Additional studies on tissue distribution have shown that after 30 days ~ 50% of the body burden is assoctated with the eviscerated whole fish while the remainder is located in and/or on the gastrointestinal tract. Of the fraction in the carcass approximately two-thirds is associated with non-edible material (bone, etc.). Therefore, + 17% of the carcass burden (0.6%-0.1% of ingested dose for Pu-citrate and Pu-fulvate, respectively) resides in edible tissue and may be available for transfer to man from this source. samples were taken prior to sacrifice (heparinized syringes). Plasma proteins were separated by polyacrylamide gel-electrophoresis and the gels were sectioned for counting. Individual tissues were dissected for radioassay and a materials balance (fractional body burden determination) on injected plutonium was performed. Plutonium-237 distribution and translocation in channel catfish following intracardial injection are basically similar to patterns in mamma 1s weight (> 10,000). after intravenous administration. The fractionat body burdens in bone, liver and kidney 17 days after injection were 31%, 24%, and 9% of the injected dose, respectively. High kidney burdens relative to mamma] s_ ; are expected, since the kidney functions as the major site of hemopoeisis in teleosts. Blood clearance rates were similar to those found in smal] mammals (Fig. 2), with the plutonium being primarily associated with the plasma proteins. Approximately 70% of the plasma-associated plutonium Theoretically, soluble plutonium, bound to dissolved humic derivatives excess iron to the plasma samples released 42% of the protein bound From these results we conclude that chelation can either enhance or reduce uptake of plutonium in the channel catfish. Plutonium citrate penetrates the gut membrane due to a net negative charge of the complex (Cleveland, 1970). Reduced uptake of Pu-fulvate may be attributable to its stability in the presence of digestive systems and high molecular (yellow acids), may be hydrologically mobile. However, if such complexes are stable in biological systems (microflora, gastrointestinal tract), then hydrologic mobility will not necessarily enhance the availability of plutonium for entry into biological systems. An increased emphasis on the speciation of Pu which accidentally may be released to surface waters is needed to provide information on its aqueous behavior and to evaluate the availability of the various chemical and physical forms for biological intake. Intracardial Injection Study In a companion experiment, we administered plutonium-237 citrate to yearling channel catfish (mean weight 78 g) via intracardial injection (Eyman et al, 1976). Because plutonium is associated primarily with sediments in aquatic systems (distribution coefficient, Kg, approximately n x 10"), we had conducted experiments to determine the uptake of plutonium by sediment-feeding organisms. We had expected that the second component of elimination in gavage studies would have a very long biological half-life measured in years rather than days. In fact the third component of elimination did fulfill this expectation. We questioned whether the relatively short second elimination component represented tissue absorption from the gut and subsequent excretion from a highly labile pool, or rather the labeling of cells in the gut wal} and sloughing of cellular materials as part of the process of gut renewal. This next experiment was designed to answer the questions raised in our gavage studies and also to provide needed information on was bound to the iron-transport B-alobulin, transferrin. plutonium in 2 hr. Addition of Note also that concentrations of plutonium-237 (expressed as % dose/gram) were highest in kidney and liver. over the 17-day period was < 10%. . Excretion The absence of sianificant excretion indicates that a short half-life component of elimination following gut clearance in gavage studies is due to plutonium labeling of the gut. Microcosm Stud In another experiment, we spiked a year-old balanced aquatic microcosm including fish (Fig. 3) with 11 uCf of plutonium-237 nitrate (Trabalka and Eyman, in press). At 90 days post-spike, the microcosm components were intensively sampled. The microcosm contained 12 1 of water and 6 1 of sediments in a large, shallow plastic photographic tray (0.2 m° surface) kept in an environmental chamber. We felt a study of plutonium distribution in a microcosm represented the next logical step beyond single organism experiments. The microcosm appears to be a useful tool in ecological studies of highly toxic materials such as plutonium. Aquatic microcosms over a wide range of size and complexity have been used as model ecosystems to study the fate of radionuclides in aquatic ecosystems (Whittaker, 1961; Duke et al,, 1969; Wilhm, 1970; Cross et al, 1971; Cushing and Watson, 1973; TrabaTka, 1971; Short et, al, 1973). Bue to the limited availability of plutonium-237, it is not feasible to use the isotope in field studies. Thus, the microcosm experiment allows us to obtain some limited answers to questions which we would Pose in field studies. A most important question is whether there are mediating the tissue distribution of plutonium in an important aquatic food Factors at the system level which alter the potential availability to organisms in the system. Each fish was given an injection of 7.5 nCi ??’Pu citrate in a 0.85% saline solution (0.5% citrate). Animals were kept in 400-liter “living streams" at 25°C as in gavage studtes. Fish were whole body counted until sacrifice at 1, 2, 3, 10, and 17 days post-injection. Blood A distribution coefficient of 9 x 10° was observed for sediment. A materials balance at 90 days post-spike provided the following estimates: 0.001% in water, 0.04% in biota, and over 99.9% in sediments. Concentrations in whole animal including fish were surprising uniform (within a factor of 10, ranging from 1.2-9.9% of mean sediment concentration). organism of man. 496 497