Behavior of Plutonium in Animals and Man (Plutonium Information Meeting January 4 and 5, 1974)

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PLUTONIUM INFORMATION MEETING +J for an Ad Hoc Subcommittee of the Advisory Committee on Reactor Safeguards Cos Alamos, New Mexico Behavior of Plutonium in Animals and Man Published December 1974 by Technical Information Center, Office of Information Services UNITED STATES ATOMIC ENERGY COMMISSION

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Behavior of Plutonium in Animals and Man By Patricia Durbin University of California Lawrence Berkeley Laboratory Most of this material is not m y own work but that of many people, and if I miss giving the credits at the times they are required, I hope you will excuse me. biological systems, their behaviors are sufficiently like Pu(lV) that small diiferences are obscured by the ordinary variability of biological systems. For the most part we will be discussing Pu(IV), at least PLUTONIUM CHEMISTRY AND I hope you all remember what we heard this morning about plutonium chemistry. but, in case you d o not, what follows is a brief review of the chemical properties of plutonium that are important t o biology. These are the valence state. hydrolysis, insolubility of compounds, and formation of complexes. This morning you heard about thP multiplicity of plutonium valence states. The Pu(lll), Pu(IV), and Pu(V1) states are important biologically. In biological experiments the quantities of plutonium involvcd a r t usually so small and tlie solutions are so dilute encc of more than one valence state) docs occur, the tcndcricy to disproportionate is not so great as i t is in more Plutonium(lV) has been studied most in biology because i t is t I ~ emost stable under [lie kinds of conditions one encounters in biological systems. As long ago as the early valr.ncr states behaved quite similarly after administration to rats. They concluded tlut I’u(lli) and Pu(VI) were not stabls in biological systems with respect to Pu(IV) and that. reprdless of the foriii administered. most of the plutonium tlik rnoriiing, that ni ~ yn o t be a correct interpretlltion, but it niay also be that. even i f Pu(I1I) and Pu(V1) are stable in as a starting material. Unless otherwise specified, “plutoMost plutonium compounds (like the compounds of other multivalent cations, such as the rare earths, the trivalent actinides, and iron) are sparingly soluble except in acid solution. Pluronium dioxide is one of the most insoluble of known compounds. Highly positively charged ions of small size, such as Pu(IV), compete with hydrogen ions for hydroxyl ions in water in the reactions that were discussed this morning. For comparison. tlie first hydrolysis constant of Pu(IV) is I .6: tendency of Pu(IV) to hydrolyze is about like that of iron and is considerably greater than that of Pu(ll1) or cerium. In neutral or slightly alkaline solutions, Pu(IV) ions d o not exist, and, in a solution of pll 8, uncomplexed plutonium is present only as the hydroxide. In dilute solutions the hydroxide exists as a colloid; in more concentrated solutions, as a polymer or a visible precipitate. Iliglily charged ions of small size also form stable polycarboxylic acids, EDTA and DTPA. These agents also form stable contpleses with the rare earths, the trivalent actinides, and iron. The multivalent cations also form complexes of variable stability with proteins in blood, liver, Although all o f the biological data have been obtained using pure plutonium coiiipounds and nearly pure pluto-

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31BEHAVIOR OF PLUTONIUM IN ANIMALS AND MAN niuni isotopes, we must be aware that in modern reactor and fuel-processing technology the plutonium is not likely t o be pure. eitlrcr c.hr.rnically or isotopically. Most of tlie bio lop xl studies haw used "Pu. However, there appear to bc sonic subtle efiects o n solubility and mobility, when the spccific alplia activity is increased by approximately 280. 2s in the case of pure 2 3 8 P u . Reactor plutoniuni is mixed. and its specific activity, although probably not so grext as that of pure 238Pu,is certainly going to be considerably higher than that of pure 2 3 9 P u . 1 1 1 addition. fuels will be largely uranium by weight. At the prncessing level the mixture also includes fission products and trivalent actinide by-products. In the event of an accident, the mixtures will also include the elements ol' tlie core assembly, the coolant, the containers, and mineral 610 LOG ICA L STUD I ES The plutonium compounds that have been studied biologically span the range of likely solubilities from the liiglily soluble Pu(VI) citrate t o highly insoluble, hightemperature-fired h O l ceramics. The routes by which plutoiiiuin compounds have been administered are shown in Fig. I . Tliey have been introduced into the lung, either by inhalation or by instillation of solutions; administered by niciullt: placed in the soft-tissue conipartriient by injection under the skin or into muscle or into the peritoneal cavity; and introduced directly into the plasma compartment by pounds have also been applied to intact or daniaped skin. ( h t c : tlie incisor tooth conipartnient applies only to rodents, and transfer from the trabecular t o the cortical bone compJrtment takes place so far as we know only during rapid growth.) Fig. 1 Kinetic model of :he metabolism of rc:inide elements in mammals. The inciwr tooth compartment u present only in rodents Reproduced from Durbin et rL (1967) with the pam isbn Although i t seems unlikely that plutonium complexed with citrate will be encountered in real life, such soluble niaterials have been studied in order t o examine the behavior of plutonium, separately from the problem o f its transport across cell barriers. I t is also unlikely in real life that insoluble plutonium particulates will be introduced directly into the plasma compartment, b u t studies have also been conducted of injected colloidal or polynieric plutonium in order t o examine the errors of earlier experiments in which supposedly soluble plutonium was administered partly in colloidal form. Insoluble plutonium compounds introduced into the gastrointestinal tract or the lung or into wounds are essentially local radiation sources. Impaired pulmonary function and lung tumors have resulted from deposition of plutonium compounds in the lung. Local tissue reactions result from plutonium deposits in wounds or beneath the skin. Daily feeding of plutonium t o rats results in radiation damage t o the intestine, and the severity is proportional to the dose. Apart from lung tumors, the amounts o f plutonium required t o produce these reactions are large, and the time for the development is long. We know almost nothing, even now, about the exact mechanisms by which small amounts o f plutonium, initially administered as insoluble compounds, are solubilized o r otherwise transported into the body interior from their initial sites, chiefly the lung, the gastrointestinal tract, and wounds. In the case of the lung and intestine, the plutonium must be either rendered soluble so that it can participate in some process that will transport it across cell membranes or it must be trapped b y cells that eventually carry or extrude their particulate contents into the body. That particulrte plutonium can be transported t o some extent is shown by the transfer of inhaled 239Pu02from the lung into the pulmonary lymph nodes and from subcutaneous implants t o local lymph nodes. Insoluble plutonium introduced directly into the circulation by intravenous injection behaves in a way that is typical not of plutonium specifically but of colloidal material in general. Depending upon their size, colloidal particles are deposited in liver, spleen, and bone marrow. If tlie particles are large enough, they also are trapped in the Microscopic examination of these tissues reveals that they contain reticuloendothelial cells that trap and hold particulate matter. Autoradiographs reveal that colloidal plutonium is inside these specialized cells. In cases of environmental or industrial contamination, it is not likely that particulate material will enter the circulation directly. Therefore, even though the literature on the distribution and behavior o f colloidal plutonium is vast, we will move on to examine the deposition of plutonium which is soluble and which is distributed in the body by virtue of its chemistry rather than its physical

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However, an understanding of the behavior of particut understanding what happens to plutonium after it is deposited. Once soluble plutonium is deposited, it may be recirculated and redistributed within the aniiiial; reticuloendotlielial cells are frequently involved in that redistribut latc plutonium trapped by phagocytes is iinportant t o PLUTONIUM TRANSPORT IN BLOOD Thanks to modern proteinchemistry techniques, we now know something about the way in which soluble plutonium is transported in the blood. There is a growing body of evidence that points t o iron-transport mechanisms logical processes that determine the fate of soluble plutoOne of the earliest observations of plutonium behavior was that intravenously injected soluble Pu(IV) or Pu(VI) remained in the circulation for many l i o u n (Fig. 2), unlike strontium or the trivalent lanthanides which were cleared from the blood very quickly. In the case o f strontium and thc trivalent lanthanide or actinide elements, there is lcss than 0.1% circulating at I day. The solid symbols are from three people who were injected in 1945-1946. The HP-2 dashed line is approximately typical of the group of human cases. The squares are data from one individual in whom the plutonium residence time in the blood was particularly The people were all middle-aged or older, and we compare them in Fig. 2 to healthy young animals-the young adult Beagle dog and a lactating Suffolk sheep (in the first or second pregnancy). Muntz and Guzman-Barron (1947) interpreted the prolonged residence of the plutonium in blood as proof DAYS AFTER INJECTION Fig. 2 Plutonium in the ric uht ion rfta intravenous injection into human rubjectr, Beagk dog. Q Suffolk ewe& Reproduced from Durbin (1972) with the b w m n of the publisher.

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BEHAVIOR OF PLUTONIUM I N ANIMALS AND MAN --o-- Activity due to Pu -0- kt iv it y dum to Am Fig. 3 Demonstration of the association of Pu(lV) and Am(lI1) with serum proteinsof small size. Column k 9.5 ml/hr. Dialyzed serum sample applied is -6 mL Reproduced from Popplewell and Boocock (1967)with the permission of the authors and publisher. that plutoriiuni was bound t o a large molecule. They used an elcctrophoretic technique t o demonstrate that plutonium was associated with a SI -globulin in serum. I t was not until about 20 years later that Popplewell and Boocock ( 1 967) in England applied niodern proteinseparation methods to this problem and identified the -globulin as transferrin, the specialized protein that norinally carries iron in niammalian blood. Figure 3 is takcn froiii a paper they presented at a Iianford symposium in 1Y67. %ruin proteins were fractionated by size; the larger glohulins lie to the left; the smaller albumins to the right. The plutonium and also 2 4 I Am are associated with the The protein peak containing tlie smaller proteins was separated by an ion-cxcliange technique into its two major conipcinents, “A” on the right, albumin; and “T” on the left. trrrnsferrin (Fig. 4 ) . All o f the plutonium is associated w ii IIt lie Iran sfc:r rin lrac t ion. I’opplewell and Boocock (1967) further found that, wlieii w d i u m citrate was added to the solution, the plutoniuni was separated from the transferrin (Figs. 5 and 6).Tliq. concluded that in the presence of excess of citrate 1 0 1 1 tlie plutc)riium-transferrin combination was not stable. petccl with iron for transferriri binding sites (Fig. 7; compare with Fig. 3). This is a size separation as in Fig. 3, Fig. 4 Demonstration of the association of Pu(1V) with the transferrin fraction o f serum proteins. Column k 28 by I.6cm albumin. Reproduced from Popplewell and Boocock (1967) with the prmirrion of the authors and publisha.

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F i g 6 Demonstration of the dissociation of Pu(IV) from serum proteins in the presence of exces citnte. Column is 30 by 1.6 c m citrate, pH 8.0. Temperature is 4°C Flow rate is - 3 0 m l / h . Volume fraction is 5 to 6 mL Sample volume applied is 1 m l Reproduced from Popplewell and Boocock (1967) with the permiss o n of the authors and publisher. Fig. 7 Demonstration of the dissociation of Pu(lV) from serum proteins in the pre rnc e of excess iron. 8 ml/lir. Reproduced from Popplcwell and Boocock (1967) with the permiuion of the authors and publisher. i in wliich the plutonium radioactivity was associated originally with fraction 111. the albuniin-transferrin peak. They addd iron io t l ~origiiul plutoniuin transferrin solution. fraction Ill to an association with macroglobulins (fract i o n I),but the bulk of the aclivity was prcscilt unbound in Next, Popplewell and Boocock (1967) added excess plutonium (Fig. 8 ; compare with Figs. 3 and 7) and observed the same net effect. The fraction of the plutonium duced. They assumed that the binding capacity Of the transferrin in thcir solution had been exceeded, and the excess plutonium was present unbound. ,The i r o n effectively shunted sonic plutonium away from still associated with the transferrin was considerably re-

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Fig. 8 Dcmonstration of I I I C saturation of tlic binding capacity of scrum proteins for Pu(IV) in the prescnce 6°C. I-low rate is 9 to IO ml/hr. Simplo applied i s 0.2 ml of scrum dilutcd with 3.4 ml of TRlS buffer. Reproduced from Popplewell and Boocock (1967) with the permission of the authors and publisher. At the Universityoi Utah, Stover e t at. (1968) allnost simultaneously performed the same kinds of experiments and confirmed the results of Popplewell and Boocock ( 1 %17). The findings wcrc extended to hunian and dog blood. They sumniari7ed the findings 3s follows: plutoniuiii is reversibly bound to transferrin; plutonium occupies the uriie binding sites that arc occupied normally by iron; the plutonium-transferrin complex is not as stable as the iron transferrin entity; uptake of plutoniuni in bone occurs because the forming red cells reject the plutonium that is transported t o them. These workers, along w i t h Turner and Taylor (1968), also showed that, if one sampled blood from rats or dogs a few hours after plutoniuni was injected, 95% of the plutonium still in the circulation was transferrin-bound. Brueriger et al. (1969) also demonstrated that, if the iron-storage protein. ferritin, were added t o a test tube con t ;I i ninF plut on iu ni hound to t ran sferrin, t tic plutonium shifted t o the ferritin molecules. Using cell honiogenization techniques, they also demonstrated that most of the plutonium deposited in dog liver was associated with various f o r m of ferritin (Stevens et at., 1971). Since then tlicy Iiuvc shown that. willi the passage of tiiiic, plutoniuni is transferred from soluble to insoluble forms of ferritin in the liver of the dog. These obsenations led, in a reexamination of the available human &ta, t o an attempt to correlate the dcptt\iti(w arid curly excrctioii o f plutcmiurii i n pcoplc …