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An interspecies comparison of the lung clearance of inhaled monodisperse cobalt oxide particles—Part VIII: Lung clearance of inhaled cobalt oxide particles in mice
J. AerosolSci., Vol. 20, No. 2, pp. 261 265, 1989.
0021 8502/89$3.00+0.00 Pergamon Press plc
Printed in Great Britain.
AN INTERSPECIES COMPARISON OF THE LUNG CLEARANCE OF INHALED MONODISPERSE COBALT OXIDE PARTICLES-P A R T VIII: L U N G C L E A R A N C E O F I N H A L E D C O B A L T O X I D E PARTICLES IN MICE R. J. TALBOTand A. MORGAN E n v i r o n m e n t a l and Medical Sciences Division, Harwell L a b o r a t o r y , Oxfordshire, O X l I 0RA, U.K.
(Received 3 May 1988; and in final form 20 June 1988)
INTRODUCTION We have used mice in our investigations of the toxicity of inhaled radionuclides for the past 10 years. These studies have concerned such topics as the fibrogenicity (Talbot and Moores, 1985), carcinogenicity (Lambert et al., 1982), pulmonary clearance (Morgan et al., 1984) and metabolism (Morgan et al., 1986) of inhaled radionuclides. In the joint study, the small size of mice compared with the other species involved imposed certain additional constraints. Firstly, the larger (1.7 #m) cobalt oxide particles were predicted to be virtually non-respirable by mice owing to their aerodynamic diameter being in excess of 2.5/~m (Morgan et al., 1983). In view of this only a small group was exposed to establish deposition parameters. Secondly, even with the small (0.8/~m) particles, we could only make accurate measurements of radioactivity in organs and excreta on grouped samples. However, individual measurements of 57Co in whole body and lung were possible for the full six months duration of the experiment. MATERIALS AND METHODS Female CBA/H mice from our inbred colony were used in the experiments. They were exposed at 8-10 weeks of age, at which time they weighed approx. 18 g. They were housed in a barrier-maintained animal room and allowed water and pelleted diet ad libitum. Groups of 59 and 5 mice respectively were exposed, nose-only, to the 0.8 and 1.7/~m particles of 57Co304 in the apparatus described by Walsh et al. (1980). Just before administration the particles were resuspended from the collection filters by ultrasonic agitation in Tween 80 solution and aerosols generated from an Acorn nebulizer (Medic-aid, England). Mean aerosol concentrations during the exposures were measured by prezalibrated in-line filters. The aerodynamic diameters of the 0.8/zm particles were measured using a quartz crystal microbalance cascade impactor (QCM, Berkeley instruments, Model C1000-A). Initial alveolar depositions (lADs) of 57Co for each exposure were defined as the mean lung contents of five randomly-selected mice killed after 24 h. At three days after exposure, all 54 mice remaining from the group exposed to the 0.8/~m particles were ~counted. For this purpose they were restrained in polypropylene tubes located mid-way between coaxial 150 mm NaI(TI) detectors. After counting, eight mice were killed by injection with sodium pentobarbitone (Sagatal, May and Baker), the organs removed, and the tissue distribution of 57Co measured. For each of these eight mice, the ratio between whole body and lung measurements of 57Co was calculated. Using the mean ratio, the lung contents of all other mice at three days were estimated. Based on these estimates the remaining mice were stratified into three classes--high, medium and low--containing 15, 16 and 15 mice respectively. At subsequent killing times, groups of three mice were selected by stratified random sampling (one from each class). Three days before killing they were transferred to a metabolism cage (Harvard Bioscience) to enable urine and faeces to be ft;; C r o w n . 261
262
R.J. TALBOT and A. MORGAN
collected separately. After their removal the cage was washed with 1% C o ( N O 3 ) 2 solution, and the washings combined with the contents of the urinary collection vessel. The mice were y-counted before killing and dissection. The 57Co contents of urine and faeces were also measured and expressed as percentages of the mean lung content at death per mouse per day. At the end of the experiment all 10 surviving mice were held in two metabolism cages for seven days before death. Two supplementary experiments were carried out. The objective of the first was to determine the excretion/retention pattern on 57Co up to seven days after the intra-gastric injection of 0.8pm 57Co304 particles. For this purpose a suspension of particles ( ~ 9.2 kBq ml-1) was agitated by ultrasound shortly before administration to eight mice. Their stomachs were intubated with a smooth-ended animal feeding needle (Popper & Sons, Inc.) and 0.1 ml of suspension injected. Four additional aliquots of the suspension were dispensed to check the 57Co content. The mice were immediately placed into two metabolism cages and held there for seven days before death. The 57Co contents of urine, faeces and carcass were measured. The aim of the second supplementary experiment was to study the excretion of 57Co administered to three groups of four mice by (i) intraperitoneal, (ii) subcutaneous and (iii) intravenous (tail vein) injection. For this purpose the 1% aqueous solution of 5 7 C o ( N O 3 ) 2 6 H 2 0 (3.2 MBq m1-1) supplied was diluted approx. 50-fold in physiological saline. Aliquots of 0.2 ml were injected and the animals y-counted immediately, then held in metabolism cages for seven days before death. Three further mice were given an intraperitoneal injection, and whole body measurements of 57Co made for three months. Subsequently the organ contents of 57Co at death were measured. RESULTS
The 0.8 #m particles were administered at a mean aerosol concentration of 1.2 kBq 1- 1 for 135 min. This resulted in a mean lAD of 1.8 + 0.11 kBq. The activity median aerodynamic diameter of the aerosol was 1.44 #m (ag 1.16). The 1.7 #m particles were only poorly deposited in the alveolar region, an aerosol concentration of 0.29 kBq 1-1 for 40 min yielding an lAD of only 0.012 kBq. At three days after exposure the mean estimated whole body content of 57Co in the mice was 2.08 +0.043 kBq (S.E.M.; n = 54). The mean lung/whole body ratio for the mice killed after three days was 85.6+ 1.7% (S.E.M.: n=8). From this ratio the mean estimated lung content of the 54 mice at three days was 1.78 kBq. Estimated fractional retentions of 57Co in both the lung and the whole body are shown in Table 1. The organ-distributions at death of these mice and of those killed after only one day, are shown in Table 2. Beyond 15 days all the organs, except the lungs, were combined before counting, thus standard errors were not available. At 296 days the 57Co contents were too low to permit meaningful estimates to be Table 1. Estimated fractional lung and whole body retentions of SYCo for mice killed with time after inhalation of 0.8 ,um 57C0304 particles Time (days)
n
3 6 9 15 22 29 43 57 71 85 I00 148 183 296
8 3 3 3 3 3 3 3 3 3 3 3 3 10
Whole body Mean S.E.M. 100 74.04 61.05 50.53 46.76 40.23 32.19 22.32 15.34 12.58 5.28 2.54 0.54
1.22 1.46 1.81 1.61 0.99 1.75 0.76 1.10 0.63 0.20 0.11 0.06
Mean
Lung S.E.M.
100.00 89.13 82.64 70.48 58.82 52.77 46.83 37.41 25.94 16.05 13.74 5.91 2.84 0.55
+ 2.04 ± 3.06 _+ 1.28 + 1.01 ± 1.98 + 2.15 ___+0.71 ± 1.93 ± 0.99 __+2.34 + 0.81 ± 0.25 __+0.19 _+_0.07
Interspecies comparison of lung clearance--VIII
263
Table 2. Organ contents after inhalation of 0.8 gm 57Co304 particles as a percentage of the total in animal Time (days)
n
Lung
TB/LN*
1
5
3
8
6
3
9
3
15 22 29 43 57 71 85 98 148 183 296
3 3 3 3 3 3 3 3 3 3 10
47.77 +3.61 78.92 __+1 , 4 4 90.59 __+1 . 2 9 94.44 +0.71 97.12 98.11 98.46 98.74 98.34 98.30 97.40 97.68 96.60 93.57 .
Mean % of activity in animal (+S.E.M.) GI tractt Liver Pelt Head
0.42 ___0.036 0.35 _.+0.053 0.27 __.0.017 0.33 +0.050 0.21 0.22 0.36 0.30 0.35 0.44 0.74 0.51 0.49 1.33 . .
15.53 +1.35 2.15 __+0,20 0.72 +0.082 0.49 +0.054 0.35 0.32 0.25 0.25 0.14 0.25 0.46 0.31 0.18 0.69 .
0.14 +0.028 0.20 +0.029 0.16 +0.031 0.17 +0.008 0.12 0.10 0.11 0.12 0.14 0.16 0.24 0.33 0.23 0.78 .
35.73 +3.47 17.99 _+1 . 4 8 7.91 _ 1.30 4.32 +0.69 1.95 0.88 0.56 0.25 0,59 0.48 0.43 0.64 0.86 1.50 .
0.15 +0.082 0.13 +0.019 0.17 __+0.045 0.14 +0.053 0.17 0.30 0,18 0.16 0.15 0.18 0.45 0.31 0.74 0.92
Carcass 0.26 +0.034 0.27 +0.036 0.18 __+0.025 0,11 +0.028 0.08 0.07 0.08 0.18 0.29 0.19 0.28 0.22 0.90 1.21
* Includes: trachea, heart, extrapulmonary bronchi and thoracic lymph nodes. t Includes: gut, spleen, kidneys and urinogenital tract.
Table 3. Metabolism summary: combined results from three mice per point as a percentage of contemporary lung content (10 mice at 296 days) Time From 3 6 12 19 26 40 54 68 82 97 145 180 289
(days) To
Faeces/ lung (% day- I)
Urine/ lung (% day- i)
Mechanical clearance (% day- i)
Translocation (% day- i)
6 9 15 22 29 43 57 71 85 100 148 183 296
8.81 4.29 2.27 2.03 1.61 1.57 1.46 1.46 1.85 1.46 1.45 1.21 1.31
0.68 0.60 0.50 0.45 0.53 0.49 0.55 0.59 0.63 0.73 1.00 1.23 2.01
8.55 4.06 2.08 1.86 1.41 1.38 1.25 1.24 1.61 1.18 1.07 0.74 0.55
0.94 0.83 0.69 0.62 0.73 0.68 0.76 0.81 0.87 1.01 1.38 1.70 2.77
Table 4. Retention and cumulative excretion at seven days after administration
(A) 0.8 #m particles intragastric
Carcass*
Faecest
Urinet
0.3
99.43
0.57
3 3 3
27.2 28.7 26.6
72.8 71.3 73.4
(B) ~7Co (NO3) 2 (i) intraperitoneal (ii) sub-cutaneous (iii) intravenous
* Mean % of total STCo recovered. t Mean % of 57Co excreted (urine and faeces). m a d e . M e t a b o l i c c a g e d a t a ( T a b l e 3) s h o w d e c r e a s i n g f a e c a l a n d i n c r e a s i n g u r i n a r y e x c r e t i o n r a t e s w i t h t i m e a f t e r e x p o s u r e . T h e h i g h f a e c a l e x c r e t i o n f r o m t h r e e t o six, a n d f r o m six t o n i n e d a y s is c e r t a i n l y i n f l u e n c e d b y s 7 C 0 3 0 4 p a r t i c l e s d e p o s i t e d o n t h e p e l t , particularly the snout, being ingested during cleaning. Also shown in Table 3 are estimates of t h e r a t e s o f r e m o v a l o f 57C0 b y t r a n s l o c a t i o n t o b l o o d a n d b y m e c h a n i c a l c l e a r a n c e , d e r i v e d
R. J. TALBOTand A. MORGAN
264
Table 5a. Mean whole body retention of ~7Co in mice after the intraperitoneal injection of 57Co(NO3): Time (days) 0 1 2 5 6 7 8 9 12 15
19 29 34 43 55 65 77 89 1(17 111
Fractional retention of 57('0 (%) 100 22.60 12.03 4.43 3.39 3.00 2.54 2.26 1.72 1.41 1.13 0.83 0.73 0.60 11.51 0.46 0,41 I),38 0,34 0.34
Table 5b. Organ distribution of 57Coat death ( 111 days) Organ
59Co content organ/body (% )
Organ Gut Lung Kidney Carcass Hcad Pelt
4.4 3.8 2.2 1.9 58.I 14.1 15.5
from the supplementary experimental data in Table 4 using the procedure described in the main paper. These suggest firstly that the uptake of 57Co from the 57CoaO 4 particles passing through the gut is negligible--only 0.6% of that administered. Secondly a correction was required to account for the ~ 27.5% of soluble material that appears in faeces. Whole body retention measurements, of 57Co after intraperitoneal injection of STCo(NOa)2 are shown in Table 5, together with the organ distribution at death. Measurements of the whole body retention of 57Co for all 10 mice sampled at the final (296 days) time point are shown in Table 6. Close inspection of these data shows in general, a consistent retention pattern between animals with time after exposure. One animal (F) however, showed a much slower clearance than average. No pathological features, or other factors, were found to explain this outlier. DISCUSSION As predicted, the 1.7/~m particles deposited poorly in the pulmonary region. Even if a higher exposure had been used, the results obtained would still have been questionable, because the small fraction deposited may represent the fine 'tail' of the particle size spectrum, with larger particles being preferentially deposited in the nose and upper airways. The deposition of the smaller (0.8 #m) particles was consistent with values reported for SAS/4 mice inhaling aerosols of 239pu02 with similar aerodynamic diameters (Morgan et al., 1981).
Interspecies comparison of lung clearance--VIII
265
Table 6. Whole body 57Co contents of 10 individual mice with time after exposure to 57Co304 Time (days)
Whole body 57Co content (Bq) A
B
C
D
E
F
G
H
I
J
3 9 15 22 29 43 57 71 85 100 148 183 296
1870 1380 1170 1020 915 710 525 405 320 250 95 50 13
1920 1430 1250 1090 980 765 580 455 340 270 100 50 8
1930 1420 1210 1060 935 755 585 455 345 265 100 50 9
2080 1620 1400 1250 1110 850 650 520 375 285 115 55 10
2130 1420 1190 1010 865 645 470 355 260 220 75 40 9
2180 1720 1510 1330 1190 930 775 635 525 415 205 110 23
2220 1620 1390 1220 1120 880 690 545 425 335 135 65 11
2260 1850 1510 1320 1170 910 715 550 415 310 120 60 11
2290 1690 1460 1170 1020 720 545 410 315 245 90 45 10
2360 1790 1610 1440 1280 980 755 570 425 330 120 55 9
Lung at death
11.0
7.4
7.7
8.6
7.8
20.5
9.8
10.0
8.8
7.3
The lungs were the only m a j o r site of 57Co retention (or a c c u m u l a t i o n ) in the body. The activities in other organs tended to reflect the o n g o i n g excretion p a t t e r n with, for instance, high gut c o n t e n t s m a t c h i n g high faecal excretion. The choice of three days as a reference p o i n t for the calculation of estimated lung c o n t e n t s is n o t o p t i m a l for mice exposed in o u r system. At this time the influence of external (pelt) a n d internal (gut) c o n t a m i n a t i o n is still quite large a n d variable with, o n average, only 79 % of the total b o d y activity associated with the lung. We usually normalize to nine day whole b o d y counts, by which time better correlations with the l u n g are achieved. The rates of mechanical clearance in this study ( ~ 1% per day) are consistent with those we have f o u n d previously from mice for other inhaled particles, for instance 1 6 9 y b 2 0 3 ( u n p u b l i s h e d observations) a n d low I A D s of 239puO2 ( M o r g a n e t al., 1984).
REFERENCES Lambert, B. E., Phipps, M. L., Lindop, P. J., Black, A. and Moores, S. R. (1982) Induction of lung tumours in mice following the inhalation of 2aOpuO2. In Radiological Protection--Advances in Theory and Practice, 3rd SRP International Symposium, Vol. 1, pp. 370-375. Morgan, A., Black, A., Moores, S. R., Pritchard, J. N., Walsh, M. and Lambert, B. E. (1981) Alveolar deposition of sized particles of 2a9puO2 in the mouse. Radiat. Res. 93, 85-92. Morgan, A., Black, A. and Moores, S. R. (1984) Retention of 239pu in the mouse lung and estimation of consequent dose following inhalation of sized 23aPuO2. Radiat. Res. 99, 272-284. Morgan, A., Black, A., Moores, S. R. and Lambert, B. E. (1986)Translocation of 239pu in mice followinginhalation of sized 239pUO2. Hlth Phys. 50, 535-539. Talbot, R. J. and Moores, S. R. (1985) The development and interlobar distribution of plutonium-induced pulmonary fibrosis in mice. Radiat. Res. 103, 135-148. Walsh, M., Pritchard, J. N., Black, A., Moores, S. R. and Morgan, A. (1980) The development of a system for the exposure of mice to aerosols of plutonium oxide. J. Aerosol Sci. 11,467-474.
AS 20:2-I
0021 8502/89$3.00+0.00 Pergamon Press plc
Printed in Great Britain.
AN INTERSPECIES COMPARISON OF THE LUNG CLEARANCE OF INHALED MONODISPERSE COBALT OXIDE PARTICLES-P A R T VIII: L U N G C L E A R A N C E O F I N H A L E D C O B A L T O X I D E PARTICLES IN MICE R. J. TALBOTand A. MORGAN E n v i r o n m e n t a l and Medical Sciences Division, Harwell L a b o r a t o r y , Oxfordshire, O X l I 0RA, U.K.
(Received 3 May 1988; and in final form 20 June 1988)
INTRODUCTION We have used mice in our investigations of the toxicity of inhaled radionuclides for the past 10 years. These studies have concerned such topics as the fibrogenicity (Talbot and Moores, 1985), carcinogenicity (Lambert et al., 1982), pulmonary clearance (Morgan et al., 1984) and metabolism (Morgan et al., 1986) of inhaled radionuclides. In the joint study, the small size of mice compared with the other species involved imposed certain additional constraints. Firstly, the larger (1.7 #m) cobalt oxide particles were predicted to be virtually non-respirable by mice owing to their aerodynamic diameter being in excess of 2.5/~m (Morgan et al., 1983). In view of this only a small group was exposed to establish deposition parameters. Secondly, even with the small (0.8/~m) particles, we could only make accurate measurements of radioactivity in organs and excreta on grouped samples. However, individual measurements of 57Co in whole body and lung were possible for the full six months duration of the experiment. MATERIALS AND METHODS Female CBA/H mice from our inbred colony were used in the experiments. They were exposed at 8-10 weeks of age, at which time they weighed approx. 18 g. They were housed in a barrier-maintained animal room and allowed water and pelleted diet ad libitum. Groups of 59 and 5 mice respectively were exposed, nose-only, to the 0.8 and 1.7/~m particles of 57Co304 in the apparatus described by Walsh et al. (1980). Just before administration the particles were resuspended from the collection filters by ultrasonic agitation in Tween 80 solution and aerosols generated from an Acorn nebulizer (Medic-aid, England). Mean aerosol concentrations during the exposures were measured by prezalibrated in-line filters. The aerodynamic diameters of the 0.8/zm particles were measured using a quartz crystal microbalance cascade impactor (QCM, Berkeley instruments, Model C1000-A). Initial alveolar depositions (lADs) of 57Co for each exposure were defined as the mean lung contents of five randomly-selected mice killed after 24 h. At three days after exposure, all 54 mice remaining from the group exposed to the 0.8/~m particles were ~counted. For this purpose they were restrained in polypropylene tubes located mid-way between coaxial 150 mm NaI(TI) detectors. After counting, eight mice were killed by injection with sodium pentobarbitone (Sagatal, May and Baker), the organs removed, and the tissue distribution of 57Co measured. For each of these eight mice, the ratio between whole body and lung measurements of 57Co was calculated. Using the mean ratio, the lung contents of all other mice at three days were estimated. Based on these estimates the remaining mice were stratified into three classes--high, medium and low--containing 15, 16 and 15 mice respectively. At subsequent killing times, groups of three mice were selected by stratified random sampling (one from each class). Three days before killing they were transferred to a metabolism cage (Harvard Bioscience) to enable urine and faeces to be ft;; C r o w n . 261
262
R.J. TALBOT and A. MORGAN
collected separately. After their removal the cage was washed with 1% C o ( N O 3 ) 2 solution, and the washings combined with the contents of the urinary collection vessel. The mice were y-counted before killing and dissection. The 57Co contents of urine and faeces were also measured and expressed as percentages of the mean lung content at death per mouse per day. At the end of the experiment all 10 surviving mice were held in two metabolism cages for seven days before death. Two supplementary experiments were carried out. The objective of the first was to determine the excretion/retention pattern on 57Co up to seven days after the intra-gastric injection of 0.8pm 57Co304 particles. For this purpose a suspension of particles ( ~ 9.2 kBq ml-1) was agitated by ultrasound shortly before administration to eight mice. Their stomachs were intubated with a smooth-ended animal feeding needle (Popper & Sons, Inc.) and 0.1 ml of suspension injected. Four additional aliquots of the suspension were dispensed to check the 57Co content. The mice were immediately placed into two metabolism cages and held there for seven days before death. The 57Co contents of urine, faeces and carcass were measured. The aim of the second supplementary experiment was to study the excretion of 57Co administered to three groups of four mice by (i) intraperitoneal, (ii) subcutaneous and (iii) intravenous (tail vein) injection. For this purpose the 1% aqueous solution of 5 7 C o ( N O 3 ) 2 6 H 2 0 (3.2 MBq m1-1) supplied was diluted approx. 50-fold in physiological saline. Aliquots of 0.2 ml were injected and the animals y-counted immediately, then held in metabolism cages for seven days before death. Three further mice were given an intraperitoneal injection, and whole body measurements of 57Co made for three months. Subsequently the organ contents of 57Co at death were measured. RESULTS
The 0.8 #m particles were administered at a mean aerosol concentration of 1.2 kBq 1- 1 for 135 min. This resulted in a mean lAD of 1.8 + 0.11 kBq. The activity median aerodynamic diameter of the aerosol was 1.44 #m (ag 1.16). The 1.7 #m particles were only poorly deposited in the alveolar region, an aerosol concentration of 0.29 kBq 1-1 for 40 min yielding an lAD of only 0.012 kBq. At three days after exposure the mean estimated whole body content of 57Co in the mice was 2.08 +0.043 kBq (S.E.M.; n = 54). The mean lung/whole body ratio for the mice killed after three days was 85.6+ 1.7% (S.E.M.: n=8). From this ratio the mean estimated lung content of the 54 mice at three days was 1.78 kBq. Estimated fractional retentions of 57Co in both the lung and the whole body are shown in Table 1. The organ-distributions at death of these mice and of those killed after only one day, are shown in Table 2. Beyond 15 days all the organs, except the lungs, were combined before counting, thus standard errors were not available. At 296 days the 57Co contents were too low to permit meaningful estimates to be Table 1. Estimated fractional lung and whole body retentions of SYCo for mice killed with time after inhalation of 0.8 ,um 57C0304 particles Time (days)
n
3 6 9 15 22 29 43 57 71 85 I00 148 183 296
8 3 3 3 3 3 3 3 3 3 3 3 3 10
Whole body Mean S.E.M. 100 74.04 61.05 50.53 46.76 40.23 32.19 22.32 15.34 12.58 5.28 2.54 0.54
1.22 1.46 1.81 1.61 0.99 1.75 0.76 1.10 0.63 0.20 0.11 0.06
Mean
Lung S.E.M.
100.00 89.13 82.64 70.48 58.82 52.77 46.83 37.41 25.94 16.05 13.74 5.91 2.84 0.55
+ 2.04 ± 3.06 _+ 1.28 + 1.01 ± 1.98 + 2.15 ___+0.71 ± 1.93 ± 0.99 __+2.34 + 0.81 ± 0.25 __+0.19 _+_0.07
Interspecies comparison of lung clearance--VIII
263
Table 2. Organ contents after inhalation of 0.8 gm 57Co304 particles as a percentage of the total in animal Time (days)
n
Lung
TB/LN*
1
5
3
8
6
3
9
3
15 22 29 43 57 71 85 98 148 183 296
3 3 3 3 3 3 3 3 3 3 10
47.77 +3.61 78.92 __+1 , 4 4 90.59 __+1 . 2 9 94.44 +0.71 97.12 98.11 98.46 98.74 98.34 98.30 97.40 97.68 96.60 93.57 .
Mean % of activity in animal (+S.E.M.) GI tractt Liver Pelt Head
0.42 ___0.036 0.35 _.+0.053 0.27 __.0.017 0.33 +0.050 0.21 0.22 0.36 0.30 0.35 0.44 0.74 0.51 0.49 1.33 . .
15.53 +1.35 2.15 __+0,20 0.72 +0.082 0.49 +0.054 0.35 0.32 0.25 0.25 0.14 0.25 0.46 0.31 0.18 0.69 .
0.14 +0.028 0.20 +0.029 0.16 +0.031 0.17 +0.008 0.12 0.10 0.11 0.12 0.14 0.16 0.24 0.33 0.23 0.78 .
35.73 +3.47 17.99 _+1 . 4 8 7.91 _ 1.30 4.32 +0.69 1.95 0.88 0.56 0.25 0,59 0.48 0.43 0.64 0.86 1.50 .
0.15 +0.082 0.13 +0.019 0.17 __+0.045 0.14 +0.053 0.17 0.30 0,18 0.16 0.15 0.18 0.45 0.31 0.74 0.92
Carcass 0.26 +0.034 0.27 +0.036 0.18 __+0.025 0,11 +0.028 0.08 0.07 0.08 0.18 0.29 0.19 0.28 0.22 0.90 1.21
* Includes: trachea, heart, extrapulmonary bronchi and thoracic lymph nodes. t Includes: gut, spleen, kidneys and urinogenital tract.
Table 3. Metabolism summary: combined results from three mice per point as a percentage of contemporary lung content (10 mice at 296 days) Time From 3 6 12 19 26 40 54 68 82 97 145 180 289
(days) To
Faeces/ lung (% day- I)
Urine/ lung (% day- i)
Mechanical clearance (% day- i)
Translocation (% day- i)
6 9 15 22 29 43 57 71 85 100 148 183 296
8.81 4.29 2.27 2.03 1.61 1.57 1.46 1.46 1.85 1.46 1.45 1.21 1.31
0.68 0.60 0.50 0.45 0.53 0.49 0.55 0.59 0.63 0.73 1.00 1.23 2.01
8.55 4.06 2.08 1.86 1.41 1.38 1.25 1.24 1.61 1.18 1.07 0.74 0.55
0.94 0.83 0.69 0.62 0.73 0.68 0.76 0.81 0.87 1.01 1.38 1.70 2.77
Table 4. Retention and cumulative excretion at seven days after administration
(A) 0.8 #m particles intragastric
Carcass*
Faecest
Urinet
0.3
99.43
0.57
3 3 3
27.2 28.7 26.6
72.8 71.3 73.4
(B) ~7Co (NO3) 2 (i) intraperitoneal (ii) sub-cutaneous (iii) intravenous
* Mean % of total STCo recovered. t Mean % of 57Co excreted (urine and faeces). m a d e . M e t a b o l i c c a g e d a t a ( T a b l e 3) s h o w d e c r e a s i n g f a e c a l a n d i n c r e a s i n g u r i n a r y e x c r e t i o n r a t e s w i t h t i m e a f t e r e x p o s u r e . T h e h i g h f a e c a l e x c r e t i o n f r o m t h r e e t o six, a n d f r o m six t o n i n e d a y s is c e r t a i n l y i n f l u e n c e d b y s 7 C 0 3 0 4 p a r t i c l e s d e p o s i t e d o n t h e p e l t , particularly the snout, being ingested during cleaning. Also shown in Table 3 are estimates of t h e r a t e s o f r e m o v a l o f 57C0 b y t r a n s l o c a t i o n t o b l o o d a n d b y m e c h a n i c a l c l e a r a n c e , d e r i v e d
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264
Table 5a. Mean whole body retention of ~7Co in mice after the intraperitoneal injection of 57Co(NO3): Time (days) 0 1 2 5 6 7 8 9 12 15
19 29 34 43 55 65 77 89 1(17 111
Fractional retention of 57('0 (%) 100 22.60 12.03 4.43 3.39 3.00 2.54 2.26 1.72 1.41 1.13 0.83 0.73 0.60 11.51 0.46 0,41 I),38 0,34 0.34
Table 5b. Organ distribution of 57Coat death ( 111 days) Organ
59Co content organ/body (% )
Organ Gut Lung Kidney Carcass Hcad Pelt
4.4 3.8 2.2 1.9 58.I 14.1 15.5
from the supplementary experimental data in Table 4 using the procedure described in the main paper. These suggest firstly that the uptake of 57Co from the 57CoaO 4 particles passing through the gut is negligible--only 0.6% of that administered. Secondly a correction was required to account for the ~ 27.5% of soluble material that appears in faeces. Whole body retention measurements, of 57Co after intraperitoneal injection of STCo(NOa)2 are shown in Table 5, together with the organ distribution at death. Measurements of the whole body retention of 57Co for all 10 mice sampled at the final (296 days) time point are shown in Table 6. Close inspection of these data shows in general, a consistent retention pattern between animals with time after exposure. One animal (F) however, showed a much slower clearance than average. No pathological features, or other factors, were found to explain this outlier. DISCUSSION As predicted, the 1.7/~m particles deposited poorly in the pulmonary region. Even if a higher exposure had been used, the results obtained would still have been questionable, because the small fraction deposited may represent the fine 'tail' of the particle size spectrum, with larger particles being preferentially deposited in the nose and upper airways. The deposition of the smaller (0.8 #m) particles was consistent with values reported for SAS/4 mice inhaling aerosols of 239pu02 with similar aerodynamic diameters (Morgan et al., 1981).
Interspecies comparison of lung clearance--VIII
265
Table 6. Whole body 57Co contents of 10 individual mice with time after exposure to 57Co304 Time (days)
Whole body 57Co content (Bq) A
B
C
D
E
F
G
H
I
J
3 9 15 22 29 43 57 71 85 100 148 183 296
1870 1380 1170 1020 915 710 525 405 320 250 95 50 13
1920 1430 1250 1090 980 765 580 455 340 270 100 50 8
1930 1420 1210 1060 935 755 585 455 345 265 100 50 9
2080 1620 1400 1250 1110 850 650 520 375 285 115 55 10
2130 1420 1190 1010 865 645 470 355 260 220 75 40 9
2180 1720 1510 1330 1190 930 775 635 525 415 205 110 23
2220 1620 1390 1220 1120 880 690 545 425 335 135 65 11
2260 1850 1510 1320 1170 910 715 550 415 310 120 60 11
2290 1690 1460 1170 1020 720 545 410 315 245 90 45 10
2360 1790 1610 1440 1280 980 755 570 425 330 120 55 9
Lung at death
11.0
7.4
7.7
8.6
7.8
20.5
9.8
10.0
8.8
7.3
The lungs were the only m a j o r site of 57Co retention (or a c c u m u l a t i o n ) in the body. The activities in other organs tended to reflect the o n g o i n g excretion p a t t e r n with, for instance, high gut c o n t e n t s m a t c h i n g high faecal excretion. The choice of three days as a reference p o i n t for the calculation of estimated lung c o n t e n t s is n o t o p t i m a l for mice exposed in o u r system. At this time the influence of external (pelt) a n d internal (gut) c o n t a m i n a t i o n is still quite large a n d variable with, o n average, only 79 % of the total b o d y activity associated with the lung. We usually normalize to nine day whole b o d y counts, by which time better correlations with the l u n g are achieved. The rates of mechanical clearance in this study ( ~ 1% per day) are consistent with those we have f o u n d previously from mice for other inhaled particles, for instance 1 6 9 y b 2 0 3 ( u n p u b l i s h e d observations) a n d low I A D s of 239puO2 ( M o r g a n e t al., 1984).
REFERENCES Lambert, B. E., Phipps, M. L., Lindop, P. J., Black, A. and Moores, S. R. (1982) Induction of lung tumours in mice following the inhalation of 2aOpuO2. In Radiological Protection--Advances in Theory and Practice, 3rd SRP International Symposium, Vol. 1, pp. 370-375. Morgan, A., Black, A., Moores, S. R., Pritchard, J. N., Walsh, M. and Lambert, B. E. (1981) Alveolar deposition of sized particles of 2a9puO2 in the mouse. Radiat. Res. 93, 85-92. Morgan, A., Black, A. and Moores, S. R. (1984) Retention of 239pu in the mouse lung and estimation of consequent dose following inhalation of sized 23aPuO2. Radiat. Res. 99, 272-284. Morgan, A., Black, A., Moores, S. R. and Lambert, B. E. (1986)Translocation of 239pu in mice followinginhalation of sized 239pUO2. Hlth Phys. 50, 535-539. Talbot, R. J. and Moores, S. R. (1985) The development and interlobar distribution of plutonium-induced pulmonary fibrosis in mice. Radiat. Res. 103, 135-148. Walsh, M., Pritchard, J. N., Black, A., Moores, S. R. and Morgan, A. (1980) The development of a system for the exposure of mice to aerosols of plutonium oxide. J. Aerosol Sci. 11,467-474.
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