Abstract
Implementation of the coal mine dust (“CMD”) interim standard of 3.0 milligrams per cubic meter (“mg/m 3 ”) in 1970 was reduced to 2.0 mg/m3 in 1972 and produced a steady decline in dust levels and prevalence of coal workers pneumoconiosis (“CWP”). Beginning in the mid-1990s, an apparent increase was reported in what was thought to be severe and rapidly progressive CWP and PMF despite stability in CMD levels. These “sentinel health” events led to further investigation and stimulated the 2010 MSHA proposal to lower the current CMD standard from 2.0 mg/m 3 to 1.0 mg/m 3 . The purpose of this study is to summarize exposure-response associations between CMD and CWP to evaluate evidence for a revised standard. There are five cohorts of UK and US coalminers with exposure-response analyses useful for assessing a proposed coal mine dust standard. Two major biases confound such an evaluation. Exposure misclassification bias occurs for exposures occurring before standards and before sampling surveillance was initiated. This bias is most obvious in the US studies where sample results collected after initiation of the standard were back-extrapolated to pre-standard time periods. The bias introduced produces a spurious steeper exposure-response slope due to overestimation of risk at higher exposure levels (>4 mg/m 3 ) and under-estimation of risk at lower exposures. Participation bias occurs in one of the US studies when survey participation rates dropped below 50% in rounds 1-4. Exposure-response evidence suggests a coal mine dust standard of 2 mg/m 3 appears to be protective from occurrence of CWP ≥2 for low rank coals. However there is excess CWP ≥2 in miners exposed to high rank coal, suggesting a lower exposure standard is needed to protect these miners.
Highlights
coal workers pneumoconiosis (CWP) was first identified in a 1928 study of the Coal Trimmers Union in Cardiff, South Wales where there were excesses of bronchitis and pneumonia, but no excesses from TB. 1Case studies showed a radiological pattern similar to silicosis
The US Public Health Service completed an important study of anthracite coal miners in Pennsylvania in 1936 [2].Radiographs identified “anthracosilicosis” in 23% of the miners and a clear exposureresponse relationship that led to a recommended standard of 50 mppcf
The important study was in Raleigh County, WV in 1963 which established that coal mine dust (CMD) exposure was producing a high occurrence of CWP (46%)and progressive massive fibrosis (PMF) (7%) that was related to tenure [3]
Summary
CWP was first identified in a 1928 study of the Coal Trimmers Union in Cardiff, South Wales where there were excesses of bronchitis and pneumonia, but no excesses from TB. 1Case studies showed a radiological pattern similar to silicosis. CWP was first identified in a 1928 study of the Coal Trimmers Union in Cardiff, South Wales where there were excesses of bronchitis and pneumonia, but no excesses from TB. This led to an understanding of a CWP entity distinct from silicosis and the modern era of studies into CWP [1]. The US Public Health Service completed an important study of anthracite coal miners in Pennsylvania in 1936 [2].Radiographs identified “anthracosilicosis” in 23% of the miners and a clear exposureresponse relationship that led to a recommended standard of 50 mppcf. This study led to a flurry of studies to document the prevalence of CWP in the US, UK and Germany
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