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Appl. Radiat. Isot. Vol. 47, No. 3, pp. 355-359, 1996 Copyright © 1996 Elsevier Science Ltd

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Intercomparison of Measurement Techniques Used in Radon Exposure Facilities for

Animals in Europe

J. C. S T R O N G 1., J. P. M O R L I E R ~, G. M O N C H A U X 2, R. W. B A R T S T R A 3, J. S. G R O E N 3 and S. T. B A K E R ~

~Aerosol Science Centre, AEA Technology, 551 Harwell, Didcot OXI1 0RA, U.K. 2Department de Pathologie et Toxicologie Experimentale, Commissariat a L'Energie Atomique,

Centre D'Etudes Nucleaires de Fontenay-aux-Roses, France 3TNO Medical Biological Laboratory, Lange Kleiweg 151, P.O. Box 5815, 2280 HV, Rijswijk,

The Netherlands

(Received 11 August 1995)

The biological effects of exposure to radon and its progeny are being studied in animals by three laboratories in Europe. The facilities used for such exposures are described, together with the methods used to estimate radon progeny concentrations and the activity deposited in the lungs of exposed animals. As the facilities and methods vary, a series of comparison exercises has been carried out at the three facilities; CEA/COGEMA, Razes, France, TNO, Rijswijk, The Netherlands and AEA Technology, Harwell, U.K. The results of the exercise are presented together with reasons for the discrepancies in results between the groups thus ensuring that estimates of exposure provided by the groups for their studies is directly comparable.

Introduction

Several laboratories in Europe are using animals to study the effects of inhalation of radon and its daughters. Exposure facilities operated by CEA/ COGEMA at Razes, TNO Medical Biological Laboratory at Rijswijk and AEA Technology at Harwell have been used for these studies. In order to effectively evaluate the radiation dose to the lung (normally in rats or mice) several radiological and aerosol parameters are required. These should include individual radon daughter concentrations (218Po, 214pb and 214Bi) together with a knowledge of the fraction of these nuclides which have not become attached to aerosol particles, normally termed the 'unattached' fraction. Measurements are also made of the deposited activity of z14pb and 2~4Bi in the respiratory tract of exposed animals by 7-ray spectrometry.

As part of the collaboration between the three groups at AEA, CEA and TNO which is sponsored in part by the European Union under the European Late Effects Project (EULEP) it was decided that the various measurement techniques used by the individ- ual laboratories should be compared under normal

*To whom all correspondence should be addressed.

operating conditions at the exposure facilities. Intercomparison exercises were therefore undertaken at the three facilities; at CEA in June 1992, TNO in May 1993 and AEA in September 1993. These have included comparisons of the techniques used to estimate radon progeny concentrations in air as well as those used to estimate the deposition of radon daughters in the respiratory tract of exposed rats.

Facilities

The exposure facility (Monchaux et al., 1994) at Razes near Limoges, France used by CEA consists of two 10 m 3 stainless steel chambers each of which can accommodate up to 250 rats. The animals are housed in wire cages so that exposures are whole-body rather than nose-only. A closed loop ventilation system is installed in order to vary the dis-equilibrium between radon gas and radon daughters. Radon gas is produced by emanation from uranium ore. A three vessel dilution system allows the quantity of radon in the chambers to be controlled. The maximum radon concentration which can be generated in the chambers is 40 MBq m -~. No extra aerosol sources are provided and the radon daughters are attached to the ambient aerosol. In order to sample air from the

355

356 J. C. S t rong et al.

chambers, ports are situated above the entrance doors. The port on each chamber consists of a stainless steel tube fitted with an air lock. A filter holder attached to a smaller tube can be passed down the tube, through the air lock and into the chamber. To avoid dilution effects, which can occur close to surfaces due to plateout, the filter holder is located 400 mm from both the ceiling and the walls. This system can also be used to expose single animals required for short duration exposure for lung deposition studies.

The TNO facility is situated at Rijswijk, The Netherlands and is based on a nose only exposure chamber in which 24 rats can be exposed. Animals are loaded into tubes which are then 'plugged' into ports on the exposure chamber. Radon is introduced at the base of the chamber and the airstream transports it up through the chamber to a small fan and air velocity sensor. After these the air passes to a unit which removes carbon dioxide and is then returned to the chamber. The total volume of the system is 15 L. The oxygen content is monitored and replenished from storage cylinders as necessary. A hot wire aerosol generator is also fitted to the chamber to provide an aerosol for radon daughter attachment. Air samples can be taken from either an animal port or from an airlock. Exhaust air from the sampling units is returned to the system. Care is taken to limit sample volumes to 1 L due to the low volume of the total system.

The AEA facility (Strong et al., 1990) is situated at Harwell, U.K. This facility is based on two separate 3.5 m 3 Gowrie chambers which will each hold a

maximum 50 rats or 200 mice. The chambers are operated in a closed loop, with circulating air conditioned in an air-handling unit where ammonia, carbon dioxide and humidity are removed and oxygen replenished. The facility has been designed to run continuously over long periods, exposure periods of up to 30 days are envisaged. Radon atmospheres in the range 300-10000 WL are provided by six separate 226Ra sources. Carnauba wax aerosol is provided continuously from a generator based on an evaporation and condensation technique. The chambers are fitted with airlocks through which filter holders can be passed to obtain air samples for subsequent analysis by gross a-counting to estimate radon daughter concentrations. A semi-continuous radon progeny monitoring device is permanently mounted next to the air lock and samples automatically every hour to determine radon

daughter concentrations in both the attached and 'unattached' states. The chambers are also fitted with 15 cm dia posting hatches so that cages containing animals can be posted in and out without losing chamber integrity.

As these studies involved the exposure of animals to radon and progeny they were carried out in accordance with the relevant national law relating to the conduct of animal experimentation.

Measurements

Before measurements were made on the chambers, sampling flowrates and 241Am references sources were also intercompared, the results of which have been reported in a preliminary report on the first two exercises at CEA and TNO (Strong et al., 1994). It was concluded that in the case of flow measurements AEA and TNO agreed within 1% while CEA underestimated by 10% for flowrates normally used for sampling. Measurements with 2~Am sources supplied by AEA and TNO indicated a 5% overestimate by AEA compared to TNO for 37 mm dia sources, however for smaller sources (7 mm dia) the overestimate increased to 15%.

Radon progeny concentrations

Grab sampling techniques followed by gross or-counting of the filter during three time periods (Thomas, 1972) were used by all three groups. AEA also provided measurement data from their semi-con- tinuous radon progeny measurement system (AEA-2) which employs or-spectrometry, this system also supplies data on the 'unattached' fractions (Strong, 1991). This device was used at CEA and AEA where the results provided by it agreed with those from the standard grab sampling method used by AEA to within __ 5%. Different sampling flowrates sampling/ counting regimes were used by the groups and these are shown in Table 1.

'Unattached' fractions were measured by using screen/filter combination techniques. However, TNO used a separate reference filter and compared the activity on this with that on a filter downstream of the screen, whereas AEA and CEA compared the a-activity on both the screen and the backing filter. Filters and screens were analysed in the same way as the plain filter samples for radon daughter concen- tration, using a three gross ~-count method (Thomas, 1972).

Table 1. Sampling and counting regimes used by the participating laboratories: AEA, CEA and TNO

Gross alpha counting periods, minutes*

Sampling Sampling First Second Laboratory flowrate (L min -L) period (min) Start-end Start-end

Third Start-end

AEA-1 2.0 2 2-5 6-20 21-30 AEA-2 2.0 2 l - I I 21-40 NA CEA 5.3 5 2-5 6-20 21-30 TNO 0.2 5 2-5 6-20 21-30

*The times given are from cessation of sampling. NA = not applicable.

Intercomparison of measurement techniques 357

Table 2. Comparison of measurements made by AEA, CEA and TNO. A value greater than unity indicates an overestimate by AEA compared to the other laboratory

Ratio of measurement results

PAEC 2'8Po 2'4Pb 2'4Bi Facility' Measuring laboratories Mean Range Mean Range Mean Range Mean Range

CEA AEA:CEA 0.98 0.8-1.2 1.03 0.9-1.2 0.97 0.8-1.1 1.02 0.8-1.2 AEA:TNO 1.08 1.6-1.2 1.05 0.9-1.2 1.09 1.6-1.2 IA0 1.6-1.2

TNO AEA:TNO 1.25 1.1-1.8 1.37 1.0-2.0 0.97 0.7-1.4 2.95 0.5-13

AEA AEA:TNO 1.27 I. I - I .9 1.25 1.0-1.7 1.26 0.8-1.9 1.56 1.1-2.6

a M e a s u r e m e n t s were made at the three facilities but only AEA and TNO made measurements at all three facilities. Measurements were compared in pairs to aid interpretation.

Deposition measurements

Estimates of the radon progeny deposited in the lungs of animals exposed for short periods, between 3 and 4 h, were also made. After exposure the animals were removed from the chambers and killed by intraperitoneal injection of sodium penta barbi- tone. The lungs were excised and then counted by ?-ray spectrometry by the three groups. CEA used a germanium detector while AEA and TNO used NaI detectors. CEA and TNO both used reference sources, uranium ore and 226Ra, respectively, to calibrate their detectors. AEA took a filter sample at the end of the exposure which was analysed by gross ~-counting (Thomas, 1972) and then 7-counted. The ~-counts provided an estimate of the individual radon progeny on the filter at the cessation of sampling from which the activity of-~'4pb and 2'4Bi at the time of 7-counting could be calculated, thus two calibration factors for -'~4pb and -"4Bi were established for each exposure. To compare the validity of this method against that used by CEA and TNO the mean calibration factors (SD of + 7.7% for 2'4pb and 2.5% for -'~4Bi) calculated from those obtained from the six exposures at AEA were used to estimate the acivity of the TNO :26Ra source (1.998 kBq). The activities of 2'4pb and 214Bi were found to be 1.67 and 1.75 kBq, thus AEA underestimate the activities of these nuclides by 16 and 12%, respectively.

Corrections for decay were made by CEA and TNO using a graphical technique to estimate the activity of 2'4pb and 2'4Bi at the end of the exposure. AEA calculated these corrections using standard decay equations. The samples were also weighed so that lung deposition could be specified in terms of activity per wet weight of tissue (Bq g- ') .

Measurement results

Measurements at the three facilities were made with animals present in the chambers: 36 rats at AEA, 200 rats at CEA and 24 rats at TNO. AEA and TNO both made radon progeny concentration measure- ments in all three facilities whereas CEA, due to the

non-portability of their equipment, only made these measurements in their own facility.

At AEA air was recirculated through the chamber at 0.7 air changes/h and carnauba wax aerosols (count median diameter 0.15 mm measured with a differential mobility particle sizer, DMPS) were generated continuously, providing 'unattached' PAEC fractions of the order 1%. Measurements were made in the CEA facility without ventilation and without aerosols being generated. At TNO the system was operated with air circulating at 12 air changes/h and with aerosols generated using the hot wire device, using the DMPS the count median diameter was estimated to be 0.05 mm. Measurements were also made at AEA with the aerosol generator switched off, to allow the measurement of PAEC 'unattached' fractions of 55%.

Radon progeny concentrations

Results of radon daughter concentration measure- ments made by AEA were compared with those from the other groups and the results of this are shown in Table 2.

Several measurements of 'unattached' PAEC fraction (fp) were made by the groups and the results from these are shown in Table 3.

Table 3. Results of 'unattached' fraction measurements made by the three laboratories

"Unattached' fraction of potential s-energy (fp) measured by:

Facility ~ AEA CEA TNO

CEA

TNO

AEA

0.14 0.21 0.13 0.10 - - 0.67 0.62 - - --- 0.11 0.21

0.58 - - 0.80

0.01 - - 0~03 0.01 - - 0.02 0.01 - - 0.04 0.01 - - 0.03 0.55 - - 0.35 0.53 - - 0.34 0.01 - - 0.03

~Facility in which the measurements were made.

358 J. C. Strong et al.

Table 4. Results of measurements made at CEA of 2~+Bi deposited in lung

Lung deposition' of 2~'Bi (Bq g-t) measured by the three laboratories b

Test No. Rat-1 Rat-2

1 2820/4820/3090 2 1920/--/2530 3 1480/--/2080 4 3020/--/4770

2030/--/2555

'After exposure in the CEA facility for a period of 3--4 h. For the first test two rats were used, for subsequent tests only one rat was used. bThe results from the three laboratories are shown in the order AEA/CEA/TNO.

Lung deposition

Rats were exposed for a minimum of 3 h. The lung samples were then circulated between the groups and analysed. ),-Ray spectrometry measurements were carried out within 40 min of removal of the animal from the chambers in order to improve counting statistics and reduce errors in estimating the activity at the time the animals were removed from the chamber. At the CEA facility four tests were made, in the first two, animals were exposed and removed from the chamber together. The results for 2Z4Bi measurements are shown in Table 4.

After these measurements had been completed the groups modified their individual procedures in order to estimate both the 2m~pb and 2~4Bi activity in the samples. Three animals were exposed and removed simultaneously from the chamber allowing each group to undertake the dissection on an animal from each exposure. Results of the measurements are shown in Tables 5 and 6.

Discussion

Comparing the results from the radon daughter measurements at all facilities there appears to be a consistent difference between AEA and TNO, especially in the case of PAEC. Differences between measurements made at AEA are similar for both the individual nuclides and PAEC. The extent of the agreement is less at TNO than at AEA especially in

the case of 214Bi, and is likely to be caused by the very low equilibrium factor (the concentration of 2t4Bi being much less than that of 2tSpo by a factor 50). Thus assessment of 2~4Bi under these conditions would be subject to large errors. Measurements made at AEA under low equilibrium conditions also showed similar discrepancies. However, there appears to be a consistent difference of 20% between TNO and AEA in the estimates of radon daughter concentrations under high equilibrium conditions and is probably due to errors, by either AEA or TNO, in estimating the counting efficiency of their counters for the size of the filter samples used. Differences in flowrates have been excluded as both groups have intercompared each others flow measur- ing devices and the differences found were only of the order of 1%.

Differences were found between AEA and TNO when measuring 'unattached' fractions. The higher value measured by TNO at their facility compared to the values measured made at AEA could be due to the sampling regime used: two samples separated by 30 min are collected for the TNO measurement, thus, if conditions change, which is likely due to the small volume of the system, then errors may occur. The measurements at AEA also show an inconsistency: AEA gives overestimates for high 'unattached' fractions while underestimating very low fractions compared with TNO, again this could be due to the two groups using different sampling techniques.

Measurements made to assess 2~Pb and 214Bi deposited in the lungs of animals show large variations between the participating groups, es- pecially at TNO. However, the results obtained at AEA are in better agreement and is probably due to the three groups making further modifications to their procedures between the exercises at TNO and AEA. These modifications were made to the methods used to calibrate the detectors and the methods used to handle the counting data to estimate the activity of 2~4pb and 2~4Bi at the moment when the animals were removed from the chambers. As expected, agreement was improved when animals were exposed

Table 5. Results of measurements made at TNO of z~4Pb and Z~Bi deposited in lung

Lung deposition' (Bq g-~) measured by the three laboratories b

Test No. Nuclide Rat-I (AEA)' Rat-2 (CEAy Rat-3 (TNOy

1 214Pb 2 4 0 / 1 0 8 0 / 9 3 0 3090 /990 /970 1680/580/990 2~4Bi --/580/1330 --/710/1660 --/210/1134

2 2 t4pb 7410/--/5480 5960/4330/6680 5120/2710/6310 a ~ B i 5850/--/7920 2860/3420/9560 3160/2000/7440

3 a~Pb 810/560/810 820/750/420 910/--/850 2J4Bi 850/420/970 3 3 0 / 9 3 0 / 3 6 0 610/--/1180

4 2~4Pb 450/550/260 540/440/270 490/370/-- ' ~4Bi 370/680/-- 250/150/430 320/440/--

5 : t 4 P b 1 1 8 0 / - - / 1 3 5 0 6 3 0 / 7 7 0 / 1 4 8 0 680/--/1140 a ' 4 B i 1 3 6 0 / - - / 1 6 5 0 1 2 4 0 / - - 1 9 1 0 1080/--/1320

'After exposure in the TNO facility for a period of 3-4 h?The results from the three laboratories are shown in the order AEA/CEA/TNO.°Three rats were used for each test, the laboratory which dissected the rat is shown in brackets.

Intercomparison of measurement techniques

Table 6. Results of measurements made at AEA of 2~4Pb and 2~Bi deposited in lung

Lung deposition" (Bq g-L) measured by the three laboratories b

Test No. Nuclide Rat-I (AEA) c Rat-2 (CEA)' Rat-3 (TNO)'

1 2,4pb 6001400/510 5 6 0 / 3 0 0 1 5 0 0 40014501190 ~141]i 8 3 0 / 6 5 0 / 1 1 5 0 8 6 0 1 4 5 0 / 6 4 0 550/650/650

2 2"Pb 800/650/-- 7 7 0 / 7 0 0 / 7 3 0 530/550/580 Z"Bi 680/800/-- 3 7 0 / 6 5 0 / 1 0 9 0 530/600/830

3 - '~ 'Pb 2290/2050/2620 1910/1900/2120 1210/--/2630 2t4Bi 4330/4100/5970 407014000t3600 3210/--/4020

4 2~4pb 2080/1900/1960 1750/1800/1410 2150/2000/1650 2~4Bi 2890/3000/3020 2410/1600/2690 2560/2500/2440

5 2 ' 4 p b 3350/3400/3130 2410/2500/2610 2410/2700/2200 :t'Bi 421014400/4480 3830/2600/3370 3560/3500/2930

"After exposure in the AEA facility for a period of 3-4 h?The results from the three laboratories are shown in the order AEA/CEA/TNO.cThree rats were used for each test, the laboratory which dissected the rat is shown in brackets.

359

to higher radon daughter concentrations which improved the counting statistics.

These intercomparison exercises have shown that the three groups are in reasonable agreement, especially in the case of PAEC, and that the three laboratories are able to produce exposure data comparable to each other.

Acknowledgements--The three laboratories were members of the Radon Working Group organised by EULEP who partially supported the studies. The AEA contribution was funded by the U.K. Department of Health. the TNO contribution was supported by the Commission of the European Community under Contract BI 7-0050 and the Dutch Ministry of Housing, Physical Planning and Environment.

References

Monchaux G., Morlier J. P., Morin M., Chameaud J., Lafuma J. and Masse R. (1994) Carcinogenic and cocarcinogenic effects of radon and radon daughters in rats. Environ. HIth Perspect. 102, 64.

Strong J. C. (1991) A combined attached and 'unattached' radon daughter measuring system. In Tenth Annual Meeting of the American Association for Aerosol Research, Traverse City, MI, 8-11 October.

Strong J. C., Walsh M., and Black A. (1990) A facility for studying the carcinogenic and synergistic effects of radon daughters in rodents. J. Aerosol Sci. 21, 459.

Strong J. C., Morlier J. P., Monchaux G., Groen J. S, Bartstra R. W. and Baker S. T. (1994) Comparison of radon daughter measurement techniques used in Euro- pean animal exposure facilities. Radiat. Protect. Dosim. 56, 259.

Thomas J. W. (1972) Measurement of radon daughters in air. Hlth Phys. 23, 783.