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NIOSH HAZARD REVIEW

Health Effects of Occupational Exposure
to Respirable Crystalline Silica
   
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  Table 15
 
Table 15. IARC*-reviewed epidemiologic studies having the least confounded investigations of an association between occupational exposure to crystalline silica and lung cancer
Reference
and country
Study design, cohort, and followup
Subgroup
Number of lung cancer deaths or cases
Risk measure†
CI‡
Smoking
information available and analyzed
Comments
Amandus et al. [1991], United States Mortality study of 714 male, North Carolina dusty trades workers diagnosed with silicosis between 1940 and 1983 and compared with the 1940–1983 lung cancer mortality rates for U.S. males.

Whites

 33
2.6
1.8–3.6
Yes
 The age- and smoking-adjusted rate ratio for white silicotics with lung cancer was 3.9 (95% CI= 2.4–6.4) compared with a referent group of metal miners.

"Exposure to respirable silica dust" was defined as working in a dusty trade and having radio-graphic silicosis.

No quantitative exposure data were available.
Nonwhites
   1
0.7
Not reported
White silicotics:

Diagnosed while employed
  28
2.5
1.7–3.7

Employed in jobs with silica exposure only§
  26
2.3
1.5–3.4

Past or current smokers
  18
3.4
2.0–5.3

Silicotics, never smoked
   5
1.7
0.5–3.9
Amandus et al. [1992], United States Mortality study of subgroup of 306 white males from Amandus et al. [1991] cohort of silicotics diagnosed and traced from 1940 through 1983. 143 of the subgroup were reclassified as silicotics, and 96 were reclassified as having a normal radiograph. 10 deaths from lung cancer occurred in the reclassified group.   Silicotics
   8
2.5
1.1–4.9
Yes
 "Exposure to respirable silica dust" was defined as working in a dusty trade and having radiographic silicosis.

No quantitative exposure data were available.
  Nonsilicotics**
   2
1.0
0.1–3.5
Smokers:
Silicotics
   5
3.4
 1.1–7.9
Nonsilicotics**
   1
1.3
0.03–7.1
Burgess
et al. [1997],
Cherry
et al. [1997], McDonald et al. [1997], United Kingdom		 Nested case-control study of lung cancer deaths within Cherry et al. [1995], including duration and intensity of exposure, smoking, and radiological changes. Cases were employed as pottery workers for >10 yr. Each death was matched with
3 or 4 controls on date of birth and date of first expo-sure.		 Cumulative exposure to respirable crystalline silica dust
>4,000 µg/m3 yr
  52
      0.60††
0.26–1.41‡‡
Yes
 ORs were adjusted for smoking and radio-graphic changes.

This was the only epidemiologic study of peak exposure effects and lung cancer. Results support significant lung cancer risk for high-intensity silica exposures.

Silica dust exposures 400 µg/m3 occurred in firing and post-firing operations. Exposures to cristobalite were possible.
Duration of employment
>20 yr
—
      0.48††
0.21–1.09‡‡
Mean intensity of silica dust exposure
>200 µg/m3
—
     1.68††
0.93–3.03‡‡
Maximum silica dust exposure >400 µg/m3
—
     2.07††
1.04–4.14‡‡
Checkoway et al. [1993; 1996],
United States		 Mortality study of 2,570 male workers at diatomaceous earth plants employed >1 yr and worked >1 day between 1942 and 1987. Cohort mortality traced for that period.
—
  59
  1.43
1.09–1.84
Limited to comparisons of smoking prevalence.
 Estimated relative risks for lung cancer (not shown) were adjusted for age, calendar year, duration of followup, and ethnicity. The risks increased significantly (P<0.05 for trend) with duration of employment and cumulative exposure to crystalline silica [Checkoway et al. 1993]. Checkoway et al. [1996] also adjusted for asbestos exposure.
Checkoway et al. [1996] reanalyzed 2,266 workers (a subset of the orig-inal cohort). Mortality traced from 1942 through 1987.
—
  52
  1.41
1.05–1.85
Cherry
et al. [1995], United Kingdom		 Mortality study of 5,115 pottery workers, excluding exposure to asbestos, foundry, and other dusts; with mortality followup to June 30, 1992.
—
  68
  1.28
1.04–1.57‡‡
No
 Lung cancer rates in pottery workers were compared with local mortality rates.
Costello and Graham [1988],
United States		 Mortality study of 5,414 white male workers in Vermont granite sheds and quarries employed between 1950 and 1982 with at least one radiologic examination in the worker surveillance program. Quarry workers
  20
  0.82
Not reported
No
 Dust exposure data were not included, limiting conclusions about exposure-response. Cohort overlaps with cohort of Davis et al. [1983].

CIs reported by IARC [1997].
Shed workers:
  98
  1.27
Not reported§§
  Started before   1940, latency   period >40 yr,   tenure >30 yr
  47
  1.81
1.33–2.41***
  Started after   1940, latency   period >25 yr,   tenure >10 yr
  17
  1.73
1.01–2.77
Costello
et al. [1995],
United States		 Mortality study of 3,246 male workers employed >1 yr between 1940 and 1980 at 20 U.S. crushed stone (i.e., granite, limestone, traprock, or sandstone) operations. Whites
  40
1.2
0.9–1.6
No
 —
Nonwhites
  11
1.9
0.9–3.3
Workers in granite facilities with >20-yr latency period and >10-yr tenure
   7
 3.5
1.4–7.3
Workers in limestone facilities
  23
1.5
1.0–2.3
Workers in traprock facilities
   3
 0.6
0.1–1.8
Dong et al. [1995], China Mortality study of lung cancer in 6,266 male silicotic and nonsilicotic refractory brick workers employed before 1962 and followed for mortality from 1963 to 1985. 11,470 nonsilicotic male steel workers used as controls. Silicotics
  35
     2.1†††
Not reported***
Yes
 Twofold excess lung cancer mortality occurred in both smokers and nonsmokers. Exposure-response trends were found for years since first employment and lung cancer mortality, and for severity of silicosis and lung cancer mortality.
Silicotics in Chinese radiological category:
  I
  21
2.0
Not reported***
  II
  10
2.3
Not reported§§
  III
   4
2.6
Not reported§§
Nonsilicotics
  30
1.1
Not reported***
Guénel
et al. [1989], Denmark

Cohort study of 2,175 Danish stone workers who met the following criteria:

  • were alive on Jan. 1, 1943, or were born later, and
  • were aged <65 when first identified in one of 6 data sources.

The cohort included 2,071 cancer cases identified in the Danish cancer registry between 1943 and 1984.

 Lung cancer cases
  44
      2.00‡‡‡
1.49–2.69
Yes

Adjusted for regional differences in smoking. Lung cancer mortality highest among Copenhagen sandstone cutters hired before 1940 prior to ventilation improvements.
McDonald et al. [1995], United Kingdom Preliminary report of proportionate mortality study of 7,020 pottery workers born between 1916 and 1945 with mortality followup to June 30, 1992. Preliminary nested case-control study of 75 lung cancer cases and
75 controls.		 Lung cancer deaths in pottery workers not exposed to asbestos
112
     1.22§§§
1.04–1.43‡‡
No
 Preliminary results
(final results in Cherry et al. [1995]).

Lung cancer rates in pottery workers were compared with local mortality rates.
Smokers and nonsmokers with >10 yr of silica exposure
  75
 1.4††
0.7–2.7‡‡
Smokers with >10 yr of silica exposure
  47
 2.8††
1.1–7.5‡‡
McLaughlin et al. [1992], China Nested case-control study of 62 pottery factory workers employed between 1972 and 1974 who died from lung can-cer before 1990;
238 controls matched by decade of birth and factory.		 Cumulative respirable silica dust exposure (µg/m3-yr):
Yes
 ORs were adjusted for age and smoking. Test for exposure-response trend was not statistically significant (P>0.05) for cumulative exposure to dust or respirable silica. High OR (7.4; CI and number of deaths not reported) for lung cancer in workers who smoked >20 cigarettes per day. CIs reported in IARC monograph [1997].
None
  11
1.0
—
  Low (0.1–8.69)
  17
1.8
1.04–2.87
  Medium   (8.70–26.2)
  27
1.5
0.99–2.18
  High ( 26.3)
   7
2.1
0.80–4.12
Merlo
et al. [1991], Italy		 1,022 male refractory brick workers employed at least 6 months between 1954 and 1977. Retrospective cohort study of mortality through 1986. All brick workers
  28
 1.51
1.00–2.18
Yes
 Smoking habits of cohort comparable with the national population (includes the men in Puntoni et al. [1988]).
Brick workers:
  <19 yr since   1st exposure   and employed   <19 yr
   7
1.05
0.42–2.16
  >19 yr since   1st exposure   and employed   <19 yr
   8
1.75
0.75–3.46
  >19 yr since   1st exposure   and employed   >19 yr
  13
2.01
1.07–3.44
Partanen
et al. [1994],
Finland		 Cohort study of
811 male silicotics, compensated and not compensated, who were diagnosed between 1936 and 1977 in Finland. Cancer incidence for 1953–1991 was obtained from the Finnish Cancer Registry.		 Length of followup from date of silicosis diagnosis:
Yes
 Update of Kurppa et al. [1986].

No evidence of confounding by tobacco smoking.
  <2 yr
   1
     0.4‡‡‡
0.01–2.3
  2–9 yr
  32
2.7
1.9–3.9
  >10 yr
168
3.3
2.5–4.1
Histology of lung cancers:
  Adenocarcinoma
    5
2.0
0.6–4.6
  Squamous-cell
  34
3.2
2.3–4.5
  Small-cell
    9
2.1
0.9–3.9
  Other/unknown
  53
3.0
2.2–3.9
Industry:
  Mining/quarrying
  (excluding   granite)
  38
3.7
2.6–5.0
  Granite
  13
2.9
1.6–5.0
  Glass/ceramic
  10
3.3
1.6–6.1
  Grinding/
  sharpening
   3
3.0
.6–8.7
  Casting/
  founding
  22
1.8
1.1–2.6
  Construction
   2
10
1.3–37
  Excavation/
  foundation
   9
5.8
2.7–11.1
Steenland and Brown [1995b],
United States		 Cohort study of 3,328 white male gold miners employed underground >1 yr between 1940 and 1965 and followed for mortality from 1977 to 1990. Mortality rates of U.S. males used for comparison.
—
115
 1.13
0.94–1.36
Yes
 High historical exposures. No exposure-response trend by cumulative dust exposure.

Low radon and arsenic exposures.
Source: IARC [1997].
*Abbreviations: CI=confidence interval; IARC=International Agency for Research on Cancer; PMR=proportional mortality ratio; OR=odds ratio; SIR=standardized incidence ratio; SMR=standardized mortality ratio; SRR=standardized rate ratio
†SMR unless otherwise noted.
‡95% CI unless otherwise noted.
§Workers who had no known exposure to other occupational carcinogens such as asbestos manufacturing, insulation work, olivine mining, talc, and foundry work.
**Nonsilicotics are subjects with normal radiographs.
††OR.
‡‡90% CI.
§§P <0.05.
***P <0.01.
†††Values in this study are SRRs.
‡‡‡Values in this study are SIRs.
§§§PMR.
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