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Exposure to Tremolite Asbestos and Respiratory Health in Swedish Dolomite Workers

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Exposure to Tremolite Asbestos and Respiratory Health in Swedish Dolomite Workers 670 Occup Environ Med 2001;58:670–677 Occup Environ Med: first published as 10.1136/oem.58.10.670 on 1 October 2001. Downloaded from Exposure to tremolite asbestos and respiratory health in Swedish dolomite workers A I Seldén, N P Berg, E A L Lundgren, G Hillerdal, N-G Wik, C-G Ohlson, L S Bodin Abstract double salt with carbon dioxide and calcium Objectives—Deposits of carbonate rock oxide called dolomite ((CaMg)CO3) is often like limestone and dolomite may contain formed. The ensuing bedrock is called dolom- tremolite asbestos. This study assessed the itic limestone or dolomite. Carbonate rocks are exposure to tremolite asbestos and the used as industrial minerals in various respiratory health of Swedish dolomite applications—for example, in the production of workers. mineral wool, iron and steel, in the paper Methods—95% of 137 eligible workers at industry, as a filler in house and road construc- two dolomite producing companies com- tion materials, in plastics, paints, and adhe- pleted a self administered questionnaire sives, and in agriculture. that included questions on respiratory Carbonate rocks with a low content of silica symptoms and were examined with spiro- have been considered to be virtually harmless.1 metry as well as chest radiography. Total A few cases of pneumoconiosis in Finnish exposure to dust was gravimetrically limestone mines have been attributed to silicate measured and the tremolite asbestos con- impurities or quartz in the rock,2 but only one tent of the dust was assessed with polari- case of pneumoconiosis associated with dolo- sation and phase contrast microscopy. mite has been properly reported in the Results—Dolomite dust concentrations international literature.3 Exposure measure- were moderate (median 2.8 mg/m3) and ments in Finnish limestone and dolomite tremolite asbestos concentrations were mines showed varying concentrations of quartz generally below the limit of detection and mineral fibres with tremolite and wollas- (<0.03 fibres/ml). Somewhat higher tonite as the most abundant fibrous silicates. values, around 0.1 fibres/ml, were ob- tained in manual stone sorting and bag- Forty per cent of the tremolite particles were ging. Respiratory symptoms suggestive of perfect fibres, of tremolite asbestos, whereas chronic bronchitis were more related to the remaining fraction was classified as either Department of smoking than to estimates of individual fibrous cleavage fragments or cleavage frag- Occupational and ments. At one dolomite mine the mean Environmental exposure to dust. The mean vital capacity was 0.2 l lower than expected after adjust- airborne concentration of perfect tremolite Medicine, Örebro 2 Medical Centre ment for sex, age, height, and smoking but fibres was over 0.1 fibres/ml. http://oem.bmj.com/ Hospital, SE-701 85 the decline in lung function was not Clusters of pleural mesothelioma and other Örebro, Sweden associated with current or cumulative health eVects related to asbestos have been A I Seldén exposure to dust in a clear cut way. Two associated with background exposure to N P Berg tremolite asbestos in various environmental C-G Ohlson definite cases of pleural plaques and one L S Bodin possible case of simple pneumoconiosis settings, notably from locally produced white- were noted, but the plaques could not be wash made from sedimentary rock.4–10 Similar Workplace Air, attributed exclusively to exposure to associations have been found in occupationally National Institute for tremolite asbestos. exposed groups—for example, in vermiculite on September 27, 2021 by guest. Protected copyright. Working Life, SE-112 Conclusions—Dolomite mining and mill- workers in the United States and Canadian 79 Stockholm, Sweden 11–14 E A L Lundgren ing may indeed entail low levels of expo- chrysotile workers. sure to tremolite asbestos, but this Tremolite asbestos occurring as a natural Department of exposure was not a strong determinant of component of the bedrock has been associated Medical Sciences, respiratory symptoms, lung function, or with pleural plaques in Swedish iron miners Respiratory Medicine pneumoconiosis in exposed Swedish without other exposure to asbestos,15 and spo- and Allergology, University Hospital, workers. This was true also for dolomite radic cases of diVuse pleural thickening or SE-751 85 Uppsala, dust. The hazards of exposure to tremolite pleural plaques have been attributed to tremo- Sweden asbestos may vary across deposits, how- lite asbestos from products containing milled G Hillerdal ever, and additional studies at other sites dolomite.16 17 of carbonate rock exploitation are war- In the area of Bergslagen in central Sweden Division of Bedrock ranted. Geology, Geological the bedrock contains metamorphosed sedi- (Occup Environ Med 2001;58:670–677) Survey of Sweden, mentary and volcanic rocks created some 1900 Kiliansgatan 10, Keywords: asbestos tremolite; dolomite; lung function million years ago. Serpentine and amphiboles SE-223 50 Lund, are common impurities in Swedish carbonate Sweden rocks but chlorite, mica, and talc are also N-G Wik Limestone and dolomite are examples of sedi- found. Occurring in both orthorhombic and Correspondence to: mentary rock which are also recognised as car- monoclinic systems, the amphibole group Dr A Seldén bonate rocks. Limestone contains more than comprises several minerals closely related in [email protected] 50% of the mineral calcite (calcium carbonate) crystallographic and other physical properties Accepted 18 May 2001 but if the carbonate rock is rich in magnesia a as well as in chemical composition. Among the www.occenvmed.com Exposure to tremolite asbestos and respiratory health in Swedish dolomite workers 671 Occup Environ Med: first published as 10.1136/oem.58.10.670 on 1 October 2001. Downloaded from The Bergslagen area Carbonate rock deposits Stockholm Figure 1 Map of Sweden with details of carbonate rock deposits (in black) in the Bergslagen area. Table 1 Mineralogical composition (% by weight) of amphiboles, created by metamorphic proc- carbonate rock samples from company A and company B esses, the tremolite-actinolite series belonging http://oem.bmj.com/ to the monoclinic system dominate. The Company B minerals usually form aggregates of long Mineral Company A Sample 1 Sample 2 prismatic crystals, sometimes fibrous and asbestiform and recognised as tremolite asbes- Dolomite 93 91 92 tos as opposed to non-asbestiform tremolite Calcite 3 6 3 Amphibole 4 2 4 cleavage fragments. The colour of tremolite is Mica Trace ND* Trace white, turning green with increasing iron Talc Trace ND Trace content. Quartz ND Trace ND on September 27, 2021 by guest. Protected copyright. Chlorite ND ND Trace The respiratory health of Swedish dolomite Total 100 99 99 workers has previously not been systematically investigated and the aim of this study was to *Not detected. conduct such a survey with special emphasis on the recent findings of occupational exposure to producing companies in the Bergslagen area tremolite asbestos. declined to participate. Preceded by small scale quarrying by local farmers, industrial dolomite mining at com- Material and methods pany A started in 1918. The current produc- COMPANIES tion facilities, including the underground mine, The study was conducted at two dolomite dated from the 1960s and contained depart- mines with adherent production facilities, here ments for stone sorting, crushing, grinding, called company A and company B, located in mixing, and packing. Over the years, various the Bergslagen area of central Sweden (fig 1). additives had been used to improve the quality Their combined produce was estimated to of local products among which asbestos was of constitute some 50% of the annual domestic particular interest for the present study. dolomite production (about 700 000 metric Circumstantial information indicated that tonnes). The mineralogical, geological, and some 40 tonnes of asbestos (possibly antophyl- chemical characteristics of the two sites were lite) were added as a fire retardant to selected similar (tables 1 and 2). Attempts to increase qualities in the 1960s and early 1970s. The use the statistical power of the study failed when of asbestos was thought to have ended when the two additional and relevant carbonate rock national restrictions were introduced, 1976 at www.occenvmed.com 672 Seldén, Berg, Lundgren, et al Occup Environ Med: first published as 10.1136/oem.58.10.670 on 1 October 2001. Downloaded from Table 2 Chemical composition (% by weight) of The questionnaire covered items of general carbonate rock (dolomite) samples from company A and health and medication, tobacco habits, and company B environmental exposure to smoke, an occupa- Company B tional history including a subjective dust Company A assessment as well as use of a respirator and Compound (mixed sample) Sample 1 Sample 2 previous exposure to asbestos. The prevalence of respiratory symptoms was assessed with a 14 SiO2 1.87 0.85 1.94 Al2O3 0.22 0.33 0.36 item questionnaire designed for use in popula- TiO <0.01 <0.01 <0.01 2 tions occupationally exposed to dust. This Fe2O3tot 0.49 0.78 0.53 MnO 0.07 0.12 0.07 questionnaire contains eight questions from CaO 30.2 30.3 30.1 the British Medical Research Council (MRC) MgO 20.4 20.7 20.9 questionnaire19 (three items referring to cough, K2O 0.03 0.02 0.04 Na2O 0.02 0.02 0.02 three to phlegm, and two to dyspnoea) and six P2O5 0.01 <0.01 <0.01 additional questions referring to simple bron- CO2 45.7 46.0 44.8 S <0.01 <0.01 <0.01 chitis with or without phlegm or to obstructive Total 99.0 99.1 98.8 symptoms. The 14 item questionnaire and the MRC questionnaire had previously been vali- dated against respiratory function tests and the latest, but no details on this issue were airways disorders classified by lung specialists available in company records. in a study of 295 asbestos cement workers.20 21 At company B open pit limestone mining, This validation suggested an optimal cut oV followed by underground mining, started in the value for sensitivity and specificity at any three early 20th century but this production almost or more symptoms—that is, the sum of positive ended in 1970.
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