Summary

Recent studies have highlighted the fact that workers in Dakota gold mines and Minnesota iron mines are being exposed to elongated mineral particles (EMPs). Moreover, Minnesota miners have a higher risk of dying from lung cancer, mesothelioma and cardiac disease than the general population. Given the renewed interest in exploring for new gold and iron deposits in northern Quebec, the number of workers in these sectors is likely to increase, and so there is a need to conduct an initial assessment of these environments. With a view to evaluating the state of knowledge about the presence of EMPs in gold and iron mines in Quebec and determining their potential role in the etiology of cancers and lung diseases, a study integrating different methods and disciplines was conducted to meet the following specific objectives: (1) carry out a survey of epidemiological studies on cancer and lung disease among gold and iron mine workers; (2) assess the state of knowledge about the toxicity of dust particles from these mines, particularly asbestiform and non-asbestiform EMPs; (3) describe the geology of world gold and iron mines where OHS conditions have been studied and compare it with that of Quebec mines.

An analysis of articles in the international literature on fibrogens and carcinogens (and exposure levels) in gold and iron mines was conducted first. This analysis identified certain regions where occupational cancers and lung diseases were reported in miners. In parallel, an analysis of toxicological studies focusing chiefly on EMPs highlighted various toxicity parameters of these particles. Another review of the literature then looked at the different geological contexts of the gold and iron mines in the countries and regions identified in the epidemiological studies, and another documentary research initiative explored the presence of amphibole EMPs in Quebec gold and iron mines. This information was supplemented by the mineralogical characterization of samples from Quebec gold and iron mines to determine whether there is a likelihood of these mines containing amphibole EMPs.

The review of international epidemiological studies led to the following observations. Exposure to silica is mentioned in all the studies, for both gold and iron mines, whereas radon, arsenic and diesel exhaust fumes are reported in only some of the studies. Exposure to EMPs was measured or estimated in only two studies on gold mines and one study on iron (taconite) mines.

For gold miners, a statistically significant increase in the risk of dying from lung cancer was highlighted, in association with length of work, general dustiness, crystalline silica concentrations in the air and work in underground mines. An increase in the number of cases of mesothelioma (cancer usually associated with exposure to asbestos), some cancers of hematopoietic organs, the prostate, stomach and colon, as well as the rectum were also found, but in lesser proportions. As for non-cancerous respiratory diseases, only silicosis and “unspecified pneumoconiosis” show a high risk in most studies. The two studies that focused in particular on EMPs did not find any relationship between exposure to fibre-containing dusts and cancers or non-cancerous lung diseases.

For iron miners, a statistically significant increase in the risk of dying from lung cancer was highlighted, in association with length of work and exposure to silica, radon and diesel exhaust emissions. An increase in the number of cases of mesothelioma with length of work in taconite mines and with cumulative exposure to EMPs has been shown in U.S. studies. An increase in some other cancers (stomach, prostate, bladder, aerodigestive tract) has also been reported, but it disappeared when the data were adjusted for tobacco use. As for non-cancerous respiratory diseases, an unusually high number of abnormalities of the pleura was reported in association with cumulative exposure to EMPs, and of deaths from pneumoconiosis and chronic bronchitis in association with exposure to silica. U.S. studies have highlighted an increased risk among taconite mine workers, but the relationship between exposure to EMPs and the risk of lung cancer no longer existed once the data were adjusted for sex, exposure to silica and asbestos, and work in hematite mines.

The geological context of Quebec gold mines makes the presence of amphibole EMPs highly probable (as the mines are situated in Archean greenstone belts). Amphibole EMPs of the actinolite-tremolite series are minerals characteristic of the basalt metamorphic facies found in abundance in these belts. The chief difference between the Quebec geological context and the Dakota context (where EMPs have been measured) is the systematic spatial association between amphibole EMPs and the ore in gold mines located near iron formations (typical of the Dakotas), whereas this association is possible, but not systematic, for Quebec gold mines. The geological context of Quebec iron mines differs slightly from that of U.S. iron mines where amphibole EMP-related health problems have been reported. Even though the iron formations found in Minnesota and Quebec mines developed at the same time and along the same continental margin, metamorphic differences between the two mean that the formation of amphibole EMPs is more likely in Minnesota. In both cases, however, a systematic spatial association between amphibole EMPs and the mined ore is to be expected. The review of the literature on the mine sites confirmed the assumptions about their geological contexts: amphibole EMPs were reported in six of the nine active gold mines and in three of the 10 closed gold mines as well as in two of the three Quebec active iron mines.

The mineralogical study of 11 gold mines and two iron mines in Quebec, some active, others closed, revealed the presence of amphibole EMPs in eight of them. An acicular morphology was also observed in seven of the mines. Unlike the Canadian mines, the Homestake Mine in South Dakota, and mines in Minnesota, where grunerite is the main source of amphibole EMPs, actinolite is the most common in Quebec mines. It should be noted, however, that the samples from the mine sites studied were not necessarily taken from mined areas.

To conclude, the documented presence of EMPs in certain Quebec iron and gold mines shows that exposure to these particles is a possibility. It would therefore be appropriate to conduct systematic petrographic studies in these mines in order to identify areas likely to contain EMPs and to take fibre measurements as part of an air sampling program. If no fibre measurements are available for the mines, it would be prudent to recommend the lowest possible levels of exposure.