Chemical speciation and bioavailability of elements in the environment and their relevance to radioecology.

The commonly used terms 'chemical speciation' and 'bioavailability' are discussed and an attempt made to produce both qualitative and quantitative descriptions of their influence on the transfer of elements in the environment. The importance of considering the presence of the many different species of radionuclides which may occur in the environment is emphasized. The limitations of using concentration ratios, which take no account of the differing bioavailability of various chemical species of radionuclides, are discussed.

The uptake of TcO-4 by plants: a mathematical description.

A model describing the uptake of TcO-4 by spinach plants was developed. The equation relates both plant and soil parameters (e.g., growth, metabolism, concentration of TcO-4 and composition of the growth medium) to the concentration of Tc in the shoot of the plant. As the soil solution is the medium from which plants obtain nutrients and non-nutrients, the modeling parameters have been obtained from uptake experiments using nutrient solutions (= simulated soil solutions) as the growth medium. Two important model assumptions are: 1) that an equilibrium exists between TcO-4 in the plant and the growth medium and 2) that the leaf TcO-4 metabolism is a pseudofirst order reaction occurring in a non-constant volume.

Evaluation of a new blood autotransfusion device.

A new autotransfusion device was evaluated in dogs. The device uses citrate phosphate dextrose as the blood anticoagulant and automatically delivers the agent in a ratio approximating that found in banked blood. Bleeding, aspiration, and autotransfusion of approximately 3 estimated blood volumes produced small changes in hematologic and coagulation studies. Blood electrolytes stayed within normal ranges. Activated clotting times stayed within normal range after autotransfusion of 2 blood volumes but increased slightly after 3 blood volume transfusions. No significant histopathologic changes were found in any organ system. Rapid infusion of citrated blood causes myocardial depression, which can be reversed by giving calcium. Overall performance of the device was excellent, suggesting further documentation in a clinical setting and evaluation with human blood.

Light Dependent Reduction of Pertechnetate (TcO(4)) by Broken Chloroplasts.

Arguments are given for a ferredoxin-mediated reduction of TcO(4) (-), preponderantly into extractable Tc(V) complexes, by illuminated, broken chloroplasts. Photosynthetic O(2)- and NADP-reduction competitively inhibit Tc incorporation. As for O(2), the reaction can be stimulated by the auto-oxidizable electron acceptor methyl viologen. Furthermore TcO(4) (-) can function as terminal acceptor in the diaphorase reaction, with NADPH as electron donor.

On the inhibitory action of cadmium on the donor side of photosystem II in isolated chloroplasts.

The inhibitory effect of the Cd2+ in the electron transport of the isolated chloroplasts has been observed by measuring the oxygen uptake from the solution and the fluorescence induction. Cd2+ is found to be an inhibitor on the donor side of Photosystem II and its action site, as determined by experiments using hydroxylamine and exogenous Mn, is supposed to be on the water-splitting enzyme itself. Moreover, physicochemical and physiological studies indicate that only the ionic form of Cd is acting at the level of the manganoprotein. It is not possible, from this work, to define precisely in which form Cd is taken up through the thylakoid membranes.