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Suggestion of a Cause-and-Effect Relationship Among Coal Rank, Airborne Dust, and Incidence of Workers' Pneumoconiosis Steven J. Page and John A. Organiscak . Department ofHealth and Human Services; Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health, Pittsburgh Research Laboratory, P.O. Box 18070, Pittsburgh, PA 15236; e-mail sep8@cdc.gov rolonged exposure to airborne re dust itself but includes all mineral dusts spirable coal mine dust is responsi produced from either within the coal scam Pble for coal workers' pneumoconi or the rock strata surrounding the coal osis (CWP). Furthermore, miners seam. The question is, what characteristics who show evidence of higher radiograpohficcoal mine dust, some of which are as categories of simple CWP are at increassoecdiated with rank, are related to the ob risk Of developing progressive massive fibro served differences, in exposure-effect rela sis (PMF). As of 1990, there were nearly tionships that have been observed? 130,000 coal miners in the United States.111 To examine these questions, numerous This excludes mines that produce less than studies'5"01 have investigated the correla 10,000 tons annually and the anthracite tion between mineral coatings that oc coal mines. Estimates indicate that at age clude the surface of a crystalline silica par 58, an average of7/1000 U.S. workers and ticle core and the rank of coal. The 89/1000 U.K. workers will have developed hypothesis is that the degree of surface PMF.'2-*1 Health research studies have iden occlusion determines, at least in part, the tified that the risk of developing and the biologically available crystalline silica in severity of CWP are directly related to (1) an inverse relationship. Other stud the amount of respirable dust exposure and ies'10 |AI have investigated the free radicals (2) the coal rank.12-*1 The rank of coal is its (electric charges) found on fresh- stage of formation in the series peat, lignite, fractured rock and coal from high rank sub-bituminous, bituminous, and anthra coal areas. These studies have suggested cite (in order of increasing rank). The rank these radicals on the surface of mineral of coal can also be represented by the com dusts may be relevant to the pathophysi mercially important characteristics specified ology that results from their inhalation. by its proximate analysis: fixed carbon, vol In particular, it has been found that fresh atile matter, mineral matter, and moisture ly broken silica dust (responsible for sili content. cosis) is more reactive in vivo than aged silica. Although not all inclusive, the above-mentioned studies represent per CHARACTERISTICS OF COAL haps the most viable argument for caus MINE DUST ative coal rank-related effects to date. Current knowledge appears to suggest uch research has been devoted to a significant cause-and-effcct relationship Midentifying cause-and-effect relation between coal rank-related charging char ships between the properties and characacteristics and the increased incidence of teristics of coal mine dust and the inci CWP in high rank coal regions. The two dence of CWP. Although evidence sug mechanisms most affected by the charg gests both physical and chemical ing characteristics are enhanced respira properties of coal mine dust contribute to tory deposition and inherent toxicity of CWP, no definitive conclusions have been airborne respirable dust (ARD). This sug reached. A great part of the difficulty is gestion is based on the following known due to the confounding nature of "coal facts: (1) higher rank coals produce a mine dust,'' which is not limited to coal higher CWP incidence rate;'2-41 and (2) higher rank coals obtain a higher electro static charge on breakage.'17-101 COAL RANK AND DUST GENERATION rior research has identified several re Plationships between coal rank and dust generation. Laboratory coal breakage studies have shown a significant and con sistent positive correlation with the amount of respirable-size particles found in the product increasing with coal rank.'20"241 These studies show conclusively that either a grinding or crushing process yields specific total dust and respirable dust generation rates (milligrams of dust in product per kilogram of product) that in crease with increasing coal rank. It is im portant to note diese results were mea surements of dust in the product and not measurements ofairborne dust. This paper invites the reader to consider recently pub lished research that may establish an im portant link between the electrostatic charging characteristics of coals and the high incidence of CWP in higher rank Coals. The Dust and Toxic Substance Control Branch at the Pittsburgh Research labo ratory has investigated ARD generation and electrostatic charging characteristics as they relate to coal rank. Organiscak and Page'171 and Page and Organiscak'1111 per formed laboratory crushing experiments on a range of low- to high-volatile bitu minous coals to investigate the various fac tors influencing fresh ARD generation and liberation from the coal product. It was shown in these studies that the amount of ARD is positively correlated with moisture content and negatively correlated with electrostatic field. This was confirmed in dependently by Page.'10' The resultant ef fect of these factors is that different per centages of coal particles of respirable size are dispersed as ARD, with the largest amount of ARD produced occurring in a narrow range of low rank coals (more than one order of magnitude range in ARD compared to higher rank coals). It is sig nificant that, for the first time, the amount of ARD produced from different coals can be predicted, based on well-known com mercial coal rank parameters. These same parameters that establish the charge/rank relationship of coals may partially explain the increased prevalence of CWP observed with high rank coals through the mechanism of increased lung deposition. It has long been known that airborne dust particles can have a signifi cant amount of electrostatic charge1-5-'1'1 and that this charge can place dusts in varying degrees of agglomeration. Lifshits et al.131" found that respirable-sized aluminum dust particles had lung deposi tion of 34% when uncharged and 66% when charged. Melandri'311 found that lung deposition of airborne particulate in creased by up to 30% with charging prop erties of the airborne particulate, relative to a similar but otherwise neutral aerosol. Furthermore, Melandri suggested the lung deposition efficiency can be greatly affect ed by the charge distribution. This in creased deposition may also be attributed to the higher lung deposition efficiency of agglomerated ultrafine submicron parti cles.'32-33' As referenced earlier, numerous studies have shown that fresh-broken coal and quartz surfaces contain highly reactive free radicals (electric charges). This establishes the potential for cytotoxicity through bond formation with the cell membrane upon inhalation. Dalai et al."51 noted that preliminary tests using the sheep redblood cell hemolysis procedure indicated that fresh-crushed anthracite coal dust ex hibits significantly higher homolvtic activ ity than the same dust left in air for several hours. Dalai et al. also remarked that since exposure of fresh coal dust to air causes a decrease in the amount of the free radicals, as well as a decrease in the cytotoxicity, it is possible that the free radicals do con tribute to the coal dust's cytotoxicity. Vallyathan et al.,16) observed that freshly ground silica dust exhibits a greater cyto toxic effect on cellular membrane integrity and that, because acute silicosis is fre quently associated with occupations in which freshly fractured crystalline silica of respirable size afe generated, fracture-gen erated silicon-based radicals may play a sig nificant role in the pathogenesis of silico sis. Although the work by Organiscak and Page focused on the charging characteris tics of freshly crushed coals, brief tests on various sandstones indicated the ARD generated exhibited much higher degrees of electrostatic charging. CONCLUSION and R.I. McCallum (eds.). Oxford: Perga- mon Press, 1994. pp. 439-445. " n view of the work by Lifshits et al.,1501 IMelandri et al.,l3n Dalai ct al.,"u5) and Vallvathan et al.,,l2J3-"" the investigations of Organiscak and Page'171 on the charging characteristics of coal suggest a significant cause-and-cffect relationship between the coal rank-related charging characteristics, enhanced respiratory deposition and tox icity of ARD, and the increased incidence of CWP in high rank coal regions. Recommendations to improve the health of coal miners would necessarily fo cus on providing more effective dust gen eration and abatement in the mining of higher ranked coals through engineering control technology. The Pittsburgh Re search Laboratory is currently pursuing more in-depth studies of coal charging characteristics and the use of water addi tives (surfactants) for water spray systems, which arc widely used in coal mines to im prove dust suppression and reduce miner dust exposure. - REFERENCES 7. LeBouffant, L., H. Daniel, J.C. Martin, and S. Bruyere: Effect of impurities and associated minerals on silica toxicitv. Ann. Occup. Hyg. 26:625-634 (1981). 8. Tourmann, J.L., and R. Kaufmann: Laser microprobe mass spectrometry (LAMMS) study of silica-related and non silica-related factors of the specific harm fulness of coal mine dust. In Annals of Oc cupational Hygiene: Inhaled Particles VII. J. Dodgson and R.I. McCallum (eds.). Ox ford: Pergamon Press, 1994. pp. 455-467. 9. Bauer, H.D.: Specific harmfulness of re spirable dusts from West German coal mines V: Influence of mineral surface prop erties (post-presentation discussion). In Annals of Occupational Hygiene: Inhaled Particles V. W.H. 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