title: 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 99mTcO4- sorption in duckweed.
abstract: 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 accumulation/kinetic studies with 99mTcO4-. In these short-term studies, relatively small BCF-values may be encountered, with related interferences in its assessment due to the presence of 99mTcO4- in the surface film medium (SF) and in the cellular water free spaces (FS). The sample handling methods used to remove the SF + FS component of the accumulated 99mTcO4- consisted of blotting, centrifugation and rinsing. The three methods were investigated using D-[1-(14)C]mannitol, 42K+, 82Br- and 99mTcO4- radioisotopes, which were measured by beta- and gamma-spectrometry, in both solution and solid samples. Centrifugation seems the most promising method to remove SF + FS 99mTcO4-. Results based on both mass analysis and radioactivity determinations in centrifugated fluids are independent of applied concentrations (10(-11) to 10(-13) mol m(-3) 99mTcO4-), and are invariably compatible with the conceptual idea of the FS as a free-entrance phase for solutes. Blotting results in an overestimation of BCF values (up to factor 3 for the 99mTcO4- experiments performed), probably due to the incomplete removal of the SF + FS, and is suggested to yield irregular results, leading to high variances in BCF values obtained. The application of an efflux/rinsing period is indicated to result in an underestimation of BCF values (up to factor 10 for the 99mTcO4- experiments performed), probably due to excess removal of (non-SF + FS) components of accumulated solutes. Here we advocate centrifugation as a routine sample handling method to avoid SF + FS interferences in short-term (kinetic) 99mTcO4- uptake studies in duckweed. Moreover, the results suggest a more general applicability of centrifugation as a sample handling method to avoid SF + FS interferences in short-term element accumulation studies; centrifugation approaches should, however, be adjusted to plant cell characteristics.
authors.affiliation: Department of Radiochemistry, Delft University of Technology, Interfaculty Reactor Institute, The Netherlands. wolterbeek@iri.tudelft.nl
authors.forename: H T
authors.initials: HT
authors.lastname: Wolterbeek
authors.forename: A J
authors.initials: AJ
authors.lastname: van der Meer
authors.forename: U
authors.initials: U
authors.lastname: Dielemans
mesh_terms: D007700:Kinetics; D019684:Magnoliopsida / Q000737:chemistry*; D008962:Models, Theoretical; D019275:Radiopharmaceuticals / Q000493:pharmacokinetics*; D015203:Reproducibility of Results; D013670:Sodium Pertechnetate Tc 99m / Q000493:pharmacokinetics*; D014018:Tissue Distribution; D014874:Water Pollutants, Chemical / Q000493:pharmacokinetics*
chemical_list: D019275:Radiopharmaceuticals; D014874:Water Pollutants, Chemical; D013670:Sodium Pertechnetate Tc 99m