Non-Asbestos Fibre Burden in Individuals Exposed to Asbestos

Abstract

The characteristics of asbestos, which cause it to be classified as a carcinogen, have been the subject of numerous investigations. While various mechanisms might contribute to its overall cancer producing potential, the physical characteristics of asbestos are widely recognized as major factors. The relationship of fibrous form to tumour production is often referred to as conforming to the “Stanton Hypothesis.” The model used by Stanton incorporated non-asbestos fibres which were of a similar dimensions to asbestos fibers. Appreciable attention has been given to assessing lung tissue asbestos burdens in a number of cohorts; however, limited information exists on the amount of “non-asbestos” fibres in the lung. Since the “Stanton Hypothesis” includes fibres of a given dimension and not mineral type, it is important to gain more information on the presence and characteristics of non-asbestos fibres and their possible contribution to the development of disease.

The present study evaluates tissue from eight former shipyard workers who were exposed to asbestos but would also have been expected to have been exposed to other fibrous dusts. A comparison is made between asbestos and non-asbestos fibre burden in lung parenchyma, lymph nodes, and pleural plaques. The analytical techniques used incorporated both light microscopy and transmission electron microscopic assessments. The data indicate that non-asbestos fibres are found in all three sites and that a small percentage of these fibres are within the dimensions conforming to the “Stanton Hypothesis” for being potentially carcinogenic.