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Table 1 Basic characteristics of participants (n = 7,665) by silica exposure level, 1960–2012

From: Combined effect of silica dust exposure and cigarette smoking on total and cause-specific mortality in iron miners: a cohort study

Characteristic

Entire cohort (n = 7,665)

Silica exposure levela

Unexposed (n = 4,007)

Low (n = 1,218)

Medium (n = 1,220)

High (n = 1,220)

Male gender (n, %)

6542 (85.35)

3023 (75.44)

1160 (95.24)

1181 (96.80)

1178 (96.56)

Year at birth

1939.50 ± 9.60

1940.23 ± 9.48

1943.15 ± 9.08

1938.77 ± 9.40

1934.15 ± 8.29

Year at hire

1962.28 ± 7.06

1963.01 ± 6.83

1965.87 ± 6.17

1962.06 ± 6.19

1956.51 ± 5.94

Age at hire (years)

22.78 ± 5.76

22.78 ± 5.89

22.72 ± 5.57

23.29 ± 5.92

22.36 ± 5.30

Ever smoker (n, %)b

5070 (66.14)

2338 (58.35)

893 (73.32)

926 (75.90)

913 (74.84)

Never smoker (n, %)b

2595 (33.86)

1669 (41.65)

325 (26.68)

294 (24.10)

307 (25.16)

Pack-years of ever smoker b

28.57 ± 15.39

28.27 ± 14.95

26.52 ± 14.11

29.03 ± 16.74

30.86 ± 15.95

Age at first exposure (years)c

23.65 ± 6.36

NA

24.54 ± 7.27

23.79 ± 6.09

22.63 ± 5.44

Cumulative total dust concentration (mg/m3-y)c

117.95 ± 70.27

NA

55.21 ± 21.94

107.32 ± 18.41

191.22 ± 67.66

Average total dust concentration (mg/m3)c

5.29 ± 3.02

NA

3.88 ± 2.49

4.66 ± 2.05

7.34 ± 3.22

Cumulative respirable dust concentration (mg/m3-y)c

18.48 ± 11.01

NA

10.34 ± 6.53

18.02 ± 7.03

27.08 ± 11.46

Average respirable dust concentration (mg/m3)c

0.83 ± 0.47

NA

0.69 ± 0.47

0.77 ± 0.37

1.03 ± 0.50

Cumulative respirable silica dust concentration (mg/m3-y)c

0.83 ± 0.80

NA

0.34 ± 0.13

0.66 ± 0.10

1.51 ± 1.07

Average respirable silica dust concentration (mg/m3)c

0.04 ± 0.04

NA

0.02 ± 0.02

0.03 ± 0.01

0.06 ± 0.06

Duration of dust exposure (years)c

23.95 ± 9.29

NA

18.12 ± 9.65

25.55 ± 7.13

28.17 ± 7.80

Pneumoconiosis cases (n, %)d

332 (9.08)

NA

21 (1.72)

79 (6.48)

232 (19.02)

Age of first diagnosis of pneumoconiosis (years)d

49.64 ± 8.83

NA

51.11 ± 12.88

50.84 ± 9.04

49.11 ± 8.29

Latency of pneumoconiosis (years)d

25.60 ± 8.00

NA

23.67 ± 9.32

24.69 ± 7.69

26.08 ± 7.96

Age upon entry to cohort (years)

24.84 ± 6.73

24.39 ± 6.61

23.63 ± 6.18

25.05 ± 6.67

27.34 ± 7.09

Median of follow-up (years)e

42.75 ± 12.00

42.34 ± 14.00

41.92 ± 5.92

43.09 ± 10.04

45.34 ± 14.33

Deceased (n, %)

2814 (36.71)

1233 (30.77)

401 (32.92)

515 (42.21)

665 (54.51)

  1. Values were generally presented as mean ± standard deviation, if not specially indicated
  2. aSilica exposure was divided into four levels, i.e. unexposed, low (0.4935 mg/m3-y or below), medium (0.4935 to 0.8423 mg/m3-y), and high level(0.8423 mg/m3-y or above)
  3. bCigarette smoking was defined as taking at least 1 cigarette per day for at least 6 months, and pack-years were calculated only among ever smokers
  4. cExposure-related results were figured out only among dust-exposed workers
  5. dPneumoconiosis-related results were figured out only among workers diagnosed with pneumoconiosis. Latency of pneumoconiosis was defined as the duration from the onset of dust exposure to the first diagnostic time of pneumoconiosis
  6. eValues hereby were presented as median ± inter quartile range
  7. NA, i.e. the unavailable values
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Environmental Health

ISSN: 1476-069X