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Endemic PCs and high incidence of malignant mesothelioma from household use of asbestos have been reported in Metsovo in northwestern Greece ("Metsovo lung"). In the present study, we present similar findings in six more areas of Greece. Like Metsovo, all these areas are located within ophiolite belts. Like Metsovo, material similar to "Metsovo whitewash" has been used for various domestic uses. Asbestos fibers (chrysotile, antigorite and tremolite) were found in three of the six areas. Also, in two, MPM has been diagnosed. These findings suggest that "Metsovo lung" occurs in several areas of Greece and has similar etiology and epidemiology.

We report four cases of pleural plaques found at autopsy in individuals who resided in or near the chrysotile mining town of Thetford Mines, Quebec, and who had never been employed in the chrysotile mining and milling industry. Three of these patients were farmers, and one was a road construction worker. Lung asbestos content of these cases was compared with that of a group of nine persons living in the same vicinity who did not have pleural plaques. The plaque group was found to have an equal chrysotile content but about a fourfold elevation in median tremolite content, a statistically significant increase. Fiber sizes were the same in both groups. Also, one plaque case had an elevated level of relatively long titanium oxide fibers. These observations suggest that environmental pleural plaques in this region of Quebec are probably caused by exposure to tremolite derived from local soil and rock and that other types of mineral fibers such as titanium oxide may occasionally also be the cause of such lesions.

Radiologic screening of 688 inhabitants of the Metsovo area in Northwest Greece revealed that 323 (46.9 percent) had pleural calcifications. The percentage of positive examinations rose with age. Calcifications were observed in all four villages of the area where a material ("luto" soil) had been extensively used for whitewashing until 1940 to 1950. In four other villages in the immediate vicinity, where "luto" had never been used, pleural calcifications were not observed. Results suggest that Metsovo tremolite may have caused pleural calcifications to all individuals born in Metsovo before 1940. This is the first study indicating that environmental asbestos exposure can cause abnormalities in everyone exposed to it.

The question of whether chrysotile asbestos ever causes mesothelioma in man has become a major public and occupational health issue. Review of the literature suggests that only 53 acceptable cases of chrysotile-induced mesothelioma have ever been reported; of these, 41 cases have occurred in individuals exposed to chrysotile mine dust, all of it naturally contaminated with tremolite. Ten cases have occurred in secondary industry workers, but here the suspicion of amosite or crocidolite contamination is high. Analysis of lung asbestos content indicates that induction of mesothelioma by chrysotile requires, on average, as great a lung fiber burden as induction of asbestosis by chrysotile, whereas amphibole (amosite or crocidolite)-induced mesotheliomas appear at a several hundred-fold smaller lung burden. Tremolite alone has definitely produced mesothelioma in man, particularly when exposure has been to long, high aspect ratio, fibers. Analysis of tremolite:chrysotile fiber ratios in human lung suggests that some, but not all tremolite is removed in milling chrysotile ores. The low incidence of mesothelioma in secondary chrysotile users may reflect the small amount of tremolite left in the product. These observations indicate that although chrysotile asbestos can produce mesothelioma in man, the total number of such cases is small and the required doses extremely large. The data are consistent with the idea that mesotheliomas seen in chrysotile miners and some secondary industry workers are produced by the tremolite contained in the chrysotile ore, but that the short length and low aspect ratio of the tremolite make its carcinogenicity quite low. However, these data are very indirect, and a role for the chrysotile fiber itself is still possible.