On the variability of plant bio-concentration factors BCF/ of environmental radionuclides: a case study on the effects of surface film and free space on the interpretation of 99mTcOy sorption in duckweed

The present paper addresses plant bioaccumulation factor BCF. variability, and specifically focuses attention upon the handling of duckweed Lemna gibba. material, sampled from experimental media, especially considering accumulationrkinetic studies with 99mTcO4y. In these short-term studies, relatively small BCF-values may be encountered, with related interferences in its assessment due to the presence of 99mTcO4y in the surface film medium SF. and in the cellular water free spaces FS.. The sample handling methods used to remove the SFqFS component of the accumulated 99mTcO4y consisted of blotting, centrifugation and rinsing. The three methods were investigated using D-w1-14Cxmannitol, 42Kq, 82Bry and 99mTcO4y radioisotopes, which were measured by b- and g-spectrometry, in both solution and solid samples. Centrifugation seems the most promising method to remove SFqFS 99mTcO4y. Results based on both mass analysis and radioactivity determinations in centrifugated fluids are independent of applied concentrations 10y11 to 10y3 mol my3 99mTcO4y., and are invariably compatible with the conceptual idea of the FS as a free-entrance phase for solutes. Blotting results in an o¨erestimation of BCF values up to factor 3 for the 99mTcOy experiments performed., probably due to the incomplete removal of the SFqFS, and is suggested to yield 4 irregular results, leading to high variances in BCF values obtained. The application of an effluxrrinsing period is indicated to result in an underestimation of BCF values up to factor 10 for the 99mTcO4y experiments performed., probably due to excess removal of non-SFqFS. components of accumulated solutes. Here we advocate centrifuga-tion as a routine sample handling method to avoid SFqFS interferences in short-term kinetic. 99mTcO4y uptake studies in duckweed. Moreover, the results suggest a more general applicability of centrifugation as a sample handling method to avoid SFqFS interferences in short-term element accumulation studies; centrifugation approaches should, however, be adjusted to plant cell characteristics