Defense Threat Reduction Agency

8725 John J. Kingman Road, MS-6201 

Fort Belvoir, VA 22060-6201

Plutonium Bioassay Testing of U.S. Atmospheric

Nuclear Test Participants and U.S. Occupation 

Forces of Hiroshima and Nagasaki, Japan

DISTRIBUTION A. Approved for public release: distribution is unlimited.

October 2015

Prepared by:

Leidos

Alexandria, VA

DTRA-TR-15-058

TECHNICAL REPORT
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1. REPORT DATE (DD-MM-YYYY)

30-10-2015

2. REPORT TYPE

Technical Report

3. DATES COVERED (From - To)

4. TITLE AND SUBTITLE

Plutonium Bioassay Testing of U.S. Atmospheric Nuclear Test 

Participants and U.S. Occupation Forces of Hiroshima and Nagasaki, 

Japan

5a. CONTRACT NUMBER

5b. GRANT NUMBER

5c. PROGRAM ELEMENT NUMBER

6. AUTHOR(S) 1

Schaeffer, Dennis M., 1Case, David R.; 2Ingraham, Joanna T.; and 

2

Blake, Paul K. 

5d. PROJECT NUMBER

5e. TASK NUMBER

5f. WORK UNIT NUMBER

7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) 1

Leidos; 2Defense Threat Reduction Agency

8. PERFORMING ORGANIZATION

REPORT NUMBER

9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES)

Nuclear Technologies Department, Attn: Dr. Blake

Defense Threat Reduction Agency

8725 John J. Kingman Road, Mail Stop 6201

Fort Belvoir, VA 22060-6201

10. SPONSOR/MONITOR'S ACRONYM(S)

DTRA J9-NTSN

11. SPONSORING/MONITORING

AGENCY REPORT NUMBER

DTRA-TR-15-058

12. DISTRIBUTION AVAILABILITY STATEMENT

DISTRIBUTION A. Approved for public release: distribution is unlimited.

13. SUPPLEMENTARY NOTES

14. ABSTRACT

This report documents DTRA’s study conducted from 1994 to 2004 to develop a urine bioassay program and 

investigate the feasibility of this method to complement the atomic veteran dose reconstruction under the Nuclear Test 

Personnel Review Program. Brookhaven National Laboratory (BNL) used fission track analysis (FTA) to estimate doses 

to the Marshallese Island population. In this study, BNL’s FTA method was evaluated to determine if it can be applied to 

atomic veterans by measuring plutonium in urine samples. Guided by Congressional legislation (PL 105-85), DTRA 

conducted a pilot study involving 100 atomic veterans to see if expanded use on atomic veterans was feasible. The 

activities in this study consisted of establishing a calibration system for measuring plutonium content in urine samples; 

determining the accuracy, repeatability, and sensitivity of FTA; and measuring background plutonium levels in a 

representative U. S. population not involved with nuclear weapons testing or plutonium work. The results for the 100 

atomic veterans were compared to those of the unexposed population, and veterans with results that were statistically 

above background were identified. Finally, bioassay results were compared to doses estimated by reconstruction.

15. SUBJECT TERMS

Nuclear Test Personnel Review, Veteran, Atmospheric Nuclear Testing, Hiroshima Nagasaki Occupation, Plutonium, 

Bioassay

16. SECURITY CLASSIFICATION OF: 17. LIMITATION OF

ABSTRACT

 U

18. NUMBER

OF PAGES

33 Pages

19a. NAME OF RESPONSIBLE PERSON 

Paul K. Blake, PhD

a. REPORT b. ABSTRACT c. THIS PAGE 19b. TELEPONE NUMBER (Include area code ) 

 (703) 767-3433
UNIT CONVERSION TABLE

U.S. customary units to and from international units of measurement*

U.S. Customary Units Multiply by International Units

Divide by†

Length/Area/Volume

inch (in) 2.54 × 10–2 meter (m)

foot (ft) 3.048 × 10–1 meter (m)

yard (yd) 9.144 × 10–1 meter (m)

mile (mi, international) 1.609 344 × 103 meter (m)

mile (nmi, nautical, U.S.) 1.852 × 103 meter (m)

barn (b) 1 × 10–28 square meter (m2)

gallon (gal, U.S. liquid) 3.785 412 × 10–3 cubic meter (m3) 

cubic foot (ft3) 2.831 685 × 10–2 cubic meter (m3) 

Mass/Density

pound (lb) 4.535 924 × 10–1 kilogram (kg)

atomic mass unit (AMU) 1.660 539 × 10–27 kilogram (kg)

pound-mass per cubic foot (lb ft–3) 1.601 846 × 101 kilogram per cubic meter (kg m–3)

Pound-force (lbf avoirdupois) 4.448 222 Newton (N)

Energy/Work/Power

electronvolt (eV) 1.602 177 × 10–19 joule (J)

erg 1 × 10–7 joule (J)

kiloton (kT) (TNT equivalent) 4.184 × 1012 joule (J)

British thermal unit (Btu) (thermochemical) 1.054 350 × 103 joule (J)

foot-pound-force (ft lbf) 1.355 818 joule (J)

calorie (cal) (thermochemical) 4.184 joule (J)

Pressure

atmosphere (atm) 1.013 250 × 105 pascal (Pa)

pound force per square inch (psi) 6.984 757 × 103 pascal (Pa)

Temperature

degree Fahrenheit (

o

F) [T(oF) − 32]/1.8 degree Celsius (oC)

degree Fahrenheit (

o

F) [T(oF) + 459.67]/1.8 kelvin (K)

Radiation

activity of radionuclides [curie (Ci)] 3.7 × 1010 per second (s

–1‡

)

air exposure [roentgen (R)] 2.579 760 × 10–4 coulomb per kilogram (C kg–1

)

absorbed dose (rad) 1 × 10–2 joule per kilogram (J kg–1§)

equivalent and effective dose (rem) 1 × 10–2 joule per kilogram (J kg–1**) *

Specific details regarding the implementation of SI units may be viewed at http://www.bipm.org/en/si/. †

Multiply the U.S. customary unit by the factor to get the international unit. Divide the international unit by the factor to get the U.S. 

customary unit.

‡

The special name for the SI unit of the activity of a radionuclide is the becquerel (Bq). (1 Bq = 1 s–1). §

The special name for the SI unit of absorbed dose is the gray (Gy). (1 Gy = 1 J kg–1). **The special name for the SI unit of equivalent and effective dose is the sievert (Sv). (1 Sv = 1 J kg–1).
i 

DTRA-TR-15-058: DRAFT Plutonium Bioassay Testing of U.S. Atmospheric Nuclear 

Test Participants and U.S. Occupation Forces of Hiroshima and 

Nagasaki, Japan

Table of Contents

List of Figures............................................................................................................................ ii

List of Tables............................................................................................................................. ii

Executive Summary ....................................................................................................................1

Section 1. Introduction ................................................................................................................2

1.1 Requirements for an NTPR Plutonium Bioassay Program.............................................2

1.2 Approach to NTPR Plutonium Bioassay Testing ...........................................................3

Section 2. Methods for Plutonium Measurement, Data Analysis, and Validation.........................6

2.1 Technical Basis for Performing Urine Bioassay ............................................................6

2.2 BNL FTA Analysis Method ..........................................................................................6

2.3 Methods for Analyzing Bioassay Data ..........................................................................7

2.3.1. Linear Regression Approach ..................................................................................7

2.3.2. Lognormal Regression Correction Approach..........................................................9

2.3.3. Definition and Determination of Minimum Detectable Activity (MDA), Lower 

Limit of Detection (LLD), and Decision Level (DL).......................................................... 10

2.4 Measurement Validation of FTA Plutonium Bioassay................................................. 11

2.4.1. Comparison of Results of Analyses of Plutonium in Urine Samples by Two 

Laboratories ...................................................................................................................... 11

2.4.2. Analysis of Comparison Results........................................................................... 11

Section 3. Plutonium in the Urine Samples of U.S. General Population and U.S. Atomic 

Veterans.................................................................................................................................... 13

3.1 Plutonium Measured in Urine of Selected Members of the U.S. General Population.... 13

3.2 Results for Initial Phase of Measurements on Veterans................................................ 14

3.3 Results of Resampling of 12 Selected Veterans........................................................... 16

Section 4. Discussion of the Results.......................................................................................... 18

4.1 Interpretation of the Results ........................................................................................ 18

4.2 Comparison of Bioassay Measurements and Dose Reconstructions............................. 18

Section 5. Conclusions.............................................................................................................. 20

Section 6. References................................................................................................................ 22

Appendix A. Compilation of Project Bioassay Test Results....................................................... 25
ii

List of Figures

Figure 1. Typical linear regression calibration curve for FTA bioassay blanks and spikes...........8

Figure 2. Spike and blank values used in calibration of the FTA method for calculation of 239Pu 

activities in veterans’ samples....................................................................................9

Figure 3. Distribution of bioassay measurements in the U.S. general population group............. 14

Figure 4. Comparison of the distributions of bioassay results for the U.S general populaton and 

atomic veterans........................................................................................................ 15

Figure 5. Comparison of FTA and TIMS sample measurements for selected veterans with 

original FTA bioassay measurements above 100 aCi/sample.................................... 17

List of Tables

Table 1. Results of 239Pu measurements by LANL and BNL .................................................... 12

Table 2. Locations and numbers of subjects contributing urine samples for the general 

population group...................................................................................................... 13

Table 3. First and second split measurements for 11 selected bioassays with original readings 

above 100 aCi/sample .............................................................................................. 16

Table 4. Comparison of bioassays for veterans followed-up with TIMS ................................... 17

Table 5. Comparison of bioassay results with reconstructions of internal dose.......................... 19

Table A-1. Results of bioassay testing of the selected U.S. population group............................ 25

Table A-2 . Results of bioassay testing of 100 eligible veterans................................................ 26
1

Executive Summary

This technical report describes the scientific and technical processes employed to conduct 

a pilot urine plutonium bioassay testing program on 100 atomic veterans using Brookhaven 

National Laboratory’s (BNL’s) Fission Track Analysis (FTA) technique. The report also 

discusses the methodology, collected data, scientific challenges, and test results of this pilot 

bioassay testing program. The Defense Threat Reduction Agency (DTRA) and its predecessor 

agencies conducted this program from 1994 to 2004 to determine whether it was feasible to use 

bioassay testing to supplement dose reconstruction techniques used to estimate atomic veterans’ 

doses under the Nuclear Test Personnel Review Program. 

Congressional action (PL 98-542, 1984, Sections 7.a.(2)(A), (B), and (C)) called for the 

evaluation of the reliability and accuracy of scientific and technical devices and techniques, and 

to consider their potential implementation for performing retrospective dose assessments on 

radiation-exposed veterans. National Research Council (NRC, 1985) also recommended bioassay 

testing of atomic veterans to assess the reliability of internal dose estimation. The results of the 

evaluation study (Boecker et al., 1991) recommended using the FTA technique already employed 

by BNL to assess doses to the Marshallese Islanders impacted by atmospheric nuclear testing. 

Following these findings, DTRA investigated the application of BNL’s FTA technique to atomic 

veterans. Early test results showed unexplainable uncertainties in initial FTA tests on personnel 

with and without histories of Pu uptake. Further congressional action (PL 105-85, 1997) directed 

DTRA to conduct a pilot study involving 100 atomic veterans to better understand FTA 

uncertainties and repeatability difficulties, and to assess whether expanded use on veterans was 

feasible.

The pilot study of 100 veterans also included bioassay testing of a representative group of 

58 persons from the general population who lived during the atmospheric nuclear test era but 

were not involved with the nuclear tests or radiation related occupations. The FTA technique is

capable of measuring 239Pu excreted in urine following intakes of plutonium in this population 

from worldwide fallout. It was essential that the technique be able to distinguish whether atomic 

veterans had plutonium intakes in excess of those from worldwide fallout estimates. This report 

shows that 85 of 100 veterans excreted low levels of 239Pu similar to those detected in general 

population group. For the remaining 15 veterans, one result was confirmed as clearly positive. 

The other 14 veteran results raised concerns because of the large observed uncertainties in values 

ranging higher than those of the general population group. Subsequently, at DTRA’s request, the 

Los Alamos National Laboratory used an alternate bioassay technique called thermal ionization 

mass spectrometry (TIMS) to independently replicate the tests on 12 of the 15 veterans. All were 

not available for resampling. The results of the TIMS tests showed that the 239Pu results for the 

resampled atomic veterans were not above those for the general population group.

This study showed that FTA’s ability to demonstrate positive or negative plutonium 

uptakes in atomic veterans was not credible. The conclusion was that FTA bioassay is not 

feasible to implement on a wide scale basis among atomic veterans or to complement the NTPR 

dose reconstruction program.
2

Section 1.

Introduction

This technical report describes the scientific and technical processes employed to conduct 

a pilot urine plutonium bioassay testing program on 100 atomic veterans1. It summarizes the 

methodology, data that were collected during the course of the program, discusses scientific 

challenges that arose during its activities, reports the results of testing and provides an 

assessment of the applicability of the results to the atomic veteran population. This report 

concludes, consistent with National Research Council’s findings (NRC, 2003), that urine 239Pu

bioassay using FTA did not enhance the capability of DTRA’s current scientific processes to 

perform accurate dose reconstructions for atomic veterans, and therefore, was not feasible for 

implementation on a wide scale basis for atomic veterans.

1.1 Requirements for an NTPR Plutonium Bioassay Program

In 1984, the Veterans’ Dioxin and Radiation Exposure Compensation Standards Act (PL 

98-542, 1984) called for the study of alternative scientific methods for performing retrospective 

dose assessments on radiation-exposed veteran populations. The National Research Council 

(NRC, 1985) also recommended bioassay testing of atomic veterans to assess the reliability of 

the internal dose estimates. The resulting study (Boecker et al., 1991) discussed plutonium

bioassay as a potential means of retrospectively testing atomic veterans to detect and quantify 

uptakes of radionuclides from nuclear detonation debris and fallout. Of the several hundreds of 

possible inhaled or ingested radionuclides, 239Pu can be detected 35 or more years after intake in 

an excreted urine sample. The extremely long half-life and very low long-term excretion rate 

makes 239Pu the most suitable isotope of interest. The radionuclide 239Pu has been found in the 

environment since 1945 in extremely small quantities, which are orders of magnitude less than 

the quantities of natural uranium (including isotopes of interest such as 238U and 235U). 

Consequently, 239Pu identification by urinalysis was proposed as a marker for significant internal 

intakes of other associated radionuclides in nuclear weapons debris due to its low natural 

background. However, intakes of 239Pu in worldwide fallout can be measured in the urine of

persons who lived during the atmospheric nuclear testing era and can confound the results of 

veteran-supplied bioassay samples if not appropriately considered.

In the mid-1990s, representatives from the Department of Veterans Affairs (VA)

Veterans Health Administration and Defense Nuclear Agency2 (DNA), the Defense Threat 

Reduction Agency’s (DTRA’s) predecessor agency, discussed the feasibility of applying 

techniques described in Boecker et al. (1991) to the atomic veteran population. VA ceded 

proponency to DTRA for initiating a feasibility program because it was better suited to DTRA’s 

mission under the Department of Defense (DoD) Nuclear Test Personnel Review (NTPR) 

Program. The technique found most promising was fission track analysis (FTA) being used by 

 1 Atomic veteran is the term that refers to veterans who participated in U.S. nuclear tests and the post-World War II 

occupation of Hiroshima and Nagasaki, including liberated POWs. 2 Hereinafter, DNA is referred to with the current agency’s name, DTRA.
3

Brookhaven National Lab (BNL) to assess 239Pu content in urine samples taken from the 

Marshallese Island population impacted by U.S. atmospheric nuclear testing (Sun et al., 1993). 

Department of Energy (DOE) was already investigating this technique as a possible way to 

estimate long-term population radiation doses of this population (Moorthy et al., 1988).

DTRA initiated tasks with BNL to enhance the sensitivity of FTA and adapt the 

experiences of the Marshallese Island urine 239Pu bioassay sample collection methods to suit a 

nationally-distributed atomic veteran population that did not reside in one geographic location. 

By 1998, BNL had refined its FTA technique to detect low masses of Pu (equivalent to activities

of tens of attocuries (aCi3) in a 24-hour urine sample from members of the general U.S. 

population exposed to worldwide fallout (Pietrzak et al., 1998). Based on this improvement in 

assay sensitivity, the NTPR Program selected BNL to measure 239Pu levels in veteran urine 

samples using the FTA technique. Equally important was establishing the lowest level of 

detection benchmark to determine whether results of bioassay samples from the U.S. general 

population could be distinguished from results of synthetic urine blanks representing no 

plutonium level.

While the initial BNL work was underway, Congress expressed urgency to begin urine 

plutonium bioassay testing of atomic veterans. Congress learned that DTRA was contemplating 

curtailment of the BNL effort due to large anomalous uncertainties and difficulties with 

measurement repeatability being uncovered. The length of time to understand and resolve these 

issues was inestimable. Congress, responding by enacting legislation as part of the National 

Defense Authorization Act for Fiscal Year 1998 (PL 105-85, 1997), proposed a limited pilot test

program as a way forward to ascertain the practical logistics of collecting samples from atomic 

veterans and to further investigate the technical problems. In addition, the limited program would 

permit assessing the feasibility of offering testing to a wider range of atomic veterans.

Consequently, bioassay testing was offered to the first 100 eligible veterans who 

contacted the NTPR Program after 1 June 1999 when the pilot program was publicly announced

(DTRA, 1999). The NTPR program confirmed veteran eligibility by confirming their

participation in U.S. atmospheric nuclear testing (1945 to 1962) or the post-war occupation of 

Hiroshima and Nagasaki, Japan. The VA assisted with collection and custody control of the 

bioassay samples sent to BNL for testing. DTRA, Science Applications International 

Corporation (now Leidos), and BNL formed a cooperative team to analyze, interpret, and report 

bioassay data and results.

1.2 Approach to NTPR Plutonium Bioassay Testing

The testing program encompassed two phases: the first being work conducted to fulfill 

the requirements under PL 98-542 and the second being work directed under PL 105-85 to 

perform a limited pilot testing of atomic veterans to determine the feasibility of continued testing 

on a wide scale basis. DTRA selected Pu bioassay as a potential method to support retrospective 

dose assessment for the following reasons:

• The radionuclide 239Pu was the only remaining long-lived and very slowly-excreted isotope

out of several hundred still being excreted by atomic veterans 35 to 50 years after an intake 

of nuclear test debris that could be measured;

 3 1 aCi = 10-18 Ci
4

• FTA was sufficiently sensitive to measure low levels of 239Pu in urine samples of veterans 

collected 35 to 50 years after an intake;

• The BNL technique could be adapted to atomic veteran sampling based on the laboratory’s 

experiences in collecting urine samples from Marshallese Islanders; and

• DTRA had already collected a wealth of dose reconstruction results on atomic veterans 

which could be used for comparisons with bioassay results to assess the feasibility of 

plutonium bioassay as a dose assessment tool. 

Before embarking on an effort to sample urine of atomic veterans to analyze for low-level 

plutonium, DTRA found it essential to perform the following technical tasks in carrying out the 

charge of PL 105-85:

• Determine the lower limit of detection (LLD) for FTA detection of 239Pu;

• Determine that urine samples without plutonium can be measured as negative (zero level) 

quantities with reliability and repeatability;

• Establish a measurement benchmark by determining if samples of the U.S. general 

population living during the atmospheric test era could be measured as positive quantities 

above the FTA technique’s LLD; and

• Determine if the 239Pu content can be measured accurately in urine samples taken from 

persons already known to have well-characterized body burdens from occupational 

exposures.

After Congress directed the performance of bioassay sampling on a limited pilot test 

basis, the tasks were expanded to include the following:

• Establish and maintain standard measurement and calibration protocols to reliably determine 

plutonium content in bioassay samples collected from selected test populations;

• Determine by FTA the activity concentrations of 239Pu excreted by a selected U.S. population 

having no history of working with plutonium or performing similar activities as veterans 

eligible for bioassay testing;

• Establish and schedule chemical, reactor irradiation, and counting procedures for batch 

processing urine samples in small groups and reporting results;

• Compare background and veteran sample measurements against the FTA technique’s

minimum detectable activity (MDA) and decide whether results are statistically positive;

• Interpret measurement results with respect to NTPR program-developed veteran dose 

reconstructions for possible correlations; and

• Corroborate measurements using other comparable urine 239Pu bioassay testing techniques if 

bioassay test results require further investigation.

This technical report covers the FTA measurement process, the methods used to analyze 

the bioassay results, FTA measurement validation, the characterization of results from the U.S. 

general population samples, the results of the 100-sample atomic veteran population, the 

discussion of the results, and conclusions. The report authors considered the use of SI units 

throughout this technical report, but their decision was to remain with the legacy units, for 
5

example attocurie (aCi) vs. microbecquerel (μBq). All of the working papers associated with the 

DTRA urine bioassay pilot program and some of the technical references supporting this 

technical report contain legacy units. Thus, the authors retain use of legacy units throughout the 

report for clarity and linkage to past work in this field of study.
6

Section 2.

Methods for Plutonium Measurement, Data Analysis, and Validation

This section summarizes the method BNL used to measure plutonium in urine samples 

collected from both veterans and the general population (Pietrzak et al., 1998, Kaplan, 1996, and 

Sun et al., 1993). The measurement of 239Pu in urine from both populations is based on the 

possibility that there is sufficient plutonium contained in debris from nuclear detonations that can 

be inhaled or ingested, deposited in bodily tissues and organs, and retained there to be measured 

in urine samples collected many years later (Boecker et al., 1991).

2.1 Technical Basis for Performing Urine Bioassay 

Intake models (ICRP, 1994a and b) formulate retention and excretion relationships that 

can be applied to internalized plutonium to predict the amount excreted in urine. Typically, about 

1/100,000 of the original amount of a 239Pu intake is predicted to be excreted daily 30–60 years 

after a detonation (Leggett, 1984 and Jones, 1985). The FTA methodology is sufficiently 

sensitive to measure amounts of plutonium as low as a few 10s of aCi (Sun et al., 1997). The 

specific plutonium isotope of interest for bioassay testing is 239Pu. Although 240Pu, another 

isotope in weapons grade plutonium, is important from a health perspective, its presence within a 

given urine sample being analyzed by FTA can only be inferred from 239Pu content.

All urine samples collected from 100 veterans and the general population were prepared, 

measured, and analyzed by BNL under procedures approved by the NTPR Program. BNL used 

its FTA technique to characterize the 239Pu activity in units of aCi (10-18 Ci) in a 24-hour urine 

sample or aCi/24-hr sample, hereinafter referred to as aCi/sample. This is an exceedingly small 

amount of radioactive material, because 1aCi is equal to 1.2 disintegrations per year. FTA is 

based on the high probability that 239Pu will undergo nuclear fission in the presence of thermal 

neutrons. 

DTRA, BNL, and VA collaborated on procedures to collect continuous 24-hour urine 

samples from the 100 veterans. DTRA’s role was to communicate with veterans throughout the 

bioassay test process. VA’s responsibility via its system of Veterans Affairs Medical Centers 

(VAMCs) was to receive the samples from veterans, perform a quality control check on the 

packaging, and maintain custody control of the sample in transport from the VAMC to BNL. 

BNL designed the packaging, handling, shipping and transport and urine collection procedures to 

insure intact samples were returned to BNL for bioassay measurement. BNL’s experience with 

collecting and measuring Pu bioassay samples from Marshallese Islanders (Sun et al., 1993 and 

Sun et al., 1997) was adapted to atomic veterans to fully ensure successful sample collections.

2.2 BNL FTA Analysis Method

The FTA procedure entailed a two-step chemical process: first, the entire urine sample,

collected from the individual and transferred to BNL, underwent co-precipitation and wet-ash 

digestion to oxidize organic matter and destroy protein complexes (Kaplan et al., 1995). At this 

point, the sample was split in half (called a split sample). The first split was prepared for FTA 

analysis and the second split was retained in case replication of the first split’s measurement 
7

should be necessary. Then, the first split underwent chemical separation of plutonium, using 

hyper-pure reagent resin exchange columns, from other fissionable materials such as uranium. 

The first split was then concentrated to a volume of a few microliters. 

Each concentrated split was transferred to an ultra-clean quartz slide, evaporated, and 

irradiated in a nuclear reactor with a quantifiable thermal neutron flux. The 239Pu fission 

fragments produced microscopic tracks in the slide’s surface. Chemical etching was performed 

to make the tracks visible, and then the slides were viewed under a microscope and the 

magnified tracks counted. The number of tracks counted, which were directly related to the mass 

of 239Pu irradiated, was proportional to the 239Pu activity in the concentrated sample.

The FTA procedure was designed primarily to measure 239Pu fissions. A primary source 

of potential interference was from the presence of 235U, an isotope of uranium that also has a 

high cross section for fission from thermal neutrons. The resin exchange process was designed to 

maximize the separation of plutonium from uranium, although some low-level presence of 235U 

in the samples was possible. The possibility of leakage was managed by monitoring for small 

increases in uncertainties of the FTA system calibration data collected for each bioassay batch 

(roughly 10 split samples per batch) over time. The resin columns were replenished for each new 

batch. If the small increases were severe enough to affect a particular batch of bioassay samples, 

the second split samples or new urine samples were obtained and processed as a new batch.

2.3 Methods for Analyzing Bioassay Data

2.3.1. Linear Regression Approach

Spikes and blanks provided calibration of the 239Pu activity corresponding to the number 

of tracks deposited on the slides. The slides were prepared using synthetic urine, chemically 

equivalent to human urine, to which known activities of 239Pu, traceable to National Institute of 

Standards and Technology (NIST), were added. The nominal activity levels of the spikes were 

25, 50, 100, 150, 200, 300, and 400 aCi. For the blanks, the synthetic urine was not spiked. The 

spikes and blanks were irradiated with every batch, alongside samples to be measured, to ensure 

that uniform reactor irradiation geometries were maintained. Activation neutron flux monitors

were used to assess the variability in neutron flux during the various irradiation batches to allow 

normalization of results. The sample array underwent preliminary testing to ensure there was no 

appreciable geometric flux inhomogeneity. These data allowed calibration of the FTA technique 

according to the following linear relationship:

Tc = mAc + B (1)

where:

Tc = observed number of tracks on the spike and blank slides;

Ac = known activities of the spike and blank slides (aCi);

m = slope of the best fit line (tracks/aCi); and

B = intercept of the best fit line (tracks).

The accumulated “spike and blank” calibration data were fit to equation (1) using linear least 

squares regression.
8

Once the relationship of equation (1) is established, the Pu activity of a test sample can be 

calculated using equation (2) as follows:

As = �

fTs − B

m � (2)

where:

As = activity (aCi) for bioassay sample having Ts tracks;

f = scaling factor to correct for using a portion of the urine sample (typically 

around a value of 2), multiplied by a neutron flux normalization factor 

(ranging from 0.90 to 1.44), which is uniquely determined for each processed 

batch; and 

Ts = number of tracks counted on a sample slide.

Historical values for m and B were 1.06 and 19.8, respectively, and varied about 3% over time. 

The correlation coefficients of the regression lines ranged from 0.95 to 0.98, indicating a very 

consistent relationship between registered tracks on slides and known quantities of 239Pu. The 

95% confidence interval for the regression relationship averaged ± 36 aCi. New calibration data 

were checked for conformance with this regression relationship to validate the stability of the 

FTA method. Figure 1 shows a graphical representation of this linear calibration approach, also 

reported in the literature. The track values for spikes falling appreciably outside the uncertainty 

band (labeled as “95% limit”) shown in Figure 1 were rejected as outlier data (Schaeffer et al., 

1999; Brodsky et al., 1999; and Schaeffer, 2002).

Figure 1. Typical linear regression calibration curve for FTA bioassay blanks

and spikes

Tc = 1.062Ac + 20.4, R2 = 0.939

-100

0

100

200

300

400

500

600

0 50 100 150 200 250 300 350 400 450

Number of Tracks (Tc)

239Pu Activity (Ac in aCi)

95% Limit Measured Tracks

95% Limit Fit Line
9

The “blank” data were analyzed separately to determine the lower limit of detection 

(LLD) of the FTA method. This analysis is crucial for taking into account the statistical 

uncertainties of measuring the “zero” activity of 239Pu in the blanks. The LLD was determined by 

converting all of the blanks data (in number of tracks) to activity (aCi) by using equation (2). The 

data were averaged and the standard deviation computed. The LLD represented a value 

corresponding to trace 239Pu present in the synthetic urine solution. The LLD established a level 

above which a bioassay result is distinguishable from the nearly zero activity of the blanks. This 

value corresponded to about 20 ± 36 aCi, roughly corresponding to the value of B intercept for 

blanks.

2.3.2. Lognormal Regression Correction Approach

The cooperative scientific team discovered over a series of five batches (consisting of 

about 10 bioassay samples per batch) that a considerable number of “spikes” data were being 

rejected as outliers in fitting calibration data using the linear regression approach. These outliers 

appeared to be commonly associated with samples of higher activity rather than at levels 

approaching the LLD. Figure 2 displays data used in the linear regression analysis along with the 

heretofore rejected outlier data. This realization led to a rejection of the linear regression 

approach outlined in section 2.3.1 and computation of new calibration curves based on 

lognormal regression. The bioassay values obtained with linear regression were replaced with 

new values computed using lognormal regression. 

Figure 2. Spike and blank values used in calibration of the FTA method for calculation of 

239Pu activities in veterans’ samples

Changes in chemistry and neutron irradiation procedures over time resulted in a greater 

variability in track numbers at given plutonium levels, which became especially pronounced at 

0

100

200

300

400

500

600

0 50 100 150 200 250 300 350

Derived Track Count

239Pu Activity (aCi)

Spikes Blanks
10

higher plutonium activities. An increasing non-homogeneous variance could be noticed with 

increasing plutonium levels. The linear regression approach (see Figure 1) showed a distribution 

of constant variance estimated to be ± 36 aCi. It was found using the data shown in Figure 2 data 

that the deviations from the mean were not consistent with a normal distribution as first thought

(see section 2.3.1). It was found that the ratios of the number of tracks for a sample divided by 

the median (estimated by an applied fit to Figure 2 data) were lognormally distributed (Klemm et 

al., 2001 and 2003). The differences between the logarithm of observed number of tracks and 

logarithm of the median value were found to be normally distributed. The distribution of the 

number of tracks, corresponding to blanks, was also found to be lognormally distributed as well 

(Klemm et. al., 2001, 2002). Likewise, the differences between the logarithm of the observed 

number of tracks corresponding to the blanks and the logarithm of the blanks’ median value were 

also found to be normally distributed.

This discovery resulted in the reanalysis of bioassay data to account for corrected 

distributions and calibration uncertainties noted in the data heretofore rejected in the linear 

regression analysis. The mathematical schemes for dealing with non-conventional uncertainty 

distributions are well documented (Brodsky et al., 1999; Brodsky, 2000, and Klemm et al., 

2003). Klemm et al. (2003) demonstrated how to apply corrections to the calibration regression 

line used to fit blanks and spikes data to equation (1) and compute the activity in aCi of the 

bioassay samples per equation (2). All reported veteran bioassay data were computed in this 

manner. For example, equations (1) and (2) above become:

Log(Tc) = m′

[log(Ac)] + B′ (3)

where Tc and Ac are defined in equation (1) and m′ and B′ are slope and the intercept of the best 

fit linear regression line of equation (3). Then, the Pu activity in a sample is calculated with:

As = 10��lll(fTs) – B′

� m′ ⁄ � (4)

where As and Ts are defined in equation (2) and m′ and B′ are defined in equation (3) above.

2.3.3. Definition and Determination of Minimum Detectable Activity (MDA), Lower Limit 

of Detection (LLD), and Decision Level (DL)

It was particularly important to develop factors for the analysis and interpretation of all 

bioassay data collected for the pilot bioassay sample program. The useful factors are MDA,

LLD, and DL. The most important factor was the MDA. 

The MDA, derived from all the blanks and background population bioassay data, 

established the level above which a veteran bioassay sample measurement was judged to be 

statistically different from the 58 person background population. This factor was derived using 

the ANSI Standard N13.30 and other references (ANSI, 1996; Boecker et al., 1991; and 

Brodsky, 1992). The MDA was based on accounting for Type I and Type II errors at the 95th

percentile (Boecker et al., 1991 and Brodsky, 1992). That is, the MDA computed to be 

280 aCi/sample was the level above which there is at least a 95% chance that a veteran’s 

bioassay sample measurement was truly positive and not a false negative. 

The LLD is the level below which bioassay results can be considered indistinguishable 

from a “zero” level of activity. The LLD was derived as the median of the distribution of the 
11

blanks. The median value was 18 aCi with the 95% percentile for Type I error value being 

± 24 aCi and Type II error value being ± 75 aCi.

The DL was a term coined for a factor derived for simply characterizing the attributes of 

the distribution of the 58-sample U.S. general population results (see Section 3.2. and Figure 3). 

The DL was further broken down into DL95 and DLmax. DL95 defined the 95th percentile level

below which 95% of the background population sample results were contained. DLmax

corresponded to the highest result in the general population distribution. The DLmax was used to 

screen out values between it and the MDA of 280 aCi/sample for further study.

2.4 Measurement Validation of FTA Plutonium Bioassay

2.4.1. Comparison of Results of Analyses of Plutonium in Urine Samples by Two 

Laboratories

In 1996/1997, Dr. Payne S. Harris, the NTPR program’s medical consultant, made 

arrangements with Los Alamos National Laboratory (LANL) to participate in a bioassay 

measurement comparison between BNL and LANL. LANL provided bioassay samples collected 

from LANL workers having prior 239Pu intakes which LANL monitored and profiled historically 

for dose assessment and workers unexposed to plutonium, except for worldwide fallout during 

the atmospheric nuclear test era. The comparison was performed to test the ability of BNL’s FTA 

technique to measure 239Pu activity in the 1 to 10 femtocurie (fCi) (10-15 Ci) range. This was 

estimated to be the highest level 239Pu excreted in urine for intakes that could be expected in 

atomic veterans. Other samples were included to assess the ability of FTA to measure samples at 

background levels. The collected bioassay samples were split between BNL and LANL to allow 

for independent analyses. The LANL results were not communicated to BNL until BNL 

processed their bioassay samples. The measurement techniques used by BNL and LANL for the 

comparison were FTA and Thermal Ionization Mass Spectrometry (TIMS). While the LLDs for 

both techniques differed somewhat, they were more than sufficient to not influence bioassay

measurements in the 1–10 fCi range. 

LANL reported (Harris, 1998 and Inkret and Efurd, 1996) the resulting measurements in 

Table 1. The measurements include LANL values determined from bioassay samples split 

between both laboratories, and BNL values determined from the other split sample which was, in 

turn, split again. Each sample represented a collection of all urine excreted during a period of 24

consecutive hours. Submitters collected the samples without supervision.

2.4.2. Analysis of Comparison Results

The 10 samples reported in Table 1 presented limited opportunities for measurement 

comparison. There appeared to be some general agreement between the BNL and LANL results. 

However, samples analyzed by LANL with reported results below 2 fCi had large fractional 

uncertainties. Two sets of measurements for each lab on samples 36726, 36737, and 36741 

showed agreement within an order of magnitude. The three samples, identified as 36729, 36744, 

and 36745, for workers not occupationally exposed to 239Pu, were consistently measured to be at 

or slightly above the LLD of the FTA technique. The measurements reflect similar levels of 

uncertainty as the blanks used to derive the LLD. The LANL TIMS technique, as opposed to the 

FTA technique, consistently appeared to yield results within its standard deviation, which was 
12

almost an order of magnitude higher than the LLD of FTA. The advertised LLD of TIMS for this 

comparison was 0.130 aCi (Inkret et al., 1998) vs. 0.029 aCi for FTA (Kaplan et al., 1995).

Table 1. Results of 239Pu measurements by LANL and BNL

Sample ID

BNL Activity 

(fCi/sample)

BNL Recheck 

Activity 

(fCi/sample)

LANL Activity 

(fCi/sample)

LANL Std Dev 

(fCi/sample)

36721 228 - 524.99 4.72

36723 lost - 69.27 1.11

36726 0.756 0.108 1.13 0.95

36729* 0.108 1.73 0.95

36733 not sent - 8.13 0.37

36737 0.07 - 0.04 0.49

36740 11.3 4.8 lost during analysis†

36741 0.06 - -0.06 0.8

36744* <0.029 - 0.55 0.62

36745* 0.065 <0.029 1.57 1.03 * Worker was not occupationally exposed to 239Pu

† Historical (LANL) measurements support values close to 11.3 fCi for this individual

DTRA’s concern at the time of the comparison was the repeatability of the FTA 

technique. Samples 36726 and 36740 showed ratios of the results of the first split sample to the 

second split sample of 7 to 1 times and 2.4 to 1 times, respectively. The reasons for these 

seemingly high relative differences were not known at the time. When compared to the constant

uncertainty limits shown in Figure 1, the split measurement repeatability was considerably out of 

the range of the limits. Figure 2 could suggest the emergence of a key insight when coupled with 

the discovery that the FTA system calibration curve and associated uncertainties followed more 

closely a lognormal than a linear relationship (Klemm et al., 2003). The lognormal calibration 

relationship shown in the Figure 2 data suggested that range of measurement uncertainty 

increased roughly by an order of magnitude with increasing measured activity level. In that 

context, BNL results for samples 36721, 36726, and 36740 could be viewed as roughly 

consistent with LANL results. The BNL split sample differences (7 to 1 and 2.4 to 1) might be 

suggestive of the FTA measurement uncertainty range increasing lognormally with increasing 

bioassay measurement levels. TIMS appeared to significantly overestimate the 239Pu background 

levels in samples 36729, 36744, and 36745 for workers not occupationally exposed to plutonium.
13

Section 3.

Plutonium in the Urine Samples of U.S. General Population 

and U.S. Atomic Veterans

3.1 Plutonium Measured in Urine of Selected Members of the U.S. General Population

To establish background levels in the U.S. population, a national cross section of 

individuals exposed only to worldwide fallout during the atmospheric nuclear testing era was 

characterized. Assessment of plutonium in urine samples from the general population group may 

be used to determine whether urine samples from veterans have significantly higher plutonium 

content than this general population group. BNL sampled the U.S. general population with the 

assistance of DOE occupational medical clinics (OMC) and VAMCs. With approval from BNL’s 

Institutional Review Board for research on human subjects, BNL circulated the collection 

protocol to various OMCs and VAMCs nationwide. Urine samples were collected from 58 males 

over 40 years of age with no history of working with plutonium or performing activities similar 

to veterans eligible for bioassay testing. The 24-hour urine samples were taken in seven 

geographical locations from workers during routine physical examinations. The workers selfcollected the urine sample over a continuous 24-hour period. 

Table 2 describes the geographical locations and numbers of subjects contributing urine

samples. Sampling of the general U.S. population overall was constrained by time and funding 

but considered technically and statistically adequate by BNL for determining background levels 

of Pu in the general population with sufficient geographic diversity.

Table 2. Locations and numbers of subjects contributing

urine samples for the general population group

Location Number of Samples

Golden, CO OMC 4

Berkeley, CA OMC 5

Cincinnati, OH VAMC 6

Rocky Flats, CO OMC 7

Oak Ridge, TN OMC 8

Pinellas, FL OMC 10

Upton, NY OMC 18

Total 58

Figure 3 shows the frequency distribution of the bioassay measurements (see 

Appendix A, Table A-1) for the background population group. About ninety-five percent of the 

population group samples measured lower than 84 aCi/sample (DL95) as defined earlier in 

section 2.3.3. The highest measurement (DLmax) in the distribution was 118 aCi/sample. This 

distribution is important for determining whether or not the measurements for the 100 veteran 

samples are statistically different from the general U.S. background population group samples.
14

The 84 aCi/sample result for the general U.S. population group compared closely to the reported 

results of other general populations exposed only to worldwide nuclear testing fallout (Ibrahim et 

al., 1999 and Hamilton et al., 2007).

Figure 3. Distribution of bioassay measurements in the U.S. general population group

3.2 Results for Initial Phase of Measurements on Veterans

One hundred (100) confirmed atomic veterans volunteered to contribute urine bioassay 

samples taken over a continuous 24-hour period. DTRA publicly announced (DTRA, 1999) the 

pilot test program, including an explanation of the significance and extent of the effort 

constrained by the amount of Congressionally-directed funding (PL 105-85, 1997).

Figure 4 provides a composite of the U.S. Population and 100 veteran bioassay results. 

These results reflected all of the first split bioassay measurements. The veterans’ results (see 

Appendix A, Table A-2 ) ranged from −2 to 2366 aCi/sample. There were four measurements 

above the FTA system MDA of 280 aCi/sample that could be considered true positives based on 

Type I and Type II statistics (Brodsky, 1992). The remaining 96 measurements were below the 

MDA.

0

2

4

6

8

10

12

14

16

Number of Samples

239Pu Activity (aCi)
15

Figure 4. Comparison of the distributions of bioassay results for the U.S general populaton 

and atomic veterans

There were 11 measurements between the maximum background population 

measurement, DLmax and MDA of 118 and 280 aCi/sample respectively. Eighty five (85) of 100 

veterans’ samples measured below the 118 aCi/sample general population maximum. Ninetyfive percent of the 85-veteran sample measurements were below 118 aCi/sample. This value is 

slightly higher than the DL95 (84 aCi/sample) for the general population group distribution.

Within the limits of FTA measurement statistics, the 85-veteran distribution of measurements 

appears to be nearly similar to the 58-background population sample.

The 15 veteran samples with results greater than 118 aCi/sample were singled out for 

further investigation. Nine (9) of the 15 samples were chosen for reanalysis of the second split 

sample. The highest one of the 15 measurements was confirmed as a true positive by comparison 

with an available employment occupational 239Pu bioassay measurement voluntarily submitted

by the veteran and was eliminated from reanalysis. Only 9 of the remaining 14 and 2 additional 

samples measuring closest to 100 aCi/sample were chosen for analysis of the second split. These

11 results were produced in the fifth and higher-numbered batches, which were suspected of 

being impacted by external trace low environmental levels of plutonium from other on-site BNL 

work.

Table 3 contains the results of the 11 samples showing first and second split 

measurements. The second split measurements are lower than the first split measurements, 

except for one. The results seemed to be confounding in that 4 of the 11 second split 

0

5

10

15

20

25

30

Number per 100 samples

239Pu Activity (aCi)

U. S.

Population

 Frequency

Veteran

 Population

 Frequency

280 

attocurie 

MDA
16

measurements are considerably lower than the first split measurements. Also, 6 of the 11 second 

split measurements were roughly comparable to the first result. In one case, the second split 

measurement was higher than the first. 

Table 3. First and second split measurements for 11 selected bioassays with original 

readings above 100 aCi/sample

Bioassay

Number

First Split Measurement

(aCi/sample)

Second Split Measurement

(aCi/sample)

P-85 1059 358

P-120 627 32

P-86 436 74

P-64 274 237

P-83 197 111

P-104 167 131

P-17 165 128

P-31 158 35

P-105 151 97

P-53 106 65

P-99 99 209

Most of the above-MDA (>280 aCi) results and all results between 100 and 

280 aCi/sample occurred during times when FTA measurements exhibited higher than expected 

calibration uncertainties. BNL reported that apparent elevated results were concurrent with fuel 

removal from a reactor decommissioning in a neighboring building, causing a temporary 

shutdown of FTA analyses to replace all of the FTA reagent chemicals. Twelve (12) veterans 

with the higher urine results were selected for re-sampling based on the availability and 

willingness of a veteran to provide a second 24-hour urine sample. This resampling provided a 

possible way to better understand the results in Table 3. To address potential background 

contributions and other experimental factors, the NTPR Program employed LANL to conduct 

follow-up 239Pu measurements using TIMS (Lyons, 1999).

3.3 Results of Resampling of 12 Selected Veterans

The follow-up bioassay test measurements, reported by LANL (Glover et al., 2003), are 

listed in Table 4 and displayed in Figure 5, which includes 10 of the 11 measurements reported 

in Table 4 for comparison. As mentioned before, not all veterans with measurements in Table 4

could be re-sampled and re-analyzed with TIMS. Two additional veterans with measurements of 

about 100 aCi/sample were available for re-sampling and those results were included in the 

comparison. 
17

Table 4. Comparison of bioassays for veterans

followed-up with TIMS

ID Number

FTA Activity

(aCi/sample)

*

TIMS Activity

(aCi/sample) *,†

P-85 1059/358 27±12/34±30

P-120 627/32 24±16/9±18

P-86 436/74 28±16/47±26

P-64 274/237 47±52/-2±24

P-83 197/111 23±24/64±174

P-104 167/131 32±28/31±26

P-17 165/128 51±24/64±20

P-31 158/35 30±20/44±76

P-105 151/97 7±32/-56±76

P-96 146 -7±28/31±20

P-106 144 68±30/18±16

P-99 99/209 17±40/41±20 * Cells with two entries reflect that both split samples were 

analyzed

† ±2 standard deviations

Figure 5. Comparison of FTA and TIMS sample measurements for selected veterans with 

original FTA bioassay measurements above 100 aCi/sample

-100

0

100

200

300

400

500

600

700

800

900

1000

1100

1200

P85 P120 P86 P64 P83 P104 P17 P31 P105 P96 P106 P99

239Pu Activity (aCi)

Sample ID

FTA 1 FTA 2 TIMS 1 TIMS 2
18

Section 4.

Discussion of the Results

4.1 Interpretation of the Results

A review of the data (Figure 4 and Appendix A, Table A-2 ) indicates that 4 of the 100 

veterans’ sample results were above the 239Pu MDA of 280 aCi/sample. Eleven (11) of 100 

results measured between 118 and 280 aCi/sample. The highest measurement in the general 

population background distribution was 118 aCi. All 58 general population samples measured 

below the MDA. Discounting the 15 measurements above 118 aCi/sample, the veteran sample 

distribution closely resembled the general population sample distribution, noting a small shift to 

slightly higher, within range, background values. 

Second split samples for 12 of the 15 veterans whose results ranged from 100 to 

< 280 aCi/sample were measured. See Table 4 for a summary of the measurements. Review of 

the values shown in Figure 2 suggested that uncertainties between the two splits increased

dramatically with increasing measured activity in the sample. This trend was also observed and 

reported as a finding to NRC/NAS (Schaeffer, 2002) and as suggested earlier in Section 2.4.2. 

The corroborating TIMS measurements (Table 4), showing excellent repeatability in their 

split sample measurements, were consistently much lower in value than the BNL-measurement 

of paired samples. LANL demonstrated tight calibration controls and excellent measurement 

repeatability on the TIMS measured samples (Lewis and Guilmette, 2002 and Glover et al.,

2003). In addition, TIMS at LANL was a Department of Energy Laboratory Accreditation 

Program accredited process (DOE, 1998) used in its occupational exposure monitoring program 

to document internal doses from 239Pu exposures. Thus, the TIMS measurements appear to be 

more credible than the corresponding BNL measurements. 

That being the case, it is highly likely that only one of the veteran sample results was 

greater than the DLmax of 118 aCi/sample. The one result from sample P-6 (see Table A-2 ) was 

corroborated by the results provided by the veteran of an earlier 239Pu bioassay performed at 

LANL. The LANL result, 2300 aCi/sample, was consistent with the BNL-measured result of 

2366 aCi/sample.

4.2 Comparison of Bioassay Measurements and Dose Reconstructions

Dose reconstruction reports in the NTPR case files of all 100 veterans were examined. 

The expected 239Pu excretion levels were estimated for veterans who had positive values of 

internal dose. Some veteran’s dose reconstruction reports did not show potential for accrual of 

internal dose. Table 5 shows a summary of the comparison, enumerating the veteran bioassay 

measurements above the MDA with dose reconstruction predicted values of 239Pu excretion and 

those below.

Table 5 indicates that 52 veterans’ dose reconstructions yielded positive values for 

internal dose that bioassay would be expected to predict. However, only 1 of 52 veteran samples 

showed a correlation to a positive internal dose reconstruction. In contrast, there were 48 dose 

reconstructions that did not predict a potential for internal dose. Forty-seven (47) of 48 sample 

measurements were consistent with a zero-valued dose reconstruction prediction. However, there 

was only one bioassay result above MDA, which did not correlate with the zero-valued dose 
19

reconstruction prediction. Fifty-one (51) samples corresponding to positive internal dose 

reconstruction predictions did not correlate with above MDA bioassay results. Table 5 indicates

that there was no discernable correlation that the predicted and measured results agreed.

Table 5. Comparison of bioassay results with reconstructions of internal dose

Internal Dose 

Reconstruction 

Prediction

Bioassay Result

Total

Number of 

Results ≤ MDA

Number of

Results > MDA

Dose > 0* 51 1‡ 52

Dose ≤ 0† 47 1 48 * Dose reconstruction reported an internal dose commitment. † Dose reconstruction reported no internal dose commitment. ‡ Does not include the 2 samples (P-120 and P-86) (see Appendix A) with first split bioassay measurements above 

the MDA and second split measurements well below the MDA.

The one measurement of particular interest was sample P-64 (274 aCi/sample) which was 

coincidentally close to the value of the FTA system MDA. The corresponding veteran was 

determined to be a participant in the post-war occupation of Nagasaki. The Nagasaki weapon, 

being a plutonium device, presented opportunities for inhaling and ingesting fallout containing 

low levels of 239Pu (McRaney and McGahan, 1980). 

Examining the activities of U.S. occupation troops at Nagasaki, the NTPR Program found 

that troops stationed around the Nishiyama reservoir, which was assumed to have received an 

appreciable amount of fallout from rainfall, could possibly excrete Pu levels as high as 

470 aCi/sample at about 45 years after exposure. Comparatively, occupation troops assigned to 

the Artillery Group could be expected to excrete about 100 aCi/sample. Considering the 95% 

confidence level (DL95) of 84 aCi/sample, sample P-64 could be attributable to worldwide fallout 

in addition to possible Nagasaki activities. The veteran could have had a sufficient intake of Pu 

to produce a urine level between 185 and 555 aCi/sample. 

The BNL results for the two split samples for P-64 were in close correspondence (see 

Table 3). Similarly, so were the two split TIMS measurements, but they were well within the 

measurement range of the background sample distribution. Determination of whether or not 

sample P-64 represented a likely positive bioassay measurement was confounded by the MDA 

level of the FTA system, and the two split TIMS measurements at values that were consistently 

at low values of the background population distribution. Thus, in consideration of the 

uncertainties in the FTA and TIMS analyses and the dose reconstruction for the veteran 

represented by sample P-64, it was not discernable whether or not the veteran received a dose 

from plutonium consistent with his activities at Nagasaki.
20

Section 5.

Conclusions

The proposal (Boecker et al., 1991) that FTA could measure 239Pu activity concentrations 

in urine samples that could be used to retrospectively quantify internal doses in eligible veterans 

has not been demonstrated in the bioassay results described herein. In all but a few cases, veteran 

bioassay samples did not measure statistically higher than samples submitted by 58 persons 

representing a sample of the U.S. population in seven geographic locations nationwide.

Plutonium uptake in veteran participants of atmospheric nuclear testing may be 

confirmed provided there is a sufficient potential to produce a positive bioassay result 35 years 

after weapon detonation. Uptake, retention and excretion of 239Pu are highly variable among 

individuals over any period of time. Given that more than 35 years had lapsed from exposure to 

measurement, FTA results confirmed intakes in a small fraction of individuals in this sample 

cohort. At these low measurement levels (around a few hundred aCi), repeatability and collective 

analyses were difficult due to observed high uncertainties. Therefore, FTA may be used to 

confirm presence of 239Pu in urine bioassays, but not to quantify 239Pu activity with an acceptable 

degree of confidence.

This finding is supported by the 10 elevated measurements in 99 veteran bioassay 

samples that were not confirmed by follow-up TIMS analyses. (One of the 100 veterans was a 

confirmed positive). Additionally, FTA did not demonstrate a 239Pu level above the MDA level

for 51 veterans for whom NTPR Program dose reconstruction reports indicated a potential for 

internal dose. Additionally, the bioassay results for 47 veterans correctly correlated to indications 

of no potential for an internal dose. The FTA technique provided one potential indicator of 

plutonium presence (see Table 5). However, due to the individual variances with respect to 

location, complexity of specific response to exposure, and confounding environmental effects 

over the elapsed time since exposure, it was difficult to find a correlation between dose 

reconstruction predictions and bioassay measurements. 

In conclusion, bioassay testing using FTA is not a reliable quantitative indicator of 

internal dose potential for the sampled veteran population. Other available analytical methods, 

developed since FTA, such as TIMS, appeared to provide quantitative bioassay results with 

higher accuracy and consistency than FTA. FTA did not reliably provide an indication of 

participation in atmospheric nuclear testing (in the absence of other information). It is important 

to note that, in the 10 of the sampled veteran population where internal doses were suggested by 

initial bioassay testing, follow-up testing at a corroborating laboratory (LANL) was unable to 

confirm the positive (i.e., above MDA) FTA-determined results for veterans who submitted

second samples. (See section 3.3.2). Performing 239Pu bioassay measurements to correlate with 

veteran dose reconstructions is scientifically daunting, given the uncertainties and technique 

variations at the levels of 239Pu being detected. Nevertheless, NTPR dose reconstructions with

internal dose components do provide positive dose results for this population. Urine bioassay 

measurements of 239Pu utilizing FTA tend to be so highly uncertain due to large variances in 

measurement results as well as uncertainties in assumed parameter values used for biokinetic 

modeling in dose calculations (NRC, 2003)— that they cannot be considered as useful predictors 

of atomic veteran internal doses.
21

This report concludes, consistent with National Research Council’s findings (NRC, 

2003), that urine 239Pu bioassay using FTA did not enhance the capability of DTRA’s current 

scientific processes to perform accurate dose reconstructions for atomic veterans, and therefore, 

was not feasible for implementation on a wide scale basis for atomic veterans.
22

Section 6.

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25

Appendix A.

Compilation of Project Bioassay Test Results

Table A-1. Results of bioassay testing of the selected U.S. population group

No. Location

239Pu

Activity

(aCi) No. Location

239Pu

Activity

(aCi)

1 Rocky Flats, CO -10 30 Oak Ridge, TN 20

2 Upton, NY -8 31 Pinellas, FL 20

3 Pinellas, FL -2 32 Golden, CO 21

4 Berkeley, CA -2 33 Rocky Flats, CO 21

5 Upton, NY -1 34 Rocky Flats, CO 24

6 Pinellas, FL 0 35 Pinellas, FL 24

7 Berkeley, CA 0 36 Upton, NY 27

8 Cincinnati, OH 3 37 Cincinnati, OH 27

9 Rocky Flats, CO 3 38 Upton, NY 28

10 Pinellas, FL 3 39 Upton, NY 29

11 Berkeley, CA 3 40 Golden, CO 33

12 Oak Ridge, TN 6 41 Upton, NY 33

13 Rocky Flats, CO 7 42 Oak Ridge, TN 34

14 Oak Ridge, TN 8 43 Pinellas, FL 35

15 Pinellas, FL 8 44 Rocky Flats, CO 37

16 Cincinnati, OH 10 45 Upton, NY 38

17 Cincinnati, OH 10 46 Pinellas, FL 40

18 Berkeley, CA 10 47 Rocky Flats, CO 47

19 Golden, CO 10 48 Upton, NY 47

20 Upton, NY 10 49 Upton, NY 50

21 Upton, NY 12 50 Upton, NY 54

22 Berkeley, CA 13 51 Upton, NY 59

23 Cincinnati, OH 15 52 Upton, NY 61

24 Cincinnati, OH 15 53 Oak Ridge, TN 64

25 Upton, NY 17 54 Oak Ridge, TN 65

26 Pinellas, FL 17 55 Upton, NY 65

27 Golden, CO 18 56 Upton, NY 84

28 Pinellas, FL 19 57 Oak Ridge, TN 94

29 Oak Ridge, TN 19 58 Upton, NY 118
26

Table A-2. Results of bioassay testing of 100 eligible veterans

ID 

No.

239Pu

Activity

(aCi)* Test Series† ID No.

239Pu

Activity

(aCi)* Test Series

P-6 2366 GH, BJ, IV,UK, CA, TP, PB P-149 43 Hiroshima/Nagasaki (N)

P-85 1059/358 TS P-89 41 IV

P-120 627/32 UK P-92 41 Nagasaki (MC)

P-86 436/74 CA,TP P-9 39 GH

P-64 274/237 Nagasaki (MC) P-23 38 Nagasaki (N)

P-55 213 Nagasaki (MC) P-60 36 UK

P-109 204 CA P-117 36 Nagasaki (MC)

P-83 197/111 Nagasaki (MC) P-35 35 CR

P-71 196 CR P-12 33 CR

P-104 167/131 IV P-5 33 CA, IV

P-17 165/128 Hiroshima P-84 33 PB

P-31 158/35 RW P-38 32 DO-1

P-105 151/97 RW, HT-1 P-42 31 CR

P-96 146 DO-1 P-97 31 Nagasaki (MC)

P-106 144 HT-1 P-27 30 Nagasaki (MC)

P-152 114 CA P-63 29 CR

P-127 112 Nagasaki (N) P-135 27 CR

P-76 109 Nagasaki (N) P-146 27 CR

P-11 109 TS P-3 25 Nagasaki (N)

P-125 108 BJ P-7 25 CR

P-53 106 Hiroshima/Nagasaki (N) P-121 25 TS

P-99 99/209 RW P-101 24 BJ, TS

P-142 94 Nagasaki (MC) P-1 22 Nagasaki (MC)

P-116 88 SS P-25 22 HT-1

P-103 83 Hiroshima P-36 21 CR

P-39 80 CR P-50 21 Nagasaki (N)

P-140 80 Nagasaki (MC) P-100 20 CR

P-79 79 CR P-4 19 UK

P-136 76 Nagasaki (N) P-51 19 Hiroshima

P-78 74 DO-1 P-107 19 Nagasaki (N)

P-26 73 CA P-123 19 CR

P-57 70 pHT-1 P-102 18 BJ

P-87 69 Nagasaki (N) P-113 18 UK

P-98 67 CR P-150 14 Nagasaki (N)

P-134 67 CR P-93 13 UK

P-80 64 BJ P-54 10 BJ

P-138 62 CA P-46 9 Hiroshima

P-94 59 BJ,TS P-8 8 GH

P-13 57 CR P-40 8 RW

P-28 57 GH P-88 8 Nagasaki (N)
27

Table A-2. Results of bioassay testing of 100 eligible veterans (cont.)

ID 

No.

239Pu

Activity

(aCi)* Test Series† ID No.

239Pu

Activity

(aCi)* Test Series

P-118 56 TS P-49 6 RW

P-18 55 Hiroshima P-81 6 Nagasaki (A)

P-110 54 CR P-62 5 CA, GH

P-139 53 TS P-32 5 DO-1

P-144 53 RW P-61 2 Nagasaki (N)

P-65 52 Hiroshima/Nagasaki (N) P-37 0 HT-1

P-58 47 RW P-73 0 Hiroshima

P-148 46 UK P-72 0 Hiroshima

P-108 45 Nagasaki (MC) P-75 -2 SS

P-30 45 BJ P-128 -2 Hiroshima *

Results for two splits are reported in the order—first split/second split; activity is on 24-h sample basis.

† Key to Test Series Entries

Nagasaki (A) – Army participant IV – Ivy

Nagasaki (MC) – Marine Corps participant UK – Upshot-Knothole

Nagasaki (N) – Navy participant CA – Castle

CR – Crossroads TP – Teapot

SS – Sandstone RW – Redwing

GH – Greenhouse PB – Plumbbob

BJ – Buster-Jangle HT-1 – Hardtack-1

TS – Tumbler-Snapper pHT-1 – post Hardtack-1

DO-1 – Dominic-1