RESEARCH REPORT
DEVELOPMENT OF A RAPID SURVEY METHOD
OF SAMPLING AND ANALYSIS FOR
ASBESTOS IN AMBIENT AIR
FINAL REPORT
Covering the Period
June 1969 through July 1971
Contract No. CPA 22-69-110
OBatteiie
Columbus Laboratories
-------
I-~--~~--~
1- -----
---
---- ._._~-
----~-_._- ._...-- -
BA TTELLE'S COLUMBUS LABORA TORI ES comprises the origi-
nal research center of an international organization devoted to research
and development.
Battelle is frequently described as a "bridge" between science and
industry - a role it has performed in more than 90 countries. It
conducts research encompassing virtually all facets of science and its
application. It also undertakes programs in fundamental research and
education.
Battelle-Columbus - with its staff of 2500 - serves industry and
government through contract research. It pursues:
. research embracing the physical and I ife sciences, engi-
neering, and selected social sciences
. design and development of materials, products, processes,
and systems
. information analysis, socioeconomic and technical eco-
nomic studies, and management planning research.
505 KING AVENUE. COLUMBUS, OHIO 43201
~-- --- -- -
--------l
-------
DEVELOPMENT OF A RAPID SURVEY METHOD
OF SAMPLING AND ANALYSIS FOR
ASBESTOS IN AMBIENT AIR
FINAL REPORT
Covering the Period
June 1969 through July 1971
Contract No. CPA 22-69-110
Prepared for: Environmental Protection Agency
Division of Atmospheric Surveillance
Project Director: W. M. Henry
Author: R. E. Heffelfinger
C. W. Melton
D. L. Kiefer
February 29, 1972
BATTELLE
Columbus Laboratories
505 King A venue
Columbus, Ohio 43201
-------
() BaUelle
Columbus Laboratories
505 King Avenue
Columbus, Ohio 43201
Telephone (614) 299-3151
Telex 24-5454
February 29,1972
Dr. Richard J. Thompson
Air Quality Analytical Laboratory Branch
Division of Atmospheric Surveillance
Environmental Protection Agency
Research Triangle Park, North Carolina 27711
Dear Dr. Thompson:
Ref. Contract CPA 22-69-110
Enclosed are twenty-five copies, including a reproducible master, of the Final Report on the above
contract titled "Development of a Rapid Survey Method of Sampling and Analysis for Asbestos in
Ambient Air". One copy of the Final Report has been forwarded to the Contracting Officer.
This Final Report, as required in the revised report schedule, is specified in the supplemental agreement
dated November 6, 1971.
As nearly as possible, the changes as suggested by you have been incorporated in this final draft revision.
The rough-draft copies were approved by you, subject to the revisions, by letter of January 21, 1972.
Very truly yours,
{t~,&/:¥-r-
Associate Chief
Environmental and Materials
Characterization Division
REH :ng
Ene. (24 plus 1 reproducible)
cc: Vincent E. Mason
Contracting Officer
Durham Contract Operations
Attention: Mail Stop DCO-S
Research Triangle Park, North Carolina
27711
-------
MANAGEMENT SUMMARY
Contract CPA 22-69-110
"Development of Rapid Survey of Sampling and Analysis for Asbestos in Ambient Air".
Objective of Research Program
This program was initiated to develop a technique for determining total amounts of asbestos,
including fibrils, in ambient air and to provide quantification of the concentrations of asbestos in various
types of urban and rural air.
Significance of Research Results
The research results show that by the use of separation and enrichment techniques the total
asbestos fibers and fibrils collected from ambient air can be identified and quantified using transmission
electron microscopy. This is highly significant from a health point of view since prior art did not
provide data on the smaller and more respirable fibers to which large portions of the population might
be unwittingly exposed.
The air-analysis results indicate that asbestos concentration in ambient air may range from a few
hundreths nanograms per cubic meter in remote areas to a few thousand nanograms per cubic meter
near point sources.
How Sponsor Can Use Results
The Environmental Protection Agency will be able to use the techniques developed to study the
concentration, sources, range, and persistence of total asbestos as an air pollutant. Such data will provide
a firm basis, not now available, for epidemiological investigations and for better criteria and standards
related to asbestos contamination in the atmosphere.
Future Effort
Additional research effort is outlined that will provide a more rapid and more automatic means for
the analysis of air for asbestos. Also, more research effort is needed to provide particle-size-frequency
information. However, the methodology as developed now can be used on collected samples to obtain
additional data needed to set criteria standards.
-------
ABSTRACT
A methodology has been developed for the determination of ashes to fiber and fibril content of
particulate samples collected from air.
This report describes the effort on development of the analytical method and gives details of the
method which includes sampling, beneficiation of asbestos fiber and fibril, and determination of total
asbestos by a transmission electron microscopic technique.
Included in the report are results of analyses of samples collected near a point source, in urban
ambient air, and in a remote rural site.
iii
-------
TABLE OF CONTENTS
MANAGEMENT SUMMARY
.. . . . . .
. . . .
. . . . .
. . . .
. . . .
ABSTRACT
. . . . .
. . . . . .
. . . . . .
. . . .
. . . . .
SUMMARY AND RECOMMENDATIONS
. . . . .
. . . . .
. . . .
. . . . .
INTRODUCTION
. . . . . .
. . . .
. . . . .
. . . . . .
OBJECTIVE. . . . . .
. . . .
. . . . .
. . . . . . . .
Previous Work by Battelle. . . .
. . . .
. . . . . .
. . . .
. . . . .
EXPERlMENT AL WORK.
. . . . .
. . . .
. . . . . .
. . . .
. . . . .
Raw Materials. . . . . . . . . . . . .
Detection and Identification of Asbestos Fiber and Fibril . . . . . . . . .
Electron Microprobe Studies. . . . . . . . . . . . . . . . .
Scanning Electron Microscopy Studies. . . . . . . . . . . . . . . .
Transmission Electron Microscopy. . . . . . . . . . . . . . . . . .
Light Microscopy. . . . . . . . . . . . . .
Sampling. . . . . . . . . . . . . . . . . . . . . . . . . . . .
Cascade Impactor. . . . . . . . . . . . . . . . . . . . . . .
All-Glass Liquid Impinger. . . . . . . . . . . . . . . . . . . . .
Membrane Filters . . . . . . . . . . . . . . . . . . . .
Beneficiation. . . . . . . . . . . . . . . . . . . . . . . .
Low-Temperature Ashing of Collected Sample. . . . . . . . . . . . . .
Ultrasonification. . . . . . . . . . . . . . . . . .
Centrifugation. . . . . . . . . . . . . . . . . . . . . . . .
Beneficiation Summary. . . . . ... . . . . . . . . . . . . . .
Quantification . . . . . . . . . . . . . . . . . . . . . . .
Standards. . . . . . . . . . . . . . . . . . . . . . . . . .
RESULTS. . . . .
. . . . . . . . . . . .
. . . . .
. . . . .
Description of the Methodology for the Analysis of Asbestos in Air . . . . . . . . .
A. Sampling. . . . . . . . . . . . . . . . . . .
B. Sample Preparation. . . . . . . . . . . . . . . . . . . . . .
C. Preparation of Specimen for Electron Microscopy. . . . . . . . . . . .
D. Examination of Specimen in the Electron Microscope. . . . . . .
E. Preparation of Standards. . . . . . . . . . . . . .
F. Analysis of Microscope Data. . . . . . . . . . . . . . . . . . .
Reliability of the Method. . . . . . . . . . . . . . . . . . . . . . .
Comparison of Results From the Method and Neutron-Activation Analyses. . . .
Radioassay. . . . . . . . . . . . . . . . . . . . . . . .
Radioassays and Results. . . . . . . . . . . . . . . . . . . . .
Replication. . . . . . . . . . . . . . . . . . . . . . . . . .
Particle Size/Frequency Measurements. . . . . . . . . . . . . . . . . .
Data From Various Sites. . . . . . . . . . . . . . . . . . . . . . .
DISCUSSION AND CONCLUSIONS
. . . . .
. . . .
. . . . .
. . . .
FUTURE WORK. . . . . . . . .
. . . . .
.. .. .. ..
. .. .. .. .. ..
.. .. . ..
v
Page
iii
2
2
3
3
3
3
4
4
5
5
5
6
6
6
6
9
9
9
11
11
11
13
13
13
13
14
14
15
15
15
15
15
17
17
18
13
23
28
-------
TABLE OF CONTENTS
(Continued)
APPENDIX A. STUDIES OF BENEFICIATION OF ASBESTOS BY DIFFERENCES
IN ELECTRICAL PROPERTIES AND DENSITY. . . . . . . . .
.. .. .. ..
Dielectric Separation. . . .. . . . . . .
Electrophoretic Batch Separations. . . . . . .
Continuous Particle Electrophoresis . . . . .
Density Separation of Asbestos From Other Materials
.. .. .. .. ..
.. .. .. .. .. ..
.. .. .. ..
.. .. .. .. .. ..
.. .. .. .. ..
.. .. .. .. .. ..
.. .. .. ..
UST OF TABLES
Table 1.
Asbestos Samples Examined in the Preliminary Study. . .
.. .. .. .. .. .. .. ..
Table 2.
Radioassay of Asbestos on Impactor Stages. . . . . . . . .
.. .. .. .. .. ..
Table 3.
Comparison of Results of Analysis of Asbestos on Impactor
Stages by Electron Microscopy and Radioassay. . . .
.. .. .. .. ..
.. .. .. .. ..
Table 4.
Replicate Results of Analyses of Selected Air Samples
.. .. .. .. .. .. .. ..
Table 5.
Analysis of Each Stage of Cascade-Impactor Samples Taken
at 1 and 2 Miles Downwind From a Point Source. . . .
.. .. .. .. .. .. .. .. ..
Table 6.
Size of Asbestos Particles Found on Stages 4, 5, and 6 of a
Cascade-Impactor Air Sampler. . . . . . . . . . . . . . . . . . .
Table 7.
Estimated Particle Number Found on Each Stage of the
Cascade-Impactor Sample Shown in Table 5. . . . .
.. .. .. .. .. .. .. .. .. ..
Table 8.
Analyses of Urban Samples Supplied by Sponsor Collected
on Reinforced Plastic Membrane Material. . . . ...
.. .. .. .. .. ..
.. .. .. ..
Table 9. . Analyses of Site Source Samples - Samples Collected by Sponsor at a
Position Downwind From a Site Source Near Cincinnati, Ohio. . . . . . . . .
Table 10. Analyses of Samples Collected From Nonurban - Remote
Site, Samples Collected Near Frankfort, Kentucky
.. .. .. .. .. ..
Table 11. Samples Collected by the Battelle Cascade-Impactor North (Downwind) From
Point Source Near Cincinnati, Ohio (February 16, 1971) . . . . . . . . . .
Table 12. Samples Collected for Preliminary Studies
.. .. .. .. ..
.. .. .. .. .. .. ..
Table 13. Vane-Pump Samples Supplied by Sponsor
.. .. .. ..
.. .. .. ..
.. .. .. .. .. .. ..
vi
Page
A-I
A-I
A-2
A-2
A-3
4
16
16
18
18
19
23
24
25
26
26
27
27
-------
Figure 1.
Figure 2.
Figure 3.
Figure 4.
Figure 5.
Figure 6.
Figure 7.
Figure 8.
LIST OF FIGURES
A Clump of Agglomerated Particles Partly Comprised of Asbestos (Chrysotile)
Asbestos Fibers Collected at Stage 5 of the Cascade Impactor. . . . . . . . .
Electron Micrograph of a Typical DepositiDn of Air Particulate From Filtered Air . .
Electron Micrograph of a Typical Deposition of Separated Fibrils. .
. . . . . .
Plot of Fiber Count per 200-Mesh Screen Opening Versus p.g Asbestos
Collected on Filter Disk. . . . . . . . . . . . . . .
. . . . . .
Electron Micrograph of Single Particle of Asbestos Collected on
Stage 4 of the Battelle Cascade Impactor. . . . . . . .
. . . . . . . .
Electron Micrograph of Single Particle of Asbestos Collected on
Stage 5 of the Battelle Cascade Impactor. . . . . . '.'
. . . . . . . .
Electron Micrograph of Single Particle of Asbestos Collected on
Stage 6 of the Battelle Cascade Impactor. . . . . . . .
. . . . . . . .
vii and viii
Page
7
7
8
10
12
20
21
22
-------
DEVELOPMENT OF A RAPID SURVEY METHOD OF SAMPLING
AND ANALYSIS FOR ASBESTOS IN AMBIENT AIR
by
R. E. Heffelfinger, C. W. Melton, D. L. Kiefer, and W. M. Henry
SUMMARY AND RECOMMENDA nONS
A methodology has been developed and demonstrated which is capable of determining total
amounts of asbestos fibers and fibrils in air ranging from as low as fractional nanograms per cubic meter
(ng/m3) of air to several micrograms/m3. The method involves the collection of samples on an absolute
mter and provides an unequivocal identification and quantification of the total asbestos contents
including fibrils in the collected samples.
The developed method depends on the trituration under controlled conditions to reduce the fibers
to fibrils, separation of the asbestos fibrils from other collected air particulates (beneficiation), and the
use of transmission microscopy for identification and quantification. Its validity has been tested by
comparative analyses by neutron activation techniques. It can supply the data needed to set emissions
criteria and to serve as a basis for assessing the potential hazard for asbestos pollution to the populace.
The key to the method is the nearly complete separation of the asbestos from other air particulate
matter and its uniform deposition on a microscope grid for observation and counting using an electron
microscope.
Analyses of about 70 sample collections show that asbestos concentrations of ambient air range
from a few tenths ng/m3 in remote areas to a few thousand ng/m3 near point sources.
The physiological process of inhalation and absorbance into body tissue is not well understood.
Both large and small asbestos bodies have been found in persons afflicted with asbestosis and meso-
themia. Perhaps the human body retains inhaled fibers intact or breaks them up, and thus their size may
be physiologically insignificant. It would be desirable, therefore, to examine also the particle size
distribution of asbestos (both fibers and fibrils) as it exists in the atmosphere. Experimental efforts do
show that asbestos fibers collected from ambient air by cascade impaction are present on all stages of
the impactor as agglomerates, fibers, and fibrils. While some estimates of particle size distribution are
made in this report, the estimates are from preliminary experiments. Generally, it has not been possible
to measure quantitatively the particle-size distribution of asbestos fiber agglomerates, fibers, and fibrils
in the airborne condition.
Further effort is needed to provide for more rapid analyses and effort should also be directed
toward continuous automatic monitoring. These efforts may include development of more rapid
sample-preparation techniques for the electron microscope as well as development of optical-microscopic
techniques, infrared techniques, and X-ray diffraction techniques. Each of these techniques would
require beneficiation of asbestos.
Certainly, further effort is needed to obtain more data on particle size distribution and number.
-------
2
INTRODUCTION
The relationship between ex!.osure to asbestos dust and lung health problems has been the subject
of much study and discussion(1, ,3), but no clear conclusions can be drawn, largely because of the lack
of an analytical method for the determination of total asbestos. To provide a background for definitive
epidemiological investigations concerned with pathology related to asbestos, and to set meaningful
emission criteria, knowledge of the total concentration, sources, range, and persistence of asbestos as an
air pollutant is required. To develop the capability for such a study, Battelle, working with Dr.
Richard J. Thompson of EPA, has devised a technique for sampling and analysis for total asbestos fiber
content including fibrils in particles collected from ambient air.
Prior to this study, the analytical technology for estimating the amount of asbestos fiber in air was
dependable only for fibers visible by optical microscopic techniques. That procedure was useful for
assessing the concentrations of asbestos in heavily loaded atmospheres such as are encountered by
workers in asbestos-product industries and by insulation workers. However, the presence of asbestos
fibrils (R:300 A in diameter) cannot be determined directly by such techniques. Fibrils are present in
ambient air, particularly near point sources. Because of their very small size these can and do remain
suspended in the atmosphere and are transported long distances. As evidence of this, there are
documented cases of asbestosis in persons having no known direct contact with industrial production or
use of asbestos products. Consequently, there was a great need for an analytical methodology for the
quantitative measurement of all forms and sizes of asbestos in ambient air.
The goal of this program was to develop such a methodology.
OBJECTIVE
The research objectives for this program as spelled out by Battelle's proposal and by the contract
scope are summarized as follows:
(1) Evaluate methods of sampling for particles in the range of 0.01 to 10 Ilm
(2) Investigate optical, physical, and chemical techniques to identify and measure asbestos
fibers
(3) Develop beneficiation procedures to isolate and differentiate asbestos from other atmo-
spheric particulate .
(4) Identify mineralogical species of asbestos
(5) Quantify asbestos analysis procedure
(6) Verify feasibility of the developed procedure for possible routine use
(7) Analyze samples taken at remote and point source sites
(8) Document procedure:
(1) Newhouse, M. L., and Thompson, H., "Mesothelioma of Plura and Peritoneum Following Exposure
to Asbestos in London Area", Brit. J. Indust. Med., 22, 261 (1965).
(2) Selikoff, I. J., and Hammond, E. C., "Community Effects of Nonoccupational Environmental
Asbestos Exposure", A. J. Ph., S8 (9),1658 (1968).
(3) Thomson, J. G., Kaschula, R.O.C., and McDonald, R. R., "Asbestos as a Modern Urban Hazard",
South African Medical Journal, 27, 77 (1963).
-------
3
Previous Work by Battelle
The results described in this report are an extension of effort carried out by Battelle on a previous
program under Contract PH-22-68-54.
In that program various means of detecting asbestos materials were employed utilizing the unique
physical and chemical properties of asbestos. These methods included electron microprobe (EMP),
scanning electron microscopy (SEM), transmission electron microscopy (TEM), and light microscopy
(LM) and are discussed in the sections below.
In addition optical emission spectrography methods, which depended on the unique chemical
composition of asbestos, and X-ray diffractometry, which depended on the unique structural character-
istics of asbestos, were investigated. However, these characteristics were buried in the makeup of
particulate samples and were undetectable.
EXPERIMENTAL WORK
Raw Materials
The following five types of raw asbestos were purchased( 4) for the purpose of making synthetic
experimental samples:
Serpentine (chrysotile, fibrous, Quebec)
Amphibole (loose fibers, white, Quebec)
Amphibole (long fiber masses, gray, Montana)
Crocidolite (dark blue, fibrous, Transvaal)
Amosite (long fiber, gray, Transvaal)
These materials were examined petrographically to ensure that they were the types represented by
the supplier.
In addition, a sample of "respirable" pure white Chrysotile was obtained from John Mansville and
used in the developmental efforts. This material was identified by its morphological detail as shown by
electron microscopy.
Detection and Identification of Asbestos Fiber and Fibril
Samples of three forms of asbestos, amosite, chrysotile, and crocidolite, were used in preliminary
investigations to determine suitable means of detection and identification of asbestos. The investigations
included the chemical properties composition and physical appearance of asbestos. In carrying out these
studies it was realized that ambient air samplings would collect not only asbestos fibers and fibrils but
other air particulates. These other air particulates either singly or in combination do contain elemental
compositions similar to the asbestos mineral compositions and many also are of a fibrous nature grossly
similar in appearance to asbestos. For these reasons it was concluded that the asbestos could not be
determined as an aggregate but would require detection of individual fibers and fibrils.
(4) Ward's Natural Science Establishment, Inc., Rochester, New York.
-------
f-------
4
The samples which were examined in the preliminary study are listed in Table 1.
TABLE 1. ASBESTOS SAMPLES EXAMINED IN THE PREUMINARY STUDY
Sample
Designation Asbestos Form Treatment
1 Amosite Ground to small particle size
4 Chrysotile Ground to small particle size
5 Crocidolite Ground to small particle size
6 Chrysotile 100 Il collected on membrane filter
7 Chrysotile Low-temperature ashing (LT A)
8 Chrysotile Low-temperature ashing (LT A) duplicate of
Sample 7
9 Chrysotile Ignited at 400 C
9a Chrysotile Ignited at 750 C
10 None Deionized H20 residue on membrane filter
11 Unknown IS-hour, low-volume air sample
12 Unknown IS-hour, low-volume air sample; subjected
to LTA
Electron Microprobe Studies
Studies of the above samples showed that the electron microprobe (EMP) is capable of identifying
asbestos fiber by its composition provided the fiber is large enough (->0.5 Ilm) and is isolated from
other particles that may contain Si, Fe, Na, or Mg. However, because asbestos fibers and fibrils were
found by other techniques to occur in sizes much smaller than 0.5 Ilm, the EMP was shown to be of
limited value in the identification of asbestos in collected air samples.
Scanning Electron Microscopy Studies
The scanning electron microscope (SEM) permits rapid viewing and photography of materials and
provides image resolutions down to about 100 A. Replicas are not required and, although a thin
conductive coating frequently must be put on the surface of a sample, SEM offers a faster and more
direct method for examining small particles than does electron microscopy.
Since SEM offers an approach which is supplementary and complementary to optical light
microscopy and electron microscopy, it could serve as both a qualitative and quantitative method for
estimating asbestos contents of ambient air samples. However, in the limited studies carried out on this
program, this has not been the case. Ambient air samples have been examined both as collected on a
membrane ftlter and after having been ashed. In both cases the SEM images have shown the fibers more
as clumps or "piled up" and interwoven groups rather than as individual particles as seen in electron
micrographs. The difference in resolution between the two techniques is accountable at least in part for
this. However thus far it has not been possible to get good estimates of the amount of asbestos present
by the use of SEM photographs alone.
This effort on the SEM also showed the SEM could not unequivocally distinguish between forms of
asbestos.
-------
5
Transmission Electron Microscopy
The samples listed in Table 1 were examined by transmission electron microscopy (TEM) by thin
section techniques and transfer replicate techniques. For the thin section examination, the samples were
imbedded in a commercially available epoxy mixture, Maraglas (available from Polyscience Inc.). Thin
sections 750 A thick were cut on a Porter-Blum MT-l microtome equipped with a Du Pont diamond
knife.
The transfer replica was made by evaporating a carbon fllm over the surface of the fllter bearing
the asbestos and dissolving the filter in acetone to leave the thin carbon film supporting the asbestos
fibers and fibrils.
The examinations showed that:
(1) The various forms of asbestos can be identified by their individual morphologies
(2) Crystallinity is a valid criterion for distinguishing between asbestos fiber and glass fiber
although not necessary because of identification by morphology
(3) Morphology and crystallinity of asbestos fiber and fibrils are both affected by ignition at
750 C
(4) A magnification of the order of 30,000X is optimum for identification of asbestos.
tight Microscopy
Light microscopy techniques were examined only briefly as a technique for identification of
asbestos because the diameter of many of the asbestos fibers and especially the fibrils are below the
resolving power of the light microscope. Dark field and dispersion staining techniques were found capable
of identifying fibers at sizes somewhat below the normal resolving power of the instrument but the
methods were not suitably specific for unequivocal identification.
In summary, transmission electron microscopy is the only technique investigated that provided
unequivocal identification of asbestos fiber as well as asbestos fibril material. TEM techniques were used
throughout the remainder of the developmental program for asbestos identification.
Sampling
Sampling methodology selection was based on two criteria: (1) it must collect asbestos particles in
the required range of 0.01 Jlm to 10 Jlm and (2) it must ultimately be suitable for use in the sampling
network of EPA. The latter dictated that sampling be fairly simple and easy to perform and, if possible,
require no complicated apparatus. The sampling techniques considered included cascade impaction, liquid
impinging, and membrane filtration. The glass fiber filter now used in the EPA air sampling network was
not considered because of the interferences introduced by glass fiber when it is present with collected
asbestos fiber.
To permit the evaluation of sampling methods, samples of airborne particulates were collected near
point sources, where asbestos would be expected to be a significant portion of the total particulate, and
at locations where asbestos would be expected to be lower than near point sources. Tables 8 through 13
show the location, sampling techniques, and the amount of asbestos found in samples collected for this
study.
-------
6
Cascade Impactor
Since the cascade impactor collects particles according to aerodynamic size on its various stages,
Battelle's objective was to determine whether asbestos fiber is selectively collected on certain stages. The
collections were made directly on carbon-coated electron-microscope grids aff1xed to each of the six
stages.
Examination by transmission electron. microscopy (TEM) showed asbestos fiber and fibril on
virtually every stage (e.g., Stages I, 3, 4, 5, and 6). Electron micrographs from Stages I and 5 of the
Cincinnati sample are shown in Figures 1 and 2. It is clear that asbestos fibers and fibrils are collected
with no obvious selection according to size.
An implication of this finding is that total air samples are necessary for analysis rather than samples
with a portion of the particulate removed by preimpaction. A study of the impactor samples revealed
also that asbestos very often is collected as loosely agglomerated fibers and fibrils in association with
other particulates. Further work with the cascade impactor to try to determine asbestos particle sizes is
described in a later section.
All-Glass Liquid Impinger
The samples collected with the all-glass liquid impingers could have been examined for the presence
of asbestos fibers by an otical-microscopic interference-contrast technique. Because of the large amount
of nonasbestos particulate collected simultaneously, the technique was considered not applicable without
beneficiation of asbestos. The interference-contrast technique also would not distinguish nonasbestos
fibers or different mineralogical species of asbestos fiber.
Membrane Filters
The membrane fIlters were evaluated by direct examination using a light microscope and by
scanning electron microscopy (SEM) for their usefulness in available sampling apparatuses. Samples of
various areas (from 25-mm circle to 30 x 30-cm square) were taken on 0.45-lJm-pore-size Millipore fIlters
(esters of cellulose), and on 0.45ilm-pore size Flotronics (silver). Direct examination of the membrane-
filter samples by light microscopy and SEM proved fruitless because of the inability to detect asbestos
fiber in the presence of larger amounts of other particulates and to resolve the smaller fibers and fibrils.
Ultimately, plastic membrane filters were found acceptable because of their low ash content, lack of
fibers of any kind, and their adaptability to field sampling procedures.
Beneficiation
Initially, collections on membrane filters were prepared for electron microscopic examination by the
transfer replicate technique on the sample as collected. It was obvious that the particulate sample, as
collected, was so loaded that asbestos particles were obscured, or so light that the asbestos particles seen
and counted were too few and too sparse to be statistically representative of the total sample. Figure 3
shows an electron micrograph of a sample as collected. It appeared, therefore, that a process was needed
to (1) concentrate or beneficiate the asbestos particles and (2) provide for a means of redistributing the
asbestos particles uniformly and in a countable frequency.
The fust of these needs was accomplished by ashing, which removed organic particulate such as
soot, and when necessary by centrifuging which removed inorganic particles which were large compared
to the asbestos particles.
-------
7
1--
- II
n
Ii
..
Ji
..
,
30,OOOX
J17767
FIGURE 1. A CLUMP OF AGGLOMERATED PARTICLES PARTLY COM-
PRISED OF ASBESTOS (CHRYSOTlLE)
This clump was collected at Stage 1 of the cascade impactor
where particles aerodynamically equivalent to 16.0-llm spheres
of water are collected.
\
4:~
~
r
~
30,OOOX J17802
FIGURE 2. ASBESTOS FIBERS COLLECTED AT STAGE 5 OF THE
CASCADE IMPACTOR
This stage collects particles which are equivalent aerody-
namically to 1.0 11m spheres of water.
-------
8
.. l
""
'f ~:;~; .' ~'~l"'; CO," i
... . ..J" .. .
, ,..t, . ' .. ~ " ".11,.." '" ""
'." ,oj ~ ..,.. ... :t.
r" .. . ", :.l . r ~ ~. 4
'....... f.... ,
. ,
. II' .' 'i
.
~ ~
.. .
~"'\.t
.. '\
- "-
..,4.......,
..'
. t,. '
\... .
"'...
.,. ,.
~,:
" ,~
.~"
.... ;I
k ;~
...- .. .
F~.
L".." "'
, "Ia.
.
.
.. "',
,
)
,;
..;
.
'"
-,
,t
;{!t' .'
. . j
..' "~~'
.~~~.;;
-
, ,
\.
.
\..
_i
.
.
I
. .:~ j
,-;. ;.;>l' .. '. if
V "
r
I.. r
, "1
I ~'
I ~
L;'. '
I.. ::',1
-",
.
. (. . ~~ ' .
. ' .1
:../. .
...;. '... .
!p. .'\ 'J.' ''''.
J' .)'. P
L \'
~ . ~.
~- --""-
.~"
. ..
,...
. -, , 1 .
,.
r -
\ I
l-
I
\..
----
57,OOOX
117092
FIGURE 3. ELECTRON MICROGRAPH OF A TYPICAL DEPOSITION OF AIR PARTICULATE
FROM FILTERED AIR
-------
9
The second of these needs was accomplished by ultrasonically dispersing the asbestos particulate in
an aqueous media and reflltering the dispersed particulate. The reflltered asbestos particulate was then
prepared for EM by the transfer replicate technique.
Low- Temperature Ashing of Collected Sample
Organic materials are eliIpinated by low-temperature combustion in oxygen. The ashing treatment
removes about half the total interfering particulate material.
It was found that the low-temperature ashing (LTA) of the deposit on the membrane fllter could
best be done in an induction-coupled oxygen plasma at about I-torr total pressure. If the collected
sample and filter are ignited in air there is danger of sample loss because of the explosive manner in
which the membrane fIlter burns. For the LTA ignition, the chance of physical loss of particulates from
the oxygen draft is virtually eliminated by placing the sample in a Pyrex test tube with the open end in
a position such that the oxygen plasma flows across the tube mouth normal to the axis of the tube.
Possible contamination from the laboratory atmosphere is eliminated by using LT A, in which the
atmosphere is tank oxygen.
The ash residue from the collected sample remains in the test tube, which is convenient for
insertion into the ultrasonic bath that is necessary to break up agglomerates of particulates in order to
provide a uniform deposit for the electron microscope.
The dry ash is suspended in water containing a surfactant (Aerosol OT) and is dispersed by
ultrasonic energy.
Ultrasonification
Asbestos fibers are composed of fibrils of fairly constant diameter, but indefinite length. If the
fibers are triturated they will be reduced to fibrils which will be of random lengths. If the energy used
in the fiber-reduction process is controlled, the fibril lengths will be random, but of a reproducible but
small range distribution of lengths. These fibrils could be considered alternate particles under fixed
conditions. By trituration of a weighed known asbestos sample and an unknown asbestos-containing
sample under controlled conditions, the fibril length distribution should be comparable in each sample.
Ultrasonification has proven to be valuable for this process because of the repeatability of the energy
utilized and the efficiency, as compared to other mechanical means, of trituration.
Centrifugation
Unlike the asbestos, the fly ash and most of the other particulates appear to retain the same size
before and after ashing and dispersion by ultrasonic treatment; therefore, centrifugation can be used for
fractionation by size. The larger particles settle, while the smaller asbestos particles remain in suspension.
The ultrasonically dispersed aqueous suspension of ashed sample is centrifuged at 900 g for about 20
minutes. The supernatant portion is then decanted and filtered on a plastic membrane fIlter.
The precipitation is repeated a second time. Additional aqueous surfactant solution is added to the
residue precipitated by the first centrifugation in order to redisperse it and to recover any of the
asbestos carried down with the precipitate. Examination of the material retained by the fUter after the
first centrifugation revealed the presence of most of the asbestos fiber plus some additional very fine
tly-ash-type particles, which indicates good separation. It is estimated that centrifuging twice eliminated
about 90 percent of the interfering particulates from most samples. Studies of synthetic standards show
that approximately 80 to 90 percent of the asbestos fiber is recovered.
-------
10
Dispersion and nItration from a selected volume of liquid onto a known nIter area provide the
advantage of allowing control of the amount of particulate deposited per unit area of nIter. The amount
is chosen to be best suited for electron microscopic examination. The amount per unit area is varied
either by using an aliquot of the aqueously dispersed particulate or by varying the size of the nIter area
on which the particulate is fmally deposited.
Any sample treatment, and especially the ultrasonic dispersal, alters the particulate so it is not
observed in the electron microscope in the same condition as while airborne or even as sampled. The
ultrasonic treatment disperses and dispenses the particulate matter and breaks the asbestos into shorter
and fmer particles, resulting in the formation of many individual fibrils of colloidal dimensions. It
should be emphasized, however, that only a relatively small portion of the sample is actually examined
by electron microscopy, so a uniform distribution is necessary to provide a statistically sound basis for
analysis of the asbestos particulate by counting only a reasonable number of asbestos fibers and fibrils.
Figure 4 is an electron micrograph of separated fibrils.
r--
I ---~- ..
' -
.
,
'~.~
'~i
....
"
c¥
f '
,j'-'\ '
Lr' ~ \
/" '1'",;~."::.- '
~ .;~. J ... .~.
...... I -....
~-
~
/ ,\
I
60,OOOX
118308
FIGURE 4. ELECTRON MICROGRAPH OF A TYPICAL DEPOSITION
OF SEPARATED FIBRILS
Investigations into other means of separating asbestos largely on the bases of their electrical
properties and density were carried out. These experiments and results, described in Appendix A, were
only partially successful.
I
-------
11
Beneficiation Summary
Battelle's recommendation for beneficiation is to ash every sample but centrifuge only when
necessary. According to recent experience, centrifugation is necessary only for a small fraction of the
samples.
Assuming no prior knowledge on a sample, the amount to be taken for analysis must be arbitrary.
Typically, 1/8 or 1/16 of the total sample or an amount that can be ashed at a low-temperature in a
few hours has been taken. As detailed in the methodology, the ash is suspended in 100 ml H20 and two
aliquots are taken, 10 ml and 90 ml.
If asbestos cannot be counted in either aliquot because of either too much nonasbestos particulate
or too little asbestos particulate, then centrifugation will be useful. In that case a larger aliquot of the
sample should be taken to be treated in the extra step of centrifugation.
Quantification
Experience showed that TEM at 30,000X is necessary to identify the asbestos fiber as to
mineralogical type and also to distinguish asbestos fiber and fibrils from any other particulate that may
have an axial ratio of 10 to 1 or more.
Because TEM operates at relatively high magnifications, only a small area can be examined in a
reasonable length of time, and the asbestos fiber and fibril must be dispersed very uniformly. Satis-
factory dispersal is carried out as described above by application of ultrasonic energy to an aqueous
suspension of ashed air particulate containing added surfactant. Subsequent ftltration of such a sus-
pension provides a uniform dispersal on the collecting media. Standards must be treated similarly.
Standards
Ordinarily, in making an analysis of particles by optical microscopic techniques, the particles in an
aliquot of a sample can be counted and the count can then be related to the total sample, provided the
particles are counted in the as-collected condition. However, after disruption and dispersal of the
asbestos by application of ultrasonic energy to obtain a uniform deposit, a particle count is meaningless
by itself. The count needs to be related to a standard.
Since there were no standards available for asbestos in air, synthetic standards were made up. The
synthetic standards were made up by dispersing and suspending known weights of asbestos in aqueous-
surfactant media and making quantitative volumetric transfers of the suspensions to Millipore mters.
For example, suspensions of asbestos containing 1.0, 0.1, 0.01, and 0.001 IJ.g/ml of asbestos were
made up. 1 ml of each of the four suspensions was then mtered through each of four Millipore filters.
Each Millipore mter then contained known amounts of asbestos and were treated as an air sample.
Figure 5 is an analytical working curve which gives the relationship of fiber count per 200 mesh screen
opening to IJ.g asbestos per 17-mm diameter filter disk.
The dispersion and suspension of asbestos fiber was promoted by the addition of Aerosol OT
(dioctyl sodium sulfosuccinate) and ultrasonic energy to break down the larger asbestos particles into
particles of fibrillar dimensions. The suspensions were useful for only two days because of the fairly
rapid dissolution of the fiber in the aqueous media.
-------
12
1000
1.0
100
01
c:
.~
0
c:
Q)
~
u
(/)
L; 10
II)
Q)
~
I
0
0
C\J
.......
II)
"-
Q)
..0
G:
x
0.1
0.001
0.01
0.1
fLg Asbestos/ 17-mm Filtering Diameter (Nominally 25-Mm Disk)
FIGURE 5. PLOT OF FIBER COUNT PER 200-MESH SCREEN OPENING VERSUS
MICROGRAMS ASBESTOS PER FILTER DISK
-------
13
Standardization is successfully carried out using only asbestos. However, to demonstrate this,
standards were prepared that contained asbestos and other particulate such as pulverized sea sand,
ignited air particulate, and fly ash.
The results for these standards when carried through the procedure for preparing and analyzing air
samples agreed with the results for standards prepared with asbestos only.
RESULTS
Description of the Methodology for the Analysis of Asbestos in Air
The methodology is described in detail so that other laboratories, even though not familiar with the
techniques employed, could follow the procedure and obtain satisfactory data.
A. Sampling
Virtually any sample collected on plastic-membrane fllter material is applicable. The procedure and
apparatus listed below are useful for relatively small samples «100 m3 depending on particle loading in
the air sampled).
(1) Collect air samples on Millipore Type HA 47 mm, 0.45-J.Lm-pore-size filter disks held in a
clean-room monitoring filter holder (such as Millipore Cat. No. XX 5004740) supplied
with a 5-liter/min limiting orifice
(2) Connect the above ftlter holder to a vacuum pump capable of maintaining a pressure
drop of at least 8 psi at a flow rate of 5 liter/min
(3) Carry out sampling for the desired monitoring period
(4) Record volume of the air sampled
(5) Removed fllter from ftlter holder and store in clean petri dish.
B. Sample Preparation
(1) Handle specimen in a clean laboratory environment, class 100 or better.
(2) Take half of ftlter (Step 5 of A), fold and put in the bottom of Pyrex test tube (1.5 cm
x 9 cm). (See Note 1.)
(3) Put test tube in a low-temperature asher for 2 hours or until sample is completly ashed.
(Low-temperature asher, such as Tracerlab-LTA 600.)
(4) Remove test tube, and add 5 rnl of ftltered deionized water and 2 rnl of 1.0 percent
Aerosol OT (Fisher So-A-292).
(5) Treat ultrasonically for 5 minutes in ultrasonic generator (such as Branson Ultrasonic
Corporation - Sonogen T-32) to disperse and suspend the ash.
-------
14
(6) Transfer the dispersed sample to a 10-ml volumetric flask; dilute to 100 ml.
(7) Tap out 10 ml while the flask is subjected to ultrasonic energy to assure dispersal, and
fllter through a 25-mm-diameter, 0.45-l1m-pore-size filter. (See Note 2.) The filter funnel
must be cylindrical (not tapered) so the suspended particles will deposit uniformly over
the fJlter surface. Filter the remaining 90 ml above as a standby in case the 100ml deposit
is so sparse that a count cannot be made.
Note 1. The portion of a filter taken to process is arbitrary. A second portion may need to be
selected to adjust for the amount of particulates finally deposited for the microscopic
examination.
Note 2. Use filtering apparatus supplied by the Millipore Corp. Cat. No. XX 10 025 00, or
equivalent, connected to a laboratory aspirator or vacuum pump.
(8) If the extraneous particulate to asbestos ratio is so high that a count cannot be made,
take another portion of the sample, carry the new portion of the sample through Steps
B-1 and B-5, and centrifuge sample at 500 to 1000 g for 20 minutes. Filter supernatant
fluid through 25-mm-diameter, 0.45-l1m-pore-size fJlter. (See Note 2.) Resuspend the
reside and again centrifuge for 20 minutes and again filter the supernatant on the same
fIlter.
C. Preparation of Specimen for Electron Microscopy
(1) Vapor deposit ~200 A layer of carbon over the ashed air sample distributed uniformly
on Millipore fIlter from Step B- 7 or B-8 above.
(2) Cut out a 5 x 5-mm piece of filter bearing the redistributed ashed and carbon-coated
airborne particulates.
(3) Dissolve the cellulose acetate Millipore filter substrate using a petri dish approximately
half filled with acetone.
(4) Aspirate the carbon film bearing the ashed, redistributed, airborne particles into a medi-
cine dropper along with a few drops of the acetone used to dissolve the Millipore fJIter.
(5) Hold the medicine dropper vertically until the carbon fJIm falls to the opening of the
medicine dropper.
(6) Deliver a drop of acetone containing the carbon film to the surface of water held in
another petri dish (about half full).
(7) Pick up the now flattened and floating carbon film from the surface of the water on a
200-electro-mesh electron-microscope copper support grid.
D. Examination of Specimen in the Electron Microscope
(1) Place specimen in electron-microscope specimen holder and examine systematically for
asbestos particles at a magnification of 30,000X with a 100-kv beam.
(2) Count fibers per grid opening on at least five openings to obtain data on average number
of fibers per opening.
-------
15
E. Preparation of Standards
(1) Simulate the sample conditions by ultrasonically suspending known quantities of asbestos
(1.0, 0.1, 0.01, and 0.001 Ilg) in about 0.5 percent Aerosol OT solution and then
collecting on membrane filters.
(2) Dry filtered preparation and ash the preparation in the low-temperature asher for 2
hours.
(3) Resuspend the ash in 5 ml of filtered deionized water plus 2 ml of 1 percent Aerosol OT
and subject the resulting suspendion to ultrasonic dispersal treatment for 5 minutes as
was done in Step B above.
(4) RefIlter on a 25-mm Millipore filter and allow to dry.
(5) Go through the entire procedure for "Preparation of Specimen for Electron Microscope"
and "Examination of Specimen in the Electron Microscope" (Steps C and D).
(6) Figure 5 gives a working curve relating fiber count to amount of asbestos.
F. Analysis of Microscope Data
(1) Compare fibers per opening for samples with comparable data for standards to obtain
micrograms of asbestos per sample.
(2) Translate the micrograms of asbestos per sample into micrograms of per cubic meter.
Note 3. Mention of a commercial product does not constitute endorsement by EPA. Equiv-
alent equipment from other manufacturers may be equally suitable.
Reliability of the Method
Comparison of Results From the Method
and Neutron-Activation Analyses
A check on the quantitativeness of the method was carried out through experiments with
neutron-activation analyses. For this experiment, neutron-activated asbestos was sampled by cascade
impaction and each stage of the impactor was analyzed by radioassay techniques. Four of the stages
were analyzed also by the TEM method developed during this program. The results of these analyses are
shown in Tables 2 and 3.
These experiments demonstrate that (1) independent analyses of the same sample provide agree-
ment within 30 percent, (2) asbestos apparently is distributed in various identifiable size ranges, and (3)
the Battelle cascade impactor appears to be capable of collecting asbestos according to size.(5)
Radioassay. The activation experiments which produced the above data are summarized here.
(5) Stober, W., Flachabart, H., and Hochrainer, D., ''The Aerodynamic Diameter of Latex Aggregates
and Asbestos Fibers", Staub-Reinhalt Luft, 30 (7) (July, 1970).
-------
16
TABLE 2. RADIOASSA Y OF ASBESTOS ON IMPACTOR STAGES
Stage
Asbestos Collected After Wet and Dry
Dispersion in Air, Ilg
Wet Dispersion Dry Dispersion
1
2
3
4
5
6
7
Final
0.1
0.1
0.5
8.3
34.0
17.6
4.7
2.3
0.1
0.1
1.7
0.7
2.9
5.7
12.5
2.4
TABLE 3. COMPARISON OF RESULTS OF ANALYSIS OF ASBESTOS ON
IMPACTOR STAGES BY ELECTRON MICROSCOPY AND
RADIOASSA Y
Stage
4
5
6
7
Asbestos, Ilg
Electron Microscopy
11.6
40.0
20.8
4.0
Radioassay
8.3
34.0
17.6
4.7
Difference, %
+29
+15
+15
- 18
-------
17
In order to determine the effect of neutron radiation on asbestos, a 100-mg sample of Johns-
Manville No. 3778-29-1 chrysotile asbestos sealed in a quartz tube was irradiated for 7 days in a neutron
flux of about 1 x 1013 n/cm2/sec. The major long-lived radioisotopes produced during the irradiation
are listed below with their nuclear properties.
Significant Quantity Produced,
Isotope Half-Life Decay Characteristics JlCi/Jlg of asbestos
45Ca 163 days (3-0.25 Mev 3.4 x 10-4
45Sc 84 days (3-0.357 Mev 1.4 x 10-5
1-0.889, 1.12 Mev
59Fe 45 days (3-0.475 Mev 1.1 x 10-5
1-0.19, 1.1, 1.29 Mev
Two experiments were performed in which the irradiated asbestos was introduced into air by
different techniques. In the nrst experiment, the activated asbestos was dispersed in 0.1 percent Aerosol
OT solution at a concentration of 20 Jlg/ml. Ten ml of the asbestos suspension (200 Jlg asbestos) was
atomized into a 4-foot-diameter sphere over a period of about 1.5 hours. Sampling was performed with
a seven-stage Battelle impactor sampler during and for 1.5 hours following the sample injection. The
flow rate through the sampler was 12.5 I/min.
In the second experiment, a 2.8-mg sample of dry irradiated asbestos was atomized into the
4-foot-diameter sphere in one burst. Sampling with the Battelle sampler at 12.5 I/min was initiated
about 15 minutes after sample injection and continued for 70 minutes. About 34 and 7 percent of the
added asbestos was recovered in the sampler in Experiments 1 and 2, respectively, showing that asbestos
was lost in the system, as expected.
Radioassays and Results
The Millipore filters from the seven impactor stages and the final fIlter (Millipore, 0.45-Jlm pore
size) were radioassayed with a Beckman Widebeta, low background, gas-flow proportional-counting
system. Counting times of 50 to 100 minutes were used, which resulted in counting errors of less than I
percent for most samples. Asbestos standards were prepared by filtering I-ml aliquots of the 0.1 percent
Aerosol OT solution of the irradiated asbestos used in the first experiment through a 0.22-J.1m Mi1lipore
fIlter. The filtrate was checked for radioactivity to assure that all the asbestos was retained on the fIlter.
The specific activity (counts/min/Jlg) of duplicate standards agreed within 2 percent. The quantities of
asbestos on the impactor stages and the final fIlter were determined by comparison of their activity
(counts/min) to the specific activity of the standards (counts/minIJlg). The weights of asbestos found in
the two experiments are summarized in Table 2.
Replication
The repeatability of the methodology was checked by analyzing several of the samples in duplicate
and triplicate.
The replicate data is given in Table 4.
The data shows an agreement between replicates of the order of :tlO to 20 percent except in one
instance where the agreement is about :t50 percent.
-------
18
TABLE 4. REPLICATE RESULTS OF ANALYSES OF
SELECTED AIR SAMPLES
Sample Identification
Lockland Post Office 9/3/70
Wyoming Municipal Bldg. 9/3/70
Lincoln Heights City Hall 9/3/70
Lincoln Heights, Mathews, and Dixie 9/3/70
Lockland Post Office 1/14/71
Lincoln Heights City Hall 1/14/71
Lockland Post Office 1/21/71
A31
A34
A43
Asbestos, Jlg/m3
280, 260
29,37,32
28,40
12,38
110,86
130, 117
7900,7200,9700
0.115,0.102,0.147
0.094,0.119, 0.106
0.028,0.024,0.026
Report Value, Jlg/m3
270.
33.
34.
25.
98.
124.
8200.
0.12
0.10
0.03
Particle Size/Frequency Measurements
On the bases of the demonstrable features of collection and analyses, project personnel proceeded
to collect air samples by cascade impaction near a point source in order to obtain size-frequency-
distribution information on a real air sample. Samples were collected at distances of 1 and 2 miles
downwind from the point source, with results shown in Table 5.
The total of 0.109 Jlg for the I-mile sample, as shown in Table 5, was obtained during a 2-hour
sampling at 12.5 l/min. The asbestos collection rate, therefore, amounted to about 0.07 Jlg/m3.
Simultaneously with the impactor sample, a sample was taken on 0.45-JJ.m-pore-size Millipore filter
material to represent a total sample collection. This was carried out to assess the overall efficiency of
the cascade impactor. The results from analysis of the total sample likewise showed a 0.07-Jlg/m3
concentration for asbestos.
TABLE S. ANALYSIS OF EACH STAGE OF CASCADE-IMPACTOR
SAMPLES TAKEN AT 1 AND 2 MILES DOWNWIND
FROM A POINT SOURCE
Stage
1 Mile From
Point Source
1
2
3
4
5
6
7
Total
0.004
0.04
0.025
0.012
0.018
0.005
0.005
0.109
Jlg Asbestos/Stage
2 Miles From.
Point Source
0.006
0.009
0.007
0.002
0.005
-------
19
Ordinarily, the cascade impactor is backed up with a glass-fiber filter to collect material that is not
impacted. Glass fiber is not applicable for analysis and the flow rate through the Millipore filter is too
low to pass the required flow through the impactor stages. Therefore, analysis of a backing filter was
not applicable.
Since the amount of asbestos found in the cascade impactor agrees with the amount in the total
collection, virtually the total mass has been collected by the impactor. Although the cascade impactor
collects the total mass of particulate efficiently, there may still be a significant number of particles in
the O.OI1Lm range that have not been collected.
In further efforts to determine particle size, an asbestos point source was sampled by the cascade
impactor for short times (20 and 4 minutes) so the particle loading on each stage would be sparse.
Isolated, single asbestos particles were thus collected and found by electron microscopy on Stages 4, 5,
and 6. Figures 6, 7, and 8 are electron micrographs of the particles. Data on approximate size of the
particles are given in Table 6.
TABLE 6. SIZE OF ASBESTOS PARTICLES FOUND ON STAGES 4, 5, AND 6
OF A CASCADE-IMPACTOR AIR SAMPLER
Calculated Range of Equivalent Calculated
Sizes of Particle as Measured Calculated Diameter(a), Particle
Stage Stokes Diameter, J.!m Dimensions, J.!m Volume, J.!m3 J.!g Wt(b), J.!g
4 2-4 11 x 0.6 4 1.97 10 x 10-6
5 1-2 8 x 0.36 1 1.25 2.6 x 10-6
6 0.5-1 1.3 x 0.15 0.03 0.38 0.08 x 10-6
(a) Calculated as spherical particles.
(b) Using density of chrysotile as 2.5 glee.
In order to demonstrate how these types of data might be used to determine particle-size
distribution, the following calculations were made.
The weight data in' Table 6 was used to estimate weights of individual asbestos particles collected
on each stage of the cascade impactor. Using the data from Stage 4 as a reference and assuming that the
weight will vary by a factor of 8 (23) these estimated weights are given as follows:
Stage
Microgram/Particle
1
2
3
4
5
6
7
5 x 10-3
6 x 10-4
8 x 10-5
1 x 10-5
1 x 10-6
2 x 10-7
2 x 10-8
The above data then provide a means of estimating the number of particles collected by each stage
of the impactor sample listed in Table 5. These calculated particle numbers are shown in Table 7.
These data give an idea of the order of magnitude of particle-number distribution, but more effort
is needed to obtain supporting data and to assess particle-size distribution from various sources and for
ambient air at various locations. '
-------
20
.
..
..
.
A
.
I
I '
I
I
I
I
.
ii>
.
,
22,OOOX
J19751
FIGURE 6. ELECTRON MICROGRAPH OF SINGLE PARTICLE OF ASBESTOS COLLECTED ON STAGE 4 OF
THE BATTELLE CASCADE IMPACTOR
'-
-------
21
D
..
~
-- -
-- --
_J
22,OOOX
119752
FIGURE 7. ELECTRON MICROGRAPH OF SINGLE PARTICLE OF ASBESTOS COLLECTED ON STAGE 5 OF
THE BATTELLE CASCADE IMPACTOR
-------
22
II
'II
II
a ' Ell
.
II
Ell J.~
..
57,OOOX
119753
FIGURE 8. ELECTRON MICROGRAPH OF SINGLE PARTICLE OF ASBESTOS
COLLECTED ON STAGE 6 OF THE BATTELLE CASCADE
IMPACTOR
-------
I" ,
23
TABLE 7. ESTIMATED PARTICLE NUMBER FOUND ON EACH STAGE OF
THE CASCADE-IMPACTOR SAMPLE SHOWN IN TABLE 5
Size Collected Percent Cumulative
Stage (Stokes Diameter), 101m Total Particles (by N umber) Percent
1 >16 0.8 0.0003 100.00
2 8-16 60.0 0.02 99.99+
3 4-8 300.0 0.1 99.97
4 2-4 1,200.0 0.5 99_8
5 1-2 18,000.0 7.5 99.3
6 0.5-1 20,000.0 8.3 91.8
7 0.25-0.5 200,000.0 83.5 83.5
Data From Various Sites
The data from analysis of some 80 samples which were mostly supplied by EPA are shown in the
following tables.
Table 8 contains the results for the analyses of Urban Samples.
Table 9 contains the results of analyses of Site Source Samples.
Table 10 contains the results of analyses of samples from a nonurban remote site.
Tables 11, 12, and 13 show the results of analyses of miscellaneous samples. Table 11 shows the
results of analyses of the various tages of samples collected by cascade impaction. This data provides an
estimate of asbestos particle-size distribution in air near a site source.
Table 12 gives the results of analyses of samples collected for preliminary studies. The data are not
necessarily significant.
The data in Table 13 are result of analyses of air samples taken from the exhausts of various vane
pumps.
DISCUSSION AND CONCLUSIONS
By utilizing the methodology as detailed in this report, it is possible to obtain a reliable analysis for
asbestos in air. The time required per sample depends mainly on whether or not the sample needs
beneficiation by centrifugation. The analytical results can be expressed in terms of weight of asbestos
per. unit volume of air or per unit weight of sample, whichever is most applicable. On the basis of
cross-check analyses, the data appear to be reliable within f30 percent of the stated amount. The
precision of the measurement appears to be of the order of f 1 0 percent as determined by triplicate
analyses of several samples. .
-------
-,-
24
TABLE 8. ANALYSES OF URBAN SAMPLES SUPPLIED
BY SPONSOR COLLECTED ON REINFORCED
PLASTIC MEMBRANE MATERIAL
(Collection Volume About 200 m3)
Sample Identification
Asbestos, ng/m3
Dayton M502 4-8-69
Dayton M508 7-9-69
Dayton M508 10-6-69
Dayton M508 1-2-70
Dayton 3167 4-8-70
Dayton 3167 7-4-70
Dayton 3178 10-7-70
3.8
5.6
11.0
0.5
4.0
0.4
5.1
Houston 2987 4-8-70
Houston 2993 7-4-70
Houston 2998 9-20-70
Houston 2997 10-7-70
6.0
4.0
4.0
4.0
Pittsburgh 2544 4-8-70
Pittsburgh 2544 7-4-70
Pittsburgh 2544 10-7-70
2.0
8.0
3.0
San Francisco 2330 4-8-70
San Francisco 2332 7-11-70
San Francisco 2339 10-14-70
40.0
1.5
3.0
Washington, D. C., No.1 3rd quarter
Washington, D. C., No.2 3rd quarter
Washington, D. C., No.1 4th quarter
Washington, D. C., No.2 4th quarter
40.
1.6
4.0
2.6
-------
TABLE 9.
25
ANALYSES OF SITE SOURCE SAMPLES - SAMPLES
COLLECTED BY SPONSOR AT A POSITION
DOWNWIND FROM A SITE SOURCE NEAR:
CINCINNATI, OHIO
(Plastic Membrane Filter Material)
Location Relative Air Asbestos,
Sample Identification to Point Source Vol, m3 ng/m3
Lockland Police Station 9/3/70 3/4 mi. NE 0.6 62
Lockland Police Station 9/3/70 3/4 mi. NE 1.87 170
Lockland Police Station 9/3/70 3/4 mi. NE 1.87 100
Lockland Post Office 9/3/70 3/4 mi. NNE 1.87 180
Lockland Post Office 9/3/70 3/4 mi. NNE 1.81 270
Wyoming Municipal Bldg. 9/3/70 5/8 mi. NNW 1.87 24
Wyoming Municipal Bldg. 9/3/70 5/8 mi. NNW 1.19 33
Lincoln ,Heights City Hall 9/3/70 1-1/4 mi. N 0.8 34
Lincoln Heights City Hall 9/3/70 1-1/4 mi. N 1.87 70
Lincoln Heights City Hall 9/3/70 1-1/4 nii. N 1.87 11
Lincoln Heights,
Mathews and Dixie 9/3/70 1-7/8 mi. N 1.87 17
Lincoln Heights,
Mathews and Dixie 9/3/70 1-7/8 mi. N 1.87 25
Blank 4 (total on
ftlter)
Lockland Post Office 1/14/71 3/4 rot. NNE 2.8 570
Lockland Post Office 1/14/71 3/4 mi. NNE 1.4 98
Lockland Post Office 1/14/71 3/4 mi. NNE 1.4 <60
Lincoln Heights City Hall 1/14/71 1-1/4 mi. N 3.7 124
Lincoln Heights City Hall 1/14/71 1-1/4 mi. N 3.7 <20
Lincoln Heights,
Mathews and Dixie 1/14/71 1-7/8 mi. N 3.7 600
Lincoln Heights,
Mathews and Dixie 1/14/71 1-7/8 mi. N 3.7 <20
Lockland Post Office 1/21/71 3/4 mi. NNE 1.4 8200
Lockland Post Office 1/21/71 3/4 mi. NNE 1.4 3400
Lockland Post Office 1/21/71 3/4 mi. NNE 3.1 5200
Lincoln Heights City Hall 1/21/71 1-1/4 mi. N 3.4 1800
Lincoln Heights City Hall 1/21/71 1-1/4 mi. N 5.8 915
Lincoln Heights City Hall 1/21/71 1-1/4 mi. N 2.3 200
Lincoln Heights,
Mathews and Dixie 1/21/71 1-7/8 mi. N 3.7 <20
Lincoln Heights,
Mathews and Dixie 1/21/71 1-7/8 mi. N 7.5 150
Lincoln Heights,
Mathews and Dixie 1/21/71 1-7/8 mi. N 3.7 160
-------
26
TABLE 10. ANALYSES OFSAMPLES COLLECTED FROM
NONURBAN - REM()TE AIR, SAMPLES
COLLECTED NEAR FRANKFORT, KENTUCKY
(Plastic Membrane Filter Material)
Sample
Air Vol, m3
Asbestos,
ng/m3
Results of Replicate Analyses,
ng/m3
A 31
A 34
A 43
2512
2191
2186
0.12
0.10
0.03
0.115,0.102,0.147
0.094,0.119,0.106
0.028,0.026,0.024
TABLE 11.
SAMPLES COLLECTED BY THE BATTELLE CASCADE-
IMPACTOR NORTH (DOWNWIND) FROM POINT
SOURCE NEAR CINCINNA n, OHIO
(FEBRUARY 16, 1971)
(2-Hour Collection at 12.5 Liter/Min (1.5 m3)
Stage
Stokes Diameter16
8-16
4-8
2-4
1-2
0.5-1
0.25-0.5
4
40
25
12
18
5
8
2 Miles From Point Source
1
2
3
4
5
6
7
>16
8-16
4-8
2-4
1-2
0.5-1
0.25-0.5
6
9
7
2
5
(a) Diameter of particle of unit density which would be collected
on the particular stage.
-------
27
TABLE 12. SAMPLES COLLECTED FOR
PREUMINARY STUDIES
(Collection on Membrane and
Paper Filter Material)
Sample Source Asbestos, ng/m3
27097-2-1 Urban 5.0
27097-2-6 Urban 0.5
27097-2-7 Point source 4.0
27097-1-6 Point source 3000.
27097-2-7 Point source 1000.
27097-2-8 Point source 4000.
27097-20-1 Urban 5.
27097-2-2 Rural 2.
New York 0.3
Phoenix 0.07
San Francisco 0.4
San Diego 0.5
St. Louis 0.4
Newark, Ohio 0.3
or New Jersey
TABLE 13. VANE-PUMP SAMPLES SUPPUED
BY SPONSOR
(Collection on Membrane Filter)
Sample Identification
Asbestos,
ng/sample
M-182 asbestos vane
M-183 carbon vane
150
60
400
120
150
250
M-184 lub vane
M-185 carbon vane
M-187 lub vane
M-188 carbon vane
-------
28
Asbestos fibers are composed of fibrils of fairly constant diameter, but indefinite length. If the
fibers are triturated they will be reduced to fibrils which will be of random lengths. If the energy used
in the fiber-reduction process is controlled, the fibril lengths will be random, but of a reproducible but
small-range distribution of lengths. These fibrils could be considered alternate particles under fixed
conditions. By trituration of a weighed known asbestos sample and an unknown asbestos containing
sample under controlled conditions, the fibril length distribution should be comparable in each sample.
Ultrasonification has proven to be a valuable experimental tool for this process.
While it would be useful for input to health-effects studies to obtain data in terms of particle
number, this method cannot provide such data. However, as discussed in previous sections, some data
were generated that show that particle-size distribution can be estimated. More effort in that direction
would be necessary to provide useful data.
All analyses results are given in nanograms per cubic meter. Except for the data shown in Table 12,
all data are reported with a confidence of ::1:30 percent. The data in Table 12 were generated before the
reproducible technique now established had been firmly determined, and less confidence is placed in
these preliminary findings.
The data in Table 9 show some sample collections where asbestos was not found and for those
samples a "less than" value is given. These data appear to be in error because other samples taken at
about the same time and place show significant asbestos content. Analysis in triplicate of the samples
where asbestos was not found confirmed these results so it is felt that these results may represent a
sampling or meteorological anomaly. A lower detection limit could be obtained by adjustment of the
sample preparation procedure.
The value of 8200 ng/m3 obtained for the sample taken at Lockland Post Office on January 21,
1971 (Table 9) appears to be high. This value appears to be valid in that triplicate analyses of the
sample gave 7,900,9,000, and 7,200 ngJm3.
FUTURE WORK
Further research effort on methods. for the determination of asbestos in air should include the
following:
. Improvement of the current method in terms of analysis speed
. Development of optical-microscopic, infrared-absorption, or X-ray diffraction techniques
. Further investigation of particle-size distribution
. Development of optical methods aimed at continuous monitoring.
Future work aimed at the improvement of the existing electron-microscopic method for the
analysis of asbestos and the development of more rapid asbestos monitoring methods is most important.
Representative specimen preparation and the time required for the analysis of a sample are of prime
concern. Consequently, developmental effort should emphasize these two factors. Development of more
rapid and effective separation and concentration of the asbestos fractions should be investigated. With
highly effective methods for separating and concentrating the asbestos fractions, other optical, infrared,
and diffraction techniques may become feasible.
After beneficiation, the concentrated asbestos fibers may be measured by employing the optical
microscope coupled with specimen preparation which exploits optical interference to render visible
-------
29 and 30
asbestos fibers and fibrils which in ordinary specimen preparations would escape detection. In this
method, fibers whose diameters are well below that size which is resolvable by optical microscopy are
made visible by multiple-beam interferometry. Some preliminary experiments using this approach for
specimen preparation have shown promise.
Another approach to the detection of fibers suspended in fluids is a technique termed streaming
birefringence. It is based on the fact that a fiber particle will become aligned with its long axis parallel
to the flow of a fluid, and when numbers of crystalline birefringent fibers are so aligned in the field of a
polarizing microscope between crossed Nicols, the light is depolarized and the presence of fibers
becomes evident. This method was used, before electron microscopy was developed, to demonstrate the
rodlike shape of the tobacco mosaic virus particle which is ~150 A in diameter but sometimes as long as
2,000 A (0.2 /Jm).
It is envisioned that it would be possible to use two polarizing microscopes with a detector on each
to implement a null method to selectively detect the contribution of fibrous structures to the
depolarization of the polarized light. It is also envisioned that the sample could be recycled for a period
of time to obtain an integrated signal attributable to the presence of asbestos.
Since asbestos exhibits characteristic infrared absorption and X-ray diffraction, these techniques
might prove effective with proper sample treatment, including asbestos beneficiation.
Finally, because of the significance to health-effects studies, it is important to continue study on
determination of particle-size distribution.
This effort would be an extension of the effort described in this report, and attempts would be
made to describe and compare various types of air such as urban, rural, and remote, as well as air inside
public buildings.
-------
APPENDIX A
STUDIES OF BENEFICIATION OF ASBESTOS BY DIFFERENCES
IN ELECTRICAL PROPERTIES AND DENSITY
-------
A-I
APPENDIX A
STUDIES OF BENEFICIA nON OF ASBESTOS BY DIFFERENCES
IN ELECTRICAL PROPERTIES AND DENSITY
Studies of beneficiation show that the distinctive difference between the separated asbestos and the
precipitated residue is mainly the shape and size of the particles in the two fractions. Length-to-diameter
ratio may be 40 or more for the fibers and is probably 4 or less for the fly ash and dust in the
remainder. No consistent chemical differences exist because both fractions are predominantly siliceous
materials. Surface properties, as indicated by interfacial charge sign or charge density, zeta potential, or
isoelectric point are, therefore, similar.
Electrical polarization is the feature most responsible to the difference in shape factors noted
above. The term polarization is used in a loose sense to include a variety of effects induced by the
separation of unlike charges at an interface.
It is well known that electrical charges tend to concentrate at an interface between two materials
or phases in contact, because of the abrupt change in physical and chemical properties in passing across
the boundary. Such an interface is provided when either needlelike asbestos fibers or blocky particles are
suspended in a liquid. Assuming that both types of particles are suspended together in the same liquid in
an electrical field, forces can be postulated which tend to affect the long fibers more than they do the
blocky particulates. If properly applied, these forces can favor migration of the fibers to the electrodes
and their attachment to the electrode surface.
A doc field is probably preferable to an a-c field because the doc field favors polarization of the
charges on the suspended particles. The fibers will undergo greater polarization along the fiber axis and
will tend to line up parallel to the field, with the ends pointed toward the electrodes. Charge separation
will tend to cause migration toward the nearest electrode. Although charges will polarize, both on fibers
and on other particulates, the effect is much stronger' on the fibers, so fiber movement is also
theoretically more rapid.
Charge polarization is likely to have a stronger influence on agglomeration than it does on
migration. Both fibers and blocky particles will tend to remain together, after random contact from
thermal or Brownian movements. Because of the pattern of polarization, charge separation causes the
fibers to line up preferentially head to tail into longer filaments. Blocky particles also tend to aggregate
but without so much preference for straight chains. Their aggregates may become large enough to settle
out; however, separation by gravity depends upon the shape of the agglomerates.
With this experience as background, dielectric separation, electrophoretic separation, magnetic
separation, and separation by the Beckman Continuous Particle Electrophoresis (CPE) instrument were
then investigated.
Dielectric Separation
A method described by Rosenholtz and Smith( 6) for separating various minerals according to
dielectric constant (0) was utilized. Their work indicated that a mineral powder such as chrysotile
suspended in a liquid could be attracted selectively to two needlepoint electrodes immersed in a liquid
having a lower dielectric constant than that of the suspended material. Conversely the suspended mineral
(6) Rosenholtz, J. L., and Smith, T. T., "The Dielectric Constant of Mineral Powders", The American
Mineralogist, 21,115-120(1936),
-------
A-2
particles were reported to be repelled from the needles when the liquid has the higher dielectric
constant. In their work, Rosenholtz and Smith employed mixtures of carbon tetracWoride (a = 2.24),
ethyl alcohol (a = 33.7), and water (a = 81) to cover a wide range of a values. In Table 1 of that
report, over 150 minerals are shown as having been concentrated by the method, including chrysotile
with a dielectric constant of about 33.7.
For the work at Battelle, a small unit similar to the one described by Rosenholtz and Smith was
assembled. The cell was a small circular glass vessel about 2 cm deep. Both electrodes were bright
platinum wire. To investigate their observation that the dielectric constant of chrysotile was greater than
33.7, a 10-mg portion of chrysotile was dispersed ultrasonically in 100 ml of ethyl alcohol. A portion of
the liquid containing the dispersed asbestos was introduced into the glass cell, and separation was
attempted at 220 volts ac. Separation could be observed under a low-power microscope and the asbestos
fibers appeared to be flocculated around each of the two electrodes. They were not strongly attached,
and about 60 percent of the fibers fell off when the electrodes were gently lifted from the solution.
During the run, the concentration of asbestos fibers around each of the electrodes appeared to be a
loosely flocculated mass. The results of this. investigation were not encouraging because an excessive
amount of effort would be required to work with available amounts of particulate in collected samples.
Electrophoretic Batch Separations
In two attempts to concentrate chrysotile by an electrophoretic batch method the cell used was a
circular glass jar about 5 cm in diameter and 5 cm deep. The platinum screen electrodes had a
submerged area of about 1.2 cm square in the electrolyte. A power source of 0 to 500 volts dc was
utilized. To determine the collecting ability of the unit, the cell was charged with 10 mg of ultra-
sonically dispersed chrysotile in 100 ml of methyl alcohol and the separation was attempted. At 500
volts, the chrysotile flocculated, and these flocs appeared to stream from the vicinity of one electrode to
the other electrode. After about a half hour, the flocks had concentrated on the positive electrode.
When the electrodes were gently lifted from the methyl alcohol, about half the fibers fell from the
positive electrode.
A second run was made with the modification that 60 mg of fly ash was added to the 10-mg
charge of chrysotile. Again the chrysotile was found to be concentrated on the positive electrode. The
fly ash appeared to have settled to the bottom of the glass cell. The positive electrode with most of the
adhering chrysotile was lifted carefully from the cell. A microscopic examination of the attached fibers
showed them to be relatively free of fly ash. While these two methods appeared to separate chrysotile
somewhat, separations of microgram amounts of asbestos appeared to require too much time and cost;
consequently, further efforts on these methods were abandoned.
Continuous Particle Electrophoresis
Effort on other programs with the Beckman continuous particle electrophoresis (CPE) instrument
indicated that it could operate in the microgram range. Consequently, the capability of the CPE was
examined in some depth.
Preliminary investigations with asbestos and other particulates indicated that the behavior of
asbestos alone in the CPE is satisfactory in that asbestos was distributed in a reasonably narrow band.
However, some other particulates of interest are also distributed over the same general band. Subse-
quently, air samples that had been ashed, suspended, and centrifuged (as described above) were utilized
in the CPE instrument to determine whether effective beneficiation could be obtained. A portion of
suspended centrifuged material to serve as a control was f1ltered on a 17-mm-diameter 0.45-l.Lm-pore-size
Millipore f1lter and a second portion was processed through the CPE.
-------
A-3
Operating conditions were:
(1) Curtain buffer B-2
(2) pH 8.6
(3) 0.001 molar
(4) Flow rate, 20 ml/min
(5) Voltage gradient, 30 volts/cm
(6) Sample feed rate, 50 Ili/min
(7) Cell coolant flow rate, 250 ml/min at 10 C.
The CPE cell effluent was collected in 48 separate fractions. Previous determinations of the
electrophoretic mobility of asbestos indicated that it should be collected in Tubes 24, 25, and 26. The
contents of these tubes plus Tubes 23 and 27 were filtered separately on 3-mm.diameter 0.45ilm-pore-
size Millipore mters. These mters plus the 17-mm mter (not CPE processed) were counted by electron
microscopy. No values were obtained for Tube 23 as it contained too many extraneous particles to see
any asbestos. Also, the samples from Tube 27 could not be counted because of interference from an
unexplained plastic film. The observed asbestos-fiber counts per screen opening for the remaining
samples (Tubes 24, 25, and 26) were corrected so as to be equivalent in terms of filter area and volume
of the control sample.
The corrected values for Tubes 24, 25, and 26 were 28, 73, and 17 asbestos particles per screen
opening, respectively. The total of the three, 118, compares well with the value of 100 asbestos particles
per screen opening obtained on the portion of the control sample not processed by CPE. The data
indicate that little if any asbestos would have been found in Tubes 23 and 27 and that essentially
complete recovery of the asbestos was obtained. Tube 25 contained 62 percent of the asbestos found.
Most of the nonasbestos particles were collected in Tubes 23 and below, while the fractions containing
the asbestos were relatively free from the extraneous particles.
It has been calculated that the centrifuged asbestos samples were enriched by factor of 5 after the
additional CPE treatment. These results are promising, since the CPE conditions were arbitrarily chosen
and operating parameters should be expected to improve with further work. However, in light of the
acceptable and useful enrichment by centrifugation alone, it appears that only in rare cases would
separation by both centrifugation and CPE be justified.
Density Separation of Asbestos From Other Materials
One of the more constant physical properties of asbestos is specific gravity and this property might
be useful to separate it from other airborne materials by selective sedimentation according to densities.
The use of two solutions having densities slightly above and slightly below the density of asbestos could
be used to separate all materials, including the asbestos, with densities in the range between the two.
solutions.
To determine the practical feasibility of such a density separation for chrysotile (specific gravity ~
2.5) solutions were made of carbon tetrachloride (specific gravity = 1.585) and 1-, 1-, 2-,
2-tetrabromoethane (specific gravity = 2.964) having densities of 2.697 and 2.406 g/cm3. Chrysotile
should settle out in the less-dense solution and float in the other.
-------
A4
Initially, problems were encountered because of the tubular and flocculated form of the chrysotile.
The fiber clumps tended to remain suspended for long lengths of time (usually several days) before the
fibers became sufficiently wetted and all air bubbles were released. In order to avoid the problems of air
entrapment the fibers were dispersed in the fluid under a vacuum. This procedure was quite satisfactory
in dispersing flocculated asbestos and indicated that the chrysotile density was within the range from 2.4
and 2.7 gjcm3.
In order to determine the effects of other particulate matter on the density separation process,
ground chrysotile and A.C. Test Dust, mixed in the ratio 1 :20 were dispersed in water using an
ultrasonic agitator, filtered and then dried into a cake. Small amounts of this caked mixture were then
dispersed into the solutions. The test dust behaved much the same as the asbestos indicating a density in
the range 2.4 to 2.7 gjcm3. One consistent problem was the tendency of the asbestos to form flocs in
the solutions. This occurred when the concentration was as low as 1 mg of the particle mixture
dispersed in 20 ml of solution.
Again, as with the electrophoretic work, it appeared as if finding optimum conditions for density
separations would require a depth of experimental work not feasible under the project effort and no
further work was done. .
------- |