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epidemiological data
Type of information:
migrated information: read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
key study
Study period:
1977 - 1981; before 1977 retrospective
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Acceptable, well-documented publication meeting basic scientific principles

Data source

Reference Type:

Materials and methods

Study type:
cross sectional study
Endpoint addressed:
repeated dose toxicity: inhalation
Test guideline
no guideline followed
Principles of method if other than guideline:
Dust concentrations were determined in various work areas of a Georgia kaolin mine by gravimetric dust sampling kit (1977-1981).
The relationship of kaolin pneumoconiosis to dust exposure and work history was evaluated using a modified Medical Research Council questionnaire as well as standard postero-anterior and lateral chest radiographs.
The extent and type of pulmonary impairment in men with kaolin pneumoconiosis was determined by spirometer, CPI, body plethysmography and arterial blood gas measurements.
GLP compliance:
not specified

Test material

Details on test material:
- Name of test material (as cited in study report): kaolin dust
- Physical state / appearance: solid dust, neither asbestiform fibres nor crystalline silica was detected in any of the respirable dust samples
The subjects in the present study worked at a mine where kaolin is still processed by the dry method, and on completion of this process 50-80% of the particles are in the respirable range.
- Analytical purity: 94-98% kaolinite and 2-6% anatare (TiO2)


Type of population:
Ethical approval:
not applicable
Details on study design:
HYPOTHESIS TESTED (if cohort or case control study): no, the study was undertaken to determine the dust concentrations in various work areas and to assess the prevalence of radiographic and pulmonary function abnormalities in 65 workers at a Georgia kaolin mine.

- Type: Questionnaire, Work history and Clinical tests as well as personal air samples collected from 1977-1981
- Details to Questionnaire: Each worker answered a modified Medical Research Council questionnaire about the presence of any symptoms, cigarette smoking, and place and duration of work
- Details to Work history: The records of present and past employment for each worker were obtained from the plant personnel office.
- Details to clinical tests: Standard postero-anterior and lateral chest radiographs were interpreted by two independent readers using the ILO 1980 classification. Spirometry was performed with a 7 litre waterless spirometer (Pulmonor, Jones Medical Instruments Company, Oak Brook, Illinois). The best forced vital capacity (FVC) and the best volume expired in the first second (FEV1) from three attempts were accepted as the subject's values. In those with radiographic evidence of pneumoconiosis flow-volume loops were performed (CPI, model 5300, Pulmo-Lab, Houstan, Texas) and lung volumes were determined by body plethysmography (Auto-box, SRL Med Inc, Dayton, Ohio) according to standard methods. Arterial blood and gas measurements were made at rest and after exercise.
- Details to qualitative and quantitative analysis of kaolin dust: For qualitative analysis, two pounds of bulk samples were taken from the overburden, from kaolin lumps, and from intermediate and processed kaolin for analysis in the laboratories of the National Institutes of Health. The bulk samples were also analysed by the United States Department of the Interior, Bureau of Mines, for mineral content and the presence of mineral fibres.
Personal air samples were collected at this mine from 1977 to 1981 from various areas by gravimetric dust sampling kit (MSA, Pittsburgh, Pennsylvania). The workers wore the sampling kit for eight hours. The free silica content of all respirable dust samples was determined by x ray diffraction.

STUDY PERIOD: five years with determination of dust levels workers exposed to

SETTING: Middleton described lung disease in china clay workers in 1936. Since then other investigators have described both radiological and pathological changes occurring secondary to kaolin exposure. This study was conducted to determine (a) kaolin dust concentrations in the various areas of kaolin production; (b) the relationship of kaolin pneumoconiosis to dust exposure and work history; and (c) the extent and type in men with kaolin pneumoconiosis.

- Total population (Total no. of persons in cohort from which the subjects were drawn): 65 workers at a Georgia kaolin mine
- Selection criteria: The entire work force of 65 men employed at a kaolin mine in Georgia was studied.
At comparison of workers with pneumoconiosis and their fellow processing area workers: One subject was excluded from intra-group analysis since he had frank congestive cardiac failure at the time.
- Total number of subjects participating in study: 65
- Sex/age/race: no data for sex (maybe only men worked at mines); mean age was 47.2 with pneumoconiosis, 37.5 without pneumoconiosis and < 5 years work and 26.9 < 5 years work; maybe negroid because predicted values for spirometry, flows and lung volumes were corrected for black subjects by an adjustment factor of 0.85.;
- Smoker/non-smoker: all five workers with pneumoconiosis were cigarette smokers
- Total number of subjects at end of study: 65
- Matching criteria: -

- Type: comparison group: workers not employed in processing (in contrast, only one of the 40 radiographs of workers not employed in processing was interpreted as category 0/1.

- Disease(s): pneumoconiosis, pulmonary impairment
- Diagnostic procedure: see details to clinical effects
Exposure assessment:
Details on exposure:
TYPE OF EXPOSURE: inhalative

TYPE OF EXPOSURE MEASUREMENT: Area air sampling / Personal sampling

EXPOSURE LEVELS: The mean respirable dust level in the processing area in 1981 was 1.74 mg/m3 and 0.14 mg/m3 in the main area. No other exact values are published - there was only a scatter diagram given.

EXPOSURE PERIOD: 8 hours per day (The workers wore sampling kits for eight hours) for different periods of employmen ; of 24 workers employed in processing, 12 had worked for less than five years in this area, seven had worked for 5-10 years, and five for more than 10 years.


DESCRIPTION / DELINEATION OF EXPOSURE GROUPS / CATEGORIES: number of years spent in a particular job was accepted as the best available measure of previous exposure
Statistical methods:
Dust concentrations from the different areas were compared with an unpaired Student's t test. Spirometric comparisons between the subgroups were performed with the Wilcoxon rank sum test. A p value of less than 0.05 was considered significant.

Results and discussion

- Number of measurements: 157: During a five year period 157 respirable dust measurements were obtained from the three main areas.
- Average concentrations: about 3 mg respirable dust/m3 at the processing area 1977 - 1981; about 0.5 mg/m3 at the maintenance area and mine 1980 - 1981

FINDINGS Kaolin pneumoconiosis radiological manifestated in 5 of 65 workers; the mean values of forced vital capacity and FEV1 of the entire group were within the normal range. When the spirometric values were expressed as a percentage of the predicted values, the FVC and FEV1 were significantly lower in the workers with kaolinosis than in other workers in the processing area. The FVC and FEV1 also declined significantly with increasing years of work in the processing area. The FEV1/FVC%, however, was not significantly altered either by the presence of kaolinosis or by an increasing number of years of work, indicating that the impairment was restrictive and hence likely to be a consequence of dust inhalation rather than smoking. In this study the highest dust concentrations occurred in the processing area, and kaolin pneumoconiosis was limited to those who had worked there. Kaolin exposure appeared to have a small but significant effect on ventilatory capacity in those with kaolin pneumoconiosis and in workers with a longer exposure. There was no association between the presence of radiographic appearances of kaolinosis and cigarette smoking or between the presence of radiographic abnormalities and reduced arterial blood gas tensions.

- Incidence/ Number of cases for each disease / parameter under consideration: Prevalence of 7.7% (5 of 65 kaolin workers)
One worker had complicated pneumoconiosis and four had simple pneumoconiosis. All of them belonged to the highest dose group (25 worked at the processing area). The worker with complicated pneumoconiosis had spent his entire working life in the processing shed (36 years), while the worker with the shortest exposure (seven years) had the least radiographic abnormality.

Confounding factors:
smoking history and age
Cigarette smoking has been thought to delay dust clearance and thus increase the incidence of dust related pneumoconiosis. Since all five workers with pneumoconiosis were cigarette smokers, it is difficult to separate the contributions of smoking and pneumoconiosis to the blood gas abnormalities.
The deseased workers were older in average than the healthy workers at the time of the evaluation.
Strengths and weaknesses:
Contamination by other dusts like silica or asbestos could be excluded by the multiple qualitative analyses of the dust.

Any other information on results incl. tables

Radiographic abnormalities were found in five workers, all of whom worked in the processing area and all of whom had symptoms of bronchitis. One worker had complicated pneumoconiosis and four had simple pneumoconiosis. The radiological manifestations of kaolin pneumoconiosis appear to be related to the amount of dust present in the lungs and to the duration of exposure.

Table 1 Radiographic interpretations (ILO category) of two observers (A and B) and teh duration of work at the processing shed






C 2/2

C 2/2


















Table 2 Comparison of workers with pneumoconiosis and their fellow processing area workers (means with one standard deviation)


With pneumoconiosis

Without pneumoconiosis


> 5 y work

< 5 y work




47.2 (10.0)

37.5 (11.2)**

26.9 (9.0)**

Smoking: pack years

15.8 (4.3)

16.1 (10.2)

9.8 (9.7)


3.34 (0.19)

4.15 (0.39)**


% predicted FVC

83.4 (3.1)

95.0 (6.8)**

100.3 (8.80)**

FEV1 (I)

2.67 (0.39)

3.54 (0.42)**

4.19 (0.86)**

% predicted FEV1

88.4 (7.7)

102.2 (11.7)*

100.1 (12.6)*





*Significantly different from pneumoconiosis (kaolinosis) group (p<0.05).

**Significantly different from pneumoconiosis (kaolinosis) group (p<0.01).

FVC-forced vital capacity.

No correlation was found between the radiographic degree of pneumoconiosis and the reduction in lung volumes, but this is hardly surprising given the small number of subjects with radiographic evidence of the condition. Nevertheless, there is reason to believe that simple kaolinosis, like simple silicosis, is likely to lead to a minimal increase in lung stiffness.

Five of the 65 kaolin workers had radiographic evidence of pneumoconiosis, a prevalence of 7.7%.

Applicant's summary and conclusion

Executive summary:

Kaolin is not universally accepted as being capable of inducing pneumoconiosis. This data, however showed, first, that kaolin pneumoconiosis is most likely to develop in workers in the processing area, where the dust levels are highest, and, secondly, that kaolin pneumoconiosis is associated with only mild effects on pulmonary function. Possible contamination by other dusts is an important consideration since silica exposure has been reported in kaolin firebrick workers; but the fact that the dust to which our men had been exposed was pure kaolin, with no free silica or asbestos, was well established by the multiple qualitative analyses of the dust. The complete absence of silica indicates that inhalation of kaolin alone can lead to pneumoconiosis.

It is clear that the highest respirable dust concentrations occur in the processing area. The subjects in the present study worked at a mine where kaolin is still processed by the dry method, and on completion of this process 50-80% of the particles are in the respirable range. The prevalence of kaolin pneumoconiosis and the respirable dust concentrations are likely to be lower in those mines where wet processing is in use.