Distribution and retention of hexavalent 233U in the beagle

The distribution, retention, and excretion of 233U was measured in seven beagles injected intravenously with 233U(VI) in citrate buffer and sacrificed from one day to 726 days post injection (P.I.). The concentration of uranium in plasma decreased rapidly. The uranium in the blood at 10 min P.I. was present either as a protein (transferrin-albumin) or a carbonate/bicarbonate complex. Up to 60% of the uranium injected was excreted during the first day, most of it in the urine. Except for the kidney, only a very small fraction of the injected U was retained in soft tissues. At 1-day P.I., about 8% of the U was found in the skeleton and this amount decreased with a biological halflife of 883 days. Initially, U was deposited nonuniformly on bone surfaces with areas of intense hot spots adjacent to other areas with intermediate and low concentrations. Of the injected U, 20% was found in the kidneys at 1-day P.I., with high concentrations localized in the proximal tubules