MINERAL FIBRE DEPOSITS IN WORK ENVIROMENTS AND WORKERS: WHERE AND WHY THEY DIFFER

Scientists have studied mineral fibre exposures and their relation to health hazard and risk assessment using the lungs of workers. Tissue from those exposed offered interdisciplinary researchers opportunities to measure long-term fibre accumulation and to relate it to exposure parameters and disease outcome.

Results are usually representative of exposure and internal dose. Examples are discussed from the author’s own research at the Jeffrey Mine in Asbestos, Quebec.

Lung chrysotile, was found in excess vs. age and sex-matched controls in a single-hospital autopsy series of those living within 40 km of this asbestos mine. None had worked in, or lived with persons who worked in, the mine itself. In separate study, workers themselves born 1891-1920 showed excesses of lung cancer, mesothelioma, asbestosis and other diseases. Analysis of their lungs was surprisingly different from community residents. Tremolite, present in low concentration in dykes surrounding and intersecting the ore body, was commonly found but well below levels seen elsewhere. More surprisingly, fibrous riebeckite (“crocidolite”) was found in the lungs of three quarters of all workers analysed, having particularly high concentrations (geometric mean 2.5 million fibres longer than 5 micrometres) in six of seven workers who developed mesothelioma. Suggestions that crocidolite might be present in the deposit were proven false by mineralogical mapping. The answers instead came from finding out more about jobs for the miners/millers and factory workers with mesothelioma who had autopsy lung analysed for fiber content by TEM. Miners and millers’ median dust exposure was an order of magnitude higher than that of factory workers (373 vs. 42 million particles per cubic foot-years, p <.05). Factory workers (five cases) were five times more likely to die from mesothelioma: 1.08 per cent of all deaths compared with one in 500 among miners/ millers.

Crocidolite was used in the factory to make military gas masks during the period those who developed disease worked. “Chrysotile” mills did mill crocidolite during some periods. By comparison, of 15 workers with mesothelioma at mines and mills elsewhere in the province, no crocidolite was present but tremolite was 105 million fibres/ gram dry lung compared to 3.4 million for the Jeffrey workers (p <.01).