Polonium is a rare and highly radioactive metallic element belonging to the chalcogen group. Chemically, it resembles tellurium and bismuth, forming compounds such as oxides and halides. Physically, it is volatile, unstable and extremely radiotoxic (even microscopic amounts can be lethal if ingested or inhaled), as it causes severe internal tissue damage, with isotopes emitting intense alpha radiation.
It is, moreover, a naturally occurring element originating from the decay chain of lead, and can therefore be widely present in food and feed. It may also be selectively accumulated by certain aquatic species, such as filtering mussels [1]. For these reasons, it must be carefully monitored throughout the entire agri-food chain. However, due to its nature as an alpha emitter, it must first be first isolated from the sample matrix—particularly from proteins to which it shows affinity [2] —and concentrated in sufficient amounts to allow its determination by alpha spectrometry or liquid scintillation counting.
The aim of the present work is to verify whether the TK221 resin (diglycolamide–phosphine oxide) is suitable for separating polonium from chemical interferents (lead and bismuth) and radiometric interferents (uranium and thorium) that are naturally present in agri-food matrices.
To this end, a series of centrifuge tubes were prepared, each containing approximately 2 mL (V) of HNO₃ or HCl solutions at different molarities, with four tubes prepared for each concentration. A known amount of Po-209 (A0) and about 25 mg of TK221 resin (w) were added to each tube. In one set of tubes, H₂O₂ was added to ensure that polonium was in the +IV oxidation state, while ascorbic acid was used to maintain the +II oxidation state. After gently agitating all tubes for approximately two hours, they were centrifuged to separate the resin from the acid solution. An aliquot of the supernatant was then analyzed by liquid scintillation counting to determine the counts per minute (CPM) of polonium remaining in solution (A). In this way, the retention coefficient (k’) of polonium on the resin was determined according to the formula [3]:
k^'=(A_0-A)/A×V/w×0,56
The results of these experiments are summarized in the graph shown in Figure 1. The main differences between the behavior of polonium (II) and polonium (IV) in chloric or nitric media are evident only at low molarities (below 1 M), while at higher molarities the difference in retention becomes minimal. The behavior observed in the chloric medium appears more suitable for loading potential liquid samples onto the resin, as the k’ value is significantly higher compared to the nitric medium. However, elution from the resin bed can be more easily achieved by exploiting the behavior in the nitric medium, which—at concentrations below 0.1 M—releases the analyte completely in an environment that is easily miscible with an organic-based scintillation cocktail. The results presented above are of primary importance in the development of a method capable of simultaneously determining all the alpha-emitting radionuclides in waters and agri-food matrices [4].
Trotta G., Bortone N., et al., Radiocontamination level of mussels (M. Galloprovincialis) collected in italy from apulian coasts and assessed dose to population, Regional Studies in Marine Science 74 (2024) 103560, https://doi.org/10.1016/j.rsma.2024.103560
Jia G., Torri G., Magro L., The fate of the main naturally occurring radionuclides in mussels (Mytilus edulis) and their radiological impact on human beings, Environ. Monit. Assess. 192(4), 217 (2020). doi: 10.1007/s10661-020-8137-1.
Papp I., Vajda N., Happel S., An improved rapid method for the determination of actinides in water Journal of Radioanalytical and Nuclear Chemistry (2022), 331:3835–3846 https://doi.org/10.1007/s10967-022-08389-9
Maxwell S., Culligan B.K. et al., Rapid determination of 210Po in water samples, (2013), J Radioanal Nucl Chem DOI 10.1007/s10967-013-2644-2