Lung asbestos content in long-term residents of a chrysotile mining town.

The effects of long-term exposure to very small amounts of chrysotile asbestos are controversial. To examine this problem, the lung asbestos content from 7 long-term (25 yr and greater) residents of Thetford Mines, Quebec, who were never employed in the chrysotile mining and milling industry, was analyzed. Thetford Mines is a chrysotile mining town with a demonstrated ambient atmospheric concentration of chrysotile asbestos approximately 200 to 500 times that in urban areas of North America. Data on the residents' lungs were compared with those obtained from 20 long-term (25 yr and greater) chrysotile industry workers from Thetford Mines and 20 members of the general population of Vancouver. The median concentrations of chrysotile and tremolite in the Thetford residents were only about one fiftieth of those of the chrysotile workers, but about 10 times that of the population of Vancouver. Because long fibers of asbestos are generally thought to be more dangerous than short ones are, the sizes of fibers from these 3 groups were also examined. The fiber size distribution of the asbestos from the Thetford residents was significantly longer than that of the Vancouver population, and resembled that of the chrysotile workers. Because epidemiologic studies have consistently failed to find an increased respiratory disease incidence in lifelong residents of Quebec chrysotile mining towns who were never employed in the chrysotile industry, these findings imply that even asbestos burdens much higher, and fiber size distributions much longer, than those of the general population of most North American cities, are not associated with demonstrable pathologic effects.