Radiosilver (llOmAg) was administered to mice, rats, monkeys, and dogs by oral and intravenous routes and also intraperitoneally to mice and rats. Retention as a function of time was determined by periodic assay in 4~ liquid scintillation detectors. The data were adequately described by exponential expressions. Ninety per cent or more of oral doses were not absorbed. In all routes of administration more than 90% of the silver excreted was in the feces. A parabolic relation between body weights and estimated equilibrium levels in small animals was extrapolated to man. From such estimates an MPC, value of 1.8 nCi/cm3 (when the whole body is the critical organ) was derived. The ICRP value of 0.3 nCi/cm3 for the lower large intestine is still the limiting value.

Radiomanganese ("Mn) was administered to mice and rats by the oral, intravenous and intraperitoneal routes and to dogs and monkeys by the oral and intravenous routes. Whole-body-counting techniques, utilizing 47r liquid scintillation counters, were used to determine whole-body-retention parameters. Retention functions consisting of the sum of three or four exponential expressions were adequate descriptions of retention until the body burden was less than 1 per cent of the administered dose. The longest effective half-times after intravenous injections were 119, 146, 99 and 68 days for mice, rats, monkeys and dogs, respectively. Tissue distribution studies in rats showed that, for most tissues, concentration as a function of time roughly paralleled whole-body retention. Both bone and brain were found to have a slower rate of loss than other tissues. Using a parabolic relation between body weights and the integrals of the retention functions, it was estimated that 6 x lO-3pc/ml was the maximum permissible concentration in water when the total body is the critical organ. This value is in good agreement with the current ICRP value of 8 x However, the value calculated for the lower large intestine (1 x lop3 pc/ml) must remain the MPC, for 54M~1.

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Whole-body retention of lo6RuC13 as a function of time was measured in mice, rats, monkeys, and dogs. Retention after oral dosage and after parenteral injection was measured in the four species. About 4% of an oral dose is absorbed in the gastrointestinal tract, and about 20% of a parenteral dose is lost with an effective halftime of about 200 days. The highest concentrations were found in the kidney, while bone maintained about 6% of the body burden over a period of 8 months. Such values are compared with values in the literature. Estimates of the maximum permissible concentration in water were greater for the target organs examined than the limiting value of pCi/cm3 set by the ICRP for the lower large intestine.INTEREST shown by health physicists in the metabolism of ruthenium is largely due to the significant fraction of fission product activity attributed to ruthenium isotopes'l) and to the appearance of such isotopes in the biosphere.(2) Several papers dealing with ruthenium metabolism have appeared during the past 20 ~r , (~-l~) and the questions raised in the papers are about as numerous as the answers supplied. Gastrointestinal absorption has been reported as being less than 0.05%(14) and as much as 13 %.(3) Various values have been reported for the halftimes for tissues. For example, THOMPSON et al.(13) reported a biological halftime of 250 days in the skeleton of rats after cessation of chronic feeding and also a biological halftime of 340 days for the skeleton after a single intraperitoneal injection. DURBIN et a1.(l6) reported a biological halftime of 11 days for rats. These papers deal with guinea pigs,(*) chickens,(g) rabbit~(3.1~) and r a t~. (~J~-l~) The chemical formadministered,(3-13J7) pH,(6J3) solvent,(l7) specific activity,(6,13) nutritional state (fasted or fed)(11) and route of administration(5,',13) have all been implicated as factors which modify ruthenium metabolism. Tissue distribution may be reported in one or more of * This work was performed under the auspices of the USAEC. the following units: % of injected dose per organ(4-6J3J') or % of absorbed dose per g tissue,(3~13) % of injected dose per g ~~s s u~(~B~*~*~ and as relative specific activity [(activity in organ/organ weight)/(activity injected/body weight)] .(4) Interspecific comparisons made at this Laboratory as part of a series of such comparisons(18-21) may be useful in evaluating radiation protection guides. METHODSThe experimental plan is given in Table 1. Female R F mice, male Sprague-Dawley rats, male Macaca mulatta monkeys, and male beagle hounds were all given oral doses of radioruthenium, the rats and mice by stomach intubation under light ether anesthesia, the monkeys by means of a contaminated sugar cube and the dogs by a gelatin capsule thrust into the esophagus. All oral doses were preceded by an 18-hr fast. Mice and rats received intraperitoneal doses by injection into the lower left abdominal quadrant. Dogs and monkeys were given an intravenous injection into the cephalic or saphenous veins, respectively. A gro...

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