silica dust, crystalline, in the form of quartz or cristobalite - IARC ...

IARC MONOGRAPHS – 100C
than in 1979–87: general contractor industry
(0.057 mg/m 3 versus 0.354 mg/m 3 ), bridgetunnel
construction industry (0.069 mg/m 3
versus 0.383 mg/m 3 ), and stonework masonry
industry (0.065 mg/m 3 versus 0.619 mg/m 3 ).
Silica exposures in the grey-iron industry also
declined by up to 54% for some occupations (e.g.
the geometric mean for “furnace operators” in
1979–87 was 0.142 mg/m 3 versus 0.066 mg/m 3
in 1988–2003). [The Working Group noted that
exposure levels may not have decreased globally.]
Table 1.3 presents the more recent studies that
assessed the levels of respirable crystalline silica
in a range of industries and countries. Other
recent exposure studies that did not measure
the respirable crystalline silica components are
presented below.
(b) Mines
As part of a cohort mortality study follow-up
in four tin mines in China, Chen et al. (2006)
developed quantitative exposure estimates of
silica mixed dust. Workers in the original cohort
were followed up from the beginning of 1972 to
the end of 1994. Cumulative exposure estimates
were calculated for each worker using their mine
employment records and industrial hygiene
measurements of airborne total dust, particle
size, and free silica content collected since the
1950s. Total dust concentrations of the main job
titles exposed were found to have declined from
about 10–25 mg/m 3 in the beginning of the 1950s
to about 1–4 mg/m 3 in the 1980s and 1990s. The
respirable fraction of total dust was estimated to
be 25 ± 4%, and the respirable crystalline silica
concentration was estimated to be 4.3% of the
total mixed mine dust
Tse et al. (2007) conducted a cross-sectional
study to investigate the prevalence of accelerated
silicosis among 574 gold miners in Jiangxi, China.
Using occupational hygiene data abstracted from
government documents and bulk dust data from
a study in another gold mine in the region, the
estimated mean concentration of respirable
silica dust were reported as 89.5 mg/m 3 (range,
70.2–108.8 mg/m 3 ). According to government
documents, the total dust concentration in
underground gold mining was in the range of
102.6–159 mg/m 3 (average, 130.8 mg/m 3 ), and
the fraction of silica in total dust was around
75.7–76.1%. No data on the proportion of respirable
dust were available.
To determine dose–response relationships
between exposure to respirable dust and respiratory
health outcomes, Naidoo et al. (2006) used
historical data (n = 3645) and current measurements
(n = 441) to characterize exposure to
respirable coal mine dust in three South African
coal mines. Jobs were classified into the following
exposure zones: face (directly involved with coal
extraction), underground backbye (away from
the coal mining face), and work on the surface.
Based on the 8-hour full-shift samples collected
respectively, mean respirable dust concentrations
in Mines 1, 2, and 3, were as follows: 0.91 mg/m 3
(GSD, 3.39; mean silica content, 2.3%; n = 102),
1.28 mg/m 3 (GSD, 2.11; mean silica content, 1.4%;
n = 63), and 1.90 mg/m 3 (GSD, 2.23; mean silica
content, 2.7%; n = 73) at the face; 0.48 mg/m 3
(GSD, 2.97; mean silica content, 1.48%; n = 30),
0.56 mg/m 3 (GSD, 3.71; mean silica content,
1.35%; n = 47), and 0.52 mg/m 3 (GSD, 4.06;
mean silica content, 0.9%; n = 41) in the backbye
zone; and, 0.31 mg/m 3 (GSD, 3.52; mean silica
content, 0.95%; n = 8), 0.15 mg/m 3 (GSD, 3.56;
n = 6), and 0.24 mg/m 3 (GSD, 7.69; mean silica
content, 0.64%; n = 11) in the surface zone. Based
on the historical data, overall geometric mean
dust levels were 0.9 mg/m 3 (GSD, 4.9), 1.3 mg/m 3
(GSD, 3.3), and 0.5 mg/m 3 (GSD, 5.6) for Mines
1, 2, and 3, respectively.
(c) Granite-quarrying and -processing, crushed
stone, and related industries
Bahrami et al. (2008) described the personal
exposure to respirable dust and respirable quartz
in stone-crushing units located in western Islamic
Republic of Iran. A total of 40 personal samples
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