Technetium and rhenium: can they be taken up as counter ions in plants?

Technetium (Tc) is a non-essential element for which accumulation mechanisms in plants have recently been discussed. From the viewpoint of long-term dose assessment the element is of great interest because one of its isotopes, technetium-99 has a long half-life of 2.11E+05 y and it is produced by thermal neutron fissions of uranium-235 and plutonium-239. The most stable chemical form of Tc in the surface environment is pertechnetate, which has a high geochemical mobility and availability for plants. The possible Tc accumulation processes are uptake with water mass flow (passive uptake) or active nutrient uptake by plants. A variety of transport proteins involved in anion uptake by plants might be involved in pertechnetate uptake. However, in addition, we hypothesized that Tc is absorbed as a counter ion in plants.We studied uptake of Tc and Re (a chemical analogue of Tc) in three kinds of plants by growing them in a nutrient solution. After three days, relative concentrations of Tc, K, Mg, Cl, and Re had excess ion fluxes, but other elements did not. High correlations of R>0.8 (p