&EPA
UnrtedStates
EnviionnwntBi Protection
Afrnoapheric Research and Exposure
AssMSfiMnt L&boFBtofy
RMMR*) Tnangk. Park, NC 27711
January 1994
Research and Dovdopment
EPA 600/R-94/016
A Preliminary Evaluation of the
Scitec MAP-3, Warrington
Microlead I, and Princeton
Gamma-Tech XK-3 Portable X-Ray
Fluorescence Spectrometers
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January 1994
U.S. EPA
OPPTS Chemical Library
EPA West Room 3379 MC7407T
1200 Pennsylvania Ave. NW
Washington DC 20460-000!
A Preliminary Evaluation of the
Scitec MAP-3, Warrington Microlead I,
and Princeton Gamma-Tech XK-3
Portable X-Ray Fluorescence Spectrometers
Prepared by
E. D. Estes
D. L. Hardison
C. O. Whitaker
J. D. Neefus
W. F. Gutknecht
Center for Environmental Measurements and Quality Assurance
Research Triangle Institute
Research Triangle Park, North Carolina 27709-2194
EPA Contract No. 68-D1-0009
RTI Project No. 91U-6960-187
Prepared for
Ms. Sharon Harper, Work Assignment Manager
Atmospheric Research and Exposure Assessment Laboratory
Office of Research and Development
U.S. Environmental Protection Agency
Research Triangle Park, North Carolina 27711
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DISCLAIMER
The information in this document has been funded wholly or in part by the
United States Environmental Protection Agency (USEPA) under EPA Contract No. 68-
Dl-0009 to the Research Triangle Institute. It has been subjected to the Agency's peer
and administrative review, and it has been approved for publication as an EPA
document. Mention of trade names or commercial products does not constitute
endorsement or recommendation for use.
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ACKNOWLEDGEMENTS
This document was prepared under the direction of Ms. Sharon L. Harper,
Atmospheric Research and Exposure Assessment Laboratory (AREAL), U.S.
Environmental Protection Agency (USEPA), Research Triangle Park, NC.
Special acknowledgement is given to Mr. Jack Suggs, AREAL/USEPA, Research
Triangle Park, NC, Mr. John Scalera, Office of Pollution Prevention and Toxics, U.S.
Environmental Protection Agency, Washington, DC and Dr. Mary McKnight, National
Institute of Standards and Technology, Gaithersburg, MD, for their careful review.
n
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EXECUTIVE SUMMARY
The potential impact on health from environmental lead has resulted in increased
interest in lead exposure by Federal, State and local government agencies. As a result,
programs committed to sampling and analysis of lead are increasing nationwide. Public
housing authorities are required, by 1994, to randomly inspect all their housing projects
for lead-based paint. Currently, the most common approach to screening housing for
the presence of lead in paint is the use of the portable X-ray fluorescence (XRF) detector,
which is relatively inexpensive (0.1 - 0.2 hours/test for labor), gives rapid results, and
can be used with minimal damage. Inconclusive XRF measurements must be confirmed
with field-collected samples back in the laboratory using a more accurate analytical
method such as atomic absorption spectrometry (AAS) or inductively coupled plasma
emission spectrometry (ICP).
The accuracies and precisions of portable XRF instruments for measurements of
lead-in-paint concentrations near the U.S. Department of Housing and Urban
Development (HUD) action level for abatement (1.0 mg/cm2) have not been well
established. Therefore, at the request of the U.S. Environmental Protection Agency
(USEPA), the Research Triangle Institute (RTI) performed a limited evaluation of three
portable XRFs currently being used for field measurements: the Scitec MAP-3, the
Warrington Microlead I, and the Princeton Gamma-Tech (PGT) XK-3. The purpose of
the evaluation was to compare these very different, commercially available portable
XRFs, on as equal a basis as possible, for their biases and precisions when measuring
lead in paint films at concentrations ranging from 0 to 7.16 mg/cm2.
Each instrument was used to make a series of measurements in order to
determine the effects of sample concentration and substrate on the precision and bias.
The samples chosen for the study were standard latex and oil-based paint films prepared
by RTI. The lead concentrations of the seven paint films ranged from nominally 0 to
7.16 mg/cm2 as confirmed by digestion using a modification of NIOSH Method 7082
and analysis by inductively coupled plasma emission spectrometry. Eight different
substrates of varying densities were chosen to represent the types of building materials
likely to be encountered in the field. The measurement plan called for triplicate
111
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measurements of each paint film on each substrate using each of the three portable XRF
instruments according to the manufacturer's instructions. The order of measurement for
the Warrington and PGT instruments followed a randomized test matrix. Because of the
availability of the instrument, the measurements for the Scitec XRF were completed
before the test matrix was developed and therefore were not performed in the same
order.
Based upon the data collected during this limited evaluation, it appears that all
three instruments measure lead in paint more accurately (as determined by inspection
of bias) on 1/2" plasterboard than on the other substrates tested. Predicted biases for
the Scitec XRF across the test sample concentration range varied from -0.6 mg/cm2 at
1.6 mg/cm2 for 5" concrete to 3.3 mg/cm2 at 0.3 mg/cm2 for solid tinderblock
Predicted biases for the Warrington XRF ranged from -0.03 mg/cm2 at 1.6 mg/cm2 for
plasterboard to 1.1 mg/cm2 at 0.3 mg/cm2 for concrete. Predicted biases for the PGT
XRF ranged from 0.1 mg/cm2 at 0.3 mg/cm2 for 4" cinderblock to -0.9 mg/cm2 at 1.6
mg/cm2 for 1/8" aluminum.
IV
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TABLE OF CONTENTS
Section Page
Disclaimer i
Acknowledgements ii
Executive Summary iii
Table of Contents v
List of Tables vii
List of Figures ix
1.0 Introduction 1
1.1 Background 1
1.2 Objectives/Purpose of the Study 2
1.3 Study Design 2
2.0 Overview of the Portable XRF 5
2.1 Instrument Basics 5
2.2 Available Instruments 7
3.0 Laboratory Tests of the Portable XRF Units 9
3.1 Introduction 9
3.2 Scitec Map-3 9
3.2.1 Description 9
3.2.2 Experimental Procedure 11
3.3 Warrington Microlead I 11
3.3.1 Description 11
3.3.2 Experimental Procedure 11
3.4 Princeton Gamma-Tech XK-3 12
3.4.1 Description 12
3.4.2 Experimental Procedure 13
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TABLE OF CONTENTS (continued)
Section Page
4.0 Results and Discussion 14
4.1 Experimental Precision and Bias 14
4.2 Linear Regression Analyses 14
4.2.1 Hypothesis Testing 18
4.2.2 Confidence Intervals 27
4.3 Predicted Bias at Selected Lead Concentrations 27
4.4 Scitec Map-3 31
4.5 Warrington Microlead 31
4.6 Princeton Gamma-Tech XK-3 32
5.0 Conclusions and Recommendations 33
5.1 Conclusions 33
5.2 Recommendations 33
6.0 References 35
Appendix A: XRF Data
VI
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LIST OF TABLES
Table Page
1 Randomized test matrix - order (1-56) for testing each combination of
sample and substrate 3
2 Test procedures 4
3 Portable XRF characteristics 10
4 Relative standard deviations and percent differences for triplicate measurements
of lead in paint films using portable XRF: Scitec 15
5 Relative standard deviations and percent differences for triplicate measurements
of lead in paint films using portable XRF: Wanington 16
6 Relative standard deviations and percent differences for triplicate measurements
of lead in paint films using portable XRF: PGT 17
7 1/2" Plasterboard 19
8 3/4" Plywood 20
9 1/8" Aluminum 21
10 1/8" Steel 22
11 4" Cinderblock 23
12 Solid cinderblock 24
vn
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LIST OF TABLES (continued)
Table Page
13 Brick 25
14 5" Concrete 26
15 HUD Guidelines for Pb testing using portable XRF instrumentation 29
Vlll
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LIST OF FIGURES
Figure Page
1 Comparison of experimentally generated slopes for portable XRF/substrate
*y
combinations across the lead concentration range of 0 to 7.16 mg/cm 28
2 Comparison of predicted biases at 1 mg Pb/cm2 for portable XRF/substrate
combinations 30
IX
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SECTION 1
INTRODUCTION
1.1 BACKGROUND
The adverse health effects resulting from exposure of young children to
environmental lead have caused increased public concern in recent years. Studies have
shown that chronic exposure even to low levels of lead can result in impairment of the
central nervous system, mental retardation, and behavioral disorders.1'2 Although young
children are at the greatest risk, adults may suffer harmful effects as well.3
Numerous programs involving research on the toxicity and bioavailability of lead,
the environmental monitoring of lead, lead abatement, and clearance testing of housing
are currently active. Examples of past projects include the U.S. Department of Housing
and Urban Development (HUD) National Survey,4 the Urban Soil Lead Abatement
Demonstration Project5 and method evaluation studies sponsored by the U.S.
Environmental Protection Agency (EPA), and abatement programs carried out by
Maryland, Massachusetts, and many other groups.
The major sources of exposure to lead in housing units are paint, dust, and soil.
Currently, lead-based paint is receiving emphasis by HUD6 as the principal source for
lead contamination and exposure. House dust contaminated with lead from
deteriorating interior paint and from tracked-in exterior paint has been implicated as the
most common route of exposure for young children.7 It is particularly hazardous when
painted walls, woodwork, and furniture are accessible to young children to touch and
to chew.
Public housing authorities are required, by 1994, to randomly inspect all their
housing projects for lead-based paint.8 Currently, the most common approach to
screening housing for the presence of lead in paint is the use of the portable X-ray
fluorescence (XRF) detector, which is relatively inexpensive (0.1 - 0.2 hours/test for
labor), gives rapid results, and can be used with minimal damage.9'10 Inconclusive XRF
measurements must be confirmed with field-collected samples back in the laboratory
using a more accurate analytical method such as atomic absorption spectrometry (AAS)
or inductively coupled plasma emission spectrometry (ICP).6
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1.2 OBJECTIVES/PURPOSE OF THE STUDY
The biases and precisions of portable XRF instruments for measurements of lead-
in-paint concentrations near the HUD action level for abatement (1.0 mg/cm2)6 have not
been well established. Therefore, at the request of the EPA, the Research Triangle
Institute (RTI) has evaluated three of the portable XRFs currently being used for field
measurements: the Scitec MAP-3, the Warrington Microlead I, and the Princeton
Gamma-Tech (PGT), XK-3. The purpose of the evaluation was to compare these very
different, commercially available portable XRFs, on as equal a basis as possible, for their
biases and precisions when measuring lead in paint on particular substrates. Biases
were calculated by comparing lead concentrations of the standards as measured by each
XRF to the lead concentrations measured by digestion/ICP analysis.11
Another goal of the project was to determine a mechanism or protocol for
comparison and evaluation of current and future portable XRFs on as equal a basis as
possible.
1.3 STUDY DESIGN
RTI's evaluation of portable XRF technology was performed using a phased
approach. When the experiments were begun in 1990, the Scitec MAP-3 was the
portable XRF that was most widely used for field measurements of lead in paint at
"scattered-site" housing. However, at that time, no paint film reference materials were
available for testing the responses of the XRF to various concentrations of lead.
Therefore, RTI developed a procedure for preparing standard latex and oil-based paint
films containing known amounts of lead.12 The lead concentrations of the paint films
that were prepared ranged from nominally 0 to 7.16 mg/cm2 as confirmed by digestion
using a modification of NIOSH Method 708211 and analysis by ICP. This range
represents that typically encountered in actual field measurements.4 Different substrates
of varying densities were chosen to represent the types of building materials likely to
be encountered in housing units. A Scitec MAP-3 portable XRF rented from Scitec
Corporation was used to make triplicate measurements for the various paint
film/substrate combinations.
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In 1992, two additional instruments, the Warrington Microlead I and the Princeton
Gamma-Tech XK-3, were available to RTI for testing. Using the information gained in
the Stitec evaluation, a measurement plan was developed for these two.XRFs to collect
data that would allow comparison of the three instruments. Mr. William Boyce of Scitec
Corporation had observed a hysteresis effect when the XRF was used to measure lead
in paint on a low density substrate after it was used to measure lead in paint on a high
density substrate. Hysteresis effects also may be observed when painted surfaces
containing low levels of lead are measured immediately following the measurement of
surfaces containing high levels of lead.13 Therefore, the measurement sequence was not
ordered by lead concentration or substrate density. Instead, a randomized test matrix,
presented in Table 1, was developed to determine the order of the measurements so that
the hysteresis effects, if present, would be randomized. No tests were performed to
determine the presence or the magnitude of the hysteresis effects. The measurement
plan called for triplicate measurements of each combination of paint film and substrate
for the Warrington and PGT instruments. In order to perform a measurement, the test
Table 1. Randomized Test Matrix - Order (1-56) for Testing
Each Combination of Sample and Substrate
Paint Sample ID (cone., me/cm2)
Substrate
1/2" Plasterboard
3/4" Plywood
Cinderblock, Std
1/8" Steel
1/8" Aluminum
5" Concrete
Brick
Cinderblock, Solid
20D1
(7.16)
18
24
17
41
18
27
34
3
20D2
(6.20)
48
5
54
20
43
14
13
4
20B2
(1.27)
37
35
40
26
2
29
28
50
20A2
(0.52)
44
32
10
9
22
23
8
6
17B
(0.00)
7
30
16
47
55
53
33
56
120-2-B
(0.07)
12
52
39
36
45
21
42
46
120-5-B
(4.%)
51
15
1
38
11
25
49
31
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paint film was placed against the substrate, and an attempt was made to position the
XRF probe on the center of the film so that the measurement would be made on
nominally the same area each time. The triplicate measurements were made
consecutively with no repositioning of the instrument between readings.
A "measurement" for each particular instrument was performed as defined in
Table 2. Scitec recommends a 60-second reading for a "test" and a 240-second reading
for "confirmation".14 For this study, an intermediate measurement time of 120 seconds
was chosen because a previous study indicated that there were no significant differences
in the biases and precisions for 60- and 120-second reading times.15 The 4-minute
reading would only be performed in the field to confirm levels within the action range.
The manufacturer's instructions for Warrington XRF defines a measurement as the
average value for the lead concentration that is displayed when the trigger is depressed
for three read cycles (approximately 15 to 20 seconds for a new source). The
manufacturer recommends that at least three measurements per test location should be
made before any conclusions are drawn concerning the presence or absence of a lead
hazard.16 The PGT manufacturer recommends that a measurement be made by taking
three readings (15 to 20 seconds each for a new source), recording the values, and
manually averaging them.17
Table 2. Test Procedures
Instrument
Scitec
Warrington
PGT
new
Measurement Procedure
Take one 120 sec reading
Take one 3-cycle reading
(15-20 sec)*, temporarily
halting after each cycle to
record the value displayed;
manually average
Take 3 readings (15-20 sec each)*,
record values and manually average
# of Measurements
3
excitation source
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SECTION 2
OVERVIEW OF THE PORTABLE XRF
2.1 INSTRUMENT BASICS
The portable XRF consists of an excitation source, a detector, and some means of
specifically determining the lead X-rays emitting from the sample.18 Characteristics of
the three portable XRFs used in the study described in this report are summarized in
Table 3, Section 3. The excitation source for portable units consists of a radioactive
source. Examples of source materials include 241Am, 109Cd, 244Cm, 57Co, and 55Fe.
These emit X-rays or gamma rays of sufficient energy to cause excitation of the target
atoms. Different isotopes are preferred for different ranges of elements because of the
need to match the energy of the excitation source emission with the energy needed to
cause excitation and X-ray emission (fluorescence) from the element of interest. 55Fe, for
example, is well suited for the light elements Al - V (K-shell X-rays) and Nb - Sb (L-shell
X-rays). 109Cd is well suited for excitation of lead L-shell X-rays, while 57Co is well
suited for both lead K- and L-shell X-rays. (The K and L designations describe X-rays
produced from electron transitions between the K and L shells, respectively, and the
higher level shells; the L X-ray is of lower energy while the K X-ray is of higher energy
and therefore can penetrate deeper.)19
Several types of detectors are available.19 The solid-state detector used in the
Scitec XRF consists of the semiconductor material SiLi. When an X-ray passes through
the material, the X-ray creates free electrons and "holes." When a voltage is applied
across this detector, and an X-ray passes through the detector, a pulse of current flows
across the detector. The number of free electrons and "holes" produced, and
subsequently the magnitude of this current pulse, is a function of the energy of the X-
ray, which, in turn, is specific to the emitting element. Specific detection of lead is
accomplished by measurement of the magnitude of the current pulse and relating this
pulse magnitude to a standard. This is done with a pulse height analyzer, that is,
complex electronic circuity which differentiates current pulses by their magnitude, deals
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with overlapping pulses, and keeps track of the number of pulses of each magnitude.
The number of pulses at a particular magnitude is directly related to the concentration
of the fluorescing element.
The Warrington XRF uses a scintillation counter composed of a cesium thallium
iodide doped crystal to convert the X-ray photon into a light photon. When radiation
interacts with the crystal, the transmitted energy excites the iodine atom and raises it to
a higher energy state. When the iodine atom returns to its ground electronic state, the
energy is re-emitted as a light pulse in the ultraviolet region which is then absorbed by
the thallium atom and re-emitted as fluorescent light. The light is detected by a 1/2"
photomultiplier tube.
The detector for the PGT XRF is a proportional counter. This is a xenon-filled
tube across which a high voltage potential is applied. When an X-ray enters the tube,
the xenon gas is ionized, producing ion pairs. The charged particles migrate toward the
appropriate electrodes under the voltage gradient. Each electron acquires sufficient
energy to produce another ion pair upon collision with another xenon atom. This
process is repeated many times so that each original X-ray entering the counter results
in a large number of electrons traveling toward the anode. An electronic pulse is
produced that is proportional to the number of electrons reaching the anode and,
accordingly, the energy of the X-ray.
The simpler XRF units are preset to count only pulses equivalent to lead X-ray
energies; these are called "direct reading" instruments. The more complex instruments,
called "spectrum analyzers," take and store the entire range of X-ray emissions in a small
on-board computer that performs the task of relating current pulse amplitude and
numbers of pulses to information stored from standards. This computer will
automatically identify the elements and determine their concentrations.
A major limitation of XRF is that the efficiency of production of the fluorescing
X-rays is very dependent upon the paint matrix and the substrate. The numbers of X-
rays produced will depend upon (1) the ability of the exciting or source X-rays to
penetrate the matrix and reach the atoms of interest; (2) secondary X-rays (created from
the interaction of the primary excitation X-rays with other elements in the sample)
reaching and causing fluorescence of the element of interest; (3) primary excitation X-
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rays being scattered by matrix and substrate components so as to hit the atoms of
element of interest from all angles; and (4) the ability of the X-rays emitted from the
atoms of interest to escape from the matrix and reach the detector without being
electromagnetically reabsorbed or scattered by the matrix. In the laboratory, great care
is taken to match the matrix of the standards and unknowns. This is very difficult in
the field, and impossible with instruments used to perform direct readings off walls,
floors, etc.
Two principal approaches are being taken to deal with this substrate problem
when analyzing lead-containing paint. In the first, which provides for a partial
correction, a reading of the surface is taken. Then the paint is scraped off the surface
and a second reading is taken to obtain a background reading, which is subtracted from
the first. This substrate correction approach was applied for the Warrington Microlead
I and Princeton Gamma-Tech XK-3 instruments. In the second approach, information
is taken from the total X-ray emission spectrum, and, using proprietary software, a
substrate correction is calculated. The software includes mathematical variables
determined from measurement of standard paint films placed on different substrates,
e.g., wood, plasterboard, metal, etc. The Scitec MAP-3 instrument evaluated in this
study uses this second approach.
2.2 AVAILABLE INSTRUMENTS
At the time of these evaluations in 1992, three manufacturers were widely
recognized as having commercially available XRFs designed for in-situ paint testing.
The instruments that were tested by RTI and addresses of these manufacturers are as
follows:
Princeton Gamma-Tech XK-3 Princeton Gamma-Tech Inc.
1200 State Road
Princeton, NJ 08540
(609) 724-7310
Warrington Microlead I Warrington Corporation
2205 West Braker Lane
Austin, TX 78758
(800) 233-9491
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Scitec MAP-3 Scitec Corporation
1029 Kellogg Street
Kennewick,WA 99336
(509) 783-9850
8
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SECTION 3
LABORATORY TESTS OF THE
PORTABLE XRF UNITS
3.1 INTRODUCTION
The Scitec, Warrington, and PGT portable X-ray fluorescence units (XRF) were
employed to measure lead in paint using standard paint films and selected substrate
materials. These instruments were pre-calibrated by the manufacturer and were not
recalibrated by RTL The paint films, containing known concentrations of lead, were
prepared by RTI from new latex and oil-based paints and pure lead salts. The
concentration of lead in each paint film was confirmed by digestions using a
modification of NIOSH Method 708211 and ICP spectrometry. The characteristics of the
three XRFs are discussed in the following sections and summarized in Table 3.
3.2 SCITEC MAP-3
3.2.1 Description
The Scitec X-ray fluorescence unit consists of the Ambient Scanner and the MAP-3
Console with battery power and cable. The MAP-3 Console is basically a portable
computer that contains the calibration data and has memory for more than 1000 entries,
including measurement values, identification numbers, analysis times and methods
chosen. The data can be retrieved by connecting the console to an IBM PC-XT. The
Ambient Scanner houses the radioactive 57Co source. The system should be returned
to Scitec once a year for source replacement and recalibration.
After connection of the Ambient Scanner to the console, the appropriate values
for calibration program, identification number, and analysis time may be chosen. The
surface to be analyzed is positioned against the rubber boot and shutter of the scanner.
The shutter then is opened to expose the sample to the source, and the analysis is
controlled from the console.
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Table 3. Portable XRF Characteristics
Type
Source
(Halflife: Days)
Decay Compensation
Detector
Shell detected
(KeV)
Substrate Correction
Potential Interferences
Range of Calibration
Substrates Used for Calibration
Calibration Materials
Strength of Source Used for
Study (Original Strength)
Recommended Source
Replacement
Scitec Warrington
MAP-3 1 Microlead 1
Spectrum Analyzer
57Co
(276)
—
SiLi
K (74.96)
L (10.55)
Proprietary Algorithm
K=Au, Bi, Hg, Tl
L=As, Cd, Cu, Mo, Zn
0 - 6.19 mg/cm2
>30
Old HUD/NIST & RTI
prepared
37.8 mCi
(40 mCi)
Once /year
Direct Reader
57Co
(276)
Source date in software
Scintillation Counter
K
(74.96)
Scrape
K, same
0.6 - 2.00 mg/cm2
up to 15
Old HUD/NIST
3.4 mCi
(10.4 mCi)
Once/ 14 months
PGT
XK-3
Direct Reader
57Co
(276)
Ta foil internal ref
Xe gas, prop, counter
K
(74.96)
Scrape
K, same
0.6 - 2.99 mg/cm2
none
Old HUD/NIST
9.1 mCi
(10.4 mCi)
Once/year
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3.2.2 Experimental Procedure
The Scitec MAP-3 unit used by RTI in this evaluation contained a new 57Co
source and had been calibrated by the manufacturer over the range of 0 to 6.19 mg/cm2
of lead using films prepared by RTI and the old HUD/NIST films. The XRF was used
in the "universal" substrate correction mode to make three 120-second measurements
each of selected paint films placed one at a time on selected substrates. The Scitec
measurements were made prior to the development of the randomized test matrix (Table
1) and, therefore, were not made in the order specified in the matrix. In addition,
several paint film/substrate combinations specified in the matrix (Table 1) had not been
made when the Scitec system was being evaluated. Measurement data are reported in
Appendix A.
3.3 WARRINGTON MICROLEAD I
3.3.1 Description
The Warrington Microlead I is a portable, microcomputer-based XRF with a 57Co
source. The instrument has built-in "Zero Standard" and "Lead Standard" functions so
the user can establish a zero reference using a "standard" substrate and check that the
analyzer reads the lead concentration correctly with a "standard" paint film provided by
Warrington. The background density is displayed with each reading to alert the
inspector to changes in substrate that might affect the accuracy of the lead reading. Up
to 1000 pieces of information (lead readings, project numbers, apartment numbers, times
and dates, for example) can be stored and subsequently printed on a portable printer.
Warrington recommends that the source be changed every 14 months.
The probe is placed against the test surface and the trigger is pulled until the
analyzer beeps and displays the lead reading. Successive readings are averaged
automatically. Warrington recommends that the trigger be depressed through three
successive cycles to obtain a lead measurement.
3.3.2 Experimental Procedure
The Warrington XRF used in this evaluation was borrowed from Dr. Mary
McKnight of the National Institute of Standards and Technology. It contained a used
11
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source with a strength of -3.4 mCi. Some measurements were performed in the "auto"
mode (by depressing the trigger through three read cycles to obtain an automatically-
calculated average) prior to the development of the randomized test matrix. In a
memorandum dated 3/26/92 to the RTIXRF team, the EPA Work Assignment Manager
recommended that the randomized tests be performed in the "manual" mode (i.e., the
trigger would be released after each read cycle so that the lead concentration read
during that cycle could be recorded and an average of the three readings be calculated
manually to represent one measurement). The reason for this modified procedure was
that Warrington's definition of a single reading was interpreted to be three count cycles
while PGT's single reading is one count cycle. This "halted" reading procedure would
allow comparison of the XRFs on a more equal basis.
When the analyst began to work through the randomized test matrix, he made
the decision to omit film/substrate combinations that had already been measured in the
automatic mode. However, since these measurements were made at a different time and
in a different mode than the randomized measurements, they were not included in this
evaluation and do not appear in the Warrington data presented in Appendix A.
A discussion with a representative of Warrington corporation revealed that the
precision obtained using the automatic mode will be better than the precision obtained
using the manual mode.20 When the trigger is depressed through three read cycles, a
"running average" is generated continuously. When the trigger is released after each
cycle, the data from the previous cycle is not included in the following cycle. In
addition to the paint film/substrate measurements, measurements were made of each
substrate alone so that the randomized data could be corrected for substrate effects. The
"zero standardize" procedure described in the user's manual was performed at the
beginning, middle, and end of each analysis day.
3.4 PRINCETON GAMMA-TECH XK-3
3.4.1 Description
The Princeton Gamma-Tech XK-3 utilizes a 57Co scintillation source with a
tantalum foil internal reference device to automatically correct for source decay. The
instrument's internal programming determines exposure time by referring to the count
12
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for the 73Ta foil. When the 73Ta counter discriminator/channel is full, the instrument
triggers a shutter release. One charge of the battery pack will provide 8 hours of
operation. The manufacturer recommends that the source be changed once a year at the
PGT factory.
The user presses the face-plate of the instrument against the surface to be
analyzed, pushing down firmly on the handle. Depression of the spring-loaded handle
opens the shutter. After 15 to 20 seconds, a reading appears on the digital display. PGT
recommends taking three successive readings and manually averaging the results to
obtain a lead measurement.
3.4.2 Experimental Procedure
The PGT XRF used in this evaluation was borrowed from Mr. Jim Hayes of the
North Carolina State Government Health Services Section. The 57Co source had been
replaced by Warrington Corporation and was new (first half-life). Mr. Hayes reported
that replacements had been made by Warrington previously and that the XRF performed
properly each time such a replacement was made.21 Three readings were taken
manually and averaged to obtain one lead measurement. In addition to the paint
film/substrate measurements, measurements were made of each substrate alone so that
the randomized data could be corrected for substrate effects. Measurement data are
reported in Appendix A.
13
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SECTION 4
RESULTS AND DISCUSSION
4.1 EXPERIMENTAL PRECISION AND BIAS
Data from the triplicate measurements of each paint film/substrate combination
using each of the three XRFs are presented in Appendix A. The effects of lead
concentration and substrate on the precision and bias of XRF measurements can be
determined by examination of the data presented in Tables 4 through 6. The tables are
ordered by decreasing lead concentration in the paint films and by increasing substrate
density as determined by the Warrington XRF. The relative standard deviation (RSD)
of each set of triplicate measurements, an indicator of precision, is calculated as
RSD = (SD/x) x 100
where X is the average value of the three measurements and
SD =
N
The percent difference (% Diff) of the XRF measured value from the ICP
measured value, an indicator of bias, is calculated as
% Diff
ICP value - x
ICP value
/
x 100
The data show that, in general, precision and bias improve as the lead
concentration in the paint film increases. No trend with respect to substrate was
apparent from visual inspection of the data; no statistical tests for substrate effects were
performed.
4.2 LINEAR REGRESSION ANALYSES
Linear regression analyses were performed on the experimental XRF data
presented in Appendix A using a standard linear calibration computer program.22
14
-------
Table 4. Relative standard deviations and percent differences for triplicate measurements of lead in paint films using
portable XRF: Scitec
ICP
Anal.
mg/cm
7.16
6.20
4.96
1.27
0'.52
0.0
I/
Plaste
RSD
8.7
15.1
NA
10.0
35.3
—
2"
rboard
%
Diff
-3.2
11.3
NA
-21.3
-16.7
—
3/
Plyv
RSD
9.2
4.9
5.0
24.1
33.3
—
4"
rood
%
Diff
-5.0
-4.3
-38.2
-50.1
-42.3
—
I/
Alum
RSD
8.0
9.1
NA
14.3
20.0
—
8"
inum
%
Diff
6.1
20.4
NA
-16.0
-3.8
—
I/
St<
RSD
3.7
11.6
NA
20.8
17.3
173
8"
:el
%
Diff
0.6
18.3
NA
15.5
28.2
—
4
Cinde
RSD
5.6
3.7
NA
142
40.0
63.0
it
rblock
%
Diff
-5.5
8.6
NA
-79.0
-3.8
—
Sc
Cinde
RSD
1.4
4.0
NA
8.5
56.8
5.1
)lid
.rblock
%
Diff
15.0
28.5
NA
275
451
—
Br
RSD
5.6
12.9
NA
173
173
—
ick
%
Diff
-10.6
3.8
NA
-92.1
-93.6
—
e
Con
RSD
18.0
16.3
NA
96.6
—
—
>"
crete
%
Diff
-29.7
-13.4
NA
-63.3
-100
—
-------
Table 5. Relative standard deviations and percent differences for triplicate measurements of lead in paint films using
portable XRF: Warrington
ICP
Anal.
mg/cm
7.16
6.20
1.27
0.52
0.07
0.0
I/
Plaste
RSD
0.8
2.3
1.4
18.6
NA
1530
2"
rboard
%
Diff
-9.2
-4.1
0.0
24.4
NA
—
3/
Plyv
RSD
0.6
1.0
8.2
16.5
NA
28.9
4"
wod
%
Diff
-10.8
-4.6
11.5
23.1
NA
—
I/
Alum
RSD
1.7
1.9
9.3
42.4
NA
31.4
8"
inum
%
Diff
-3.6
2.6
11.0
75.0
NA
—
I/
St
RSD
2.5
0.3
6.0
10.1
22.3
32.9
8"
eel
%
Diff
1.7
4.0
55.1
176
1267
—
4
Cinde
RSD
1.0
1.3
22.7
—
13.7
30.3
M
rblock
%
Diff
-1.7
2.7
27.8
—
424
—
Sc
Cinde
RSD
2.5
3.8
12.1
45.5
149
13.9
did
rblock
%
Diff
-5.4
0.8
5.8
42.9
105
—
Br
RSD
2.0
2.6
6.4
8.2
31.5
28.2
ck
%
Diff
-5.5
6.1
40.9
101
467
—
<
Con
RSD
6.1
0.0
7.7
5.7
12.2
12.2
>"
crete
%
Diff
-6.1
11.9
74.8
235
1362
—
-------
Table 6. Relative standard deviations and percent differences for triplicate measurements of lead in paint films using
portable XRF: PGT
ICP
Anal.
mg/cm
7.16
6.20
4.96
1.27
0.52
0.07
0.0
I/
Plaste
RSD
5.8
6.3
5.5
16.5
5.9
32.9
—
2"
rboard
%
Diff
-15.1
-10.6
11.3
-3.9
-1.9
424
—
3/-
Plyw
RSD
1.0
4.9
3.4
25.8
54.1
24.7
68.7
4"
/ood
%
Diff
-20.8
-16.5
-39.2
-48.3
3.2
-300
—
I/
Alum
RSD
1.7
5.3
6.8
67.9
NA
20.1
163
8"
inum
%
Diff
-27.1
-26.2
-17.9
-65.1
NA
-976
—
I/
St<
RSD
1.3
2.0
6.7
14.6
243
8.2
2.3
8"
:el
%
Diff
-18.8
-6.8
8.3
-68.8
-103
1110
—
4
Cinde
RSD
NA
2.6
3.2
37.8
71.6
82.0
86.7
it
rblock
%
Diff
NA
-21.6
23.6
-23.4
10.3
224
—
Sc
Cinde
RSD
2.4
7.7
3.9
41.4
32.8
208
456
>lid
.rblock
%
Diff
-21.3
-26.9
9.2
-38.8
-46.8
-243
—
Br
RSD
6.6
7.9
10.9
28.2
39.3
121
24.2
ick
%
Diff
-26.2
-28.5
-26.9
-16.8
-42.3
-371
—
<
Con
RSD
0.6
3.9
10.2
29.3
6.0
4015
17.2
>"
crete
%
Diff
-34.6
-28.9
-6.3
-24.7
-44.2
114
—
-------
Regression parameters were calculated for each substrate for each portable XRF using
the model y = a + bx, where a is the intercept and b is the slope. The data were entered
as x,y pairs where x is the lead concentration of the paint film measured in the
laboratory using acid digestion/ICP and y is the concentration measured by XRF. A
least squares analysis assumes that the independent variable, x, is measured without
error. The laboratory analysis of the paint films showed some variability. However,
least squares analysis can be used if the error of x is less than one-tenth of the average
scatter of the x's from their mean.23 Examination of the paint film laboratory analysis
results revealed that this condition was met. Results of the linear regression analyses
are presented in Tables 7 through 14.
4.2.1 Hypothesis Testing
After the regression values were computed, tests were performed to determine
slopes that are statistically equal to one at the 95 percent confidence level according to
the following:
b = 1 if
b-1
(se)b
< t, /i
1 - a/2, n-.,
where b = slope, (se)b = standard error of the slope and
ti-^/2, n.2 = critical value with (n-2) degrees of freedom.
Similarly, tests were performed to determine intercepts that are statistically equal
to zero at the 95 percent confidence level according to the following:
a = 0 if
a
fee).
< *1 - a/2,n - 2
where a = intercept, (se)a = standard error of the intercept and
*!—12, n-2 = critical value with (n-2) degrees of freedom.
Slopes that are statistically equal to one and intercepts that are statistically equal
to zero are indicated by asterisks in Tables 7 through 14.
18
-------
Table 7. %" Plasterboard
No. of Data Pairs
Slope
SDslope
Intercept
SD
•-^intercept
Corr. Coef.
Residual Variance, %
Standard Error of Estimate
of X from Y
Estimated
bias* and
95%
confidence
interval
at:"
0.3 mg/cm2
0.8 mg/cm2
1.0 mg/cm2
1.3 mg/cm2
1.6 mg/cm2
Scitec
15
1.043*
0.051
-0.108**
0.216
0.9851
2.96
0.539
-0.09 ± 1.35
-0.07 ± 1.34
-0.06 ± 1.34
-0.05 ± 1.33
-0.04 ± 1.33
Warrington Warrington
(uncorrected) || (corrected)
15
0.915
0.014
0.413
0.060
0.9985
0.30
0.172
+0.39 ± 0.37
+0.34 ± 0.37
+0.33 ± 0.37
+0.30 ± 0.37
+0.28 ± 0.37
15
0.915
0.014
0.103**
0.060
0.9985
0.30
0.172
+0.08 ± 0.37
+0.04 ± 0.37
+0.03 ± 0.37
-0.01 ± 0.37
-0.03 ± 0.37
PGT
(uncorrected)
21
0.812
0.032
0.386
0.129
0.9859
2.80
0.494
+0.33 ± 0.91
+0.24 ± 0.91
+0.20 ± 0.90
+0.14 ± 0.90
+0.09 ± 0.90
PGT
(corrected)
21
0.812
0.032
0.096**
0.129
0.9859
2.80
0.494
+0.04 ± 0.91
-0.05 ± 0.91
-0.09 ± 0.90
-0.15 ± 0.90
-0.20 ± 0.90
\D
* Slope (b) = 1 at the 95% level of confidence
** Intercept (a) = 0 at the 95% level of confidence
a
(se).
t
1 - afZ, n - 2
f Bias is calculated as XRF predicted value minus the known concentration of the paint film.
ft Lead concentraUons chosen by reference to HUD Guidelines (see Table 15).
-------
Tables. 3/4" Plywood
No. of Data Pairs
Slope
SDslope
Intercept
sn
JLJ intercept
Corr. Coef.
Residual Variance, %
Standard Error of
Estimate of X from Y
Estimated
bias* and
95%
confidence
interval
at:"
0.3 mg/cm2
0.8 mg/cm2
1.0 mg/cm2
1.3 mg/cm2
n
1.6 mg/cm
Scitec
18
0.934*
0.056
-0.341**
0.248
0.9721
5.5
0.689
-0.36 + 1.53
-0.39 + 1.52
-0.41 + 1.51
-0.43 + 1.50
-0.45 + 1.50
Warrington
(uncorrected)
15
0.873
0.014
0.651
0.060
0.9983
0.34
0.182
+0.61 + 0.38
+0.55 + 0.38
+0.52 + 0.37
+0.49 + 0.37
+0.45 + 0.37
Warrington
(corrected)
15
0.873
0.014
0.301
0.060
0.9983
0.34
0.182
+0.26 + 0.38
+0.20 + 0.38
+0.17 + 0.37
+0.14 + 0.37
+0.10 + 0.37
PGT I PGT
(uncorrected) || (corrected)
21
0.799
0.031
0.231**
0.125
0.9863
2.72
0.487
+0.17 + 0.88
+0.07 + 0.88
+0.03 + 0.87
-0.03 + 0.87
-0.09 + 0.87
21
0.799
0.031
-0.199**
0.125
0.9863
2.72
0.487
-0.26 + 0.88
-0.36 + 0.88
-0.40 + 0.87
-0.46 + 0.87
-0.52 + 0.87
N>
O
* Slope (b) = 1 at the 95% level of confidence
b - 1
(se)b
Intercept (a) = 0 at the 95% level of confidence —
(se)
ll - «/2. n - 2
t
1 - «/2. o -2|
f Bias is calculated as XRF predicted value minus the known concentration of the paint film.
ft Lead concentrations chosen by reference to HUD Guidelines (see Table 15).
-------
Table 9. 1/8" Aluminum
No. of Data Pairs
Slope
SDslope
Intercept
SDintercept
Corr. Coef.
Residual Variance, %
Standard Error of Estimate
of X from Y
Estimated
biast and
95%
confidence
interval
at:ft
0.3 mg/cm2
0.8 mg/cm2
1.0 mg/cm2
1.3 mg/cm2
1.6 mg/cm2
Scitec
15
1.137
0.044
-0.117**
0.186
0.9906
1.87
0.428
-0.08 + 1.17
-0.01 + 1.16
+0.02 + 1.15
+0.06 + 1.15
+0.10 + 1.14
Warrington Warrington
(uncorrected) | (corrected)
15
0.931
0.020
0.267
0.086
0.9970
0.60
0.243
+0.25 + 0.54
+0.21 + 0.53
+0.20 + 0.53
+0.18 + 0.53
+0.16 + 0.53
15
0.931
0.020
1.387
0.086
0.9970
0.60
0.243
+0.37 + 0.54
+0.33 + 0.53
+0.32 + 0.53
+0.30 ± 0.53
+0.28 + 0.53
PGT
(uncorrected)
18
0.773
0.031
0.188**
0.136
0.9875
2.48
0.476
+0.12 + 0.86
+0.01 + 0.85
-0.04 + 0.85
-0.11 + 0.85
-0.18 + 0.84
PGT
(corrected)
18
0.773
0.031
-0.492
0.136
0.9875
2.48
0.476
-0.56 + 0.86
-0.67 + 0.85
-0.72 + 0.85
-0.79 + 0.85
-0.86 + 0.84
* Slope (b) = 1 at the 95% level of confidence
b - 1
(se)h
** Intercept (a) = 0 at the 95% level of confidence
a
(se).
ll - «/2, n - 2
- a/2. n - 2
f Bias is calculated as XRF predicted value minus the known concentration of the paint film.
ft Lead concentrations chosen by reference to HUD Guidelines (see Table 15).
-------
Table 10. 1/8" Steel
No. of Data Pairs
Slope
SDslope
Intercept
"^intercept
Corr. Coef.
Residual Variance, %
Standard Error of Estimate
of X from Y
Estimated
biast and
95%
confidence
interval
at:ft
0.3 mg/cm2
0.8 mg/cm2
1.0 mg/cm2
1.3 mg/cm2
1.6 mg/cm2
Scitec
15
1.064*
0.046
0.115**
0.199
0.9879
2.41
0.486
+0.13 ± 1.24
+0.17 + 1.23
+0.18 + 1.23
+0.20 + 1.22
+0.22 + 1.22
Warrington
(uncorrected)
18
0.893
0.013
-0.575
0.051
0.9983
0.34
0.177
-0.61 + 0.36
-0.66 + 0.36
-0.68 + 0.36
-0.71 + 0.36
-0.75 + 0.36
Warrington
(corrected)
18
0.893
0.013
0.895
0.051
0.9983
0.34
0.177
+0.86 + 0.36
+0.81 + 0.36
+0.79 + 0.36
+0.76 + 0.36
+0.72 + 0.36
PGT
(uncorrected)
21
0.917*
0.043
0.484
0.175
0.9797
4.02
0.591
+0.46 + 1.24
+0.42 + 1.23
+0.40 + 1.23
+0.38 + 1.22
+0.35 + 1.22
PGT
(corrected)
21
0.917*
0.043
-0.756
0.175
0.9797
4.02
0.591
-0.78 ± 1.24
-0.82 + 1.23
-0.84 + 1.23
-0.86 + 1.22
-0.89 + 1.22
N)
N)
* C
Slope (b) = 1 at the 95% level of confidence
** Intercept (a) = 0 at the 95% level of confidence
ll - a/2. n - 2
(se).
t
1 - a/2, n - 2
f Bias is calculated as XRF predicted value minus the known concentration of the paint film.
ft Lead concentrations chosen by reference to HUD Guidelines (see Table 15).
-------
Table 11. 4" Cinderblock
No. of Data Pairs
Slope
SDslope
Intercept
"^intercept
Corr. Coef.
Residual Variance, %
Standard Error of Estimate
of X from Y
Estimated
biast and
95%
confidence
interval
at:ft
0.3 mg/cm2
0.8 mg/cm2
1.0 mg/cm
1.3 mg/cm2
1.6 mg/cm2
Scitec
15
1.017*
0.055
-0.155**
0.236
0.9814
3.69
0.601
-0.15 + 1.48
-0.14 + 1.47
-0.14 + 1.46
-0.13 + 1.46
-0.13 + 1.45
Warrington Warrington
(uncorrected) | (corrected)
15
0.929
0.019
1.796
0.082
0.9972
0.56
0.239
+1.77 + 0.53
+1.74 + 0.52
+1.72 + 0.52
+1.70 + 0.52
+1.68 + 0.52
15
0.929
0.019
0.486
0.082
0.9972
0.56
0.239
+0.46 + 0.53
+0.43 + 0.52
+0.41 + 0.52
+0.39 + 0.52
+0.37 + 0.52
PGT
(uncorrected)
18
0.717
0.028
0.405
0.091
0.9883
2.33
0.388
+0.32 + 0.64
+0.18 + 0.64
+0.12 + 0.64
+0.04 + 0.63
-0.05 + 0.63
PGT
(corrected)
18
0.717
0.028
0.155**
0.091
0.9883
2.33
0.388
+0.07 + 0.64
-0.07 + 0.64
-0.13 + 0.64
-0.21 + 0.63
-0.30 + 0.63
NJ
OJ
* Slope (b) = 1 at the 95% level of confidence
b - 1
(se)b
** Intercept (a) = 0 at the 95% level of confidence —5-
y(se)B
ll - «/2. n - 2
ll - a/2. n -2
f Bias is calculated as XRF predicted value minus the known concentration of the paint film.
ft Lead concentrations chosen by reference to HUD Guidelines (see Table 15).
-------
Table 12. Solid Cinderblock
No. of Data Pairs
Slope
SDslope
Intercept
"^intercept
Corr. Coef.
Residual Variance, %
Standard Error of Estimate
of X from Y
Estimated
biast and
95%
confidence
interval
at:ft
0.3 mg/cm2
0.8 mg/cm2
1.0 mg/cm2
1.3 mg/cm2
*+
1.6 mg/cm
Scitec
15
0.697
0.075
3.434
0.321
0.9323
13.08
1.132
+3.34 + 2.01
+3.19 + 1.99
+3.13 + 1.99
+3.04 + 1.98
+2.95 + 1.97
Warrirtgton Warrington
(uncorrected) | (corrected)
18
0.934
0.020
1.851
0.078
0.9964
0.72
0.260
+1.83 + 0.56
+1.80 + 0.55
+1.79 + 0.55
+1.77 + 0.55
+1.75 + 0.55
18
0.934
0.020
0.251
0.078
0.9964
0.72
0.260
+0.23 + 0.56
+0.20 + 0.55
+0.19 + 0.55
+0.17 + 0.55
+0.15 + 0.55
PGT
(uncorrected)
21
0.749
0.032
0.401
0.130
0.9832
3.33
0.539
+0.33 + 0.92
+0.20 + 0.91
+0.15 + 0.91
+0.07 + 0.91
0.00 + 0.91
PGT
(corrected)
21
0.749
0.032
-0.189
0.130
0.9832
3.33
0.539
-0.26 + 0.92
-0.39 + 0.91
-0.44 + 0.91
-0.51 + 0.91
-0.59 + 0.91
NJ
Slope (b) = 1 at the 95% level of confidence
b - 1
(se)b
Intercept (a) = 0 at the 95% level of confidence
a
(se).
- «/2, n - 2
ll - «/2. n - 2
f Bias is calculated as XRF predicted value minus the known concentration of the paint film.
ft Lead concentrations chosen by reference to HUD Guidelines (see Table 15).
-------
Table 13. Brick
No. of Data Pairs
Slope
SDslope
Intercept
SDintercept
Corr. Coef.
Residual Variance, %
Standard Error of Estimate
of X from Y
Estimated
biast and
95%
confidence
interval
at:"
0.3 mg/cm2
0.8 mg/cm2
1.0 mg/cm2
1.3 mg/cm2
«
1.6 mg/cm
Scitec 1 Warrington
1 (uncorrected)
15
1.019*
0.056
-0.495**
0.238
0.9812
3.72
0.604
-0.49 + 1.49
-0.48 + 1.48
-0.48 + 1.47
-0.47 + 1.47
-0.46 + 1.46
18
0.918
0.021
2.118
0.081
0.9959
0.82
0.276
+2.09 + 0.58
+2.05 + 0.58
+2.04 + 0.57
+2.01 + 0.57
+1.99 + 0.57
Warrington
(corrected)
18
0.918
0.021
0.528
0.081
0.9959
0.82
0.276
+0.50 + 0.58
+0.46 + 0.58
+0.45 + 0.57
+0.42 + 0.57
+0.40 + 0.57
PGT
(uncorrected)
21
0.721
0.036
0.373
0.146
0.9772
4.51
0.627
+0.29 + 1.03
+0.15 + 1.03
+0.09 + 1.03
+0.01 + 1.02
-0.07 + 1.02
PGT
(corrected)
21
0.721
0.036
-0.227**
0.146
0.9772
4.51
0.627
-0.31 + 1.03
-0.45 + 1.03
-0.51 + 1.03
-0.59 + 1.02
-0.67 + 1.02
N)
Ul
* Slope (b) = 1 at the 95% level of confidence
b - 1
(se)b
** Intercept (a) = 0 at the 95% level of confidence
a
(se).
- a/2. n - 2
ll - a/2. n - 2
Bias is calculated as XRF predicted value minus the known concentration of the paint film.
t Lead concentrations chosen by reference to HUD Guidelines (see Table 15).
-------
Table 14. 5" Concrete
No. of Data Pairs
Slope
SDslope
Intercept
^intercept
Corr. Coef.
Residual Variance, %
Standard Error of Estimate
of X from Y
Estimated
biast and
95%
confidence
interval
at:ft
0.3 mg/cm2
0.8 mg/cm2
1.0 mg/cm2
1.3 mg/cm2
1.6 mg/cm
Scitec
15
0.809
0.058
-0.279**
0.248
0.9682
6.26
0.783
-0.34 ± 1.55
-0.43 + 1.54
-0.47 + 1.54
-0.53 + 1.53
-0.58 + 1.53
Warrington
(uncorrected)
18
0.854
0.030
2.288
0.119
0.9901
1.97
0.430
+2.24 + 0.85
+2.17 + 0.84
+2.14 + 0.84
+2.10 + 0.84
+2.05 + 0.84
Warrington
(corrected)
18
0.854
0.030
1.098
0.119
0.9901
1.97
0.430
+1.05 + 0.85
+0.98 + 0.84
+0.95 + 0.84
+0.91 + 0.84
+0.86 + 0.84
PGT
(uncorrected)
21
0.669
0.030
0.370
0.120
0.9820
3.57
0.557
+0.27 + 0.85
+0.11 + 0.84
+0.04 + 0.84
-0.06 + 0.84
-0.16 ± 0.84
PGT
(corrected)
21
0.669
0.030
-0.150**
0.120
0.9820
3.57
0.557
-0.25 + 0.85
-0.41 + 0.84
-0.48 + 0.84
-0.58 + 0.84
-0.68 + 0.84
K)
* Slope (b) = 1 at the 95% level of confidence
b - 1
(se)b
ll - «/2, n - 2
Intercept (a) = 0 at the 95% level of confidence
a
(se).
t
1 - a/2, n - 2 I
f Bias is calculated as XRF predicted value minus the known concentration of the paint film.
tf Lead concentrations chosen by reference to HUD Guidelines (see Table 15).
-------
4.2.2 Confidence Intervals
The slopes of the calibration curves with their 95 percent confidence intervals are
plotted in Figure 1 for each portable XRF and each substrate. The graph shows that the
slopes are not significantly different from one for the Scitec XRF on plywood,
plasterboard, 4" cinderblock, brick and steel and for the PGT XRF on steel. However,
the standard deviations for PGT and Scitec XRFs generally are greater than the standard
deviations for the Warrington XRF. Also, the PGT and Scitec XRFs show more scatter
in the slopes for the various substrates than does the Warrington.
If the confidence interval of a given slope overlaps the center estimate of another
slope, there is probably no difference between the two slopes. However, overlapping
of intervals where neither interval overlaps the center estimate of the other is not a
strong indication that the slopes are equivalent24
4.3 PREDICTED BIAS AT SELECTED LEAD CONCENTRATIONS
The linear regression equations were used to calculate predicted values for y (the
lead concentration measured by XRF) at various observed values of x (the "true" lead
concentration of a paint film as measured by ICP). The values of x were chosen by
reference to the HUD Guidelines6 as summarized in Table 15.
The predicted values were used to estimate the biases, and their 95 percent
confidence intervals, of the lead concentrations as measured by XRF compared to the
laboratory analyzed concentrations. A negative bias indicates that the concentration
measured by XRF is predicted to be lower than the "true" lead concentration in the paint
film; conversely, a positive bias indicates that the concentration measured by the XRF
is predicted to be higher than the "true" lead concentration.
The estimated biases and their 95 percent confidence intervals for each
XRF/substrate combination at 1 mg Pb/cm2 are plotted in Figure 2. This lead
concentration level was chosen because it is the HUD level of hazard. The biases
include zero for all combinations except the Warrington XRF on steel and concrete and
the Scitec XRF on solid cinderblock. The 95 percent confidence intervals for both the
Scitec and PGT XRFs are generally larger than those for the Warrington XRF.
27
-------
PGT
H Plywood
—i Plasterboard
Aluminum
4" Cinderblock
i Brick
i •-
-• 1 Concrete
i • 1 Solid Cinderblock
Steel
Warrington
Plywood
i—•—i Plasterboard
i • 1 Aluminum
i • 1 4" Cinderblock
i • 1 Brick
i—•—i Steel
-• 1 Concrete
i • 1 Solid Cinderblock
Scitec
H Plywood
1 Plasterboard
Aluminum
-" 4" Cinderblock
Brick
1 Steel
Concrete
Solid Cinderblock
i i
0.5 0.6 0.7 0.8 0.9 1 1.1 1.2
Slope of Calibration Curve (with 95% Confidence Interval)
1.3
Figure 1. Comparison of experimentally generated slopes for portable
XRF/substrate combinations across the lead concentration range
of 0 to 7.16 mg/cm2.
28
-------
Table 15. HUD Guidelines for Pb Testing Using Portable XRF Instrumentation
Type of
Dwelling
Multi-family
Multi-family
Scattered Site
Scattered Site
XRF Type
Direct Reading*
Spectrum
Analyzer
Direct Reading*
Spectrum
Analyzer
XRF Measured
Pb Level Considered
Negative (mg/cm2)
<0.5
<0.8
**
<0.3
XRF Measured
Pb Level Requiring
Abatement (mg/cm2)
>1.6
> 1.3
> 1.6
> 1.3
* Concentrations are substrate corrected.
Pb levels of 1.5 mg/cm2 or less require confirmatory testing.
»*
29
-------
-2
-1
- 1/2' Plasterboard
Ph
Wl
Sh
P = PGT
W = Warrington
S = Scitec
- 3/4' Plywood
Ph
W
Sh
1/8" Aluminum
PI •-
Sh
0)
O
8
0>
1/8' Steel
PI—
W|
- 4' Cinderblock
Ph
-• 1
Sh
Solid Cinderblock
PI
Wh
Sh
- Brick
Ph
W|
Sh
• 5* Concrete
Ph
Wh
Sh
-2 -1
Bias (with 95% Confidence Intervals), mg/cm2
Figure 2. Comparison of predicted biases at 1 mg Pb/cm2 for portable
XRF/substrate combinations.
30
-------
Again, if the interval of a given bias overlaps the center estimate of another bias,
there is probably no difference between the two biases. However, overlapping of
intervals where neither interval overlaps the center estimate of the other is not a strong
indication that the biases are equivalent.
4.4 SCITEC MAP-3
The Scitec instrument was evaluated using the "universal" calibration installed by
the manufacturer to cover the range from 0 to 6.19 mg/cm2. In an earlier study, to
determine whether the Scitec results could be improved by applying a substrate
correction, the Scitec was used to measure the bare substrate alone for wood,
plasterboard, 4" cinderblock, brick, aluminum siding and 1/8" steel.15 All substrates
gave readings very dose to 0 mg/cm2 (0.00 to 0.03 mg/cm2). Therefore, no substrate
correction was applied for this evaluation. The standard paint films yielded correlation
coefficients ranging from 0.93 for solid cinderblock to 0.995 for 1/8" steel. The standard
error of the estimate of x from y ranged from 0.30 mg/cm2 for 1/8" steel to 1.13 mg/cm2
for solid cinderblock. The bias of the predicted values ranged from -0.6 mg/cm2 at 1.6
mg/cm2 for 5" concrete to 3.3 mg/cm2 at 0.3 mg/cm2 for solid cinderblock. The bias
of the predicted values for solid cinderblock is nearly an order of magnitude greater
than the bias for any other of the substrates tested. With the exception of 4" cinderblock,
all substrates showed a change in predicted bias with a change in concentration of lead;
the predicted bias for 4" cinderblock was nearly constant at -0.15 to -0.13 mg/cm2 over
the range 0.3 to 1.6 mg/cm2. The data in Table 4 show that, in general, the Scitec
precision improves as the lead concentration in the paint film increases; no trend with
respect to substrate was observed.
4.5 WARRINGTON MICROLEAD I
The Warrington instrument was evaluated by first measuring the lead
concentration in the paint films placed on the various substrates and then measuring the
"apparent lead concentration" of the substrates alone so that a substrate correction could
be applied. The correlation coefficients were consistent, ranging from 0.990 for concrete
to 0.998 for plasterboard, plywood and steel. The standard error of the estimate of x
31
-------
from y was nearly constant, ranging from 0.2 mg/cm2 for plasterboard, plywood and
steel to 0.4 mg/cm2 for concrete. The data that had not been corrected for substrate
effects showed a positive predicted bias for all substrates except 1/8" steel. Application
of a substrate correction decreased the magnitude of the predicted bias for all substrates
except 1/8" aluminum and 1/8" steel. For 1/8" steel, the substrate correction changed
the sign of the predicted bias from negative to positive (from -0.68 mg/cm to +0.79
mg/cm2 at 1.0 mg/cm2). The largest predicted biases observed were for the more dense
substrates cinderblock (4" and solid), brick and concrete. The predicted biases ranged
from -0.03 mg/cm2 at 1.6 mg/cm2 for plasterboard to 1.1 mg/cm2 at 0.3 mg/cm2 for
concrete and were found to change with a change in concentration for all substrates.
The data in Table 5 show that, in general, the Warrington precision improves as the lead
concentration in the paint film increases; no trend with respect to substrate was
observed.
4.6 PRINCETON GAMMA-TECH XK-3
The PGT instrument was evaluated using the same substrate correction procedure
as described in Section 4.5 for the Warrington XRF. The correlation coefficients were
consistent, ranging from 0.977 for brick to 0.988 for 1/8" aluminum and 4" cinderblock.
The standard error of the estimate of x from y ranged from 0.39 mg/cm2 for 4"
cinderblock to 0.63 mg/cm2 for brick. Application of a substrate correction generally
changed the sign of the predicted bias from positive to negative and increased the
magnitude of the bias. The predicted bias after correction ranged from 0.1 mg/cm2 at
0.3 mg/cm2 for 4" cinderblock to -0.9 mg/cm2 at 1.6 mg/cm2 for 1/8" aluminum; The
predicted bias was found to change with a change in concentration for all substrates; the
largest changes were observed for concrete and 4" cinderblock. The data in Table 6
show that, in general, the PGT precision improves as the lead concentration in the paint
film increases; no trend with respect to substrate was observed.
32
-------
SECTION 5
CONCLUSIONS AND RECOMMENDATIONS
5.1 CONCLUSIONS
Based upon the data collected during this limited evaluation of the Scitec,
Warrington, and Princeton Gamma-Tech portable XRFs, using the experimental
conditions and test design described in Section 1.3, it appears that all instruments
measure lead in paint films more accurately (as determined by inspection of bias) on
1/2" plasterboard than on the other substrates tested. The Warrington XRF gave a lower
standard error of the estimate of x from y and a lower residual variance than the Scitec
and PGT instruments for each of the eight substrates. Also, the standard deviations of
the slope and intercept for the Warrington XRF were lower than those for the Scitec and
PGT XRFs for all substrates, with one exception; the Warrington and PGT XRFs had the
same standard deviation of the slope for 5" concrete.
The predicted biases for the three instruments on each of the eight substrates are
not significantly different except for two cases: (1) the bias of the Scitec XRF is predicted
to be significantly higher than the biases of the PGT and Warrington XRFs on solid
cinderblock and (2) the bias of the Warrington XRF is predicted to be higher than that
of the PGT XRF on 1/8" steel and 5" concrete.
The data show that, in general, precision and bias improve as the lead
concentration in the paint film increases. No trend with respect to substrate was
apparent from visual inspection of the data.
5.2 RECOMMENDATIONS
The data presented in this report should be considered preliminary. Several
improvements have been made to the portable XRFs and their calibration procedures.
It is recommended that the evaluation be repeated with care being taken to ensure that
the instruments are compared on as equivalent a basis as possible with a minimum
number of tests. This would include the following:
1) Careful selection of instruments so that source age is similar for XRFs from
each of the three manufacturers.
33
-------
2) Testing of multiple XRFs (at least 3) from each manufacturer to obtain
more representative data.
3) Careful definition of "measurement" so that each XRF is being used as
intended by the manufacturer to obtain data that are directly comparable.
4) Following a randomized matrix, in the order specified, for each XRF.
5) Using the new NIST-certified standard paint films (SRM-2759) and any
other characterized research materials that have become available since this
limited evaluation was performed.
6) Refining the test matrix to minimize the number of substrates tested.
34
-------
SECTION 6
REFERENCES
1. Agency for Toxic Substances and Disease Registry. The Nature and Extent of
Lead Poisoning in Children in the United States: A Report to Congress, U.S.
Department of Health and Human Services. 1988.
2. Grand, L.D. and J. M. Davis. Effects of Low Level Lead Exposure on Pediatric
Neurobehavioral Development: Current Findings and Future Direction. In:
Smith, M.S., L.D. Grant, and A.I. Sors, eds. Lead Exposure and Child
Development: An International Assessment. London. Kluwer Academic
Publishers, pp. 49-115,1989.
3. Goyer, R.A. Toxic Effects of Metals. In: Klassen, CD., M.O. Amdur, and J.
Doull, eds., Casarett and Doull's Toxicology, Third Edition, Macmillan, New York.
1986.
4. U.S. Department of Housing and Urban Development. Comprehensive and
Workable Plan for the Abatement of Lead-Based Paint in Privately Owned
Housing, A Report to Congress. Washington, D.C., December 1990.
5. Elias, Robert. Overview of the Urban Soil Lead Abatement Demonstration
Project. In Proceedings of U.S. EPA Symposium on Urban Soil Lead Abatement,
Research Triangle Park, NC, August, 1992. (in preparation)
6. Lead-Based Paint: Interim Guidelines for Hazard Identification and Abatement
in Public and Indian Housing, Office of Public and Indian Housing, Department
of Housing and Urban Development, April 1,1990.
7. Abbritti, G., G. Muzi, C. Cicioni, M.P. Accattoli, T. Fiordi, and P. Morucci. Effects
of Low Doses of Lead on Children's Health. In: Caroli, S., G.V. lyenzar, and H.
Muntau, eds., Bioelements: Health Aspects, Ann. Inst. Super. Sanita. 25(3): 437-
488,1989.
8. Lead-Based Paint Poisoning Prevention Act, 42 U.S.C. 4822 (d)(2)(A), 1971.
Amended 1991.
35
-------
9. McKnight, M.E., W.E. Byrd, and W.E. Roberts, Measurine Lead Concentration in
Paint Using a Portable Spectrum Analyzer X-Rav Fluorescence Device. National
Institute of Standards and Technology, NISTIR W90-650, May 1990.
10. Estes, E.D., and W.F. Gutknecht. Workshop Report: Identification of Performance
Parameters for Portable X-Ray Fluorescence Measurement of Lead in Paint. EPA
600/R-93/130, U.S. Environmental Protection Agency, Research Triangle Park,
North Carolina, 1993.
11. Binstock, D.A., D.L. Hardison, P.M. Grohse, and W.F. Gutknecht. Standard
Operating Procedures for Lead in Paint by Hotplate- or Microwave-based Acid
Digestions and Atomic Absorption or Inductively Coupled Plasma Emission
Spectrometry. EPA 600/8-91/213, U.S. Environmental Protection Agency,
Research Triangle Park, North Carolina, 1991 (19 pp). Available from NTIS,
Springfield, VA; NTIS PB92-114172.
12. Gutknecht, W.F., L.L. Hodson, H.H. Dutton, and D.A. Binstock. Preparation of
Lead-in-Paint Standard Films. EPA Contract No. 68-D1-0009, Report in
preparation.
13. International Organization of Legal Metrology. First Preliminary Draft
Recommendation on Portable and Transportable X-Ray Fluorescence
Spectrometers for Field Measurements of Hazardous Elemental Pollutants. OIML
Reporting Secretariat PS17/RS5: U.S.A., October 1992.
14. Scitec MAP-3 Operator's Manual. Available from Scitec Corporation, 1029
Kellogg Street, Kennewick, Washington 99336. Tel. No. (509) 783-9850.
15. Hardison, D.L., Whitaker, C.O., Neefus, J.D., Estes, E.D., and Gutknecht, W.F.,
"Evaluation of Portable X-Ray Fluorescence Spectrometer for Measurement of
Lead in Paint, Soil and Dust, EPA 600/A-92/245, U.S. Environmental Protection
Agency, Research Triangle Park, NC1992. Available from NTIS, Springfield, VA;
NTIS PB93-121010.
16. Warrington Microlead I Operator's Manual. Available from Warrington
Corporation, 2205 West Braker Lane, Austin, Texas 78758. Tel. No. (800) 233-9491.
36
-------
17. Princeton Gamma-Tech XK-3 Operator's Manual. Available from Princeton
Gamma-Tech Inc., 1200 State Road, Princeton, New Jersey 08540. Tel. No.
(609 724-7310.
18. Woldseth, R. X-Ray Energy Spectrometry. Kevex Corporation, Burlingame, CA
1973.
19. Willard, H. H., L. L. Merritt, Jr., J. A. Dean, and F. A. Settle, Jr. Instrumental
Methods of Analysis, Sixth Edition. D. Van Nostrand Company, New York, NY,
10020, 1981 (pp. 249-260).
20. Personal Communication with Gary Stafford, Warrington, Corporation, Tel. No.
(512) 251-7771. December 20,1993.
21. Personal Communication with Jim Hayes, State of North Carolina Environmental
Health Services Section, Tel. No. (919) 733-2884. June 4, 1993.
22. Hartley, T. F. Computerized Quality Control. John Wiley & Sons, New York, NY,
1987 (pp. 16 - 28).
23. Daniel, C, F. S. Wood and J. W. Gorman. Fitting Equations to Data, Computer
Analysis of Multifactor Data for Scientists and Engineers. Wiley-Interscience, New
York, New York, 1971 (p. 32).
24. Nelson, Lloyd S. Evaluating Overlapping Confidence Intervals. Tournal of Quality
Technology, 21(2): 140-141, 1989.
37
-------
APPENDIX A
XRF DATA:
Scitec
Warrington Uncorrected
Warrington Substrate Corrected
PGT Uncorrected
PGT Substrate Corrected
-------
Scitec
mg/cm2
Sample ID
20D1
20D2
120-5-B
20B2
20A2
120-2-B
17B
ICP
Analyzed
Cone
7.16
6.20
4.96
1.27
052
0.07
0.00
1/2"
Plasterboard
7.0
6.3
75
5.7
75
75
N/A
0.9
1.1
1.0
0.3
0.4
0.6
N/A
0
0
0
3/4"
Plywood
6.1
7.0
73
6.1
6.1
5.6
2.9
3.2
3.1
05
0.6
0.8
0.2
0.4
0.3
N/A
0
0
0
1/8"
Aluminum
8.3
72
7.3
6.7
8.0
7.7
N/A
1.1
1.2
0.9
05
0.4
0.6
N/A
0
0
0
1/8"
Steel
7.5
7.1
7.0
6.5
73
82
N/A
1.2
1.4
1.8
0.6
0.6
0.8
N/A
0.1
0
0
4"
Cinderblock
7.2
6.6
65
7.0
65
6.7
N/A
0.1
0
0.7
0.3
05
0.7
N/A
05
0.5
0.1
Solid
Cinderblock
8.3
8.3
8.1
8.1
7.6
8.2
N/A
4.7
5.2
4.4
4.0
3.6
1.0
N/A
3.7
4.1
3.9
Brick
6.8
63
6.1
6.7
7.1
55
N/A
03
0
0
0
0
0.1
N/A
0
0
0
5"
Concrete
4.9
42
6.0
6.1
4.4
5.6
N/A
0.9
05
0
0
0
0
N/A
0
0
0
N/A - Not Analyzed
-------
Warrington Randomized Test - Unconnected Data
mg/cm2
Sample ID
20D1
20D2
20B2
20A2
120-2-B
17B
ICP
Analyzed
Cone
7.16
6.20
1.27
052
0.07
0.00
1/2"
Plasterboard
6.87
6.80
6.77
6.23
6.13
6.40
1.60
157
157
0.97
0.83
1.07
N/A
0.10
0.50
0.37
3/4"
Plywood
6.70
6.73
6.77
6.33
6.23
6.23
1.93
1.67
1.70
0.87
1.03
1.07
N/A
0.80
0.77
0.60
1/8"
Aluminum
6.90
6.77
6.67
6.13
6.23
6.37
1.43
1.27
1.17
0.87
1.13
0.37
N/A
0.40
0.43
0.17
1
1/8"
Steel
5.93
5.90
5.60
5.00
4.97
4.97
0.40
0.47
0.63
0.03
-0.20
0.07
-0.27
-0.60
-0.67
-0.30
-0.63
-0.87
4"
Cinderblock
8.27
8.40
8.37
7.77
7.60
7.67
333
2.60
2.87
N/A
1.67
1.73
1.63
1.93
1.83
2.23
Solid
Cinderblock
853
8.40
8.20
7.87
7.60
8.07
2.83
2.87
3.13
220
2.73
2.10
150
1.83
1.90
2.00
2.07
2.13
1
Brick
823
850
833
837
8.07
8.07
337
350
327
2.60
2.73
257
1.93
1.90
2.13
220
1.97
227
5"
Concrete
837
757
7.80
8.13
8.13
8.13
323
3.43
357
2.83
3.03
2.93
227
2.07
230
220
2.00
220
A - Not Analyzed
-------
Warrington Randomized Test - Substrate Corrected Data
mg/cm2
Sample ID
Substrate
only
20D1
20D2
20B2
20A2
120-2-B
17B
ICP
Analyzed
Cone
_
7.16
6.20
1.27
052
0.07
0.00
1/2"
Plasterboard
0.31
6.56
6.49
6.46
5.92
5.82
6.09
1.29
1.26
1.26
0.66
052
0.76
N/A
-0.21
0.19
0.06
3/4"
Plywood
0.35
6.35
6.38
6.42
5.98
5.88
5.88
158
1.32
1.35
052
0.68
0.72
N/A
0.45
0.42
0.25
1/8" I! 1/8"
Aluminum Steel
|
-0.12
7.02
6.89
6.79
6.25
6.35
6.49
155
139
1.29
0.99
1.25
0.49
N/A
052
055
0.29
-1.47
7.40
7.37
7.07
6.47
6.44
6.44
1.87
1.94
2.10
150
127
154
1.20
0.87
0.80
1.17
0.84
0.60
4"
Cinderblock
1.31
6.96
7.09
7.06
6.46
6.29
636
2.02
1.29
156
N/A
0.36
0.42
0.32
0.62
052
0.92
Solid
Cinderblock
1.60
6.93
6.80
6.60
6.27
6.00
6.47
1.23
127
153
0.60
1.13
050
-0.10
0.23
030
0.40
0.47
053
Brick
159
6.64
6.91
6.74
6.78
6.48
6.48
1.78
1.91
1.68
1.01
1.14
0.98
034
031
054
0.61
038
0.68
5"
Concrete
1.19
7.18
638
6.61
6.94
6.94
6.94
2.04
124
238
1.64
1.84
174
1.08
0.88
1.11
1.01
0-81
1.01
N/A - Not Analyzed
-------
PGT Randomized Test - Unconnected Data
mg/cm2
Sample ID
20D1
20D2
120-5-B
20B2
20A2
120-2-B
17B
ICP
Analyzed
Cone
7.16
6.20
4.96
1.27
052
0.07
0.00
1/2"
Plasterboard
6.77
6.20
6.13
6.03
5.43
6.03
3.77
3.73
3.43
153
1.70
1.30
0.77
0.80
0.83
0.77
0.67
0.53
0.07
0.30
0.50
3/4"
Plywood
6.07
6.17
6.07
5.50
5.43
5.90
3.33
3.47
353
0.90
1.13
1.23
0.83
0.77
1.30
0.33
0.27
0.27
0.10
0.23
0.37
1/8"
Aluminum
5.93
5.80
5.97
5.07
553
5.17
3.47
3.60
3.23
1.47
0.93
0.97
N/A
-0.07
0.17
0.10
0.43
0.40
0.80
1/8" Steel
7.10
6.97
7.10
7.03
6.90
7.13
3.73
4.07
4.00
1.67
1.67
157
1.20
1.20
1.27
050
0.60
050
050
050
0.47
4"
Cinderblock
N/A
5.17
5.20
4.97
353
3.73
3.70
1.40
0.80
1.47
1.17
0.93
037
0.27
053
0.63
0.40
0.70
033
Solid
Cinderblock
6.37
6.10
6.20
4.77
5.13
5.47
330
3.47
327
1.03
1.67
1.40
0.80
0.97
0.83
0.73
037
037
0.10
0.63
0.80
Brick 5" Concrete
1
5.90
553
6.23
5.00
4.70
5.40
2.93
3.40
2.93
150
1.47
2.00
0.77
0.93
1.00
033
0.23
0.67
020
0.07
027
5.17
520
523
5.13
4.83
4.83
333
2.83
2.97
133
130
1.80
0.80
0.83
0.80
0.97
033
023
0.07
020
0.10
N/A - Not Analyzed
-------
PGT Randomized Test - Corrected Substrate Data
mg/cm2
Sample ID
Substrate
only
20D1
20D2
12Q-5-B
20B2
20A2
120-2-B
17B
ICP
Analyzed
Cone
7.16
6.20
4.96
1.27
0.52
0.07
0.00
1/2"
Plasterboard
0.29
6.48
5.91
5.84
5.74
5.14
5.74
3.48
3.44
3.14
1.24
1.41
1.01
0.48
0.51
0.54
0.48
0.38
0.24
-0.22
0.01
0.21
3/4"
Plywood
0.43
5.64
5.74
5.64
5.07
5.00
5.47
2.90
3.04
3.10
0.47
0.70
0.80
0.40
0.34
0.87
-0.10
-0.16
-0.16
-0.33
-0.20
-0.06
1/8"
Aluminum
0.68
5.25
5.12
5.29
4.39
4.85
4.49
2.79
2.92
2.55
0.79
0.25
0.29
N/A
-0.75
-0.51
-0.58
-0.25
-0.28
0.12
1/8" Steel
1.24
5.86
5.73
5.86
5.79
5.66
5.89
2.49
2.83
2.76
0.43
0.43
0.33
-0.04
-0.04
0.03
-0.74
-0.64
-0.74
-0.74
-0.74
-0.77
4"
Cinderblock
0.25
N/A
4.92
4.95
4.72
3.28
3.48
3.45
1.15
055
1.22
0.92
0.68
0.12
0.02
0.28
0.38
0.15
0.45
0.08
Solid
Cinderblock
059
5.78
551
5.61
4.18
454
4.88
2.71
2.88
2.68
0.44
1.08
0.81
021
0.38
024
0.14
-0.22
-0.22
-0.49
0.04
021
Brick
0.60
5.30
4.93
5.63
4.40
4.10
4.80
233
2.80
233
0.90
0.87
1.40
0.17
033
0.40
-0.27
-0.37
0.07
-0.40
-053
-0.33
5" Concrete
052
4.65
4.68
4.71
4.61
431
431
2,81
231
2.45
0.81
0.78
128
028
031
028
0.45
-0.19
-029
-0.45
-032
-0.42
N/A - Not Analyzed
------- |