The So-called Short-Fiber Controversy: Literature Review and Critical Analysis

Abstract

Context Numerous articles in the scientific literature indicate that pathogenic fibers with respect to asbestos-related diseases are those that exceed 5 μm in length. Nonetheless, some authors have expressed concerns regarding pathogenicity of shorter fibers. Objective To review the scientific evidence regarding pathogenicity (or lack thereof) of fibers less than or equal to 5 μm in length, with particular attention to publications indicating that such fibers might be hazardous. Data Sources The scientific literature was reviewed for experimental animal studies and human studies that address the role of fiber size in causation of disease. Sources included original studies, as well as review articles related to the topic. Conclusions Experimental animal studies involving inhalation of fibers have demonstrated that fibers greater than 5 μm in length are associated with both pulmonary fibrosis (ie, asbestosis) and malignancies (carcinoma of the lung and mesothelioma). There is no convincing evidence for a pathogenic effect for fibers that are 5 μm or less in length. Fiber analyses of human lung tissue samples provide further support for pathogenicity of long fibers, particularly the more biopersistent amphibole fibers. Similar observations have been reported for nonasbestos mineral fibers. Concerns expressed by some authors (eg, the greater abundance of short fibers) do not alter these conclusions. Similarly, in vitro studies demonstrating biological activity of short fibers do not override inhalational studies of whole animals or the epidemiological findings in humans.