United States
Environmental Protection
Agency
Environmental Monitoring
Systems Laboratory
Las Vegas NV 89114
Research and Development
EPA/600/S4-86/027 Dec. 1986
SERA Project Summary
Test Procedure for Gross
Alpha Particle Activity in
Drinking Water: Interlaboratory
Collaborative Study
E. L. Whittaker
A new test procedure for measuring the
concentration of gross alpha particle activ-
ity in drinking water samples was multi-
laboratory tested with 18 laboratories in
a collaborative study. Gross alpha activity
values were calculated with four different
alpha emitting radionuclide standard count-
ing efficiencies to see which standard was
best for gross alpha activity determina-
tions. Thorium-230, a pure alpha emitter,
appeared to be the best standard for gross
alpha counting efficiency.
Water samples A, B, C, and D contained
gross alpha concentrations of 74.0 pCi/L,
52.6 pCi/L, 4.8 pCi/L, and 10.0 pCi/L, re-
spectively, at three hours after separation
of the alpha emitting radionuclides from
the water by coprecipitation with iron
hydroxide and barium sulfate. A statistical
analysis of the test results from the 18
laboratories, using the Th-230 counting
efficiency, showed coefficients of variation
for repeatability (within-laboratory preci-
sion) of 7.9 percent, 7.8 percent, 8.7 per-
cent, and 8.8 percent, respectively, for an
average of 8.3 percent. The analysis also
showed coefficients of variation for repro-
ducibility (combined within- and between-
laboratory precision) of 20.4 percent, 16.8
percent, 18.7 percent, and 18.5 percent,
respectively, for an average of 18.6
percent.
A comparison of the 18 laboratory grand
average results (calculated with the
Th-230 counting efficiency) with the
known gross alpha particle concentrations
showed accuracy indexes of 91.9 percent,
99.4 percent, 122 percent, and 94.5 per-
cent, respectively, for an average accuracy
index of 102 percent. The t-test to show
significant difference applied to the data
showed a significant bias (+) for sample
C but no significant bias for the other three
samples.
A secondary purpose in this study was
to see how well the Ra-226 concentration
of a drinking water sample could be esti-
mated from an early gross alpha count
(three hours after separation) subtracted
from a late gross alpha count (seven days
after separation) and calculated from the
equation provided in the test procedure.
Water samples A, B, C, and D contained
Ra-226 concentrations of 47.2 pCi/L, 20.5
pCi/L, 3.0 pCi/L, and 0.0 pCi/L, respec-
tively. A statistical analysis of the test
results from the 18 laboratories (17 labor-
atories for sample C) showed coefficients
of variation for repeatability (within-
laboratory precision) of 8.2 percent, 9.5
percent, and 14.8 percent for samples A,
B, and C, respectively, for an average of
10.8 percent. The analysis also showed
coefficients of variation for reproducibility
(combined within- and between-laboratory
precision) of 20.5 percent, 25.8 percent,
and 23.8 percent, respectively, for an
average of 23.4 percent.
A comparison of the 18 laboratory (17
laboratories for sample C) grand average
results with the known Ra-226 concentra-
tions showed accuracy indexes of 98.3
percent, 102 percent, and 96.7 percent,
respectively for samples A, B, and C, for
an average of 99.0 percent. The t-test to
show significant differences applied to the
data showed no significant bias in the
method.
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This method for gross alpha particle
concentration measurement eliminates the
dissolved solids interference problem
(which is a significant problem for the EPA
approved method) and provides for greater
sensitivity by allowing for the use of much
larger samples in the analysis, ft is recom-
mended that the method be accepted as a
validated method for gross alpha activity
in drinking water. It is further recom-
mended that the method be accepted as
a valid method for the estimation of
Ra-226 concentrations in drinking water.
This Project Summary was developed
by EPA's Environmental Monitoring Sys-
tems Laboratory, Las Vegas, NV, 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
The National Interim Primary Drinking
Water Regulations (NIPDWR) require a
gross alpha activity measurement of all
public drinking water supplies as a screen-
ing determination of the presence of alpha
emitting radionuclides. The need for speci-
fic radionuclide analysis of water supplies
is therefore dictated by the gross alpha
activity test results of those supplies.
Alpha emitting radionuclides are not
separated from the dissolved solids of the
sample in the Environmental Protection
Agency (EPA) approved test procedures
for gross alpha activity. An aliquot of the
sample is simply evaporated to dryness,
and the residue is counted for alpha
activity. Drinking water supplies vary
widely in dissolved solids concentrations
(from less than 100 to over 5,000 mg per
liter). The recommended maximum evap-
orated dissolved solids residue in a 2-inch
diameter counting dish is 100 mg (5 mg
per square centimeter) because of the
sample residue self-absorption of the
alpha particles. For drinking water supplies
with dissolved solids greater than 500 mg
per liter, the approved test procedure for
gross alpha activity measurement is lim-
ited because of the small aliquots that can
be analyzed and because of the very long
counting times that are necessary to meet
the required sensitivity of measurement (3
pCi/liter).
A new test procedure for gross alpha
activity was reported by Robert Lieberman
of the EPA Eastern Environmental Re-
search Facility (EERF) at the 1982 Health
Physics Meeting in Las Vegas, Nevada.
The new procedure (see Appendix B of the
Project Report) coprecipitates all alpha
emitting actinides with barium sulfate and
iron hydroxide carriers, and thereby
separates the alpha emitting actinides
from other sample dissolved solids. Larger
sample aliquots can be analyzed so that
the alpha measurement sensitivity is
improved, and the necessary counting
time is minimized.
This new procedure, "Test Procedure for
Gross Alpha Particle Activity in Drinking
Water by Coprecipitation," has been
tested by 18 laboratories in a collaborative
study, and the results are described in this
report.
A major purpose for gross alpha activity
measurements of all public water supplies
has been to screen those supplies for a
potential Radium-226 health hazard to the
public. A secondary purpose in this study
was to determine how well an estimate of
the Radium-226 content of a water sam-
ple could be made by an early and by a late
count of the gross alpha activity after
separation from the water sample.
Precision, accuracy, and bias statements
are made in this report for both gross alpha
activity measurements and for the esti-
matted Radium-226 content of each
sample.
The study was conducted by the author
while employed at the EPA Environmental
Monitoring Systems Laboratory at Las
Vegas, Nevada, and this reporting of that
study was done as an employee of
Lockheed Engineering and Management
Co., Inc. (LEMSCO), for the EPA under
Contract No. 68-03-3249, Task 70.12
Procedures
Analytical Test Procedure
The analytical test procedure (method)
used in this study is described in detail in
Appendix B of the Project Report. The
method provides for quantifying drinking
water gross alpha particle concentrations
from liter size samples and for estimating
the Ra-226 concentrations in those sam-
ples. The method provides for coprecipi-
tating all non-gaseous alpha emitting
radionuclides in drinking water samples
with barium sulfate and iron hydroxide
which is followed by counting the alpha
particle emissions from the coprecipitate.
Two alpha counts of the coprecipitate, one
early (three hours) and one late (seven
days) after coprecipitate separation, are
used to estimate the Ra-226 concentra-
tion of the sample.
Collaborative Test Procedure
Twenty-eight laboratories responded to
an invitation to participate in the test of
the method Eighteen laboratories submit-
ted test results. Participants were provided
with standard solutions (four standards)
for determining standard counting effici-
encies. They were also provided with four
sample concentrates which were to be
diluted with their tap water according to
the detailed instructions (provided in
Appendix C of the Project Report).
Data Processing Procedures
The data from the 18 laboratories were
tested for outliers by the ASTM recom-
mended criterion for rejection (ASTM
1980), Equation 1.
T, = (X, - X)/S
(1)
where: T, = test criterion
X, = a test result for a
_ given sample
X = arithmetic average of
all \n values
S = the estimate of the
population standard
deviation based on the
sample data
Critical values for T for a five percent, two-
sided level of significance were used for
the rejection criterion.
A statistical evaluation of the test re-
sults was carried out by the procedures
described in E-691, E-177, and E-178 of the
ASTM Standard Part 41, 1980. The stand-
ard deviations, other statistical parame-
ters, and equations for their calculations
are listed below. The standard deviation of
individual participant (or laboratory) test
results, S|j, was determined by Equation
2.
[—1
nij _
z
h = 1 J
(2)
where: X|jh = the result reported for
the h replicate of the j
_ sample material by lab i
X,j = the mean of the
individual results for
sample j for lab i
njj = the number of
replicates reported for
sample j by lab i
The repeatablity (within-laboratory stand-
ard deviation, srj, for each sample was
determined by Equation 3 since the
number of replicates was the same (three)
for all participants.
P
Sr. = I 1/P V d..2 \ -- (3)
where: P = the number of participants
in the study.
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The standard deviation of the grand
average for each sample sXj, was deter-
mined by Equation 4.
Xj = I (Xij - Xj)2/(P-1)
1/2
(4)
where: Xjj = the average of the test
results for sample material
_ ji by Lab i
Xj = the grand average for
sample material j
The standard deviation of between-
laboratory precision for each sample ma-
terial, sLj, was determined by Equation 5.
1/2
SU =
The reproducibility (combined within- and
between-laboratory) standard deviation
for each sample, sRj, was determined by
Equation 6.
1/2
(6)
The percent coefficient of variation for
repeatability (within-laboratory precision
[also called repeatability index]) for sam-
ple j, vrj% was determined by Equation 7.
= 100 Sr,/Xj
(7)
The percent coefficient of variation for
between-laboratory precision for sample
J, vLj% was determined by Equation 8.
= 100 Sl/X (8)
The percent coefficient of variation for
reproducibility (combined within- the
between-laboratory precision [also called
reproducibility index]) for sample J, vRj%
was determined by Equation 9.
vR% = 100
(9)
The accuracy index, a percent relationship
of the grand average to the known value
for the j sample, Aj%, was determined by
Equation 10.
Xi
AJ% = 100-
i i
(10)
where
YJ = the known value for the j sam-
ple material (pCi/L)
Percent Bias was determined by Equation
11.
Y-Xj
% Bias = x 100 (11)
Y
where
Y = The known value
The t-test to determine significant differ-
ences or systematic error for sample j, tj
was performed using Equation 12.
, (P-1) degrees of freedom(12)
p',
1/2
where
P = number of participants
YJ = known value of the sample j con-
taminant concentration
tc = critical value for the number of
participants, values for tj greater
than tc are significantly different
and show a systematic error.
(5) Results and Discussion
Summaries of the statistical evaluation
of the gross alpha concentration test
results for the four samples, as calculated
with the four standard counting efficien-
cies, are given in Tables 1 through 4 of this
report. The multilaboratory data tables
from which these evaluations were made
are given in the Project Report.
Water samples A, B, C, and D contained
gross alpha concentrations of 74.0 pCi/L,
52.6 pCi/L, 4.8 pCi/L, and 10.0 pCi/L,
respectively, at three hours after separa-
tion from the water samples by coprecipi-
tation. A statistical analysis of the test
results from the 18 laboratories, using the
Th-230 counting efficiency, showed coef-
ficients of variation for repeatability
(within-laboratory precision) of 7.9 per-
cent, 7.8 percent, 8.7 percent, and 8.8
percent, respectively, for an average of 8.3
percent. The analysis also showed coeffi-
cients of variation for reproducibility (com-
bined within- - and between-laboratory
precision) of 20.4 percent, 16.8 percent,
18.7 percent, and 18.5 percent, for an
average of 18.6 percent.
A comparison of the 18 laboratory grand
average results (calculated with the
Th-230 counting efficiency) with the
known gross alpha particle concentrations
showed accuracy indexes of 91.9 percent,
99.4 percent, 122 percent, and 94.5 per-
cent, respectively, for an average accuracy
index of 102 percent. The t-test to show
significant difference, when applied to the
data, showed significant bias (+) for sam-
ple C but no significant bias for the other
three samples.
A secondary purpose of this study was
to see how well the drinking water sample
Ra-226 concentration could be estimated
from an early gross alpha count (three
hours after separation) subtracted from a
late gross alpha count (seven days after
separation) and calculated from the equa-
tion provided in the test procedure. A sum-
mary of the statistical analyses of the
estimated Ra-226 concentrations of the
samples is given in Table 5 of this report.
The multilaboratory data table from which
these evaluations were made is given in
the Project Report.
Water samples A, B, C, and D contained
Ra-226 concentrations of 47.2 pCi/L, 20.5
pCi/L, 3.0 pCi/L, and 0.0 pCi/L, respec-
tively. A statistical analysis of the test
results showed coefficients of variation for
Table 1. Gross Alpha Particle Activity in Water Sample A Precision,
Accuracy and Bias Summary
Sample A, pCi/L using various standard efficiency factors
Parameter9
Am-241
Ra-226
Th-230
Uranium
YjtpCi/L)
Xj(pCi/LI
AJ(%)
Bias (%f>
SjjtpCi/U
Srj
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Table 2. Gross Alpha Particle Activity in Water Sample B Precision,
Accuracy and Bias Summary
Sample B, pd/L using various standard efficiency factors
Parameter3
YjIpd/U
Xj(pd/Ll
At<%)
Bias (%)b
SjjtpCi/U
SntpCi/U
SLl(pd/U
SRl(pCi/LI
Vr/(%)
VLj(%>
VRjl%)
Tf
Am-241
52.6 ± 2.6
38.0
72.2
-27.7
7.1
2.8
6.9
7.4
7.4
18.1
19.5
8.74
Ra-226
52.6 ± 2.6
48.4
92.0
-8.0
8.6
3.7
8.3
9.1
7.6
17.1
18.8
2.07
Th-230
52.6 ± 2.6
52.3
99.4
-0.6
8.2
4.1
7.8
8.8
7.8
14.9
16.8
0.15
Uranium
52.6 ± 2.6
58.9
112.0
+ 12.0
10.5
5.0
10.1
11.3
8.5
17.1
19.2
2.54
aParameters are described in text.
bThe sign before the number indicates the direction of bias.
°The critical value (tc) for significant difference for 18 participating labs is 2.11
at the 5 percent significance level.
Table 3. Gross Alpha Particle Activity in Water Sample C Precision,
Accuracy and Bias Summary
Sample C, pCi/L using various standard efficiency factors
Parameter3
YjIpd/U
XjtpCi/L)
AJ(%)
Bias (%)"
S^lpd/U
Srj(pd/U
SLl(pd/U
SRjfpCi/U
Vr/(%)
VLj(%)
VR>(%)
Tf
Am-241
4.8 ±
4.29
89.4
-10.6
0.83
0.37
0.81
0.89
8.6
18.9
20.7
2.55
Ra-226
0.24 4.8 ±
5.38
112.0
+ 12.1
1.01
0.53
0.96
1.10
9.8
17.8
20.4
2.42
Th-230
0.24 4.8 ±
5.87
122.0
+ 22.3
1.02
0.51
0.98
1.10
8.7
16.7
18.7
4.32
Uranium
0.24 4.8 ± 0.24
6.53
136.0
+ 36.0
1.18
0.57
1.13
1.26
8.7
17.3
19.3
6.04
aParameters are described in text.
bThe sign before the number indicates the direction of bias.
°The critical value
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Table 4. Gross Alpha Particle Activity in Water Sample D Precision,
Accuracy and Bias Summary
Sample D, pd/L using various standard efficiency factors
Parameter8
Yj(pCi/U
Xjfpd/U
A:(%i
Bias (%)b
S^jfpCi/U
Srj(pCi/U
SL/(pCi/L>
Spj(pCi/U
Vrj-/%)
VL/(%I
VRJt%)
Tf
Am-241
10.O ± 0.5
6.95
69.54
-30.5
1.60
0.57
1.56
1.66
8.2
22.4
23.9
8.03
Ra-226
10.0 ± 0.5
8.83
88.3
-11.7
2.12
0.77
2.07
2.21
8.7
23.4
25.0
2.34
Th-230
10.0 ± 0.5
9.45
94.5
-5.5
1.61
0.83
1.54
1.75
8.8
16.3
18.5
1.45
Uranium
10.0 ± 0.5
10.59
106.0
+ 6.0
1.46
0.90
1.36
1.63
8.5
12.8
15.4
1.73
coprecipitated by the method be used for
gross alpha particle determinations of
drinking water samples.
It is recommeded that this test proce-
dure be considered a valid method for
estimation of Ra-226 concentrations in
drinking water.
aParameters are described in text.
bThe sign before the number indicates the direction of bias.
cThe critical value ltc) for significant difference for 18 participating labs is 2.11
at the 5 percent significance level.
Table 5. Estimated Radium-226 in Water Samples Precision,
Accuracy and Bias Summary
Water Samples1'
Parameter*
YjIpd/L)
Xjipd/U
AJ(%)
Bias (%lb
Sxj(pCi/U
Sr/(pCi/L)
SLjlpCi/U
SRllpCi/L)
Vrjf%)
VLJ(%)
Vf,j(%)
Tf
A
47.2 ± 2.4
46.4
98.3
-1.7
8.8
3.8
8.7
9.5
8.2
18.7
20.5
0.39
B
20.5 ± 1.0
20.9
102.
+ 1.9
5.1
2.0
5.0
5.4
9.5
23.9
25.8
0.33
C
3.0 ± 0.1
2.9
96.7
-3.3
0.6
0.43
0.55
0.69
14.8
19.0
23.8
0.71
D
0.0
0.0
aParameters are described in text.
bSee the text for water sample radionuclide content.
°The sign before the number indicates the direction of bias.
dThe critical value (tc> for significant difference for 18 participating labs is 2.11
at the 5 percent significance level. The tc for 17 labs (sample C) is 2.12.
factor into a single factor (referred to as
the counting efficiency factor in this
report) appears to be acceptable when
standards are carried through the same
analytical process as the samples. Copre-
cipitate weights reported by the labora-
tories for the standard samples and water
samples (listed in the Project Report)
showed good precision within laboratories.
Recommendations
It is recommeded that the method
tested in this study be considered a valid
alternate test procedure for the determina-
tion of gross alpha particle concentrations
in drinking water.
It is recommeded that the Th-230
counting efficiency of standard samples
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Table 6.
Sample Spike Concentrations and Gross Alpha Test Results
Sample Spike
Concentrations Gross Alpha pd/La
Am-241
Fta-226
777-230
Uranium
Sample A
Fta-226
Po-210
bGross
Alpha
Sample B
Ra-226
Po-210
Uranium
bGross
Alpha
Sample C
Ra-226
Po-210
bGross
Alpha
Sample D
Uranium
bGross
Alpha
47.2pCi/L 49.5 ±11.7
24. 1 pd/L
74.0pCi/L
20.5pCi/L 38.0 ± 7.1
10.4 pd/L
20.5pCi/L
52.6 pd/L
3.0 pd/L 4.29 ± .83
1.5pCi/L
4.8pCi/L
10.0 pd/L 6.95 ± 1.60
W.OpCi/L
62.7 ± 11.7 68.0 ± 13.2 73.7 ± 12.0
48.4 ± 8.6 52.3 ± 8.2 58.9 ± 10.5
5.38 ± 1.01 5.87 ± 1.02 6.53 ± 1.18
8.83 ± 2.12 9.45 ± 1.61 10.59 ± 1.46
"Gross alpha activity values for each sample as determined with the four standard
counting efficiencies.
bGross alpha activity at three hours after separation.
E. L. Whittaker is with Lockheed Engineering and Management Services
Company, Incorporated, Las Vegas, NV 89114.
A. N. Jarvis is the EPA Project Officer (see below).
The complete report, entitled "Test Procedure for Gross Alpha Particle Activity in
Drinking Water: Interlaboratory Collaborative Study," (Order No. PB 86-236
957'/AS; Cost: $ 11.95, subject to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Environmental Monitoring Systems Laboratory
U.S. Environmental Protection Agency
Las Vegas, NV 89114
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