Annex B. Dosimetry 

B.1. Ultrafine Disposition 

Table B-1. Ultrafine disposition in humans. 

Reference Study Group Aerosol Study Protocol Observations 

Mills et 

al.(2006, 

088770) 

Healthy 

nonsmokers 

(5 M, 5 F; 

21-24 yr) 

Carbon - 

99mTc 

108 nm 

CMD 

(σg = 2.2) 

Technegas 

Generator 

Lung activity in the lung was measured at 0, 1, 

and 6 h post aerosol inhalation. 

On avg, lung activity decreased 3.2 ± 0.7% during the first h and 

1.2 ± 1.7% over the next 5 h. With 95.6% of the particles in the lungs 

at 6 h post inhalation and no accumulation of radioactivity detected 

over the liver or spleen, findings did not support rapid translocation 

from the lungs into systemic circulation. 

Möller et al. 

(2008) 

Healthy 

nonsmokers 

(n = 9; 

50 ± 11 yr) 

Smokers 

(n = 10; 

51 ± 10 yr) 

COPD patients 

(n = 7; 

69 ± 10 yr) 

Carbon - 

99mTc 

~100 nm 

CMD 

Technegas 

Generator 

On two separate occasions, subjects inhaled 

100 mL aerosol boli to target front depths of 

150 and 800 mL into the lungs to target the 

airways and alveoli, respectively. Retention 

measured at 10 min, 1.5, 5.5, 24 and 48 h 

post inhalation. Isotope (99mTc) leaching from 

particles assessed via filters in saline, blood, 

and urine. 81mKr utilized to assess ventilation.

Shallow airways boli-Total deposition in airways (shallow boli) similar 

between groups. Pattern of deposition was significantly more central 

in the healthy subjects which was thought due to non-uniform 

ventilation distribution in smokers and COPD patients as visualized 

by gamma-camera scans. Airway retention after 1.5 h was 

significantly lower in healthy subjects (89 ± 6%) than smokers (97 ± 

3%) or COPD patients (96 ± 6%). At 24 and 48 h, retention 

significantly remained higher in COPD patients (86 ± 6% and 82 ± 

6%) than healthy subjects (75 ± 10% and 70 ± 9%). 

Deep alveolar boli - Total deposition in alveoli (deep boli) significantly 

greater in smokers (64 ± 11%) and COPD patients (62 ± 5%) than 

healthy subjects (50 ± 8%). Alveolar retention of particles similar at all 

times between groups. For example, at 48 h, 97 ± 3% in healthy 

subject, 96 ± 3% in smokers, and 96 ± 2% in COPD patients. 

Retention at 24 and 48 correlated with isotope leaching, suggesting 

that the small amount of clearance primarily reflected the 

disassociation of 99mTc from the particles with little transport of 

particles from the lungs. 

Wiebert et al. 

(2006, 

156154) 

Subjects having 

varied health 

status (9M, 6F; 

46-74 yr) 

6 healthy 

5 asthmatic 

4 smokers 

Carbon - 

99mTc 

87 nm CMD 

(σg = 1.7) 

Technegas 

Generator 

Technegas system was modified to reduce 

leaching of 99mTc radiolabel from particles. 

The avg tidal volume during aerosol inhalation 

was 1.8 L (range 0.8-3.3). Activity in chest 

region measured at 0, 2, 24, 46, and 70 h after 

inhalation. Leaching assessed in vitro and via 

urine collection. 

Lung function not significantly different between healthy and affected 

lungs. The aerosol deposition fraction was 41 ± 10%. Lung retention 

was 99 ± 3%, 99 ± 5%, and 99 ± 10% at 24, 46, and 70 h post 

inhalation. Cumulative in vitro leaching by 70 h was 2.6 ± 0.96%. 

Except for radiotracer leaching from particles (1.0 ± 0.6% of initially 

deposited activity in urine by 24 h), there was not significant 

clearance from the lungs by 70 h. Individual leaching was not 

correlated with individual retention. 

Wiebert et al. 

(2006, 

157146) 

Healthy 

subjects (4M, 

5F; 56 ± 9 yr) 

Asthmatics (2M, 

3F; 59 ± 6 yr) 

Control (1M; 

50 yr) 

Carbon - 

99mTc 

34 nm CMD 

(σg = 1.5) 

Technegas 

Generator 

Slow deep aerosol inhalations with 10 s breath 

hold. Mean inhalation time of 6 min. Control 

subject inhaled aerosol with loosely bound 

radiolabel. Retention scans at 10 min, 60 min, 

100 min, and 24 h post inhalation. Leaching 

assessed in vitro and via collection of blood 

and urine. 

Avg deposition fraction of 60 ± 17% which was correlated with tidal 

volume during aerosol inhalation (p = 0.01). Activity excreted in urine 

over 24-h post inhalation was 51% in the control subject (high 99mTc 

disassociation) and 3.6 ± 0.9% of deposited activity. In the blood of 

the control subject, activity was 30%, 31%, and 5% of the deposited 

activity at 20 min, 80 min, and 24-h (respectively), whereas it was 

only 0.9 ± 0.6%, 1.1 ± 0.4%, and 1.5 ± 0.5% the other 13 subjects at 

these times. Lung retention in the control subject was 30% at 1-h and 

18% at 24 h. In the remainder of subjects, lung retention was 

approximately 100% through 24 h. 

 

Note: Hyperlinks to the reference citations throughout this document will take you to the NCEA HERO database (Health and 

Environmental Research Online) at http://epa.gov/hero. HERO is a database of scientific literature used by U.S. EPA in the process of 

developing science assessments such as the Integrated Science Assessments (ISA) and the Integrated Risk Information System (IRIS). 

December 2009 B-1 
Table B- 2. Ultrafine disposition in animals. 

Reference Study Group Aerosol Study Protocol Observations 

Bermudez et 

al.(2004, 

056707) 

Fischer 344 rats, 

females (6 wk) 

B3C3F1 mice, 

females (6 wk) 

Hamsters, 

females (6 wk) 

TiO2: 1.29-1.44 μm 

MMAD 

(σg = 2.46-3.65), 21 

nm primary particles 

Animals exposed 6 h/day, 5 day/wk, 

for 13 wk to 0.5, 2 and 10 mg/m3

. 

Control animals exposed to filtered 

air. Animals sacrificed at 0, 4, 13, 

26, and 56 (49 for hamsters) postexposure. Groups of 25 animals per 

species and time point. 

TiO2 pulmonary retention half-times for the low-, mid-, and highexposure groups, respectively: 63, 132, and 365 days in rats; 48, 40, 

and 319 days in mice; and 33, 37, and 39 days in hamsters. 

Burden of TiO2 in lymph nodes increase with time postexposure in 

mid- and high-dosed rats; in high-dosed mice; but was unaffected in 

hamsters at any time or dosage group. In high-exposure groups of 

mice, epithelial permeability remained elevated (~2× control groups) 

out to 52 wk without signs of recovery. Epithelial permeability was 

3-4× control in high exposed rats through 4 wk post exposure, but 

approached control by 13 wk . Epithelial permeability was unaffected 

in all groups of hamsters. 

Chen et al. 

(2006, 

087947) 

Sprague-Dawley 

male rats 

(220 ± 20 g) 

Polystyrene 

125I radiolabel 

Ultrafine: 56.4 nm 

Fine: 202 nm 

Intratracheal instillation of particles 

in healthy rats or those pretreated 

with LPS (12 h before particle 

instillation). Healthy rats sacrificed 

between 0.5-2 h and at 24 or 48 h 

post-instillation. LPS treated rats 

were sacrificed 0.5-2 h 

post-instillation. 

In healthy rats, there were no marked differences in lung retention or 

systemic distribution between the ultrafine and fine particles. Results 

for healthy animals focused on ultrafine particles which were 

primarily retained in lungs (72 ± 10% at 0.5-2 h; 65 ± 1% at 1 day; 

62 ± 5% at 5 days). Initially, there was rapid particle movement into 

the blood (2 ± 1% at 0.5-2 h; 0.1 ± 0.1% at 5 days) and liver (3 ± 2% 

at 0.5-2 h; 1 ± 0.1% at 5 days). At 1 day post-instillation, about 13% 

of the particles where in the urine or feces. Following LPS treatment, 

ultrafine accessed the blood (5 vs. 2%) and liver (11 vs. 4%) to a 

significantly greater extent than fine particles. 

Geiser et al. 

(2005, 

087362) 

Also included 

in in vitro 

studies 

Wistar rats 20 

adult males 

(250 ± 10 g) 

TiO2 (22 nm CMD, 

1.7 σg) 

Spark generated 

0.11 mg/m3

7.3 × 106 

particles/cm3

Rats exposed 1-h via endotracheal 

tube while anesthetized and 

ventilated at constant rate. Lungs 

fixed at 1 or 24-h postexposure. 

Distributions of particles among lung compartments followed the 

volume distribution of compartments and did not differ significantly 

between 1 and 24-h post-inhalation. On avg, 79.3 ± 7.6% of 

particles were on the luminal side of the airway surfaces, 4.6 ± 2.6% 

in epithelial or endothelial cells, 4.8 ± 4.5% in connective tissues, 

and 11.3 ± 3.9% within capillaries. Particles within cells were not 

membrane-bound. 

Kapp et al. 

(2004, 

156624) 

Charles River 

rats 

5 young adult 

male 

(250 ± 10 g) 

TiO2 (22 nm CMD, 

1.7 σg) 

Spark generated 

Rats exposed 1-h via endotracheal 

tube while anesthetized and 

ventilated at constant rate. Lungs 

fixed immediately postexposure. 

Of particles in tissues, 72% were aggregates of 2 or more particles; 

93% of aggregates were in round or oval shape aggregates, 7% 

were needle-like. The size distribution of particles in lung tissues (29 

nm CMD, 1.7 σg) was remarkably similar to the aerosol; the small 

discrepancy may have been due to differences sizing techniques. A 

large 350 nm aggregate was found in a type II pneumocyte, a 37 nm 

particle in a capillary close to the endothelial cells, and a 106 nm 

particle within the surface-lining layer close to the alveolar 

epithelium. 

December 2009 B-2 
Table B- 3. In vitro studies of ultrafine disposition. 

Reference Animal Particles Study Protocol Observations 

Edetsberger 

et al. (2005, 

155759) 

Human cervix 

carcinoma cells 

(HeLa cells) 

Polystyrene spheres 

(0.020 μm) 

Cells incubated with polystyrene particles 

having negative surface charges. Cell 

cultures were naïve or treated with 

Genistein or Cytochalasin B (CytB) prior 

to particle application. Genistein inhibits 

endocytotic processes, expecially 

caveolae internalization. CytB inhibits 

actin polymerization and phagocytosis. 

Particles translocated into cells by first measurement (~1 min 

after particle application) independent of treatment group. In 

naïve cells, agglomerates of 88-117 nm were seen by 15-20 

min and of 253-675 nm by 50-60 min after particle 

application. Intracellular aggregates thought to be result from 

particle incorporation into endosomes or similar structures. In 

treated cells, only a small number of agglomerates (161-308 

nm) were found and only by 50-60 min. At 50-60 min, 90% 

and 98% of particles were in the 20-40 nm range in naïve and 

treated cells, respectively. Particles did not translocate into 

dead cells, rather they attached to outside of the cell 

membrane. 

Geiser et al. 

(2005, 

087362) 

Also included 

inhalation 

study 

Porcine lung 

macrophages (106 

cell/mLuman red 

blood cells (RBC; 8 

× 106 cells/mL) 

Fluorescent 

polystyrene spheres 

(0.078, 0.2, and 

1 μm) 

Gold shheres 

(0.025 μm) 

Cells cultured for 4 h with each sized 

polystyrene spheres. RBC were 

employed as a model of nonphagocytic 

cells. Some macrophages cultures were 

treated with cytochalasin D (cytD) to 

inhibit phagocytosis. In addition, RBC 

were also cultured with gold particles. 

Of the non-cytD treated macrophages, 77 ± 15%, 21 ± 11%, 

and 56 ± 30% contained 0.078, 0.2, and 1 μm particles, 

respectively. CytD treatment of macrophages effectively 

blocked the phagocytosis of 1 μm particles, but did not alter 

the uptake of the 0.078 and 0.2 μm particles. Human RBC 

were found to contain 0.078 and 0.2 μm polystyrene spheres 

as well as the 0.025 μm gold particles, which were not 

membrane bound. In contrast, the RBC did not contain the 

larger 1 μm polystyrene spheres. Results suggest that 

ultrafine and fine (0.078 and 0.2 μm diameter) particles cross 

cellular membranes by a non-endocytic (i.e. not involving 

vesicle formation) mechanisms such as adhesive interactions 

and diffusion. 

Geys et al. 

(2006, 

155789) 

Human alveolar 

(A549) and 

bronchial (Calu-3) 

epithelial cellsRat 

primary type II 

pneumocytes 

Amine- and 

carboxyl-modified 

fluorescent 

polystyrene (46 nm) 

Cells cultured in clear polyester 

transwells with 0.4 or 3 μm pores. 

Monolayer considered “tight” when <1% 

sodium fluorescein moved from apical to 

basolateral compartment. Particle 

translocation assessed in transwells with 

and without cells. Cells incubated with 

particles for 14-16 h to assess 

translocation from apical to basolateral 

compartment. 

Without cells, 13.5% of carboxyl-modified particles passed 

through the 0.4 μm pores (n = 7) and 67.5% through 3 μm 

pores (n = 3). Movement of the amine-modified particles was 

4.2% through 0.4 μm pores (n = 7) and 52.7% through 3 μm 

pores (n = 3). The integrity of the monolayer was insufficient 

for translocation studies using the A549 cells (0.4 and 4 μm 

pore size) and rat pneumocytes (0.3 μm pore). Using 0.4 μm pores, there was no detectable translocation through either 

Calu-3 or rat pneumocyte monolayers. Using 3 μm pores, 

~6% of both particle types passed through the Calu-3 

monolayer; however, results were highly variable with no 

translocation in 2 (of 5) and 3 (of 6) trials with carboxyl- or 

amine-modified particles, respectively. 

B.2. Olfactory Translocation 

Table B-4. Olfactory particle translocation. 

Reference Study Group Aerosol Study Protocol Observations 

DeLorenzo 

(1970, 

156391) 

Squirrel 

monkeys 

Young males 

(1 kg) 

Silver-coated colloidal 

gold (50 nm) 

Intranasal instillation of 1 mL particle 

suspension. Animals sacrificed at 0.25, 

0.5, 1, and 24-h after instillation. 

Rapid movement (30-60 min) into olfactory bulbs. Within 

30 min of being placed on nasal mucosa, particle 

aggregates were seen in axoplasm of the fila olfactoria 

Within 1 h, particles were in olfactory glomerulus. 

Particles in the olfactory bulb were located preferentially 

in mitochondria and not free in the cytoplasm. 

Dorman et 

al. (2001, 

055433) 

Crl: CD rats 

Males (6 wk old) 

Soluble and insoluble 

Mn particle types; 

MMAD = 1.3-2.1 μm; 

GSD<2 

Whole body exposure (6 h/day, 14 

consecutive days) to 0, 0.03, 0.3, and 

3 mg Mn/m3

. Tissues analyzed in six 

animals per concentration exposed to 

soluble (MnSO4) or insoluble (Mn3O4) 

aerosols. 

Increased Mn levels in olfactory bulb observed following 

MnSO4 of ≥ 0.3 mg Mn/m3

 and following Mn3O4 of 3 mg 

Mn/m3. At 3 mg Mn/m3, Mn levels were significantly 

greater in olfactory bulb (1.4-fold) and striatum (2.7-fold) 

following soluble MnO4 than insoluble Mn3O4. Mn levels 

in the cerebellum were unaffected following all 

exposures. 

December 2009 B-3 
Reference Study Group Aerosol Study Protocol Observations 

Dorman et 

al. (2004, 

155752) 

Crl: CD rats 

Males (6 wk old) 

Soluble and insoluble 

Mn particle types; 

MMAD = 1.5-2 μm; 

GSD = 1.4-1.6 

Whole body exposure (6 h/day, 

5 days/wk, 13 wk) to MnSO4 at 0, 0.01, 

0.1, and 0.5 mg Mn/m3. Compared to 

Mn phosphate (as hureaulite) 

exposure of 0.1 mg Mn/m3

. Brain Mn 

levels assessed immediately following 

90 days of exposure or 45 days 

postexposure. 

Relative to air, the insoluble hureaulite was significantly 

increased at 90 days of exposure in the olfactory bulb, 

but not striatum or cerebellum. The soluble Mn 

phosphate showed a dose dependent increase in 

olfactory bulb Mn levels at 90 days. At 0.1 mg Mn/m3

, Mn 

levels following Mn phosphate were significantly 

increased in the olfactory bulb and striatum relative to 

hureaulite and air exposures. At 45 days postexposure, 

relative to air, olfactory bulb Mn levels only remained 

increased Mn phosphate group at 0.5 mg Mn/m3

. 

Elder et al. 

(2006, 

089253) 

Fisher 344 rats 

Males 

(200-250 g) 

Mn oxide (~30 nm 

equivalent sphere with 

3-8 nm primary 

particles) 

Spark generated 

0.5 mg/m3

18 × 106 particles/cm3

Whole body inhalation exposure to 

either filtered air or Mn oxide for 12 

days (6 h/day, 5 days/wk) with both 

nares open or Mn oxide for 2 days (6 

h/day) with right nostril blocked. 

Intranasal instillation in left nostril of 

Mn oxide particles or soluble MnCl2 

suspended in 30 μL saline. Analyzed 

Mn in the lung, liver, olfactory bulb, and 

other brain regions. 

After 12 day exposure via both nostrils, Mn in the 

olfactory bulb increased 3.5-fold, whereas in the lung Mn 

concentrations doubled; there were also increases in the 

striatum, frontal cortex, and cerebellum. After the 2 days 

exposure with the right nostril blocked, Mn accumulated 

in the mainly in the left olfactory bulb (~2.4-fold increase) 

in to a lesser extent in the right olfactory bulb (1.2-fold 

increase). At 24-h post instillation, the left olfactory bulb 

contained similar amounts of the poorly soluble Mn oxide 

(8.2 ± 0.7%) and soluble MnCl2 (8.2 ± 3.6%) as a 

percent of the amount instilled. 

Oberdörster 

et al. (2004, 

055639) 

Fisher 344 rats 

Males (14 wk; 

284 ± 9 g) 

13C (36 nm CMD, 1.7 

σg) 

Spark generated 

Rats (n = 12, 3 per time point) exposed 

to 160 μg/m3 for 6 h in whole-body 

chamber and sacrificed at 1, 3, 5, and 

7 day postexposure. Lung, olfactory 

bulb, cerebrum, and cerebellum 

removed for 13C analysis. Tissue 

13C-levels were determined by isotope 

ratio mass spectroscopy and 

background corrected for 13C levels in 

unexposed controls (n = 3). 

At 1 day postexposure, the lungs of rats exposed to ultrafine 

13C particles contained 1.34 ± 0.22 μg of 13C 

(1.39 μg/g-lung) following background corrected. By 7 days 

postexposure, the 13C concentration had decreased to 

0.59 μg/g-lung. There was a significant and persistent 

increase in 13C in the olfactory bulb of 0.35 μg/g on day 1, 

which increased to 0.43 μg/g by day 7. Day 1 concentrations 

of 13C in the cerebrum and cerebellum were also 

significantly increased but the increase was inconsistent, 

possibly reflecting translocation of particles from the blood 

across the blood-brain barrier into brain regions. 

Persson et 

al. (2003, 

051846) 

Sprague-Dawley 

male rats (150 g) 

Freshwater Pike 

female (3 kg) 

65ZnCl2 dissolved in 

0.1 M HCl 

Rats: intransal (0.03 μg Zn in 10 μL) or 

intraperitoneally (0.03 μg Zn in 100 μL); 

autoradiography and γ spec at 1 day or 

1, 3, or 6 wk postexposure. 

Pike: instilled (0.12 μg Zn in 10 μL) in 

right or both olfactory chambers, assayed 

2 wk postexposure 

Zn uptake in olfactory epithelium and transport along 

olfactory neurons to olfactory bulb. Zn continued into 

interior of olfactory bulb and in rat went into anterior 

olfactory cortex. Zn found bound to both cellular 

constituents and cytosolic components. Some Zn bound 

to metallothionein in olfactory mucosa and olfactory bulb. 

Wang et al. 

(2007, 

156147) 

CD-1 (ICR) mice Rutile TiO2 

21 and 80 nm 

Anatase TiO2 155 nm 

Twenty mice (n = 5 per group) 

exposed 0 or 0.01 g-TiO2 per mL DI. 

Instilled 25 μL each day for 5 days, 

then inhaled 10 μL every other day. 

Mice sacrificed after 1 mo. 

Rutile particles were observed to be column/fiber 

shaped, whereas anatase was octahedral. TiO2 particles 

taken up by olfactory bulb via the olfactory nerve layer, 

olfactory ventricle, and granular cell layer of the olfactory 

bulb. Fine TiO2 showed greater entry into the olfactory 

bulb presumably due to aggregation of smaller rutile 

particles that was not seen for the fine anatase particles. 

Yu et al. 

(2003, 

156171) 

Sprague-Dawley 

male rats, 6 wk 

old (218 ± 10 g) 

Stainless steel 

welding-fume 

<0.5 μm 

Whole body exposure 2 h/day for 1, 

15, 30, or 60 days 

Low: 64 ± 4 mg/m3

 (1.6 mg/m3 Mn) 

High: 107 ± 6 mg/m3

 (3.5 mg/m3 Mn) 

Significant increases in cerebellum Mn at 15-30 days of 

exposure. 

Slight increases in Mn in substantia nigra, basal ganglia, 

temporal cortex, and frontal cortex after 60 days. 

Significant increase at 30 days in basal ganglia at low 

dose. Authors suggested that pharmacokinetics and 

distribution of welding fume Mn differs from pure Mn. 

December 2009 B-4 
B.3. Clearance and Age 

Table B-5. Studies of respiratory tract mucosal and macrophage clearance as a function of age. 

Reference Animal Particles Study Protocol Observed Effect(s) 

NASAL AND TRACHEAL CLEARANCE 

Ho et al. 

(2001, 

156549) 

Human, 

males and 

females 

Not applicable Ninety subjects (47 M, 43 F; 52 ± 23 yr) 

between 11 and 90 yr of age were recruited 

to measure nasal saccharine clearance and 

ciliary beat frequency. 

Ciliary beat frequency (n = 90; r = -0.48, p 

<0.0001) and nasal mucociliary clearance time 

(n = 43; r = 0.64, p <0.001) were correlated with 

subject age. Nasal clearance times were 

significantly (p <0.001) faster in individuals 

under 40 yr of age (9.3 ± 5.2 min) versus older 

subjects (15.4 ± 5.0 min). Results similar 

between males and females. 

Goodman et 

al. (1978, 

071130) 

Humans, 

males and 

females 

Radiolabed Teflon disks (1 mm 

diameter, 0.8 mm thick) 

Tracheal mucus velocity following delivery via 

bronchoscope to the tracheal mucosa. Ten 

young (2 M, 8 F; 23 ± 3 yr) and ten elderly (2 

M, 5 F; 63 ± 5 yr) nonsmokers served as 

control subjects. Measurements were also 

made in young smokers, ex-smokers, and 

individuals with chronic bronchitis. 

Young nonsmokers had a tracheal mucus 

velocity of 10.1 ± 3.5 mm/min which was 

significantly faster than the velocity of 

5.8 ± 2.6 observed in the elderly 

nonsmokers. 

Whaley et al. 

(1987, 

156153) 

Beagle 

dogs, 

males and 

females 

Macroaggregated albumin99mTc 

labelled 

Intratracheal instillation of 10- μl droplet of 

labelled albumin in saline. Tracheal clearance 

followed 25 min. Longitudinal measure 

measurements in 5 males and 3 females when 

young adults (2.8-3 yr), middle-aged (6.7-6.9 yr), 

and mature (9.6-9.8 yr). Additional 5 females 

and 3 males comprised immature group (9-10 

mo) and 4 males and 4 females used as aged 

group (13-16 yr). 

Tracheal mucus velocity significantly 

(p <0.05) greater in young (9.7 ± 0.6 [SE] 

mm/min) and middle-aged (6.9 ± 0.5) groups 

than in immature (3.6 ± 0.4), mature 

(3.5 ± 0.8), and aged (2.9 ± 0.5) dogs. 

Yeates et al. 

(1981, 

095391) 

Humans, 

males and 

females 

Radioaerosols 99mTc labelled Tracheal mucus velocities compiled for 74 

healthy non-smoking subjects (60 M, 14 F; 

10-65 yr, mean 30 yr) from prior studies. 

Forty-two (32 M, 10 F) inhaled albumin in 

saline droplets (6.2-6.5 μm MMAD), Yeates et 

al. (1975); twenty-two (21 M, 1 F) inhaled iron 

oxide (4.2 μm MMAD), Yeates et al. (1981b); 

and ten (7 M, 3 F) inhaled monodisperse iron 

oxide aerosol (7.5 μm MMAD), Leikauf et al. 

(1981). Inhalations were via a mouthpiece 

with an inspiratory flow of ~1 liter/sec. 

A lognormal distribution of tracheal mucus 

velocities was reported. Age did not appear 

to affect velocities, e.g., 4.7 ± 2.5 mm/min in 

18-24 yr olds vs. 4.6 ± 3.2 mm/min in 

individuals >30 yr of age. However, it should 

be noted that only 2 subjects were greater 

than 45 yr of age and that the data was 

complied from three studies using differing 

experimental techniques. Rather similar 

tracheal mucus velocities in males (4.7 ± 3.0 

mm/min) and females (4.9 ± 2.4 mm/min). 

BRONCHI AND BRONCHIOLES CLEARANCE 

Puchelle et 

al. (1979, 

006863) 

Human, 

males 

7.4 μm MMAD99mTc labelled 

resin 

Mucociliary clearance measured for 1 h post 

aerosol inhalation in 19 healthy non-smoking 

males (21-69 yr of age). Clearance measure 

on two occasions in 16 individuals. 

Negative correlation (r = -0.472, p <0.05) 

between mucociliary clearance and age. 

Younger subjects (n = 9; 21-37 yr) had 1-h 

clearance of 34 ± 14% which was 

significantly greater than the 22 ± 8% found 

in the older subjects (n = 5; >54 yr). 

Separated by 5.4 wk (on avg), there was a 

good correlation between repeated 

clearance measurements (r = 0.65, p 

<0.001) 

Svartengren 

et al. (2005, 

157034) 

Humans, 

males and 

females 

6 μm MMAD111In labelled Teflon Small airway clearance measured in five age 

groups (≤ 24 yr, n = 13; 25-29 yr, n = 8; 

30-49 yr, n = 7; 50-64, n = 9; >65 yr, n = 9) of 

healthy subjects. Aerosol inhaled via 

mouthpiece at extremely slow rate of 0.05 

L/s. Activity in lungs measured at 1 day, 2 

days, and 1, 2, and 3 wk post-exposure. 

Under the presumption that most large airway 

clearance was complete by 24 h, retention at 

24 h was normalized to 100%. 

Large and small airway clearance slowed 

with increasing age. Clearance correlated 

with age at all times (r = -0.46 to -0.50, -0.55, 

-0.66, and -0.70 at 1 day, 2 days, 1 wk, 2 wk, 

and 3 wk, respectively). Based on linear 

regression, the clearance from 1 to 21 days 

post-exposure was 47% in a 20 yr-old 

versus 23% in an 80 yr-old. Lung function 

was not a significant predictor of clearance 

when age considered. 

December 2009 B-5 
Reference Animal Particles Study Protocol Observed Effect(s) 

Vastag et al. 

(1985, 

157088) 

Humans, 

males and 

females 

Monodisperseerythrocytes99mTc 

labelled 

Clearance measured for 1-h post-inhalation 

in eighty healthy (59 M, 21 F; 43 ± 17 yr) 

subjects who had never smoked. Smokers 

and ex-smokers also studied. Aerosol 

inhalation not described. 

Clearance significantly associated with age. 

Based on linear regression, total mucociliary 

clearance at 1-h post-exposure was 46% in 

a 20 yr old versus 23% in an 80 yr old. 

Similar results for males and females. 

ALVEOLAR CLEARANCE 

Muhle et al. 

(1990, 

006853) 

Fischer 

344 rats 

3.5 μm MMAD 85Sr labelled 

polystyrene latex 

Control animals compared across several 

studies. Aerosol inhaled by short-term nose 

only exposure. Alveolar clearance determined 

by exponential fit to thoracic activity 

measured over 75-100 days excluding the 

first 15 days post-exposure. 

Typical alveolar clearance half-time of 45 

days in 5-mo-old rats compared to 74 days 

in 23-mo-old rats. Statistical significance of 

findings not proved. 

December 2009 B-6 
Annex B References 

Bermudez E; Mangum JB; Wong BA; Asgharian B; Hext PM; Warheit DB; Everitt JI (2004). Pulmonary responses of 

mice, rats, and hamsters to subchronic inhalation of ultrafine titanium dioxide particles. Toxicol Sci, 77: 347-357. 

056707

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Note: Hyperlinks to the reference citations throughout this document will take you to the NCEA HERO database (Health and 

Environmental Research Online) at http://epa.gov/hero. HERO is a database of scientific literature used by U.S. EPA in the process of 

developing science assessments such as the Integrated Science Assessments (ISA) and the Integrated Risk Information System (IRIS). 

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December 2009 B-8 

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