Effect of pH and temperature on the sorption of Np and Pa to mixed anaerobic bacteria.

While considering the geological disposal of radioactive wastes, the behaviour of the radionuclide Np and its daughter element Pa was investigated in the presence of a mixture of anaerobic bacteria (MAB). Originally, MAB were used for the treatment of pulp and paper wastewater. The interaction between radionuclides and bacteria was evaluated by determining distribution coefficients (Kd) over 10 days and at 5 degrees C and 35 degrees C. Kd for Np at 35 degrees C after 5 days had a low value around 10(-2) After 10 days, however, Kd was > 100-fold higher. On the other hand, Kd at 5 degrees C was low (10(-2)) throughout, without any significant increase over time. The interaction between Pa and MAB was found to be stronger than that for Np, with Kd for Pa about 100 times higher. The Kd was controlled by some basic factors, the activity of MAB, the complexing capacity of MAB, and the chemical conditions in the solution such as pH and Eh.

Influence of nutritional factors on 239Np and 233Pa retention in weanling rats.

The estimated intestinal absorption after a single administration of 239Np-nitrate to fasted weanling rats (about 2% of the oral dose) was ten times higher than that of 233Pa administered as the chloride. Rats drinking tomato juice, apple juice or tea instead of water had a similar retention to the control group. However, when a small amount of tea was administered immediately before 239Np, the absorption and retention values were six times lower. When animals received only milk or glucose, the whole body retention of 239Np and 233Pa increased about 20 and 200-300 times, respectively, due mainly to a very high retention in the large intestine. When rats were fed milk plus rat chow, the whole body and gut retention of 233Pa was only two and three times higher, respectively; in the other organs less 233Pa was found than in control animals. This indicates that the extremely high retention of radionuclides in the gut contents of young rats fed only milk is temporary and disappears when solid food is available.

Biochemical binding and distribution of protactinium-233 in the rat.

Following intravenous injection into male Sprague-Dawley rats 233Pa, like other elements, deposits predominantly in the skeleton (ca. 70-80 per cent), but unlike Pu and Am the liver deposition of 233Pa is low, about 2-3 per cent between 1 and 7 days. About 99 per cent of the injected 233Pa is lost from the plasma compartment in 3 days, a clearance comparable to that of Pu but much slower than that of Np, Am or Cm. On entering the liver cell cytosol 233Pa is bound rapidly to an unidentified protein of molecular mass 200 kDa and to a protein of 80 kDa, which is probably transferrin. Within a few hours the metal migrates to bind to a protein of greater than 400 kDa which has been tentatively identified as ferritin. Some 233Pa remains bound to small ligands until virtually all the intracellular 233Pa has been deposited in the lysosomes, or to a lesser extent in some other, as yet, unidentified organelles.