EPA-650/2-75-004
JANUARY 1975
Environmental Protection Technology Series
I
55
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al
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RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development, U.S. Environ-
mental Protection Agency, have been grouped into series. These broad
categories were established to facilitate further development and applica-
tion of environmental technology. Elimination of traditional grouping was
consciously planned to foster technology transfer and maximum interface
in related fields. These scries arc.
1. ENVIRONMENTAL HEALTH EFFECTS RESEARCH
2. ENVIRONMENTAL PROTECTION TECHNOLOGY
3. ECOLOGICAL RESEARCH
4. ENVIRONMENTAL MONITORING
5. SOC1OECONOMIC ENVIRONMENTAL STUDIES
6. SCIENTIFIC AND TECHNICAL ASSESSMENT REPORTS
9. MISCELLANEOUS
This report has been asbigned to thu ENVIRONMENTAL PRO'i ECT1ON
TECHNOLOGY series. This series describes research performed to
develop and demonstrate instrumentation, equipment and mc-thodology
to repair or prevent environmental degradation from point and non-
point sources of pollution. This work provides the new or improved
technology required for the control and treatment of pollution sources
to meet environmental quality standards.
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EPA-650/2-75-004
QUANTITATIVE ANALYSIS
OF AIRBORNE ASBESTOS
BY X-RAY DIFFRACTION:
FINAL REPORT
ON FEASIBILITY STUDY
by
L. S. Birks, M. Fatemi,
J. V. Gilfnch, andE. T. Johnson
Naval Research Laboratory
Washington, D. C 20375
Interagency Agreement FPA-IAG-085(D)
ROAP No. 26AAN
Program Element No. 1AA010
EPA Project Officer: Dr. Jack Wagman
Chemistry and Physics Laboratory
National Environmental Research Center
Research Triangle Park, North Carolina 2Y711
Prepared for
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
WASHINGTON, D.C. 20460
January 1975
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EPA REVIEW NOTICE
This report has been reviewed by the National Environmental Research
Center - Research Triangle Park, Office of Research and Development,
EPA, and approved for publication. Approval does not signify that the
contents necessarily reflect the views and policies of the Environmental
Protection Agency , nor does mention of trade names or commercial
products constitute endorsement or recommendation for use.
This document is available to the public for sale through the National
Technical Information Service, Springfield, Virginia 2Z161.
11
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CONTENTS
Abstract. iv
Problem Status iv
Authorization iv
INTRODUCTION 1
SPECIAL X-RAY DIFFRACTION GEOMETRY 2
SPECIMEN PREPARATION 5
RESULTS 8
DISCUSSION 9
REFERENCES 10
APPENDIX 11
FIGURES
1. (a) X-ray diffraction pattern from
randomly oriented asbestos fibers 2
(b) Diffraction pattern from a
bundle with preferred orientation 2
2. Morphology of chrysotile asbestos 3
3. Standard diffractometer geometry 3
4. Special x-ray optics for quantitative
measurement of aligned asbestos fibers 4
5. Backlighted macrograph of asbestos sample .... 5
6. Experimental arrangement of the
ultrasonic "cell disrupter" 6
7. Special multielectrode grid used in the
alignment of asbestos fibers 7
8. Photomicrograph of aligned asbestos sample ... 7
iii
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ABSTRACT
Special x-ray diffraction geometry has been developed to
distinguish chrysotile asbestos from serpentine and other clay
minerals. The x-ray method requires alignment of the chrysotile
fibers, and the technique for accomplishing this alignment has been
developed and tested. A limit of detection of 0.2 fig asbestos has
been achieved routinely for chrysotile in the absence of extraneous
material from real air samples.
PROBLEM STATUS
This report is the final report by the X-Ray Optics Branch on
the feasibility study of quantitative analysis of airborne asbestos.
AUTHORIZATION
NRL Problem P04-06
EPA-NRL Interagency Agreement No. EPA-IAG-085 (D)
This report has been reviewed by the Environmental Protection
Agency and approved for publication. Approval does not signify
that the contents necessarily reflect the views and policies of the
Agency, nor does mention of trade names or commercial products
constitute endorsement or recommendation for use.
IV
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Quantitative Analysis of Airborne Asbestos
by X-Ray Diffraction:
Final Report on Feasibility Study
INTRODUCTION
The purpose of this report is to introduce a novel x-ray diffrac-
tion technique for the measurement of airborne asbestos. It has
been recognized for some time that the determination of pollutant
levels of asbestos by conventional x-ray diffraction is impractical
for two primary reasons: 1.) The x-ray diffraction pattern of
chrysotile (which comprises nearly 90% of all asbestos used world-
wide) is almost identical to a number of clay minerals of similar
chemical composition; 2.) at the concentration levels of interest the
x-ray diffraction lines of asbestos are relatively weak and they
occur in the presence of a very large background.
As is the case for all fibrous materials, the intensity of a specific
diffraction peak of chrysotile or amphibole asbestos is enhanced if the
fibers are aligned parallel to each other. Further, if the aligned
fibers can be mounted on a suitably thin (low mass) substrate, the
background (due to scattering of the incident x-ray beam) can be
minimized. In order to investigate the applicability of the x-ray dif-
fraction principle to the asbestos problem, a feasibility study was
conducted which addressed the following questions:
1.) Can a scheme be devised for aligning small quantities of
standard chrysotile fibers and mounting them on a low-mass
substrate?
2.) Can a special x-ray diffraction geometry be developed which
would be optimized for measuring these aligned fibers quantitatively?
Both parts of the task have been accomplished successfully for
laboratory samples, of chrysotile. The 3a limit of detection for
chrysotile standards is 0.2 fig,for ten-minute measurements. Thus,
the method appears feasible and ready for further development into
a practical tool for quantitative analysis of source or ambient air
s ample s.
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SPECIAL X-RAY DIFFRACTION GEOMETRY
Chrysotile asbestos, like all crystals, has a characteristic x-ray
diffraction pattern. However, platy serpentine has almost exactly the
same x-ray pattern as chrysotile and many other clay minerals have
very similar patterns. Therefore, preferred orientation of the
chrysotile fibers offers the only hope of distinguishing chrysotile
uniquely. Figures la and Ib show x-ray patterns from random orien-
tation and preferred orientation, respectively. In a mixed sample of
platy serpentine and chrysotile, the serpentine rings would be super-
posed on the chrysotile arcs. The net intensity due to chrysotile is
obtained by measuring the intensity at the arc position (A in Figure 1),
and subtracting the intensity of the ring at 90° to the arc, position B.
This simple principle forms the basis for the method developed at the
Naval Research Laboratory. But several factors make the problem
difficult as will be described in the following paragraphs.
I <*»' I
(a) (b)
Figure 1. X-ray diffraction patterns (a) from randomly
oriented asbestos fibers and (b) from a bundle with
preferred orientation.
The first factor which makes measurement of asbestos difficult
is that the quantity which can be collected from a reasonable amount
of air is far too small to measure with x-ray film cameras. There-
fore, diffractometers with electronic detectors are required, but this
introduces a second difficulty because of the peculiar morphology of
chrysotile. This morphology, which is that of a "rolled up" sheet of
crystalline matter, is shown schematically in Figure Z. The a-axis
of the monoclinic structure is parallel to the fiber axis; the c-axis is
nearly perpendicular to the tube wall. Thus the axes b and c take
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Figure 2. Morphology of chrysotile asbestos.
Ot= y = 90°, 0 = 93° 16'.
different orientations depending on where on the fiber they are set up.
This means that standard diffractometer geometry cannot be used even
with an oriented sample because the major crystal plane, (002), dif-
fracts equally well for either orientation; see Figure 3. Therefore a
special geometry was developed specifically for asbestos.
detector
Figure 3. Standard diffractometer geometry. Diffraction from
(002) planes is possible for air fiber rotations (where the axis of
rotation is in the diffraction plane and perpendicular to fiber axis).
3
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The geometry employed is shown schematically in Figure 4. Be-
cause of the manner in which the alignment is accomplished (described
in the following section), the sample of asbestos is distributed over a
circular area of about 1 cm diameter (as shown in Figure 5). In order
to achieve diffraction from the entire sample, resulting in the highest
signal, a large-cross-sectional-area x-ray beam is required^1) in
order to maintain good resolution, fine collimation is required. Fig-
ure 4 illustrates the use of a tubular-collimated broad x-ray beam
from a spectrographic x-ray tube rather than a diffraction tube. The
sample is mounted perpendicular to the x-ray beam to give an
oriented pattern conceptually similar to Figure Ib. Using a chromium
target x-ray tube the 28 value for diffraction from (002) planes,
2d = 14.6 A, is 18°. By placing detectors at the two positions shown
in Figure 4, the signal and background intensities are recorded sim-
ultaneously. During this feasibility study only one detector was
available, so the signal and background were measured sequentially
by rotating the sample 90° in its own plane between readings.
detector
detector I
aligned fibers
collimator
x-ray tube
Figure 4. Special x-ray optics for quantitative measurement of
aligned asbestos fibers.
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Figure 5. Backlighted macrograph of asbestos sample showing the
distribution of aligned fibers on the multielectrode
alignment grid; 3 X magnification.
SPECIMEN PREPARATION
Electrostatic alignment of asbestos fibers appeared to be the most
obvious approach and had been suggested by an early patent. (2) This
patent, however, concerned itself with bulk alignment of relatively
large quantities of fibers in a liquid dielectric medium. For the
small amounts of asbestos to be measured by the x-ray technique, the
procedure described in reference 2 did not succeed in aligning the
fibers completely enough to achieve optimum x-ray sensitivity nor was
it possible to recover the specimen quantitatively from the alignment
medium.
A significantly different alignment procedure (described below) was
employed to produce a sample which was directly suitable for the x-ray
measurements. Initial attempts did not accomplish adequate align-
ment, however, because of the "silky" nature of the chrysotile fibers.
Breaking these "silky" fibers into straight fibrils was necessary if the
full potential of the x-ray technique was to be realized. Ordinary
ultrasonic cleaners were unsatisfactory, but the "cell disrupter" type,
illustrated in Figure 6, succeeded in reducing the fiber size sufficiently.
Without going into detail on the numerous variations in sample pre-
paration which were tried, the following procedure has been adopted
and used successfully for orienting chrysotile standards:
Step 1. 3.0 mg of UICC standard Canadian chrysotile is placed in
1/2 ml of 1% aerosol OT solution in water. (The OT is necessary as a
dispersing agent. ) The suspension is sonicated for 45 minutes at
100 watts power using the cell disrupter as shown schematically in
Figure 6.
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I
1
sonic
'generator
^asbestos
"in liquid
Figure 6. Experimental arrangement of the ultrasonic
"cell disrupter" for reducing the size of the fibers.
Step 2. The sonicated suspension is diluted to 500 mljmaking the
asbestos concentration 6 jllg/ml.
Step 3. A 25 ml aliquot of the diluted suspension (containing 150
of asbestos) is vacuum filtered onto a 25-mm disk of millipore.
Step 4. The millipore disk is folded and placed in a test tube and
ashed for 2-1/2 hours in a low-temperature radio-frequency asher.
Step 5. 30 drops of a 0. 001% solution of parlodion in distilled
amyl acetate is added to the ashed residue, and the suspension is
sonicated for 8 minutes to insure homogeneous distribution of asbestos.
Step 6. One drop of the suspension containing 5 jig asbestos is
placed on a.special grid, Figure 7, and 240 volts AC is applied to the
electrodes (preparation of the grid is described in Appendix 1). It
takes about 5 minutes for the amyl acetate to evaporate (the voltage
is kept on the electrodes until evaporation is complete). Figure 5
shows the appearance of the dried sample,and Figure 8, at higher
magnification, shows the alignment of the chrysotile fibers.
Step 7. A solution of 2. 5% parlodion in amyl acetate is sprayed
gently onto the dried sample to embed the fibers in a thin plastic film
which can easily be removed by dipping the grid plate into water.
This film has a mass density of about 60 jig/cm^; the reason for
wanting a thin film is to minimize the background intensity contributed
by x-ray scattering from the film.
6
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Figure 7. Special multielectrode grid used in the alignment of
asbestos fibers. Inter electrode distance is approximately
0. 8 mm.
Figure 8. Photomicrograph of aligned asbestos sample;
500 X magnification.
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RESULTS
Seven inexperienced test subjects were selected to try out the
alignment procedure as described above. Their results are shown
in Table I.
TABLE I. MEASUREMENTS OF ASBESTOS STANDARDS
Analyst
1
2
3
4
5
6
7
Quantity
of Asbestos
per sample
(Mg)
4.89
4.38
4.75
4.75
4.32
4.75
4.75
Average
Relative
Signal
Above
Background
(c/s)
32.9
27.9
21.5
30.3
23.3
19.6
30.7
32.9
33.3
21.4
21.0
24.7
25.9
24.5
25.6
28.4
28.5
27.9
32.9
31.4
31.2
23. 1
28.2
24.4
Background
(c/s)
48.3
63.0
55.0
55.5
44.5
51.7
36.9
54.5
50.3
39.5
33.8
46.7
54.4
48.0
35.8
33.4
28.4
35.2
35.4
31.9
36.4
45.0
67.5
59.1
Standard Deviation =
Sensitivity
S
(c/a/jlg)
6.8
5.7
4.4
6.2
5.3
4.5
7.0
6.9
7.0
4.5
4.4
5.2
5.4
5.2
5.9
6.6
6.6
6.5
6.9
6.6
6.6
7.0
5.9
5.1
5.9
16%
•*»
0*g)
0. 14
0.18
0.22
0.16
0. 17
0.22
0. 12
0. 14
0.14
0.19
0. 18
0. 18
0. 18
0. 18
0. 13
0. 12
0.11
0. 12
0. 11
0.11
0. 12
0.13
0. 19
0.20
0. 16
"Limit of Detection, CT , from the Formula
j-i
CT = S/N^/tS X Time),
J-i D
where NR is the background over the counting interval,
which conforms to the definition recommended by IUPAC.
In this table, CT is calculated for a 500-second counting interval.
L
8
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DISCUSSION
The feasibility study has demonstrated that chrysotile asbestos
can be aligned reproducibly and measured by x-ray diffraction. The
sensitivity of the x-ray method is sufficient to give a limit of detection
of 0.2 fig for 500 sec counting time; it is estimated that this figure
may degrade to 0.4 or 0. 5 fig for samples containing extraneous
material.
The number of samples which can be analyzed in an eight-hour day
using the special x-ray instrument depends primarily on the x-ray
counting time. The total time per sample can be estimated by adding
two minutes to the nine minutes counting time to record data and
change the sample. This 11 minutes per sample would correspond to
44 samples in an eight-hour day.
It is germane, at this point, to estimate the costs and manpower
necessary for a complete asbestos analysis laboratory. The prototype
research instrument which is to be developed at NRL will be designed
for the purpose of measuring individual asbestos samples and there-
fore will require the attention of the operating analyst; in a routine
analytical laboratory, the procedure obviously should be automated.
This would require modification of the prototype or perhaps fabrication
of a second-generation instrument designed specifically for automatic
operation. Assuming that forty samples per day is a reasonable work
load for an automatic instrument, a two-per son staff, both involved in
all stages of sample preparation, should be adequate. At a labor and
overhead cost of 200 dollars per day per staff member, the cost per
sample would reduce to ten dollars. Sample preparation equipment
(asher, filtration bands, sonicator, etc.) may have to be duplicated in
order to avoid queuing delays.
The specific nature of the laboratory procedure will depend some-
what on the type of sample being measured (from an asbestos source
or from ambient air). We assume at this time that all the critical
questions regarding sample preparation have been resolved. "Source"
samples will have a high ratio of asbestos to extraneous material
(perhaps 1:1 to 1:10), while ambient air samples will have a smaller
ratio (1:100 to 1:1000). La the former the removal of the extraneous
material should not be as important as in the latter. On the other
hand, "source" samples may contain a larger population of long,
silky fibers which require longer sonication time before alignment;
ambient air samples are less likely to contain these long fibers and
long sonication can be avoided.
There are several uncertainties which must be investigated if the
advantages of the x-ray method in speed and economy are to be ex-
ploited: First, the extraneous pollutant material which will be present
in real air samples will affect the limit of detection because it will
increase the scattered background signal. Second, the extraneous
material may or may not affect the alignment of asbestos fibers or the
9
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concentration of parlodion in the amyl acetate used as the alignment
medium (preliminary tests indicate that alignment may be sensitive to
parlodion concentration). Other effects, unknown at present, may
have to be considered.
The next stage in the research program will be to collect partic-
ulate pollution from real air samples and spike it with known amounts
of asbestos. These samples will be processed by the method devel-
oped in the feasibility study; variations in sample preparation may. be
required to achieve alignment of chrysotile in the presence of the
extraneous material. Finally, unspiked air samples will be analyzed
and the results compared with, electron microscope measurements of
the same samples.
It seems obvious that the x-ray method is applicable to asbestos
in water as well as in air and to other forms of asbestos such as
amphiboles; it should also be applicable to asbestos in food stuffs
or other organic material which can be removed by ashing.
REFERENCES
(1) L. S. Birks and M. Fatemi, Parallel-Beam X-Ray Optics for Measuring Asbestos, NRL
Patent-Disclosure Docket #8949, July 1974.
(2) A. A. Winer and H. M. Woodrooffe, U. S. Patent No. 3,497,419, Feb. 1970.
(3) M. Fatemi anti L. S. Birks, Multielectrode Apparatus and Technique to Prepare
Aligned Asbestos Fibers on a Thin Substrate, NRL Patent-Disclosure Docket #8948,
July 1974.
10
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APPENDIX 1
Fiber alignment was accomplished by the use of a special multi-
electrode grid. (3) Several considerations were important in the
design of this device:
1. ) The required electrostatic field for asbestos alignment in the
medium ranges from 3000 to 5000 volts/cm.
a
Z. ) Because of the need to align the fibers in the plane of the sub-
strate, it was necessary to incorporate thin (low profile) electrodes
which would permit the liquid dielectric medium to spread freely over
the surface. Initially a single pair of electrodes were used, about one
centimeter apart. Such an arrangement causes a large population of
fiber to align adjacent to the electrodes with virtually no asbestos in
the center of the field. This observation led to the final configuration
as shown in Figure 7. The relatively short distance between electrodes
has the advantage of lower applied voltage, improving operational
safety.
Fabrication procedure for these alignment grids is a standard
technique used in microelectronics:
1. ) A "master" is prepared ten times as large as the desired
product and photoreduced on a quartz flat.
2. ) Quartz discs with a 1200-A layer of evaporated chromium are
obtained either commercially or from a vacuum evaporation facility.
Quartz is desirable because it cleans better than glass and vacuum
deposition is more suitable than sputtering due to its more gentle
treatment.
3.) The disks are sprayed with photoresist and baked.
4. ) The original is placed in contact with the photoresist and
exposed to ultraviolet light.
5.) The exposed disk is "developed" to remove the unexposed
photoresist.
6.) The exposed chromium is etched away.
7.) The photoresist is dissolved and the grid is washed, dried^and
inspected for continuity.
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1 REPORT NO.
EPA-650/2-75-004
2.
3. RECIPIENT'S ACCESSION NO.
4. TITLE AND SUBTITLE
Quantitative Analysis of Airborne Asbestos by X-ray
Diffraction: Final Report on Feasibility Study
5 REPORT DATE
January 1975
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
L.S. Birks, M.Fatemi, J.V. Gilfrich,
E.T. Johnson
8. PERFORMING ORGANIZATION REPORT NO.
NRL Report 7874
10. PROGRAM ELEMENT NO.
1AA010 (26AAN-010)
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Naval Research Laboratory
Washington, D. C. 20375
11. CONTRACT/GRANT NO.
EPA-IAG-085(D)
12. SPONSORING AGENCY NAME AND ADDRESS
Office of Research and Development
U.S. Environmental Protection Agency
Washington, D. C. 20460
13. TYPE OF REPORT AND PERIOD COVERED
Final - 2 vrs.ending 10/74
14. SPONSORING AGENCY CODE
IS. SUPPLEMENTARY NOTES
16. ABSTRACT
Special x-ray diffraction geometry has been developed to distinguish chrysotile
asbestos from serpentine and other clay minerals. The x-ray method requires
alignment of the chrysotile fibers, and the technique for accomplishing this
alignment has been developed and tested. A limit of detection of 0.2 yg asbestos
has been achieved routinely for chrysotile in the absence of extraneous material
from real air samples.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS
c. COSATI Field/Group
Asbestos
Serpentine
Airborne wastes
Air pollution
X-ray diffraction
Alignment
Quantitative analysis
Chrysotile
18 DISTRIBUTION STATEMENT
Release unlimited
19. SECURITY CLASS (This Report)
Unclassified
21. NO. OF PAGES
20
20 SECURITY CLASS (This page)
Unclassified
22. PRICE
EPA Form 2220-1 (9-73)
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