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

IARC MONOGRAPHS – 100C
(US diatomaceous earth workers; Finnish and
US granite workers; US industrial sand workers;
Chinese pottery workers, and tin and tungsten
miners; and South African, Australian, and US
gold miners). Occupation- and time-specific
exposure estimates were either adopted/adapted
or developed for each cohort, and converted to
milligrams per cubic metre (mg/m 3 ) respirable
crystalline silica. The median of the average
cumulative exposure to respirable crystalline
silica ranged from 0.04 mg/m 3 for US industrial
sand workers to 0.59 mg/m 3 for Finnish granite
workers. The cohort-specific median of cumulative
exposure ranged from 0.13 mg/m 3 –years for
US industrial sand workers to 11.37 mg/m 3 –years
for Australian gold miners.
In a cross-sectional survey, Hai et al. (2001)
determined the levels of respirable nuisance and
silica dusts to which refractory brickworkers
were exposed at a company in Ha Noi, Viet
Nam. Respirable dust levels were in the range
of 2.2–14.4 mg/m 3 at nine sample sites. The
estimated free silica content of dust was 3.5%
for unfired materials at the powder collectors
(n = 8 samples), and 11.4% in the brick-cleaning
area following firing (n = 1 sample).
Burgess (1998) investigated processes associated
with occupational exposure to respirable
crystalline silica in the British pottery industry
during 1930–1995, and developed a quantitative
job–exposure matrix. Exposure estimates were
derived from 1390 air samples, the published
literature, and unpublished reports of dust
control innovations and process changes. In
the matrix, daily 8-hour TWA airborne concentrations
of respirable crystalline silica ranged
from 0.002 mg/m 3 for pottery-support activities
performed in the 1990s to 0.8 mg/m 3 for firing
activities in the 1930s. Although exposure estimates
within decades varied, median concentrations
for all process categories displayed an
overall trend towards progressive reduction in
exposure during the 65 year span.
2. Cancer in Humans
2.1 Cancer of the lung
In the previous IARC Monograph (IARC,
1997) not all studies reviewed demonstrated an
excess of cancer of the lung and, given the wide
range of populations and exposure circumstances
studied, some non-uniformity of results had been
expected. However, overall, the epidemiological
findings at the time supported an association
between cancer of the lung and inhaled crystalline
silica (α-quartz and cristobalite) resulting
from occupational exposure.
The current evaluation has a primary focus
on studies that employed quantitative data on
occupational exposures to crystalline silica dust
(α-quartz and cristobalite). The establishment
of exposure–response relationships not only
provides critical evidence of causation, but the
availability of quantitative exposures on crystalline
silica and other exposures of relevance
facilitates the accurate assessment of exposure–
response relationships in the presence of potential
confounders. In addition to the focus on
quantitative exposure–response relationships, a
summary of findings from eight published metaanalyses
of lung cancer was also elaborated. Of
these, the seven meta-analyses involving absolute
risk summarize the information from the many
studies that did not consider quantitative exposure–response
relationships, while the eighth is a
meta-analysis of exposure-response.
Findings from cohort studies are given
in Table 2.1 available at http://monographs.
iarc.fr/ENG/Monographs/vol100C/100C-08-
Table2.1.pdf, and those for the case–control
studies are provided in Table 2.2 available at
http://monographs.iarc.fr/ENG/Monographs/
vol100C/100C-08-Table2.2.pdf. Given that there
was concern by the previous IARC Working
Group that different exposure settings (including
the nature of the industry and the crystalline
silica polymorph) may give rise to different (or
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