Potential environmental risk of 223Ra-labelled hydroxyapatite nanoparticles

Introduction: Nanoparticles have been used in many technological and consumer products worldwide. One of the new attractive field is their use in radionuclide therapy. Radium-223 labelled hydroxyapatites seem to be prospective... [ view full abstract ]

Introduction: Nanoparticles have been used in many technological and consumer products worldwide. One of the new attractive field is their use in radionuclide therapy. Radium-223 labelled hydroxyapatites seem to be prospective carrier of Radium intended for the treatment of cancer after proper targeting. After medical use the applied nanoparticles are excreted by usual ways into the ecosystem. Thus they can attack water and soil and can enter into plants which are common source of animal and human food. The investigation of possible contamination of plants is therefore needed because the adverse effects of nanoparticles and radioactivity on human and animal health are reported.

Methods: The uptake and translocation of nanoparticles was tested using in vitro sterile cultivated plants Zea mays and Avena sativa at cultivation with tap water enriched with Ra-223 labelled hydroxyapatite nanoparticles (ca. 1 kBq, 0,3 mg) for three weeks. Then the uptake and translocation of the radioactivity was evaluated by electronic autoradiography and scintillation counting.

Results: Experiments with Zea mays plants showed the uptake of 36 % of applied radioactivity into plant tissues of which 88 % was localized in root and 12 % in shoot parts, respectively. In Avena sativa plants the total activity uptake was 53 %, of which 88 % was present in roots and 12 % in shoots.

Discussion: From the results it is clear that Radium is extracted into plant tissues. The simplest explanation is to consider the entry of nanoparticles through the pores of the root membrane. Then the extraction efficiency would be limited by the pore size (e.g. 6 nm in diameter at Zea mays). On the other hand, the penetration of even larger nanoparticles than the pore size is known from the literature, but the mechanism of the process is not clear yet. It is also possible that soluble Radium ions are formed and then translocated. Regardless of the mechanism, it can be concluded that the Radium and/or radioactive nanoparticles uptake by plants is possible. Therefore there is a real risk of ecosystem contamination and on the other hand, the technological possibility of removing radioactive contaminants using plant biotechnology.