‘data to the (Eq. 4) Q = 500 uro7 4, amination clearance mechanisms. One can then describe trans- fer to the systemic circulation as: rer, whether iterized data Substitution of known values for t and U lations as allows one to estimate total-body burden at time. ures are ‘of exposure in the same units that are used for U mic model of (i.e., count rate, Mass, or activity). (Eq. 6) Assuming that each increment transferred is Similarly, data ob- ‘the body burden (Q,) at any time t following re[peated exposure may be calculated by using the total excreted according to the function shown in Eq. £ short life elimination coefficient and assuming multiple in- the excretion rates from each increment. lutonium puts as 4 summation process. m and col- 5. Langhan l, the total excretion may be described as the sum of Time (t) is relative to elapsed time since transfer from the lung rather than time since inhalation. A major difficulty in evaluating human expo- Using R r function gures has been the problem of reservoirs of pluto- as the time urine samples are obtained after inhala- te to body pium in various organs tion, the excretion rate (EY) is: (not bone) that are slowly sed to released to the circulatory system at rates that ons char- depend on many factors such as location within the and release body, particle size, E, = 0.002 A_ Q, f° et (R - cy 70774 dt. and physiochemical form. (Eq. 7) 'This slowly translocated plutonium is subsequently ecent analents and deposited in other tissues and ultimately lost from either the the body via urinary and fecal excretion. Unfortunately, Eq. 7 is not integrable and must be solved for individual values of 4, R, and t by expansion of the exponential term and solving until The concept of slow, continuous release of functions the series converges. on patterns .° bound plutonium into the body fluids, first formtained dur- several groups of investigators.°?? some The overall transfer rate (A) was thought to be composed of two components: alized by Healy,’ has been built into models by (1) The rate of rate of transfer into the systemic circulation periods up urinary or fecal excretion of plutonium in persons (ADs and (2} rate of loss via ciliary clearance ed on the chronically exposed can be estimated from Eqs. 1 mechanisms (A). expressions " and 2 by summation of individual administrations. as 4. Healy's model regards relatively insoluble pluto- ecal excre- excretion and for the amount of plutonium in blood. nium in che lung as a reservoir tsolated from ra period Figure 1 shows the calculated relation between | normal body metabolism yet continually releasing plutonium into the bloodstream. The model has no any portion of the lung or body; therefore, particles transiocated from the lung to lymph nodes (Eq. 2) behave in the same manner as those in the lung, 1ttom of the provided the rate of solution and entry into the 2 days fol- systemic circulation is the. same. iown time, lung and then utilizes the systemic model developed by Langham, 29 fF ing acute deposition after initial clearance of an , Smount (Q\) of insoluble plutonium is: (Eq. 5) (Eq. 3) = The overall elimination rate (A) actually represents both solubilization and transfer to the systemic circulation and discharge from the lung by ciliary ¥ Ptr tT ¥ Trey r ‘ ~ > of - Z io T T ——¥70.002T-9-74 - anne cee, ;4 4 A Ey20.002As Qof"eMa-wroT | --0--A3=0,001{T/2 =693 DAYS) 1 --e- Ag=0.01(1/2"69 DAYS) I~ [ g Ur ere LUNG EXPOSURE MODEL ‘N t < TU SYSTEMIC EXPOSURE MODEL ye 4 4 2 ec we o£ 5 Of 4 tore 3 o ”q z wy vo re w 4 3 f -~ The quantity (Q) in the lung at time t follow- irine speci- ired ina The model assumes a constant fractional removal per unit time from the time of ig Eq. 1 and iot,- , constraints regarding the positionof plutonium in (Eq. 1) Healy assumed that As was the same Similar expressions were derived for fecal & c 2 4 ° 1 x 10-4 a 0° Ie Fig. 1. ft A hed ro! a oe aa ee eee Dertahrreetieriedatal- io® 10° TIME AFTER EXPOSURE (DAYS) 10° heedee cd tL 10 Fractional urinary excretion as a function of time after acute exposure based on the systemic and lung exposure models. 27