Defining Disease, Determining Cause
The detection, definition, and recognition of occupational disease have been subjects of contention from the late 19th century to the present. The way we define a disease and its cause is a dollars-and-cents issue that affects the assignment of responsibility for prevention, treatment, and compensation of the sick. Historically, workers and employers tended to be on opposite sides in determining what constituted an occupational disease, and physicians have wrestled with scientific uncertainty and economic loyalties as arbiters of those debates.
The handful of diseases that gained acceptance in the early 20th century as having an occupational etiology were primarily the result of exposure to toxins such as lead and radium, where cause and effect were ultimately difficult to deny.1 Pneumoconiosis and other respiratory diseases related to the dusty trades have been more controversial, complicated by terminology, measurement of the amount and duration of dust exposure, methods of detecting symptoms, differences in observers’ interpretation of clinical data, long latency periods, lack of research, and attempts to determine a single reason for cause, despite contributing factors such as working conditions, infectious disease, and smoking.2,3
In light of the recent revelations about mesothelioma among taconite workers on Minnesota’s Iron Range, it is interesting to look at the historical medical literature that was available 75 to 100 years ago to Dr. Charles Bray, who ran the Biwabik hospital at the beginning of the 20th century. Despite the availability of statistical evidence in the early 20th century that metal miners suffered more respiratory disease and greater morbidity and mortality than even coal miners, iron mining-related pneumoconiosis and possible links between iron-mining and cancer received little attention from physicians and scientists.4 A 1917 Public Health Service study of “miners’ consumption” in zinc miners used X-ray evidence to support the empirical, common-knowledge observation that men who worked amid dynamite, damp, and dust experienced respiratory problems related to their work.5 Two studies in the early 1930s related iron mining or iron foundry work to silicosis and pneumonia, but two experimental animal studies found no single characteristic silicosis caused by iron ore, nor a link between pneumoconiosis from occupational dust inhalation and pulmonary carcinoma.6-9 After that, little research was done on iron mining respiratory disease until French physicians began exploring lung cancer in iron miners around 1960.10,11
“Primary malignant pleural tumours” were reported in the medical literature as far back as 1767, but the term “mesothelioma” (for the tumors of the pleural or peritoneal lining caused by occupational exposure to asbestos) was first used in Britain and Germany between 1935 and 1938, after pulmonary fibrosis or silicosis had been linked to asbestos mining.12,13 The environmental protection lawsuit against the Reserve Mining Company over the dumping of taconite tailings in Lake Superior stimulated a flurry of research on the health effects of taconite in the 1980s.
Taconite is a mineral relative of amosite asbestos. One study by Canadian and U.S. researchers concluded that taconite workers were at risk for silicosis but found no cases of mesothelioma among workers with 20 or more years of exposure to taconite dust.14 Three other studies of taconite miners and workers between 1983 and 1992 found bronchial symptoms to be correlated with cigarette smoking and lower-than-expected rates of cancer, and no evidence of asbestos-related disease.15-17 Some have questioned those conclusions, as the three studies were sponsored by the Reserve Mining Company and the trade association for the iron ore industry and used data supplied by the iron ore companies.18 —J.G.
References
1. Legge RT. Progress of American industrial medicine in the first half of the 20th century. Am J Public Health. 1952;42:905-12.
2. Weeks JL. The fox guarding the chicken coop: monitoring exposure to respirable coal mine dusts, 1969-2000. Am J Public Health. 2003;93(8):1236-44.
3. Musch DC, Landis JR, Higgins IT, Gilson JC, Jones RN. An application of kappa-type analyses to interobserver variation in classifying chest radiographs for pneumoconiosis. Stat Med. 1984;3(1):73-83.
4. Thompson WG. The Occupational Diseases: Their causation, symptoms, treatment and prevention. New York: D. Appleton and Co., 1914.
5. Lanza AJ. Miners’ consumption: a study of 433 cases of the disease among zinc miners in southwestern Missouri. Public Health Bulletin No. 85. Washington, DC: GPO, 1917.
6. Lawson GB and Gardner JE. Pneumoconiosis in Iron Miners. JAMA. 1931;96:1129-31.
7. Brundage DK, Russell AE, Jones RR, Bloomfield JJ, Thompson LK. Frequency of pneumonia among iron and steel workers. Public Health Bulletin No. 202. Washington, DC: GPO, 1932.
8. Naeslund C. Experimental investigations concerning the liability to silicosis amongst workmen in iron mines. J Indust Hyg. 1938;20:435-53.
9. Vorwald AJ, Karr JW. Pneumoconiosis and pulmonary carcinoma. Am J Path. 1938;14:49-57.
10. Monlibert L, Roubille R. [Apropos of bronchial cancer in an iron miner.] J Fr Med Chir Thorac. 1960;14:435-9.
11. Antoine D, Braun P, Cervoni P, Schwartz P, Lamy P. [Should the lung cancer of iron-miners in Lorraine be considered an occupational disease?] Rev Fr Mal Respir. 1979;7(1):63-5.
12. McDonald JC, McDonald AD. The epidemiology of mesothelioma in historical context. Eur Respir J. 1996;10(11):1932-42;.
13. Greenberg M. Correspondence: History of mesothelioma. Eur Respir J. 1997;10:2690-1.
14. Clark TC, Harrington VA, Asta J, Morgan WK, Sargent EN. Respiratory effects of exposure to dust in taconite mining and processing. Am Rev Respir Dis. 1980;121(6):959-66.
15. Higgin IT, Glassman JH, Oh MS, Cornell RG. Mortality of Reserve Mining Company employees in relation to taconite dust exposure. Am J Epidemiol. 1983;118(5):710-9.
16. Cooper WC, Wong O, Graebner R. Mortality of workers in two Minnesota taconite mining and milling operations. J Occup Med. 1988:30:506-11.
17. Cooper WC, Wong O, Trent LS, Harris F. An updated study of taconite miners and millers exposed to silica and non-asbestiform amphiboles. J Occup Med. 1992;34:1173-80.
18. Huffman TR. Exploring the legacy of Reserve Mining: what does the longest environmental trial in history tell us about the meaning of American environmentalism? J Policy History. 2000;12:339-68.