vvEPA
United States
Environmental Protection
Agency
Environmental Monitoring Systems
Laboratory
Research Triangle Park NC 27711
Research and Development
EPA-600/S4-82-021 May 1982
Project Summary
Bulk Sample Analysis for
Asbestos Content:
Evaluation of the Tentative
Method
E. P. Brantly, Jr., K. W. Gold, L E. Myers, and D. E. Lentzen
The U.S. Environmental Protection
Agency Office of Pesticides and Toxic
Substances, Washington, DC, and the
USEPA Environmental Monitoring
Systems Laboratory, Research Trian-
gle Park, NC, jointly sponsored an
effort to produce a practical and
objective analytical protocol for the
qualitative and quantitative analysis of
asbestos in bulk materials. Draft pro-
cedures were written for analysis of
bulk samples by polarized light micros-
copy (PLM) and X-ray powder diffrac-
tion (XRD). Following review, the
Tentative Method for the Determina-
tion of Asbestiform Minerals in Bulk
Insulation Samples (March 1980) was
submitted to a performance testing
program that involved multiple labora-
tory analysis of prepared samples with
known asbestos content. This report
presents the results of the testing
study and provides preliminary obser-
vations and characterization of the
utility and operational, parameters of
the tentative Method.
PLM quantitative analysis employs a
point counting procedure to estimate
the relative area occupied by asbestos
fiber within the microscope fields of
view. PLM data must be compared
with the known weight of asbestos in
the sample in order to characterize the
accuracy of the method, Data pro-
duced by the point counting procedure
are also compared with those pro-
duced by the typical quantisation pro-
cedures used by some of the partici-
pating laboratories. Accuracy and
precision of the point counting pro-
cedure are considered in two contexts:
(1) as PLM is currently used, regarding
reported data as a direct estimate of
weight percent of asbestos present
and (2) allowing adjustments of the
data to account for bias and variance
in the relationship between the relative
area occupied by asbestos and the
known weight percent of asbestos in
the sample. Information is also pre-
sented on within-laboratory variance
and the frequency of false negatives
and false positives.
A very limited amount of data was
returned for characterizing the XRD
protocol. Both thin-layer and thick-
layer (bulk) techniques were used for
quantitative XRD analysis. Because of
the small number of XRD reports and
the nonequivalence of methods em-
ployed, it is not possible to draw any
firm conclusions on the precision and
accuracy of the XRD protocol. A
general comparison of bulk and thin-
layer techniques with respect to pre-
cision, accuracy, and sensitivity is
made.
This Project Summary was develop-
ed by EPA's Environmental Monitoring
Systems Laboratory, Research Trian-
gle Park, NC, to announce key findings
of the research project that is fully
-------
documented in a separate report of the
same title (see Project Report ordering
information at back).
Introduction
An interlaboratory study was conduc-
ted to evaluate the accuracy, precision,
and general utility of the Tentative
Method forthe Determination of Asbes-
tiform Minerals in Bulk Insulation
Samples (March 1980). Twenty-two
commercial and four government labora-
tories were each supplied with 11
samples. Eight of the samples were
-formulated with a known weight of
amosite or chrysotile and a matrix
material containing primarily gypsum.
Within-laboratory duplicates, blanks,
and "real-worjd" samples of sprayed
insulation were also included in the
materials distributed to laboratories. Four
laboratories (two commercial, two gov-
ernment) chose not to participate in the
study. Th#22 participating laboratories
provided a total of 30 polarized light
microscopy (PLM) reports and six X-ray
powder diffraction (XRD) reports.
The Tentative Method includes proce-
dures for qualitative and quantitative
analysis of bulk samples by PLM and
XRD. Identification of asbestos fibers by
PLM requires the observation of six
optical properties:_morphology, color and
pleochroism, refractive indices (or dis-
persion staining colors), birefringence,
extinction characteristics, and sign of
elongation. PLM quantitative analysis
uses a point counting procedure to
estimate the percent area occupied by
asbestos fiber within the microscope
fields of view. The prepared samples
distributed in this study contained a
known weight percent of asbestos.
Because PLM analysis produces an
estimate of the relative area occupied by
asbestos, the relationship between re-
ported area percent and the known
weight percent of asbestos was investi-
gated.
Identification of sample components
by XRD analysis is accomplished by
comparison of the sample diffraction
pattern with standard reference powder
diffraction patterns. Quantitative anal-
ysis involves measuring the integrated
areas of diagnostic peaks selected from
the full XRD scan of a thin-layer sample.
Quantitative analysis must include a
correction for matrix absorption effects
and comparison with suitable external
standards. XRD affords information only
on crystal lattice structure and not on
crystal morphology. XRD analysis, there-
fore, cannot distinguish between asbes-
tos minerals and their nonasbestiform
varieties. The presence of fibrous parti-
cles in a sample must be determined by
an optical technique such as PLM.
Conclusions
Linear regression in natural logarith-
mic coordinates was used to study the
relation between the reported data, in
terms of percent asbestos by area, and
the known values, in terms of percent
asbestos by weight. The fact that'a
considerable amount of the variation in
the data was removed by regression in
logarithmic coordinates is consistent
with the assumption that area percent
and weight percent are related toy a
power function. Analysis of the regres-
sion shows that variation in the area-
weight relationship is attributable to
differences between laboratories, differ-
ences between asbestos types (chryso-
tile and amosite), and interactions
between laboratory and asbestos type.
Reported PLM data were divided into
three groups based on the quantitation
procedure(s) used by the reporting labor-
atory.
Group P—(Point count) PLM asbes-
tos area percent determi-
nations by the point count
procedure (Tentative
'. Method).
Group B—(Both) PLM asbestos area
percent determinations
by the laboratories' own
methods for laboratories
that also provided data
by the point count
method.
Group O—(Other) PLM asbestos
area percent determina-
tions by the laboratories'
own methods for labora-
tories declining to use
the point count method.
Considering reported PLM results as
direct esti mates of the weight percent of
asbestos (i.e., ignoring the problem of
relating area percent and weight per-
cent), it was found that Group O is
significantly more biased than Group P.
Groups P and B are similarly biased.
Point counting has a greater positive
bias on amosite samples than on chryso-
tile samples. For a sample containing 10
percent chrysotile by weight, the aver-
age bias (b) of Group P is 18.5 percent;
for 50 percent chrysotile, b = -24.2
percent; for 10 percent amosite, b =
118.5 percent; for 50 percent amosite, b
= 12.1 percent.
A regression relating standard devia-
tions and means of reported PLM results,
when performed'in natural logarithmic
coordinates, did not establish any differ-
ences among Groups P, B, and O with
respect to precision. The standard devi-
ation of Group P is directly related to the
mean reported value. Precision may be
expressed as the coefficient of variation
(CV). The CV is less than 100 percent on
samples containing more than approxi-
mately 6 percent asbestos by area, and
less than 50 percent on samples con-
taining more than approximately 32
percent asbestos by area. At a mean
reported value (MP) of 10 percent asbes-
tos, CV & 79 percent; at M P = 20 percent,
CVs61 percent; at MP = 50 percent, CV
s=41 percent.
Analyses were performed on trans-
formed data to investigate improve-
ments in data quality that might be
made by adjusting (calibrating) individ-
ual laboratory results. If the parameters
of the area-weight relationship are used
to transform reported area percent data
to predicted weights, a considerable
gain in accuracy is achieved, as meas-
ured by the average percent absolute
error. By this measure Of accuracy.
Group O has a greater error than Group
P on samples containing less than 20
percent asbestos by weight. Residual
variance in the transformed data is
measured by the mean squared error
about the regression line. Bythis meas-
ure of variance. Group P was foundto be
significantly more precise than Groups
B and O. Further analysis of adjusted
data indicates that laboratories using
point count analysis are. better able to
distinguish samples containing more
than 7 percent from those with less than
7 percent asbestos by weight than they
are able to distinguish samples with
more than 1 percent from those with
less than 1 percent asbestos by weight.
Samples from the chrysotile series
were included as within-laboratory dup-
licates. Although a more extensive effort
would be required .to adequately eval-
uate the precision of the PLM protocol
on repeated analysis of the same sam-
ple, a gross estimate using'the present
data indicates that within-analyst vari-
ability accounts for less than 25 percent
of the total variance.
One of the important characteristics
of the point count procedure to be
evaluated is the likelihood of its gener-
ati ng fa Ise positives and false negatives.
-------
A false positive occurs when an analyst
reports asbestos present in a sample
that does not contain asbestos. A false
negative occurs when an analyst reports
no asbestos present in an asbestos-
containing sample. Data produced by
point counting included five false nega-
tives out of a total of 19 analyses of the
1.2 percent chrysotile sample. One false
negative out of 19 analyses was reported
for the 4.9 percent chrysotile sample.
No false negatives were reported for any
amosite samples or for any samples
containing more than 5 percent chryso-
tile by weight. The reporting of false
negatives is more likely due to the vari-
ability of sample and slide preparation
steps than to the point counting proce-
dure perse. One false positive out of 19
analyses was reported for the series of
blank samples and was probably due to
contamination. The probability of a false
negative on the 4.9 percent chrysotile
sample was 0.05 (1/19). EPA currently
recommends the analysis of at least
three samples of a suspect material. The
rate of false negatives is such that the
analysis of three samples, if each con-
tained at least 5 percent asbestos by
weight, would result in three false
negatives with a probability less than
0.03 and possibly as low as 0.001.
The six laboratories reporting XRD
results were gfouped into two general
categories for p urposes of data ana lysis.
These categories, thin-layer and bulk,
were defined on the basis of the XRD
technique used for quantitative ana lysis.
Three of the laboratories performed the
requested analyses using some varia-
tion of the thin-layer method ofquanti-
tation included in the Tentative Method.
The remaining three laboratories used
alternative bulk or thick-layer methods
of quantitation. It should be emphasized
that within categories none of the
methods used were strictly equivalent.
Moreover, within the thin-layer group,
no laboratory followed the Tentative
Method protocol exactly.
Because of the small number of
participating laboratories reportingXRD
results, and the nonequivalence of
methods employed, it is not possible to
draw any firm conclusions from the
reported results about the accuracy and
precision of the XRD method. However,
from a general comparison of bulk vs.
thin-layer methodology, two observa-
tions can be made.
First, bulk methods appear to be at
least as accurate/and precise as thin-
layer methods over the range of samples
included in this study and significantly
more accurate for the analysis of chryso-
tile.
Second, there is a suggestion that
thin-layer methods of analysis may be
more reliable (i.e., more sensitive) than
bulk methods at the 1 percent level of
chrysotile in a simple matrix.
Data produced by thin-layer methods
of analysis included one false negative
out of three analyses of the 4.9 percent
chrysotile sample. The same laboratory
reported chrysotile false positives for all
amosite samples and for the blank
sample with reported chrysotile values
ranging from <1 to 8 percent. A second
laboratory reported one false negative
out of three analyses in the 19.4 percent
'chrysotile sample.
Data produced by bulk methods of
analysis included two false negatives
out of three analyses of the 1.2 percent
chrysotile sample. One of these labora-
tories also reported a false positive
amosite in the 4.9 percent chrysotile
sample.
Recommendations
The study presented in this report is a
preliminary evaluation designed to de-
termine the precision and accuracy of
the Tentative Method as applied to
carefully prepared samples. It should be
emphasized that the samples analyzed
consisted of only two types of asbestos
fiberand a single matrix material. Only
one type of asbestos was included in
any given sample. One of the main
obstacles to reliable analysis of bulk
samples is the variability of sample
composition. Complete characterization
of the method requires that several
issues be addressed, as discussed be-
low. The highest priority; however,
should be assigned to investigations
that will extend the application of the
method to a range of real-world samples
involving different fiber types and mat-
rices.
Polarized Light Microscopy
Several aspects of the PLM method
.require further investigation. Briefly,
future studies should be designed to
determine the following:
1. The feasibility of specifying defini-
tive sample preparation proce-
dures to be used for quantitative
PLM analysis;
2. The proportion of total variance
attributable to individual proce-
dures of the method, i.e., sample
preparation, sub-sampling, and
point counting;
3. The proportion of total variance
contributed^ by within-laboratory
variability;
4, The effect of specific variables
within the point counting proce^
dure, including the number of
points to be counted, magnification
used, and the possible bias intro-
duced by the use of a 25-point
reticle instead of a cross-hair
reticle;
5. The possibility of introducing a
staged point counting process that
would allow.fewer counts to be
determined on samples with a
high percentage of asbestos;
6. The effect of the presence of more
than one type of asbestos in a bulk
sample;
7. The feasibility of individually cali-
brating PLM laboratories with
information derived in round robiri
sample analysis programs.
Recommendations for specific
changes to the method include elimina-
tion of the confidence interval calcula-
tion and revision of the rule for reporting
1 percent asbestos.
It is apparent from the results of this
study that some type of training would
be required to achieve comparable
application of the PLM protocol between
laboratories. While point counting is a
classical petrographic technique, it is
notastandard procedure inthe majority
of laboratories currently analyzing bulk
samples for asbestos. Training alterna-
tives might include regional courses
and distribution of split samples analo-
gous to the NIOSH program for. the
asbestos afr sampling method.
It should also be noted that the PLM
method presented, although an improve-
ment over subjective techniques, is still
a procedure for estimating the relative
area occupied by asbestos fiber and
matrix material. Alternative analytical
techniques that measure weight percent
directly or that provide an empirically
more satisfying relationship to relative
weight of asbestos fiber should be
sought and investigated.
X-Ray Powder Diffraction
There are two major areas in the
application of XRD techniques to quanti-
tative analysis of asbestiform minerals
in bulk materials that require further
investigation: identification andcharac-
-------
terization of standard reference mate-
rials, and further development and
evaluation of thin-layer and bulk meth-
ods of analysis.
The most common concern of labora-
tories participating in the evaluation of
the XRD protocol was the lack of well-
characterized, readily available refer-
ence materials. A thorough, systematic
investigation of asbestiform materials
for use as standard materials should be
undertaken. This should include identifi-
cation of major sources; determination
of availability and cost; and complete
mineralogical characterization and de-
termination of purity, particle size distri-
butions, and powder diffraction patterns
of materials from these sources.
Since asbestos minerals vary in com-
position depending on the source and
exhibit different behaviors in grinding,
peak positions and/or relative intensi-
ties of XRD patterns may vary from
sample to sample. This variability is
particularly problematic for the amphi-
bole minerals. A quantitative study to
assess the comparability of X-ray re-
sponse of asbestos minerals from dif-
ferent sources should be conducted. If
possible, observed differences between
different samples of the same asbestos
variety should be correlated with specific
sample characteristics (e.g., chemical
composition and particle size).
The need for further development and
evaluation of both thin-layer and bulk
methods of XRD analysis is underscored
by the following observations: few
laboratories .are currently set up to
routinely perform the thin-layer analysis
as prescribed; the proposed thin-layer
method of quantitation is considerably
more time-consuming and costly than
bulk or thick-layer methods; and for
samples analyzed in the methods evalu-
ation study, the;bulk method was at
least as acc.urate and precise as the
thin-layer method.
In particular, a comparison of the bulk
and thin-layer methods should be made
over a variety of asbestos types and
matrix materials, with attention given to
sample preparation requirements, instru-
ment requirements, sensitivity, preci-
sion, accuracy, and speed and cost of
analysis.
For both bulk and thin-layer methods,
the following areas of investigation are
proposed:
1. Assessment of sample preparation
requirements;
2. Assessment of preferred orienta-
tion effects on quantitative.anal-
ysis;
3. Assessment of the effect of the use
of the step-scanning mode of
analysis on the limits of detection;
and
4. Assessment of absorption correc-
tion requirements and techniques.
Results and Evaluation
Polarized Light Microscopy
Eleven sample series were distributed
to laboratories. Eight of the series were
targeted at specific weight percents of
asbestos fiber. Two species of asbestos
were used, chrysotile and amosite. One
matrix material, containing primarily
gypsum, was used in all prepared sam-
ples. Target weights were designed to
cover a wide range of asbestos concen-
trations approximately equally spaced
on a logarithmic scale. Blanks (Series F)
were provided as controls and for deter-
mining the method's potential for pro-
ducing false positives. The "real-world"
sample (Series J) was included for
comparison of between-laboratory var-
iance. Duplicates (Series K) were in-
cluded to estimate the average within-
laboratory variance. Target weights and
allowable limits for matrix and asbestos
fiber in each sample series are presented
in Table 1.
Table 1. ' Sample Composition
.Group means and standard deviations
are summarized in Table 2. Note that in
six of nine cases the mean (MP) of the
point count group is closer to the
nominal weight than the mean (MB) of
Group B. This is not a significant differ-
ence, and it appears that Groups P and B
are comparably biased. Note also in
Table 2 that estimates by Group 0 are
consistently higher .than those by
Groups P and B. Sign tests suffice to
show that Group 0 is significantly more
biased than Groups P and B. Ninety-
percent confidence intervals were cal-
culated for Group P data. Using the
midpoints of the confidence intervals,
the average percentbias was calculated
at several weight percent levels. These
are presented in Figure 1. The percent
bias varies with weight percent -of
asbestos similarly for amosite and chry-
sotile samples. Point counting has a
greater positive bias on amosite samples
than on chrysotile samples and, in fact,
underestimates asbestos content in
samples containing more than about 18
percent chrysotile by weight.
The standard deviation of reported
PLM data increases as the mea n reported
area percent of asbestos increases for
all groups. Precision may be expressed
as the percent-relative standard devia-
tion or CV. CV is related to means (MP)
for Group P in Figure 2. The CV is less
than 100 percent on samples with more
Series
C
A
E
1
H
G
D
B
F
J
Aft-
Target
Wt. %
1
; .4
16
64
2
8
16
32
0
-
Varies
Actual
Wt. %
1.2
4.9
19.4
74.5
2.5
9.8
19.4
38.8
0
50,0*
Varies
Fiber
Type
Chrysotile
Chrysotile
Chrysotile
Chrysotile
Amosite
Amosite
Amosite
Amosite
None
Chrysotile
Chrysotile
Wt. of
Asbestos (g)
0.05
0.20
0.80
3.20
0.10
0.40
0.80
1.60
±
±
±
±
±
±
±
±
.005
.01
.01
.01
.01
.01
.01
.01
None
-
—
Wt. of
Matrix (g)
.4.95
4.80
4.20
1.80
4.90
4.60
4.20
3.40
3.0
±
±
' ±
±
•±.
±
±
±
— -
-
—
.05
.05
.05
.05
.05
.05
..05
.05
5.0
*Mean of reported areapercents, Groups P and B.
•f Series K samples were provided as duplicates and included samples from series C, A,
E, and I.
4
-------
Table 2. Means and Standard Deviations of Reported PLM Results, by Group (P
B, 0)
(percent asbestos by area)
Means
Standard Deviations
Series Type
Weight
MP
MB
MO
SP
SB
SO
C
A
E
1
H
G
D
B
F
J
Chrysotile
Chrysotile
Chrysotile
Chrysotile
Amosite
Amosite
Amosite
Amosite
None
Environmental
1.2
4.9
19.4
74.5
2.5
9.8
19.4
38.8
0.0
-
4.2
7.3
21.7
64.3
12.5
26.2
37.8
48.9
0.2
50.7
5.3
4.9
19.0
63.0
18.0
29.3
42.3
57.7
0.0
49.3
7.4
24.8
42.0
85.6
24.0
40.0
41.4
65.0
1.0
65.0
4.5
6.3
14.8
19.6
8.6
16.9
17.7
19.5
0.9
16.1
5.3
2.9
5.9
. 17-.3
13.9
17.3
17.5
17.4
0.0
14.7
7.3
27.5
24.6
4.7
18.3
12.7
12.4
21.5
2.2
11.2
than approximately 6 percent asbestos
by area and less than 50 percent on
samples with more than approximately
32 percent asbestos by area. At M P= 10
percent asbestos, CV = 79 percent; at
MP = 20 percent, CVs 61 percent; atMP
= 50 percent, CV = 41 percent.
It is of interest to evaluate the accuracy
of the PLM methods after adjusting for
the relationship between reported area
percent and th.e known weight percent
of the sample,^. This allows not only a
better understanding of what reported
PLM data mean but also indicates what
improvements might be made in data
quality by adjusting PLM area percent
estimates to better represent weight
percent. Area percent data were ad-
justed for laboratory and asbestos-type
effects to yield predicted weight percent
values for each individual result. The
most obvious and expected result in
comparingthe average percent absolute
errors of treated and untreated data is
the considerable gainin accuracy (reduc-
tion of error) that results from the trans-
formation. After transformation, the
average Group P inaccuracy is only one-
fifth of the original. Adjusted Group P
data are significantly more precise than
those of Groups B and 0. If laboratories
had access to information with which
they could calibrate their results (accord-
ing to the area-weight relationship for
each laboratory and asbestos type),
considerable gains in accuracy and
precision of results could be achieved.
The gains in precision would be greater
for laboratories using the point counting
quantitation procedure than for labora-
tories using alternative procedures.
X-Ray Powder Diffraction
Means and standard deviations of all
reported XRD results are shown in Table
3. Average reported values for XRD are
shown for bulk methods, thin-layer
methods, and both methods together.
Except for Series G, the means of the
bulk method are closer to the reference
values than those of thethin-layer meth-
od. Estimates of precision/given by the
coefficient of variation, showed no sig-
nificant difference between bulk and
thin-layer methods. Considering individ-
ual CVs, those for bulk are all less than
or equal to those for thin-layer, except
for Series C and B, further suggesting
that bulk methods are at least as precise
as thin-layer'methods, as applied by
laboratories in this study.
Comparison of the bulk and thin-layer
methods by asbestos type i ndicates that
for analysis of Chrysotile, bulk methods
are significantly less biased than thin-
layered methods. No significant differ-
ence in slopes (bias) was observed
between bulk and thin-layer methods
for amosite.
The results do give evidence that XRD
is capable of detecting chrysotile at the
1 percent level in a simple matrix and
suggest that at this level the thin-layer
method may be more reliable. Further
investigation is required to determine
reliable detection limits over a variety of
sample materials for both procedures.
Bulk methods appear to be at least as
accurate and precise as thin-layer meth-
ods over the range of samples included
in this study and significantly more
accurate for the analysis of chrysotile.
Since chrysotile is the most commonly
occurring asbestos mineral jn bulk
insulation materials, and since most
laboratories routinely performing quan-
titative analysis of asbestos in insulation
samples use bulk methods of analysis,
use of bulk methods of XRD analysis
(ancillary to PLM) should be given
further consideration.
-------
100
80
60
40
I
20
-20
-40
amosite
chrysolite
<20 40 60 -»„.. 80
Asbestos we.fght percent
100
Figure 1. Average percent bias of Group P (point count} data.
-------
7.7
7.0
.5
I
1
.7
.6
.5
.4
chrysotlle
amosite
20
40 60
Group P mean
80
100
Figure 2. Coefficient of variation of Group P (point count) data.
Table 3. Means and Standard Deviations of Reported XRD Results
(percent asbestos)
Weight Thin-Layer Bulk Pooled
Series
C
A
E
1
H
G
D
B
F
Type
Chrysotile
Chrysotile
Chrysotile
Chrysotile
Amosite
Amosite
Amosite
Amosite
None
%
1.2
4.9
19.4
74.5
2.5
9.8
19.4
38.8
0
M
3.0
3.3
3.7
50.0
1.5
7.0
28.0
61.0
0.2
S
2.0
3.5
3.5
7.1
0.7
5.7
12.7
11.3
0
M
1.0
4.3
18.0-
74.5
3.0
21.7
24.0
52.0
0
S
1.7
4.2
11.4
0.7
1.4
4.2
6.9
22.5
0
M
2.5
4.3
10.8
62.2
2.8
15.8
25.6
55.6
0
S
1.8
3.3
10.9
14.7
1.0
9.0
8.3
17.6
0
*USGPO: 1982—559-092/3407
i
-------
E. P. Brantly, Jr., K. W. Gold. L E. Myers, and D. E. Lentzen are with the
Research Triangle Institute. Research Triangle Park, NC 27709.
J. J. Breen and M. E. Beard are the EPA Project Officers (see below).
The complete report, entitled "Bulk Sample Analysis for Asbestos Content:
Evaluation of the Tentative Method." (Order No. PB 82-196 841; Cost:
$13.50, subject to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield. VA 22161
Telephone: 703-487-4650
The EPA Project Officers can be contacted at:
Environmental Monitoring Systems Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711 ,
United States
Environmental Protection
Agency
Center, for Environmental .Research
Information
Cincinnati OH 45268
Postage and
Fees Paid
Environmental
Protection
Agency
EPA 335
Official Business
Penalty for Private Use $300
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