U.S. DEPARTMENT Of COMMENCE
National Technical Information Service
PB80-152879
Interim Method for
Determining Asbestos in
Water
(U.S.) kiivironmentnl Research Lab,. Athens, GA
Jan 80
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United States
Environmental Protection
Agency
Environmental Research
Laboratory
Athens GA 30605
EPA 600
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RESEARCH REPORTING SERIES
Research r^-eons of me Office 01 Research anc: Development U S Environmental
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The nine series are
1 Environmental Health Eftecis Research
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2 Ecological Research
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3 'Special' Reoorts
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This report has been ass.gned 'o the ENVIRONMENTAL MONITORING series
This series describes research conducted to develop new or improved meihods
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TECHNICAL REPORT DATA
/Please read Insirui'tiuiis on the /vrmr beJJre completing)
1. Rcr'ORT NO.
EPA-600/4-80-OOS
3. RECIPIENT'
O.
j. TITLE A/MO SUBTITLE
Interim Method for Determining Asbestos
in Water
5. REPORT DATE
January. 1980 issuing date
6. PERFORMING ORGANIZATION CODE
•>. AUTHOR(S)
8. PERFORMING ORGANIZATION REPORT NO.
Charles H. Anderson and J. MacArthur Long
9. PERFORMING ORG \NIZATION NAME AND ADDRESS
Environmental Research Laboratory
U.S. Environmental Protection Agency
Athens, Georgia 30605
10. PROGRAM ELEMENT NO.
A37B1D
11. CONTRACT/GRANT NO.
12. SPONSORING AGSNCY NAME AND ADDRESS
Environmental Research Laboratory-Athens, GA
Office of Research and Development
U.S. Environmental Protection Agency
Athens, Georgia 30605
13. TYPE OF REPOR-r AND PERIOD COVEHF.O
Intarim, 7/76-12/78
14. SPONSORING AGENCY CODE
EPA/600/01
15. SUPPLEMENTARY NOTES
16. ABSTRACT
This manual describes an interim electron microscope (EM)
procedure for measuring the concentration of asbestos in water samples.
The main features of the method include filtering the sample through a
sub-micron polycarbonate membrane filter, examining an EM specimen grid
in a transmission electron microscope (TEM) , and verify.ing fiber
identity by selected area electro'n diffraction (SAED) .
This interim method is a revision of the procedure issued in
1976 and reflects the improvements that have been made in asbestos
analytical methodology since that time.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
Water pollution
Asbestos
Serpentine
Amphiboles
Electron Microscopy
Electron Diffraction
bJC/ENTIFIERS/OPEN ENDED TERMS
Asbestos Measurement
c. COSATI Field/Group
07D
14B
68D
013 rmguTiON STATEMENT
Release to Public
19. SECURITY CLASS (Thi\ Reran/
Unclassified
21. NO. OF PAGES
44
JO. SECURI TY CLASS I'l'llis paRf)
Unclassified
22. PRICE
EPA Form 2220-1 (9-7?)
• US'
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EP^-600/4-80-005
January 1980
INTERIM METHOD FOR DETERMINING ASBESTOS IN WATER
by
Charles H. Anderson and J. MacArthur Long
Analytical Chemistry Branch
Environmental Research Laboratory
Athens, Georgia 30605
ENVIRONMENTAL RES2ARCH LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
ATHENS, GEORGIA 30605
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DISCLAIMS*
This report has been reviewed by the Environmental
Research Laboratory, U.S. Environmental Protection Agency,
Athens, Georgia, and approved for publication. Mention of
trade names or commercial products does not constitute
endorsement or recommendation for use.
ii
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FOREWORD
Nearly every phase
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PREFACE
In July 1976, the Preliminary Interim Method for Deter-
mining Asbestos in Water was issued by the U.S. £avironmental
Protection Agency's Environmental Research Laboratory in
Athens, Georgia. That method was perceived as representing
the current state-of-the-art in asbestos analytical method-
ology. The objective of writing the method was to present a
procedure that analytical laboratories could follow chat woulJ
result in a better agreement of analytical results. Since
that time, a significant amount of additional experimental
work has generated data that provide the basis for a more
definitive method than was possible previously.
This revised Interim "ethod reflects the improvements
that have been made in asbestos analytical methodology since
the initial procedure was drafted. The general approach to
the analytical determination, however, remains the same as
previously outlined. That is, asbestos fibers are separated
from water by filtration on a sub-micron pore size membrane
filter. The asbestos fibers are then counted, after
dissolving the filter material, by direct observation in a
transmission electron microscope.
The major change in the initial procedure is the elimina-
tion of the condensation washer as a means of sample prepara-
tion. Intra- and inter-laboratory precision data for the
method are presented. Also, a suggested statistical evalua-
tion of grid fiber counts is included.
iv
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ABSTRACT
An interim electron microscope (KM) procedure for
measuring the concentration of asbestos in water samples is
described. The main features of the method include filtering
the samples through a sub-micron polycarbonate membrane
filter, examining an EM specimen grid in a transmission
electron microscope (TRM), and verifying fiber identity by
selected area electron diffraction.
This interim method is a revision of the procedure issued
in 1976 and reflects the improvements that have been made in
asbestos analytical methodology since that time.
This report covers a period from July 1976 to December
1978 and work was completed as of December 1978.
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CONTENTS
Foreword iii
Preface iv
Abstract v
Figures and Tables ix
1. Scope and Application 1
2. Summary of Method 1
3. Definitions 2
4. Sample Handling and Preservation 3
4.1 Containment Vessel .... 3
4.2 Quantity of Sample .... 3
4.3 Sample Preservation .... 3
5. Interferences 4
5.1 Misidentification 4
5.2 Obscuration 4
5.3 Contamination 5
5.4 Freezing 5
6. Equipment and Apparatus 5
6.1 Specimen Preparation
Laboratory 5
6.2 Instrumentation 6
6.3 Apparatus Supplias and
Reagents 7
7. Preparation of Standards ., . . . 11
7.1 Chrysotile Sto< k
Suspensirn 11
7.2 Amphibole Stozfc
Suspension 11
7.3 Identification Standards . . 11
8. Procedure 11
8.1 Filtration 11
8.2 Preparation of Electron
Microscope Grids ... 13
8.3 Nuclepore Filter, Modified
Jaffe Wick Technique . 14
8.4 Electron Microsccspic
Examination 16
8.5 Ashing 22
8.6 Determination of Blank
Level 23
vii
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9.
10.
11.
12.
13.
Calculations
9.1
9.2
9.3
Reporting
Precision
11.
11.
Accuracy .
12
12
Fiber Concentrations
Estimated Mas:-;
Concentration .
Aspect Ratio . . .
Intra-Laboratory
Inter-Laboratory
1 Fiber Concentrations
,2 Mass Concentrations
Suggested Statistical Evaluation of
Grid Fiber Counts ...
Bibliography
24
24
25
26
26
26
26
27
27
27
29
2?
32
Vlll
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FIGURES
Number
1.
2.
Modified Jaffe Wick Method
Illustration of Counting Rules for
Field-of-View Method"
Page
8
20
TABLES
Number
1.
2.
Intra-Laboratory Precision
Inter-Laboratory Precision
28
28
IX
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INTERIM METHOD
FOR DETERMINING ASBESTOS IN WATER
1. Scope and Application
1.1 This method is applicable to drinking water and
water supplies.
1.2 The method determines the number of asbestos fibers
per liter, the size (length and width) of the
fibers, the size distribution, and the total mass.
The method distinguishes chrysotile from amphibole
asbestos. The detection limits are variable and
depend upon the amount of total extraneous pacticu-
late matter in the sample as well as the contamina-
tion level in the laboratory environment. Under
favorable circumstances, 0.01 million fibers per
liter (MFL) can be detected. The detection limit
for total mass of asbestos ribers is also variable
and depends upon the fiber size and size distribu-
tion in addition to the factors affecting the total
fibar count. The detection limit under favorable
conditions is in the order of 0.1 nanogram per
liter (ng/L).
1.3 The method is not intended to furnish a complete
characterization of all the fibers in water.
1.4 It is beyond the scope of this method to furnish
detailed instruction in electron microscopy,
electron diffraction, or crystallography. It is
assumed that those using this method will be suffi-
ciently knowledgeable in these fields to understand
th« methodology involved.
2. Summary of Method
2.1 A variable, known volume of water sample is
filtered through a 0.1 micrometer (ura) Nuclepore
filter to trap asbestos fibers and the filter is
then carbon coated. A small portion of the carbon
coated filter with deposited fibers is placed on- an
electron microscope grid and the filter material is
removed by gentle solution in organic solvent. The
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material remaining on the electron microscope grid
is examined in a transmission microscope at a
magnification of about 20,900X. The asbestos
fibers are identified by their morphology and
electron diffraction patterns and their lengths and
widths are measured. The total arsa exaaiir.e<3 in
the electron microscope is determined and the
nurobsr of asbestos fibers in this area is counted.
The concentration in MFL is calculated from the
number of fibers counted, the amount of water
filtared, and the ratio of the total filtered area/
sampled filter area. The mass per liter is calcu-
lated from the assumed density and the volume of
the fibers.
3. Definitions
Asbestos - A generic term applied to a variety of
commercially useful fibrous silicate minerals of
th« serpentine or amphibole mineral groups.
Fiber - Any particulate that has parallel sides and a
length/width ratio greater than or equal to 3:1.
Aspect Ratio - The ratio of length to width.
Chrysotile - A nearly pure hydrated magnesium silicate,
the fibrous form of the mineral serpentine,
possessing a unique layered structure in which the
layers are wrapped in a helical cylindrical manner
about the fiber axis.
Amphibole Asbestos - A double chain fibrous silicate
mineral consisting of Si^O^^, laterally linked by
various cations such as aluminum/ calcium, iron,
magnesium, and sodium. Amphibole asbestos consists
of crocidolite and araosite (the fibrous form of
cummingtonite-gruenerite) , and the fibrous forms of
tremolite, actinolite, and ant-' jphyllite. These
minerals consist of or contain fibers formed
through natural growth processes. Mineral frag-
ments that conform to the definition of a fiber and
that are formed through a crushing and milling
process are analytically indistinguishable from the
naturally formed fibers by this method.
Detection Limit - The calculated concentration in MFL,
equivalent to one fiber above the background or
blank count (Section 8.6).
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Statistically Significant - Any concentration based upon a
total fiber count of 5 or more in 20 grid squares.
4. Sample Handling and Preservation
It is beyond the scope of this procedure to furnish
detailed instructions for field sampling; the general
principles of obtaining water samples apply. Some
specific considerations apply to asbestos fibers, how-
ever, because they are a special type of part.-'.culate
matter. These fibers are small, and in water range in
length from 0.1 ym to 20 um or more. Because of the
range of size there may be a vertical distribution of
particle sizes. This distribution will vary with depth
depending upon the vertical distribution of temperature
as well as local meteorological conditions. Sampling
should take place according to the objective of the
analysis. If a representative .sample of a water supply
is required, a carefully designated set of samples should
be taken representing the vertical as well as the hori-
zontal distribution and these samples should be
composited for analysis.
4.1 Containment Vessel
The sampling container shall be a clean, screw-
capped, polyethylene bottle capable of holding at
least 1 liter. The bottle should be rinsed at
least two times with the water that is being
sampled prior to sampling.
4.2 Quantity of Sample
A minimuir of approximately 1 liter of water is
required. Leave air space at the top of the
container to allow for shaking the sample. It is
desirable to obtain two samples from one location.
4.3 Sample Preservation
No preservatives should be added during sampling
and the addition of acids should be particularly
avoided. If the sample cannot be filtered in the
laboratory within 48 hours of its arrival, suffi-
cient amounts (1 milliliter per liter of sample) of
a 2.71% solution of mercuric chloride to give a
final concentration of 20 ppm of Hg may be added tc
prevent bacterial growth.
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NOTE 1: It has been reported that the growth of
algae in water samples can be prevented by storing
the samples in the dark.
NOTE 2: Refrigeration of sampler at about 5°C
minimize bacterial and alga] growth.
5. Interferences
5.1 Misidentification
The guidelines set forth in this method for
counting fibrous asbestos require a positive
identification by both morphology and crystal
structure as shown by an electron diffraction
pattern. Chrysotile asbestos has a unique tubular
structure, usually showing the presence of a
central canal, and exhibits a unique characteristic
electron diffraction pattern. Although halloysite
fibers may show a streaking similar to chrysotile,
they do not exhibit chrysotile's characteristic
triple set of double spots or 5.3A layer line. It
is highly improbable that a nou-asbestiform fiber
would exhibit the distinguishing chrysotile
features. Although amphibole fibers exhibit
characteristic morphology and electron diffraction
patterns, they do not have the- unique properties
exhibited by chrysotiie. It is possible, there-
fore, though not probable for misidentification to
take place.
It is important to recognize that a significant
variable fraction of both chrysotile and axphibole
asbestos fibers do not exhibit the required
confirmatory electron diffraction pattern. This
absence of diffraction is attributable to unfavor-
able fiber orientation and fiber sizes. The
results reported will be low, therefore, as
compared to the absolute number of asbestos fibers
that are present.
5.2 Obscuration
If large amounts of other materials are present,
some small asbestos fibers may not be observed
because of physical overlapping. This will result
in low values for the reported asbestos content.
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5.3 Contamination
Although contam5.nat.ion is not strictly considered
to be an interference, it is an important source of
erroneous results, particularly for chrysotile.
The possibility of contamination, therefore, should
always be a consideration.
5.4 Freezing
The effect of freezing on asbestos fibers is not
known but there is reason to suspect that fiber
breakdown could occur and result in a higher fiber
count than was present in the original sample.
Therefore, the sample should be transported to the
laboratory under conditions that would avoid
freezing.
6. Equipment and Apparatus
6.1 Specimen Preparation Laboratory
The ubiquitous nature of asbestos, especially chry-
sotile, demands that all sample preparation steps
be carried out to prevent the contamination of the
sample by airborne or other source of asbestos.
The prime requirement of the sample preparation
laboratory is that it be sufficiently free from
asbestos contamination that a specimen blank deter-
mination using 200 ml of asbestos-free water yields
no more than 2 fibers in 20 grid squares of a
conventional 200 mesh electron microscope grid.
In order to achieve this low level of contamina-
.tion, the sample preparation area should be a
separate conventional clean room facility. The
room should be operated under positive pressure and
have incorporated electrostatic precipitators in
the air supply to the room, or as an alternative,
absolute (HEPA) filters. No asbestos floor or
ceiling tiles, transite heat-resistant boards, or
asbestos insulation should be used in construc-
tion. Work surfaces should be stainless steel or
Formica or equivalent. A laminar flow hood should
be provided for sample manipulation. Disposable
plastic laboratory coats and disposable overshoes
are recommended. Alternatively, new shoes for all
operators should be provided and retained for clean
room use only. A mat (Tacky Mat, Liberty
Industries, 589 Deming Road, Berlin, Connecticut
06037, or equivalent) should be placed at the
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entrance to the room to trap any gross contamina-
tion inadvertently brought into the room on contam-
inated shoes. Normal electrical and water
services, including a distilled water supply should
be provided. In addition, a source of ultra-pure
water from a still or filtration-ion exchange
system is desirable.
6.2 Instrumentation
6.2.1 Transmission Electron Microscope. A trans-
mission electron microscope thac operates
a): a minimum of 80 kv and has a resolution
of better than 1.0 nm and a magnification
range of 300 to 100,000 is required. If
the upper limit is not attainable directly
it may be attained through the use of
auxiliary optical viewing. Jt is mandatory
that the instrument &
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6.2 Apparatus/ Supplies and Reagents
6.3.1 Jaffe Wick Washer. The J'affe Wick Washer
for dissolving Nuclepore filter is
described in 8.3.1, and is illustrated in
Figure 1.
6.3.2 Filtering Apparatus. A 47-mm funnel (Cat
No. XX1504700, Millipore Corporation, Order
Service Dept . , Bedford, MA 01730) or
equivalent is used to filter water
samples. A 25-mm funnel (Millipore Cat No.
XX1002500) or equivalent is used to filter
dispersed ash samples.
6.3.3 Vacuum Pump. A pump, for use in sample
filtration, should provide vacuum up to
about 500 mm of mercury.
6.3.4 e>l Grids. Grids of 200 -mesh copper or
nickel covered with formv.ir film for use
with the Nuclepore-Jaf f e sample preparation
method are required. These grids may be
purchased from manufacturers of electron
microscopic supplies or prepared by
standard electron microscopic grid prepara-
tion procedures. Finder grids may be
substituted and are useful if the re-exami-
nation of a specific grio opening is
desired.
6.3.5 Membrane Filters.
47-mm diameter Millipore membrane filter,
type HA, 0.45-um pore size. Used as a
Nuclepore filter support on top of glass
frit.
47-mm diameter Nuclepoire membrane filter;
0.1-um pore site (Nuclepore Corp., 7035
Commerce Circle, Pleasanton, CA 945C.6) .
Used to filter tha water sample.
25-mm diameter Millipore membrane ::ilter,
type HA; 0.45-ym pore size. Used as Nucle-
filter support on top of glass frit.
25-mm diameter Nuclepore membrane ::ilter;
0.1-um pore size. Used to filter dispersed
ashed Nuclepore filter.
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Screen Support
with Grid
Petri Dish
Ridge
Glass Slides
A
Layer of
Filter Papers
Nuclepore Filter
\
Carbon
Carbon
Chloroform
Forrnvar
Grid
B
Figure 1. Modified Jaffe Wick Method.
A. Washing Apparatus
B. Washing Process
8
Grid
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6.3.6 Glass Vials. SO-.iun diameter x 80-ram long.
Used to hold filter during ashing.
6.3.7 Glass Slides. Used to support Nuclepore
filter during carbon evaporation.
6.3.8 Scalpels.
6.3.9 Scissors.
6.3.10 Tweezers. Several pairs are needed for the
many handling operations.
6.3.11 Double-sided Tape. Used to hold filter
section flat on glass slide while carbon
coating is applied.
6.3.12 Disposable Petri Dishes, 50-mm diameter.
Used for storing membrane filters.
6.3.13 Static Eliminator, 50C microcuries Po-210.
INuclepore Cat. No. V090POL00101) or equiv-
alent. Used to eliminate static charges
from membrane filters.
6.3.14 Carbon Rods. Spectrochemically pure, 1/8
in. dia., 3.6 mra x 1.0 mm neck. Used for
carbon coating.
6.3.15 Carbon rod sharpener. (Cat. No. 1204,
Ernest F. Fullam, Inc., P. 0. Box 444,
Schenectady, NY 12301) or equivalent. Used
for sharpening carbon rods to a neck of
specified length and diameter.
6.3.16 Ultrasonic Bath. (50 watts, 55 kHz). Used
for dispersing ashed sample and for general
cleaning.
6.3.17 Graduated Cylinder, 500 ml.
6.3.18 Spot Plate.
6.3.19 10-yl Microsyringe. Used for administering
drop of solvent to filter section during
sample preparation.
6.3.20 Carbon Grating Replica, 2160 lines/mm.
Used for calibration of EM magnification.
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6.3.21 Filter Paper. S & S #589 Black Ribbon
(9-cm circles) or equivalent absorbent
filter paper. Used for preparing Jaffe
Wick Washer.
6.3.22 Screen supports (copper or stainless steel)
12 mm x 12 mm, 200 mesh or equivalent.
Used to support specimen grid in Jaffe Wick
Washer.
6.3.23 Chloroform. Spectro grade, doubly
distilled. Used for dissolving Nuclepore
filters.
6.3.24 Asbestos. Chtysotile (Canadian), Crocido-
lite, Amosite. UICC (Union Internationale
Centre le Cancer) Standards. Available
from Duke Standards Company, 445 Sherman
Avenue, Palo Alto, CA 94306.
6.3.25 Petri Dish. Glass dish (100 mm diameter x
15 mm high). Used for modified Jaffe Wick
Washer.
6.3.2(> Alconox. (Alconox, Inc., New York, NY
10003) or equivalent. Used for clean-ng
glassware. Add 7.5 g Alconox to a liter of
distilled water.
6.3.27 Parafilm. (American Can Company, Neenah,
WI) or equivalent. Used as protective
covering for clean glassware.
6.3.28 Pipets. Disposable, 5 ml and 50 ml pipets
are required.
6.3.29 Distilled or Deionized Water. Filter if
necessary through 0.1-ym Nuclepore filter
for making up all reagents, for final
rinsing of glassware, and for preparing
blanks.
6.3.30 Mercuric chloride, 2.71% solution w/v.
Used as sample preservative. See 4.3. Add
5.42 g or reagent grade mercuric chloride
(HqCl2) to 100 ml distilled water and
dissolve by shaking. Dilute to 200 ml with
additional water. Filter through O.i-ym
Nuclepore filter paper before using.
10
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7. Preparation of Standards
Reference standard samples of asbestos that can be used
for quality control for a quantitative analytical method
are not available. It is, however, necessary for each
laboratory to prepare at least two suspensions, one of
chrysotile and another of a representative amphibole.
These suspensions can then be used for intra-laboratory
control and to furnish standard morphology photographs
and diffraction patterns.
7.1 Chrysotile Stock Suspension.
Grind about 0.1 g of UICC chrysotile to a powder in
ar. agate mortar. Transfer 10 mg to a clean 1-liter
volumetric flask, add several hundred ml of
filtered distilled water containing 1 ml of a stock
mercuric chloride solution and then make up to 1
liter with filtered distilled water. To prepare a
working solution, transfer 10 ml of the above
suspension to another 1-liter flask, add 1 ml of a
stock mercuric chloride solution and make up tc 1
liter with filtered distilled water. This suspen-
sion contains 100 yg per liter. Finally transfer 1
ml of this suspension to a 1-liter flask, add 1 ml
of a stock mercuric chloride solution and make up
to volume with filtered distilled water. The final
suspension will contain 5 to 10 MFL and :'s suitable
for laboratory testing.
7.2 Amphibole Stock Suspension.
Prepare amphibole suspensions from UICC amphibole
samples as in Section 7.1.
7.3 Identification Standards.
Prepare electron microscopic grids containing the
UICC asbestos fibers according to Section 8 and
obtain representative photographs of each fiber
type and its diffraction pattern for future
reference.
8. Procedure
8.1 Filtration.
The separation of insoluble material, including
asbestiform minerals, through filtration and subse-
quent deposition on a membrane filter is a critical
step in the procedure. The objective of the
11
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filtration is not only to separate, but also to
distribute the particulate matter uniformly such
that discrete particles are deposited with a
minimum of overlap.
The volume filtered will range from 50 to 500 ml.
In an unknown sample, the volume can not be speci-
fied in advance because of the presence of variable
amounts of particulate matter. In general, suffi-
cient sample is filtered such that a very faint
stain can be observed on the filter medium. The
maximum loading that can be tolerated is 20 yg/cm2,
or about 200 yg on a 47-mm diameter filter; 5
pg/cm2 is near optimum. If the total solids
content is known, an estimate of the maximum volume
tolerable can be obtained. In a sample of high
solids content, where less than 50 ml is required,
the sample should be diluted with filtered
distilled water so that a minimum total of 50 ml of
water is filtered. This step is necessary to allow
the insoluble material to deposit uniformly on the
filter. The filtration funnel assembly must be
scrupulously cleaned before each filtration. The
filtration should be carried out in a laminar flow
hood.
NOTE: The following cleaning procedure has been
found to be satisfactory.
Wash each piece of glassware three times with
distilled water. Following manufacturer's recom-
mendations, use the ultrasonic bath with an
Alcor.ox-water solution to clean all glassware.
After the ultrasonic cleaning, rinse each piece of
glassware three times with distilled watc»r. Then
rinse each piece three times with deionized water
that has been filtered through O.l-ym Nuclepore
filtar. Dry in an asbestos-free oven. After the
glassware is dry, seal openings with parafilm.
a. Assemble the vacuum filtration
apparatus incorporating the 0.1-ym Nucle-
pore backed with 0.45-ym Millipore filter.
See 8.3.2.
b. Vigorously agitate the water sample in
its container. Treatment of the sample in
an ultrasonic bath may be required to
evenly disperse the particulate material.
12
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c. If the required filtration volume can
be estimated, either from turbidity esti-
mates of suspended solids or previous
experience, immediately withdraw the proper
volume f.rom the container and add the
entire volume to the 47-mm diameter
funnel. Apply vacuum sufficient for
filtration but gentle enough to avoid the
formation of a vortex. If a completely
unknown .sample is being analyzed, a
slightly modified procedure must be
followed. Pour 500 nil of a well-mixed
sample into a 500-ml graduated cylinder and
immediately transfer the entire contents to
the prepared vacuum filtration apparatus.
Apply vacuum gently and continue suction
until all of the water has passed through
the filter. If the resulting filter
appears obviously coated or discolored,
another filter should be prepared in the
same manner, but this time using only 200
or 100 ml of sample.
NOTE 1: Do not add more water after
filtration has started and do not rinse the
sides of the funnel.
NOTE 2: Nuclepore filter is basically a
hydrophobia material. The manufacturer
applies a detergent, to the surface of the
filter in order to render it hydrophilic;
this process, nowever, does not appear to
be entirely satisfactory in some batches.
Pretreatment of the filter in a low temper-
ature asher at 10 watts for 10 seconds can
be used to render the surface of the filter
hydrophilic. This process will signifi-
cantly decrease the islands of sparse
deposit that are frequently observed.
d. Disassemble the funnel, remove the
filter, and dry it in a covered petri dish.
8.2 Preparation of Electron Microscope Grids.
Prsparation of the grid for examination in the
microscope is a critical step in the analytical
procedure. The objective is to remove the organic
filter material from the asbestos fibers with
minimum loss and *'.ovement =>nd with minimum breakage
of the grid support film.
13
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If the sample contains large amounts of organic
matter that interfere with fiber counting and
identification a preliminary ashing step is
required. See 8.5.
8.3 Nuclepore Filter, Modified Jafie Wick Technique.
8.3.1 rreparation of Modified Jaffe Washer
Place three glass microscope slides (75 mm
x 22 mm) one on top of the other in a petri
dish (100 mm x 15 mm) along a diameter.
Place 14 S & S 1589 Black Ribbon filter
papers; (9-cm circles) in the petri dish
over \:he stack of microscope slides. Place
three copper mesh screen supports (12 mm x
12 mm) along the ridge formed by the ?,tack
of slices underneath the layer of filter
papers. Place an EM specimen grid on each
of the screen supports. See Fig. 1.
NOTE: A stack of 30 to 40 S & S filters
(7-cm circle), or equivalent, can be
substituted for the 14 filters and micro-
scope slides in preparing the Jaffe washer.
8.3.2 Vacuum Filtration Unit
Assemble the vacuum filtration unit. Place
a 0.45-um Millipore filter type HA on the
glass frit ar.d then position a 0.1-ym
Nuclepore filter, shiny side up, on top of
the Millipore filter. Apply suction to
center the filters flat on the frit.
Attach the filter funnel and shut off the
suction.
8.3.3 Sample Filtration
See 8.1.
8.3.4 Sample Drying
Remove the filter funnel and place the
Nuclepore filter in .a loosely covered pe'cri
dish to dry. The petri dish containing the
filter may be placed in an asbestos-free
oven at 45° C for 30 minutes to shorten
the drying time.
14
-------
Alternatively, the Nuclepore filter section
may be mounted on a glass slide prior to
drying the filter.
8.3.5 Selection of Section for Carbon Coating
Using a small pair of scissors or sharp
scalpel, cut out a rectangular section of
the Nuclepore filter. The minimum approxi-
mate dimensions should be 15 mm long and 3
mm wide. Avoid selection near the perim-
eter of the filtration a.vea.
3.3.6 Carbon Coating the Filter
Tape the two ends of the selected filter
section to a glass slide using double-sided
tape. Take care not to stretch the filter
section. Identify the filter section using
a china marker on the slide. Place the
glass slide with the filter section into
the vacuum evaporator. Insert the necked
carbon rod and, following manufacturer's
instructions, obtain high vacuum. Evapo-
rate the neck, with the filter section
rotating, at a distance of approximately
7.5 cm from the filter section to obtain a
30 to 50 nm layer of caroon on the filter
paper. Evaporate the carbon in several
short bursts rather than continuously to
prevent overheating the surface of the
Nuclepore filter.
NOTE 1: Overheating the surface tends co
crosslink the plastic, rendering :he filter
dissolution in chloroform difficult.
NOTE 2: The thickness of the carbon film
can be monitored by placing a drop of oil
on a porcelain chip that is placed at the
same distance from the carbon electrodes as
the specimen. Carbon is not visible in the
region of the oil drop thereby enabling the
visual estimate of the deposit thickness by
the contrast differential.
8.3.7 Grid Transfer
Remove the filter from the vacuum evapo-
rator and cut out three sections somewhat
less than 3 mm x 3 mm and such that the
15
-------
square of Nuclepore fits within the circum-
ference of the grid. Pass each of the
filter sections over a static eliminator
and then place each of the three sections
carbon-side down on separate specimen grids
previously placed in the modified Jaffe
Washer. Using a microsyringe, place a
10-ul drop of chloroform on each filter
section resting on a grid and then saturate
the filter pad until pooling of the solvent
occurs below the ridge formed by the glass
slides inserted under the layer of filter
papers. Place the cover on the petri dish
and allow the grids to remain in the washer
for approximately 24 hours. Do not allow
the chloroform to completely evaporate
before the grids are removed. To remove
the grids from the washer, lift the screen
support with the grid resting upon it and
set this in a spot plate depression to
allow evaporation of any solvent adhering
to the grid. The grid is now ready for
analysis or storage.
8.4 Electron Microscopic Examination
8.4.1 Microscope Alignment and Magnification
Calibration
Following the manufacturer's recommenda-
tions carry out the necessary alignment
procedures for optimum specimen examination
in the electron microscope. Calibrate the
routinely used magnifications using a
carbon grating replica.
NOTE: Screen magnification is not neces-
sarily equivalent to plate magnification.
8.4.2 Grid Preparation Acceptability
After inserting the specimen into the
microscope, adjust the magnification low
enough (300X-10COX) to permit viewing
complete grid squares. Inspect at least 10
grid squares for fiber loading and distri-
bution, debris contamination, and carbon
film continuity.
16
-------
Reject the grid for counting if:
1) The grid is too heavily loaded with
fibers to perform accurate counting and
diffraction operations. A new sample
preparation either from a smaller volume of
water or from a dilution with filtered
distilled water must then be prepared.
2) The fiber distribution is noticeably
uneven. A new sample preparation is
required.
3) The debris contamination is too severe
to perform accurate counting and diffrac-
tion operations. If the debris is largely
organic the filter must be ashed and redis-
persed (see 8.5). If it is inorganic, the
sample must be diluted and again prepared.
4) The majority of grid squares examined
have broken carbon films. A different grid
preparation from the same initial filtra-
tion must be substituted.
8.4.3 Procedure for Fiber Counting
Two methods are conunonly used for fiber
counting. In one method (A), 100 fibers
contained in randomly selected fields of
view are counted. The number of fields
plus the area of a field of view must be
. known when using this irethod. In the other
method (B), all fibers (at least 100) in
several grid squares or 20 grid .squares are
counted. The number of giid squares
counted and the average area of one grid
square must be known when using this method.
NOTE: The method co use depends upon the
fiber loading on the grid and it is left to
the judgment of the analyst to select the
optimum method. The following guidelines
can be used: If it is estimated that a
grid square (80 ;im x 80 um) contains 50 to
100 fibers at a screen magnification of
20000X, it is convenient to use the field-
of-view counting method. It' the estimate
is less than 50, the grid square method of
counting should be chosen. On the other
17
-------
hand, if the fiber count is estimated to be
over 300 fibers per grid square/ a new grid
containing fewer fibers must be prepared
(through dilution or filtration of a
smaller volume of water).
8.4.3A Field-of-View Method
After determining that a fibeL count can be
obtained using this method, adjust the
screen magnification to 15,000 to 20,OOOX.
Select a number of grid squares that would
be as representative as possible of the
entice analyzable grid surface. Prom each
of these squares, select a sufficient
number of fields of view for fiber
counting. The number of fields of view per
grid square is dependent upon the fiber
loading. If more than one field of view
per grid square is selected, scan the grid
opening orthogonally in an arbitrary
pattern that prevents overlapping of fields
of view. Carry out. the analysis by
counting, measuring and identifying (see
8.4.4) approximately 50 fibers on each of
two grids.
The following rules should be followed when
using the field of view method of fiber
counting. Although these rules were
derived for a circular field of view they
can be modified to apply to square or
rectangular designs.
1) Count all fibers contained within the
counting area and not touching the circum-
ference of the circle.
2) Designate the upper right-hand quadrant
as I and number in clockwise order. Count
all fibers touching or intersecting the arc
of quadrants I or IV. Do not count fibers
touching or intersecting the arc of quad-
rants II or III.
3) If a fiber intersects the arc of both
quadrants III and IV or I and II count it
only if the greater length was outside the
arc of quadrants IV and I, respectively.
18
-------
4) Count fibers intersecting the arc of
both quadrants I and III but not those
intersecting the arc of both II and IV.
These rules are illustrated in Fig. 2.
8.4.3B Grid Square Method
After determining that a fiber count can be
obtained using this method adjust the
screen magnification to 15,OOC to 20,OOOX.
Position the grid square so that scanning
can be started at the left upper corner of
the grid square. While carefully examining
the grid, scan left to right, parallel to
the upper grid bar. When the perimeter of
the grid square is reached, adjust the
field of view down one field width and scan
in the opposite direction. The tilting
section of the fluorescent screen may be
used conveniently as the field of view.
Examine the square until all the area has
been covered. The analysis should be
carried out by counting, measuring, and
identifying (see 8.4.4) approximately 50
fibers on each of two grids or until 10
grid squares on each of two grids have been
counted. Do not count fibers intersecting
a grid bar.
8.4.4 Measurement and Identification
Measure and record the length and width of
each fiber having an aspect ratio greater
than or equal to three. Disregard obvious
biological-bacteriological fibers and
diatom fragments. Examine the morphology
of each fiber using optical viewing if
necessary. Tentatively identify, by
reference to the UICC standards, chrysotile
or possible amphibole asbestos. Attempt to
obtain a diffraction pattern of each fiber
utilizing the shortest camera length
possible. Move the suspected fiber image
to the center of the screen and insert a
suitable selected area aperture into the
electron beam so that the fiber image, or a
portion of it, is in the illuminated area.
The size of the aperture and the portion of
the fiber should be such that particles
other than the one to be examined are
19
-------
— Counted
- Not Counted
Figure 2. Illustration of Counting Rules for
Field of View Method.
20
-------
excluded from the selected area. Observe
che diffraction pattern with the binocular
attachment. It an incomplete diffraction
pattern is obtained, move the particle
image around in the selected area to get a
clearer diffraction pattern or to eliminate
possible interferences from neighboring
particles.
Determine whether the fiber is chrysotile
or an araphiboie by comparing the diffrac-
tion pattern obtained to the diffraction
patterns of known standard asbestos
fibers, Confirm the tentative identifica-
tion of chrysotile and amphibole asbestos
fi.om their electron diffraction patterns.
Classify each fiber as chrysotile, amphi-
bole, non-asbestos, no diffraction, oc
ambiguous.
NOTE 1: It is convenient to use a tape
recorder during the examination cf the
fibers to record all pertinent data. This
information can then be summarized on data
sheets or punched cards for subsequent
automatic data processing.
NOTE 2: Chrysotile fibers occur as single
fibrils or in bundles. The fibrills
generally show a tubular structure with a
hollow canal, although the absence of the
canal does not rule out its identifica-
tion. Amphibole asbestos fibers usually
exhibit a lath-like structure with irreg-
ular ends, but occasionally will resemble
chrysotile in appearance.
NOTE 3: The positive identification of
asbestos by electron diffraction requires
some judgment on the part of the analyst
because some fibers give only partial
patterns. Chrysotile shows unique promi-
nent streaks on the layer lines nearest the
central one and a triple set of double
spots on the second layer line. The
streaks and the set of double spots are the
distinguishing characteristics of chryso-
tile required for identification. Amphi-
bole asbestos requires a more complete
diffraction pattern to be positively iden-
tified. As a qualititative guideline,
21
-------
layer lines for amphibole, without the
unique streaks (some streaking may be
present) of chrysotile, should be present
and the arrangement of diffraction spots
along the layer lines should be consistent
with the amphibole pattern. The pattern
should be distinct enough to establish ,
these criteria.
NOTE 4: Chrysotile and thin amphibole
fibers may undergo degradation in an elec-
tron beam; this is particularly noticeable
in small fibers. It may exhibit a pattern
for 1 to 2 seconds and disappear and the
analyst must be alert to note the charac-
teristic features.
NOTE 5: An ambiguous fiber is a fiber that
gives a partial electron diffraction
pattern resembling asbestos, but is insuf-
ficient to provide positive identification.
8.4.5 Determination of Grid Square Area
Measure the dimensions of several represen-
tative grid squares from each batch of
grids with an optical microscope. Calcu-
late the average area of a grid square.
This should be done to compensate for
variability in grid square dimensions.
8.5 Ashing
Some samples contain sufficiently high levels of
organic material that an ashing step is required
before fiber identification and counting can be
carried out.
Place the dried Nuclepore filter paper containing
the collected sediment into a glass vial (28 mm
diameter x 80 mm high). Position the filter such
that the filtration side touches the glass wall.
Place the vial in an upright: position in the low
temperature asher. Operate the asher at 50 watts
(13.56 MHz) power and 2 torr oxygen pressure. Ash
the filter until a thin film of white ash remains.
The time required is generally 6 to 8 hours. Allow
the ashing chamber to slowly reach atmospheric
pressure and remove the vial. Add 10 ml of
filtered distilled water to the vial. Place the
vial in an ultrasonic bath for 30 minutes to
disperse the ash. Dilute the sample if required.
22
-------
Assemble the 25-mm diameter filtering apparatus.
Center a 25-rnrr. diameter 0.1-um Nuclepore filter
(with the 0.45-um Millipore backing) on the glass
frit. Apply suction and recenter the filter if
necessary. Attach the filter funnel and turn off
the suction. Add the wator containing the
dispersed ash from the vial to the filter funnel.
Apply suction and filter the sample. After drying,
this filter is ready to be used in preparing samrle
gr ids as in 8.3.
NOTE 1: In specifying a 25-mm diameter filter it
is assumed that the ashing step is necessary mainly
because of the presence of organic material and
that the smaller filtering area is desirable from
the point of view of concentrating the fibers. If
the sample contains mostly inorganic debris such
that the smaller filtering area will result in
overloading the filter, the 47-ram diameter filter
should be used.
NOTE 2: It will be noted that a 10-.ml volume is
filtered in this case instead o£ the minimum 50-ml
volume specified in 8.1. These volumes are consis-
tent when it is considered that there is approxi-
mately a 5-fold difference in effective filtration
area between the 25-mm diameter and 47-mm diameter
filters.
NOTE 3: Cross contamination is probable when
ashing more than one sample at a time.
8.6 Determination of Blank Level
Carry out a blank determination with each batch of
samples prepared, but a minimum of one per week.
Filter a fresh supply (500 ml) of distilled,
deionized water through a clean 0.1-um membrane
filter. Filter 200 ml of this water through a
0.1-um Nuclepore filter, prepare the electron
microscope grid, and count exactly as in the proce-
dures 3.1 - 8.4. Examine 20 grid squares and
record this number of fibers. A maximum of two
fibers in 20 grid squares is acceptable for the
blank sample.
NOTE: Monitoring the background level of asbestos
is an integral part of the procedure. Upon initia-
ting asbestos analytical work, blank samples must
be run to establish the initial suitability of the
laboratory environment, cleaning procedures, and
23
-------
reagents for carrying out asbestos analyses.
Analytical determinations of asbestos can be
carried out only aft^r an acceptably low level of
contamination has been established.
Calculations
9.1 Fiber Concsntrfitions
Gr id Square Counting Method - If the Grid Square
Method of counting is employed, use the following
formula to calculate the total asbestos fiber
concentration in MFL.
C = (F x Af)/(Ag x V0 x 1000) (1)
where: C = Fiber concentration (MFL)
F = Average number of fibers per grid
opening
A, = Effective filtration area of filter
paper (mm2) used in grid preparation
for fiber counting
A = Average area of one grid square (mm2)
VQ » Original volume of sample filtered (ml)
If ashing is involved, use the same formula but
substitute the effective filtration area of the
25-nun diameter filter for Af instead of that for
the 47-mm diameter filter. If one-half the filter
is ashed, multiple C by two.
Field-of-View Counting Method - If the Field-of-
View Me-thod of counting is employed, use the
following formula to calculate the total asbestos
fiber concentrations (MFL}.
C = (F x Af x 1000)/(AV x V0) (2)
where: C = Fiber concentration
F = Average number of fibers per field of
vii»w
AJ = Effective filtration ar^a of filter
paper (mm2) used in grid preparation
for fiber counting
24
-------
Ay = Area of one field of view (ym2)
V0 = Original volume of sample filtered (ml)
If ashing is involved, use the same formula but
substitute the effective filtration area of the
25-mm diameter filter for Ar instead of that for
the 47-mir diameter filter.
9.2 Estimated Mass Concentration
Calculate ".he mass (pg) of each fiber counted using
the following formula.
M = L x W2 X D x 1CT6
If the fiber content is predominantly chrysotile,
the following formula may be used.
M=lxLxW2xDx i.0~6 (3)
4
where: M = Mans (ug) '
L = Length (um)
W = Width (MTU)
D = Density of fibers (g/cm^)
Then calculate the mass concentration (yg/1)
employing the following formula.
Mc = C x Mf x 106
where: M = mass concentration (yg/1)
C =» fiber concentration (MFL)
Mf = mean mass per fiber (ug)
To calculate Mf use the following formula.
Mf - 1 MVn (4)
where: M^= mass of each fiber, respectively
n = number of fibers counted
25
-------
NOTE 1: Because many of the amphibole fibers are
lath shaped rather than square in cross section the
computed mass will tend to be high because laths
will, in general, tend to lie flat rather than on
edge.
NOTE 2: Assume the following densities: chryso-
tile 2.5, amphibole 3.25.
9.3 Aspect Ratio
The aspect ratio for each fiber is calculated by
dividing the length by the width.
10. Reporting
10.1 Report the following concentration as MFL for
sample and blank using 95% confidence intervals.
a. Chrysotile
b. Amphibole
c. Total asbestos fibers
10.2 Use two significant figures for concentrations
greater than 1 MFL, and one significant figure for
concentrations less ihan 1 MFL.
10.3 Tabulate the size distribution, length and width.
10.4 Tabulate the aspect ratio distribution.
10.5 Report the calculated mass as ug/1.
10.6 Indicate the detection limit in MFL.
10.7 Indicate if less than five fibers were counted.
10.8 Include remarks concerning pertinent observations,
(clumping, amount of organic matter,, debris) amount
of suspected though not identifiable as asbestos
fibers (ambiguous).
11. Precision
11.1 Intra-Laboratory
The precision that is obtained within an individual
laboratory is dependent upon the number of fibers
counted. If 100 fibers are counted and the loading
26
-------
is at least 3.5 fibers/grid square, -computer
modeling of the counting procedure shows that a
relative standard deviation of about 10% can be
expected.
In actual practice some degradation from this
precision will be observed but should not exceed ^
15% if several grids a-'e prepared from the same
filtered sample. The relative standard deviation
of analyses of the same water sample in the same
laboratory will increase as a result of sample
preparation errors and a relative standard devia-
tion of about about + 25 to 35% will occur. As the
number of fibers counted decreases, the precision
will also decrease approximately proportional to /N
where N is the number of fibers counted. The
precision for mass concentration is generally
poorer than that for fiber concentration.
Based upon the analysis of one laboratory utilizing
a different analyst for each of three water
samples, intra-laboratory precision data are
presented in Table 1.
11.2 Inter-Laboratory
Based upon the analysis by various government and
private industry laboratories cf filters prepared
from nine water samples, inter-laboratory precision
data of the method are presented in Table ^.
12. Accuracy
12.1 Fiber Concentrations
As no standard reference materials are available,
only aoproximate estimates of the accuracy of the
procedure can be made. At 1 M?L, it is estimated
that the results should be within a factor of 10 of
the actual asbestos fiber content.
This method requires the positive identification of
a fiber to be asbestos as a means for its quantita-
tive determination. As the state-of-the-art
precludes the positive identification of all of the
asbestos fibers present, the results of this
method, as expressed as MFL, will be biased on the
low side and, assuming no fiber loss, ^represent 0.4
to 0.8 of the total asbestos fibers present.
27
-------
TABLE 1. INTRA-LABORATORY PRECISION
NJ
CO
Sample Number of Mean Fiber Precision, Mass Precision,
Type Sample Concentration Relative Concentration Relative
Aliquots MFL (millions of Standard (py/1) Standard
Analyzed asbestos fibers/1) Deviation Deviation
Chrysotile
(UICC)
Crocidolite
(UICC)
Taconite
(raw water)
26 23
2C 8
2U 16
37%
36%
24%
0.32 71%
1.5 48%
10.5 65%
TABLE 2. INTER-LABOPATORY PRECISION
Sample Number of
Type Labs
Reportiny
Chrysotile 1C
9
11
9
9
3
Amphibole 11
4
14
Mean Fiber
Concentration,
MFL (millions of
asbestos fibers/1)
877
119
59
31
28
25
139
95
36
Precision,
Relative
Standard
Deviation
35%
43%
41%
65%
32%
35%
50%
52%
66%
-------
12.2 Mass Concentrations
As in the case of the fiber cone^ntirat ions, no
standard samples of the size distribution found in
water are available. The estimated mass concentra-
tion is oft^n very inaccur~.-~ because or pc-cr
counting statistics assoo^ai-ed with larce r.bers
that are few in number out represent most or the
actual mass concentration.
13. Suggested Statistical Evaluation of Grid Fiber Counts
13.1 Because the fiber distribution on the sample
filter, resulting from the method of filtration,
has not been fully characterized, the fiber distri-
bution obtained on the electron microscope grids
for each sample should be tested statistically
against an assumed distribution and a measure of
the precision of the analysis should be provided.
13.2 Assume that the fibers are uniformly and randomly
distributed on the sample filter and grids. One
method for confirming this assumption is given
below.
Using the chi-square test, determine whether the
total number of fibers found in individual grid
openings are randomly and uniformly distributed
among the openings using the following formula.
(n.-np.)
(5)
np^
where: X = Chi-square statistic
N = Number of grid openings examined for
the sample
n- = Total number of fibers found in each
respective grid opening
n = Total number of fibers found in N grid
openings
p- = Ratio of the area of each respective
grid opening to the sum of the areas
of all grid openings examined
29
-------
13.3
NOTE: If an average area for the gri^ squares has
been measured as outlined in 8.4.5, the tarm np^
represents the mean fiber count per grid square.
If the value for X2 exceeds the value listed in
statistical tables for the 0.1% significance level
with N-l degrees of freedom, the fibers are not
considered to be uniformly and randomly distributed
among the grid openings. In this case, it is
advisable to try to improve the uniformity of fiber
deposition by filtering another aliquot of the
sampla and repeating the analysis.
If uniformity and randomness of fiber deposition on
the microscope grids has been demonstrated as in
13.2, and the fiber concentration is assumed to be
normally distributed aocut the mean value, the 95%
confidence interval about the mean fiber concentra-
tions for chrysotile, amphibole, and total asbestos
fibers may be determined using the following
formulae.
s '
N
N I
N(N-l)
1/2
[6)
where: SG = Standard deviation of the chrysotile
fiber count
N = Number of grid openings examined for
the sample
X^ = Number of chrysotile fibers in each
grid opening, respectively
Obtain the standard deviations of the fiber counts
for amphibole asbestos fibers and for total
asbestos fibers by substituting the corresponding
value of X into equation (6).
X = X +
u
tS
7)
- tSc
X— V —
— ~~ f\ __
L /N
(8)
30
-------
where: Xu = Upper value of 95% confidence interval
for chrysotile
XL = Lower value of 95% confidence interval
for chrysotile
X = Average number of fibers per grid
opening
t = Value listed in t-distribution tables
at the 95% confidence level for a two
tailed distribution with N-l degree of
freedom
Sc - Standard deviation of the fiber counts
for chrysotile
N = Number of grid openings examined for
the sample
The values of Xu and XT can be converted to concen-
trations in millions of fibers per liter using the
formula in section 9 and substituting either Xu or
XL for the term F.
Obtain the upper and lower values of the 95% confi-
dence interval for amphibole asbestos fibers and
total asbestos fibers by substituting the corres-
ponding values of X and S into equations (7) and
(8).
Report the precision of the analysis, in terms r>f
the upper and lower limits of the 95% confidence
interval, for chrysotile, amphibole, and total
asbestos fiber content. If a lower limit is found
to be negative, report the value of the limit as
zero.
31
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SELECTED BIBLIOGRAPHY
' «^
Beaman, D. R. and D. M. File. Quantitative Determination of
Asbestos Fiber Concentrations. Anal. Cnem. 48(1): 101-110,
1976.
Lishka, R. J., J. R. Millette, and E. F. McFarren. Asbestos
Analysis by Electron Microscope. Proc. AWWA Water Quality
Tech. Conf. American Water Works Assoc./ Denver, Colorado
XIV-1 - XIV-12, 1975.
Millette. J. R. and E. F. McFarren. EDS of Waterborne
Asbestos Fibers in TE.M, SEM and STEM. Scanning Electron
Microscopy/1976 (Part III) 451-460, 1976.
Cook, P. M., I. B. Rubin, C. J. Maggiore, and W. J.
Nicholson. X-ray Diffraction and Electron Beam Analysis of
Asbestiform Minerals in Lake Superior Waters. Proc. Inter.
Conf. on Environ. Sensing and Assessment 34(2): 1-9, 1976.
McCrone, W. C. and I. M. Stewart. Asbestos. Amer. Lab. 6(4):
10-18, 1974.
Mueller, P. K., A. E. Alcocer, R. L. Stanley, and G. R.
Smith. Asbestos Fiber Atlas. U.S. Environmental Protection
Agency, Research Triangle Park, North Carolina, Technology
Series, EPA 65U/2-75-036, 1975.
Glass, R. W. Improved Methodology for Determination of
Asbestos as a Water Pollutant. Ontario Research Foundation
Report, April 30, 1976, Mississauga, Ontario, Canada.
Saroudra, A. V. Optimum Procedure for Asbestos Fibers Identi-
fication from Selection Area Electron Diffraction Patterns in
a Modern Analytical Electron Microscope Using Tilted Speci-
mens. Scanning Electron Microscopy, Vol. I, proceedings of
the Workshop on Analytical Electron Microscopy, March, 1977.
Chicago, Illinois.
Chatfield, E. J., R. W. Glass, and M. J. Dillon. Preparation
of Water Samplss for Asbestos Fiber Counting by Electron
Microscopy. U.S. Environmental Protection Agency, Athens,
Georgia. EPA-600/4-78-011, January 1978.
32
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Asher, I. M. and, P. P. McGrath. Symposium on Electron
Microscopy of Microf iberi,. Proceedings of the First PDA
Office of Science Summer Symposium, August 1976. Pennsylvania
State University.
Chopra, K. S. "Interlaboratory Measurements of Amphibole and
Chrysotile Fiber Concentrations in Water." Journal of Testing
and Evaluation, JTEVA, Vol. 6, No. 4, July 1978, pp. 241-247.
Chatfield, E. J. Preparation and Analysis of Particulate
Samples by Electron Microscopy, with Special Reference to
Asbestos. Scanning Electron Microscopy, April 16-20, 1979,
Washington, DC.
National Bureau of Standards Special Publication 506.
Proceedings of the Workshop on Asbestos: Definitions and
Measurement Methods held at NBS, Gaitnersbarg, MD, July 18-20,
1977. (Issued March 1978).
33
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