Current Clinical Practice: Attribution of Chronic Airways Disease to Occupational Dust Exposures

Abstract

Particulates not otherwise classified (PNOC) and particulates not otherwise regulated (PNOR) are the terms used by the American Conference of Governmental Industrial Hygienists and by the Occupational Safety and Health Administration (OSHA), respectively, for those dusts not already identified and covered by a specific OSHA standard, as listed in 29 CFR 1910.1000. The rubric of PNOC/R therefore covers the vast majority of dusts likely to be encountered in the workplace. However, these dusts are associated with only a small number of claims for workers' compensation or reports of occupational disease. Pneumoconioses caused by these dusts are uncommon and usually confer little functional impairment compared with the fibrogenic dusts such as asbestos, silica, and coal dust. The attribution of airways disease to nonfibrogenic dusts has been highly controversial. It is common practice, in the absence of a clear guideline to the contrary in the clinical literature, to consider exposure to nonfibrogenic dusts as a secondary risk factor for clinical lung disease, significant only as a potential aggravating factor. Recent evidence suggests that a common denominator in the contribution by dust to fixed airflow obstruction is a process of inflammatory change which persists beyond the short-term reversible airways reactivity of asthma independent of obvious symptoms of bronchitis such as cough and sputum production. These PNOC/R dusts may include particles that are antigenic, that have intrinsic toxicity not explicitly recognized, or that are apparently chemically and biologically inert but provoke a nonspecific response in the lung, such as macrophage overload. Each presents a different management problem. Current methods may not be sufficient to accurately assess the effects of the three types of PNOC/R or to investigate other problems involving nontraditional occupational lung disorders. A set of research priorities is recommended.