Toxicology of Industrial Compounds

108 CARCINOGENIC POTENTIAL OF MAN-MADE VITREOUS FIBERS
TLA of 1.94 f cm −3 and an 8-h TWA of 0.97 f cm −3 (Lees et al., 1993a).
Removal of fiber glass insulation created an aerosol of 0.042 f cm −3 (Jacob
et al., 1993). Fiber concentrations of 0.004 f cm −3 were reported for
buildings recently insulated with FG (Jacob et al., 1992). However this figure
includes all types of fibers as it was obtained using optical microscopy. The
background level prior to fiber glass installation was 0.001 f cm −3 .
Ambient environmental exposures to airborne vitreous fibers were
extremely low; exposure levels of product-related vitreous fibers reported
for outdoor air was 0.0007 f cm −3 (Tiesler and Draeger, 1994).
In addition to manufacturing and field use surveys, release of fibrous
glass during actual use of products, particularly fiber released from air
filter media, has been monitored. To determine possible exposure of
building occupants to fibrous glass, ambient air was sampled in a number
of public buildings in which fibrous glass air filtration products had been
installed. These evaluations showed no significant release of fibers from the
filters (Balzer et al., 1971; Cholak and Schafer, 1971).
To evaluate the efficiency of fibrous glass filter blankets, several high
volume air samples were collected at various points in the ductwork of a
large office complex at the intake and the exhaust prior to changing the
filter media, and at the exhaust 23 days after installation of the new filter.
Analyses of the samples using electron microscopy indicate little initial
fiber release which decreases rapidly thereafter to the limit of detection
(Schuller, 1987).
Rock and slag wool
Airborne concentrations of dust and fibers reported from US mineral wool
plants is generally higher than in US glass wool facilities. This includes both
airborne fibers and total particulate matter. Fiber levels reported ranged
from 0.01 to 1.4 f cm −3 , compared with 0.1–0.3 f cm −3 for glass wool.
Total particulate matter sample results ranged from 0.05 to 23.6 mg m −3 in
the mineral wool facilities and 0.09–8.48 mg m −3 for glass wool (Esmen et
al., 1980).
Comparison of Human MMVF exposures used in the
recent rat chronic inhalation studies
When using animal inhalation studies for assessment of potential risk to
human health of airborne fibers, it is critical to demonstrate that the
characteristics and concentrations of the experimental fiber aerosols are
comparable with those in human exposure situations. It is also important
for risk assessment that the actual target organ dose in the animal model
reach or exceed that found in exposed humans. To illustrate, consider
levels of fiber glass published in a number of recent reports. A qualitative