitotenv.2021.152656), physicists from the Institute of Nuclear Physics PAS in Kraków describe the discovery of unexpectedly high concentrations of artificial radionuclides in samples collected from depressions in the surface of a Norwegian glacier.

'This is the first study of cryoconite from a Norwegian glacier that looks at natural and artificial radioisotopes. We focused on the Blaisen Glacier, located less than 200 kilometres west of Oslo', says Dr. Edyta Łokas (Institute of Nuclear Physics PAS), the first author of the paper, quoted in the release.

Researchers remind that glacier surface is not uniformly white. In some places, it is black, which is caused by cryoconite holes. 'The process of formation of such a hole begins in summer when impurities such as particles of rock matter are carried onto the bright surface of the glacier by wind, water and animals. Due to their colour being darker than their surroundings, these particles heat up more than ice. As a result, a water-filled depression appears around them, which only increases the efficiency of capturing the particles moving around in their vicinity', the scientists describe.

A typical cryoconite hole is no more than a few dozen centimetres in diameter and depth. Its bottom is lined with a dark sediment called cryoconite. In addition to natural mineral substances, it can contain such contaminants as heavy metals, pesticides, antibiotics or micro-plastics. A significant part of the cryoconite mass is biological matter - bacteria, including cyanobacteria, protozoa, rotifers and tardigrades. Previous research shows that this microbiome effectively captures radionuclides from its environment.

'The analysed samples came from twelve holes. We collected the material just before a heavy rain. When it stopped, we also took a sample from each remaining hole to check whether the flow of water can change the amount of artificial radionuclides in cryoconite', says Dr. Krzysztof Zawierucha of the Adam Mickiewicz University in Poznan.

According to the press release, the presence of artificial radionuclides in the Blaisen Glacier is related to the radioactive contamination from Chernobyl and Novaya Zemlya, the main nuclear weapons testing ground in the Soviet era. In Scandinavia, rainfall is a particularly favourable factor for the accumulation of atmospheric pollutants, effectively transporting radionuclides from the atmosphere to the surface.

According to the researchers, the Blaisen Glacier cryoconite samples had very high concentrations of artificial isotopes, in particular caesium-137 (clearly linked to the Chernobyl disaster), americium-241, bismuth-207, plutonium-239 and plutonium-240. 'However, these concentrations did not change in the material taken after the intense rainfall. This fact contradicts the intuitively plausible hypothesis of possible leaching of radionuclides from cryoconite by rainwater', we read in the release.

The scientists were intrigued by the fact that compared to cryoconite from other Scandinavian or Arctic glaciers, the share of organic matter in the samples was significantly higher, at a level of 40%. 'The correlation between the increased radioactivity of cryoconite and the higher amount of organic matter within it is probably not a coincidence. According to the researchers, lemming populations that live near the glaciers may play a role here. These small mammals eat plant food, accumulating radioactive contaminants in their organisms. Many lemmings end their lives on glaciers, where their bodies decompose and release the pollutants that eventually end up in the cryoconite', the researchers explain in the release.

'The concentrations of artificial radionuclides in Norwegian cryoconite are among the highest found in the northern hemisphere. Higher levels have only been observed in some glaciers in Austria. In fact, the cryoconite of the studied Norwegian glacier is several times more radioactive than the cryoconite of the Svalbard glaciers', notes Dr. Łokas, whose research was funded by the Polish National Science Centre.

The researchers emphasize that radiation emitted by Norwegian cryoconite does not pose a direct threat to humans or animals on the glacier.

'Although currently stable and acceptable, the situation regarding the presence of artificial radionuclides in Norwegian glaciers may worsen in the near future. Due to climate warming, the rate at which glaciers melt is increasing. This process is beginning to be noticed especially in the southernmost areas, which in the case of Scandinavia are more densely populated. As the ice melts, the radioactive contaminants it contains fall to the exposed ground, from where they can then be transported together with flowing water. It can therefore be expected that in the near future local bodies of water will start to accumulate radionuclides from a large area in their vicinity, from whence they will find their way into the bodies of fish and animals, and eventually end up on our plates. At this stage of research, however, it is difficult to assess the potential scale of such a phenomenon and the associated risks', we read in the Institute of Nuclear Physics PAS press release.

PAP - Science in Poland

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