Silicosis -- South Dakota, Wisconsin

In 1982 and 1983, two surveys among workers exposed to crystalline (free) silica were completed by the National Institute for Occupational Safety and Health (NIOSH); both confirmed the presence of silicosis. The first survey was conducted in several plants processing minerals in South Dakota (1); the second, in a foundry in Wisconsin (2).

South Dakota: Diagnoses of silicosis in two former mineral plant workers prompted an environmental and medical survey, which was completed in March 1983. Investigators visited three plants in southwestern South Dakota that purchase feldspar, quartz rocks, and mica chips from independent miners and process them by crushing and milling. The products are used in ceramics, crystal glassware, and asphalt shingles, respectively. Seventy-seven current and former production workers participated in the health survey. Silicosis was diagnosed in five (11%) of 47 current and four (20%) of 20 former employees (with at least 1 year of exposure) when NIOSH-certified radiologists interpreted a posteroanterior chest radiograph as positive, based on the 1971 international standard classification (3).

The Mine Safety and Health Administration (MSHA) provided measurements of respirable crystalline silica dust for these worksites from 1979 to 1982. These showed that seven (26%) of 27 samples exceeded the MSHA standard for exposure to crystalline silica.* Respirable dust contained 6% quartz at the plant processing feldspar, 8% at the plant processing mica, and 38% at the plant processing quartz. No other forms of crystalline silica were detected. In 25 (38%) of 66 measurements taken by NIOSH, respirable dust samples demonstrated levels of crystalline silica that exceeded the MSHA standard. Workers with the greatest exposure included baggers, mill operators, and handlers of bulk products.

Three current workers with less than 1 year of exposure to silica dust showed no radiographic evidence of silicosis. Of the nine current and former workers with silicosis and at least 1 year of exposure, six (67%) had simple pneumoconiosis, and three (33%) had progressive massive fibrosis (PMF). Two of the nine workers had been employed only at the plant processing feldspar; three, only at the plant processing quartz; and four, at more than one worksite. Although the mean duration of exposure to silica dust among workers with silicosis was 12 years, four of the nine had less than 5 years of exposure. Results of spirometry varied considerably among the workers with silicosis; since all but one person smoked, however, attribution of pulmonary function abnormalities to silicosis was difficult. The one worker who did not smoke had PMF after 4.5 years of exposure and exhibited a moderately severe restrictive ventilatory impairment (forced vital capacity = 54% of predicted).

Wisconsin: In March 1982, as part of a health hazard evaluation at a foundry producing iron castings, 64 (61%) of 105 current workers and three (10%) of 30 retired workers were examined. Respiratory disease was evaluated by questionnaire, spirometry, and review of chest radiographs taken by the company. Assessment of the work environment included sampling for total and respirable dust and analyzing respirable dust samples by x-ray diffraction for content of crystalline silica.

Chest radiographs were submitted to NIOSH-certified radiologists for classification according to the 1971 international standards (3). Six workers (9%), whose length of employment at the foundry varied from 10 to 36 years, had radiographic evidence of silicosis. Spirometry was normal in all workers, except one with a 40-pack-year history of smoking (number of years smoking times number of packs of cigarettes per day).

Environmental sampling showed that 16 (64%) of 25 samples of dust from the core and molding areas exceeded the NIOSH recommendation of 50 ug/m((3)) (range 50-130 ug/m((3))). All 12 dust samples obtained in the finishing area exceeded the enforceable standards of MSHA and the Occupational Safety and Health Administration (OSHA) (4), as well as NIOSH-recommended limits. Reported by Mining Hazard Evaluation and Technical Assistance Program, Clinical Investigations Br, Div of Respiratory Disease Studies, Hazard Evaluation and Technical Assistance Br, Div of Surveillance, Hazard Evaluations, and Field Studies, NIOSH, CDC.

Editorial Note

Editorial Note: Silicosis is a form of diffuse interstitial pulmonary fibrosis resulting from the deposition of respirable crystalline silica in the lung. The present investigations document one of the oldest occupational diseases in two high-risk industries. The relatively short exposures and the high proportion of PMF cases observed here among the mineral workers contrast sharply with the long latent periods and less advanced stages of pneumoconiosis observed among foundry workers. Conditions of exposure may affect both the occurrence and severity of silicosis. Although it usually occurs after 15 or more years of exposure, some forms with latent periods of only a few years are well recognized and are associated with intense exposures to respirable dust high in free silica (5). Early, simple silicosis usually produces no symptoms. However, both acute and complicated silicosis (PMF) are associated with shortness of breath, intolerance for exercise, and a marked reduction in measured pulmonary function. Diagnosis is most often based on a history of occupational exposure to free silica and the characteristic appearance of a chest radiograph. Respiratory failure and premature death may occur in advanced forms of the disease. Individuals with silicosis are also at increased risk of contracting tuberculosis. No specific treatment is available, and the disease may progress even after a worker is no longer exposed to silica.

Silicosis is largely preventable by technology available to control exposure to dust. In selected industries, such as foundries, it may be eliminated by substituting other materials for silica (6). Because the disease is preventable, a specific objective of the U.S. Public Health Service for accomplishment by 1990 states: "Among workers newly exposed after 1985, there should be virtually no new cases of . . . silicosis" (7).

References

1. National Institute for Occupational Safety and Health. Health hazard evaluation report no. GHETA 82-174. Morgantown, West Virginia: National Institute for Occupational Safety and Health, 1983.

2. National Institute for Occupational Safety and Health. Health hazard evaluation report no. HETA 78-121-1071. Cincinnati, Ohio: National Institute for Occupational Safety and Health, 1982.

3. Jacobson G, Lainhart W. ILO U/C 1971 international classification of radiographs of the pneumoconioses. Med Radiogr Photogr 1972;48:65-110.

4. Occupational Safety and Health Administration. Safety and health standards. 29 CFR 1910.1000. Occupational Safety and Health Administration, revised 1980.

5. Ziskind M, Jones RN, Weill H. Silicosis, state of the art. Am Rev Respir Dis 1976;113:643.

6. National Institute for Occupational Safety and Health. An

7. Occupational Safety and Health Administration. Safety and health standards. 29 CFR 1910.1000. Occupational Safety and Health Administration, revised 1980.

8. Ziskind M, Jones RN, Weill H. Silicosis, state of the art. Am Rev Respir Dis 1976;113:643.

9. National Institute for Occupational Safety and Health. An evaluation of health hazard control technology for the foundry industry. Department of Health, Education, and Welfare (National Institute for Occupational Safety and Health) Publication no. 79-114. 1978.

10. CDC. Implementing the 1990 prevention objectives: summary of CDC's seminar. 1983;32:21-4.

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