Radioactive plutonium is released into the environment as a result of nuclear weapons tests, satellite failures and nuclear power plant accidents. Traces are relatively easy to find in sediments accumulating on glaciers. Research on plutonium traces was conducted in the northern and southern hemispheres by scientists from the Institute of Nuclear Physics of the Polish Academy of Sciences.
Radioactive elements are present in the environment as a result of natural processes and human activity. Artificial radionuclides, such as plutonium, are released into the environment mainly through nuclear tests, reactor accidents or failures of satellites and space probes containing radioactive sources of energy. These substances, transported mainly through the atmosphere, accumulate in different ecosystems, including glaciers, in the form of dark sediments called cryoconites.
A typical cryoconite hole is no more than a few dozen centimetres in diameter and depth. At its bottom, there is a dark sediment called cryoconite. It contains organic material and contaminants, i.e. radionuclides, heavy metals, pesticides, microplastics, or antibiotics. This sediment may pose a potential threat to local ecosystems. The analysed samples of cryoconite came from 49 glaciers of nine regions of the world, including the Arctic, the Alps, the Himalayas, and Antarctica. The material was collected by an international team of researchers over the years 2000-2020, and the project was financed by the Polish National Science Centre. The Institute of Nuclear Physics PAS issued in a press release on the research published in Science of the Total Environment.
The latest research conducted at the Institute of Nuclear Physics of the Polish Academy of Sciences with the use of novel methods of mass spectrometry allowed researchers to create a database for plutonium isotopes (238, 239, 240Pu) in the glaciers of the Northern and Southern Hemispheres.
The concentration of 239+240Pu activity turned out to be much higher in the Northern than the Southern Hemisphere, reflecting an uneven deposition of Pu from nuclear weapon tests between the hemispheres. As for the Northern Hemisphere, the highest concentrations are observed in Scandinavia and the Alps. No relevant differences have been noticed between the hemispheres in the case of 238Pu. The cryoconite from the Southern Hemisphere is characterized by high heterogeneity in terms of both Pu activity and mass ratio.
'These are the first analyses of plutonium concentration in cryoconite samples carried out on such a large scale', says Edyta Łokas, PhD, from the Institute of Nuclear Physics PAS, the initiator and first author of the papaer published in „Science of the Total Environment”.
According to the release, the isotope ratios of 238Pu/239+240Pu, so far unprecedented in the literature, have been for the first time observed in the cryoconite of the Exploradores Glacier in Patagonia. Researchers hypothesise that the excess of 238Pu may be related to the fall of the Soviet space probe MARS-96, which sank in the ocean off the coast of Chile in 1996. The space probe contained a generator with 238Pu, which may explain higher concentrations of this isotope on the nearby glacier.
The results of the study are the first observations of their kind showing anomalies in plutonium isotope ratios in the Southern Hemisphere. Additionally, the cryoconite samples from South American glaciers demonstrated 240Pu/239Pu mass ratios significantly deviating from those found in the literature, which may suggest that the dominant source of Pu is related to low-altitude nuclear tests conducted in the area of French Polynesia.
'The concentrations of plutonium activity in the cryoconite that we have observed are - especially in the Northern Hemisphere - orders of magnitude higher than in other environmental matrices used to monitor the environment, such as lichen, moss, soil, and sediments. Simultaneously, our discoveries emphasize the importance of cryoconite in the accumulation of radioactive contaminants that may pose a potential threat to the surrounding fauna and flora, and at the same time they may help us to track the diffusion of those pollutants', Łokas says.
Researchers from the Institute of Nuclear Physics PAS continue their work. Further investigations, conducted in collaboration with the AGH University in Kraków, took place at the ice cap of Jostedalsbreen in Norway. The expedition, organized in August 2024, was aimed at better understanding the processes and sources of contaminant accumulation in glaciers. (PAP))
Science in Poland, Ludwika Tomala
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