Draft 

SC&A Technical Response to NIOSH Regarding Data Completeness of 

Proposed In-Vivo Thorium Coworker Model for Fernald 

Contract No. 200-2009-28555 

Prepared by 

Robert Barton III 

Harry Chmelynski 

SC&A, Inc. 

1608 Spring Hill Road, Suite 400 

Vienna, VA 22182 

August 2011 

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. 

Fernald – Data Completeness 

Effective Date: 

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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 Technical Response to NIOSH Regarding Data 

Completeness of Proposed In-Vivo Thorium Coworker 

Model for Fernald 

Page 2 of 46 

Task Manager/Lead Author: 

______________________________ Date:____________ 

John H. Stiver, MS, CHP 

Supersedes: 

N/A 

Project Manager: 

______________________________ Date:____________ 

John Mauro, PhD 

Peer Reviewer(s): 

 John Stiver 

 John Mauro 

 

Record of Revisions 

Revision 

Number 

Effective 

Date Description of Revision 

0 (Draft) 08/04/2011 Initial issue 
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TABLE OF CONTENTS 

Abbreviations and Acronyms ..........................................................................................................7 

1.0 Introduction..........................................................................................................................8 

2.0 Summary of Findings:..........................................................................................................9 

3.0

................................................................................................10 

Section 1: Comparison of the In-Vivo Records for Identified Thorium Workers 

versus Chemical Operators

3.1 Analysis of Raw Data Unadjusted for the Stated MDA of 6 mg Th .....................10 

3.2 Additional Analysis of Worker Subgroup Data.....................................................13 

3.3 Analysis of Positive Thorium In-Vivo Results at or Above 6 mg Thorium..........25 

4.0

.................................................................................................................................26 

Section 2: Correlation between Sampling Frequency and Magnitude of Lung 

Burden for In-Vivo Uranium and Thorium during Majority of Thorium Production 

Period

5.0 References..........................................................................................................................29 

Attachment 1: Linear Correlation Between the Magnitude and Frequency of Sampling for 

Individual Workers for all In-Vivo Radionuclides............................................................30 
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LIST OF TABLES 

Table 1.

...........................................................................17 

Statistics for All Workers, Thorium Workers, Chemical Operators, and NonThorium Chemical Operators, 1968

Table 2.

...........................................................................17 

Statistics for All Workers, Thorium Workers, Chemical Operators, and NonThorium Chemical Operators, 1969

Table 3.

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

Statistics for All Workers, Thorium Workers, Chemical Operators, and NonThorium Chemical Operators, 1970

Table 4.

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

Statistics for All Workers, Thorium Workers, Chemical Operators, and NonThorium Chemical Operators, 1971

Table 5.

...........................................................................19 

Statistics for All Workers, Thorium Workers, Chemical Operators, and NonThorium Chemical Operators, 1972

Table 6.

...........................................................................19 

Statistics for All Workers, Thorium Workers, Chemical Operators, and NonThorium Chemical Operators, 1973

Table 7.

...........................................................................20 

Statistics for All Workers, Thorium Workers, Chemical Operators, and NonThorium Chemical Operators, 1974

Table 8.

...........................................................................20 

Statistics for All Workers, Thorium Workers, Chemical Operators, and NonThorium Chemical Operators, 1975

Table 9.

...........................................................................21 

Statistics for All Workers, Thorium Workers, Chemical Operators, and NonThorium Chemical Operators, 1976

Table 10.

...........................................................................21 

Statistics for All Workers, Thorium Workers, Chemical Operators, and NonThorium Chemical Operators, 1977

Table 11.

...........................................................................22 

Statistics for All Workers, Thorium Workers, Chemical Operators, and NonThorium Chemical Operators, 1978

Table 12.

...............................................23 

95 Percentile of Thorium In-Vivo Test Results with 95% Confidence Interval 

for the 95 Percentile for All Workers, Thorium Workers, Chemical Operators, 

and Non-Thorium Chemical Operators, 1968 to 1978

th

th

Table 13.

.............................................................................24 

Mean Thorium In-Vivo Test Results of 95% Confidence Interval for the Mean 

for All Workers, Thorium Workers, Chemical Operators, and Non-Thorium 

Chemical Operators, 1968 to 1978

Table 14. Overview of Positive Th Results................................................................................25 

Table 15.

.........................26 

Excel Calculated Linear Trend Line Formulas and Correlation Coefficients for 

Uranium and Thorium Data during Periods of Thorium Production

Table 16.

.............................................................................30 

Excel Calculated Linear Trend Line Formulas and Correlation Coefficients for 

All Data over All Measured Years

Table 17.

.............31 

Excel Calculated Linear Trend Line Formulas and Correlation Coefficients for 

All Data over All Measured Years Excluding Three Outlier Measurements
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LIST OF FIGURES 

Figure 1.

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

Comparison of In-Vivo Results (mg Th) for All Thorium Worker Job Titles 

versus Non-Thorium Chemical Operators in 1968

Figure 2.

..........................................12 

Rank-Ordered Comparison of In-Vivo Results (mg Th) for 

Thorium Workers and Chemical Operators (1968–1979)

Figure 3.

..................................................................13 

Rank-Ordered Comparison of In-Vivo Results (mg Th) for Chemical Operators 

and All Monitored Workers (1968–1979)

Figure 4.

.................................................................................15 

Time Series Plot of the 95 Percentile of the Thorium Test Results for Four 

Groups of Workers, 1968–1978

th

Figure 5.

..............................................................................................16 

Time Series Plot of the Mean Thorium In-Vivo Test Results for Four Groups 

of Workers, 1968–1978

Figure 6. Median U-235 Result versus Number of Samples per Worker (1968–1978) ............27 

Figure 7.

...........................................................................................................................27 

Median Uranium (U) Result versus Number of Samples per Worker (1968–

1978)

Figure 8. Median Thorium Result versus Number of Samples per Worker (1968–1978).........28 

Figure 9. Average U-235 Result versus Number of Samples per Worker.................................31 

Figure 10.

....................................................................................................................32 

Average U-235 Result versus Number of Samples per Worker (scales 

truncated)

Figure 11. Median U-235 Result versus Number of Samples per Worker..................................32 

Figure 12.

....................................................................................................................33 

Median U-235 Result versus Number of Samples per Worker (scales 

truncated)

Figure 13. Maximum U-235 Result versus Number of Samples per Worker..............................33 

Figure 14.

........................................................................................................34 

Maximum U-235 Result versus Number of Samples per Worker 

(scales truncated)

Figure 15. Average Uranium Result versus Number of Samples per Worker.............................34 

Figure 16.

........................................................................................................35 

Average Uranium Result versus Number of Samples per Worker 

(scales truncated)

Figure 17. Median Uranium Result versus Number of Samples per Worker..............................35 

Figure 18.

........................................................................................................36 

Median Uranium Result versus Number of Samples per Worker 

(scales truncated)

Figure 19. Maximum Uranium Result versus Number of Samples per Worker..........................36 

Figure 20.

........................................................................................................37 

Maximum Uranium Result versus Number of Samples per Worker 

(scales truncated)

Figure 21. Average Thorium Result versus Number of Samples per Worker.............................37 

Figure 22.

........................................................................................................38 

Average Thorium Result versus Number of Samples per Worker 

(scales truncated)
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NOTICE:

Figure 23. Median Thorium Result versus Number of Samples per Worker ..............................38 

Figure 24.

........................................................................................................39 

Median Thorium Result versus Number of Samples per Worker 

(scales truncated)

Figure 25. Maximum Thorium Result versus Number of Samples per Worker..........................39 

Figure 26.

........................................................................................................40 

Maximum Thorium Result versus Number of Samples per Worker 

(scales truncated)

Figure 27. Average Actinium Result versus Number of Samples per Worker............................40 

Figure 28.

........................................................................................................41 

Average Actinium Result versus Number of Samples per Worker 

(scales truncated)

Figure 29. Median Actinium Result versus Number of Samples per Worker .............................41 

Figure 30.

........................................................................................................42 

Median Actinium Result versus Number of Samples per Worker 

(scales truncated)

Figure 31. Maximum Actinium Result versus Number of Samples per Worker.........................42 

Figure 32.

........................................................................................................43 

Maximum Actinium Result versus Number of Samples per Worker 

(scales truncated)

Figure 33. Average Pb-212 Result versus Number of Samples per Worker ...............................43 

Figure 34.

........................................................................................................44 

Average Pb-212 Result versus Number of Samples per Worker 

(scales truncated)

Figure 35. Median Pb-212 Result versus Number of Samples per Worker.................................44 

Figure 36.

........................................................................................................45 

Median Pb-212 Result versus Number of Samples per Worker 

(scales truncated)

Figure 37. Maximum Pb-212 Result versus Number of Samples per Worker ............................45 

Figure 38.

........................................................................................................46 

Maximum Pb-212 Result versus Number of Samples per Worker 

(scales truncated)
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ABBREVIATIONS AND ACRONYMS 

CI confidence interval 

μg microgram 

MDA minimum detectable activity 

mg milligrams 

MIVRML Mobile In-Vivo Radiation Monitoring Laboratory 

nCi nanocurie 

NIOSH National Institute for Occupational Safety and Health 

SC&A S. Cohen and Associates (SC&A, Inc.)
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1.0 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 (NIOSH 2008). This technical response presents additional analyses relevant to the SC&A 

2010 review prompted by subsequent work group discussions on some of the key issues, as 

described below. It is important to note that while the NIOSH coworker model spans the period 

from 1968–1989, the main subject of these additional analyses is the in-vivo data given in 

milligrams (mg) of Th for the operational thorium period from 1968–1979.1 After 1979, there 

were no known thorium processing campaigns, so thorium exposure potential would be related to 

the storage, handling, and repackaging of thorium materials, as Fernald became the national 

repository for thorium beginning in 1972. Potential thorium exposures incurred in the “postoperational” thorium period (1980–1989) are discussed in SC&A 2010, Section 3.3, and 

elsewhere in that report. 

 

On February 3, 2011, NIOSH posted responses to a number of the findings identified in SC&A 

2010 (NIOSH 2011). The issues relating to the completeness of thorium monitoring coverage 

were discussed briefly at the February 9, 2011, work group meeting, and more thoroughly at the 

April 19, 2011, work group meeting. This addendum presents an additional analysis that 

pertains to two of the major discussion points that arose from NIOSH’s initial response and were 

discussed in the work group meetings. The two issues in question can be summarized as 

follows: 

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

records. Therefore, it is unknown whether their exposure potential was sufficiently 

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

types. 

 

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

monitoring; however, it has been suggested that workers with the higher exposure 

potential (and therefore higher in-vivo results) were targeted more frequently for 

monitoring. This would result in a correlation between the frequency of monitoring and 

the distribution of lung burdens, which should be evident in the data.

In relation to these issues, NIOSH stated the following in their February 3, 2011, response: 

SRDB 38124 [Redacted 2007] states that chemical operators were not selected 

for counting on the basis of if they did thorium work or not. All chemical 

operators were treated the same for selection. Selection was based on a routine 

schedule, or based on involvement with an event, or due to previously high invivo counts... measurements were not limited to those identified as ‘thorium 

workers.’ It would seem likely that, given some of the high in-vivo results came 

from other individuals, the site was targeting individuals known to be 

performing rad work and who were likely to have intakes. [Emphasis added.] 

 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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Subsequent discussions during the February 9th work group2

 meeting further expanded on this 

response and concluded with the statement by NIOSH that thorium exposures can be bounded by 

the in-vivo results for chemical operators, because that category represents workers with the 

highest exposure potential. Furthermore, NIOSH asserted that the available monitoring data are 

sufficiently bounding, because chemical operators are not under-represented, and workers with 

higher potential for intakes were targeted more frequently. 

During the April 19th work group meeting, SC&A presented additional analysis that compared 

the thorium lung burdens for identifiable thorium workers to those for the chemical operator 

group. These comparisons, along with some explanatory text, are presented in Section 3.1 of this 

report. The premise that workers with higher thorium exposures were targeted more frequently 

is analyzed in Section 2.0, which explores the correlation between the number of times a worker 

was sampled (sampling frequency) and the relative magnitude of their intake for both uranium 

and thorium. Attachment 1 expands upon the analysis presented in Section 2.0 and includes data 

outside the operational thorium period (post-1979). 

2.0 SUMMARY OF FINDINGS: 

Finding 1: When comparing the rank-ordered lung burdens for identifiable thorium workers to 

the monitoring records for chemical operators, the thorium worker in-vivo results were generally 

higher than chemical operators at almost all percentiles and, therefore, do not appear to be 

bounded by chemical operator lung burdens. In light of these perceived differences between the 

two subgroups in the rank-order analysis, a more robust analytical approach was adopted that 

compares the data on an annual basis. The results of this analysis show that the thorium 

subgroup 95th percentiles are higher in all but 4 years when compared with either the all workers 

or chemical operator 95th percentiles, and the means for the thorium samples are higher than the 

means for the other two groups in all but a few years. However, with the exception of 1971, no 

significant differences were found between the thorium subgroup, the chemical operators, and all 

worker categories when comparing the non-parametric 95% confidence intervals for the 95th

percentiles of the three groups. (Please refer to Sections 3.1 and 3.2.) It is noteworthy that no 

evidence was found that the all worker or chemical operator groups provide a definitive upper 

bound for the thorium worker exposure. 

Finding 2: Less than 3% of the in-vivo records for mg Th are at or above the assumed minimum 

detectable activity (MDA) of 6 mg. This, combined with uncertainties regarding the accuracy 

and veracity of the MDA, call the utility of the model into question. Nonetheless, thorium 

workers appear to be well represented among the in-vivo results at or above the MDA. Whereas 

thorium workers only comprise 7% of the total number of workers monitored, they make up over 

20% of the workers who had positive results. Similarly, thorium worker samples comprise only 

13% of the total samples, while they make up nearly 33% of the positive results identified.

Finding 3: When comparing a worker’s monitoring frequency to the relative magnitude of their 

lung burden results, it was observed that thorium monitoring actually had a slight negative bias at 

the median and average lung burdens. That is, there was no positive linear correlation 

2

 NOTE: The February 9, 2011, work group transcript is currently unavailable. 
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observed between the number of times a worker was monitored for thorium intake and the 

actual magnitude of their results. Conversely, uranium monitoring results showed a much 

better linear correlation between monitoring frequency and the relative magnitude of results. 

This strongly suggests that the in-vivo program may have been targeting higher risk workers 

based on uranium activities and not thorium projects. (Please refer to Section 4.0 and 

Attachment 1.) 

3.0 SECTION 1: COMPARISON OF THE IN-VIVO RECORDS FOR IDENTIFIED 

THORIUM WORKERS VERSUS CHEMICAL OPERATORS 

3.1 Analysis of Raw Data Unadjusted for the Stated MDA of 6 mg Th 

As presented in the introduction, perhaps the most important facet of the thorium in-vivo 

coworker model is whether the most highly exposed workers are adequately represented in the 

database that underlies the thorium coworker model. Sections 3.1.1 and 3.1.2 of SC&A 2010 

present analyses which suggest that the limited set of workers who could be identified as thorium 

workers had a significantly higher exposure potential than the entire worker population. 

This finding was first discussed briefly during the February 2011 Fernald Work Group meeting, 

with the original response from NIOSH being that the dose to thorium workers is adequately 

bounded by the dose to chemical operators as a whole. That is, NIOSH contends that the 

chemical operator subgroup comprises the workers with the highest risk for thorium exposure. 

That premise had not been investigated in SC&A’s original review (SC&A 2010); therefore, an 

additional analysis is presented in this section to address the comparison of thorium workers 

specifically to chemical operators. 

As stated in SC&A 2010, there are difficulties in establishing who worked with thorium and 

during what periods for all years except 1968 (the first year of in-vivo monitoring). Just prior to 

1968, a memo was produced by Bob Starkey (Starkey 1967) that listed thorium workers (51 in 

total) with the explicit purpose of having them counted when the Mobile In-Vivo Radiation 

Monitoring Laboratory (MIVRML) was available on site. Based on the available records, 

approximately 55% of the 51 identified workers were counted in 1968. The Starkey memo is a 

useful resource, as it directly ties lung burdens to workers who were identified with thorium at 

the time. The data for the thorium workers in 1968 were compared against the chemical operator 

lung burdens during that same year; these data are presented in Figure 1. It is important to note 

that chemical operators who were identified as thorium workers in 1968 were not included in the 

‘chemical operator’ subgroup of Figure 1, as this would have resulted in double counting.3

As seen in Figure 1, the thorium worker lung burdens overlap with chemical operators at about 

the 15th, 75th, and 95th percentiles, but clearly exceed the chemical worker burdens from about 

3

 The Starkey memo was used to assign job titles in instances where no job title was specified in the in-vivo 

records. In 1968, nearly 60% of the records had no job title specified, so it is likely that a significant portion of 

those records were also for chemical operators. Of the 79 samples identified for chemical operators in 1968, 49 (or 

62%) were identified via the Starkey memo, so there is considerable overlap. The double-counting effect was less 

pronounced in subsequent years. 
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the 20th to the 67th percentiles. Also of note is that the three highest results in 1968 were all for 

thorium workers. 

Figure 1. Comparison of In-Vivo Results (mg Th) for All Thorium Worker Job Titles 

versus Non-Thorium Chemical Operators in 1968 

After 1968, it is very difficult to identify who worked with thorium and during which years; this 

makes it more difficult to compare the lung burdens for the thorium subgroup to chemical 

operators or other groups of workers. The only other resource that identifies thorium workers is 

the worker in-vivo log sheets, as outlined in Section 3.1.2 of SC&A 2010. However, there is no 

direct connection to suggest when, if at all, thorium was handled by these workers during the 

production period of interest (1968–1979).4

 For the purposes of comparison, SC&A assumed 

that every worker identified in the Starkey memo, as well as those identified as thorium workers 

on their individual log sheets (about 60 workers in total), handled thorium during their entire 

period of employment. This expanded subgroup of thorium workers is the subject of the 

remainder of this section, as well as the statistical analysis presented in Section 3.2. It is 

important to note that it is unlikely that any worker actually handled thorium during their entire 

period of employment, due to the intermittent processing of thorium at Fernald (Morris 2008). 

Thus, many of the thorium in-vivo measurements would actually be representative of uranium 

work instead of thorium work. 

 4

 As noted in the introduction, the period under consideration for in-vivo thorium monitoring extends from 

1968 until 1989. However, thorium production at Fernald ceased in 1979; therefore, 1968–1979 is the period under 

consideration for this analysis. Analyses specifically for Th ceased in 1978; therefore, this analysis does not include 

data for 1979. 
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Based on the assumption of continuous thorium exposure during all periods of employment, the 

expanded thorium worker subgroup was compared to the chemical operators during the period of 

interest (1968–1979); the results are presented in Figure 2. As shown in Figure 2, the 

expanded thorium worker subgroup appears to bound the chemical operator subgroup for 

almost all percentiles. Interestingly, Figure 2 also shows that chemical operators who were 

never identified with thorium work (either through the Starkey memo or the individual log 

sheets) have a slightly lower exposure potential than the chemical operator group as a whole. 

Figure 2. Rank-Ordered Comparison of In-Vivo Results (mg Th) for 

Thorium Workers and Chemical Operators (1968–1979) 

Finally, Figure 3 compares the rank-ordered lung burdens for all chemical operators to those of 

all the workers monitored for thorium during the operational period. As the figure shows, the 

rank-ordered lung burdens for chemical operators are indistinguishable from the distribution for 

all workers. This strongly suggests the chemical operator subgroup does not bound doses for all 

workers. 
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Figure 3. Rank-Ordered Comparison of In-Vivo Results (mg Th) for Chemical Operators 

and All Monitored Workers (1968–1979) 

3.2 Additional Analysis of Worker Subgroup Data 

To better understand the potential differences in thorium lung burden distributions in the 

subgroups of interest, additional statistical analyses beyond simple rank-ordered comparisons 

were performed. The subgroup of thorium workers analyzed in this section assumes that all 

workers identified in the 1968 Starkey memo and also by their in-vivo logbooks worked with 

thorium during the entire production period. Also note that in this analysis, chemical operators 

and thorium workers are not mutually exclusive; that is, there is some overlap between the two 

groups of workers. Table 1 shows selected statistics describing the distribution of thorium invivo test results in 1968 for all workers and for three subgroups of workers—thorium workers, 

chemical operators, and non-thorium chemical operators. Tables 2 through 11 contain similar 

information for the years 1969 through 1978, respectively. 

In Table 1, the sample size in 1968 of 289 for all workers includes 75 samples for workers 

identified as thorium workers and 79 as chemical operators. Of the 79 chemical operator 

samples, all but 15 were also identified as thorium workers. The statistics reported for each 

group include the arithmetic mean, with the upper and lower bounds of the 95% confidence 

interval for the estimated mean, and the standard error of the mean. The spread of the 

distribution of test results is measured by the next eight statistics: the variance, the standard 

deviation and the coefficient of variation; the 5th, 25th, 50th, 75th and 95th percentiles of the 

distribution of test results. Due to the wide variety of distributions encountered in the 4 groups 

over the 11-year period, nonparametric estimates of the upper and lower 95% confidence bounds 

(highlighted) for the 95th percentile are shown in the table. Examination of the nonparametric 

confidence bands for the 95th percentile shows that most of the estimates of the 95th

percentile for the four groups of workers do not differ significantly. Summary statistics for 

the distribution of test results are shown at the bottom of Tables 1 through 11, including the 
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maximum and minimum sample values, and the skew and kurtosis of the distribution. Note that 

the skew and kurtosis are 0 for a normal distribution. 

The estimates of the 95th percentile and the nonparametric 95% confidence interval for the 95th

percentile are summarized for 1968 through 1978 for the four groups of workers in Table 12. 

Examination of the 95th percentile values in Table 12 shows that the 95th percentile of the 

thorium worker samples exceeds the 95th percentile for all workers and for all chemical operators 

in 7 of the 11 years. However, examination of the nonparametric confidence bands for the 95th

percentile shows that the only significant difference between these two groups occurs in 1971. 

Figure 4 shows time series plots of the 95th percentiles for the four groups of workers in 

Table 12. The 95th percentile of the distribution for chemical operators tracks closely with the all 

worker distribution over the entire period. The 95th percentiles for all four groups are very 

similar from 1972 on. Prior to 1972, the following differences are observed: 

 In 1968, the 95th percentile for thorium workers is approximately the same as for 

chemical operators and higher than for all workers. 

 In 1969, the 95th percentile for thorium workers is below that for chemical operators and 

all workers. 

 The ordering is reversed in 1970 and 1971, with the 95th percentile for thorium workers 

exceeding the other two groups. 

Based on the confidence intervals shown in Table 12, 1971 is the only year with a 

significant difference between the thorium workers and all workers 95th percentiles. 

Viewed from the claimant perspective, however, there is no year when the all worker 95th

percentile or the chemical operator 95th percentile is significantly higher than the 95th percentile 

for the thorium workers. Hence, there is no evidence that either of these two groups provides a 

definitive upper bound for the upper end of thorium worker exposures. The 95th percentile for 

non-thorium chemical operators is lower than the other three groups prior to 1973. 

In Table 1, the mean values for two groups in 1968 appear to differ significantly from the other 

two, since the lower bounds of the confidence intervals (CIs) for the mean for the thorium and 

chemical operators exceed the upper bounds of the confidence intervals for the all worker and 

non-thorium chemical operator subgroups. This apparent difference in mean values is suspect, 

however, since the groups are non-exclusive. The means of the four groups of workers are 

plotted for the years 1968 through 1978 in Figure 5. The apparently significant difference 

between the all worker group and the thorium and chemical operator group only occurs in 1968. 

In 1969, the means are very close. From 1970 to 1972 and in 1978, the mean value for the 

thorium workers is somewhat higher than the means for the other groups. 

The estimates of the mean thorium in-vivo test result and the 95% confidence interval for the 

mean are summarized for 1968 through 1978 for the four groups of workers in Table 13. 

Examination of the mean values in Table 13 shows that the mean of the thorium worker samples 

exceeds the mean for all workers in all but one year (1975), and the mean of the thorium worker 

samples exceeds the mean for the all chemical operator group in 8 of the 11 years. The 
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confidence intervals indicate the thorium worker mean value is significantly higher than the all 

worker mean in 1968, and the difference may have borderline significance in 1970, 1971, and 

1972. The mean for the thorium workers does not appear to be significantly higher in later years. 

On the other hand, there is no year when the all worker mean or the chemical operator mean is 

significantly higher than the thorium worker mean. This brings into question whether either of 

these two groups provides a plausible upper bound for the thorium worker exposures. 

95TH PERCENTILE

0

2

4

6

8

10

1966 1968 1970 1972 1974 1976 1978 1980

All Workers All Thorium Workers 

All Chemical Operators Non-Thorium Chemical Operators

Figure 4. Time Series Plot of the 95th Percentile of the Thorium Test Results for Four 

Groups of Workers, 1968–1978 
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MEAN

0

1

2

3

4

5

1966 1968 1970 1972 1974 1976 1978 1980

All Workers All Thorium Workers 

All Chemical Operators Non-Thorium Chemical Operators

Figure 5. Time Series Plot of the Mean Thorium In-Vivo Test Results for Four Groups 

of Workers, 1968–1978 
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Table 1. Statistics for All Workers, Thorium Workers, Chemical Operators, and NonThorium Chemical Operators, 1968 

Statistic All 

Workers 

All Thorium 

Workers 

All Chemical 

Operators 

Non-Thorium 

Chemical 

Operators 

 Number of Samples 289 75 79 15 

 Upper Bound of 95% CI for Mean 2.2 3.8 3.6 2.3 

 Mean 1.9 3.3 3.1 1.4 

 Lower Bound of 95% CI for Mean 1.7 2.8 2.5 0.4 

 Standard Error of Mean 0.13 0.25 0.26 0.48 

 Variance 4.6 4.7 5.4 3.4 

 Standard Deviation 2.1 2.2 2.3 1.8 

 Coefficient of Variation 1.1 0.6 0.8 1.4 

 5th Percentile -1.3 0.0 -0.1 -1.0 

 25th Percentile 0.7 1.9 1.3 0.6 

 Median 1.8 3.0 3.0 0.7 

 75th Percentile 3.1 4.6 4.6 2.3 

 Lower Bound of 95% CI for 95th Percentile 4.8 5.9 5.9 3.0 

 95th Percentile 5.5 6.9 6.8 4.6 

 Upper Bound of 95% CI for 95th Percentile 6.6 10.2 10.2 4.7 

 Maximum 10.2 10.2 10.2 4.7 

 Minimum -8.8 -0.5 -1.7 -1.7 

 Range 19.0 10.7 11.9 6.4 

 Skew -0.14 0.51 0.46 0.61 

 Kurtosis 3.15 0.35 0.06 -0.17 

Note that the results for 1968 presented here will differ from the analysis presented in Figure 1 of Section 3.1 because 

Figure 1 only analyzed the thorium workers identified in the Starkey memo while this section analyzes the ‘expanded 

group’ of thorium workers which includes those identified in their logbooks. 

Table 2. Statistics for All Workers, Thorium Workers, Chemical Operators, and NonThorium Chemical Operators, 1969 

Statistic All 

Workers 

All Thorium 

Workers 

All Chemical 

Operators 

Non-Thorium 

Chemical 

Operators 

 Number of Samples 87 24 11 4 

 Upper Bound of 95% CI for Mean 4.6 5.0 6.3 3.9 

 Mean 3.7 4.0 4.3 2.0 

 Lower Bound of 95% CI for Mean 2.7 2.9 2.3 0.1 

 Standard Error of Mean 0.49 0.54 1.00 0.96 

 Variance 21.1 7.1 11.0 3.7 

 Standard Deviation 4.6 2.7 3.3 1.9 

 Coefficient of Variation 1.3 0.7 0.8 1.0 

 5th Percentile 0.0 0.4 0.5 0.0 

 25th Percentile 0.9 1.8 2.3 0.8 

 Median 2.7 4.3 4.4 2.0 

 75th Percentile 4.7 5.6 5.3 3.2 

 Lower Bound of 95% CI for 95th Percentile 7.0 5.7 5.7 1.1 

 95th Percentile 9.0 6.8 9.1 4.0 

 Upper Bound of 95% CI for 95th Percentile 32.5 12.4 12.4 4.2 

 Maximum 32.5 12.4 12.4 4.2 

 Minimum -0.9 0.2 -0.2 -0.2 

 Range 33.4 12.2 12.6 4.4 

 Skew 3.69 1.16 1.32 0.06 

 Kurtosis 19.18 3.03 3.27 -1.89 
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Table 3. Statistics for All Workers, Thorium Workers, Chemical Operators, and NonThorium Chemical Operators, 1970 

Statistic All 

Workers 

All Thorium 

Workers 

All Chemical 

Operators 

Non-Thorium 

Chemical 

Operators 

 Number of Samples 155 18 27 20 

 Upper Bound of 95% CI for Mean 2.7 5.0 3.2 2.3 

 Mean 2.4 3.8 2.4 1.6 

 Lower Bound of 95% CI for Mean 2.1 2.5 1.6 0.9 

 Standard Error of Mean 0.16 0.65 0.42 0.35 

 Variance 3.9 7.6 4.7 2.4 

 Standard Deviation 2.0 2.8 2.2 1.5 

 Coefficient of Variation 0.8 0.7 0.9 1.0 

 5th Percentile -0.3 0.5 -0.1 -0.2 

 25th Percentile 1.0 2.8 1.1 0.4 

 Median 2.1 3.1 1.7 1.4 

 75th Percentile 3.7 3.9 3.8 2.2 

 Lower Bound of 95% CI for 95th Percentile 4.8 5.9 4.6 2.8 

 95th Percentile 5.7 8.6 6.2 4.6 

 Upper Bound of 95% CI for 95th Percentile 7.5 11.8 8.0 4.8 

 Maximum 11.8 11.8 8.0 4.8 

 Minimum -1.5 0.4 -0.5 -0.5 

 Range 13.3 11.4 8.5 5.3 

 Skew 1.00 1.66 0.87 0.88 

 Kurtosis 2.54 3.45 0.29 0.14 

Table 4. Statistics for All Workers, Thorium Workers, Chemical Operators, and NonThorium Chemical Operators, 1971 

Statistic All 

Workers 

All Thorium 

Workers 

All Chemical 

Operators 

Non-Thorium 

Chemical 

Operators 

 Number of Samples 583 52 178 136 

 Upper Bound of 95% CI for Mean 2.6 4.0 3.0 2.9 

 Mean 2.4 3.4 2.7 2.6 

 Lower Bound of 95% CI for Mean 2.3 2.7 2.4 2.2 

 Standard Error of Mean 0.08 0.34 0.15 0.16 

 Variance 3.7 6.0 3.9 3.4 

 Standard Deviation 1.9 2.4 2.0 1.8 

 Coefficient of Variation 0.8 0.7 0.7 0.7 

 5th Percentile -0.3 -0.1 -0.1 -0.1 

 25th Percentile 1.1 1.5 1.4 1.4 

 Median 2.3 3.0 2.6 2.5 

 75th Percentile 3.5 5.1 3.8 3.5 

 Lower Bound of 95% CI for 95th Percentile 5.3 6.8 5.3 5.0 

 95th Percentile 5.7 7.3 5.9 5.4 

 Upper Bound of 95% CI for 95th Percentile 6.3 9.6 7.4 10.0 

 Maximum 11.6 9.6 10.0 10.0 

 Minimum -2.5 -0.5 -1.9 -1.9 

 Range 14.1 10.1 11.9 11.9 

 Skew 0.80 0.42 0.85 0.88 

 Kurtosis 1.74 -0.54 1.75 2.64 
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Table 5. Statistics for All Workers, Thorium Workers, Chemical Operators, and NonThorium Chemical Operators, 1972 

Statistic All Workers All Thorium 

Workers 

All Chemical 

Operators 

Non-Thorium 

Chemical 

Operators 

 Number of Samples 239 34 122 92 

 Upper Bound of 95% CI for Mean 2.3 3.3 2.3 2.1 

Mean 2.1 2.7 2.0 1.7 

 Lower Bound of 95% CI for Mean 1.9 2.2 1.7 1.4 

 Standard Error of Mean 0.11 0.28 0.15 0.17 

Variance 2.8 2.7 2.9 2.8 

 Standard Deviation 1.7 1.6 1.7 1.7 

 Coefficient of Variation 0.8 0.6 0.9 1.0 

 5th Percentile -0.5 0.6 -0.5 -0.6 

 25th Percentile 0.8 1.5 0.7 0.4 

Median 2.0 2.1 1.9 1.8 

 75th Percentile 3.3 4.1 3.2 2.8 

 Lower Bound of 95% CI for 95th Percentile 4.5 4.5 4.1 3.6 

 95th Percentile 4.9 5.3 4.7 3.8 

 Upper Bound of 95% CI for 95th Percentile 5.3 5.9 5.9 9.1 

Maximum 9.1 5.9 9.1 9.1 

 Minimum -3.0 0.2 -3.0 -3.0 

 Range 12.1 5.7 12.1 12.1 

Skew 0.36 0.34 0.60 0.70 

 Kurtosis 0.58 -1.12 1.78 3.23 

Table 6. Statistics for All Workers, Thorium Workers, Chemical Operators, and NonThorium Chemical Operators, 1973 

Statistic All 

Workers 

All Thorium 

Workers 

All Chemical 

Operators 

Non-Thorium 

Chemical 

Operators 

 Number of Samples 205 28 106 83 

 Upper Bound of 95% CI for Mean 1.8 2.2 1.9 1.9 

 Mean 1.5 1.8 1.6 1.6 

 Lower Bound of 95% CI for Mean 1.3 1.4 1.3 1.2 

 Standard Error of Mean 0.13 0.22 0.15 0.17 

 Variance 3.3 1.3 2.3 2.5 

 Standard Deviation 1.8 1.1 1.5 1.6 

 Coefficient of Variation 1.2 0.6 1.0 1.0 

 5th Percentile -1.5 0.1 -1.3 -1.4 

 25th Percentile 0.5 0.8 0.7 0.7 

 Median 1.6 2.0 1.7 1.7 

 75th Percentile 2.7 2.7 2.8 2.7 

 Lower Bound of 95% CI for 95th Percentile 3.6 2.9 3.3 3.3 

 95th Percentile 4.1 3.2 3.9 3.9 

 Upper Bound of 95% CI for 95th Percentile 4.9 4.2 5.0 5.0 

 Maximum 11.7 4.2 5.0 5.0 

 Minimum -2.8 -0.2 -2.4 -2.4 

 Range 14.5 4.4 7.4 7.4 

 Skew 0.65 0.04 -0.34 -0.38 

 Kurtosis 4.13 -0.93 -0.11 -0.19 
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Table 7. Statistics for All Workers, Thorium Workers, Chemical Operators, and NonThorium Chemical Operators, 1974 

Statistic All 

Workers 

All Thorium 

Workers 

All Chemical 

Operators 

Non-Thorium 

Chemical 

Operators 

 Number of Samples 279 27 128 108 

 Upper Bound of 95% CI for Mean 1.2 2.4 1.3 1.3 

 Mean 0.8 1.2 0.9 0.8 

 Lower Bound of 95% CI for Mean 0.5 -0.1 0.4 0.3 

 Standard Error of Mean 0.19 0.64 0.23 0.25 

 Variance 9.7 11.0 6.9 6.6 

 Standard Deviation 3.1 3.3 2.6 2.6 

 Coefficient of Variation 3.8 2.9 3.0 3.2 

 5th Percentile -3.2 -6.3 -2.9 -2.9 

 25th Percentile -0.5 0.1 -0.1 -0.1 

 Median 1.1 1.7 1.0 1.0 

 75th Percentile 2.5 2.9 2.3 2.0 

 Lower Bound of 95% CI for 95th Percentile 4.4 4.1 3.6 3.5 

 95th Percentile 4.8 5.5 5.1 5.1 

 Upper Bound of 95% CI for 95th Percentile 5.8 5.9 5.9 6.0 

 Maximum 18.0 5.9 6.0 6.0 

 Minimum -16.0 -8.1 -11.9 -11.9 

 Range 34.0 14.0 17.9 17.9 

 Skew -0.88 -1.42 -1.41 -1.42 

 Kurtosis 8.08 2.72 5.61 6.43 

Table 8. Statistics for All Workers, Thorium Workers, Chemical Operators, and NonThorium Chemical Operators, 1975 

Statistic All 

Workers 

All Thorium 

Workers 

All Chemical 

Operators 

Non-Thorium 

Chemical 

Operators 

 Number of Samples 233 23 111 92 

 Upper Bound of 95% CI for Mean 1.4 1.3 1.6 1.7 

 Mean 1.1 0.5 1.2 1.2 

 Lower Bound of 95% CI for Mean 0.8 -0.3 0.7 0.7 

 Standard Error of Mean 0.15 0.41 0.21 0.25 

 Variance 5.4 3.9 5.1 5.5 

 Standard Deviation 2.3 2.0 2.3 2.4 

 Coefficient of Variation 2.1 3.7 1.9 1.9 

 5th Percentile -2.2 -2.6 -1.5 -1.5 

 25th Percentile -0.2 -0.5 0.0 0.0 

 Median 1.0 0.4 1.4 1.5 

 75th Percentile 2.5 2.0 2.6 2.5 

 Lower Bound of 95% CI for 95th Percentile 4.0 2.6 3.5 3.6 

 95th Percentile 4.6 3.1 4.0 4.4 

 Upper Bound of 95% CI for 95th Percentile 5.8 4.0 6.3 6.9 

 Maximum 8.3 4.0 6.9 6.9 

 Minimum -10.0 -4.5 -10.0 -10.0 

 Range 18.3 8.5 16.9 16.9 

 Skew -0.39 -0.56 -1.00 -1.10 

 Kurtosis 2.81 0.76 5.13 5.34 
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Table 9. Statistics for All Workers, Thorium Workers, Chemical Operators, and NonThorium Chemical Operators, 1976 

Statistic All 

Workers 

All Thorium 

Workers 

All Chemical 

Operators 

Non-Thorium 

Chemical 

Operators 

 Number of Samples 215 24 114 93 

 Upper Bound of 95% CI for Mean 1.9 2.4 2.4 2.5 

 Mean 1.6 1.7 1.8 1.8 

 Lower Bound of 95% CI for Mean 1.2 1.0 1.2 1.0 

 Standard Error of Mean 0.18 0.34 0.31 0.37 

 Variance 7.3 2.8 10.7 12.5 

 Standard Deviation 2.7 1.7 3.3 3.5 

 Coefficient of Variation 1.7 1.0 1.9 2.0 

 5th Percentile -1.5 -0.6 -1.2 -1.4 

 25th Percentile 0.2 0.4 0.2 0.0 

 Median 1.3 1.5 1.1 1.0 

 75th Percentile 2.6 2.8 2.9 2.8 

 Lower Bound of 95% CI for 95th Percentile 4.4 3.5 4.9 4.9 

 95th Percentile 5.2 4.8 5.6 6.0 

 Upper Bound of 95% CI for 95th Percentile 6.2 5.2 25.0 -2.4 

 Maximum 25.0 5.2 25.0 25.0 

 Minimum -2.8 -1.1 -2.4 -2.4 

 Range 27.8 6.3 27.4 27.4 

 Skew 3.95 0.54 4.15 4.03 

 Kurtosis 29.73 -0.36 25.40 22.76 

Table 10. Statistics for All Workers, Thorium Workers, Chemical Operators, and NonThorium Chemical Operators, 1977 

Statistic All 

Workers 

All Thorium 

Workers 

All Chemical 

Operators 

Non-Thorium 

Chemical 

Operators 

 Number of Samples 188 29 97 73 

 Upper Bound of 95% CI for Mean 1.3 1.9 1.3 1.3 

 Mean 1.1 1.4 1.0 0.9 

 Lower Bound of 95% CI for Mean 0.9 0.9 0.7 0.6 

 Standard Error of Mean 0.11 0.26 0.14 0.16 

 Variance 2.1 1.9 2.0 2.0 

 Standard Deviation 1.5 1.4 1.4 1.4 

 Coefficient of Variation 1.3 1.0 1.4 1.5 

 5th Percentile -1.0 -0.5 -0.9 -1.0 

 25th Percentile -0.1 0.6 -0.1 -0.1 

 Median 1.0 1.3 1.0 0.9 

 75th Percentile 2.0 2.0 1.8 1.8 

 Lower Bound of 95% CI for 95th Percentile 3.2 2.9 2.9 2.7 

 95th Percentile 3.6 3.9 3.6 3.4 

 Upper Bound of 95% CI for 95th Percentile 4.5 4.8 4.8 4.5 

 Maximum 5.3 4.8 4.8 4.5 

 Minimum -2.6 -1.4 -2.4 -2.4 

 Range 7.9 6.2 7.2 6.9 

 Skew 0.29 0.49 0.41 0.32 

 Kurtosis 0.06 0.59 0.03 -0.20 
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NOTICE:

Table 11. Statistics for All Workers, Thorium Workers, Chemical Operators, and NonThorium Chemical Operators, 1978 

Statistic All Workers All Thorium 

Workers 

All Chemical 

Operators 

Non-Thorium 

Chemical 

Operators 

 Number of Samples 144 18 70 53 

 Upper Bound of 95% CI for Mean 2.5 4.1 2.7 2.6 

Mean 2.2 3.1 2.2 2.0 

 Lower Bound of 95% CI for Mean 1.9 2.1 1.8 1.5 

 Standard Error of Mean 0.17 0.51 0.24 0.27 

Variance 4.0 4.7 4.2 3.9 

 Standard Deviation 2.0 2.2 2.0 2.0 

 Coefficient of Variation 0.9 0.7 0.9 1.0 

 5th Percentile -0.7 0.2 -0.9 -1.1 

 25th Percentile 0.8 1.5 0.9 0.9 

Median 2.0 3.0 2.1 1.9 

 75th Percentile 3.7 4.5 3.4 3.3 

 Lower Bound of 95% CI for 95th Percentile 5.0 5.7 4.4 4.1 

 95th Percentile 5.7 6.1 6.1 5.3 

 Upper Bound of 95% CI for 95th Percentile 6.9 7.3 7.5 7.5 

Maximum 7.5 7.3 7.5 7.5 

 Minimum -2.2 0.1 -2.2 -2.2 

Range 9.7 7.2 9.7 9.7 

Skew 0.32 0.25 0.43 0.44 

 Kurtosis -0.22 -0.83 0.25 0.65 
Effective Date: 

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Table 12. 95th Percentile of Thorium In-Vivo Test Results with 95% Confidence Interval for the 95t

Workers, Thorium Workers, Chemical Operators, and Non-Thorium Chemical Operators, 196

(Note: Values above the assumed MDA of 6 mg Th are highlighted.) 

All Workers All Thorium Workers All Chemical Operators No

 Year 

Lower 

Bound of 

95% CI for 

95th

Percentile 

95th

Percentile 

Upper 

Bound of 

95% CI for 

95th

Percentile 

Lower 

Bound of 

95% CI for 

95th

Percentile 

95th

Percentile 

Upper 

Bound of 

95% CI for 

95th

Percentile 

Lower 

Bound of 

95% CI for 

95th

Percentile 

95th

Percentile 

Upper 

Bound of 

95% CI for 

95th

Percentile 

Lo

Bou

95% 

9

Perc

1968 4.8 5.5 6.6 5.9 6.9 10.2 5.9 6.8 10.2 31969 7.0 9.0 32.5 5.7 6.8 12.4 5.7 9.1 12.4 1970 4.8 5.7 7.5 5.9 8.6 11.8 4.6 6.2 8.0 21971 5.3 5.7 6.3 6.8 7.3 9.6 5.3 5.9 7.4 51972 4.5 4.9 5.3 4.5 5.3 5.9 4.1 4.7 5.9 31973 3.6 4.1 4.9 2.9 3.2 4.2 3.3 3.9 5.0 31974 4.4 4.8 5.8 4.1 5.5 5.9 3.6 5.1 5.9 31975 4.0 4.6 5.8 2.6 3.1 4.0 3.5 4.0 6.3 31976 4.3 5.2 5.8 3.5 4.8 5.2 4.7 5.4 17.0 41977 3.2 3.6 4.5 2.9 3.9 4.8 2.9 3.6 4.8 21978 5.0 5.7 6.9 5.7 6.1 7.3 4.4 6.1 7.5 4

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NOTICE

wever, th

Table 13. Mean Thorium In-Vivo Test Results of 95% Confidence Interval for the Mean for All W

Workers, Chemical Operators, and Non-Thorium Chemical Operators, 1968 to 1978 

All Workers All Thorium Workers All Chemical Operators Non-T

Year

Lower 

Bound of 

95% CI for 

Mean 

Mean 

Upper 

Bound of 

95% CI for 

Mean 

Lower 

Bound of 

95% CI for 

Mean 

Mean 

Upper 

Bound of 

95% CI for 

Mean 

Lower 

Bound of 

95% CI for 

Mean 

Mean 

Upper 

Bound of 

95% CI for 

Mean 

Lowe

Bound 

95% CI 

Mea

1968 1.7 1.9 2.2 2.8 3.3 3.8 2.5 3.1 3.6 0.4 1969 2.7 3.7 4.6 2.9 4.0 5.0 2.3 4.3 6.3 0.1 1970 2.1 2.4 2.7 2.5 3.8 5.0 1.6 2.4 3.2 0.9 1971 2.3 2.4 2.6 2.7 3.4 4.0 2.4 2.7 3.0 2.2 1972 1.9 2.1 2.3 2.2 2.7 3.3 1.7 2.0 2.3 1.4 1973 1.3 1.5 1.8 1.4 1.8 2.2 1.3 1.6 1.9 1.2 1974 0.5 0.8 1.2 -0.1 1.2 2.4 0.4 0.9 1.3 0.3 1975 0.8 1.1 1.4 -0.3 0.5 1.3 0.7 1.2 1.6 0.7 1976 1.2 1.6 1.9 1.0 1.7 2.4 1.2 1.8 2.4 1.0 1977 0.9 1.1 1.3 0.9 1.4 1.9 0.7 1.0 1.3 0.6 1978 1.9 2.2 2.5 2.1 3.1 4.1 1.8 2.2 2.7 1.5 
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3.3 Analysis of Positive Thorium In-Vivo Results at or Above 6 mg Thorium 

For the comparisons in Sections 3.1 and 3.2, the veracity and utility of the underlying data were 

not questioned. This section provides an overview of the monitoring records that were at or 

above the stated MDA of 6 mg. Overall, there were 2,667 thorium measurements performed 

from 1968 through 1978, with only 76 (<3%) of those measurements at or above the assumed 

MDA of 6 mg. Table 14 provides a summary of the available positive records and how they are 

distributed between the groups of interest. Chemical operators had more positive results than 

thorium workers by a factor of about 1.25; however, chemical operators had more than 3 times 

the number of total samples when compared to thorium workers. 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%).

The median results for all three worker groups are very close in magnitude, with thorium 

workers slightly higher at 7 mg Th. Thorium workers have the lowest average positive result, 

which is likely due to the fact that the maximum result for this worker subgroup was less than 

half that of chemical operators. The very highest result (32.5 mg Th) was for a worker whose 

job title is unknown, but whose plant was designated as “QA or QC.” Curiously, over 1/3 

(~35.5%) of the positive samples were identified with Plant 5, which had no known thorium 

production campaigns.

Table 14. Overview of Positive Th Results 

Worker 

Category 

# Workers 

with Positive 

Results 

# Positive 

Samples 

% of Total 

Samples 

Average 

Result (mg) 

Median 

Result (mg) 

Maximum 

Result (mg) 

Thorium 

Workers1 12 25 7.1% 7.55 7 12.4 

Chemical 

Operators2 21 33 3.1% 8.24 6.8 25 

All Workers3 57 76 2.8% 8.51 6.95 32.5 1

 Includes one worker who had measurements on consecutive days; otherwise, there were at least 4 months between 

samples 2

 All workers had at least 4 months between samples 

3

 Includes one worker who had measurements 1 month apart; otherwise, there were at least 4 months between 

samples 

Thorium workers appear to be well represented when examining the in-vivo results at or above 

the assumed MDA of 6 mg Th. Thorium workers comprised over 20% of the workers who had 

positive results and nearly 1/3 of all positive samples. By comparison, thorium workers 

comprised ~7% of the total number of monitored workers and ~13% of the total samples for Th. 
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4.0 SECTION 2: CORRELATION BETWEEN SAMPLING FREQUENCY AND 

MAGNITUDE OF LUNG BURDEN FOR IN-VIVO URANIUM AND THORIUM 

DURING MAJORITY OF THORIUM PRODUCTION PERIOD 

The second issue discussed in this report regards the premise that workers were selected for 

monitoring frequency based on their exposure potential. According to this premise, the highest 

exposed workers are adequately represented by the available data, and any derived coworker 

model would be biased towards higher exposures. To examine this premise, SC&A compared 

the number of times a particular worker was sampled to the relative magnitude of their calculated 

lung burden (average, median, and maximum in-vivo results). If the frequency of monitoring 

was biased towards the higher exposed individuals, then one would expect a positive linear 

correlation between the two variables. The results of this comparison for uranium (U and U-235) 

and thorium (Th) are summarized in Table 15. Figures 6 through 8 plot the median in-vivo count 

results versus the sampling frequencies for the sampling types presented in Table 15. As in 

Section 1.0, only the period of known thorium production and thorium sampling was examined 

(1968–1978). It is important to note that for this analysis, all negative values were assumed to be 

‘non-detects’ and converted to zero to avoid biasing the results. In-vivo results that were 

positive but less than the assumed MDA of 6 mg were assumed to represent real positive results. 

Table 15. Excel Calculated Linear Trend Line Formulas and Correlation Coefficients 

for Uranium and Thorium Data during Periods of Thorium Production 

Measured Linear Trend Line Formula and Correlation Coefficients 

Radionuclide Average Median Maximum 

U-235 y = 0.0626x + 1.525 

R2 = 0.1469 

y = 0.0535x + 2.0219 

R2 = 0.1133 

y = 0.0531x + 0.4556 

R2 = 0.3895 

U** y = 0.0009x + 4.4191 

R2 = 0.0001 

y = 0.1665x + 3.0844 

R2 = 0.05 

y = 0.1456x + 2.3789 

R2 = 0.2037 

Th y = -0.0475x + 4.1759 

R2 = 0.0003 

y = -0.1657x + 4.402 

R2 = 0.0041 

y = 0.6643x + 1.8825 

R2 = 0.1375 

 * U-235 in-vivo samples may indicate monitoring for enriched uranium 

 ** It is not known what was specifically being measured for the results labeled as ‘U;’ however, that is outside the scope 

of this report and not relevant to the analysis 

As seen in Table 15, the average and median thorium results actually show a slight negative 

linear bias, which does not indicate that the job categories with high exposure potential to 

thorium were counted more frequently. The correlation between the maximum thorium in-vivo 

counting results and the frequency of monitoring showed a positive correlation, but its linear 

correlation coefficient was almost 1/3 that of U-235 and much less than U. With the possible 

exception of average elemental uranium, the average, median and maximum uranium (U and 

U-235) in-vivo results were all positively correlated with the frequency of monitoring. 

Though the coefficients were low, indicating weak correlation, the results may suggest that 

the in-vivo program was driven by exposure potential to uranium5

 (if at all) and not 

thorium. This possibility was discussed in SC&A 2010, Section 3.2, which showed that all 

thorium in-vivo sampling was done at the same time uranium sampling was done, which might 

suggest it was incidental to uranium instead of focused on thorium operations. 

 5

 Table 15 shows that the strongest correlations are for U-235, which might indicate the program was 

actually geared towards workers exposed to enriched uranium. 
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Figure 6. Median U-235 Result versus Number of Samples per Worker (1968–1978) 

Figure 7. Median Uranium (U) Result versus Number of Samples per Worker (1968–

1978) 
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Figure 8. Median Thorium Result versus Number of Samples per Worker (1968–1978) 

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5.0 REFERENCES 

[Redacted] 2007. Interview with [Redacted]and [Redacted] Regarding FEMP. Documented 

Communication – National Institute for Occupational Safety and Health – Oak Ridge Associated 

Universities. August 30, 2007. SRDB Ref ID: 38124. 

Morris 2008. “FMPC Thorium Timeline with Attribution and Annotation.” National Institute 

for Occupational Safety and Health (NIOSH). February 29, 2008. SRDB Ref ID: 42940. 

NIOSH 2008. ORAU Team White Paper Thorium In-Vivo Coworker Study for FEMP – A 

Proposed Attachment for ORAUT-TKBS-0017-5, Rev. 1. National Institute for Occupational 

Safety and Health – Oak Ridge Associated Universities. January 8, 2008. 

NIOSH 2011. Response to SC&A comments on Fernald Th232 coworker study. National 

Institute for Occupational Safety and Health. Posted: February 3, 2011. 

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

for ORAUT-TKBS-0017-5, Rev. 1.” S. Cohen and Associates. June 2010. 

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

SRDB REF ID: 43069. 
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ATTACHMENT 1: LINEAR CORRELATION BETWEEN THE MAGNITUDE AND 

FREQUENCY OF SAMPLING FOR INDIVIDUAL WORKERS FOR ALL IN-VIVO 

RADIONUCLIDES 

While Section 2.0 of this report concentrated on the uranium and thorium monitoring during the 

period of thorium production (1968–1978), this attachment will present all of the in-vivo data for 

all periods of in-vivo measurements. As outlined in Section 2.0, all negative results were 

assumed to be ‘not detectable’ and converted to zero to avoid unduly biasing the results. 

Table 16 displays the linear trend lines and correlation coefficients as calculated by Excel; 

Figures 9 through 38 display the corresponding linear plots. 

Table 16. Excel Calculated Linear Trend Line Formulas and Correlation Coefficients 

for All Data over All Measured Years 

Measured Linear Trend Line Formula and Correlation Coefficients 

Radionuclide Average Median Maximum 

U-235* y = 0.0436x + 3.2901 

R2 = 0.0743 

y = 0.052x + 3.2039 

R2 = 0.0743 

y = 0.0151x + 3.6879 

R2 = 0.086 

U** y = 0.0009x + 4.4191 

R2 = 0.0001 

y = 0.0048x + 4.3994 

R2 = 0.0007 

y = 0.0151x + 3.6879 

R2 = 0.086 

Th*** y = -0.0475x + 4.1759 

R2 = 0.0003 

y = -0.1657x + 4.402 

R2 = 0.0041 

y = 0.6643x + 1.8825 

R2 = 0.1375 

Ac-228 y = 0.8626x + 2.8596 

R2 = 0.0059 

y = 0.6876x + 2.8728 

R2 = 0.0032 

y = 0.9993x + 2.8099 

R2 = 0.0289 

Pb-212 y = 13.236x + 2.6644 

R2 = 0.0759 

y = 11.96x + 2.7432 

R2 = 0.0541 

y = 10.915x + 2.4887 

R2 = 0.1609 

* U-235 analysis includes outlier value of 3,635 μg U-235 in 1987, worker was sampled five times the high result was 

this worker’s final sample 

** U analysis includes outlier value of 1,186 mg U in 1987, worker was only sampled one time 

*** Th analysis includes outlier value of 32.5 mg Th in 1969, worker was only sampled one time 

As noted in Table 16, there were three outlier values (taken for U-235, U and Th) 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. 
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Table 17. Excel Calculated Linear Trend Line Formulas and Correlation Coefficients 

for All Data over All Measured Years Excluding Three Outlier Measurements 

Measured Linear Trend Line Formula and Correlation Coefficients 

Radionuclide Average Median Maximum 

U-235 y = 0.0617x + 2.8509 

R2 = 0.1045 

y = 0.052x + 3.2032 

R2 = 0.0744 

y = 0.0638x + 1.4554 

R2 = 0.3613 

U y = 0.0009x + 4.4191 

R2 = 0.0001 

y = 0.3219x + 2.9252 

R2 = 0.0786 

y = 0.2417x + 2.154 

R2 = 0.2959 

Th y = -0.0183x + 4.1133 

R2 = 3E-05 

y = -0.2155x + 4.4886 

R2 = 0.0042 

y = 0.8224x + 1.392 

R2 = 0.1743 

Figure 9. Average U-235 Result versus Number of Samples per Worker 
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Figure 10. Average U-235 Result versus Number of Samples per Worker 

(scales truncated) 

Figure 11. Median U-235 Result versus Number of Samples per Worker 
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Figure 12. Median U-235 Result versus Number of Samples per Worker 

(scales truncated) 

Figure 13. Maximum U-235 Result versus Number of Samples per Worker 
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Figure 14. Maximum U-235 Result versus Number of Samples per Worker 

(scales truncated) 

Figure 15. Average Uranium Result versus Number of Samples per Worker 
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Figure 16. Average Uranium Result versus Number of Samples per Worker 

(scales truncated) 

Figure 17. Median Uranium Result versus Number of Samples per Worker 
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Figure 18. Median Uranium Result versus Number of Samples per Worker 

(scales truncated) 

Figure 19. Maximum Uranium Result versus Number of Samples per Worker 
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Figure 20. Maximum Uranium Result versus Number of Samples per Worker 

(scales truncated) 

Figure 21. Average Thorium Result versus Number of Samples per Worker 
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Figure 22. Average Thorium Result versus Number of Samples per Worker 

(scales truncated) 

Figure 23. Median Thorium Result versus Number of Samples per Worker 
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Figure 24. Median Thorium Result versus Number of Samples per Worker 

(scales truncated) 

Figure 25. Maximum Thorium Result versus Number of Samples per Worker 
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Figure 26. Maximum Thorium Result versus Number of Samples per Worker 

(scales truncated) 

Figure 27. Average Actinium Result versus Number of Samples per Worker 
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Figure 28. Average Actinium Result versus Number of Samples per Worker 

(scales truncated) 

Figure 29. Median Actinium Result versus Number of Samples per Worker 
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Figure 30. Median Actinium Result versus Number of Samples per Worker 

(scales truncated) 

Figure 31. Maximum Actinium Result versus Number of Samples per Worker 
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Figure 32. Maximum Actinium Result versus Number of Samples per Worker 

(scales truncated) 

Figure 33. Average Pb-212 Result versus Number of Samples per Worker 
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Figure 34. Average Pb-212 Result versus Number of Samples per Worker 

(scales truncated) 

Figure 35. Median Pb-212 Result versus Number of Samples per Worker 
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Figure 36. Median Pb-212 Result versus Number of Samples per Worker 

(scales truncated) 

Figure 37. Maximum Pb-212 Result versus Number of Samples per Worker 
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Figure 38. Maximum Pb-212 Result versus Number of Samples per Worker 

(scales truncated) 

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