Draft White Paper 

SC&A POSITION ON IN-VIVO THORIUM 

MONITORING COMPLETENESS 

Contract Number 200-2009-28555 

Prepared by 

Robert Barton III 

Harry Chmelynski 

S. Cohen & Associates 

1608 Spring Hill Road, Suite 400 

Vienna, Virginia 22182 

Saliant, Inc. 

5579 Catholic Church Road 

Jefferson, Maryland 21755 

January 2012 

Disclaimer 

This document is made available in accordance with the unanimous desire of the Advisory Board on 

Radiation and Worker Health (ABRWH) to maintain all possible openness in its deliberations. However, 

the ABRWH and its contractor, SC&A, caution the reader that at the time of its release, this report is predecisional and has not been reviewed by the Board for factual accuracy or applicability within the 

requirements of 42 CFR 82. This implies that once reviewed by the ABRWH, the Board’s position may 

differ from the report’s conclusions. Thus, the reader should be cautioned that this report is for 

information only and that premature interpretations regarding its conclusions are unwarranted.
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Document No. White Paper –

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Effective Date: 

 Draft – January 20, 2012 

S. COHEN & ASSOCIATES: 

Technical Support for the Advisory Board on 

Radiation & Worker Health Review of 

NIOSH Dose Reconstruction Program Revision No. 

0 (Draft) 

SC&A Position on In-Vivo Thorium Monitoring 

Completeness Page 2 of 19 

Task Manager: 

________________________ Date:____________ 

John Stiver, CHP 

Supersedes: 

N/A 

Project Manager: 

________________________ Date:____________ 

John Stiver, CHP 

Peer Reviewer(s): 

 John Mauro 

 Joyce Lipsztein 

Record of Revisions 

Revision 

Number 

Effective 

Date Description of Revision 

0 (Draft) 01/20/2012 Initial issue 
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TABLE OF CONTENTS 

Introduction......................................................................................................................................5 

1.0 SC&A Summary Statement of Position...............................................................................6 

2.0 Issue 1 – Identification of Thorium Workers and Their Relative Exposure Potential.........6 

2.1 Summary of Original Issue ......................................................................................6 

2.2 Summary of NIOSH 2011 Response to Issue 1.......................................................7 

2.3 SC&A Response to NIOSH 2011............................................................................7 

3.0 Issue 2 - Number of Positive Results Identified During the Production Period ................13 

3.1 Summary of Original Issue ....................................................................................13 

3.2 Summary of NIOSH 2011 Response to Issue 2.....................................................14 

3.3 SC&A Response to NIOSH 2011..........................................................................14 

4.0 Issue 3 – Monitoring Criteria for Inclusion in the MIVRML Lung Count Program.........15 

4.1 Summary of Original Issue ....................................................................................15 

4.2 Summary of NIOSH 2011 Response to Issue 3.....................................................16 

4.3 SC&A Response to NIOSH 2011..........................................................................17 

References......................................................................................................................................19 
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LIST OF TABLES 

Table 1. Comparison of Different Groups of Chemical Operator Records for 1968 .................8 

Table 2. Shapiro-Wilk Test of Normality for Defined Groups of Workers .............................10 

Table 3. Levene’s Test for Equal Variance ..............................................................................10 

Table 4. Two-sample Kolmogorov-Smirnov (K-S) Test Results.............................................12 

Table 5. Wilcoxon-Mann-Whitney Test Summary ..................................................................12 

Table 6. Wilcoxon-Mann-Whitney Test Statistics ...................................................................12 

Table 7. Two-Independent-Samples t-Test for Equality of Means ..........................................13 

Table 8. Summary of 1968 Records at or Above the Stated MDA of 6 mg Th .......................15 

Table 9.

..............................................................................................18 

Recreation of the Thorium (mg of Th) Sections of Tables 16 and 17 from 

SC&A 2011 Showing Calculated Linear Trend Lines both with and without 

Identified Outlier Value

LIST OF FIGURES 

Figure 1. Comparison of Thorium Workers with All Non-Starkey Chemical Operators............9 

Figure 2.

..........................................................................9 

Comparison of Thorium Workers with Chemical Operators after Removing 10 

Operators Noted as Thorium Workers

Figure 3. Normal Quantile-Quantile Plot of Samples from Thorium Workers .........................10 

Figure 4. Normal Quantile-Quantile Plot of Samples from Chemical Operators......................11 

Figure 5.

.................................................11 

Normal Quantile-Quantile Plot of Samples from Chemical Operators after 

Removing 10 Operators Noted as Thorium Workers

Figure 6. Recreation of Figure 8 from SC&A 2011 as Cited in NIOSH 2011 ..........................17 
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INTRODUCTION 

In June of 2010, SC&A transmitted its review (SC&A 2010) of the proposed National Institute 

for Occupational Safety and Health (NIOSH) thorium coworker model for the period of 1968–

1989 (ORAUT 2008). NIOSH responded to this review in a brief informal document transmitted 

in February 2011 in preparation for discussions at the Work Group meeting later that month. 

Subsequent to the discussions at that meeting, SC&A prepared a second white paper transmitted 

in August of 2011 (SC&A 2011) on thorium data completeness to expand on the concerns first 

raised in SC&A 2010. This second white paper was discussed in depth at the August 2011 Work 

Group meeting. NIOSH responded to this second report in a documented response transmitted in 

November 2011. This white paper represents SC&A’s final response and position on the issue of 

thorium-232 in-vivo data completeness. Note that the arguments put forth in this document are 

based on a general assumption that the underlying data are adequate for use in a coworker model. 

SC&A has identified several unresolved issues regarding data adequacy, which, if not resolved, 

will render moot this discussion of data completeness. Those concerns are the subject of a 

companion document on data adequacy. 

It must be noted that the bulk of material related to thorium data completeness focuses on the 

years in which thorium production campaigns were undertaken at Fernald (1968–1979).1 The 

three main issues discussed in this third and final SC&A white paper are as follows: 

 Aside from 1968, thorium workers cannot be adequately identified in the in-vivo 

records. Therefore, it cannot be established whether their exposure potential was 

sufficiently monitored or can be reasonably bounded by monitoring data for non-thorium 

worker job types in subsequent years. Evidence in 1968 suggests that thorium workers 

had a higher exposure potential than non-thorium workers. This is discussed in 

Section 1. 

 A large portion of the in-vivo data in mg Th is below the assumed minimum detectable 

activity (MDA) of 6 mg. However, workers who were involved in thorium operations 

have a higher proportion of samples above the MDA, which indicates they likely had a 

higher exposure potential than non-thorium workers. This is discussed in Section 2. 

 

 Evidence suggests that thorium workers were not targeted directly for in-vivo 

monitoring; site-specific interviews suggest that (aside from 1968) workers were 

selected for “overall exposure potential, but not necessarily thorium exposure potential.” 

Interviews also state that, “aside from 1968, no special effort was made to monitor 

thorium workers.” This is discussed in Section 3. 

Each of these issues is discussed in Sections 2 through 4, respectively. Section 1 provides a 

summary of SC&A’s position on the issue of data completeness.

1

 While the operational period extended until 1979, in-vivo data expressed in mg Th ended in 1978, so the 

analyses will focus on the available mg Th data. 
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1.0 SC&A SUMMARY STATEMENT OF POSITION 

SC&A believes that the in-vivo monitoring records for thorium are essentially complete, in that 

no significant chronological gaps were identified, nor is there evidence to suggest the highest 

exposed worker population was systematically excluded from the monitoring program. 

However, given the inability to identify which workers handled thorium (with the notable 

exception of 1968), as well as the uncertainty as to what portion of these workers were 

monitored for thorium exposure, SC&A believes that if the data are determined to be sufficiently 

accurate, NIOSH should select a sufficiently upper bound intake rate to assure that assigned 

doses are favorable to the entire population of potentially exposed workers. Currently, the 

proposed coworker model (ORAUT 2008) calculates 50th and 84th percentile intake values along 

with the associated geometric standard deviation; however, there is no specific guidance 

included as to how the coworker model should be applied to assure claimant favorability. 

2.0 ISSUE 1 – IDENTIFICATION OF THORIUM WORKERS AND 

THEIR RELATIVE EXPOSURE POTENTIAL 

2.1 SUMMARY OF ORIGINAL ISSUE 

SC&A has previously presented analyses comparing the empirical cumulative probability 

distribution of lung burdens for different groups of workers, including thorium workers, 

chemical operators (including some thorium workers), chemical operators (excluding thorium 

workers), and the all worker population in 1968 (SC&A 2010 and 2011). The year 1968 was 

chosen as it is the only year in which there is a specific list of thorium workers, including badge 

number and job title (Starkey 1967). This empirical comparison of lung burdens in 1968 was the 

focus of NIOSH’s most recent response (as discussed in Section 2.2). 

 

In addition to this, SC&A attempted to expand the subgroup of thorium workers past 1968 to 

include workers who had ‘thorium worker’ or ‘former thorium worker’ written on their 

individual logbook sheets. One of the limitations of this type of approach is that it is not known 

exactly when, or for how long, each worker handled thorium. Therefore, it is not possible to tie 

specific monitoring results to the periods of potential thorium exposure for these workers. 

However, for the purposes of comparison, SC&A assumed that these workers handled thorium 

for their entire employment period. The results of these rank-ordered lung burdens showed 

visually separated curves when comparing the thorium subgroup and the other subgroups 

analyzed; therefore, a more robust analytical approach was adopted to statistically analyze the 

assumed subgroups (see Section 3.2 of SC&A 2011). 

SC&A concluded that the workers identified as “thorium workers” had a higher exposure 

potential than workers who did not appear to work with thorium, and that adequate evidence has 

not been presented to assert that “thorium worker” doses are clearly bounded by the exposure 

potential to the chemical operator subgroup. 
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2.2 SUMMARY OF NIOSH 2011 RESPONSE TO ISSUE 1 

NIOSH agrees that it is not feasible to identify thorium workers in years subsequent to 1968; 

however, NIOSH disagrees with SC&A’s analytical approach, in which the assumption was 

made that workers who were identified with thorium work were involved with thorium 

production during their entire work history for the period of interest. Specifically, NIOSH 2011 

states: 

This assumption is not in agreement with interviews where it is suggested that 

thorium workers were assigned based on availability and the number of people 

involved was variable (ORAUT, 2007, p. 23 and p. 26). Thus, any hypothesis test 

based on this assumption cannot be valid. 

NIOSH does agree, however, that a comparison of thorium workers in 1968 (as established by 

the Starkey memo) and non-thorium chemical operators is a valid test. To accomplish this, 

NIOSH visually analyzed Figure 1 of SC&A 2011 and performed a Kolmogorov-Smirnov (KS) 

test. NIOSH concluded: 

... the KS test statistic (D) equals 0.2552 and associated p-value of 0.2054 leads 

to the conclusion that there is no reason to believe that thorium workers and 

chemical operators came from different parent populations of workers. 

(NIOSH 2011, pg. 3) 

2.3 SC&A RESPONSE TO NIOSH 2011 

SC&A agrees that the assumption that identified thorium workers always worked with thorium is 

not probable, but disagrees with the notion that the comparison of lung burdens made using this 

assumption lacks validity. By making the stated assumption, SC&A has included many 

monitoring records in the thorium worker subgroup, which would not be reflective of thorium 

work and hence thorium exposure potential. The stated assumption (which essentially acts as a 

dilution mechanism) and associated analysis would logically underestimate the actual lung 

burdens associated with thorium work, since many of the records included in the thorium worker 

subgroup would be reflective of non thorium-related work. Therefore, while SC&A agrees that 

the aforementioned analysis does not represent a precise representation of thorium worker 

exposures, it provides a conservative basis with which to compare lung burdens between 

different worker groups, since the data presented for thorium workers likely underestimate the 

actually exposure potential. 

NIOSH’s position is that only the comparison between 1968 chemical operators and the thorium 

workers identified in the 1967 “Starkey memo” is appropriate. However, it must be understood 

that even this comparison requires the back extrapolation of job titles, since actual job 

designations were rarely recorded until 1971. Therefore, the direct comparison of chemical 

operators to thorium workers in 1968 is not possible without making certain assumptions. 

Specifically, the assumption had to be made that the chemical operators identified in 1971 and 

later on were also chemical operators 3 years earlier. 
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Nevertheless, using this back extrapolation of job titles yields a group of 25 samples taken in 

1968 for ‘chemical operators’ who are not named in the Starkey memo as thorium workers. 

Notably, 10 of the 25 samples are for workers who had ‘thorium worker’ or ‘former thorium 

worker’ written at the top of their individual log sheets. These 10 samples comprise 10 of the 

top 14 lung burdens measured for this group in 1968 (and cover each of the top 5 lung burdens 

for this group). It has not been established that the Starkey memo is a comprehensive list of 

thorium workers for 1968, so it is likely that some or all of these 10 samples actually do 

represent thorium work. One indication in support of this is the fact that 9 of the 10 samples 

were associated with the Pilot Plant, with the remaining sample for Plant 8 (both areas were 

involved in thorium work in 1968). To put this in perspective, of the 51 thorium workers listed 

in the Starkey memo, only 2 workers were identified with the Pilot Plant and only 1 identified 

with Plant 8. Therefore, it seems probable that the Starkey memo is not a comprehensive list of 

thorium workers. If these 10 samples are removed from the group of non-thorium chemical 

operators, the resulting distribution of lung burdens would decrease markedly, as shown in 

Table 1. 

Table 1. Comparison of Different Groups of Chemical Operator Records for 1968 

Worker Grouping # Samples Average Median Max 

Chemical Operators not identified with Thorium Work 

(either via Starkey or by individual log sheets) 15 1.35 -0.67 4.7 

Chemical Operators not named in Starkey Memo 25 2.48 2 7.3 

All Starkey Thorium Workers 62 3.24 3 10.2 

Chemical Operators named in Starkey Memo 54 3.33 3.1 10.2 

 

NIOSH came to their conclusion that there is no reason to believe that thorium workers and 

chemical operators came from different parent populations of workers based on performing the 

KS test on a visual interpretation of Figure 1 from SC&A 2011. However, this analysis includes 

the 10 chemical operator samples that have thorium worker labeled on the in-vivo log sheet. 

Since it is not possible to determine in these 10 cases whether the ‘thorium worker’ label applies 

to 1968 or subsequent years, it may not be appropriate to include these samples in either group 

for the purpose of comparison. Furthermore, SC&A does not believe that the KS test is the most 

appropriate metric to evaluate the two groups of workers. If the data appear to be normally 

distributed, then a parametric statistical comparison, such as the two sample t-test, would have 

greater power to detect a significant difference and thus be more claimant favorable. Other nonparametric tests also may have more power to detect differences in this setting, for example the 

Wilcoxon-Mann-Whitney test. 

In the following analysis, the Shapiro-Wilk test is applied to check for normality and Levene’s 

test is applied to check for equality of variances. The results of these preliminary tests support 

the use of the t-test in a parametric framework. Before applying the two-sample t-test, it is 

necessary to confirm that the two datasets have approximately normal distributions and 

approximately equal variances. As shown in Figures 1 and 2, the two distributions appear to be 

normally distributed with approximately equal variances. Furthermore, the Shapiro-Wilk test 

was applied to test for normality of the three datasets involved in the two comparisons (nonStarkey chemical operators, thorium workers, and chemical operators identified as thorium 

workers or former thorium workers). The test results are shown in Table 2, which indicates that 
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the assumption of normality cannot be rejected for any of the datasets. The normal quantilequantile plots shown in Figures 3, 4, and 5 confirm the test results and show only small 

departures from normality. Levene’s test was then applied to test for equality of variance. 

Levene’s test results shown in Table 3 indicate that the assumption of equal variances cannot be 

rejected in either of the two comparisons. 

Figure 1. Comparison of Thorium Workers with All Non-Starkey 

Chemical Operators2

Figure 2. Comparison of Thorium Workers with Chemical Operators after 

Removing 10 Operators Noted as Thorium Workers 

 2

 The group “All Non-Starkey Chemical Operators” includes 10 samples that have “thorium worker” 

written at the top of the logbook sheets; it cannot be determined to what time period this label applies. 
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Table 2. Shapiro-Wilk Test of Normality for Defined Groups of Workers 

Shapiro-Wilk Test Category Name 

Statistic df Sig. 

Chemical 

Operator .955 25 .328 

Test 1 – NIOSH Test Subgroups Thorium 

Worker .970 62 .133 

Chemical 

Operator .906 15 .118 Test 2- NIOSH Subgroups with 10 COs 

noted as Th Workers Removed Thorium 

Worker .970 62 .133 

Table 3. Levene’s Test for Equal Variance 

Levene's Test for Equality of 

Test Variances 

F Sig. 

Test 1-NIOSH 0.695 0.407 

Test 2-Remove CO noted as Th Worker 0.602 0.440 

Figure 3. Normal Quantile-Quantile Plot of Samples from Thorium Workers 
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Figure 4. Normal Quantile-Quantile Plot of Samples from Chemical Operators 

Figure 5. Normal Quantile-Quantile Plot of Samples from Chemical Operators after 

Removing 10 Operators Noted as Thorium Workers 
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In the following analysis, the KS, Wilcoxon-Mann-Whitney, and t-tests are used to compare the 

two groups of workers. The comparison of the two datasets defined by NIOSH using the KS test 

is shown in the upper part of Table 3. The KS test has a p-level of 0.15, which indicates that the 

two distributions have no significant differences. The lower part of Table 4 shows the KS test 

result when the 10 questionable samples are removed. In this case the p-level falls to 0.003, 

providing strong evidence that the thorium worker distribution is significantly higher than the 

chemical operator distribution.

Table 4. Two-sample Kolmogorov-Smirnov (K-S) Test Results 

Test Test Statisticsa Worker Category In-Vivo Th 

Most Extreme Differences Absolute .270 

Kolmogorov-Smirnov Positive .070 

Z Negative -.270 

Asymp. Sig. (2-tailed) 1.138 

Test 1 - NIOSH

Total .150

Most Extreme Differences Absolute .524 

Kolmogorov-Smirnov Positive .000 

Z Negative -.524 

Asymp. Sig. (2-tailed) 1.820 

Test 2 - Remove CO noted as 

Th Worker

Total .003

 a. Grouping Variable: Worker Category 

The test statistics for the Wilcoxon-Mann-Whitney test are shown in Tables 5 and 6. The 

Wilcoxon-Mann-Whitney test shows the same result as the KS test. The test indicates no 

significant difference (p=0.197) using the two datasets defined in NIOSH’s recent response, 

while the thorium worker distribution is significantly higher (p=0.006) when the 10 questionable 

samples are removed. 

Table 5. Wilcoxon-Mann-Whitney Test Summary 

Test Worker Category N Mean Rank Sum of Ranks

In-vivo Th Thorium Worker 62 46.22 2865.50 

Chemical Operator 25 38.50 962.50

Test 1 - NIOSH

Total 87

In-vivo Th Thorium Worker 62 42.44 2631.00

Chemical Operator 15 24.80 372.00

- Test 2 - Remove CO noted 

as Th Worker

Total 77

Table 6. Wilcoxon-Mann-Whitney Test Statistics 

Test In Vivo Th

Mann-Whitney U 637.500

Wilcoxon W 962.500 

Z -1.290

Test 1 - NIOSH

Asymp. Sig. (2-tailed) .197

Mann-Whitney U 252.000 

Wilcoxon W 372.000

Z -2.740 

Test 2 - Remove CO noted

as Th Worker

Asymp. Sig. (2-tailed) .006

 Grouping Variable: Worker Category 
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Since the two distributions appear to be approximately normally distributed, one additional 

comparison was conducted using a parametric statistical test, the two-independent-samples t-test. 

As stated previously, Levene’s test indicates equal variances. None-the-less, two versions of the 

t-test are reported in Table 7; one using the assumption of equal variances, and a second 

assuming unequal variances. The results of the equal-variance t-test confirm the results of the 

nonparametric KS and Wilcoxon-Mann-Whitney tests. The equal-variance t-test indicates no 

significant difference (p=0.160) when the two datasets defined by NIOSH are compared, while 

the thorium worker distribution mean is significantly higher than the chemical operator 

distribution mean (p=0.003) when the 10 questionable CO samples are removed. As suggested 

by Levene’s test result, the t-test with unequal variances produces very similar results for both 

comparisons. 

Table 7. Two-Independent-Samples t-Test for Equality of Means 

95% Confidence 

Interval of the 

Test t df Difference Sig. (2-

tailed) 

Mean 

Difference 

Std. Error 

Difference 

Lower Upper 

Equal 

Variances 

Assumed 

Test 1-NIOSH 1.417 85 .160 .7547 .5325 -.3040 1.8134 

Equal 

Variances not 

Assumed 

1.378 41.935 .175 .7547 .5476 -.3504 1.8598 

Equal 

Variances 

Assumed 

Test 2-Remove 3.052 75 .003 1.8808 .6162 .6532 3.1084 

CO noted as 

Th Worker 

Equal 

Variances not 

Assumed 

3.408 24.705 .002 1.8808 .5519 .7435 3.0182 

3.0 ISSUE 2 - NUMBER OF POSITIVE RESULTS IDENTIFIED 

DURING THE PRODUCTION PERIOD 

3.1 SUMMARY OF ORIGINAL ISSUE 

SC&A 2011 noted that less than 3% of the identified chest counts (given in mg of Th) were at or 

above the stated MDA of 6 mg, which might call into question how useful the dataset is in 

developing a viable coworker model. SC&A also noted that the percentage of samples with 

positive chest counts (results greater than 6 mg Th) was higher for workers associated with 

thorium operations than other worker groups. Specifically, SC&A 2011 states: 

Approximately 7% of the samples taken for thorium workers were at or above the 

assumed MDA, while about 3% of those for chemical operators were above the 

MDA (this is slightly higher than the percentage for all workers, at 2.8%). 

(SC&A 2011, pg. 25) 
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It is important to note that the ‘thorium workers’ as referenced above refer to both the list of 

Starkey workers in 1968, as well as all workers who had ‘thorium worker’ or ‘former thorium 

worker’ written on their logbook sheets. It was assumed in the prior analysis that all workers 

who were associated with thorium work handled the material throughout their employment. It is 

important to note that this assumption was brought into question by NIOSH in Section 3 of 

NIOSH 2011 and was discussed in Sections 2.2 and 2.3 of this document. 

3.2 SUMMARY OF NIOSH 2011 RESPONSE TO ISSUE 2 

In Section 4 of NIOSH’s response, it is stated that the value of the MDA and the relative 

magnitude of results in relation to the stated MDA are not relevant in the formulation of a 

coworker model. All of the data (no matter if it is positive, below the MDA, or even negative) is 

compiled and analyzed without any censorship. NIOSH also responds to Finding 8 from SC&A 

2010 regarding an apparent negative bias in the Pb-212 chest count data and summarizes their 

approach to correcting the negative bias via an adjustment factor. 

3.3 SC&A RESPONSE TO NIOSH 2011 

The policy of including all available monitoring data without any form of censorship is a global 

dose reconstruction issue and therefore is outside the scope of this discussion of data 

completeness. SC&A notes, however, that the inclusion of sub-MDL data in coworker model 

construction does not imply that such data have meaning in regard to intake. That topic is 

investigated in depth in SC&A’s analysis of data adequacy. Furthermore, the use of an 

adjustment factor on the Pb-212 chest count results was not the subject of Finding #2 of SC&A 

2011 and does not apply to chest count data given in mg of Th. 

The main issue, as presented above, is the higher proportion of ‘thorium workers’ who had 

results above the stated MDA of 6 mg as compared to the ‘chemical operator’ and ‘all worker’ 

groups. This piece of evidence was offered to indicate that workers who handled thorium had 

higher exposure potential than workers who did not. However, as noted in Section 2.1 above, the 

analysis originally assumed that all workers who were labeled as thorium workers at some point 

during the period of interest were thorium workers throughout their employment. SC&A’s 

position on the validity of any analyses based on this assumption is discussed in Section 1.3 of 

this report and will not be repeated here. 

Nevertheless, SC&A has compiled the data at or above the MDA for the known thorium workers 

(as listed in the Starkey memo) versus the ‘all worker’ and ‘chemical operator’ groups for 1968 

only, the results of which are shown below in Table 8. Based on Table 8, it still appears that 

workers who handle thorium have a higher exposure potential than those who do not. In fact, the 

identified chemical operators who were not identified with thorium work (either by the Starkey 

memo or individual logbooks) did not have any positive results in 1968. The only chemical 

operators (2) who had positive results in 1968 (that were not listed in the Starkey memo) had 

‘thorium worker’ written at the top of their in-vivo logbook sheets. 
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Table 8. Summary of 1968 Records at or Above the Stated MDA of 6 mg Th 

Worker Grouping # 

Samples 

# Positive 

Samples 

% 

Positive 

Samples 

Average Median Max 

Chemical Operators not identified 

with Thorium Work (either via 

Starkey or individual in vivo log 

sheets) 

15 0 0% NA NA NA 

Chemical Operators not named in 

Starkey Memo 25 2* 8.0% 6.7 6.7 7.3 

All 1968 Monitored Workers 290 10 3.5% 7.24 6.75 10.2 

All Starkey Thorium Workers 62 6 9.7% 7.6 7.25 10.2 

Chemical Operators named in 

Starkey Memo 54 6 11.1% 7.6 7.25 10.2 

 *Note: both positive results in this category were workers labeled as ‘Thorium Worker’ on their in-vivo log sheets; 

however, they were not contained in the Starkey list. 

4.0 ISSUE 3 – MONITORING CRITERIA FOR INCLUSION IN THE 

MIVRML LUNG COUNT PROGRAM 

4.1 SUMMARY OF ORIGINAL ISSUE 

Aside from the relative magnitude of lung burdens observed for thorium workers, the other 

major facet of data completeness is the monitoring coverage for the highest exposed group. It 

was SC&A’s contention that, aside from 1968, the thorium in-vivo monitoring program was not 

focused on thorium workers, but rather the much larger uranium operations at the site. One 

indication that this might be the case is the fact that thorium chest counts are always coupled 

with uranium lung counts; the reverse is not always true. 

In addition, Section 3.2 of SC&A 2010 analyzed the in-vivo records by plant number and found 

no specific bias towards plants and times with thorium operations. In fact, there were a couple of 

instances where plants and years with thorium operations had no in-vivo samples taken. Most of 

the samples were taken for Plant 5, which had no known thorium operations during the period of 

interest. 

SC&A 2011 performed another scoping test to characterize thorium monitoring practices in 

Section 4 of that report. In this test, SC&A plotted the relative lung burdens for individual 

workers versus the number of times that the worker was monitored to establish if there is a 

discernible correlation between the magnitude of results and the number of times the worker was 

targeted by the in-vivo program. While the results of that analysis showed very weak correlation 

coefficients across the board for both uranium and thorium, thorium showed a slightly negative 
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correlation when analyzing the median and average lung burdens, while uranium showed a 

slightly positive correlation. 

4.2 SUMMARY OF NIOSH 2011 RESPONSE TO ISSUE 3 

NIOSH presents a specific site interview that sheds light into how workers were selected for 

inclusion in the MIVRML monitoring program. The concluding statements of the interview 

portion are recreated here: 

[Interviewer #1]: It would be helpful to find that [Starkey memo]. I want to 

validate that people chosen for lung counts were chosen for overall exposure 

potential, not especially for thorium exposure potential. 

[Manager #1]: That is correct. 

[Interviewer #1]: So thorium operators would be included in that group? 

[Manager #1]: For the initial visit of the mobile counter, there was an effort to 

get the people on [name redacted]’s list through the in vivo counter. After getting 

through this list, no special effort was made to count thorium workers in 

subsequent visits. (NIOSH 2011, pg. 6) 

Using this interview, NIOSH concludes: 

Based on this information the hypotheses posited by SC&A, that a worker’s 

monitoring frequency and the relative magnitude of the lung burden results must 

necessarily be correlated, is moot. 

NIOSH then states that the basis for SC&A concluding that there was no positive linear 

correlation between the number of times a worker was monitored for thorium intake and the 

actual magnitude of the results is statistically lacking. NIOSH concludes with the following 

statement: 

In support of this finding SC&A provides linear fits to data sets. Figure 8 from 

the SC&A report is shown below to illustrate the misleading nature of this 

assertion. NIOSH does not believe that the fit of a line to the data, including the 

outlier point near 33 mg, adequately captures the trend present in the data.” 

(NIOSH 2011, pg. 6) 

Figure 8 from SC&A 2011 is recreated for reference below as Figure 6 of this report. 
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Figure 6. Recreation of Figure 8 from SC&A 2011 as Cited in NIOSH 2011 

4.3 SC&A RESPONSE TO NIOSH 2011 

NIOSH and SC&A appear to agree that the in-vivo monitoring program was not focused on 

thorium workers, with the exception of 1968 when there was a distinctive effort to get the 

thorium workers counted. However, to put this in perspective, Starkey’s list of thorium workers 

contained 51 individuals and only about half of these workers (roughly 55%) were actually 

monitored in the first year of MIVRML operation. In subsequent years, the percentage of 

thorium workers monitored was probably much less. In addition, SC&A agrees in principle that 

“people chosen for lung counts were chosen for overall exposure potential, not especially for 

thorium exposure potential” (NIOSH 2011, p. 6). 

As noted in SC&A’s most recent response on data adequacy, hardcopy in-vivo records often 

show calculations estimating lung burdens for uranium over a number of years for comparison 

with established max permissible lung burden levels. No such calculations or comparisons for 

thorium results were found, which is indicative of the monitoring focus on uranium intakes and 

not thorium. Furthermore, SC&A found no evidence that positive thorium samples were 

followed up with multiple measurements, in order to adequately characterize the potential 

thorium intake. SC&A’s belief remains that workers were most likely targeted if they had 

significant exposure potential to uranium during uranium operations, which constituted the vast 

majority of radiological operations at Fernald. 

With regard to the linear correlation analysis, SC&A acknowledges that this only represents a 

first-order characterization study to attempt to gain insight into the monitoring practices beyond 
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the available anecdotal evidence. The limited conclusions drawn from such an analysis were 

simply that in this scoping calculation, no evidence was found to suggest workers with relatively 

high thorium lung burdens also had a higher number of lung counts taken. Also, there was 

certainly no evidence that workers with relatively high thorium lung burdens had more samples 

taken than workers with similarly high uranium lung burdens. 

The overall value and significance of conclusions derived from such a limited scoping 

calculation is certainly debatable; however, SC&A disagrees with the notion that the analysis 

was misleading because it included certain outlier values in the linear fits (i.e., “the point near 33 

mg”). In SC&A’s original report (SC&A 2011), the issue of outlier values was discussed on 

pages 30 and 31 with the following statement and related calculations: 

As noted in Table 16, there were three outlier values (taken for U-235 [3635 ug], 

U [1186 mg], and Th [32.5 mg]) in which a worker had an unusually high result 

with few (sometimes only 1) measurements taken. Since no direct evidence could 

be found to invalidate these results, they are included in the Figures 9-38 

analyses. However, to give the reader an idea of how the linear correlations 

change if those three samples are omitted, the linear trend lines and associated 

correlation coefficients are recalculated in Table 17. As seen in Table 17, the 

correlations increase markedly for the maximum uranium (U and U-235) 

categories, as well as the median uranium (U) category, in comparison to 

Table 16 values. The correlation between the maximum thorium values 

increased, though the average and median correlations remained slightly 

negative. (SC&A 2011, pg. 30)

The portions of Tables 16 and 17 from SC&A 2011 covering the results in mg of Th are 

recreated in Table 9. 

Table 9. Recreation of the Thorium (mg of Th) Sections of Tables 16 and 17 from 

SC&A 2011 Showing Calculated Linear Trend Lines both with and without Identified 

Outlier Value 

Linear Trend Formula and Correlation Coefficients Measured Radionuclide Average Median Maximum 

Mg of Th 

(including outlier – 

from Table 16)

y = -0.0475x + 4.179 

R2

 = 3E-04 

y = -0.1657x +4.402 

R2 = 0.0041 

y = 0.6643x + 1.8825 

R2 = 0.1375 

Mg of Th 

(excluding outlier – 

from Table 17)

y = -0.0183x + 4.1133 

R2

 = 3E-05 

y = -0.2155x + 4.4886 

R2 = 0.0042 

Y = 0.8224x + 1.392 

R2 = 0.1743 
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REFERENCES 

NIOSH 2011. Morris, R., Labone, T., Response to SC&A Report on In-Vivo Thorium Coworker 

Model Data Completeness, Rev. 0. National Institute for Occupational Safety and Health, 

Cincinnati, Ohio. September 14, 2011. 

ORAUT 2007. Documented Communication with [redacted] and [redacted] August 30, 2007 on 

FMPC Operations. Oak Ridge Associated Universities Team, Cincinnati, Ohio. 2007. SRDB 

Ref ID: 38124. 

ORAUT 2008. Thorium In Vivo Coworker Study for FEMP – A Proposed Attachment for 

ORAUT-TKBS-0017-5, Revision 1. Oak Ridge Associated Universities Team, Cincinnati, Ohio. 

January 8, 2008. 

SC&A 2010. Review of “Thorium In-Vivo Coworker Study for FEMP – A Proposed Attachment 

for ORAUT-TKBS-0017-5, Rev. 1.” SC&A, Vienna, Virginia, and Saliant, Inc., Jefferson, 

Maryland. June 2010. 

SC&A 2011. SC&A Technical Response to NIOSH Regarding Data Completeness of Proposed 

In-Vivo Thorium Coworker Model for Fernald. Authors: R. Barton and H. Chmelynski, SC&A, 

Vienna, Virginia, and Saliant, Inc., Jefferson, Maryland. August 2011. 

Starkey, R.H., 1967. Thorium Workers. National Lead Company of Ohio. December 26, 1967. 

SRDB Ref ID: 43069.