Inhalation Toxicology, 20:1199–1214, 2008Copyright c© Informa UK Ltd.ISSN: 0895-8378 print / 1091-7691 onlineDOI: 10.1080/08958370802136749

Product Stewardship in Wollastonite Production

L. Daniel Maxim and Ron NieboEverest Consulting Associates, Cranbury, New Jersey, USA

Salvatore LaRosaNYCO Minerals Inc., Willsboro, New York, USA

Brad JohnstonElk Valley Coal Corp., Calgary, Alberta, Canada

Kimberly AllisonRJ Lee Group, Inc., Monroeville, Pennsylvania, USA

E. E. McConnellToxPath, Inc., Raleigh, North Carolina, USA

In July 2002, NYCO Minerals, Inc., discovered a heretofore unknown contaminant in its wol-lastonite ore. The contaminant was first believed to be tremolite asbestos. Immediate effortswere made to eliminate this material. Additional studies were initiated to fully characterizethe contaminant and its distribution in the ore body. Subsequent study by NYCO and theirconsultants led to the identification of the contaminant as a transition material (TM) inter-mediate between tremolite and talc. In vitro dissolution rate measurements indicated that theTM dissolved much more rapidly than tremolite asbestos. This article provides backgroundinformation on wollastonite mineralogy and NYCO’s product stewardship program (PSP). Atpresent, NYCO Minerals uses selective mining to control the trace levels of TM in the ore andfinished product verified by periodic monitoring of workplace air and finished product.

NYCO Minerals, Inc., developed a product stewardship pro-gram (PSP) to identify, manage, and control occupational risksassociated with the production and use of wollastonite. This ar-ticle presents a short case history of the discovery, identification,and control of what was initially considered to be a potentially

Received 9 April 2008; accepted 17 April 2008.This research was supported by NYCO Minerals, Inc. However, the

findings and conclusions are those of the authors and not necessarilythose of NYCO Minerals, Inc. We acknowledge the kind assistance ofDr. Bruce Zoitos of Unifrax Corp. in making the durability measure-ments and the useful insights and thoughtful comments on this articleby Dr. Richard J. Lee and Drew R. Van Orden of the RJ Lee Group, Inc.The support of numerous personnel from NYCO Minerals in collect-ing the samples and RJ Lee Group, Inc. in their analyses should alsobe acknowledged as well as the assistance furnished by MSHA person-nel. Portions of these results were presented at the Industrial MineralsAssociation—North America (IMA-NA) spring meeting, April 25–27,2007, Washington, DC. All uniform resource locators (URLs) werevalid as of 15 June 2007.

Address correspondence to Dr. Dan Maxim, Everest ConsultingAssociates, 15 North Main Street, Cranbury, NJ 08512, USA. E-mail:postsf@aol.com

toxic impurity in the host rock and orebody. Results will be ofinterest to those who mine or use wollastonite, but also to thosewho process or use other industrial minerals.

BACKGROUNDNYCO Minerals, Inc., is a leading producer of wollastonite.

NYCO’s wollastonite mining operations includes a facility inWillsboro, NY (opened in 1953), and another (Minera RocaRodando) located in Pilares, Sonora, Mexico (opened in 1997).NYCO also markets the mineral tripoli (a microcrystalline formof quartz) through the American Tripoli Company, Seneca, MO.

WOLLASTONITEWollastonite (CASRN 13983-17-0, EINECS no. 237-772-

5), is a naturally occurring calcium silicate (CaSiO3, molecu-lar weight 116.2). It was named wollastonite in 1822 to honorthe English chemist and mineralogist William Hyde Wollas-ton. (Synthetic wollastonite is also produced in relatively minorquantities.)

Natural wollastonite occurs as prismatic crystals that breakinto massive (irregular form) to acicular (needlelike) fragments

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(Virta, 2003). Acicular fragments are desirable for certain ap-plications (e.g., fillers and extenders) because the long, thin par-ticles improve the flexural modulus, sag resistance, flexural andtensile strengths, and thixotropic properties of the paints, plas-tics, and rubber products in which they are used (Virta, 2003).Wollastonite is typically white or cream in color but may alsobe gray, brown, or red, depending on its composition (Virta,2003).

Natural wollastonite deposits are mined (both undergroundand surface mines) in several countries of the world. World pro-duction of crude wollastonite ore reportedly exceeded 600,000tonnes in 2005 (Virta & Revette, 2006), up from 36,800 tonnes in1959 (DiFrancesco & Virta, 2006). Leading world producers in2005 ranked in descending order of wollastonite output includeChina (395,000 tonnes), India (169,000 tonnes), the UnitedStates (115,000 to 127,000 tonnes), Mexico (27,100 tonnes), andFinland (16,800 tonnes) (Virta, 2005a). Potentially economicdeposits have been identified (and some actually mined) inAustralia, Brazil, Canada Chile, Cuba, Czech Republic,Greece, Kenya, Morocco, Namibia, New Zealand, North Korea,Pakistan, Japan, Spain, Turkey, and Uzbekistan (Crooks, 1999;Dumont, 2005; Fattah, 1994; Lueck, 1997; Palfi, 2002; Parkison,1990; Virta, 1994, 2003; Watters, 1995).

After mining and beneficiation, wollastonite can also besurface treated or modified with various materials (includingstearates, zircoaluminates, titanites, and organosilanes) for im-proved performance in certain high-value applications (Fattah,1994). Among other benefits, surface treatments improve theadhesion between the wollastonite and the polymers to which itis added.

Wollastonite is used for diverse applications—including as-bestos replacement (Andrews, 1970; Fattah, 1994). Domesticmarkets (with estimated 1999 share in parentheses) include plas-tics (37%), ceramics (28%), metallurgical applications (10%),paint (10%), friction products (9%), and miscellaneous others(6%) (Virta, 2003). More recent estimates are not materiallydifferent (Virta & Revette, 2006).

Wollastonite Toxicology/EpidemiologyBecause some wollastonite structures/fibers are respirable

and also because wollastonite has been suggested as a possiblereplacement for asbestos in some applications, several investi-gators have studied the toxicology and epidemiology of wollas-tonite. Maxim and McConnell (2005, p. 451) summarized theavailable data on wollastonite toxicology and epidemiology andconcluded:

We conclude that there is inadequate evidence for the carcino-genicity of wollastonite in animals and, based on strong evidencethat wollastonite is not biopersistent, believe that a well-designedanimal inhalation bioassay would have a negative result. The epi-demiological evidence for wollastonite is limited, but does not sug-gest that workers are at significant risk of an increased incidence ofpulmonary fibrosis, lung cancer, or mesothelioma. Morbidity stud-ies have demonstrated nonspecific increase in bronchitis and reduced

lung function. It is prudent, however, to continue product stewardshipefforts by wollastonite producers to control workplace exposures andto monitor scientific developments.

More recently, a workshop was held in 2006 by the WorldHealth Organization on mechanisms of fiber carcinogenesis andassessment of chrysotile asbestos substitutes (United NationsEnvironment Program, 2006, p. 5). Wollastonite was amongseveral fibers evaluated as a possible substitute for chrysoliteasbestos. The Consensus Report of the Workshop concluded thefollowing with respect to wollastonite:

Natural wollastonite contains respirable fibers. In occupationalsettings exposure is mainly to short fibers. In chronic studies wol-lastonite did not induce tumours after intraperitoneal injection inanimals; however, samples of wollastonite were active in differentstudies for genotoxicity. After considering this apparent discrepancyit was concluded that the hazard was likely to be low.

The working group considering wollastonite also noted (dur-ing the deliberations) that impurities in wollastonite might posea hazard—an appropriate concern (at least in principle) withmany products of natural origin.

Regulatory StatusThe International Agency on Cancer (IARC) examined wol-

lastonite on two occasions (IARC, 1987, 1997); in 1997 IARCplaced wollastonite into Group 3 (cannot be classified as to itscarcinogenicity to humans) based on the finding that there wasinadequate evidence in both humans and animals for the car-cinogenicity of wollastonite. The National Toxicology Program(NTP) does not list wollastonite as either known or reasonablyanticipated to be a carcinogen. The U.S. Environmental Protec-tion Agency (EPA) provides no listing of wollastonite on theIntegrated Risk Information System (IRIS).

In the United States, wollastonite falls under the particu-lates not otherwise regulated (PNOR) standard for an occupa-tional exposure limit (OEL). Some countries have establisheda specific OEL applicable to wollastonite; in Quebec, Canada,and Denmark, for example, the OEL is 1 fiber per cubic cen-timeter (f/cm3), whereas in Sweden it is 0.5 f/cm3 (Maxim &McConnell, 2005).

Product Stewardship ProgramNYCO developed a PSP for its wollastonite operations. The

basic goal of the PSP is to protect NYCO’s workers against oc-cupational health and safety risks and to provide products thatcan be used safely by NYCO’s customers. Operationally, thePSP is directed by senior management with the staff support ofa Health Committee. This committee, consisting of NYCO per-sonnel and external consultants, identifies possible issues/topicsfor analysis, analyzes data, and formulates recommendations forrisk management strategies. Key elements of the PSP summa-rized in Figure 1 include:

• Monitoring (exposure): Measurement of workplace(airborne) concentrations of selected materials (see

PRODUCT STEWARDSHIP IN WOLLASTONITE PRODUCTION 1201

FIG. 1. Elements of NYCO’s product.

below) to ensure compliance with published OELsand/or internal NYCO exposure guidelines. In the eventthat measured concentrations exceed these target lev-els, NYCO investigates methods for exposure controlin accord with the traditional hierarchy of controls (en-gineering controls, followed by altered workplace prac-tices, followed by use of personal protective equip-ment).

• Monitoring (bulk): Measurement of bulk concentra-tions of selected materials at various parts of the pro-cess as well as of finished products to ensure adherenceto published specifications and any applicable regula-tions. Implicit in the monitoring activity is the commit-ment to reduce exposures to the extent feasible.

• Communications: Development of accurate and infor-mative material safety data sheets (MSDSs) and liter-ature for customers on handling guidelines for wollas-tonite. Preparation of appropriate pre-manufacturingnotices (PMNs) to the U.S. EPA for surface-treatedwollastonite products.

• Toxicology research: Conduct of in vivo and invitro studies. For example, NYCO has sponsored invivo studies of the biopersistence of wollastonite andsurface-treated wollastonite (Muhle et al., 1991, 1994;Bellmann & Muhle, 1994). Biopersistence is believedto be an important determinant of the toxicity of fibers;wollastonite fibers have an estimated half-time of 10–21 days in female Wistar rats, which is believed bymany to be the reason why wollastonite has not pro-duced lung disease in lifetime bioassays.

• Medical surveillance: Health surveillance of employ-ees, including annual chest x-rays and pulmonary func-tion tests is an important part of the PSP. In the past, theNational Institute of Occupational Health and Safety(NIOSH) also conducted morbidity studies of a cohortof workers in the Willsboro facility (Shasby et al., 1979;Hanke & Sepulveda, 1982; Hanke et al., 1984). Thesestudies indicated pneumoconiosis in 3% of the workersand (among those with >30 dust years of exposure) astatistically significantly lower ratio of FEV1 to FVCand a lower peak flow rate than 86 age-matched controlworkers from a nearby electronics plant.

Based on the available wollastonite health effects data, it isappropriate that the focus of the PSP should be on possible con-taminants of wollastonite rather than the mineral itself. Accord-ingly, a literature search was undertaken to identify materialsreportedly associated with wollastonite, either in the ore itselfor in materials found in proximity to the ore—an important stepin identifying materials of potential interest to the design of astewardship program. These materials are summarized next.

Minerals Associated With WollastoniteWollastonite forms when impure limestones are metamor-

phosed (subjected to heat and pressure) or silica-bearing fluidsare introduced into calcareous sediments during metamorphism(Virta, 2005a). Pure wollastonite has a theoretical compositionof 48.3% calcium oxide and 51.7% silicon dioxide. In natureit is found in mineral deposits that typically contain severalother minerals (foreign materials). Both the ore (material with

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economically recoverable wollastonite) and the overburden (sur-rounding material with less than an economically determinedcutoff grade) may contain these foreign materials. The iden-tities and amounts of these materials vary with the particularwollastonite deposit. Table 1 contains a list of the specific min-erals that have been associated with wollastonite; these includematerial in the host rock, gangue material (non-economic mate-rial distributed in the ore), and minerals that may be recovered asbyproducts or co-products. Not all of these materials are foundin each wollastonite deposit; the compositions and concentra-tions of these foreign materials vary from deposit to deposit.These differences are partly related to the type and level of as-sociated mineral contamination and, more importantly, to thelevel of metamorphism of the sediments and the volcanic and/ormeteoric water migration through the ore body (Dumont, 2005).

For example, the NYCO Willsboro deposit (DeRud-der & Beck, 1962) reportedly contains wollastonite-garnet-clinopyroxene with accessory apatite and sphene. In 1962, nearlypure wollastonite constituted approximately 64% of the deposit,red garnet comprised approximately 21% of the ore body, andgreen clinopyroxene comprised about 15% (DeRudder & Beck,1962).

As a second example, the Ihalainen deposit (in southeast Fin-land) contains 20–24% wollastonite (Dumont, 2005) and a suiteof other minerals, largely calcite (http://www.geology.neab.net/locality/finland/ihalaine.htm).

The amount and composition of the minerals in the wollas-tonite deposit determine:

• The type of mining and beneficiation steps requiredto produce the finished product(s). Figure 2 showsa generic process flow diagram for mineral min-ing and beneficiation. The specific steps requireddepend upon the deposit. For example, dry process-ing is used on underground or surface-mined wol-lastonite ore from NYCO’s Willsboro deposit. (Ad-ditional Willsboro-specific information is includedin Figure 2.) This entails primary, secondary, andtertiary crushing and sizing. The various size frac-tions are passed through high-intensity magnetic sep-arators to remove garnet and diopside, which arefurther separated using an electrostatic method andhigh intensity rare earth permanent magnets. (Gar-net is sold as a by-product.) As another example,wet processing is used to beneficiate wollastonitefrom Norkalk’s Ihalainen limestone quarry in Lappeen-ranta, Finland. This mine has a significantly differ-ent mineralogy (see e.g., http://www.geology.neab.net/locality/finland/ihalaine.htm) than the Willsboro de-posit. The wet process consists of primary crushing andthe wollastonite is separated from limestone and wasterock by photometric sorting. The wollastonite “accept”fraction is further crushed and calcite is floated fromwollastonite and the wollastonite “tailing” is further

TABLE 1Possible associated minerals/impurities/gangue

materials/byproducts/co-products in or near wollastonitedeposits

Material Empirical formula

Actinolite Ca2(Mg, Fe)5Si8O22(OH)2

Adularia KAlSi3O8

Akermanite Ca2Mg(Si2O7)Albite NaAlSi3O8

Allanite Ca(Ce,La,Y,Ca)Al2(Fe2+,Fe3+)(SiO4)(Si2O7)O(OH)

Andradite Ca3Fe+22 (SiO4)3

Anorthite Ca(Al2Si2O8)Anthophyllite Mg7Si8O22(OH)2 or (Mg, Fe)7Si8O22(OH)2

Apatite Na0.05Ca0.95Al1.95Si2.05O8

Apophyllite (K,Na)Ca4Si8O20(F,OH) − 8H2OAugite Ca0.9Na0.1Mg0.9Fe+2

0.2Al0.4Ti0.1Si1.9O6

Bustamite (Mn2+,Ca)[SiO3]Calcite CaCO3

Chalcopyrite CuFeS2

Calophonite Ca3Fe4(SiO4)3

Chlorite (Fe, Mg, Al)6(Si, Al)4O10(OH)8

Chondrodite (Mg,Fe+2)5(SiO4)2(F,OH)2

Clinopyroxene (Ca,Mg,Fe,Na)(Mg,Fe,Al)(Si,Al)2O6

Clinozoisite Ca2Al3(SiO4)3(OH)Diopside CaMg(Si2O6)Dolomite CaMg(CO3)2

Epidote Ca2Fe+32.25Al0.75(SiO4)3(OH)

Feldspar XAl(1-2)Si(3-2)O8 where the X site can beNa, Ca, K

Garnet Various, e.g., A3B2(SiO4)3 where the A siteis usually occupied by divalent cations(e.g., Ca, Mg, Fe+2) and the B site bytrivalent cations (Al, Fe+3, Cr)

Graphite CGrossular Ca3Al2(SiO4)3

Hedenbergite CaFeSi2O6

Hematite Fe2O3

Hornblende Ca2(Mg4Al)(Si7Al)O22(OH)2 andCa2(Fe2+

4 Al)(Si7Al)O22(OH)2

Hubeite Ca2Mn+2Fe+3Si4O12(OH)(H2O)2

Idocrase Ca10(Mg, Fe)2Al4(SiO4)5(Si2O7)2(OH)4

Inesite Ca2Mn+27 Si10O28(OH)2·5(H2O)

Larnite Ca2(SiO4)Magnesite MgCO3

Magnetite Fe3O4

Melanite CaFeTi(SiO4)3

Merwinite Ca3Mg(SiO4)2

Microcline K(Al3SiO8)Montmorillonite (Na,Ca)0.33(Al,Mg)2(Si4O10)(OH)2 · nH2OMuscovite KAl3Si3O10(OH)1.8F0.2

(Continued on next page)

PRODUCT STEWARDSHIP IN WOLLASTONITE PRODUCTION 1203

TABLE 1Possible associated minerals/impurities/gangue

materials/byproducts/co-products in or near wollastonitedeposits (Continued)

Material Empirical formula

Pectolite NaCa2[HSi3O9]Plagioclase Na(AlSi3O8) – Ca(Al2Si2O8) (albite to

anorhtite)Prehnite Ca2Al2Si3O10(OH)Pseudowallastonite CaSiO3

Pyrite FeS2

Pyrolucite MnO2

Pyrrhotite FeSQuartz SiO2

Rhodonite MnSiO3

Rothoffite (Ca,Mg)3Fe2(SiO4)3(an unusualmanganese-rich andradite garnet)

Salite Ca(Mg,Fe)SiO6(also known as Diopside)Scapolite (Na,Ca)4(Al,Si)6SI6O24(Cl,CO3,SO4)Sphene CaTiSiO5

Spurrite Ca5(SiO4)2(CO3)Stevensite (Ca0.5,Na)0.33(Mg,

Fe++)3SiO4O10(OH)2.nH2OTalc Mg3Si4O10(OH)2

Titanite CaTiSiO5

Tremolite [Ca2Mg5Si8O22(OH)2]n

Vesuvianite Ca10Mg2Al4(Si2O7)2(SiO4)5(OH)4

Zircon ZrSiO4

Zoisite Ca2Al3(SiO4)3(OH)

Note. Not all of these materials are found in every wollastonite de-posit. Each deposit has a particular profile of associated minerals. Nu-merous sources were consulted in the preparation of this table. Thesesources include Burnham, 1995; Crooks, 1999; DeRudder and Beck,1962; Dumont, 2005; Grammatikopoulos et al., 2003; Higgins et al.,2001; Johnson, 2003; Lueck, 1997; Orris and Bliss, 1991; Pawley et al.,1996; Simandi et al., 1999; Strunz and Nickel, 2000; Virta, 2005a; Virta,2005b; Watters, 1995; Yang and Prewitt, 1999; Amethyst Galleries,Inc., available online at http://www.galleries.com/minerals/silicate/wollasto/wollasto.htm; www.britannica.com; webmineral.com; miner-alszone.com; smartmineral.com; mindat.org (for example, seeactinolite at http://www.mindat.org/min-18.html); Mineral DataPublishing, available online at http://rruff.geo.arizona.edu/doclib/hom/wollastonite.pdf.

beneficiated by wet high-intensity separation to removeiron oxides (Dumont, 2005).

• The types of wollastonite (acicular or powder grades)products that may be economically produced. Localvariations in temperature and pressure that occurredduring metamorphism of the sediment are known tohave markedly affected both crystal formation and aci-cularity (Dumont, 2005).

• The types of byproducts or coproducts made. For ex-ample, the Lappenranta, Finland mine produces prin-cipally limestone for cement production; wollastoniteis produced in lower amounts. The NYCO process inWillsboro recovers garnet as a byproduct.

• The necessary elements of the product stewardship pro-gram, including the need for (and type of) exposuremonitoring, separation techniques, applicable occupa-tional exposure limits (OELs), and necessary controlson finished product purity.

The focus of this study is on the links between the composi-tion of the deposit and product stewardship/industrial hygiene.One key element of an exposure monitoring program is to iden-tify the possible components of the material being handled thatmight have toxic effects. The list of materials shown in Table 1is a useful starting point, but not all these materials are foundat each mine and not all of these materials have toxic effects.The list of materials given in Table 1 is believed to be complete;however, as the Mine Safety and Health Administration (MSHA)noted in its proposed 2005 asbestos standard (Federal Register,2005, p. 43953), “a specific rock formation may contain a con-tinuum of minerals from one end member of a series to the otherend member, creating a solid solution of intermediate miner-als. These intermediate minerals are sometimes given names,while at other times they are not” and “a mineral may also un-dergo transition to a different mineral series.” Thus, it is possiblethat wollastonite host rock or deposits contain other unnamedand/or transition minerals. In commenting on the Willsboro de-posit DeRutter and Beck (1962, p. 188) noted:

Talc, the dominant material in the most intensely altered zonebordering the solution channelway, was formed by the continuingaction of magnesium-bearing solutions on stevensite. Stevensite hasa defect structure, i.e., a deficiency in the total number of ions in octa-hedral coordination. The addition of magnesium from hydrothermalsolutions to the octahedral layer of stevensite converts this mineralto talc, concomitantly freeing interlayer cations and water.

Thus, it is reasonable to expect that in addition to specific(named) minerals there will be a series of transition materials ofintermediate composition in or near the orebody.

Table 2 shows the recommended exposure limits (RELs) es-tablished by NIOSH and the permissible exposure limit (PELs)set by the Occupational Safety and Health Administration(OSHA). Specific OELs have been established for only a fewof the materials given in Table 1. Those mineral dusts with-out specific PELs all fall under the standard for particulatesnot otherwise regulated (PNOR, formerly called the “nuisancedust” standard). Based on the characteristics of the Willsboroand Pilares deposits, the available toxicological information, andthe applicable OELs, the possible materials of potential interest(in addition to wollastonite) include respirable crystalline sil-ica (RCS as crystalline quartz), talc, total and respirable dust(for PNOR), and asbestiform amphiboles, including actinolite,anthophyllite and tremolite. (From a regulatory perspective, it

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TABLE 2Occupational exposure limits (OELs) associated with possible associated minerals/impurities/gangue

materials/by-products/co-products in or near wollastonite deposits for which NIOSH RELs or OSHA PELs have been published

Materiale NIOSH REL OSHA PEL

Actinolite TWA 0.1 f/cm3 TWA 0.1 f/cm3a

Anthophyllite TWA 0.1 f/cm3 TWA 0.1 f/cm3a

Calcite TWA 10 mg/m3 (total) TWA 5 mg/m3

(resp)bTWA 15 mg/m3 (total) TWA 5 mg/m3

(resp)Dolomite TWA 10 mg/m3 (total) TWA 5 mg/m3

(resp)TWA 15 mg/m3 (total) TWA 5 mg/m3

(resp)Graphite TWA 2.5 mg/m3 (resp) TWA 15 mppcfd

Magnesite TWA 10 mg/m3 (total) TWA 5 mg/m3

(resp)TWA 15 mg/m3 (total) TWA 5 mg/m3

(resp)Muscovite TWA 3 mg/m3 (resp) TWA 20 mppcf (total)Particulates not otherwise

Regulated (pnor)dTWA 15 mg/m3 (total) TWA 5 mg/m3

(resp)Quartz TWA 0.05 mg/m3 (resp) TWA 30 mg/m3/(%SiO2+ 2) [total] TWA

10 mg/m3/(%SiO2+ 2) [resp]Talc TWA 2 mg/m3 (resp)c TWA 20 mppcfTremolite TWA 0.1 f/cm3 TWA 0.1 f/ cm3a

aIdentical with the proposed Mine Safety and Health Administration (MSHA) standard (70 Federal Register 145, pp. 43949–43989). Standardapplies only to asbestiform material.

bThe notation (resp) indicates the respirable fraction.cContaining no asbestos and less than 1% quartz.d Units are million particles per cubic foot.ePresumably each of the materials given in Table 1 for which no specific OEL has been established fall under the PNOR limits. The American

Conference of Industrial Hygienists (ACGIH) has a similar category, particulates not otherwise classified (PNOC), for which the threshold limitvalues are 10 mg/m3 (total) and 3 mg/m3 (resp).

FIG. 2. Generic steps in mineral production and additional detail on wollastonite mining and beneficiation.

PRODUCT STEWARDSHIP IN WOLLASTONITE PRODUCTION 1205

should be noted that OELs applicable to asbestos [either fromOSHA or MSHA] do not apply to the nonasbestiform actinolite,tremolite, and anthophyllite.∗ These are the suite of materialsmonitored as part of the NYCO PSP. The monitoring programincludes personal and area monitoring for monitoring compli-ance with OELs and analysis of ore and finished product toverify compliance with MSDSs and various product technicalspecifications.

Although the list of materials given in Table 2 was developedspecifically for the Willsboro wollastonite deposit, some of thematerials are of more general interest in view of their widespreaddistribution at mining sites. Crystalline silica (quartz), for exam-ple, is reportedly a component of nearly every mineral deposit(Greskevitch et al., 1992).

A Case History, Discovery of “Tremolite Asbestos”in Willsboro Deposits

As noted earlier, one of the functions of the PSP is to en-sure that finished products meet technical specifications and thatoccupational exposures to wollastonite and other materials towhich workers are exposed are in compliance with applicableOELs. One incident serves as a useful example of the PSP inaction and is also of scientific interest. During July 2002, ex-ternal laboratory tests reported low concentrations (<0.3%) of“tremolite asbestos” (i.e., asbestiform tremolite) in bulk wol-lastonite shipped from NYCO’s Willsboro mine (see Hawley,2003; 70 Federal Register 145, pp. 43949–43989). NYCO hadthe bulk material retested, results of which appeared to confirmthe initial finding. The apparent finding was plausible in termsof materials reportedly found at or near other wollastonite de-posits. However, asbestiform tremolite (tremolite asbestos) wasnot previously detected in the Willsboro ore or product usingphase-contrast optical microscopy (PCOM), the traditional testmethod. Subsequent analyses, conducted retrospectively usingtransmission electron microscopy (TEM) were able to detect“tremolite asbestos” in certain bulk and personal monitoringsamples.†

NYCO’s parent company (Fording Canadian Coal Trust at thetime) agreed with mine management and opted for full disclosureof these findings. Some of the immediate events and actions inthe wake of this initial finding included:

• A temporary MSDS was prepared (July 2002). ThisMSDS reflected regulations (HAZCOM standards) formixtures (CFR 1910.1200(g)(2)(i)(C)(1)) that require

∗For a discussion of this point, see the proposed rule on the asbestos exposurelimit (70 Federal Register, No. 145, pp. 43950–43989 and especially 43954).On June 8, 1992 OSHA (see 57 Federal Register 24310–24311) deleted thenonasbestiform types of these minerals from the scope of its asbestos standards.OSHA found insufficient evidence that nonasbestiform actinolite, tremolite, andanthophyllite presented “a risk similar in kind and extent” to their asbestiformcounterparts.

†As shown later in the text, the material initially thought to be “tremoliteasbestos” was actually misidentified. Quotes are used to indicate the uncertaintyof the identity of the material.

listing of the chemical and common names of all in-gredients that comprise 1% or greater of the compo-sition, except that chemicals identified as carcinogens(asbestos in this case) are required to be listed if theconcentrations are 0.1% or greater.

• Announcements were made to all employees, contrac-tors of NYCO at the site, relevant government agen-cies (e.g., MSHA and Health Canada), and port facilitypartners. A concurrent news release was issued (August2002).

• Based on testing results, certain products in Canadaand the EU were either recalled or quarantined (August2002). An experienced analytical laboratory (RJ LeeGroup, Inc.) was retained to undertake the analyticalinvestigations as to the characterization of the “tremo-lite asbestos” as well as routine testing of bulk andpersonal monitoring samples.

• MSHA occupational hygienists visited the site, con-ducted industrial hygiene monitoring in the mill andthe pit, and began a cooperative program with NYCO(August 2002). Several of the initial personal moni-toring samples reportedly exceeded the MSHA OEL(MSHA, 2005; Federal Register, 2005). NYCO ac-celerated follow-up exposure monitoring using TEManalyses.

• NYCO site personnel began testing the deposit to mea-sure and localize (if possible) the degree of contami-nation. The source of the contamination was identifiedand characterized and the mining location altered toavoid and quarantine suspect material pending furthertesting. Over the next 2 months, standard practices andprocedures were developed to ensure all ore from themine was in compliance with known worldwide stan-dards for asbestiform tremolite (<0.1% in bulk). (Thisstandard was later made more stringent [nondetectable]prior to release from the mine.)

• A complete cleanup of all surfaces in the processingplant was completed over the period from October 2002to January 2003.

• NYCO began monitoring raw ore and product bulksamples on weekly composites of plant production. Thefrequency and extent of air sampling was increased.

• A longer term research program was initiated to char-acterize the “tremolite asbestos” in terms of its chem-ical identity, morphology, crystallography, size distri-bution, and dissolution rates.

NYCO took an integrated set of actions: short-term actionsto address the problem immediately and longer term actions tolearn more about the nature of the contaminant.

As part of a systematic survey of the composition of the ore,it was found that the contaminant was not uniformly mixed (saltand pepper) with the wollastonite ore, but rather found in rela-tively large (2–10 cm or more) inclusions. These inclusions were

1206 L. D. MAXIM ET AL.

FIG. 3. Portion of Willsboro wollastonite deposit showing acontaminated area (lighter colored material) amid the wollas-tonite ore.

colored differently and thus easily able to be visually (as well aschemically) distinguished from the ore. Figure 3 shows a photo-graph of the orebody and one of the larger contaminated areas.

A fortuitous result of the way that the contaminant was dis-tributed among the wollastonite ore was that this material couldbe avoided during the mining process. The intent of this pol-icy was to ensure that both ore and finished wollastonite prod-uct(s) had low (<0.1%) or nondetectable contamination fromthe “tremolite asbestos.”

Monitoring Results (Bulk and Personal Monitoring)The effectiveness of the initial PSP actions was evaluated by

measureing the “tremolite asbestos” content of the ore beingused, the finished wollastonite products, and by exposure mon-itoring (personal monitoring samples) of workers in the mine,mill, and beneficiation facilities.

During the course of its research project the RJ Lee Group hadsome doubts about the “tremolite” identification based upon thescientific results from both bulk and personal monitoring sam-ples analyzed via TEM and other techniques (more below), butNYCO made a policy decision to regard the material as tremo-lite asbestos pending further analysis and sought to minimizethe amount of this material in the ore and finished product byavoiding certain areas in the deposit. The effectiveness of thispolicy was checked by periodic TEM analysis of both ore andfinished product.

2002 2003 2004 2005

Year

1E-5

0.0001

0.001

0.01

0.1

1

Wt

% "

trem

olit

e as

bes

tos"

DiscoveryPSP controlmonitoring

Limit ofdetection

Regulatorythreshold

Smoothedvalues

FIG. 4. Analysis of weekly (later biweekly) Willsboro ore com-posites (2002–2005).

Figure 4 shows results of weekly (later biweekly) analyses ofthe composite ore samples analyzed using American Society forTesting and Materials (ASTM) method D5756-02. The points inthis plot show results of individual analyses (weight percentageof “tremolite asbestos”) plotted on a logarithmic scale versustime. The limit of detection (LOD) of these analyses (shownas the dotted line near the bottom of Figure 4) varied with thesample, but was in all cases ≤2 × 10−5 (wt%). Each sample ≤LOD is conservatively plotted as the maximum LOD in Figure4. A threshold of 0.1% (the dashed line in Figure 4) was initiallyselected as the target upper limit value, which was later loweredto the LOD. Shown also in this figure is a smoothed value (thesolid line) using single exponential smoothing. (The value ofthe smoothed statistic at time t , St (x), is given by St (x) = αxt+(1 – α)St−1(x), where xt is the measured concentration at timet and St−1(x) is the value of the smoothed statistic at time t –1; the smoothing parameter α was somewhat arbitrarily set to0.2∗ in Figure 4. For details on exponential smoothing see, e.g.,Brown [1963], Chatfield [2004], or Makridakis et al. [1998].)Figure 4 also shows TEM analyses of ore sample compositesretrospectively analyzed during the early months of 2002 priorto initiation of the expanded sampling program. As can be seen,although there is substantial sample-to-sample variability in theore composite analysis data, the avoidance strategy proved suc-cessful and the apparent concentration of tremolite asbestos

∗The mean squared error (MSE) of the difference between xt and St values isa function of the smoothing parameter α. In this example, the MSE is minimizedfor a value of α of .34. However, the MSE function is very flat in the vicinityof the optimum, so that the value of the MSE function at an α of .2 is littledifferent from that at .34. In any event, choice of a higher smoothing constantwill have the effect of lowering the forecast tremolite concentration in the latertime periods as the majority of these observations are at the LOD. The intent ofplotting the smoothed values is to illustrate the point that in the later months,concentrations approach the LOD.

PRODUCT STEWARDSHIP IN WOLLASTONITE PRODUCTION 1207

TABLE 3TEM air sampling results (f/cm3 “tremolite asbestos”) from

personal monitoring samples taken from workers in theWillsboro mine, mill, and processing facilities as analyzed by

the RJ Lee Group

f/cm3 2002 2003 2004 2005 2006

>1 0 0 0 0 00.5–1.0 1 0 0 0 00.4–0.5 0 0 0 0 00.3–0.4 0 0 0 0 00.2–0.3 0 1 0 0 00.1–0.2 1 1 0 0 0LOD–0.1 4 4 0 0 0≤LOD 28 167 104 88 29Total number 34 173 104 88 29% ≤ LOD 82.4 96.5 100.0 100.0 100.0

Note. Table entries are the number of samples with measured time-weighted average (TWA) “tremolite asbestos” concentrations in therange indicated. The LOD varies from sample to sample and variesfrom 0.003 to 0.011 f/cm3.

decreased during 2003 and 2004. More recent ore and prod-uct analyses have all been less than or equal to the LOD, so thisstrategy continues to work.

Another component of the monitoring program included per-sonal monitoring samples to determine time-weighted average(TWA) workplace concentrations for workers at the Willsboromine, mill, and processing facilities. Initially (following the dis-covery of “tremolite asbestos”), these samples were collected byMSHA personnel. NYCO began analyzing these data using a va-riety of microscopy methods to avoid possible misidentificationof fibers and increase the accuracy of the TWA measurements.Table 3 shows air sampling results; table entries are the num-ber of samples with measured TWA “tremolite asbestos” fiberconcentrations in the indicated class intervals. NIOSH method7402 was used for the airborne samples. As can be seen, all sam-ples were non-detects from 2004 to 2006. Personal monitoringcontinued beyond 2005, but by this time the RJ Lee Group con-cluded that the “tremolite asbestos” was, in fact, misidentified(see later discussion).

Personal monitoring of NYCO workers is also conducted forother purposes, such as measuring wollastonite fiber concen-trations and compliance with crystalline silica, talc, and PNOROELs. These data are also analyzed to identify jobs or tasks withrelatively high exposure and to track exposure trends. Over theyears engineering controls were added to various process steps.

Characterization of NYCO Contaminant(s)The RJ Lee Group conducted analyses on bulk and air sam-

ples for two purposes. The short-term objective was to track“tremolite asbestos” concentrations to monitor the effectivenessof the PSP in reducing these concentrations. The longer term

objective was to correctly identify and characterize the con-taminant originally identified as “tremolite asbestos.” Variousmethods were used for this characterization, including PCOM,scanning electron microscopy (SEM) (to characterize the mor-phology of the material), and TEM with energy-dispersive x-rayspectroscopy (EDS) (to investigate the chemical composition ofthe material) and selected area electron diffraction (SAED)∗ (tocharacterize the crystal structure of the material). Additionally,in vitro dissolution studies were undertaken to measure the dura-bility of this material in simulated lung fluid.

As noted above, both actinolite and tremolite (not necessar-ily asbestiform) have been associated with some wollastonitedeposits,† so it was possible that one or both of these materialsmight be found in the Willsboro ore body. However, so too havemany other minerals (see e.g., Table 1). Additionally, studiesof the Willsboro deposit (DeRudder & Beck, 1962) examinedhydrothermal alteration products of wollastonite. In particular,they characterized “alteration halos” (one of the physical andchemical changes effected by hydrothermal solutions passingthrough the Willsboro wollastonite deposit) within or borderingfaults and shear zones. One of these alteration halos was report-edly composed predominantly of talc and also included calcite,garnet, salite, and quartz. A second of these halos was reportedlycomposed predominantly of montmorillonite and also includedcalcite, quartz, and talc with relicts§ of garnet and salite. Accord-ing to DeRudder and Beck (1962), talc, the dominant materialin the most intensely altered zone bordering the solution chan-nel way, was formed by the continuing action of magnesium-bearing solutions on stevensite. Several other investigators haveexamined the relations among wollastonite, stevensite, montmo-rillonite, and talc (see, e.g., Whitney & Eberl, 1982; Christidis& Mitsis, 2006; Imai et al., 1973; Sakamoto et al., 1975; Tazakiet al., 1986; Leveille, 2000). Talc can also be formed from alter-ation of tremolite materials (Ross et al., 1968).

Figure 5 shows the results of TEM EDS analyses of tremo-lite (top spectrum), the NYCO contaminant (middle spectrum),and fibrous talc (lower spectrum). Spectroscopy data are pre-sented on a plot of counts versus energy (keV). The peakscorrespond to characteristic elemental emissions. This compar-ison suggests that the NYCO material has a chemical signa-ture more closely resembling fibrous talc (Mg3Si4O10(OH)2)than tremolite ([Ca2Mg5Si8O22(OH)2]n). (The two peaks to thefar right are from the copper grid, an artifact of the analyticalmethod.) The peaks at approximately 6.4 and 7 keV are iron (Fe).The apparent chemical composition of the NYCO contaminant

∗A useful explanation of electron diffraction can be found at http://nvl.nist.gov/pub/nistpubs/jres/106/6/j66ben.pdf.

†See, e.g., http://minfile.gov.bc.ca/Summary.aspx?minfilno=092GNW052,http://www.em.gov.bc.ca/DL/ArisReports/07257.PDF, http://www.amonline.net.au/geoscience/earth/metamorphism.htm, http://franklin-sterlinghill.com/dunn/ch17/wollastonite.stm, and http://www.und.edu/instruct/mineral/geol318/webpage/kanupuru/.

§ Defined as “Of or relating to something that has survived, as structures orminerals after destructive processes.”

1208 L. D. MAXIM ET AL.

FIG. 5. Transmission electron microscopy (TEM) combined with energy-dispersive x-ray spectroscopy (EDS) analysis of tremolite(top image), NYCO material (middle image), and fibrous talc (lower image). The two peaks to the far right are from the coppergrid. The peaks at approximately 6.4 and 7.0 keV are Fe. Source: RJ Lee Group, Inc.

PRODUCT STEWARDSHIP IN WOLLASTONITE PRODUCTION 1209

FIG. 5A. Another sample of the NYCO contaminant, with agreater percentage of calcium.

varied from sample to sample—some samples more closely re-sembled tremolite, most were intermediate in composition, andothers more closely resembled talc. Figure 5A shows anothersample of the contaminant, with a higher calcium concentra-tion.

Figure 6 shows SAED patterns of tremolite (top image),NYCO contaminant (middle image), and fibrous talc (lower im-age). The row spacing in these images is approximately 5 A.This series of images illustrates that the crystal structure of theNYCO contaminant (a hexagon) is more consistent with that offibrous talc than tremolite asbestos (a rectangle).

RJ Lee Group used TEM and field emission scanning elec-tron microscopy (FESEM)∗ to investigate the morphology (formand structure) of the contaminant. Figure 7 shows TEM and FE-SEM images of tremolite (top image), the NYCO contaminant(middle image), and fibrous talc (the bottom image). (Note thatthere are differences in the scale of these images.) In this seriesof images the morphology of the NYCO contaminant appearsto resemble the fibrous talc rather than asbestiform tremolite.The structures more closely resemble cleavage fragments thanasbestiform fibers. The asbestiform tremolite sample has “poly-filamentous” characteristics. The fibers show generally parallelsides, rather than the tapered or irregularly shaped sides evidentin the middle and lower images in Figure 6.

One of the most conclusive diagnostic indication of alter-ation transitional phases verses amphibole (or pyroxene) is thatthe structure simultaneously exhibits mineralogical characteris-

∗A field-emission cathode in the electron gun of a scanning electron micro-scope provides narrower probing beams at low as well as high electron energy,which enable both improved spatial resolution and minimized sample chargingand damage. FESEM produces clearer, less electrostatically distorted imageswith spatial resolution down to 1.5 nm, some 3 to 6 times better than conven-tional SEM.

FIG. 6. Selected area electron diffraction (SAED) patterns oftremolite asbestos (top image), contaminate phase in the NYCOore (middle image), and fibrous talc (lower image). The rowspacing in these images is approximately 5.3 A (1 A = 1 × 10−10

m). This series of images illustrate that the crystal structure ofthe NYCO contaminant is consistent with that of fibrous talc.

tics of both the amphibole (or pyroxene) and the talc mineralphases. The degree of weathering dictates if the characteristicsof one or the other end member is more apparent. As amphibolesand pyroxenes alter, there is a substitutionof the magnesium ion

1210 L. D. MAXIM ET AL.

FIG. 7. TEM (left-hand column) and FESEM (right-hand column) images of tremolite (a and b), the NYCO contaminant (c andd), and fibrous talc (e and f). (Note that there are differences in the scales of these images.)

for the calcium ion. This ion replacement is accompanied bya re-alignment of the silica tetrahedrons in the unit cell. Thechange in chemistry relative to standard reference material is themost obvious result. However this difference may go unnoticedwithout calibration and quantification of the EDS system. Thecrystallographic changes in the unit cell can only effectively bedetermined through multiple-zone SAED. In addition to the talcreflection, these particles may exhibit a remnant amphibole (orpyroxene) reflection. A reflection superimposing both the talczone and the amphibole (or pyroxene) is also possible. Becausethe alteration of one phase to another requires a re-alignmentof some part of the unit cell, the resulting external effect onthe crystal can be extensive. The crystal will appear to exfoliatealong the transformation plane. This phenomenon produces apseudo-parting.

Cleavage fragment is a term applied to the pieces of singlecrystals that are produced with crushing. Crushed crystals breakpredominately along crystal planes called cleavage planes. Often

somewhat elongate particles are produced with relatively smoothsides and possibly irregular ends. When asbestiform structuresare crushed, the bundles begin to separate into smaller bundlesor even single fibrils. Though breakage of the individual fibersdoes occur, the high tensile strength associated with this crystalhabit produces very high aspect ratio (length/width) particlessignificantly greater then 40:1. The fiber sides are smooth andparallel and show no crystal faces. Ground sheet silicates tendto exfoliate individual flakes. With sufficient grinding, tearingof the flakes will occur, producing irregular and ragged edges.Ground alteration phases, because they retain some remnant ofthe original minerals crystal structure as well as the develop-ing sheet silicate lattice, produce elongate ribbon-like structureswith ragged sides.

The contaminant in the NYCO Willsboro wollastonite de-posit exhibits all of these characteristics. The magnesium (Mg)is substituting for calcium (Ca), producing a lower than expectedCa and higher than expected Mg. Though many of the structures

PRODUCT STEWARDSHIP IN WOLLASTONITE PRODUCTION 1211

have only a talc SAED reflection, a portion of the populationshow a remnant reflection of the original mineral phases. Mor-phologically all of the particles exhibit the characteristic exfo-liating that produces thin ribbon-like structures. Samples of thealteration phase were very friable and easily ground into a finepowder.

The preceding figures suggest that most samples of theNYCO contaminant have a chemical composition intermedi-ate between tremolite asbestos and talc and that both the crystalstructure and morphology differ and are more consistent withfibrous talc. The RJ Lee Group judged, on the basis of this andother evidence, that the “tremolite asbestos” was, in fact, a nonas-bestiform intermediate alteration phase between pyroxene andamphibole to talc or perhaps stevensite to talc (or transitionalmaterial [TM] for short). In any event, they concluded that thiscontaminant was not asbestiform tremolite. If correct, this con-clusion has clear regulatory implications.

The NYCO Health Committee and the RJ Lee Group rec-ommended that additional tests be conducted on the TM. Dura-bility/biopersistence measurements were recommended becausethese might clarify the interpretation of the electron microscopyresults and, moreover, would provide a more direct indicationof the possible toxicity of the TM.

DURABILITY MEASUREMENTSTo complement the RJ Lee Group’s investigations, NYCO

Minerals decided to measure the durability/biopersistence ofthe contaminant. Biopersistence of long (≥20 µm) fibers isknown to be a determinant of the toxicology of synthetic vit-reous fibers (SVFs) (see, e.g., Maxim et al., 2006), and the rel-atively low biopersistence of wollastonite (see, e.g., Maxim &McConnell, 2005, and contained references) is believed to be akey reason for its relatively low toxicity. The biopersistence ofchrysotile asbestos is subject to some debate (recent measure-ments,e.g., Bernstein et al., 2003, suggest that the biopersistenceof pure chrysotile is less than previously measured), but it isgenerally acknowledged that the biopersistence of amphiboleasbestos forms (including amosite, crocidolite, and tremolite)is very high. Bernstein et al. (2003, p. 1403) concluded from ashort-term (5-day exposure) rat inhalation study that the clear-ance half-time of long Calidria chrysotile fibers (≥ 20 µm) wasless than 1 day, whereas for tremolite “the longer tremolite fibers(L > 20 µm) that deposit in the lung show an initial shorter termclearance probably associated with the clearance of fibers whichdeposited in the tracheal-bronchial tree followed by no furtherclearance.” The weighted half-time of long tremolite asbestoswas essentially infinite. Hesterberg et al. (1998) reported thatthe weighted half-times of long (≥20 µm) amosite and crocido-lite asbestos (both amphibole forms) fibers in the rat lung were418 and 817 days, respectively. Finkelstein and Dufresne (1999)used regression analysis to estimate half-times for various formsof asbestos from the analysis of lung burdens of chrysotile min-ers and millers. They estimated a tremolite clearance half-timeof 15.8 yr (95% confidence interval [6.4, ∞]) for fibers between

5 and 10 µm long and 150 yr (95% CI [11, ∞]) for those longerthan 10 µm.

The recent IARC review of talc carcinogenicity concludedthat the deposition, retention, and clearance of talc were insuf-ficiently studied. Talc is often placed in the category of poorlysoluble particles, suggesting a relatively long clearance time.Jurinski and Rimstidt (2001) studied dissolution rates of talc insimulated lung fluid and concluded that the lifetime for completedissolution of a 1-µm talc particle was approximately 8 yr.

The preceding data suggest that there are substantial differ-ences between the durability or biopersistence of wollastonite(half-times of 2 or 3 wk) and either talc or amphibole asbestos(half-times measured in years). In view of the probable impor-tance of fiber or particle durability/biopersistence to toxicityassessment, NYCO decided to examine the TTM to learn moreabout this contaminant.

For a large number of SVFs (and amosite and crocidoliteasbestos) there is good correlation between the durability ofthe fiber measured in simulated lung fluid (either in terms ofhalf-times or Kdis, an estimated dissolution rate constant) andhalf-times measured during in vivo inhalation experiments inrodents (Maxim et al., 1999, 2006). NYCO submitted samplesof wollastonite, the TTM, and asbestiform tremolite to Unifrax(Niagara Falls, NY) for dissolution rate measurements using theapparatus and technique described by Zoitos et al. (1997).

Durability DataFor the durability measurements, several samples were tested

in duplicate. NYAD G wollastonite was used as one control. Twosamples of the TM (“transitional A” and “transitional B”) wereselected from the contaminated ore and crushed and ground priorto testing. A sample of commercial tremolite from South Koreawas also included as a second control in the experiment. (Ad-dison and McConnell [2005] summarized data on this materialand concluded that it was relatively potent.) Although the vari-ous test materials were ground using a similar procedure, therewere dimensional differences, which required that the half-timesbe corrected for differences in specific surface area. Surfacearea measurements (BET surface area, m2/g) were made by Mi-cromeritics Analytical Services. The surface areas were used toadjust the empirical half-times to calculate corrected Kdis values.

Table 4 shows the half-times from the raw data (uncorrectedfor differences in surface area) and the calculated dissolutionconstants adjusted for these differences. As can be seen, the wol-lastonite half-times were generally consistent with other mea-surements from in vivo methods. At the other end of the spec-trum, the estimated half-time for tremolite, approximately 17.5yr, is consistent with literature estimates in order-of-magnitudeterms. The calculated value of Kdis for the tremolite is approxi-mately the same as the geometric mean of several experimentalvalues for crocidolite (another amphibole) reported in Maximet al. (2006). The data on half-times or Kdis values for thetransition materials clearly show that while these materials aremore durable than wollastonite, they are also less durable than

1212 L. D. MAXIM ET AL.

TABLE 4Measured half-time (wk) and calculated Kdis for duplicatesamples of wollastonite, transition materials, and tremolite

Material

Estimated half-timecalculated fromraw data (wk)

Calculated Kdis

adjusted for differencesin surface area Kdis

(ng/cm2/h)

Wollastonite 3.29 317.5Wollastonite 3.31 315.6Transitional A 16.57 2.07Transitional A 24.14 1.42Transitional B 27.31 3.29Transitional B 33.91 2.65Tremolite 908.4 <0.001

tremolite by more than two orders of magnitude. The disso-lution kinetics data indicate that the TM is significantly dif-ferent from asbestiform tremolite. To the extent that durabil-ity/biopersistence determines toxicity for crystalline materials(as it does for SVFs), these data suggest that the TM presentsless of a health hazard than asbestiform tremolite.

The dissolution rate data can be used to infer a reasonablevalue for a recommended exposure guideline (REG) to be usedby NYCO as an internal exposure limit. The PEL (either MSHAor OSHA) for asbestos is now 0.1 f/cm3 and tremolite has arelatively low Kdis. Various glass wools have Kdis values >100and a PEL of 1.0 f/cm3. Refractory ceramic fiber (RCF) has aKdis of approximately 7.6 (Maxim et al., 2006) and an REG of0.5 f/cm3. These comparisons suggest that a reasonable REGfor the TM based on the durability results would be between 0.1and 0.5 f/cm3; the NYCO Health Committee recommended that0.2 f/cm3 be used as the REG pending the outcome of ongoingstudies.

The dissolution kinetics results were of interest for two rea-sons: (1) They showed clearly that the TM differed from asbesti-form tremolite in this important respect—just as it does in crystalstructure and morphology, and (2) they provided a reasonablebasis for setting an REG.

The PSP is an ongoing effort. Exposure monitoring contin-ues, as does bulk sampling of the ore body and finished product.Since very shortly after the discovery of the TM in the wollas-tonite product, workplace TWAs of TM dropped to the REG orlower. And gravimetric TWAs for PNOR and RCS were consis-tently at or beneath applicable OELs. The longer term researchprogram on characterization of the TM is ongoing. As a pre-caution, prequalification and selective mining of the ore bodyalso continues. Taken together, these and other steps in the PSPhelp to ensure that risks associated with production and use ofwollastonite are controlled.

CONCLUDING COMMENTSThe activities and events summarized in this article deal

principally with stewardship activities for one wollastonite orebody (although the same approach is used for NYCO’s Pilaresmining–processing complex). These show the importance ofproduct stewardship in identifying and managing the risks asso-ciated with the mining, milling, beneficiation, production, anduse of wollastonite. Although wollastonite is properly regardedas a relatively benign material, the presence of other materialsin the host rock and ore body justifies a proactive approach tomanage possible occupational risks associated with these con-taminants. The various elements of the PSP, including occupa-tional exposure monitoring, bulk sampling of crushed ore andfinished product, medical surveillance, toxicology research, andcommunications, have proven successful. A particular lessonto be learned with mineral products is that it is important toinclude possible contaminants in the PSP, which entails theiridentification, assessment of their potential health hazards, reg-ulatory status, and applicable OELs. The results presented hereshould be viewed as a “snapshot in time” of a program designedto ensure continuous improvement—a basic tenet of any PSP.

These results may be of more general interest to those whomine, process, or use other industrial minerals. Naturally oc-curring industrial minerals are widely used (by one estimate,Galloway et al., 2001, the average American uses about 1 mil-lion lb of industrial minerals during a lifetime) and economi-cally important∗ but, as found in nature, may contain potentiallytoxic contaminants—the risks of which need to be identified andmanaged. Enlightened product stewardship, along with other ap-proaches to achieve sustainable development of industrial miner-als, is necessary to capture the economic value of these mineralswithout paying an unacceptable social cost.

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Andrews, R. W. 1970. Wollastonite. London: Institute of GeologicalSciences, Her Majesty’s Stationary Office.

Bellmann, B., and Muhle, H. 1994. Investigation of the biodurabilityof wollastonite and xonolite. Environ. Health Perspect. 102(Suppl.5):191–195.

Bernstein, D. M., Chevalier, J., and Smith, P. 2003. Compari-son of Calidria chrysotile asbestos to pure tremolite: Inhalation

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Brown, R. G. 1963. Smoothing, forecasting and prediction of discretetime series. Englewood Cliffs, NJ: Prentice Hall.

Burnham, K. D. 1995. Wollastonite mining in Essex County. Originalpapers compiled by L. W. Choate. Willsboro, NY: NYCO Minerals.

Chatfield, C. 2004. The analysis of time series. Boca Raton, FL:Chapman and Hall, CRC Press.

Christidis, G. E., and Mitsis, I. 2006. A new Ni-rich stevensite fromthe ophiolite complex of Othrys, Central Greece. Clays Clay Min.54(6):653–666.

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Greskevitch, M. F., Turk, A. R., Dieffenbach, A. L., Roman, J. M.,Groce, D. W., and Hearl, F. J. 1992. Quartz analyses of the bulk dustsamples collected by the National Occupational Health Survey ofMining. Appl. Occup. Environ. Hyg. 7(8):527–531.

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