DEPOSITION OF MMMF (CERAMIC FIBERS)
IN THE LUNGS OF GUINEA PIGS

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Dissertation Abstract

Asbestos fibers have hemolytic activity and cytotoxic potency to macrophages in vitro

cultures.  In vivo, Asbestos also clearly caused diseases such as fibrosis, lung cancer,

and mesothelioma.  Because of its serious health effects, asbestos is now substituted

by a variety of materials including man-made mineral fibers (MMMF).  Since the toxic
properties of asbestos are size related, long and thin MMMF may also induce similar

effects if they maintained their integrity in lung tissues.

This study was undertaken to determine the deposition of ceramic fibers in guinea

pig lungs.  It was a part of an effort to predict the potential health effects of man-made

mineral fibers (MMMF) in general and of ceramic fibers in particular.  The objectives

of this study were to determine the deposition / retention and clearance rates of various

fiber sizes in the respiratory system of the guinea pig and to evaluate the factors

influencing these activities.

Nineteen male Hartly albino guinea pigs (GP) were exposed by inhalation (nose only) to

a polydispersed ceramic fiber dust at a concentration of 297 ± 25.5 fibers/cc of air,

for 6 continuous hours.  Minute volume for each individual guinea pig was determined by

applying Guyton's equation.  Exposed animals were divided into three groups; group (I)

was sacrificed immediately following exposure, group (II) 24 hours later and group (III)

5 days later.

Trachea and lung lobes of each animal were carefully separated, digested with Clorox

bleach and filtered on membrane filters.  The nasopharyngeal airways were washed three

times with 10 ml of saline and the wash fluid was added to the trachea's samples.  Filters

for air and biologic samples were then counted by phase-contrast microscopy at 1000X
magnification to determine the number and size distributions of the fibers in each sample.

The counts median length (CML) and median diameter (CMD) for airborne fibers were

13.3 and 0.917 μm with geometric standard deviations (GSD) of 2.64 and 1.96 μm

respectively.

The average total number of fibers recovered from the entire respiratory tract (ERT) of

groups I, II and III were 8.5 ± 0.73, 7.6 ± 0.56,  and 6.2 ± 0.69 million fibers/GP. 

Overall fiber retention as percent of inhaled fibers for the three groups were

30.8 ± 1.61, 27.1 ± 1.33, and 21.9 ± 1.66.  The CML and CMD of fibers recovered

from the lungs decreased slightly from 10.6 μm and 0.76 μm in the first group to

9.95 μm and 0.75 μm in the second group and to 9.25 μm and 0.71 μm in the third group.

Concentration and size distribution of fibers in the lobes indicated that fiber retention,

CML and CMD were not dependent on the size of lobe.  The highest and lowest

evenness indices among all lobes of animals in the three groups were consistently for the

upper left lobe (UL) and the middle left lobe (ML) respectively.

Results also showed that the short-term clearance of fibers was associated with two

clearance half-lives; the first was about 25 hours representing fast clearance in the

ciliated airways (URT), and the second was about 362 hours representing slow

clearance of fibers in the non-ciliated airways or the pulmonary compartment (LRT).

The results also indicated that the impaction equivalent diameter (D_ie) and mass

equivalent Diameter (D_me) are more efficient descriptors of fiber retention in the

lungs in comparison to the conventional aerodynamic equivalent diameter (D_ae).

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For Dissertation Summaries and Program Description:

DISSERTATION HIGHLIGHTS

DISSERTATION CONCLUSIONS

TULANE UNIVERSITY  (Institution Granting Doctorate)