DEPOSITION AND CLEARANCE OF FINE PARTICLES IN THE HUMAN RESPIRATORY TRACT

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1 PII: S0003^t878(96) Ann. oup. Hyg., Vol. 41, Supplement 1, pp , British Oupational Hygiene Soiety Published by Elsevier Siene Ltd. All rights reserved Printed in Great Britain /97 $ Inhaled Partiles VIII DEPOSITION AND CLEARANCE OF FINE PARTICLES IN THE HUMAN RESPIRATORY TRACT C. Roth, W. G. Kreyling, G. Sheuh, B. Bush and W. Stahlhofen National Researh Centre for Environment and Health, Institute for Inhalation Biology, Ingolstadter Landstr. 1, Neuherberg, Germany INTRODUCTION Total deposition of respirable partiles in the human respiratory trat is well determined by experimental data and model alulations whereas regional deposition is still under disussion, partiularly in the size range from urn partile diameter. Experimental data on regional deposition of radiolabelled aerosol partiles an be derived from gamma amera images on the basis of the partile learane kinetis during the first few days after inhalation, sine the limited resolution of the planar image allows no separation between the peripheral and the bronhial airways. When partiles are deposited in the human respiratory trat, two distint phases of learane from the thorax are usually observed: a fast leared fration during the first hours after inhalation followed by muh slower learane. It is generally assumed that the fast phase, ompleted within about 24 h, represents predominantly muoiliary learane of partiles deposited in the traheobronhial tree, whereas the slow phase represents predominantly learane from the alveolar region (Lippmann, 1977; Stahlhofen etal., 1980). Nevertheless, during reent years the assumption that there also exists a slow leared omponent from the traheobronhial region has been onfirmed by a large number of experiments (Sheuh, 1991; Stahlhofen et al, 1994). Reently, a new radio-aerosol "Tehnegas" (TG; Tetley Manufaturing Ltd, Luas Heights, Australia) was developed for lung ventilation sans in nulear mediine. "Tehnegas" (TG) is a ondensation type aerosol onsisting of hydrophobi inert graphite partiles. For the prodution of TG \i\ of Na" m TO 4 in saline is put into the avity of a graphite ruible whih is dried at C. Thereafter the avity of the ruible is heated to 2500 C in an atmosphere of pure argon for 5 s suh that arbon as well as the salt and 99m T evaporates, followed by ondensation during ooling. This proedure is similar to the prodution of the C-60 moleules, named bukminster-fullerenes (Kroto et al., 1985). Therefore, it was assumed that TG onsists of ultrafine spherial partiles whih are formed via homogenous ondensation from fullerene vapor at temperatures > 500 C. More reent investigations have shown that these ultrafine partiles agglomerate rapidly to fine partiles (Lemb et al., 1993). The latter is in agreement with the fat that the distribution of deposited TG applied to the lungs of normal subjets was found in the entire ventilated lungs, that is, it is transported in the lungs like a gas. 503

2 504 C. Roth et al. The aim of this study was the appliation of the new radio-aerosol TG in order to determine its lung deposition and learane kinetis from the lungs. Sine the median diameter of this aerosol was reported to be 0.1 um or even less it would provide regional deposition data in a size range laking information (Roth et al., 1994). A unique feature of this aerosol is its high speifi 99m T radioativity of > 100 MBq/L aerosol reported to be tightly bound to the partile matrix (Burh et al., 1986) allowing gamma amera analysis after single breath inhalation. MATERIALS AND METHODS The partile size distribution of the TG-aerosol was determined with a Differential Mobility Analyser (DMA; Hauke GmbH, A-4810 Gmunden, Austria). To balane the prodution effiieny of the generator using 50 ul Na" m TO 4 saline, the whole aerosol of 6 L volume produed during one run was olleted on a filter. The 99m T ativity of the initial 50 ^il sample was ompared to that of the filter and the ruible. To investigate the salt ontent of the aerosol partiles, the filter was washed with distilled water and the Na + -ion onentration was determined using a Na + -ion sensitive eletrode (PHM 95, Radiometer, Copenhagen) to alulate the sodium hloride mass. To test the hygrosopi behaviour of the TG-partiles a Tandem Differential Mobility Analyser was used, onsisting of two DMAs and ontrolled humidifiers for the sheath air and aerosol flow of the seond DMA. With the first DMA, a monodisperse fration of the polydisperse TG-aerosol was separated and subsequently moistened to a relative humidity RH > 90%. The altered size distribution due to the growth of the partiles related to their hygrosopi ontent was determined by the seond DMA (Bush et al., 1994). Six healthy non-smokers (age 46 ± 9 years, 1 female, 5 males) with normal lung funtion volunteered for the measurements of lung deposition and retention with an inhalation apparatus desribed before (Sheuh et al., 1989). After several breaths of lean air the subjet started the inhalation of the aerosol from the "Tehnegas" generator for one single breath. The subjet inhaled with a onstant flow rate of 250 m 3 s -1 and with a tidal volume of 1000 m 3. Three subjets performed a breath-hold of 10 s at the end of inhalation, the other three exhaled immediately after inhalation without any breath-hold. A system of four shielded and ollimated Nal(Tl) detetors (lung ounter) has been used for the determination of the 99m T ativity of the partiles present in the head, hest and stomah (Stahlhofen et al., 1980). The ativity was measured immediately after inhalation and at subsequent intervals up to 30 h. Total deposition was alulated from the lung deposit, the exhaled " m T ativity olleted on an exhalation filter and the 99m T ativity of a 250 m 3 sample drawn from the TG-generator onto a filter. To determine partile dissolution inluding TG-partile disintegration and leakage of 99m T from TG, urine was measured after quantitative sampling for 24 h using the lung ounter. RESULTS The size distribution of the TG-aerosol is plotted in Fig. 1. Charaterizing this

3 Fine partiles in the human respiratory trat 505 > O 0 or 0 - -TG partiles -*-grown fration (0.13 /L/m) - -grown fration (0.25 fjrr\) ^graphite J i A A A JL /^r^t^r^-^ ^^^^^A j i i i ' ' ' partile diameter d, nm Fig. 1. Size distribution of TG and the graphite aerosol (without Na" m TO 4 saline). Additionally, two distributions of 0.13 and 0.25 urn monodisperse frations grown in the humid atmosphere (ount mode diameters of the frations seleted by the first DMA are indiated by arrows). polydisperse distribution by a log-normal distribution yielded a ount median diameter (CMD) of 0.13 [Am, a mass median diameter (MMD) of 0.55 ^m and a geometri standard deviation (GSD) of o g = 2.0. For omparison the size distribution of the graphite aerosol without Na" m TO 4 -saline in Fig. 1 presents the same distribution for partiles < 200 nm, but does not show the shoulder at 300 nm. The size distribution showed the same ount median diameter but a muh smaller geometri standard deviation of o g = 1.4. Figure 1 gives also the size distributions of initially monodisperse TG-partile frations after hygrosopi growth in humid atmosphere (RH > 90%). Both frations of 0.13 and 0.25 urn partiles seleted by the first DMA showed onsiderable partile growth of about a fator of 2 in diameter. Table 1 gives the balane of radioativity and the partition of NaCl with respet to the entire aerosol of 6 1. volume produed during one run. Sodium hloride is Table 1. Balane of radioativity and NaCl during TG-aerosol prodution 50 ul/sample of Na TO 4 -saline TG-partiles on filter Cruible Wall losses Relative " m T-ativity, % Mass of sodium hloride, ug

4 506 C. Roth et al. g a> *-> CD ^ D) CCD H 0.7 A with breath-hold without breath-hold i 10 T time after inhalation, h i Fig. 2. Intrapulmonary retention of TG-partiles obtained from all six volunteers, data of eah subjet are fitted with a funtion of 2 exponential terms (note: the vertial axis is interseted). ompletely evaporated and ondensed partially on the aerosol partiles. It an be washed off in distilled water. The number onentration of the TG-aerosol of 6 1. volume was measured to be 2 x 10 7 m" 3 and, therefore, the alulated mass of arbon of the TG partiles produed during one run is about the same as the mass of NaCl given in Table 1. Monitoring the aerosol onentration photometrially in front of the mouth of the volunteer showed an at least two-fold inrease of the photometer signal of the exhaled air ompared to that of the inhaled air onsistent with the hygrosopi growth of the exhaled TG aerosol due to its NaCl-ontent as desribed above. Total deposition DE with breath-hold (DE = 47 ± 4%) is about twie the value of that without breath-hold (DE = 27 ± 4%). The new ICRP model (ICRP 66, 1994) provides DE = 29.3% for a log-normal size distribution with a MMD of 0.55 urn, a GSD of o g = 2.0, at the same breathing onditions. Figure 2 shows lung retention urves obtained from all six subjets to demonstrate the rather small intersubjet variability and the fast v. slow phase of learane. All data are orreted for physial deay of 99m T. Fitting the data obtained from all six volunteers with 2 exponential terms, yielded a mean lung retention (± SEM) of: {(0.086 ± 0.024) exp((1.03 ± 0.79)t)} + {(0.91 ± 0.019) exp((0.003 ± )t)} Rates are given in h orresponding to half-lives of 1.6 h and 228 h (9 d). The dissolution of " m T ativity from the partiles as determined from urine samples proved to be relatively onstant at 9 ± 2.1% of the inhaled 99m T ativity

5 Fine partiles in the human respiratory trat *: h-retention ^ ^ long-term retention m dissolution o v» > <D <D E I JO o 't <D O T C\J Fig h retention, long-term retention and dissolution for six subjets. for all six subjets. Dissolution ourred predominantly during the first 6 h after inhalation. Figure 3 shows the retained fration 24 h after inhalation and the dissolved fration for eah subjet. Estimation of the fast leared partile fration as the differene between partile deposition v. partile dissolution and 24 h retention yielded 5.5 ± 3.5%. DISCUSSION TG-partiles are not ultrafine but agglomerates with a polydisperse size distribution of a ount median diameter of the distribution of 0.13 (j,m and a mass median diameter of 0.55 um. The TG-partiles ontain NaCl. As a result, they grow in the humid atmosphere of the respiratory trat at least an order of magnitude in mass (more than a fator of 2 in diameter). This was indiated by aerosol photometry of the in- and exhaled aerosol and shown by the Tandem-DMA measurements. Due to this dynami behaviour, the distribution of the deposited TG-partiles in the lungs is diffiult to predit. Aording to the ICRP model (ICRP 66, 1994) total deposition does not vary very muh for mass median diameters between um. Therefore, the measured total deposition agrees well with the predited values for both the dry mass median partile diameter and the estimated diameter after partile growth. Partiles in the diameter range between 0.2 and 1 um have very low intrinsi motion and are therefore onsidered as a nondiffusive gas. Based on these measurements and taking the growth of TG

6 508 C. Roth et al. partiles into aount, it is likely that partiles will be deposited in all regions ventilated during the single breath maneuver. There is modest TG partile dissolution in the lungs whih either might reflet leakage of the radio-traer or partile disintegration and dissolution. In addition to the 24 h retention and TG dissolution, the long-term retention is given in Fig. 3 for eah subjet. The latter is the long-term retention fration of a funtion of 2 exponential terms fitting the data of eah subjet. Note that the long-term retention value is not neessarily ompatible with the long-term fration and the orresponding A-value reported earlier (Stahlhofen et al., 1980) sine the latter would require lung retention measurements of more than 3 days. Interestingly, the long-term retentions of those subjets performing a breath-hold were signifiantly smaller than those of the subjets performing no breath-hold. Aordingly, fast partile learane was deteted after breath-hold while virtually no fast partile transport was observed for the other subjets, see Fig. 3. During breath-hold, deposition of these fine TG partiles inreased throughout the lungs as shown by the deposition data given above. This is true partiularly in small airways ontributing to the fast partile learane. Therefore, the fast leared fration of 6.0 ± 2.6% is more distint in those subjets whih performed a breath-hold when ompared to the others. The ICRP model (ICRP 66, 1994) predits that the fast leared fration represents only half of the bronhiolar deposition, the other half is long-term retained. Based on our data of 5.5% of fast-leared partiles, 11% deposited 99m TG partiles in the bronhiolar region, a bronhiolar dose as high as 330 usv/mbq is obtained. With the reommended loading ativity of MBq and an inhaled fration of 10% of the produed aerosol, a dose of 7-14 msv is delivered to the airways (Bailey, 1996). This high dose needs areful onsideration. REFERENCES Bailey, M. R. (1996) National Radiologial Protetion Board, Didot, U.K. (personal ommuniation). Burh, W. M., Sullivan, P. J. and MLaren, C. J. (1986) Tehnegas a new ventilation agent for lung sanning. Nul. Med. Commun. 7, Bush, Ferron, G., Karg, E., Silberg, A. and Heyder, J. (1994) The growth of atmospheri partiles in moist air. J. Aerosol Si. 25 (Suppl. 1), International Commission of Radiologial Protetion (1994) Human Respiratory Trat Model for Radiologial Protetion: a report of a task group of the ICRP. Elsevier Siene Ltd, Oxford (ICRP publiation 66). Kroto, H. W., Heath, J. R., O'Brien, S. C, Curl, R. F. and Smalley, R. E. (1985) C-60: bukminsterfullerene. Nature 318, Lemb, M., Oei, T. H., Eifert, H. and Giinther, B. (1993) Eur. J. Nul. Med. 20, Lippmann, M. (1977) Handbook of Physiology Reation to Environmental Agents (Edited by Lee, D. H. K.), p Am. Physiol. So, Bethesda. Roth, C, Sheuh, G. and Stahlhofen, W. (1994) Clearane measurements with radioatively labelled ultrafine partiles. Ann. oup. Hyg. 38 (Suppl. 1), Sheuh, G., Gebhart, J., Heigwer, G. and Stahlhofen, W. (1989) A new devie for human inhalation studies with small aerosol boluses. /. Aerosol Si. 20, Sheuh, G. (1991) Dispersion, deposition and learane of aerosol partiles in the human respiratory airways. Ph.D thesis, J. W. Goethe-University, Frankfurt/M. Stahlhofen, W., Gebhart, J. and Heyder, J. (1980) Experimental determination of the regional deposition on aerosol partiles in the human respiratory trat. Am. ind. Hyg. Asso. J. 41, Stahlhofen, W., Sheuh, G. and Bailey, M. R. (1994) Measurement of the traheobronhial learane of partiles after aerosol bolus inhalation. Ann. oup. Hyg. 38 (Suppl. 1),