Dose Coefficients and Assessment of Intake After Inhalation of Contaminated Dusts from Palomares (Journal Article Radiation Protection Dosimetry Vol. 79 Nos 1-4 PP. 179-182 1998)

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Radiation Proiccuon Dosimetry Nuclear Tcchnoitiiiy Puhlishme DOSE COEFFICIENTS AND ASSESSMENT OF INTAKE AFTER INHALATION OF CONTAMINATED DUSTS FROM PALOMARES ^National Radiological Protection Board. Chilton. Didcot. Oxon. 0X11 ORQ, UK ?Centro de Investigaciones Energeticas Medioambientales y Technologicas (C1EMAT) Avenida Complutense 22. 28040 Madrid. Spain Abstract — The inhalation of dust panicles beanng -"’Pu and 1:41 Am resulting from the aviation accident at Palomares in 1966 in still a potential health hazard for persons living or working in the vicinity. The dose coefficient for the dust and the behaviour ot these actinides in members of the public have been predicted by combining absorption parameters from the lungs into blood derived Irom animal studies witn human data from the most recent age-dependent biokinetic models published by the International Commission on Radiological Protection. For an aerosol of I p.m activity median aerodynamic diameter it is concluded that the most appropriate dose coelhcients for adults. 10 vear old and 1 year old children are 2.3 x 10~'. 2.6 x I0r5 and d.8 x ICr' Sv.Bq'1 respectively. For assessing intakes of the dust, measurements of :,wPu in unne could be used with advantage provided fission track or mass spectrometnc methods of analysis were used. On 17 January 1966 an aviation accident occurred in Figure I. Protocol for assessing consequences of humar exposure based on animal studies. the airspace over Palomares in the Spanish province of Almeria. Four thermonuclear bombs fell to the ground, three of them on land and one into the sea. Two of the bombs failed to deploy their parachutes and on impact conventional explosions were followed by the release and ignition of pan of the fissile material. As a conse quence. about 226 hectares of farmland and brush were contaminated. From the standpoint of human health the most important radionuclides were -v>*3'*0Pu (referred to hereafter as -’’Pu) and subsequently :4,Am. Despite extensive decontamination measures carried out at the time, some contamination persists and is still regarded as a potential risk to human health. The principal route of intake of -”Pu and Am by members of the public living or working in the Palom ares area is considered to be inhalation of dust panicles derived from the contaminated soils. The purpose of the work described here which summarises the most important aspects of a more comprehensive repon"’. was intended to improve the basis for assessing internal doses and interpreting bioassay data. Biokinetic studies of -’’Pu and :4,Am were undertaken after deposition in the rat lung of respirable dust fractions derived from a chemically and mineralogically defined soil. The results have been interpreted taking account of the most recent and biokinetic modeIs' u’' published by the International Commission on Radiological Protection (ICRP) and the computer codes designed to implement these models. MATERIALS AND METHODS Preparation and analysis of dust samples The parent soil sample was obtained during Nov ember 1986 from a site close to the point of impact of one of the damaged thermonuclear bombs. It consisted essentially of a sand-bearing silt. The detailed chemical

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mineralogicaJ and actinide content of the following par ticle size fractions the lowest and highest concentrations of whilst the 20—U) p.m fraction contained the highest amount (429H of the radionuclide. The -■"’Pu to :4lAm ratio, by radioactivity in the various fractions ranged from about Studies on the biokinetics of ^Pu and :4lAm in rats were resuicted to the natural respirable fraction of the soil (<5 p-mi and the respirable components derived from the total soil. 125-250 |xm and 20-40 p-m frac tions; the latter were obtained by milling of the soij frac tions and sedimenting out the larger particles in a col umn of absolute ethanol. Autoradiographic studies on all four components showed that the alpha activity was present as paniculate and dispersed forms" ’ presumably as a consequence of wet-dry cycling. The respirable components of the four dust fractions were administered to rats by intratracheal instillation. The objective of these studies was to obtain values of the absorption parameters of -:,9Pu from lungs to blood over an interval of I y. The results showed that the most and least transportable forms of -"’Pu and -4lAm were present in the <5 pm fraction, and the respirable component derived from the 125-250 pm fraction of and the consequent radiological implications after inhaling these materials are reponed here. The activity median aerodynamic diameter (AMAD) and geometric Figure 2. Urinary excretion of after a chronic intake r Note. Curves obtained using absorption parameters derived fo Table 1. Lung retention and absorption of u*Pu and 241 Am after intratracheal instillation. Lungs To blood Lungs To blooo •Mean r standard error, number of animals per group - 6

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form in the environment1and a compound usually assigned to Type S' ", nor to the behaviour of a Type M compound the assumptions of which are now recommended for ;”Pu in the environment in the absence of material specitic data'-". The data in Figure 2(a) can be used to calculate intakes ana hence doses from the measured concen trations of :,4Pu in urine provided it is assumed that public exposure has occurred at a uniform rate. Of criti cal importance in these assessments is the minimum detectable activity (MDA). The MDA value for unne analysis using chemical separation and alpha spec trometry is about 5 x I0-* Bq.!'1'7’. The value using fission track analysis is cutremly about 2 x 10“5 Bq.i“' but concentrations of 4 x I O’7 Bq.l“‘ are thought to be achievable'7>. The MDA by mass spectrometry is 4 x I0“7 Bq.l*"71 but recent developments have reduced this by an order of magnitude (i. Kelly. Batteile Pacific Northwest Laboratory, personal communication. 1996). For companson. the average background level of :1<>Pu in urine from fallout etc. is about 3 x I0-® Bq.l"''7' For the purpose of this paper it is assumed that the MDA equates to the 24 h output. It can be deduced from Figure 2(b) that chronic intakes of the <5 p.m fraction equivalent to a dose of I mSv.y" (see Table 3) could not be identified using alpha spectrometnc methods of analysis until about 30 y after commencement of exposure (MDA 3 X I0-* Bq.d"'). However, ten times this value could be identified within about 200 d. In contrast fission track analysis should be capable of identifying chronic intakes within a few weeks (MDA 2 x IQ-* Bqxl“') whilst mass spectrometry (MDA 4 x 10-7 Bq.d“‘) will be effective This paper is based on a collaborative programme of work undertaken by NRPB and CIEMAT. It was partially funded by the Commission of the European Communities under contract F13P-CT920064a. The authors are indebted to the scientific and technical I. Stndiine. G. N. and II others. Dost Coefficients and Assessment ot Intake alter Inhalation of Contaminated Dusts from Palomares. Repon M692 (Chilton: National Radiological Protection Board) (1996). I. International Commission on Radiological Protection. 1990 Recommendations of the International Commission on Radiological Protection. ICRP Publication 60 (Oxford: Pergamon Press) Ann. ICRP 21(1-3) (1991). 3. International Commission on Radiological Protection. Age-dependent Doses to Members of the Public from Intakes of Radio nuclides. Part 4: Inhalation Dose Coefficients. ICRP Publication 71 (Oxford: Elsevier Science) Ann. ICRP 25(3/4) (1995). 4. International Commission on Radiological Protection. Human Respirators Tract Model for Radiological Protection. ICRP Publication 66 (Oxford: Elsevier Science) Ann. ICRP 240-3) (1994). 5. International Commission on Radiological Protection. Age-dependent Doses to Members of the Public from Intakes of Radio nuclides: Part 2. Ingestion Dose Coefficients. ICRP Publication 67 (Oxford: Elsevier Science) Ann. ICRP 23(3/4) (1993). 6. Birchail. A.. Bailey. M. R. and Jarvis. N. S. Application of the New ICRP Respirators Tract Model to Inhaled Plutonium Nitrate using Experimental Biokinetic Data. In: Proc. Int. Conf. on Radiation Dose Management in the Nuclear industry. Procedures to Detect and Quantify Previous Exposures to Radioactive Materials. Health Phys. 64XSupp. 1). 45-100 (1991)

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standard deviation tor.) for aerosols generated from the suspensions were 1.86 (im to. 1.53) and 1.52 jim to. The absorption parameters for :'gPu and :4lAm are given in Table 2. They were derived using the computer Algorithm for f/Tting) and are in a form appropriate for implementation of the human respiratory tract model1''’. The biokinetic data on which these values are based are described in detail elsewhere'1'. Interpretation of experimental data The protocol used for evaluating the dose coefficients for the dust and interpreting the results of human data is shown in Figure 1. The computer code PLEIADES has been used recently by ICRP to derive the dose coef ficients for members of the public”'. For this study, the data used in PLEIADES combined absorption parameters derived from the animal studies, assumed to be species independent, with information on particle deposition and clearance from the respiratory tract model'4’ and on tissue distribution and excretion from the most recent biokinetic models for -"Pu and 241 Am'-'1. Detailed studies on the particle size distri bution of actinide-beanng dusts at Palomares will be undertaken under the CEC’s Fourth Framework Pro gramme. For the purpose of this paper the reference value of I p.m AMAD for members of the public is used1'1. In view of the poor transportability of ;'<>Pu and :*'Am deduced from the animal studies, the f, values used for uptake from the gastrointestinal tract, are the IMPLICATIONS FOR HUMAN EXPOSURE Dow coefficients and limits on intake The predicted dose coefficients for adult members of the public. 10 yoid children and I y old infants are Table 2. Absorption parameter values for 23*Pu and 441 Am. Pu Am Pu Am L s. and s. are the rapidly dissolved fraction, rapid and slow Values of the model parameters s^. s^ and s, can be calculated aeadily from them'4'. In the absence of data during the early clearance phase the default value of 100 d-' for s, was shown in Table 3: also included for comparison are the values for Type M and Type S compounds. It should be noted that the dose coefficients for the dust are based on the current :,gPu to -11 Am ratio of 5:1. These data, and the assessment of intake, would need to be revised if these ratios were appreciably different, e.g. in the per iod immediately after the incident. For interpreting per sonal monitoring data from current or recent intakes the information associated with the natural respirable frac tion should be used. It can be deduced from Table 3 that the amounts of radioactivity inhaled which would give nse to a committed effective dose of 1 mSv. are 43 Bq. 38 Bq and 21 Bq for adults, children and infants respectively: 837r of these amounts are due to ;,<’Pu Assessment of intake Two possibilities exist for the assessment of intake of the dust, external measurement of :4lAm in chest or the assay of -’’Pu in urine. For the purpose of this paper consideration is given only to adult members of the pub lic. The predicted biokinetics of44' Am in the lungs sug gest that external measurements will be of limited prac The predicted daily urinary excretion of -’‘’Pu after a chronic intake of 1 Bq.d'1 is shown in Figure 2(a). Also shown for comparison are the excretion characteristics for Type M and Type S compounds. The figure shows that the urinary excretion of -’’Pu does not conform either to the behaviour of -"’PuCK. the initial chemical fable 3. Dose coefficients (committed effective dose per unit intake) and intake limits of 4J4Pu for members of the public *Doie coefficients based on a -"’Pu:441 Am ratio of 5:1. **Data based on dose coefficients of -"’Pu and 441 Am as listed

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form in the environment1" and a compound usuaily assigned to Type S' ", nor to the behaviour of a Type M compound the assumptions of which are now recommended for -•1,Pu in the environment in the absence of material specitic data ". The data in Figure 2(a) can be used to calculate intakes and hence doses from the measured concen trations of -"•Pm in urine provided it is assumed that public exposure has occurred at a uniform rate. Of criti cal importance in these assessments is the minimum detectable activity (MDA). The MDA value for urine analysis using chemical separation and alpha spec trometry is about 5 x lO-* Bq.!""7’. The value using fission track analysis is currently about 2 X I0~* Bq.l-1 but concentrations of 4 x 10*7 Bq.l'1 are thought to be achievable17’. The MDA by mass spectrometry is 4 x 10"’ Bq.l*"71 but recent developments have reduced this by an order of magnitude (J. Kelly. Batteile Pacific Northwest Laboratory, personal communication. 1996). For comparison, the average background level of ;l<,Pu in urine from fallout etc. is about 3 x I0“*> Bq.l'"71. For the purpose of this paper it is assumed that the MDA equates to the 24 h output. It can be deduced from Figure 2(b) that chronic intakes of the <3 pm fraction equivalent to a dose of I mSv.y'1 (see Table 3) could not be identified using alpha spectrometnc methods of analysis until about 30 y after commencement of exposure (MDA 5 X 10-* Bq.d"'). However, ten times this value could be identified within about 200 d. In contrast fission track analysis should be capable of identifying chronic intakes within a few weeks (MDA 2 x |0~* Bq-d'1) whilst mass This paper is based on a collaborative programme of work undertaken by NRPB and CIEMAT. It was partially funded by the Commission of the European Communities under contract F13P-CT920064a. The authors are indebted to the scientific and technical 1. Stradling. G. N. and 12 others. Dose Coefficients and Assessment of Intake after Inhalation of Contaminated Dusts from Palomares. Report M692 (Chilton: National Radiological Protecuon Board) (19%). 2. International Commission on Radiological Protection. 1990 Recommendations of the International Commission on Radiological Protection. ICRP Publication 60 (Oxford: Pergamon Press) Ann. ICRP 21(1-3) (1991). 3. International Commission on Radiological Protection. Age-dependent Doses to Members of the Public from Intakes of Radio nuclides. Pan 4: Inhalation Dose Coefficients. ICRP Publication 71 (Oxford: Elsevier Science* Ann. ICRP 25(3/4) (1995). 4. International Commission on Radiological Protection. Human Respiratory Tract Model for Radiological Protection. ICRP Publication 66 (Oxford: Elsevier Science) Ann. ICRP 24(1-3) < 1994). 5. International Commission on Radiological Protection. Age-dependent Doses to Members of the Public from Intakes of Radio nuclides: Part 2. Ingestion Dose Coefficients. ICRP Publication 67 (Oxford: Elsevier Science) Ann. ICRP 23(3/4) (1993). 6. Birchail. A.. Bailey. M. R. and Jarvis. N. S. Application of the New ICRP Respiratory Tract Model to Inhaled Plutonium Nitrate using Experimental Biokinetic Data. In: Proc. Int. Conf. on Radiation Dose Management in the Nuclear Industry. Procedures to Detect and Quantify Previous Exposures to Radioactive Materials. Health Phys. 60(Supp. 1). 45-100 (1991).

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Radiation Protection Dosimcln Nuclear Technology Publishing ASSESSMENT OF-BeSES-TO-ABdlJLT MEMBERS OF THE PUBLIC IN PALOMARES FROM INHALATION OF ^CIEMAT. Avda Complutense 22. Madrid E-28040. Spain zNational Radiological Protection Board Chilton. Didcot. Oxon 0X11 ORQ. UK Abstract — The doses to adults in Palomares resulting from an aviation accident in 1966 are reappraised. For this purpose, siteand material-specific data on …