Archive description
This 4 page document is a preliminary draft with a handwritten title "biomedical considerations related to inhaled alpha-emitting particles". There is no author identified and the document seems to be dated 1974 but the first part of the date is garbled. The 4 pages are titled section v. Radiation protection standards for pu-239. The document addresses succinctly the evolution of the permissible body burden from the manhattan project days to the present. The document goes on to address potential changes. It quotes bair and thompson (see document #700086) who say the current standard for plutonium for bone was several fold "less safe" than for radium. They also are quoted as saying that due to the absence of data at lower levels of pu-239, the margin of safety is "less than totally reassuring." also discussed is the possibility of the tracheobronchial lymph nodes or the liver being the critical organ.
Document text
Machine-read from the scan, so expect some errors. Lines that couldn’t be read are left out.
Page 1
Recent reviews of radiation protection standards for 239Pu have been 700089 published by Langham (1972) and Healy (1970) . Both of these reviews trace the current standards back to primarily human data derived from individuals containing quantities of 226Ra o r those exposed to external X- o r gamma irradiation. In 1943, during the early days of the Manhatten Project , there were only three tolerance values available: 0 . 1 R/day for external X - o r gamma irradiation, 0.1 vg body burden for tation denonstrated the bone-seeking nature of 239Pu when it was absorbed into body fluids i n some forms. Because the work of Evans --et a l . (1943) on humans containing body burdens of 226Ra was available in this t i n e period, it was natural that comparisons of the expected toxicity of 239Pu in man be made with that observed for 226Ra i n humans. During the early days cf the Manhatten Project, the permissible body burden of 239Pu i n 1944 w a s initially taken as 0.3 pCi but was reduced to 0.06 or 0.03 liCi With the availability of comparative toxicity data for 226Ra and 239Pu in rodents, the permissible body burden for 233Pu was reviewed at the Tripartite Permissible Doses Conference held at Chalk River , Canada in September 1349. At t h i s time, a permissible body burden of 0.006 VCi was agreed upon. Shortly thereafter, the value was revised to 0.04 pCi based on an analysis by D r . Austin Rrues that accounted for (a) a 15: 1 toxicity ratio for 239Pu relative to 226Ra based on injected body burden for 226Ra was, and still is, 0 . 1 VCi, the resulting value for 239Pu was 0.04 pCi. This permissible body burden for 239Pu based on the skeleton as the critical organ has been used by the ICRP since 1950, National Bureau of Stan dards (1951) and the NCRP since 1953, National Bureau of Cognizance of the differences that i n--vivo solubility of an inhaled material can play i n the subsequent tissue distribution was made by 1951 when they tabulated the maximum permissible body burden, hlPBB, in both solvkle m d izsoixhlc iorms, :.aticnal Bureau of Standards (1953) .
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,y calculation based on a permissible wreeXly mean crgan dose of 0.3 rep/ .&e the RBE for alpha particles wzs apparently taken as 20. The ICRP shed a value of 0.02 derived similarly in 1955 using an RBE of 10. Subsequent Jications by the NCRP and ICRP have listed maximum permissible air concentran n s , MPC, for insoluble forms of 239Pu derived from calculations in which the annual dose to lung was limited to 15 rem. Although corresponding MPBB values have not been listed, an annual average dose of this magnitude to lung would be associated with a lung burden of 0.016 pCi. Thus, the recommended velue for insoluble 239Pu in the lung is besed on irradiation limits to a critical tissue, a concept that traces back originally to human experience with external irradiation . The 1959 recommendations of the NCRP, Nationel Bureau of Standards (1959) and the ICRP (1960) regarding mexizun permissible body burdens and associated maximum permissible concentretions in currently accepted values ,are given belciv: Soh ble Bone 0.04 air and water for 239Pu which are the Current AEC stzcdards as published in P-ECM 0524, USAEC (1968) and 10 CFR20, USAEC (1971) for 239Pu for 40 hours per week exposures in restricted areas a r e the same as thcse rec3mmendea by A'CRP and ICRP. One cf the main problems r i t h these standards, as they now exist, is the differentiation beteen soluble and i n s ~ l u b l eforms of 233Pu in the industrial solubilities for different conpour.ds of *"PU, it is no; cleEr on what basis the decision should be made reG;ardinq use c.f t h e soluble or insoluble limits. decision is an imporiant one because t h 2 lirriits now differ by a factor of 20. Reccsnizing that there is prcbebly an entire spectrum of i n--vitro A s was indicated cbove, the permissible annual dose to lung, 15 rem, can be traced back to human experience :.-iih exierr:al irrzdistion. More needs to be learned of the relationship betvieen t h e uillforrn dose prcduced by t h e external irra-
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The standard for soluble 239Pu assumes that essentially all of the internally deposited 239Pu is in the skeleton. Results from animal experimentation have shown that the partitior, of 239Pu between liver and skeleton after it reaches the bloodstream is variable end influenced by route of administration, chemical form and other factcrs . Thus, s star.aard that requires all 239Pu to be in the skeleton is unrealistic. Bair and Thoripson (1974) have proposed a scheme with 45% in skeleton, 45% in liver and the rezaicing 10%in soft tissue and excreta. Bair and Thor ps on (1974), in their recent review of the biomedical aspects oi plutoniurn, examined the reletionship of present standards to existing animal data. Using ccrnpsrative csta cn 226Ra and 239Pu obtained with Beagle dogs at the University of Utah and n a k i r g some assumptions regarding difierences in bone surface/ volume ratios and turnover of 239Pu on bone surfaces for humans, they concluded that the current stsndard for plctoniGm v:as severalfold "less safe" for bone than the current standard for r a d i u x . FurLTer, they compared the lung burden in man associated with an annual dose of 15 r e r s , 6.016 pCi, with lung burdens shown to have produced pulmonary r,eoplssia indqs. Gn a coficentration basis, an initial lung concentration of -1 nCi/g;n rni5ht EC.: s?~rterithe lifespan of t h e dog. This value can be cornpared with the permissible k n g coxcen;raticn in man of 0.016 nCi/gn . Because of t h e ebsence of reassuring . I t They also pcir.ted out differences thst could be incurred if the tracheobronchial lymph Eodes o r the li-:er v:ere considered the critical organ. They summarized their thoughts in this x e s b y inoica;ir:g that they both feel that there will be some lowering of pernissible ex?osures tc 239Pu within the next few years but that t h e In a recer,t re-.-.;ievi,Dolphin (1972) discussed problems associated with selection of a critical crgsn for control of the exposure of people to plutonium. H e reviewed the animal dzta and the observation of long-term effects in lung, lymph tiss u e associated with lunc , Lcne and liver and concluded that the choice was cot clearcut, particulariy considerinq the differences between the high body burdens required to produce observable charces i n lajoratory animals compared with the low levels and anticipated mir x msl response expected in a human population. He then used a revised versior. of 3 :LE; -:,el deri*:ed by the ICRP Task Group on Lung Dynzmics (1966) that zcccurted f c r diffei-r-:-.t retprtion times for different compounds in the lung and its Ci?sSCCiE;?.d iyr.;;: ncLSs, a d also tocl: account of differences in aerosol particle
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diameter of 1 pn, he concluded that a MPC, of 1 x 10-l’ pWcc would give adequate protection for both Class W and Class Y compounds. This value would be 4 times more restrictive than the current MPC, for insoluble 239Pu but 5 times less restrictive than the current MPC, for soluble forms.