Particle Toxicology - Chapter 2 ppt

2 Mineralogy and Structure of Pathogenic Particles TimJones School of Earth,Ocean, and Planet ary Sciences, CardiffUniversity Kelly Be ´ ruBe ´ School of Biosciences, CardiffUniversity CONTENTS 2.1 Introduction 13 2.2 Ortho- and Ring Silicates 14 2.3 Chain Silicates 16 2.4 Sheet Silicates 17 2.5 Tecto- (Framework) Silicates 19 2.6 Non Silicates 21 2.7 Rock Quarrying and Airborne Rock Dusts 23 2.8 Urban, Rural, and Technogenic Particles 26 References 34 2.1 INTRODUCTION It is estimated that the element silicon makes up 27.7% of the earth’s continental crust. The majority of this silicon is in the form of crystalline silicon dioxide (SiO 2 )asthe polymorph quartz, awell- established respiratory hazard (Rimala, Greenbergac, and William 2005). However, silicon is also present in numerous other minerals, and therefore, “silicates and non-silicates” have been used by mineralogists as aframework, further based on structure (ortho-,ring, chain, sheet, and tecto-), to describeall minerals (Deer, Howie, and Zussman 1966). This framework has been used in this chapter, but onlymineralsthatare knownorsuspected to be respiratory hazards(Guthrie andMossman 1993) areincluded(Figure2.1 andTable 2.1).The chemistryand structureof minerals is complicated by the fact that many minerals exist in solid state series and in different shape“habits.” Forexample,the chain silicate, amphibole, cummingtonite (Mg,Fe C 2 ) 7 [Si 8 O 22 ](OH) 2 -grunerite (Fe C 2 ,Mg) 7 [Si 8 O 22 ](OH) 2 series.Grunerite is thenamefor themore iron-rich end-members, and is of significance here, because in its fibrous habit it is the mineral amosite; carcinogenic asbestos (Nolan, Langer,and Wilson 1999). In addition to the chemistryand habit, the formation conditions of the minerals can have bearings on the toxicity, e.g., SiO 2 .The vast majority of crystalline SiO 2 occurs as the polymorph quartz, amineral that usually forms at relatively low temperatures and high pressures. However, if SiO 2 forms at high temperatures and low pressures, such as near the surface in avolcanicdome,itforms the SiO 2 polymorph cristobalite. Concerns over the possible toxicity of volcanic ash particles have led to research which has shown 13 © 2007 by Taylor & Francis Group, LLC that respirable quartz and cristobalite have different bioreactivities in the lung (Housleyetal. 2002; Be ´ ruBe ´ et al. 2004; Forbes et al. 2004). Minerals are the building blocks of rocks,therefore, on occasion we have to consider assemb- lages of minerals forming arock type, which itself has been implicated in adverse respiratory health effects. An exampleofthiswould be “bauxite,” the common name for aluminum ore derived from weathered igneous rocks. Bauxite consistsofamixture of aluminum hydroxide minerals,the most abundant of which is gibbsite, plus other major,minor, and trace minerals. There is an occupational respiratory disease uniquetobauxite miners, “Shaver’s Disease,” but this has only been linked to the ore “bauxite,” and not to any individual component mineral (Dinman 1988; Radon et al. 1999; Kraus et al. 2000). Another issue that arises when considering rock typesasrespiratory hazards is the matter of natural mineral contamination; vermiculite is agood exampleofthis. Vermiculite is an important industrial and domestic materialand is composed of clays that have been artificially expanded by heating.The problem is that the clay minerals, which are amenable to this process, can be naturally contaminated by potentially carcinogenic, asbestiformminerals,suchastremolite(McDonald, Harris, and Armstrong 2004). Serious precautions are thereforeneeded when usingvermiculite, although it is probably not the vermiculite itself that is dangerous: rather, it is the trace amounts of contaminating tremolite that pose the hazard (Wright et al. 2002). In addition to recognized patho- genicmineralsand rocks, this chapter includesdescriptions of thechemistry and structureof pathogenic particles that, at first glance, would appeartobe“non-mineral,” yet upon close exami- nation show amineral component.Anexample of this would be “soot” from the combustion offossil fuels. Soot is the mostabundant component in urban PM 2.5 and has been linked to anumber of respiratory issues, such as the increaseinchildhoodasthma (Brauer et al. 2002; Nicolai et al. 2003). Examination of the carbon microspheres, that are the building blocks of soot particles, showsthat they are largely composed of microcrystallites of the mineral graphite. 2.2 ORTHO- AND RING SILICATES Theorthosilicates, which include syntheticmullite,are based on SiO 4 K 4 ,where thetetrahedral oxygen atoms are not shared with other tetrahedral. Also called nesosilicates, they are adiverse group of minerals. They tend to be rather hard and dense minerals with agenerally poor cleavage. The ringsilicates contain only three common species, and are isostructural with six-member rings Silicates Ortho- Ring silicates Sheet silicates Tecto- silicates Mullite Amphiboles Serpentines Micas Clay minerals Chrysotile Talc Wollastonite Quartz Cristobalite Erionite ZeolitesSilica Mesolite Mordenite Natrolites Scolecite Thomsonite Crocidolite Amosite Montasite Anthophyllite Tremolite Actinolite Muscovite Kaolinite Bentonite Palygorskite (Attapulgite) Sepiolite Vermiculite Chain silicates FIGURE 2.1 The distribution of some respiratory hazards within the silicates. Particle Toxicology14 © 2007 by Taylor & Francis Group, LLC TABLE 2.1 Some Minerals and Particles and Their Known or Suspected Health Issues Mineral Some Known or Suspected RespiratoryHealth Issues Silicate Minerals Synthetic mullite Irritationofthe respiratory system, silicotuberculosis Crocidolite Asbestosis, lung cancers, mesothelioma, pleural plaques, ferruginous bodies Amosite Asbestosis, lung cancers, mesothelioma, pleural plaques, ferruginous bodies Montasite Asbestosis, lung cancers, mesothelioma AnthophylliteAsbestosis, lung cancers, mesothelioma, plural calcification Tremolite Asbestosis, lung cancers, mesothelioma Actinolite Asbestosis, lung cancers, mesothelioma, non-malignant pleural lesions Wollastonite Lung fibrosis, respiratory morbidity, pulmonary toxicity Chrysotile Asbestosis, lung cancer, mesothelioma, pleural tumors Talc Talc pneumoconiosis (talcosis), pulmonary oedema, fibrotic pleural thickening Muscovite Pulmonary interstitial fibrosis, severe pneumoconosis Kaolinite Kaolin pneumoconiosis, simple and complicated Kaolinosis, COPD Bentonite Fuller’s earth pneumoconiosis, “bentonite” granulomas, silicosis Palygorskite (attapulgite) Bronchoalveolar hyperplasia, alveolar tumors, mesothelioma Sepiolite Deterioration of lung function, co-carcinogen, fibrosis Vermiculite Natural asbestos contamination Quartz Fibrosis, silicosis, lung cancer Tridymite Fibrosis, silicosis CristobaliteFibrosis, silicosis Erionite Lung cancer, mesothelioma,non-malignant fibrotic lung disease Zeolites: mesolite, mordenite, natrolite, scolecite, thomsonite Lung cancer Non-Silicate Minerals Anatase Chronicinflammation, lung tumors (rats), impaired pulmonary clearance Apatite Decrease in pulmonary function, hemolytic activity Bauxite Occupational pulmonary disability (Shaver’s disease) Fluorite Bronchitis, silicosis, pulmonary lesions Graphite Graphite pneumoconiosis, focal emphysema,fibrosis and small fibrous nodules Haematite Siderosis Siderite Siderosis, “mottled” chest x-rays Rock Quarrying and Airborne Rock Dusts Basalt Pulmonary airway obstruction Coal dust Emphysema, coal-worker’s pneumoconiosis Dust storms Desert lung syndrome Pumice Occupational silicosis, sclerosis of lymphatic glands, Liparitosis Volcanic ash Lymph node granuloma and delayed lung inflammation Urban, Rural, and Technogenic Particles PM 10 –PM 2.5 ,PM 2.5 –PM 0.1 Asthma, pneumonia, bronchitis, heart failure Nanoparticles Asthma, pneumonia, bronchitis, heart failure Fly ash Asthma, pneumonia, bronchitis Soot Asthma, chronic bronchitis, radiological changes, skin cancer Water-soluble component Pulmonary inflammation, sudden cardiac death Amorphoussilicon dioxide Inflammation, oedema, meta- and hyperplasia, fibrosis Diatomaceous earth Fibrosis, silicosis Glass fiber/MMMF Inflammation, occupational asthma, pleural plaques Metals aerosols Inflammation, lung cancer,metal fume fever Mineralogy and Structure of Pathogenic Particles 15 © 2007 by Taylor & Francis Group, LLC stacked on top of each other. Withinthe ortho- and ring silicates, amineral of respiratory toxico- logical interest is synthetic (technogenic)mullite, acommon refractory product (Carleton, Giere, and Lumpkin 2002). Particles of mullite are found in urban air, from sources such as coal-fired power stations(Giere, Carleton,and Lumpkin2003).Mullite (3Al 2 O 3 2SiO 2 )occurs in most ceramic products containing alumina and silica. The mulliteparticles consist of needle-like inter- locking crystals, growth of which is promoted by the presence of impurities. There have been concerns that workersinthe ceramics industryexposedtomullitecould suffer from irritation of the respiratorysystem (Fishman and Velichkovskii2001; Fishman et al. 2001; Fishman 2003; Brownetal. 2005). 2.3 CHAIN SILICATES The chain silicates are notable as they contain the carcinogenic minerals crocidolite and amosite. Chain silicates are agroup of minerals with their tetrahedronsinsingle or multiple chains, with two oxygen atoms of each tetrahedron forming part of the adjoining tetrahedron. Amphiboles are a group of inosilicate minerals, containing hydroxyl (OH) groups,with double chains of aligned silicatetetrahedra. They exist in two different systems, orthorhombic(orthoamphibole) and mono- clinic(clinoamphibole). Crocidolite ð Na 2 Fe C 2 3 Fe C 3 2 ½ Si 8 O 22 ðOHÞ 2 Þ is commonlyknownasblueasbestos,and is the highly-fibrousformofriebeckite in theglaucophane-riebeckitegroup (Gibbons 2000). It has straight blue fibers that have agreater tensile strength than the most common asbestos chrysotile (sheet silicate), but less heat resistance. The fibers are prone to splintering whenmechanically damaged. The size of the fibers plays an important roleinasbestos-induced disease.The World Health Organization (WHO)defines fibers in the workplace as having adiameter of less than 3 m m and alength of morethan 5 m m, with an aspectratio of 1:3 or more; however,concerns have been raised about other issues such as biopersistence (Donaldson and Tran 2004). The fibers are believed to be hazardous to health since they are capable of entering and being deposited in the lungs,and have also adegreeofmigrationcapability within the lung (Stanton et al. 1981; Davis et al. 1986; Platek, Riley, and Simon 1992; Roller et al. 1996). Amosite (Fe 2 C Mg) 7 [Si 8 O 22 ](OH) 2 is the characteristic fibrous iron-rich form of cummingto- nite–grunerite, and is commonly knownasbrown asbestos. It has straight, brittle fibers that are light gray to pale brown. It has good heat insulation properties and was commonly used in thermal systemsinsulation. Within the sameseries, the otherasbestiform mineral of commercial import- ance is montasite, which is the softer and moremagnesium-rich variety. Amosite is believedtohave an equivalent health risk to crocidolite (Acheson et al. 1981;McDonaldand McDonald 1996; Nolan, Langer,and Wilson 1999; Britton2002). Anthophyllite Mg 7 Si 8 O 22 (OH) 2 is white to greenish-gray and is the magnesian end-memberof the orthorhombic anthophyllite–gedrite series (Zeigler et al. 2002). Most anthophyllite crystals are prismatic or acicular. Fibersofanthophyllite are extremely flat and thin; the characteristic shape resembles that of aknife, and tends to be of generally uniform size. Tremolite and actinolite are asbestiform calcium amphiboles. Tremolite is aclinoamphibole and has the chemical formula, Ca 2 Mg 5 Si 8 O 22 (OH) 2 .ActinoliteCa 2 (Mg,Fe) 5 Si 8 O 22 (OH) 2 hasasimilar composition, with iron replacing some magnesium.WollastoniteCaSiO 3 is afairly common pyroxenoid inosilicate with industrial applications in ceramics and as filler. The mineral can be found as tabular crystals butis more commonly seen as lamellar radiating masses or fibrous aggregates. It is soluble in hydro- chloric acid. Mechanical damage tends to result in elongate uneven splinters.All of the above fibrous minerals have recognized health issues [e.g., anthophyllite (Kiviluoto 1960; Dodson and Levin 2001; Dodson et al. 2005), tremolite (McConnell et al. 1983;Roggli et al. 2002; Luce et al. 2004), actinolite (Spurney et al. 1979; Metintas et al. 2005)and wollastonite (Huuskonen et al. 1983; Hanke et al. 1984; Wozniak et al. 1996; Tatrai et al. 2004; Maxim and McConnell 2005)]. Particle Toxicology16 © 2007 by Taylor & Francis Group, LLC 2.4 SHEET SILICATES The sheet silicates, or phyllosilicates, are composed of extending sheets of SiO 4 tetrahedra with the formula (Si 2 O 5 ) 2 K .Neighboring tetrahedrashare the three oxygens of each tetrahedron. Asecond layer is formed from the apical oxygens that are attached to externalions. These external ions are in octahedralcoordination.Different combinations of thesetwo layersresult in thedifferent sheets silicates. Chrysotile Mg 3 (Si 2 O 5 )(OH) 4 is agenerictermfor undifferentiated, asbestiform,serpentine group species,consisting of amonoclinic mineral (clinochrysotile), and orthorhombic minerals (orthochrysotile and parachrysotile). Lizardite and antigoriteare closelyrelated serpentine group species (Kulagina and Pylev 1985). The mostcommonly used industrial asbestiform material, it consistsofsoft, silky white/green/yellow/gray bunchesofflexible fibers. Thefibers of chrysotile are formed by the crystalline sheet structure rolling into ascroll or coil form, giving acurly, tubular, hydrophilic fiber. This contrasts to the crystalline chain structure of the asbestiform amphiboles which exhibit astraight hydrophobic fiber. Health issues for the serpentines (chrysotile) are awell- researched issue (McDonaldetal. 1993; Liddell, McDonald, and McDonald et al. 1997; Yano et al. 2001; Li et al. 2004). Talc Mg 3 [Si 4 O 10 ](OH) 2 is atriclinicmineral composed of Si 2 O 5 sheets with magnesium sandwiched betweensheets in octahedral sites, and in tri-octahedral arrangement. Talc appears to be unabletoform chemical-replacement series by accepting iron or aluminum into its structure. Rarely existing in an asbestiform habit, the major respiratory hazard posed by talc (Blejer and Arlon 1973; Wagner et al. 1977; Gibbs et al. 1992; Scancarello, Romeo,and Sartorelli 1996)isfine dust createdbythe milling to PM 10 of soapstone and steatite. Commonlyrecognized as the primary ingredient in talcum powder, it is no longer recommendedfor dermal use (i.e., nappy powder), but it is stillasignificant industrialmineral. It is an importantfiller material forpaints, rubber and insecticides (DiLorenzoetal. 2003). In the food industry (Tomasini et al. 1988; Canessa et al. 1990), particularly in Asia, it is used as amild abrasive in the polishingofcereal grains such as rice, potentially exposingworkers handling the processedcereals to airbornetalc (Breeling 1974). Muscovite KAl 3 Si 3 O 10 (OH) 1.8 F 0.2 is the mostcommon of the mica group minerals,and is typicallyfound as massive crystalline “books”orinflaky grains. In the micaceous habit it has a platy texturewith flexible plates.Muscovite has asheet structure,ofwhich basicunits consist of two polymerized sheets of silica tetrahedrons positioned with the vertices of their tetrahedrons pointing towardeach otherand cross-linked with aluminum. Found in manydifferent rock types, it is clear to milky-white with apearly luster on cleavage faces, often with asparkling appearance. Mica exposure is frequent in mines, mills, agriculture, construction, and industry and has been shown to induce pneumoconiosis (Landas and Schwartz 1991; Zinman et al. 2002). This health issue extends to people living aroundmica mines, as well as the workersinthe associated mica- processing factories (Venter et al. 2004). In the clay minerals group, the minerals associated with health concerns (Elmore 2003)include kaolinite, bentonite,palygorskite [attapulgite](Huggins, Dennyand Shell 1962;IARC 1980; Lipkin 1985), sepiolite(Baris, Sahin, and Erkan 1980)and vermiculite (Howard 2003). There is some debate on the actual health effects that can be attributed to the clay minerals themselves, since this groupoften hasassociated minerals with recognizedadverse health effects.For example, kaolinite often has crystalline silica contamination, and vermiculite has both asbestos and crystal- line silica as common contaminants. Kaolinite Al 2 Si 2 O 5 (OH) 4 is commonly knownaskaolinor“Chinaclay.”The structure of kaolinite consists of tetrahedralsilica sheets alternatingwithoctahedralaluminasheets. The sheets are arranged so that the corners of the silicatetrahedrons form acommon layer with the adjacent octahedral sheet.The charges within the structure are balanced, and analyses have shown that there is rarely substitution in the lattice. Visible crystals of kaolinite are extremelyrare, with a typical grain size of 2–5 m m, with rare examples up to 1mmacross. When viewed under SEM, Mineralogy and Structure of Pathogenic Particles 17 © 2007 by Taylor & Francis Group, LLC the pseudohexagonal crystals have aplaty appearance: both fibers and spheres have been observed under Scanning Electron Mircroscopy (SEM).“China clay” typicallycontains otherminerals as contaminants,inparticular quartzand muscovite, the former of whichhas knownrespiratory hazards (Lapenasetal. 1984; Wagneretal. 1986; Morgan et al. 1988; Gao et al. 2000). This is aresult of the typical genesis of kaolinite from the weathering of feldsparingranite, where two othercommon granite components are the quartz and mica. The occupational respiratory disease associated with kaolinite has been variouslynamed as complicated pneumoconiosis, kaolin pneu- moconiosis,orkaolinosis (Mossman andCraighead 1982).Anecdotal evidence suggeststhat kaolinite workers in the enclosed spaces of the processing and storage buildings are more prone to illness than the workersout in the quarries. The symptoms are similar to silicosis; however, postmortem shows aprofusion of small opalicities, and peribronchiolar nodules transversed by fibrous bands (Oldham 1983; Lapenas et al. 1984; Sheers 1989; Rundle,Sugar, and Ogle 1993; Parsons et al. 2003). Bentonite is the common or generic name for “Wyoming” bentonite, swelling (sodium)bento- nite, andnon-swelling(calcium)bentonite. Montmorilliniteclay ((1/2Ca,Na)(Al,Mg,Fe) 4 (Si,Al) 8 O 20 (OH) 4 nH 2 O), which is part of the smectite group of clayminerals, is the main constitu- ent of bentonite (Gibbs and Pooley1994). The clay is formed by the alteration of volcanicash, and where it shows ahigh absorbencycapacityiscommonly knownas“Fuller’s Earth.” It is usually commercially seeninafinelygroundpowderedform, butisoccasionallyavailable as coarse particles, and has uses as diverse as cat litter to oil-well drilling mud. The potential of bentonite to cause fibrogenicityand granulomas (Boros and Warren 1973)inthe lung has been investigated. In in vitro studies, bentonite showed ahigh membrane-damaging(lysis) potential, shownashemo- lytic activity in humanerythrocytes (Geh et al. 2005). Human epidemiological studies reviewing workerschest x-rays showed 44% silicosis in bentonite workers (Phibbs,Sundin,and Mitchell 1971). Other studies report seven months to eight yearsexposures to bentonite resulting in pneu- moconiosis (Rombala and Guardascione 1955). Palygorskite(Mg, Al) 2 Si 4 O 10 (OH)4H 2 O, also knownasattapulgite,occurs as afibrous chain- structure mineral in clay deposits in hydrothermal deposits, soils, and along faults. It is of commer- cial importancefor arange of uses, typically as an absorbent. The fiber characteristics vary with the source, but fiber lengths in commercial samplesare generally less than 5 m m. It can form matted masses that resemble wovencloth. Unlikemost otherclayminerals, palygorskite can form large crystals. The results of studies in animals suggestthat carcinogenicity is dependent on the pro- portion of long fibers ( O 5 m m) in agiven dust sample (Jaurand et al. 1987; Rodelsperger et al. 1987; Meranger and Davey 1989; Renier et al. 1989). In an inhalation studyinrats, in which about 20% of the fibers were longer than 6 m m, bronchoalveolar hyperplasia and benign and malignant alveolar tumors and mesotheliomas were observed. Intratracheal instillation studies with palygorskite fibers in sheep and rat lungs demonstrated significant and sustained inflammatory and fibrogenic changes (Begin et al. 1987;Lemaireetal. 1989). Sepiolite Mg 2 H 2 (SiO 3 ) 3 XH 2 Oisasimilar clay mineral to palygorskite; it occurs as afibrous chain-structure mineral in clays, with major commercial deposits in Spain.Sepiolite fiber lengths in commercial (e.g., animal/pet litter)samples are generally less than 5 m m. Inhalation/instillation into rat lungs of short and long fibers from different geological locations (i.e., Spain [short],Finland [long], China [long]) suggested that long sepiolitefibers, with slow elimination rates, were import- antfactors fortheir adverse biological (fibrosis)reaction (Bellman, Muhle, andErnst 1997). Sepiolite appears to be strongly hemolytic in many classic assays, and may act as acocarcinogen (Denizeau et al. 1985). Lung function has been shown to deteriorate rapidlyinworkers who are occupationally exposed to the commercial dust (McConnochie et al. 1993). Vermiculite Mg 1.8 Fe 2 C 0.9 Al 4.3 SiO 10 (OH) 2 4(H 2 O) is the name giventohydrated laminar mag- nesium–aluminum–iron silicate, amineral that resembles mica. Vermiculite deposits contain arange of other minerals that were formed at the same time.Ofparticular concern are vermiculite deposits from some sources that have been found to contain amphibole asbestiform minerals (Van Gosen et al. Particle Toxicology18 © 2007 by Taylor & Francis Group, LLC 2002; Gunter 2004; McDonald, Harris, and Armstrong 2004; Pfau et al. 2005), such as tremolite and actinolite. When subjected to high temperatures, vermiculite has the unusual property of exfoliating or “popping” intoworm-like pieces (Latin vermiculare:tobreed worms). The process occurs as a result of the rapid conversion of contained water to steam that mechanically separates the layers. The exfoliation is the basis for the commercial and domestic use of the mineral, the increase in bulk typicallygrades from ! 8to ! 12, but can reachashigh as ! 30. If the vermiculite contains asbesti- form minerals, the exfoliation process releases fibers into the atmosphere. Vermiculite is used in the construction, agricultural, horticultural and industrial markets. The U.S. Environmental Protection Agency (EPA) has completed astudytoevaluate the level of asbestos in domestic vermiculiteattic insulation, and whether there is arisk to homeowners (USEPA 2005). There does not appeartobeany indications that vermiculite itself is arespiratory hazard. 2.5 TECTO- (FRAMEWORK) SILICATES Tectosilicates, formerly known as framework silicates, are minerals in which the silicatetrahedra share all four O 2 K corners with adjacent tetrahedra. The result is astrong three-dimensionallattice. The large range of tectosilicates is aresult of the partialsubstitution of Si by Al, balanced by cations such as K, Na, or Ca accommodated in the relatively open frameworks. The tectosilicatesinclude many of the main rock-forming minerals,such as quartz and feldspars. Crystalline silica dioxide occurs in five different SiO 2 structures: quartz, cristobalite, coesite, tridymite, and stishovite. Three of the polymorphs: quartz, cristobalite, and tridymite have closelyrelated temperature/pressure related crystallographic structures. Naturally-occurring coesite and stishovite are associated with meteoriteimpacts into silicadioxide-rich rocks, althoughcoesite hasalsobeen found in kimberlite pipes in association with diamonds. From ahuman respiratory health perspective, only quartz, cristobalite, and tridymite are of importance(Fubini 1998; Occupational Safety &Health Admin- istration [OSHA] 2005; Rimala, Greenbergac,and William2005). The relative toxicities of quartz, cristobalite,and tridymite in thelunghavebeen investigatedbyanumber of workers, often generating differentordersoftoxicity.Itisnoteworthythatthe OSHA permissible exposure limit values forcristobalite andtridymiteare 0.05 mg/m 3 ,whereas quartzis0.1 mg/m 3 (Castranova, Dalal, and Vallyathan 1997). There are two dimorphsofquartz, a -quartz and b -quartz,with very similar structures. The determining factor for type of dimorphistemperature,with the boundary at 5738 C. The structures are composed of networksofSiO 2 tetrahedrathat are arranged in spiral chains (helices) around three- and six-fold screwaxes. Alpha-quartz is trigonaland stable below 5738 C. Above 5738 Cheat- induced agitation is sufficient to overcome aslight skewness in the structure and it converts to hexagonal b -quartz.The occupational developmentofacute silicosisand numerous different toxicological methods have shownthat freshly-fractured silicadust is the most toxic (Castranova, Dalal, and Vallyathan 1997; Fubini 1998; Fubini and Hubbard, 2003; Rimala, Greenbergac, and William2005). The consensus of opinion is that freshly cleaved crystal planes have surface proper- ties that are morebioreactive with lung tissue,resulting in pulmonary disease.Itissuggested that the silicon-based radicals ( % Si and Si–O % )created on the surface are of importance(Vallyathan et al. 1995; Fubini et al.2001).Thishas been supported by electronspinresonance(ESR) spectra showing high values for freshly ground silica, followed by decay in the signal with time after grinding(Fubini et al. 1990). When shattered, the fresh crystal surfacesofthe SiO 2 show greater or lesser degrees, andthicknesses of structuraldisorder(Baumann 1979).The size of theSiO 2 particlesisalsocritical, as smaller masses have greater surface areas. Baumann (1979) calculated that powdered crystalline SiO 2 with asurface areaof11.8 m 2 /gmhad aperturbedsurfaceof approximately 9%. In addition to the surface disorder (Altree-Williams et al. 1981), there is an internal component acting as potential boundaries between crystallites, potentially providing planes of weakness when the SiO 2 is powdered. Mineralogy and Structure of Pathogenic Particles 19 © 2007 by Taylor & Francis Group, LLC Themonoclinic polymorph a -tridymite is stable at temperatures below8708 C(Smith 1998). At temperatures between8708 Cand 14708 Citishexagonal a -tridymite. Tridymite is only meta- stable at normal surface temperatures tending to alter,over thousands of years, to quartz. It retains its original, overall crystal morphology; thus much “tridymite”isreally quartz pseudomorphs after tridymite. Tridymitewas once considered to be rare, but it is now knownthat different volcanic rocks (e.g., in California, Colorado, and Mexico) can contain small to microscopiccrystals of tridymite (USGS2005).Nevertheless, it is still muchlesscommon thanquartzorcristobalite andoccupationalexposures to tridymite couldbeexpected in workersminingorprocessing powdered igneous rocks.Tridymite(and cristobalite) is produced in some industrial operations whenalpha quartz or amorphoussilica is heated (suchasfoundryprocesses, calcining of diato- maceous earth, brick and ceramics manufacturing, and silicon carbide production (NIOSH 1974; Weill, Jones, and Parkes 1994). Burning of agricultural waste or products such as rice hulls may also cause amorphous silica to becometridymite and cristobalite (Rabovsky 1995). Forexample, in Asian countries, the burning of rice husk ash (RHA),asameans to cover the demands for energy and silicaresource (i.e., cement industry, lightweight construction products, abrasives, and absor- bents), has been showntogenerate cristobalite and tridymite (Shinohara and Kohyama 2004). The silica content in airbornedust for workers in RHA production factories, in power generation plants usingrice hull, and engagedinfarming operations that include the burning of rice husk, are now beingcontrolled in the workplace due to the occurrence of pneumoconiosis in workersengagedin the packing and screening of RHA products (Liu, Liu, and Li 1996). Cristobalite is the low pressure, high temperature SiO 2 polymorph, and is relatively abundant in volcanic rocks (Baxter et al. 1999). Cristobalite is only metastable at surface temperatures; the conversion to quartz is believedtooccur exceedingly slowly. It is the presence of cristobalite in volcanic rocks that has prompted manyofthe concerns about the possible respiratory toxicity of volcanic ash (Baxter 1999;Baxter, Bernstein, and Buist 1986;Baxter et al. 1999). This is a subject of greatinterest,particularly after the May 18, 1980, eruption of Mount St. Helens (Baxter et al. 1981; Beck, Brain, and Bohannon 1981). There are also concerns for workersengagedin certain industries that can produce cristobalite as aby-product, such as glassmanufacture (NIOSH 2002). Most cristobalite is believed to crystallize in ahigh temperature phase called b -cristobalite, with an isometricsymmetry. It later cools, and the crystals convert to a -cristobalite. Alpha-cristo- balitehas an octahedron crystal form; however,when convertedto a -cristobalite, the crystals retain the outward b -cristobalite form. As with quartz, it is the freshly-fractured faces of cristobalite that are of most respiratory concern. Erionite is afibrous zeolite (Gottardi and Galli 1985), with the approximateformula(K 2 ,Na 2 , Ca) 2 Al 4 Si 14 O 36 14H 2 O. It is ahydratedpotassium sodium calciumaluminum silicate. Erionite forms wool-like, fibrous masses in the hollows of rhyolitictuffs and in basalts. Approximately 40 natural zeolites have been identified, and they are notedfor their very open crystalline lattices, with large internal surface areas. They are able to lose or gain water molecules, and exchange cationswithoutmajor structural changes; this ability hasled to many industrial applications, including use as “molecularsieves.” Erionite is the mostcarcinogenicmineral fiber documented in man and in rodentinhalation studies.There is scientific consensus about the adverse effects of erionite in DNAstrand breaks (Eborn and Aust 1995)ormesothelioma induction (Wagneretal. 1985). The considerable toxicity of erionite may be due to its fibrous nature and size, which ensures penetration into the lungs, and its surface chemistry, which promotes the formation of hydroxyl radicals (Hansen and Mossman 1987; Mossman and Sesko 1990; Fubini and Mollo 1995; Fubini, Mollo, and Giamello 1995; Fach et al. 2002). Epidemiological studies in populatedregions with high levels of naturally occurring erionite, (i.e., the Anatolian region of Turkey), have linked environmental exposure to erionite fibers with the development of malignant mesothelioma and non-malignant fibrotic lung disease (Baris et al. 1987;Artvinli and Baris 1979). The spectrumofcancers, fibrosis, and otherpulmonary abnor- malities associated with exposure to erionite is markedly similar to the range of health effects Particle Toxicology20 © 2007 by Taylor & Francis Group, LLC described for occupational exposure to the amphibole asbestos, crocidolite, but the incidence of disease is increased dramatically. Human epidemiological studies have shownvery high mortality from malignant mesotheliomainparticularTurkish villages. This is an area where erionite is found in the local volcanic tuffs and the locals live in rock-built houses and caves (Lilis 1981; Artvinliand Baris 1982; Maltoni, Minardi, and Morisi 1982; Emrietal. 2002; Emriand Demir 2004). There is significant local airborne contamination from erionite, and the locals are exposed to the fibers from birth. Postmortem investigations found erionite fibers in lung tissue samplesfrom casesofpleural mesothelioma. The inhabitantsincontaminated villages had higher levels of ferruginous bodies than inhabitantsofcontrolvillages(Dumortier et al. 2001).Several othernatural zeolites, in addition to erionite, alsocan have afibrous habit. Of particular health concern (i.e., “biologically active”) are mesolite, Na 2 Ca 2 Al 6 Si 9 O 30 8H 2 O; mordenite, (Ca,Na 2 ,K 2 )Al 2 Si 10 O 24 7(H 2 O); natrolite, Na 2 Al 2 Si 3 O 10 2H 2 O; paranatrolite, Na 2 Al 2 Si 3 O 10 3H 2 O; tetranatrolite, Na 2 Al 2 Si 3 O 10 2H 2 O; scole- cite, CaAl 2 Si 3 O 10 3H 2 O: andthomsonite,NaCa 2 Al 5 Si 5 O 20 6H 2 O(Wright,Rom,and Moatmed 1983; Gottardi and Galli1985; Fach et al. 2002). 2.6 NON SILICATES The minerals anatase,rutile, and brookite are all naturally-occurring polymorphs with the same chemistry, TiO 2 ,but they have different structures. Anatase shares properties such as luster,hard- ness, and density with the othertwo polymorphs. It has atetragonal symmetry, with the structure based on octahedrons of titanium oxide sharing four edges to produceafour-fold axis structure. Naturally-occurring anatase can be associated with quartz and is relatively rare in nature, occurring in cavities in schists, gneisses, granites, and other igneous rocks. Titanium dioxide (TiO 2 )ismanufactured worldwide in large quantitiesfor use in awide range of applications. It is most widelyused as awhite pigment. This is due to its high refractive indexand reflectance combinedwith its ease of dispersion in avarietyofmedia and non-reactivity towards those media duringprocessing and throughout product life. Thetwo main processes for making TiO 2 pigments are the sulfateprocess and the chloride process. The sulfate process was the first to be developed on acommercial scale in Europe and the U.S., around1930. It was the primary process until the early 1950s, when the chloride process was researched and developed. Currently, the chloride process accounts for w 60% of the world’sTiO 2 pigment production. Pure TiO 2 is extracted from its mineral feedstock by reaction with either sulfuric acid or chlorine, and then it is milled and treated to producearange of products that are designed for specific end uses. The majority of TiO 2 products are based on the crystal- “type rutile, with aprimary particle size range of 200–300 nm. In this context it is called “pigment grade.” At this particle size, TiO 2 pigments offer maximumopacity, as well as impart whiteness and brightness to the paints, coatings, papers, and plastic products in which they are used. These TiO 2 pigmentsare also used in many white or coloredproducts including foods, pharmaceuticals, cosmetics, ceramics, fibers,and rubber products, to mention only afew. One of TiO 2 properties is its efficient absorption of ultraviolet light which makes it avery effective sunscreen for use in cosmetics. Usually its opacity is not requiredinthis application, so very low particle size material(size 10–20 nm) is used and this is commonly called“ultrafine” or UF. Thefinal productisofaparticle size that could become airborneand inhaled. Titanium dioxide is highly insoluble, non-reactive with other materials, thermally stable, and non-flammable, which has led to it being considered to pose little risk to respiratory health. This is supported by the toxicological database on TiO 2 and the fact that it has been used traditionally for many years as a “negative control”dust in many in vitro and in vivo toxicological investigations. However, this view was challenged whenlung tumors were found in the lungs of rats after lifetime exposure to very high concentrations of pigment grade TiO 2 (Lee, Trochimowicz, and Reinhardt 1985)and ultrafine TiO 2 (Bermudezetal. 2004;Hext, Tomenson,and Thompson 2005). In contrast, Mineralogy and Structure of Pathogenic Particles 21 © 2007 by Taylor & Francis Group, LLC no tumors wereseen in similarly exposed mice and hamsters (Muhleetal. 1989; Warheit et al. 1997; Bermudez et al. 2002). These apparent species differences suggestedthat the experimentally- induced lung tumors werearat-specific, thresholdphenomenon, dependent upon lung overloading andaccompanied by chronicinflammationtoexert theobserved tumorigenicresponse. The relevance of this phenomenon to human exposures remains questionable but, to date, epidemiolo- gical studies conducted do not suggestacarcinogenic effect of TiO 2 dust on the human lung (Hext, Tomenson, and Thompson 2005). Apatite Ca 5 (PO 4 ) 3 (F,OH,Cl)isagroup of hexagonal minerals,usually subdivided into the three minerals; fluorapatite,chlorapatite,and hydroxylapatite. The fundamental unit of the apatites is the tetrahedral (PO 4 ) 3 K anionic group. The three types may partially replace each other, and it is hard to distinguish betweenthem; therefore they are usually simplycalled “apatite.” The mostcommon of the three, by far, is fluorapatite. Apatite is the mostcommon phosphate mineral, and is essential in the manufacture of phosphate-basedfertilizers, and is important in the chemical and pharma- ceutical industries.Concerns have been raised about theoccupationalrespiratoryhazardsof phosphates (Sebastien et al. 1983)and apatite (Mikulski et al. 1994a). Epidemiological studies have been undertaken on the respiratory function of smoking and non-smoking workersexposedto apatite dust. It was concluded that occupational exposure to phosphorite and apatitedusts causesa decrease in pulmonary function in non-smoking workers(Mikulski et al. 1994b). Aluminum ore, called bauxite, is usually formed in deeply weathered volcanic rocks,such as basalt.Bauxite is aheterogeneous material, mostly composed of severalaluminum hydroxide minerals, plus varying amounts of silica,ironoxide,aluminosilicate,and otherminor or trace minerals. The principal aluminum hydroxide minerals,Al(OH) 3 in bauxites are gibbsite and its polymorphs boehmite and diaspore.Ingibbsite, the fundamental structure is alayer of aluminum ions,sandwiched between two sheets of tightly-packed hydroxyions;onlytwo of the three octa- hedrally-coordinated sites are occupied by cations.Aluminum ore dust,orbauxite dust inhalation, canresultin“Shaver’s Disease,”corundumsmelter’slung, bauxitelung, or bauxitesmelters’ disease(Dinman 1988; Radon et al.1999; Krausetal. 2000).Thisoccupationaldisease in bauxite minersisaprogressive form of pneumoconiosis causedbyexposure to bauxite fumes which containaluminumand silica particulates. Initially, thediseaseappears as alveolitisand then progresses to emphysema. Patientsmay develop pneumothorax (collapsed lung).Itistypically seen in workersinvolved in the smeltingofbauxite to produce corundum (crystalline form of aluminumoxide andone of therock-formingminerals). Duetocorundum’s hardness,itis commonly used as an abrasive in machining, from huge machines to sandpaper. Emeryisan impure and less abrasivevariety. Themineral calcium fluoride or fluorite, CaF 2 ,occurs as cubic crystals and cleavable masses. The calcium ions are arranged in acubic lattice,with the fluorine ions at the center of smaller cubes derived by dividing the unit cell intoeightcubes.When pure, it is colorless, however, impurities cause color, andsomevarieties fluoresce. It is commoninlimestone anddolomites, andhas multipleuses in the fiberglass, ceramic, and glass industries. The respiratory hazards of fluorite are related to the fluorine and silica content. Acute inhalation hasbeen linked to gastric, intestinal, circulatory, and nervous system problems. Chronicinhalation or ingestion can result in weight and appetite loss,anemia,and boneand teethdefects.The symptoms aretherefore like thoseof fluorinosis, adisease associated with the ingestion of fluorine, usually in water or from contami- nated land.Ithas been suggested that fluorite promotes silica fibrogenicity (pneumoconiosis) in the lungs (Xuetal. 1987). Fluoriteminers have reported bronchitis,silicosisand pulmonary lesions (Xuetal. 1987). Themineral graphite is acrystalline form of elemental carbon. Each carbon atom is covalently bonded, with bond length 1.42 A ˚ ,tothree others in the sameplane, with abond angle of 1208 .The carbon atoms thus form linked six-member rings to form flat or, occasionally, buckled planes. The sheets are usually stacked in an ABABarray, or less commonly in an ABCABC array. In compari- son to the covalent bonds (1.42 A ˚ )forming the sheets, the sheets are widely separated at alength Particle Toxicology22 © 2007 by Taylor & Francis Group, LLC [...]... al 20 04; © 20 07 by Taylor & Francis Group, LLC 34 Particle Toxicology Yu et al 20 04) Welding “smoke” is a mixture of fine particles and gases, with the components including toxic metals such as; chromium (Yu et al 20 01; Antonini et al 20 05; Sorensen et al 20 05), nickel (Antonini et al 20 05), manganese (Yu et al 20 04), beryllium (Stefaniak et al 20 04), cadmium (Binks et al 20 05; Jakubowski et al 20 05),... pyrophyllite, and zeolite, Int J Toxicol., 22 (1), 37–1 02, 20 03 Emri, S and Demir, A U., Malignant pleural mesothelioma in Turkey, 20 00 20 02, Lung Cancer, 45 (1), S17–S20, 20 04 Emri, S., Demir, A., Dogan, M., Akay, H., Bozkurt, B., Carbone, M., and Baris, I., Lung diseases due to environmental exposures to erionite and asbestos in Turkey, Toxicol Lett., 127 (1–3), 25 1 25 7, 20 02 Fach, E., Waldman, W J., Williams,... and allergic symptoms in children, Am J Respir Crit Care Med., 166 (8), 10 92 1098, 20 02 Breeling, J L., Potential hazard from eating rice coated with glucose and talc, J Am Med Assoc., 22 8, 101, 1974 Britton, M., The epidemiology of mesothelioma, Semin Oncol., 29 (1), 18 25 , 20 02 © 20 07 by Taylor & Francis Group, LLC 36 Particle Toxicology Brockmann, M., Fischer, M., and Muller, K M., Exposure to carbon... around the solid nucleus evaporates away The particles are thus characterized by an “eroded” solid particle that was the original mineral nucleus, surrounded by usually “well-formed,” water-soluble crystals An example of the © 20 07 by Taylor & Francis Group, LLC 32 Particle Toxicology 5 μm (a) (c) 2 μm (g) (d) 5 μm (e) 5 μm (b) (f) (h) 1 μm 2 μm 1 μm 2 μm FIGURE 2. 5 (a) Microcrystals of anhydrite (CaSO4)... cobalt (Dunlop et al 20 05; Krakowiak et al 20 05), copper (Santec et al 20 05), lead (Binks et al 20 05), and zinc (Karlsen et al 19 92; Fine et al 1997; Fine et al 20 00) The metal particulates tend to be in the form of oxides, with the critical issue being their bioavailability Particle sizes range from 5 nm to 20 mm, with 10%–30% larger than 1 mm (Zimmer, Baron, and Biswas 20 02) Short-term exposure to metal... burning of poor-quality coals © 20 07 by Taylor & Francis Group, LLC 24 Particle Toxicology The types and differing proportions of the different minerals to be found in “coal dust” thus relates to the geology of the coal mine or opencast (Figure 2. 2a) Coal seams are found in sedimentary rocks, therefore are typically associated with sandstones, siltstones and shales (Figure 2. 2b–Figure 2. 2d) Some of the... have now focused on the crystalline SiO2 content, a well` established respiratory hazard Consequently, the eruption of the Soufriere Hills volcano on Montserrat has been extensively studied (Wilson et al 20 00; Horwell et al 20 01; Housely et al ´ ´ 20 02; Searl, Nicholl, and Baxter 20 02; Horwell et al 20 03; BeruBe et al 20 04; Forbes et al 20 04; Lee and Richards 20 04), and the varying percentage of cristobalite... fume particles and grinding dusts, Am Ind Hyg Assoc J., 53 (5), 29 0 29 7, 19 92 Kelleher, P., Pacheco, K., and Newman, L S., Inorganic dust pneumonias: the metal-related parenchymal disorders, Environ Health Perspect., 108 (4), 685–696, 20 00 Kim, B G., Han, J S., and Park, S U., Transport SO2 and aerosol over the Yellow Sea, Atmos Environ., 35, 727 –737, 20 01 © 20 07 by Taylor & Francis Group, LLC 40 Particle. .. recognized, and this enabled the “finger-printing” of local crustal PM10 Nanoparticles have been broadly defined as microscopic particles with dimensions less than 100 nm (Figure 2. 2a, Figure 2. 3b–Figure2.3d), however, “engineered” nanoparticles are more precisely defined as having one dimension less than 100 nm Many nanoparticles are prone to rapid agglomeration, forming larger “particles” with dimensions much... different sites within a power plant, Mol Cell Biochem., 25 5 (1 2) , 25 7 26 5, 20 04 Antonini, J M., Leonard, S S., Roberts, J R., Solano-Lopez, C., Young, S H., Shi, X., and Taylor, M D., Effect of stainless steel manual metal arc welding fume on free radical production, DNA damage, and apoptosis induction, Mol Cell Biochem., 27 9 (1 2) , 17 23 , 20 05 Artvinli, M and Baris, I., Malignant mesotheliomas in . Na 2 Ca 2 Al 6 Si 9 O 30 8H 2 O; mordenite, (Ca,Na 2 ,K 2 )Al 2 Si 10 O 24 7(H 2 O); natrolite, Na 2 Al 2 Si 3 O 10 2H 2 O; paranatrolite, Na 2 Al 2 Si 3 O 10 3H 2 O; tetranatrolite, Na 2 Al 2 Si 3 O 10 2H 2 O; scole- cite,. amphibole, cummingtonite (Mg,Fe C 2 ) 7 [Si 8 O 22 ](OH) 2 -grunerite (Fe C 2 ,Mg) 7 [Si 8 O 22 ](OH) 2 series.Grunerite is thenamefor themore iron-rich end-members, and is of significance here,. CardiffUniversity CONTENTS 2. 1 Introduction 13 2. 2 Ortho- and Ring Silicates 14 2. 3 Chain Silicates 16 2. 4 Sheet Silicates 17 2. 5 Tecto- (Framework) Silicates 19 2. 6 Non Silicates 21 2. 7 Rock Quarrying