Temporal trends in coal workers' pneumoconiosis prevalence. Validating the National Coal Study results.

Evidence from four successive rounds of the National Study of Coal Workers' Pneumoconiosis indicates diminishing prevalence of coal workers' pneumoconiosis (CWP) from 1969 to 1988. However, methodological inconsistencies across surveys have raised concerns. This study confirms the reported downward trend in CWP prevalence, utilizing a standardized methodological approach. A single team of three x-ray readers using the 1980 International Labour Office classification independently re-evaluated 3143 Appalachian-region cases to derive overall, tenure- and age-specific prevalences. Prevalence of small rounded opacities declined, with 12.7% in Round 1, 11.2% in Round 2, 3.0% in Round 3, and 3.9% in Round 4. These findings support the National Institute for Occupational Safety and Health's recommendation of a reduced exposure limit of 1 mg/m3 because the present coal dust standard does not sufficiently protect miners against adverse health effects over a working lifetime of exposures.