Effects of Low Concentrations of Asbestos

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Abstract
Low-level asbestos exposure, as occurs in pipe coverers in new ship construction, has not been considered dangerous. We surveyed 101 such workers and 94 controls matched for age, duration of employment and smoking habits in a New England yard. Dust exposure, under surveillance for 20 years, had been near the then recommended threshold limit value of 5 million particles per cubic foot (mppcf). "Asbestosis" was defined by presence of three or more of five standardized clinical abnormalities including dyspnea, rales, finger clubbing, reduced vital capacity and x-ray shadows. The latter were judged by three observers unaware of the exposure history. "Asbestosis" was 11 times more common among pipe coverers than among controls; it was found first after 13 years of exposure or 60 mppcf-years, and the prevalence was 38 per cent after 20 years. This study emphasizes that low concentrations of asbestos can lead to pulmonary fibrosis and supports the need for lower threshold limit values.