Wollastonite Exposure and Lung Fibrosis

ENVIRONMENTAL
RESEARCH
30, 291-304
Wollastonite
(1983)
Exposure
and Lung Fibrosis
MATTI S. HUUSKONEN,’
ANTTI TOSSAVAINEN, HEIKKI KOSKINEN,
ANDERS ZITTING, OLLI KORHONEN, JUHA NICKELS,
KARI KORHONEN, AND VESA VAARANEN
Institute of Occupational
Health, Haartmaninkatu
I, SF-00290 Helsinki 29, Finland
ReceivedDecember 12, 1981
Wollastonite is a naturally occurring acicular or fibrous metasilicate used in ceramics and
as a substitute for asbestos in some applications. Wollastonite fibers are rather similar in
form, length, and diameter to amphibole asbestos fibers but mineralogically they are different. Dust measurements in both the Finnish limestone-wollastonite
quarry and in the flotation plant yielded high concentrations of both total dust and respirable fibers in some operational stages. The clinical study comprised a total of 46 men who had been exposed to
wollastonite at the quarry for at least 10 years. Three of the fifteen nonsmokers showed
chronic bronchitis. Radiographs revealed slight lung fibrosis among fourteen men, and slight
bilateral pleural thickening among thirteen men. Their sputum specimens were normal.
Spirometry and nitrogen single breath tests indicated the possibility of small airways disease.
I. INTRODUCTION
Wollastonite
is an acicular or fibrous silicate mineral (CaSiO,). The basic
structure of this mineral is an infinite silicon-oxygen
chain held together by
calcium ions. The natural cleavage of the mineral causes the formation of fibrous
fragments. Wollastonite
is used in ceramic tiles and the mineral has received
considerable attention as a substitute for asbestos fibers in some applications
(Andrews, 1970; Leineweber, 1980; Korhonen and Tossavainen, 1981).
The largest deposits of wollastonite are located in the United States, Mexico,
and Finland. In Finland, wollastonite occurs in small quantities in many contact
metamorphic limestone deposits. The commercially
mined deposit is located in
Lappeenranta,
where the limestone quarry has been in operation since 1911.
Initially, wollastonite was only a nuisance. In 1962, 2440 tons of wollastonite were
produced; in 1979 production exceeded 10,000 tons. Since 1950 wollastonite has
comprised about 7% of the total tonnage of all quarried materials and nowadays its
proportion is about 15%. The percentage of quartz in the quarried stone ranges
from 2 to 3%. All operational stages, from drilling to line crushing, are done using
the same equipment used for the main product (calcite). Only the final purification
of wollastonite is performed in a separate flotation plant, which has been in operation since 1967.
The aim of the present study was to determine the relationship between occupational exposure and the clinical features, the radiographic,
functional, and
cytological tindings among Finnish limestone-wollastonite
workers.
* To whom all correspondence
should be addressed.
291
0013-9351/83/020291-14$03.00/O
Copyright
AU rights
0 1983 by Academic Press, Inc.
of reproduction
in any form reserved
292
HUUSKONEN
ET AL.
II. EXPOSURE
In the quarry the wollastonite stone goes through several operational stages: (1)
drilling, (2) blasting, (3) loading and transport, (4) primary crushing, (5) manual
sorting, (6) automatic sorting, (7) secondary crushing, (8) tine crushing, (9) fine
milling, (10) flotation, and (11) bagging. Stages l-3 are done in the open quarry,
Stages 4-7 inside the mine, 8 in a building on ground level, and 9- 11 in a separate
flotation plant.
For the last few years the workers of the crushing, automatic sorting, and
flotation stages have stayed within ventilated cabins and operating rooms for most
of their work hours. Crushers, automatic sorters, and bagging machines are now
equipped with local exhausts. In the primary and secondary crushing plant, both
the crushers and some conveyor belts are also equipped with water sprayers, for
the purpose of collecting dust. Respiratory protectors are not normally used.
The dust measurements were taken both in the breathing zones of the workers
and within the working areas. The concentrations of total dust were measured by
sucking air through membrane filters which were then weighed. Samples for fiber
counting were collected either on Millipore filters (phase-contrast optical microscopy) or on Nuclepore filters (scanning electron microscopy @EM)). The counting technique was the same as that used for asbestos fibers: fibers over 5 pm
in length, less than 3 pm in diameter, and with an aspect ratio over 3:l were
counted. The magnifications
used were 500x for optical microscopy and 3000x
for SEM analysis. When the fiber concentrations obtained by the two methods are
compared, one must take into account the difference in detection limits (ca. 0.5
pm for optical microscopy and ca. 0.05 pm for SEM). The fibrous character of
wollastonite is easily observed in the electron microphotographs
(Fig. 1).
Table 1 presents the concentrations
of total dust and fibers during different
operational stages and the number of workers on one work shift. The respirable
fraction of 12 dust samples from drilling, crushing, and sorting contained, in
addition to calcite, 15% wollastonite and 3% quartz as determined by X-ray diffraction. The airborne dust in the flotation plant was mainly composed of wollastonite.
III. SUBJECTS
AND METHODS
During February and March of 1981, we examined a total of 55 workers (46 men
and 9 women) exposed to dust in the limestone-wollastonite
mine for at least 10
years. The number of females was so small that they were omitted from the
analysis. The 46 men (mean age 48.0 years, range 32-64) comprised the series for
the analysis of the clinical features. The data on their occupational exposure and
smoking habits are summarized in Table 2. Smokers were defined as persons who
habitually carried cigarettes or pipe tobacco for their own use whereas exsmokers
had given up smoking at least one yr earlier. Age-matched (*5 years) referent
groups-46
lumberjacks,
46 peat workers, and 46 men in tobacco manufacturing-were
selected for the radiographic
comparison.
A total of 15 of 46
(33%) lumberjacks were smokers. The respective figures were 16 (35%) for peat
workers and 29 (63%) for tobacco manufacturers. The percentage of exsmokers
WOLLASTONITE
EXPOSURE
AND LUNG FIBROSIS
FIG. 1. Electron micrograph of wollastonite
293
on Nuclepore filter. 3000 X.
was 37%, 37%, and 17%, respectively for the lumberjacks, the peat workers, and
the tobacco manufacturers.
The clinical examinations were performed by the same two physicians (M.S.H.
and H.K.). The examination included a standardized questionnaire on respiratory
symptoms (Medical Research Council, 1960) and a medical history. It also included an appraisal of the overall health status, auscultation, and a recording of
crepitations in the chest. Crepitations were recorded as nonmusical explosive
sounds during inspiration (Harris, 1973). The presence of clubbing was also estimated (Harris, 1973).
The radiographic examination included two full-size posterior-anterior
ftims
and one lateral film as well as one enlarged film of the lower part of the right lung.
The radiographic technique has been described in detail by Zitting and co-workers
(1978). The chest films were all examined by three persons, i.e., a radiologist
21
073
398
44
23
3,3
67
10
43
11
41
22
27
3
6
15
11
2
3
2
6
2
5
6
2
Mean
6
N
IS-30
25-28
2-20
7-60
10-11
30-56
3-4
48-84
2-6
l-99
2-7
0,2-0,4
11-59
Range
5
2
2
3
6
N
21
19
69
33
5,1
Mean
Optical method
8-37
15-23
6-7
26-45
l-14
Range
Concentration
n All fibers over 5 pm in length, below 3 pm in diameter, and with an aspect ratio over 3: 1 were counted.
b The number in parentheses denotes the number of workers on the work shift.
Drilling (l-2)*
By automatic machine
(outside the cabin)
By handtools
Loading and
transport (3 -4)
Primary crushing plant (1)
Inside control room
Outside control room
Manual sorting (13)
Automatic sorting (1)
Inside control room
Outside control room
Secondary crushing plant (1)
Inside control room
Outside control room
Fine crushing plant (1)
Inside control room
Outside control room
Flotation plant (2)
(including fine
milling)
Bagging (3)
Operation
Concentration
(mg/m” total dust)
4
3
2
2
3
16
4
5
5
N
30
36
11
52
674
w
23
2,6
598
Mean
SEM
of fibers (tibers/cm3)”
TABLE 1
CONCENTRATIONOFTOTALDUSTANDFIBERSDUR~NGDIFFERENTOPERATIONALSTAGES
15-45
27-42
11-12
42-63
4-10
2-50
7-10
l-5
1-21
Range
.F
2
8
z
z
WOLLASTONITE
EXPOSURE
AND LUNG
295
FIBROSIS
TABLE 2
CLASSIFICATION OF QUARRY WORKERS ACCORDING TO SMOKING
HABITS AND DURATION OF EXPOSURE
Exposure (years)
Smokers
lo- 19
20-29
230
Total
Average duration
of exposure
Average duration
since initial
exposure
4
9
1
14
8
6
3
17
3
9
3
15
15
24
7
46
21.3
19.7
23.7
21.5
21.9
21.6
24.9
22.8
Exsmokers
Nonsmokers
Total
(A.Z.) and two specialists in occupational medicine (M.S.H. and H.K.) using the
IL0 International
Classification of radiographs of pneumoconioses
(1980). The
films were read independently,
without knowledge of the occupational history of
the subjects. If the assessments did not agree, the films were reviewed by the
readers together; the score which was determined jointly was then used as the
classification.
The lung function tests included dynamic spirometry, diffusing capacity, and
nitrogen single breathing tests. A Bernstein type spirometer (Kifa, Sweden) was
used to measure the vital capacity (VC), the forced expiratory volume in 1 set
(FEV,,,), and the maximal midexpiratory
flow (MMEF). The carbon monoxide
diffusing capacity (DL,,) was measured according to the method of Cotes (1975)
with transfer test apparatus (Morgan, England). The nitrogen single breath tests
were done with Pulmo-Lab 5300 apparatus (Cardio-Pulmonary
Instruments Corp.),
according to the method of Buist and Ross (1973a,b) and delta-N, (the slope of
phase III) and closing volume were calculated as a percentage of VC.
Three consecutive specimens of sputum were collected from each subject in the
morning. The first specimen was usually collected in the clinic, and the other two
were collected at home. All sputa were fixed directly into 70% alcohol. Two
smears were prepared from each subject; the smears were stained according to the
Papanicolaou method. The preliminary screening was performed by a laboratory
technician who recorded all the useful findings. The final report was made by a
cytopathologist
(J.N.). The cytological findings were reported according to the
classification of Papanicolaou, i.e., class 0 to class V. Free alveolar macrophages
had to be identified before the smear was considered adequate; otherwise the
smear was considered to be insufficient (Papa cl 0). Eosinophils and inflammation
were also recorded when found in the sputum specimens. The presence of inflammation was recorded cytologically
when sputum smears revealed a marked
representation of neutrophils in comparison with cells. When this relation was
extremely clear, the cellular picture was interpreted as a purulent inflammatory
finding. The smear was checked for the presence of ferruginous bodies.
The x2 test was used for the statistical analyses. In some comparisons, when the
frequencies were low, Fisher’s exact probability test was used. Student’s t test
was also used.
296
HUUSKONEN
ET
AL.
IV. RESULTS
Symptoms
and Signs
Eight (26%) of the thirty-one smokers and exsmokers had symptoms of chronic
bronchitis defined as a cough and the production of phlegm for 3 months per year
for a period of at least 2 years (Table 3). Two of the eight men (one 34 years old
and the other 57 years old) had been exposed to dust for less than 20 years (15 and
19 years, respectively).
The remaining six men (mean age 48.5 years, range
44-55) had been exposed to dust for more than 20 years (mean 24.8 years, range
20-35). Three of the fifteen nonsmokers had chronic bronchitis; they had been
exposed in the quarry for 16, 20, and 26 years. The medical history of these three
men contained no other explanation for the chronic bronchitis.
Ten of the forty-six workers showed breathlessness defined as shortness of
breath when hurrying on level ground or when walking up a slight hill (Table 3).
Smoking habits had little effect on the prevalence of dyspnea. The chest films of
three of these ten subjects showed slight fibrosis (l/O), whereas bilateral pleural
changes (at least a, 3) were found for 8 of the 10 men.
Two of the forty-six workers had crepitations. Clubbing was found in three of
the workers.
TABLE
PREVALENCE
OF CHRONIC
BRONCHITIS
ACCORDING
TO SMOKING
AND
HABITS
3
DYSPNEA~
AMONG
46 QUARRY WORKERS,
AND DURATION OF EXPOSURE
Duration of exposure
and fmdings
Smokers and
exsmokers
lo- 19 years
Subjects examined
Chronic bronchitis
Dyspnea
12
2
2
3
1
1
15
3 (20)’
3 (20)
20-29 years
Subjects examined
Chronic bronchitis
Dyspnea
15
5
4
9
2
2
24
1 (2%
230 years
Subjects examined
Chronic bronchitis
Dyspnea
4
1
1
3
0
0
I
1 (14)
1 (14)
Total
Subjects examined
Chronic bronchitis
Dyspnea
31
8
I
15
3
3
46
11 (24)
10 (22)
Nonsmokers
Total
6 (25)
a Defined as cough and the production of phlegm for 3 months per year for at least 2 years.
* Defined as shortness of breath when hurrying on level ground or when walking up a slight hill.
c Numbers in parentheses are percentages.
WOLLASTONITE
Radiographic
EXPOSURE
AND
LUNG
297
FIBROSIS
Findings
The presence of pulmonary fibrosis (14/16 = 31%) among quarry workers was
more common than among referents (l-3146 = 2-7%; 0.001 < P < 0.01; Table 4).
The fibrotic changes were mild in profusion (l/l for eight men and l/O for six men),
and the opacities were irregular (s/t or t/s), except in one case where irregular and
rounded opacities (t/p) were found. Fibrosis was found in the middle and lower
zones of the lungs of eight men. Fibrosis was found in all zones of the lungs of six
men.
The duration of exposure of quarry workers with lung fibrosis (2 l/O), on average, was 22 years (lo-35 years); the duration of exposure of quarry workers
without any fibrotic changes was, on average, 18.8 years (14-30 years). Two
(13%) of the fifteen workers with less than 20 years of exposure to dust showed
TABLE
GENERALRADIOGRAPHIC
4
WORKER.YANDAMONGTHEREFERENTS
FINDINGSAMONGTHEQUARRY
Group
N
Quarry workers
Subjects examined
Pulmonary fibrosis only”
Pleural thickening only *
Both changes’
All fibrosis”,’
All pleural thickeningbsc
46
7
6
7
14
13
Lumberjacks
Referents examined
Pulmonary fibrosis only
Pleural thickening only
Both changes
All fibrosis
All pleural thickenings
46
1
1
0
1
1
Peat workers
Referents examined
Pulmonary fibrosis only
Pleural thickening only
Both changes
All fibrosis
All pleural thickening
46
2
3
1
3
4
Tobacco manufacturers
Referents examined
Pulmonary fibrosis only
Pleural thickening only
Both changes
All fibrosis
All pleural thickening
46
2
2
0
2
2
a As defined at least l/O (ILO, 1980).
’ As defined bilateral pleural thickening at least a, 3 (ILO, 1980).
c Combination of fibrosis and pleural thickening as defined above.
Percentage
15
13
I5
30
28
298
HUUSKONEN
ET AL.
fibrosis. A total of 24 workers had been exposed for 20-29 years; nine (38%) of
them showed fibrosis. Three (43%) of the seven workers who had been exposed
for at least 30 years showed fibrosis (Table 5). Three (20%) of the fifteen
nonsmokers had fibrosis; the respective figure was 11 (35%) for the 31 smokers
and exsmokers (Table 5). The prevalence of chest film changes by age for the
study and referent populations is presented in Table 6. Minimal fibrotic changes in
the lungs (O/l) were found for ten of the quarry workers; the corresponding figures
were nine for the lumberjacks, four for the peat workers, and eight for the men in
tobacco manufacturing.
Bilateral pleural thickening defined as a finding of at least “a” (width) and 3
(extent) (IL0 1980), without obliteration of both costophrenic angles, was found
for 13 (28%) of the 46 men. Similar changes were found for one, two, and four
subjects in the referent series (0.01 < P < 0.05) (Table 4). The average duration of
exposure for men without pleural thickening was 19.2 years (14-30 years); men
with bilateral pleural thickening had been exposed for an average of 22.4 years
(lo-41 years). Four of the fifteen workers who had been exposed for less then 20
years showed bilateral pleural thickening; the corresponding figures were 6 of the
24 men exposed for 20-29 years, and 3 of the 7 men exposed for more than 30
years (Table 5). Smoking did not greatly affect the presence of pleural thickening.
One worker who had been exposed for 41 years had calcified bilateral diaphragmatic thickening.
Two of the quarry workers with fibrosis (5 l/O) had been exposed to librogenic
TABLE
PREVALENCE
OF LUNG FIBROSIS
46 QUARRY WORKERS, ACCORDING
Duration of exposure
and findings
5
AND BILATERAL
PLEURAL THICKENING*
AMONG
TO SMOKING
HABITS AND DURATION
OF Exnosua~
Smokers
Exsmokers
Nonsmokers
Total
lo- 19 years
Subjects examined
Fibrosis
Pleural thickening
4
1
1
8
1
2
3
0
1
15
2 (13)”
4 (27)
20- 29 years
Subjects examined
Fibrosis
Pleural thickening
9
5
3
6
2
3
9
2
0
24
9 (381
330 years
Subjects examined
Fibrosis
Pleural thickening
1
1
1
3
1
0
3
1
2
7
3 (431
3 (431
14
I
5
17
4
5
15
3
3
46
14 (30)
13 (28)
Total subjects examined
Fibrosis
Pleural thickening
a Defined as at least l/O (ILO, 1980).
* Defined as at least a, 3 (ILO, 1980).
c Numbers in parentheses are percentages.
6 (25)
WOLLASTONITE
EXPOSURE
RADIOGRAPHIC
AMONG
Age
af time
of examination
Quarry workers
40
40-49
50-59
260
Lumbejacks
40
40-49
50-59
260
Peat
workers
40
40-49
50-59
360
Tobacco manufacturers
40
40-49
50-59
~60
FINDINGS
THE
REFERENTS
AND
TABLE
6
AMONG
THE
IN RELATION
Total
in age
category
Normal
4
21
17
4
46
3 (75)
11 (52)
10 (59)
2 (50)
26 (57)
3
21
22
0
46
LUNG
QUARRY
299
FIBROSIS
WORKERS
TO ATTAINED
Pulmonary”
fibrosis
0 (0)
AND
AGE
Bilateral pleural
thickening”
105)
6 (2%
7 (33)
6 (35)
I (25)
14 (30)
5 (29)
1(W
13 (28)
3 (100)
19 (90)
22 (100)
0 (0)
44 (96)
0 (0)
0 (0)
4
18
24
0
46
4(100)
16 (89)
19 (79)
0 (0)
39 (85)
3
18
20
5
46
3 (100)
18 (100)
17 (85)
4 (80)
42 (91)
l(5)
l(5)
0 (0)
0 (0)
0 (0)
0 (0)
l(2)
l(2)
0 (0)
0 (0)
l(6)
2(8)
l(6)
3 (7)
3 (13)
0 (0)
4 (9)
0 (0)
0 (0)
0 (0)
0 (0)
l(5)
lG3J)
2 (4)
2(1Q
0 (0)
0 $9
2 (4)
a Defined as in Table 4.
dust prior to the present exposure. Fifteen years ago, one worker had been exposed to silica dust for one year as a driller; this exposure was followed by 13
years of exposure as a driller at his present job. The other man had been exposed
to silica dust for 15 years before working at his present job, at which he had been
working for 19 years. In both frms, the latter worker had been employed as a
supervisor.
Respiratory Physiological Measurements
Among the 46 male workers who participated in the respiratory physiological
measurements, the VC was normal (~30% of the predicted) for 44 (96%). The
FEV,,, was decreased (GO% of the predicted) for one man. For four subjects
(9%) the MMEF was decreased (<70%), whereas the DLco was decreased for two
men.
The subjects were grouped according to smoking habits, the profusion of
radiographic opacities, VC, FEVI,o, MMEF, and DLco (Table 7). In addition to
300
HUUSKONEN
ET AL.
TABLE
I
VITAL CAPACITY (VC), FORCED EXPIIUTORY
VOLUME
IN 1 set (FEV,.,),
MAXIMAL
MIDEXPIRATORY
FLOW (MMEF),
AND CARBON MONOXIDE
DIFFUSION
CAPACITY (DL,d
OF 46
QUARRY WORKERS WITH RESPECT TO SMOKING HABITS AND PROFUSION OF RADIOGRAPHIC
OPACITIES
Profusion
vc
of radiographic
FEV,,
opacities
MMEF
J&o
Smoking
habits
O/O-O/l
Nonsmokers
N
Mean
SD
12
102.8
13.1
3
98.0
7.1
12
113.5
12.4
3
103.5
5.0
12
118.9
41.1
3
75.0
14.1
12
113.9
14.8
3
111
7.1
Exsmokers
N
Mean
SD
13
98.5
13.4
4
91.3
12.9
13
107.8
13.0
4
102.8
13.8
13
110.8
17.3
4
116.3
19.6
13
108.6
17.1
4
105.5
12.9
N
Mean
SD
I
97.5
11.4
I
96.9
10.5
7
105.5
13.8
I
103.4
14.4
I
104.0
25.8
7
97.1
36.8
7
98.5
15.0
I
95.3
16.1
Total
N
Mean
SD
32
99.9
12.9
14
95.5
10.5
32
109.4
13.0
14
103.3
12.2
32
112.4
28.1
14
91.9
27.0
32
108.4
16.0
14
101.6
13.3
of predicted
values.
Note. Mean
values
l/O-l/l
are percentages
O/O-O/l
l/O-l/l
O/O-O/l
l/O-l/l
O/O-O/l
l/O-l/l
opacities, the presence of bilateral pleural thickening (at least a, 3 (ILO)) was
evaluated, and the various groups were compared with respect to pleural thickening and respiratory function (Table 8). No significant differences were found.
The closing volume was increased for seven subjects, and two subjects had an
increased delta-N,. Thus, 9 (20%) of the 46 showed signs indicating small airways
disease. Three of these nine men were nonsmokers, three were exsmokers, and
three were smokers; one in each smoking category had chronic bronchitis. The
chest films of six of these nine men showed fibrosis of at least l/O, two had findings
of O/l, and no signs of fibrosis were found for one man.
Cytological
Findings
Five subjects (10.9%) had insufficient sputum specimens. Neither malignant nor
suspicious cytological findings were found for any of the subjects examined. Ferruginous bodies were not found.
V. DISCUSSION
The attention paid to the hazards
fibers other than asbestos has been
mesothelioma
and pleural radiologic
people who were exposed to a group
of exposure to naturally occurring mineral
proven to be justified. A high incidence of
abnormalities
in Turkey was found among
of volcanic nonasbestos silicate fibers called
WOLLASTONITE
EXPOSURE
AND
TABLE
LUNG
301
FIBROSIS
8
VITAL CAPACITY (VC), FORCED EXPIRATORY
VOLUME
IN 1 set (FEV,,,), MAXIMAL
MIDEXPIRATORY
FLOW (MMEF), AND CARBON MONOXIDE
DIFFUSON
CAPACITY (DL,,)
OF 46 QUARRY WORKERS
WITH RESPECT TO PROFUSION OF SMALL RADIOGRAPHIC OPACITIES AND
PRESENCE OF BILATERAL
PLEURAL THICKENING
Bilateral pleural thickening
Profusion
of small
pulmonary
opacities
Present
Absent
Present
Absent
Present
Absent
Present
Absent
O/O-O/l
N
Mean
SD
6
93.3
15.3
26
101.7
11.8
6
104.0
19.4
26
111.1
10.9
6
108.3
33.2
26
114.0
30.4
6
99.4
10.9
26
110.6
17.0
l/O- l/l
N
Mean
SD
7
94.7
11.1
7
96.0
10.5
7
105.1
12.4
7
101.0
13.2
7
107.7
33.2
7
90.2
29.1
7
98.0
11.7
7
104.2
18.4
Total
N
Mean
SD
13
94.1
13.0
33
100.5
11.5
13
104.6
15.6
33
109.0
11.4
13
108.0
33.2
33
109.0
30.1
13
98.6
11.4
33
109.2
17.3
vc
MMEF
FEV,.,
J&o
Note. Mean values are percentages of predicted values.
zeolites (Baris et al., 1978 and Lilis, 1981). The size of the zeolite fibers, and their
fibrogenic and carcinogenic effects in animals are comparable to those of asbestos
(Yasunosuke, 1981). The possible health hazards associated with other naturally
occurring fibrous minerals such as wollastonite, sepiolite, and attapulgite have
also been discussed recently (Shasby et al., 1979; Sors et al., 1979; Baris et al.,
1980; Leineweber, 1980; Binon et al., 1980, and Leineweber, 1981).
Wollastonite includes fibers which in form, length, and diameter are comparable
to the fibers of amphibole asbestos (Korhonen and Tossavainen, 1981). Respirable
fibers, characteristically
0.2-0.3 pm in diameter and several micrometers
in
length, can be found in airborne dust. Clinical and epidemiological
data on wollastonite workers are scarce. Shasby et al. (1979) found an increased prevalence of
chronic bronchitis among wollastonite workers. Smoking is known to be the chief
etiologic factor of chronic bronchitis, and the effect of smoking frequently overshadows the influence of weaker, e.g., occupational, agents. In the present study
three of the 15 nonsmokers had chronic bronchitis for which no explanation could
be found other than exposure to dust. Hence these results are in agreement with
the report of Shasby and co-workers (1979). However, as far as chronic bronchitis
is concerned, it is difficult to distinguish any influence of wollastonite from the
total exposure to dust in the quarry.
This study showed that breathlessness, crepitations, and clubbing are not sensitive indices for slight pulmonary changes, a finding which agrees with the results
of earlier research.
302
HUUSKONEN
ET
AL.
Exposure to sepiolite and attapulgite may cause lung fibrosis (Baris et al., 1980;
Bignon et al., 1980; Sors et al., 1979). The prevalence of radiological abnormalities among quarry workers was found to be widespread in the present study.
Radiographs of the IL0 classification (1980) were used as a comparison set when
the changes of the lungs were evaluated. The films were checked by experienced
readers. The interobserver difference was insignificant.
Thus the results were
considered reliable. The fibrosis found among the quarry workers was similar in
type, location, and profusion to the fibrosis found among patients with early
asbestosis (Zitting et al., 1978). The level of exposure to fibers in the Finnish
anthophyllite
asbestos mine was about the same as the concentrations measured
in the limestone - wollastonite quarry. About one-third of limestone - wollastonite
quarry workers who had been exposed for at least 10 years (mean 21.5 years) had
lung fibrosis, whereas about one-half of the anthophyllite asbestos quarry workers
exposed for at least 5 years showed lung fibrosis (Huuskonen et al., 1980).
In the present study fibrosis of the lungs was mild, even when the level of
exposure to wollastonite fibers in some operations had been heavy. However, all
32 anthophyllite
asbestos workers examined at the Institute between 1964 and
1979 also had mild fibrosis of the lungs at the time of diagnosis; 14 cases belonged
to group O/l, nine cases to group l/O, and nine cases to group l/l (Zitting et al.,
Suoranta et al., 1982). The duration of exposure for the anthophyllite
asbestos
subjects was 19.5 years (5-30), and the latency time from initial exposure was
23.3 years (8-37). The respective figures in the present study were 21.5 years
(10-41) and 22.8 years (10-41). Among the age-matched referents, radiological
changes were minimal in comparison to the quarry workers.
The dust of the quarry also contains limestone and silica. The combined effects
of wollastonite and silica in the etiology of fibrosis are not known, but exposure to
silica alone does not explain the extent or type of lung fibrosis. However, in the
present study, the fiber effect in chest films is predominant,
i.e., diffuse lung
fibrosis without nodular components and bilateral pleural thickening, in one case
even calcified.
Smoking seems to be a promoting agent in the rise of lung fibrosis (Weiss, 1969),
but different smoking habits in this study could not explain the excess of fibrosis
among quarry workers when compared with the referent groups.
Conventional lung function tests are not sensitive enough to find milk fibrosis of
the lungs. Signs indicating some kind of destruction or obstruction (Thurlbeck,
1979) in the peripheral airways were found among the nonsmoking group, tot’
especially the lower MMEF and abnormal nitrograph (delta-N, and closing volume). Deteriorated lung function showed a slight but overall tendency to become
more prominent along with the radiological changes. The diffusing capacity was
normal for all but two workers. The functional profile of the pulmonary changes is
more indicative of obstruction in the airways than of parenchymal fibrosis. In
these respects, however, this group was too small to justify definite conclusions.
Potts and co-workers (1978) have shown the hemolytic activity of wollastonite
on rat erythrocytes which may indicate its fibrogenity in vivo. The solubility of
wolastonite in body tissues is unknown. Most authors think that ferruginous bodies
are rarely formed if the mineral fibers are less than 5- 10 pm in length and if the
WOLLASTONITE
EXPOSURE
AND
LUNG
FIBROSIS
303
diameter is beyond 0.1 to 0.3 pm (Churg and Warnock, 1981). Wollastonite fibers
are comparable to anthophyllite
or tremolite asbestos fibers as far as fiber dimensions are concerned. No ferruginous bodies were found in this study. However,
this study group was small, and it is also known that amphibole asbestos fibers
may remain uncoated (Churg and Warnock, 1981). The reasons for the differences
of fibers in the production of ferruginous bodies are not known in detail.
Further follow-up of workers exposed to wollastonite is required before the
health hazards of wollastonite can be evaluated in full. A mortality study is in
progress. However, the total number of people exposed to wollastonite is so small
that no answer with regard to its carcinogenicity
can be expected.
ACKNOWLEGDMENTS
We are especially indebted to the Partek Company for their valuable assistance throughout the
entire work. We also wish to extend our appreciation to the workers who participated in the study, and
to Ms. Tuula Fahlstrdm for aid in statistical treatment of the data, and to Ms. Irma Saari for typing the
manuscript. Ms. Sheryl Hinkkanen has kindly revised the English of the text.
REFERENCES
Institute of Geological Sciences, H. M. Stationary Offtce,
Andrews, R. W. (1970). “Wollastonite.”
London.
Baris, Y. I., Sahin, A. A., and Erkan, M. L. (1980). Clinical and radiological study in sepiolite workers. Arch. Environ.
Health
35, 343-346.
Baris, Y. I., Sahin, A. A., Ozesmi, M., Kerse, I., Ozen, E., Kolacan, B., Altinors, M., and Gotkepeli,
A. (1978). An outbreak of pleural mesothelioma and chronic fibrosing pleurisity in the village of
KarainlUrgiip in Anatolia. Thorax 33, 1st - 192.
Bignon, J., Sebastian, P., Gaudichet, A., and Jaurand, M. C. (1980). Biological effects of attapulgite.
In “Biological Effects of Mineral Fibers,” (J. C. Wagner and W. Davis, Ed%), Vol. 1, pp.
163- 181. International Agency for Research on Cancer, Lyon.
Buist, A. S., and Ross, B. B. (1973a). Predicted values for closing volumes using a modified single
breath nitrogen test. Amer. Rev. Respir. Dis. 107, 744752.
Buist, A. S., and Ross, B. B. (1973b). Quantitative analysis of the alveolar plateau in the diagnosis of
early airway obstruction. Amer. Rev. Respir. Dis. 108, 1078- 1087.
Churg, A. M., and Warnock, M. L. (1981). Asbestos and other ferruginous bodies, their formation and
clinical significance. Amer. J. Pathol. 102/3, 447-456.
Cotes, J. E. (1975). “Lung function. Assessment and application in Medicine,” 3rd ed. Blackwell,
Oxford.
Harris, P. G. (1973). Clinical signs. In “Biological Effects of Asbestos,” (P. Bogovski, et al., Eds.),
pp. 19-24. International Agency for Research on Cancer, Lyon.
Huuskonen, M. S., Ahlman, K., Mattsson, T., and Tossavainen, A. (1980). Asbestos disease in
Finland. J. Occup. Med. 11, 751-754.
International
Labor Office (1980). “IL0
International
Classification
of Radiographs
of
Pneumoconioses,” Occupational Safety and Health Series No. 22 (rev.), Geneva.
Korhonen,
K., and Tossavainen, A. (1981). Wollastoniitti-kuituinen
teollisuusmineraali.
(Wollastonite-a
fibrous industrial mineral). Vuoriteollisuus
39, 38-45.
Leineweber, J. P. (1980). Dust chemistry and physics: Mineral and vitreous tibres. In “Biological
Effects of Mineral Fibers” (J. C. Wagner and W. Davis, Eds.), Vol. 2, pp. 881-900. International
Agency for Research on Cancer, Lyon.
Leineweber, J. P. (1981). Fiber toxicology. J. Occup. Med. 6, 431-434.
Lilis, R. (1981). Fibrous zeolites and endemic mesothelioma in Cappadocia, Turkey. 1. Occup. Med. 8,
548-550.
Medical Research Council’s Committee on the Aetiology of Chronic Bronchitis (1960). Standardized
questionnaire on respiratory symptoms. Bit. Med. J. 2, 1665.
304
HUUSKONEN
ET AL.
Potts, W. J., Lederer, T. S., and Gehring, P. I. (1978). Hemolysis of washed rat erythrocytes in vitro
by dust particles. Ann. Ind. Hyg. Assoc. J. 39, 497-502.
Shasby, D. M., Petersen, M., Hodous, T., Boehlecke, B., and Merchant, J. (1979). Respiratory
morbidity of workers exposed to wollastonite through mining and milling. In “Dust and Disease,” (R. Lemen and J. M. Dement, Eds.), pp. 251-256, Pathotox, Park Forest South, Ill.
Sors, H., Gaudichet, A., Sebastian, P., Bignon, J., and Even, P. (1979). Lung fibrosis after inhalation
of fibrous attapulgite. Thorax 34, 695.
Suoranta, H., Huuskonen, M. S., Zitting, A., and Juntunen, J. (1982). Radiographic progression of
\ asbestosis. Amer. J. Ind. Med. 3, 67-74.
Thurlbeck, W. M. (1979). Structural abnormalities of the peripheral airways, In “Proceedings of a
Symposium, Copenhagen, March 29-30” (J. Sadoul et al., Eds.), pp. 3-8. Excerpta Medica,
Amsterdam.
Weiss, W. (1969). Cigarette smoking and diffuse pulmonary fibrosis. Amer. Rev. Respir. Dis. 99,
67-72.
Yasunosuke, S. (1981). Carcinogenic and fibrogenic effects of zeolite. In “Abstracts of XX International Congress on Occupational Health, Cairo, Egypt, September 25-October 1, 1981,” p. 488.
Zitting, A., Huuskonen, M. S., Alanko, K., and Mattsson, T. (1978). Radiographic and physiological
fmdings in patients with asbestosis. Sand. J. Work Environ.
Health
4, 275-283.