Document gD8mg4JRX6Ee00YvBjvkrQ6jq
FILE NAME: RT Vanderbilt (RTV)
DATE: 1989
DOC#: RTV082
DOCUMENT DESCRIPTION: Journal Article - The Regulatory and Mineralogical Definitions of Asbestos and Their Impact on Amphibole Dust Analysis
Am. Ind. H>$. Assoc. J. 5t> CayMgsfSijOjiKOH.F,) Ca,|Mg.Fe)5|Si0.)(OH.F);,
ribackile (177B7-87-0)
eurflmingionile-gruneriie (1 6 7 - 6 1 -4)
amhophyittte (17060-76-3)
trem olile (14567-73-8) `
actinotite (13768-OO-B)
"'The pres once ol an asterisk following a CAS Registry Number indicates that me registra tion is (or ft substance which CAS floes nol treat in ils regular CA Index processing as a unique chemical entity. Typically, this occurs when the material is one ol variable compo sition: a biological orgams m. a botanical entity, an oil orexlract ol plant or animal origin, or a malnal that Includes some description ol physical specificity, such os morphology.
in the interest of clarity to specific definitions only. To reflect '' the miner logical characteristics of asbestos in a definition, a group of mineral scientists agreed to the following.101
A. Asbcstos-~A collective mineralogica) term that de scribes certain silicates belonging to the serpentine and amphibole mineral groups, which'have Crystal lized in theasbestiform habif causing them lobe easily separated into long, litio, flexible, strong fibers when crushed or processed. Included in the definition arc chrysolite: crocidoliie.asbesliformgfuneritc(amosite); anthophyiliteasbestos; tremolile asbestos: and actinolite asbestos.
B. Asbestos Fibers--Asbcstiform mineral fiber popula tions generally have the following characteristics when viewed by light microscopy.
1. Many particles wiihaspeci ratios ranging from 20:1
to 100:1 or higher (> 5 pm length)
2. Very thin fibrils genetally less than 0.5 pm in width,
and
3. In addition to the mandatory fibrillar crystal growth, two or more ol the following attributes:
(a) Parallel fibers occurring in bundles:
tb) Fibers displaying splayed ends:
.
(c) Matted masses ot individual fibers: and
(d) Fibers showing curvature*11
Mnnv if those who contributed to this definition and support n t listed criteria have published extensively on ibr problems associated with the MOSH definitions and the
membrane filter m e t h o d T h i s definition has been incorporated in a proposed American Society for Testing and Materials (ASTM) medtod submitted to committee D-22.05 (January 14. 1988). The criteria have long been endorsed by the U.S. Department of the lmerior.rtUJ',
While a I) mineral scientists may not agree with every entry in this definition, ii does present a more mineralogically accurate description of asbestos and asbestos fibers than docs the regulBiorydefinition. This is especially truewhenit is applied to a dust population rather than on a particle by particle basis. The definition, therefore, will be used in the remainder of this paper as the" mineralogical"definition or asbestos. It might be noted that the width criterion (0.5 pm) represents a dimension below which all individual "fibrils'* and clumps or masses o fibrils would be encountered in processed asbestos. Unprocessed clumps or masses may exceed this width, bur such particles would not be represen tative of common airborne asbestos libers.
The Study Environment One of the most controversial workpla'ce exposures asso ciated with this definitional issue involves the mining and mi.Jing of New York State tremoliric talc. Accordingly, a study was undertaken io contrast dust data obtained it) this environment /i'h both the regulatory and mineralogical
dis it sed above. N w Vqi Ic b>aic ircmolnic talc is an industrial grade talc u,,ed exti-sively i,i the ceramics, nie.and paint industries, since 1924 the R.T. Vanderbilt Company. Inc., las owned 1 operated the only \c w Vork State iremolitic talc mine.
*
>jvfjn&t) )989
We S000375
Talc mined from this operation vanes somewhat in mineral content but an assay of the ore generally reflects40%-60% tremolitc. l% -\0% anthophyllite. 20%-40% ialc,20%-30% serpentine (amigoriie-lizardilc). and 0%-2% quartz.08'
The R .T. VahderbiJt Company states that allofthc tremoliteand anihophyllile in its talc products appear only in lire nonasbestiform habit.lISi' In 1980. however, NIOSH pub lished a technical report entitled Occupational Exposure to Talc Containing Asbestor111' specifically addressing this mineral dust exposure. In the report. NIOSH applied its regulatory asbestos definition to bulb and airborne dust samples collected at this mine and reported over 70% asbes tos for airborne fibers satisfying the 3:1 or greater aspect ratio and greater than 5-pro length limit (NIOSH PCM m ethod). Particles were identified as tremolile and anthophyllite by standard X-ray diffraction technique.
M ethod of Study Sam ples for particulate analysis were collected on open faced. 37-mm diameter Milliporc type AA filters (0.8-pm pore size. Milliporc Corp.. Bedford, Mass.). Precalibrated M ine S afety Appliances'Modcl G pumps were used tod raw a ir through these filters at a rate of 1.7 L/min. Although fiber sampling technique has changed since, (his technique was used in order to compare results with data previously collected. Filters were changed throughout a full work shift
ASBESTIFORM
In th e a s b e s lif o rm habit, m ineral c ry stals g ro w in a
s in g le d im e n sio n , in a straight line until they form long, th r e a d -lik e fib ers with asp e c t ratios ol 20:1 lo 1000:1 a n d h ig h e r . W h en p re s su re Is ap p lied , th e fib ers d o n o t s h a tte r b u t sim ply bend m uch like a wire. Fibrils of a sm a lle r d iam eter are produced as bundles of fibers are p u lle d a p a rt. T his bundling effect is referred to as polyfilam entous.
NONASBESTIFORM
In th e n o n a s b e s tifo rm variety, cry stal g ro w th is ra n d o m , form ing m ullldim enslonal prism atic patterns. W h e n p re s s u re is applied, the crystal traclu res easily, frag m en tin g into prism atic parm es. Som e of the par ticles or cleavage fragm ents are acicuiar or needle s h a p e d a s a result ol the tendency ol am phibole m inerals to cleave alo n g two dln,e" sions but not along the third. S ta ir-s te p clea v ag e along the e d g e s of som e particles is c o m m o n , and Oblique extinction is exhibited under the m ic ro sc o p e . C leavage fragm ents never show curvolure.
Figure 1--Asbesliform and n o n asb esh lo rm graphics
m tnij #t*f *5'C J (50)
HBvnnbct
as needed to pievem overloading. In all, 22 air samples were Obiained representing nine work activities in the R.T. Vanderbilt Co., GoUverncur, New York, mine and mill. Work activilies sampled included milling (H ardinge and WhceJeV mills), drying, packing, bag stacking, crushing, mine drilling, scraping, and tramming.
Analyses were performed by The R.J. Lee Group, Inc., of Monroeville. Pennsylvania (Project No. 86-12318). Analytical techniques employed included phase contrast microscopy (PCM).polarized light microscopy(PLM),scanningtleciron microscopy (SF.M), computer-controlled scanning electron microscopy(CCSEM),and transmission electron microscopy (TEM). In accordance with NIOSH method 7400, all sam ples received PCM particle counts at400X magnification in Walton-Bcckett graticule measuring at least S-pm long with a 3; I or grcatcraspcct ratio. Beyond these specified parame ters, exact particle widths and lengths were not measured. For each sample, 100 fields or 100 particles, whichever came first, were counted (with a minimum of20 fields). In all, 2295 particles were counted and sized by PCM.
A separate wedge was cut from each filter fo r PLM analy sis. Particles were lapped, then gently scraped from the wedge to a glass slide. Any remaining particles were cap tured by rolling a needle moistened with 1,592 refractive index (R l) liquid over the surface of the filter wedge (Rl selected for low-iron talc). Additional 1.592 Rl liquid was added to thesJideand used to wash particles from the needle onto the slide. It should be noted that this transfer technique could bias the PCM analysis if very fine particles were lost In the transfer. Additional analysis of particles not removed from the filter (another filter section) suggests such bias is unlikely for tremolile (see SEM partible width discussion below). PLM counts were made in a 1,592 RJ oil to differen tiate talc from allamphiboles on all 22 air samples. Follow ing this basic cut, tremolitc was differentiated from anthophyllite by angle of extinction (tremolitc has an inclined extinction of 14 to 17, whilcanthophyllitc exhibits parallel extinction). Since all asbestos exhibits parallel extinction, mineral habit (asbesliform or nonasbestiform) then was decided on the basts of criteria noted in the mineralogical definition. Depending on particle concentration for each of thc22 samples, 100 to 200 points were counted and charac terized at 100X magnification, yielding a minimum of 2200 panicles subjected to PLM analysis. If positive particle iden tification could not be made at IOOX total magnification, higher magnifications (up lo400X) were applied on a parti cle by particle basis. As in the PCM analysts, only particles with an aspect ratio of 3:1or greater and a length of 5 pm or more were so characterized. Although exact length and width measurements were not obtained, particles were sized by basic aspect ratio catcgories(/.e., thosc3:l orgrealer. 10:1 or greater, ere-). One additional step was taken in the PLM analysis in which panicles presumed to be anthophyllitc(> I.S92 RI) w -re tested for "transitional" phases (meaning talc
eriwincd w .th or evolving from anihophyllitc an d /o r bio p; libles). Vhi-; was accom plished by finding pan icles which most d c .-'lv ap p ro : 'm ated ihexam esi; ' tnd rm rphological characteristics of these suspect purndrS on unrulier pornon
WES000376
EXAMPLES Amphiboles with Separate Names:
RAW ORE
Amphiboles with the Same Name:
EXAMPLES Amphiboles with Separate Names;
MICROSCOPIC
265X Magnification, 2.75jum/Divi$ion
Amphiboles with the Same Name:
Irem olfe
ASBESTIFORM
trem olile
NONASBESTIFORM
nt
irrt f<\) h,, I 150t
M: bSil
WES000377
of the filler and testing them at 1.608 Rl (the low gamma index lor anthophylliie). Because of problems inherent in this technique, testing the same pani'clc with different Rl liquids was not possible. Particles with an index of refraction between 1.592 and 1.608 were classed a s `'transitional.'*In all, 6 samples underwent this additional analysis.
To lest further the differences and similarities between asbestifortn dust populations and the tremolitic tale dust environment, electron microscopy was employed on 5 sam ples most representative of common mine and mill exposures(e.,, product packaging).SUM with energy dispersive X-ray (EDX) first required the mounting of another 1/8 niter wedge from each sample on a carbon-coated stub. Fifty fields at 2000X magnification then were analyzed for count, size, and identity of all particles in every field with an aspect ratio greater than 3:1and a length greater than 5 ^m- For the five fillers, a total of 183 panicles were characterized in this way. Particles below and above a width of 0.25 pm Were noted as well. This width was selected primarilybecause it is used in references against which the findings of this study shall be com pared.1 These references generally refer to this width as the approximate lower resolution limit of the light microscope.'/'',, While other references report lower
width scnslvly,lM,6, it generally is agreed this lower lirrtil varies with the quality of the microscope, use of dispersion staining and background contrast, magnification, and the microscopisL involved. CCSEM with EDX was used on the sam e carbon-coated filter wedges to scan a total of 2500 particles (500 per sample) at magnifications of 35X, I00X, a n d 50OX. Particles were sized by the preselected parame
ters, and the chemical composition of all particles was noted. Particle distribution was expressed in volume percent and all trcmolite particles w'ir' counted. TEM with selected area electron diffraction (SAFO) also was employed on new carbon-coated filter wedges front the same five filters. Chem ical composition by EDX analysis and SAED patterns of individual fibers which measured 10 pm or greater on four grid squares per wedge were obtained a/lcr the filter matrix wasdissolved from the carbon film. While considerable data were lhus generated from this multiple analytical approach, only data summaries which directly address the definitional comparison are included in this paper.
It should be noted lltai the EDX chemistries obtained through the CCSEM analysis and the SAED patterns obtained through TEM analysis were not adequate to distin guish talcand anlhophyllite. While an in-depth discussion of this problem is beyond the scope of this paper, in summary it should be said that talc may present the same X-ray spec trum as anthophylliie because talc displays a similar2:1 Si/ Mg ratio and overlapping range. KcgardingSAED patterns, talc in the fibrous form often reflects he ame 5.3 A spacing as anlhophyllite. Talc/anthophylliie in an intermediate or transitional phase poses further identification problems when electron diffraction analysis is restricted to one point per panicle. This is more fully described in other papers.<2,'2i)
Study Results and Definitional Comparison Table II contrasts bulk trcmolite asbestos particles described in the literature118*to iremolile panicles reflected on five New
Samples
TABLE 11 Balio C om parison of Bulk Trem olile A sbestos* to N.Y. S tale Tremolile
In Five Air S am p les'1by Optical and E lectron M icroscopy
Ratio ol Tremolile Pal tides
3:1 aspect ratio (a.r.) or Greater to Total Tremolite O 5 yrn length)
SEMC
10:1 a.r. or Greater to Total Tremolite > S pm L)
SEM
20:1 a.r. or Greater to-Toial Tremolile |> 5 f is L )
SEM
Tremolilc asbestos"
i in t.6
1 in 2.6
. 1 In 4.6
TromolHe asbestos" tf total tremolite panic'es per sample (all sizes): 200
1 Ip 1,8 (approx. 55%)
1 in 2.3 (approx. 41%)
1 In 2.S (approx. 31%)
10:1 a.r. or Greater 103:1 a.r. or Greater
Oplu SEM
1 in l.fr 1 in 1.6
1 >n 1.6
i in 1,2
1 in 1.3 (66%)
Tremolite in 5 N.Y. air samples"
a total iremolile particles {all sizes): 949
I in 6.2
(16%) CCSEM
1 1n 949 or greater
(0.1%) CCSEM
0 in 949
(0%) CCSEM
Opt.
1 in 101
or greater
CCSEM li n 152 or greater
1 in 146 f gfcoier !0 6% )
'D ata (rom U.S. D cpl. ol Interior. B ureau ol M ines R epori ol Investigation 5367, p a g e 13. T able 2 (1979)." -'' " P re s e n t study: CCSEM an aly sis o( 5 aif sa m p les ai 35X. MPT. a n d 6Q0X m i g n lllcalio n s. {2500 iota) parlicle count (all sizes)). O ptical IPC-M a n d PLM) and),-vi ol the sa m e 5 sam ples up to 400X ma9n>l>cationS 5 3 1 total p a rtic le s with a 3:1 a r or greater > 5 pm length). ' P an icles counted using SFM with m agntlicaiion up to en '- V ' " P a n ic le s c o u n te d using n p ucaH igni m icroscopy at 250X m m nlllcation (2C0 irem olile particles counted per n ite/ ' O O lained lio m C ahlorm a n o .'Ih er d e se n p b o n ol lit. r* tu .e(. W iic, ." 'led. "O b ta in e d lio m m useum sam ple (torn flaiasihan, Ind a 'Viley milled
Am tod v; - lit 1 ODI
w>vci|>r> i??,5
II) WES000378
TABLE III Average ol 22 Mine and Mill Air S am ples (2295 Particles) by C om position, Aspect Ratio 3:1 or G reater
(> 5 fim length), a n d Mineral Habit by Light Microscopy**l
Aspect Ratio:
3:1-10:1
Aof Total >10:1-20:1
> 20;i
Particles per CC (TWA) 3:1-10:1 > 10:1-20:1 >20:1
Total Particles pet CC
(9-hr TWA)
% Asbestiform by
Mincralogical Del.
Trcmoiite
35.a
33
0
.45
.009
0
0.459
0
Transitional11
0.0
.76
0
0.00
.015
0
0.0)5
0
Tate
SB.Z
4 60
0
.67
053
0
0 728
0
All particles
93.0
7.00
0
1.1?
0.002
0
1.210
0
*Mincral type and % by aspect ratio.were obtained by PLM analysis at 100X to 400X magnification. Total particles per cc were obtained by PCM at 400X magnification,
l'%Ta Ic/anlhophyllile transl llonal particles were extrapolated from SdI 22 air samples based on a relractive index beiween 1.592 and 1.609 lor me gamma index. No pure amhophyllite particles were noled in me lieid analysed.
York state tremolilic talc air samples by both optica! and
electron microscopy. In this comparison, the ratio of tremo-
lite particles which satisfy ihe regulatory definition of a fiber
(3:1 o r greater aspect ratio, > 5 pm length) and those that
exceed a 10:1 and 20;I aspecl ratio (> 5 /m length) are
addressed.
'
O f the 2500 total particles scanned by CCSEM on 5 air
samples, 38% or949 were iremolite. Of these iremolite parti
cles. 16% or 152 satisfied the regulatory size criteria.for a
fiber. This represents a ratio of 1 lrcroolitc regulatory fiber in
every 6.2 trcmolite panicles. In contrast, tremotiicasbestos
reflected an average of I regulatory size fibey in every 1.7^
panicles (55%). Most striking, however, is (he difference
reflected at 10:1 and 20:1 aspect ratios. For the New York
state trcmolite, only I iremolite particle in 949 (total
counted) exceeded a 10:1 aspect ratio (0.1%). Fortremoiite
asbestos this ratio wasapproximately I inevery2.5 particles
or 40%. At a 20:1 aspecl ratio or greater* no New York
iremolite particles were counted, while I in every 3 (approx
imately) were found for iremolite asbestos. Significant vari
ation in these ratios was not noted under Optical microscopy
Tor the same samples at the magnifications applied.
While a bulk to airborne particle comparison is not ideal,
the dimensional differences likely would be even greater if
two airborne particle distributions were compared, since
wider width, lower aspect ratio particles are more common
in bulk particle distributions. Published particle distribu
tions for airbbrne asbestos dust populations support this
contention and support the basic dimensional similarity of
iremolite asbestos lo other asbestiform minerals (sec the
extended discussion on airborne particle aspect ratio distri
butions below). Accordingly, on a iremolite to iremolite
basis, an entirely different particle-size distribution would be
expected in the New York stale tremolitic talc samples :f 'his
iremolite were asbestifotm,
Table III reflects the average of all 22 air samples by
percent mineral composition, aspect ratio H I or greater),
:id crystal growth habit (asbestiform or nonaibcsiiforui;.
Results in this table rcllcct the combined appiua.ion of th
PCM and PLM methods outlined above
In the liclds analyzed by PLM. no parities exceeded a
20:1 a>[n'ci ratio or shout'd splayed ends, curvotuu-. m
parallel fibers occurring in bundles. Using the mineralgica! definition, therefore, no asbestos was found: ho wever, 0.459 particles/ec would be noled if the regula lory definition were used (talc and transitional particles excluded). A total of 1.21 particles/cc would be reported if talc and transitional particles were counted. Proper characterization of talc, anchophylliie and transitional particles is extremely difficult in this ore body except by PLM, While PLM air sample data reflect no asbestiform libers, both talc and transiliooal par ticles can appearina fibrous, asbestiform and/or nonasbes. tiform habit in this ore body.07' If misclassified as aothophyllire, these asbestiform fibers would be characterized as asbestos under both the regulatory and mineralgica! defini tions. TEM SAED analysis with multiple electron diffrac tion patternsfeach indexed) confirmed the presence orboth nOnasbestifcrm and asbestiform transitional and fibrous talc particles in a random scan or fields not included in the PLM analysis. No effort to quantify these fibers was made. Because uf the rarity of these fibers and their marginal significance io the definitional distinctions being addressed here, further deiail in this area is beyond the scopeand intent of this paper.
Tabic IV reflects a comparison of fiber counts obtained in (his study uiih data previously obtained in the same mine and mill (same or similar work activities). These data con firm'a marked difference in what is reported as asbestos, depending upon the definition used. Note that the average of all regulatory fibers counted by PCM (Column 2) shows far less variancebctwccn invesligatorsihan ihe percent of pani cles considered asbestifotm (Column 5). Mincralogical dis tinctions made reflect consideration of the characteristics described in the mincralogical definition. Although none of the particles in the study dust population exceeded a 20:1 aspect ratio by light microscopy, this factor alone did r n' dictate habit characterization Ior the 22 samples analyzed. Although the lack ol 20:1 aspect uiio particles in a dust population certainly suggests a nonasbestifor.r. dust envi ronment, aspect ratiosaloncare not pivotal toa mineralgi ca! sound definition of asbestos
To test definitional specificity further, a comparison nf basic diniemicm.il charactewin'? common to asbestiform dust populations. nonasbesiilormtclcnvageiragmenOamphi-
stt
;r -. Ili
W e s o o o W '50
Source and Year
R. Lee(1908) MSHA (1984-85)' Insurance (19a4)c NIOSH (1975)k Dunn (1902^
TABLE IV Historical Air Sam ples'' by Delinillonal Approach
Average ot All
Pertides/CC Mill and Mine
Range
PsrUciM/CC MIH and Mine"111
Definitional Approach
%'PartcIes/
Classed as Asbestos
t.21
0.14-3.56'"
mineralogies!
0.00
2.39
O.M-iMff*" mineralogies!
0.40
1.0
1,36-2. IS"1
not glassed
-
4.5
t.5-3.4r" "
regulatory
72.00
0.65
0.03-1.38'"1
mincralogical
but classifica
tion completed
on bulk sam
ples only
Particles/ Considered
Asbestos
0.000 0.009u
3312
aAII panicles 3:1 or greater In aspect ratio. > 5 am In length and resolvable under the light microscope.
"(n) * number ot air samples.
''Mine Safety and Health Administration Survey Reports dated: 7/17/85.7/30/85,5/22/65.6/12/84,1/9/84.
UMSHAperlarms analysis lor liber type only on inters with elevated total liber goon Is. Ol the 38 tillers, 22were
so analyzed. 01 these. 2 tillers were repottedas containing 2% asbestilorm libers. All other inters were lound
or assumed to con lain 0%.
`
'Hartford Insurance Company Report dated November 1984 to R.T. Vanderbilt Company. Inc.
^NIOSH Technical Report, Occupational and Exposure to Taic Containing Asbestos. Table 7 (1980)1,11
l!Dunn Geoscience Core, report to R.T. Yenderbill Company (1905),
bole d u st populations, and the study dust population -was population particle widths obtained by SCM. With regard to
undertaken. Figure 3 compares airborne asbestiform and
the tremolile found in the talc air samples (the only amphi-
nonasbestiforrn particles which Tall above and below a width 'bolc noted), all tremolile particles (88 out of 183 total parti
of 0.25 ftm r described in the literature,tM| with study dust >" cles) were wider than 0.25 pm. Particle widths noted in
*
%
100%
%
1O0%
TOO
too
'
BO
80
60 ACLMEPAHVIABGOELE FRAGMENTS'
40
GO
N.Y. STATE TREMOLITIC
talc
40
TREMOLlTE
width
20
0%
<025
width
>0.25
20
0%
<0.25 w id th
>0.25
'From: J.G . Snyder. ft L. Virle. and J.M . Sep/PI: "Evaluallon ol the Phase Contrast Microscop" Method lor the detection
ot Fibrous and Other Elongation Mineral Parlicuh tes by Comparison with a STEM Teen/uoi'c *Am. tnd. Hyg Assoc J. 4S(5)*.71-477 p9B?) Table IV. AVer ,ge 0117! samples.
From: Auersce ol S air sam ples rmolyzed by SEM irepresems SOparticle* oul u> .0? total panicles),
F ig u re 3 - A verage airborne p an icle W idti. c u m p a fia -n hy elec Iron m icroscopy (s'<i particles I Or greater asp ect r$no. 5 p m o < m ore length)
Am Inti tifi ' i!CC J fiOl
Noribc> 19*9
sis WES000380
TABUE V A spect Ratio C om parison
Airborne Asbestos Panicles* (Mining and Sagging)
> OjtS pm Width, > 5 pm Length
Airborne Cleavage Fragments1' (Approx. 4500 Total Particles) > 0.25 pbt Width, > 5 pm Lenglh
% 0/ Particles Seen a t
V* Ol Parliclei Seen at:
Aspect Ratio: 3:1 10:1 15:1 > 2 0 :1
Aspect Ratio:
3;t 10:1 15:1 > zon
Crcidoifle
100 100 91.5 64.5
Amoslte
1O0 100 89.> 58.0
Chrysolite
too 100 86.0 37.0
Average: lOO 100 89
53
cunrvmingtonUe
10O 2a 10
6
cumminglonile
100 32
7
3
acnnolite
100 . 15
A
3
grunerile/Bcliriolllc 100 6
0
0
tremotltic talc1'
100 7 N D U 0
Average: 100 17
0
2.4
'T a k e n from G.W. G ibbs an d C. Y. H w ung, Dimensions of Airborne Asbestos Fibers, jAfiC Scientific Pub. #30 Lyon, Fiance, pp. 79-65.""
*Taken from A.G, Wylie, H.LYirle.ano E.Russok. "Characterizing and Discriminating Airborne Fibers: 1m-
plicpiions lorthcNIOSH Method," American Industrial Hygiene Association Jootfiel.Voi. At. pp, 197-201.';'
r Dala taken from the R.J.Lee Group Oust Analysis Project prepared for the R.7. Vanderbilt Co., me , 1968. Reflects PCM/PLM analysis ol 22 filters; % represents 2295 total particles.
ND = not determined.
asbesiiform dust populations by STEM differ markedly,
with an average of 35% (ranging from 9% to 81%) reported
to fail below a 0.25-vm width."*' The similarity between
amphibole cleavage fragment particle width and tremolile
widths noted in the study dust population, therefore, sug
gests a nonasbestiform habit. It also might be noted that,,
since all tremolile particles exceeded a 0.25-pin width, they
should all be rcsolvablcatlhelowermagniiica cions used for
both PCM and PLM analysis. Further, it is unlikely that
particles o f this width would be lost in the transfer of parti
cles from the litter to the glass slide in preparation for the
PLM analysis.
.
In terms of aspect ratio. majordifferenccS between nonas-
bestiform amphibole cleavage fragments and asbestiform
particles also exist. Table V makes such n comparison for
airborne particles which meet or exceed a 3:t aspect ratio
and a greater than 5-pm length. Variances shown in this
table typically are found in the literature.18'1'74' Figure 4
graphically depicts these data and further c!a rifles the differ
ence. In terms of the study dost population, particle aspect
ratio distribution is included inTable V under the cleavage
fragment column where it best fits. Interestingly, total par
ticulate aspect ratios noted in this study (based on 2295
particles) would represent the lowend of the cleavage frag
ment line in Figured. Unfortunately,an airborne dust size
characterisation for asbestiform tremolile could not be
found for inclusion in this comparison. Although asbesti
form iremolile is rare and is not exploited for commercial
use. localized occurrences do exist :n the United States (i.e..
California. Montana). At least one industrial hygiene study
exists of a mining operation containing asbestiform treino-
Lle. but detailed airborne size characterization i; not avail-
able.'1'" An aspect ratio d istrib u te.. Iv.vcver, wtu obtained
on bulk asbestilorm tremolile rom ik|Mmine.""' Fcr parti
cles longer than 5
Icli above I0;l. <0% above 15:1,
and 52Cf above 20'-1. These ru-h/s correlate most closely to
Sio
theaverage airborne asbestos ratios teflected inTable Vand Figure 4 of 100%. 89%. and 53%. respectively.
In summary, when the study dust population is contrasted with the minera logical definition--as well as the dimen sional characteristics of asbestiform and nonasbestiform particles reflected in the literature--the nonasbestiform nature of New York Slate tremolitic talc is quite apparent. The authors believe this reaffirms the nonspccificity of the NIOSH PCM method and the regulatory definitions it underpins when applied to mineral dust environments con taining common nonasbestiform cleavage fragments.
Corrective Measures
Given the differences between asbesiiiorm and nonasbestiform particulates, the least dramatic change necessary to improve specificity would involve an upward adjustment in the aspect ratio. As seen in Figure 4, airborne asbestiform particles exceed a 10:1 aspect ratio with very few less than 15;I. Cleavage fragments, in contrast, rartly exceed a 10:1 aspect ratio with fewer still exceeding 15:1. Any aspect ratio adjustment, however, should be applied as a screening tool only because there is some aspect ratio overlap between asbestiform and nonasbestiform particles. It, therefore, is considered essential that a miners logically correct definition of asbestos and criteria specific to asbestos should be reflected in regulations.
Discussion
Although it is not the intent of this caper toaddress health issues, the subject cannot be ignored In any discussion regarding the definition of asbestos, li can be argued, for example, that rcgulniorv definitions arc designed tonddiesx human health c neerns and not the realities of physical science. This argimem suffers, however, when it ts under-
ity( -r" . I tW :
lii'i-r'Wft I9S9
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NOTE: The majority ot cleavage fragments do not tall in this range
.
(most reflect lengths of< 5 nm). The 100%. iherefora, represents
the starting point for 3:1 aspect ratio particle counting and noI
the total w of airborne cleavage fragments
Figure 4 --Airborne a sb e s lo s v e rso s cleavage fragm ent a sp e c t ratio com parison (parlicules with an a sp ect ratio of 3:1 o r g re a te r. > 5 pm length. > 0.25 p m width). From Table V.
stood that health effects attributable to asbestos are not reasonably demonstrated for nonasbestiform exposures.01'381 Moreover, It can be argued that any environmen lal exposure ' ought io be studied and regulated for what it is. To do otherwise presents needless bias.
It also has been argued that any change in the regulatory definition of asbestos would confuse the extensive data base developed for commercially used asbestos. Nonasbestiform amphiboles, however, cannot and are nol used for applica* lions typically reserved for asbestos (e.g...insulation, struc tural binding, fire proofing, brake linings,'etc.). Accord ingly, this asbestos data base would not be affected signifi cantly if a mtnera logically correct definition of asbestos were adopted. The definitional ambiguity discussed here relaLcs to dust populations which do contain nonasbestiform min eral cleavage fragments. Such environments commonly involve hard rock and aggregate mining operations and industries who use their mineral products (e.g.. ceramics, construction, paint, e'c.). Whatever asbestos data exist for these enviro nments may be misleading and, therefore, ought to be corrected.
Conclusion
M ajor differences in crystal growth patterns, lengths, and widths exist bclwccn usbestiform particles and common, hard rock-forming mineral d e.r >gc fragments. Current regulatory asbestos definitions and fiber gia.ttification methods do not address these disv.nut ms adeip a cly. Thus, nonasbestiform dust pOpt ' :t rns r-.-. and haw been mis taken ns .asbestiform. Confusion is likely to persist until ;i
regulatory definition and analytical approach specific to asbestos is adopted.
\
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