f/EPA
United States
Environmental Protection
Agency
Office of Toxic Substances EPA No. 660/5-SS42S
Exposure Evaluation Division Oocumcrt No. NHATS-SS-01
401 M St. SW Septembt 30.1885
Washington D.C. 20460
Toxic Substances
Baseline Estimates and
Time Trends for
Beta-benzene hexachloride,
Hexachlorobenzene, and
Polychlorinated Biphenyls in
Human Adipose Tissue
1970-1983
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V '4'**' " * . *.* • ' -" *• * -1* •
t •- .......'••.
it
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Baseline Estimates and
Time Trends for
6-BHC, BCB and PCBs
in Human Adipose Tissue
1970-1983
Document No. NHATS-SS-01
Prepared by
Gregory A. Mack
BATTELLE COLUMBUS LABORATORIES
505 King Avenue
Columbus, Ohio 43201
and
Leyla Mohadjer
WESTAT, INC.
1650 Research Boulevard
Rocfcville, Maryland 20850
September 30, 1985
Contract No. 68-01-6721
Rich Levy and Janet Remmers, EPA Task Managers
Joseph Carra and Joseph Breen, EPA Project Officers
i Prepared for
Design and Development Branch
Field Studies Branch
Exposure Evaluation Division
' Office of Pesticides and Toxic Substances
1 U.S. Environmental Protection Agency
Washington, D.C. 20460
U.S. Environmental Protection Agency
Region 5, Library (PL-12J)
77 West Jackson Boulevard, 12th Floor
Chicago, IL 60604-3590
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TABLE OP CONTENTS
ACKNOWLEDGMENTS
PREFACE , .
EXECUTIVE SUMMARY
1.0 INTRODUCTION
1.1 Background
1.2 Objectives and Scope of the Statistical
Analysis
2.0 DATA COLLECTION AND PREPARATION
2.1 Survey Design
2.2 Available Data and Data Preparation
2.2.1 Available Data
2.2.2 Data Preparation
2.3 Sample Weights
2.4 Limitations of Statistical Inference
3.0 RESULTS OF THE STATISTICAL ANALYSIS
3.1 Estimates of population Baseline Levels
3.1.1 Population Estimates for B-BHC
3.1.2 Population Estimates for RCB
3.1.3 Population Estimates for PCBs
3.2 Time Trend Analyses
3.2.1 Time Trend Estimates for B-BHC
3.2.2 Time Trend Estimates for RCB
3.2.3 Time Trend Estimates for PCBs
4.0 REFERENCES
LIST OF APPENDICES
APPENDIX A
APPENDIX B
B.1 STATISTICAL MODELS ,
B.2 APPROACH TO THE TIME TREND MODELING
B.2.1 National Time Trends
B.2.2 investigation of Time Trend Differences
Across Subpopulations ,
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ACKNOWLEDGMENTS
The authors would like to thank the EPA Task Manager, Mr.
Rich Levy, for his assistance in performing this study. Bis
suggestions and technical comments were invaluable in producing a
more comprehensive, higher quality statistical analysis.
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11
PREFACE
This document is one in a series that collecti'
describes the operation and results of the National Human Adi;
Tissue Survey (NHATS). Each document provides -the comp
details for a particular aspect of the NRATS program. This re;
presents the results of a statistical analysis of baseline le
and time trends for several toxic compounds. The anal
addresses the three compounds: Beta-benzene hexachloride (6-8
hexachlorobenzene (RGB), and polychlorinated biphenyls (PCBs)
is based on data collected through fiscal year 1983.
Other documents in the NHATS series describe
statistical survey design, the chemical analysis and
techniques/ and other statistical analyses and special stu
related to NHATS. (See the list of documents on the next page
References to the series provide interested individ
complete information concerning the NHATS program. Each docu
in the series is being maintained and updated as modification
the NHATS program requires it. Additional documents wil]
added as special analyses or studies are conducted.
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Ill
Documentation Series for the
National Human Adipose Tissue Survey
NHATS-ST-01
NHATS-SD-01
NHATS-SS-01
NHATS-SS-02
NHATS-DM-01
Mack, G.A., and Stanley, J. "Program Strategy
for the National Human Adipose Tissue Survey",
prepared by Battelle's Columbus Laboratories
and Midwest Research Institute for the Office
of Toxic Substances of the U.S. Environmental
Protection Agency, Washington, D.C., 20460
(August, 1984).
Mack, G.A., Leczynski, B., Chu, A., and
Monadjer, L. "Survey Design for the National
Human Adipose Tissue Survey", prepared by
Battelle's Columbus Laboratories and Westat,
Inc. for the Office of Toxic Substances
of the U.S. Environmental Protection Agency,
Washington, D.C., 20460 (November, 1984).
Mack, G.A., and Mohadjer, L. "Statistical
Analysis of Toxic Residue Levels of 8-BHC,
HCB, and PCBs in Human Adipose Tissue
1970-1983", prepared by Battelle's Columbus
Laboratories and Westat, Inc. for the Office
of Toxic Substances, U.S. Environmental
Protection Agency, Washington, D.C., 20460
(November, 1984).
Leczynski, B., and Stockrahm, J. "An
Evaluation of Hexachlorobenzene Body Burden
Levels in the General U.S. Population",
presented by Battelle's Columbus Laboratories
for the Office of Toxic Substances of the
U.S. Environmental Protection Agency,
Washington, D.C., 20460 (January, 1985).
•National Human Adipose Tissue Survey,
Documentation Manual, Data Base Structures
and Program Descriptions", prepared by
Battelle's Columbus Laboratories for the
Office of Toxic Substances of the U.S.
Environmental Protection Agency, Washington,
D.C., 20460 (May, 1985).
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I
I
I
iv
1 EXECUTIVE SUMMARY
* The National Human Adipose Tissue Survey (NHATS) is
I annual program to collect and chemically analyze a nationw
i sample of adipose tissue specimens for the presence-of specif
toxic compounds. The objective of the program is to detect <
quantify the prevalences of toxic compounds in the gene:
population. The specimens are collected from autopsied cadavi
j and surgical patients according to a statistical survey desii
The survey design ensures that specified geographical regions <
demographic categories are appropriately represented to peri
valid and precise estimates of baseline levels, time trends .
comparisons across subpopulations. The NHATS data are used
address part of OTS's mandate under TSCA to assess cheraii
exposure risk and environmental burden to the U.S. populatii
Since NHATS involves human monitoring, it provides dir<
evidence of exposure of the toxic chemicals to humans.
In order to obtain full use of the NHATS progr<
statistical analyses are periodically conducted on the collec
data. This report presents the analysis results for the compoui
beta-benzene hexachloride (8-BHC), hexachlorobenzene (HCB), i
polychlorinated biphenyls (PCBs). These compounds were selec
for this study due to their prevalence and toxicity and th<
industrial uses which put them under the jurisdiction of TS(
The analyses involve data collected through fiscal year 191
with the results for 1981 and 1983 being of particular inter*
since they are based on additional data collected since the 1<
statistical analysis.
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The major findings of the analysis are as follows:
B-BHC
• The estimated 1983 national median* level
is 0.08 ppm compared to an historic**
level of 0.14 ppm.
• The median levels tend to increase with
age but do not differ across sexes or race
groups.
• The South Census Region has a higher
median level than any of the other
regions.
• The median level has been steadily
decreasing over time but the percentage of
the population having at least a
detectable level has remained near 100
percent.
HCB
The estimated 1983 national median level
is 0.031 ppm compared to an historic level
of 0.037 ppm.
The levels do not differ significantly
across the age, sex and race groups.
The West Census Region has a higher median
level than any of the other regions.
Median levels have remained relatively the
same over the past ten years with the
exception of a modest estimated drop of
about 0.01 ppm in 1983. The percentage of
the population having at least a
detectable level of HCB has remained near
100 percent.
* Median level refers to that value for which half the
population have residue levels exceeding this value and half
have residue levels below it.
** Historic level refers to the median level computed using data
for all years for which NHATS data are available.
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t
* PCBS
VI
• The 1983 estimated percentage of the
population having a PCB level exceeding 1
ppm is 5.5 percent compared to an historic
level of 28.9 percent.
• The percentage having a PCB level
exceeding 1 ppm increases with age. Males
have a higher percentage exceeding 1 ppm
than females. No significant race
difference exists.
• The Northeast Census Region historically
had the greatest percentage exceeding 1
ppm but the difference has disappeared in
recent years.
• The percentage of the population having
PCB levels exceeding 1 ppm is steadily
decreasing over time; however, the
percentage having at least a detectable
level has increased to nearly 100 percent.
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' 1.0 INTRODUCTION
' 1.1 Background
I
I The National Human Adipose Tissue Survey (NHATSJ is one
of the main programs of the National Human Monitoring Program
i
j (NHMP). NHMP is an ongoing chemical monitoring network designed
to fulfill the human and environmental monitoring mandates of the
Toxic Substances Control Act (TSCA). The NHMP was first
•established by the U.S. Public Health Service in 1967, and was
subsequently transferred to EPA in 1970. During 1979 the program
i
was transferred within EPA to the Exposure Evaluation Division of
< the Office of Toxic Substances (OTS).
The data for the National Human Adipose Tissue Survey
are generated on an annual basis by collecting and chemically
analyzing adipose tissue specimens for selected toxic substances,
historically organochlorine compounds and polychlorinated
biphenyls (PCBs). The 20 compounds that have been monitored are
listed in Table 1-1.
TABLE 1-1 COMPOUNDS MONITORED IN THE NATIONAL
HUMAN ADIPOSE TISSUE SURVEY
£, £' - DDT Aldrin
o, £' - DDT Dieldrin
£, £' - DDE Endrin
o, £' - DDE Heptachlor
£, £' - DDD Heptachlor epoxide
o, £' - DDD PCBs
a - BHC ' Oxychlordane
6 - BHC ' Mirex
Y - BBC (Lindane) trans-Nonachlor
6 - BHC Hexachlorobenzene
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I
The adipose tissue specimens are obtained fron
I statistically selected sample of surgical patients and autops
• cadavers. Selected pathologists and medical examiners collect
, tissue specimens on a continuing basis throughout the fiscal j
i along with a limited amount of demographic, occupational,
medical information on the individual.
1 Statistical analyses are periodically conducted on
collected data. The analyses provide updated informal
concerning baseline levels of the toxic residues in the I
population and provide evidence of any changes in tine trer
This report presents the results of the most recent statist:
analysis for the compounds: 6-8HC, HCB, and PCBs. The anal]
were conducted during the summer of 1984 and include
information on residue levels through fiscal year 1983.
1.2 Objectives and Scope of the Statistical Analysis
The purpose of the NHATS program is the detection
quantification of the prevalences of selected toxic compounds
the general population. The presence of toxic substances in
adipose tissue of the U.S. population is an indication of tl
presence in the environment. By selecting and chemici
analyzing the tissues of a representative sample of individu.
i information is gathered concerning existing toxic residue le1
in the U.S. population and its various subpopulations.
specific objectives of the NHATS program are:
i
1. To assess the prevalences of toxic
substances in the adipose tissue of the
* U.S. population
i 2. To establish baseline levels for these
compounds in adipose tissue
3. To measure time trends of these concen-
trations, and
4. To assess the effects of regulatory
actions.
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These objectives are addressed by statistically analyz-
ing the collected data. The analyses include:
• Estimation of percentages of the
population having detectable residue
levels or levels exceeding specified
values;
• Estimation of average residue levels for
the entire nation and for various subpop-
ulations involving geographic (census
regions) and demographic (age, sex, and
race) categories;
• Estimation of trends to assess changes
over time in various population residue
level characteristics such as:
average residue level
- median level
- percentage of population having detect-
able residue levels
percentages of the population exceeding
various specified levels
• Regression analyses to assess differences
in the trends across the various
geographic and demographic subpopulations.
The specific data used in the analyses are described in
the next section along with information concerning their collec-
tion and preparation.
7
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2.0 DATA COLLECTION AND PREPARATION
2.1 Survey Design
i The NHATS program uses a statistical .based sur
sampling design to obtain adipose tissue specimens from
] national sample of autopsied cadavers and surgical patients. '
use of a statistical design provides for control of the possil
estimation errors due to sampling only a portion of
population of interest. The use of a statistical design alL
the magnitudes of the sampling errors to be quantified and t
used to calculate bounds on the likely errors (standard erro
associated with the population residue level estimates that <
made.
The target population for this study corresponds to
set of all non-institutionalized individuals in the contermim
U.S. However, due to the invasive nature of collecting adip
tissue samples, the sampling population is limited to cadav<
and surgical patients. The sampling procedure used to addr<
this population is a complex multi-stage process. The
conterminous states are stratified into the nine D..S. cen
divisions (Refer to the U.S. map given in Figure 2-1). Hit:
each census division, population centers (ie. SKSAs- stand
metropolitan statistical areas) are selected with probabilit
proportional to their respective populations. The number
SNSAs selected from each census division is determined by
division's total SMS A population relative to the total SI
population of the entire U.S. Within each selected SMSA one
more hospitals and/or associated pathologists/medical examine
are identified and asked to contribute tissue specimens accord
to design specifications involving age, sex, and race. '
categories considered are:
• Age group (0-14 years, 15-44 years, 45* years)
• sex (male, female)
• race (white, non-white).
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The design specifications are based on the corresponding age,
and race U.S. census population figures for the census divis
to which the SMSA belongs. The actual specimens are otherv
selected in a non-probabilistic manner according to the judgem
of the pathologists/medical examiners involved.
An overview of the sampling stages is presented
Figure 2-2. The geographic stratification used in the dec
ensures a representative sample from all regions of the count
Design specifications for the age, sex and race categories en*
the proper representation for each of these different subp
ulations. A detailed description of the current survey design
be found in Mack et. al. (5).
Although the actual survey design uses census divis
as the stratification variable, geographical comparisons in
statistical analyses are based on census regions (
Figure 2-1). The use of census regions in the analysis redu
the number of subpopulation comparisons and reduces the degr
of-freedom needed for model fitting. No additional techni
problems are introduced and all results remain statistica
valid.
2.2 Available Data and Data Preparation
2.2.1 Available Data
The amount of data used in the statistical analy
varied for the three compounds of interest due to missing d
and various problems encountered during the earlier years of
NBATS program. Table 2-1 summarizes the specific years
numbers of specimens available for the analysis for e
compound.
The data for 1981 and 1983 correspond to only a port
of the specimens actually collected. For each of these
years, subsamples of specimens were selected and chemica
analyzed so that some information would be available as quic
as possible concerning existing residue levels. Each subsam;
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Stratify by
Geographical
Region
Nine Census Divisions
Select Probability
Sample of SNSAs
Within Bach Region
Two to Seven SMSAs
Within Bach Region
Select One or
More Hospitals
Prom Each SMSA
Approximately 40
Hospitals in
Total Survey
Select Specimens
.According to Design
Specifications Based
On Age, Sex and Race
Approximately 1,000 - 1,500
Specimens in Annual Survey
Pigore 2.2. Overview of the annual selection process
7
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TABLE 2-1. SUMMARY OF DATA USED IN THE
ANALYSES FOR EACH COMPOUND
Fiscal Year
1970
1971
1972
1973
1974
1975
1976
1977
1978
1979
1980
1981
1982
1983
B-BHC
1403
1587
1993
1186
1025
895
778
926
948
910
--
402
--
200
HCB
•» • mt
~
—
--
1025
895
777
927
947
908
--
402
--
200
PCBs
^—
..
1826
1183
1025
895
779
927
951
910
--
402
--
200
corresponded to a representative sample of the entire collec
of that year's specimens. Additional subsamples are to
analyzed as money and time permit. The fiscal year
data included in this study correspond to three sepa
subsamples while the 1983 data correspond to two subsamp
Since the sample size affects the size of the standard e
associated with a population estimate, estimates for 1981
1983 tend to have larger error bounds associated with them.
2.2.2 Data Preparation
Due to the nature of the chemical analysis proo
there txists a threshold value below which the chemist ca
accurately quantify the residue level of a target compound :
given specimen. This threshold is called the level
quantification (LOQ). Below the LOQ there exists ano
threshold called the level of detection (LOD) below which
chemist cannot even declare that the presence of the compoum
detected. Values below the LOD are recorded as "not detect*
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Measured values between the LOD and LOQ are called trace values.
Trace values indicate the target compound has been detected but
at a level below which an accurate determination can be made of
the specific amount. See Table B.I in Appendix B for approximate
values of the LOD and LOQ for each of the compounds addrefsed in
this study.
In the statistical analyses, residue values reported as
being below the LOD ("not detected") were set equal to zero.
Trace values for a given compound and fiscal year were all set
equal to the minimum positive residue value, above the LOD,
reported for that year.
The residue data were also adjusted for the percent
lipid content of the associated tissue specimen. The
adjustment formula used is as follows:
Unadjusted Level ,nn.
Adjusted Level - % Lipid * xuu*
Since the chemicals addressed in the report tend to be located
only in the lipid portion of the tissue, the adjustment makes the
observed residue levels more comparable across tissue samples
having varying levels of percent lipid. The statistical analyses
excluded any specimens having less than 10 percent lipid content.
Such specimens do not permit precise determinations to be made of
the actual residue level.
In some of the statistical analyses the data were
transformed by taking logarithms of the original data. In those
cases where the original data value was zero (e.g., no analyte
was detected), a small positive number (e.g., .0005 ppm),
representing a value between zero and the LOD, was substituted
for zero. Any resulting bias is expected to be negligible since
there were relatively few such cases.
The data for PCBs were handled somewhat differently.
The PCB level for each specimen was reported by the chemical
analysis labs only as belonging to one of four categories:
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I
4 10
• Not detected (below LOD)
• Detected but less than 1 ppm
• Between 1 and 3 ppm
• Greater than 3 ppm.
The PCB data were categorized due to the nature of
chemical analysis methods that made it difficult to obtain
accurate determination of the actual amount.
Due to the categorical nature of the reported PCB da
they were not lipid adjusted (however, Lucas (3) has shown t
the effect of not lipid adjusting is inconsequential for PCB
and the statistical analyses did not address the estimation
average levels. Rather, estimates wer« made of the populat
percentages belonging to various range levels of interest.
2.3 Sample Heights
Calculation of unbiased estimates of regional
national population residue levels and trends require the use
weighted statistical data. Individuals from some demograp
groups represent smaller segments of the U.S. population
therefore the observed residue levels associated with t
deserve less weight when estimating population residue leve
Although design specifications are given regarding the number
specimens to be collected from each age, race, sex and cen
division category, the NHATS program does not produce se
weighting samples for several reasons:
• The small sample sizes for each SMSA
(approximately 27 specimens) do not permit
the exact proportionate selection of the
appropriate number of specimens from each
age, race, and sex category and
geographical region; and
Discrepancies between the actual number of
samples collected and the design specifi-
cations for each collection site..
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11
The weight assigned to each individual specimen
reflects the number of individuals in the general population
represented by that specimen. Various adjustments are performed
so that the sum of the sample weights for a given geographical
region and demographic category equals the corresponding
population count according to the U.S. Census. The weights for
1970 through 1972 are based on the 1960 Census; the 1973 through
1979 weights are based on the 1970 Census; and the 1981 and 1983
weights are based on the 1980 Census. The details of the
methodology used to construct the sample weights are given in
Appendix A of a report by Lucas et.al. (3).
2.4 Limitations of Statistical Inference
The sampling population for the NHATS program includes
only surgical patients and autopsied cadavers. Since the sampled
population is different from the target population (i.e., the
entire U.S.), validity of any inferences requires the assumption
that the prevalences and levels of the toxic substances of
interest are the same in both populations.
Other limitations result from the survey design and its
implementation. Since population centers (SMSAs) form the
sampling frame, areas that are rural in character are excluded
from the sample. A sizable percent of the U.S. population resides
in these rural areas. The real percentage of omission is most
likely somewhat less, however, because the service areas of
hospitals in the SMSAs extend into neighboring rural areas.
Nonetheless, the urban nature of the sample does result in some
undercowrage of the rural population;
Limitations also result from the purposeful selection
of the medical examiners and pathologists and the lack of
probability sampling used by them in selecting tissue specimens
for the study. The purposeful selection methods may result in
biases in estimates derived from the sample. However, the biases
are expected to be minimal for several reasons:
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12
(1) The selection of specimens are done on a
pseudo-random basis without regard to
Iany factors that are likely to be
systematically related to toxic residue
levels.
! (2) The specimens are screened so that- the
1 selected ones involve only traumatic
deaths and specific diseases not
• expected to influence the toxic residue
levels in the body.
(3) Target quotas control the number of
specimens collected with respect to some
of the most important factors: age,
race, and sex. Further, deviations from
target quotas are minimized by the use
of weights applied to each specimen when
making statistical estimates.
Any remaining biases are expected to be negligible relatii
the magnitudes of the trends and other subpopulation differ
that have been observed.
The chemical analysis techniques employed over
years in the NHATS program is another potential source for
The analysis methods changed at the end of 1974. However
investigation by Lucas et.al. (3) of the possible effects o:
change on PCS trends indicated that the effects are inc
quential.
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13
I
3.0 RESULTS OP THE STATISTICAL ANALYSIS
• The objective of the NHATS program is the detection and
, quantification of the prevalences of selected toxic chemicals in
the U.S. population. To address this objective a statistical
analysis was performed on the collected data. The -analysis
included:
• Estimation of population residue levels
for the purpose of establishing baseline
levels;
• Estimation of time trends to assess
changes in residue levels over time; and
• Comparison of various subpopulations to
identify geographic and demographic fact-
ors associated with differences in the
toxic residue levels.
The results of these analyses for the compounds 6-BHC,
HCB and PCBs are described in the following sections.
3.1 Estimates of Population Baseline Levels
Estimation of population baseline levels involves the
calculation of various summary values that characterize
particular aspects of the distribution of residue levels. The
following population characteristics were estimated:
• Average individual residue level
• Median (50th percentile),residue level
• Percentage of individuals having detecta-
ble levels of the toxic compound
• Percentage of individuals having quantifi-
able levels
• Percentages of individuals having residue
levels exceeding . specific values of
interest.
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I
I
14
j
To provide support concerning the reliability of t
estimates the following auxiliary information is also given:
I
• standard errors of the estimates
• sample sizes used in the calculations
• size of the population represented by each
estimate.
The estimates were made both for a single comb
population representing the entire nation, and for var
subpopulations defined by age, sex, race, and geographic re
categories. The estimates were calculated in two different w
(1) using combined data for all fiscal years; and (2) separa
by fiscal year.
A computer program called SESUDAAN (6) was used
calculate the estimates. The techniques used by SESUDAAN
required because of the complex survey design used to collect
sample specimens. The results for the three compounds addre
in this report are presented in the following sections.
3.1'. 1 Population Estimates for 6-BHC
Table 3.1-1 presents estimated population res
levels for the compound B-BHC. Estimates are given separately
each subpopulation as well as for the entire nation.
estimates are based on combined data for all fiscal years
represent baseline levels for the presence of 6-BHC in the
population. For the entire nation the estimated levels are:
• Average individual residue level—0.27 ppm
• Median residue level--0.14 ppm
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] • Percent of the population having detect-
able levels of B-BHC—98.7 percent
I • Percent of the population having
quantifiable levels of B-BHC—92.8
( percent.
I
The baseline levels vary across the diffe
• geographic and demographic groups. A comparison of these sub
ulations indicate:
• AVERAGE B-BHC LEVELS
- Average levels increase with age*
South Census Region has a higher
average level than the Northeast and
North Central regions
• MEDIAN B-BHC LEVELS
Levels increase with age
South Census Region has a higher median
level than all the other regions
• DETECTABLE LEVELS OF B-BHC
- There are no differences in subpop-
ulations with respect to the percentage
of individuals having detectable levels
of B-BHC
• QUANTIFIABLE LEVELS OF B-BHC
- The "0-14 yrs" age group has a lower
percentage of individuals having
quantifiable levels of B-BHC; no other
differences exist among subpopulations
*A difference in levels was declared whenever individual
confidence intervals for the true average levels for two or i
subpopulations were non-overlapping.
-------
17
Tables A.I - A. 12 in Appendix A present the baseline
estimates separately for each fiscal year. Comparison of the
subpopulations separately for each fiscal year indicates the sane
general results as obtained for the combined data. The increasing
trend in B-BHC levels vith age group tends to hold for each year.
Similarly, the South Census Region consistently had much higher
average levels than the others. Although the differences are
often not statistically significant for a given year (due to
smaller sample sizes), the differences are meaningful since they
consistently occur over the different years.
Tables A. 11 and A. 12 for fiscal years 1981 and 1983,
respectively, show that the baseline levels for the median
residue amounts have decreased relative to earlier years. Table
3.1-2 on the next page summarizes the differences.
3.1.2 Population Estimates for BCB
Table 3.1-3 presents the baseline estimates for HCB.
The estimates are based on the combined data for all fiscal
years. The estimated baseline levels for the nation are as
follows:
• Average individual residue level—0.053
ppm
• Median (50th percentile) residue level—
0.037 ppm
e Percentage of the population having
detectable levels of HCB--98.8 percent
e Percentage having quantifiable levels—
92.9 percent.
-------
18
TABLE 3.1-2.
COMPARISON OF 6-BHC BASELINE MEDIAN LEVELS 1
FOR 1981 AND 1983 AGAINST ALL TEARS COMBINE!
Estimated Median Residue Level*
All Years
Subpopulation Combined 1981 1983
Age (in years):
0-14
15-44
45+
Sex:
Male
Female
Race:
White
Non-White
Census Region:
Northeast
North Central
South
West
Entire Nation
.08
.14
.26
.14
.15
.14
.16
.13
.12
.21
.12
.14
.05
.08
.18
.08
.11
.09
.12
.07
.09
.14
.06
.09
.06
.06
.17
.08
.09
.08
.08
.07
.07
.13
.06
.08
*parts per million, adjusted for lipid content of specimen
-------
19
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Comparison of the residue levels across the sub]
ulations indicates the following results:
• AVERAGE HCB LEVELS
I
I - No age, sex or race differences exis.£
I - West Census Region has a higher average
! level than the North Central and South
regions
j • MEDIAN HCB LEVELS
• "0-14 yrs" age group has a lover median
level than the older age groups; no
other age, sex or race differences
exist
- West Census Region has a significantly
higher median than all the other
regions
• DETECTABLE LEVELS OF HCB
- No differences exist among any of the
subpopulations
• QUANTIFIABLE LEVELS OF HCB
- The "0-14 yrs" age group has a much
lower percentage than the older groups;
no other age, sex, race or census
region differences exist.
Tables A. 13 through A. 20 in Appendix A present
baseline estimates separately for each fiscal year.
I differences among subpopulations are generally not statistic
significant and not always consistent in trend. However,
appears that some meaningful differences do exist since cer
differences tend to be present for many of the years. The
Region has much higher HCB levels than the others; and the "
years" age group has lower percentages of individuals ha
quantifiable levels.
-------
21
Table 3.1-4 presents a comparison of median RGB levels
I for 1981 and 1983, respectively, against the overall median
* calculated using data for all years combined. The values for
11983 show a decline in HCB levels relative to the levels
calculated for all years and also relative to the 1981 levels
alone.
* •
3.1.3 Population Estimates for PCBs
i
\
Since only categorical data are available for PCBs, the
statistical analyses were directed at estimating population
percentages falling into various residue range levels. Table
3.1-5 presents these results for the range levels of interest.
The estimated national baseline percentages are as follows:
• Percentage of the population having
detectable levels of PCBs — 95.3 percent
• Percentage having levels exceeding 1 ppm
-- 28.9 percent
e Percentage having levels exceeding 3 ppm
-- 5.1 percent
1 Comparison of results across subpopulations indicate
the following:
i
• PERCENTAGE HAVING DETECTABLE LEVELS
I - The "0-14 yrs" age group has a smaller
percentage having detectable levels of
. PCBs
• PERCENTAGE EXCEEDING 1 PPM
| - The "0-14 yrs" age group has a smaller
percentage of individuals exceeding
1 ppm
I
- Males have a higher percentage
exceeding 1 ppm than females
,L
-------
22
TABLE 3.1-4. COMPARISON OF HCB MEDIAN LEVELS FOR 1981
AND 1983 AGAINST ALL TEARS COMBINED
Estimated Median Residue Level*
All Years
Subpopulation Combined 1981 1983*
Age (in years) :
0-14
15-44
454-
Sex:
Male
Female
Race:
White
Non-White
Census Region:
Northeast
North Central
South
West
Entire Nation
.030
.039
.042
.039
.035
.037
.033
.036
.033
.030
.063
.037
.033
.041
.050
.043
.040
.041
.044
.036
.040
.038
.059
.041
.028
.029
.037
.034
.028
.031
.031
.031
.032
.024
.044
.031
*parts per million, adjusted for lipid content of specimen
-------
23
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24
• PERCENTAGE EXCEEDING 3 PPM
- The "0-14 yrs" age group has a smaller
percentage of individuals exceeding 3
ppm
I
i - The percentage of non-whites exceeding
3 ppm is greater than the percentage of
uV J k A mt
- Northeast Census Region has a greater
percentage of individuals exceeding 3
ppm than all the other regions.
Baseline data for the individual fiscal years a
presented in Tables A. 21 through A.30. The trends previous
cited generally hold for the individual years as well. T
percentages of individuals having PCB levels exceeding 1 ppm a
consistently smaller for the "0-14 years" age group. Mai
consistently had greater percentages exceeding 1 ppm than d
females. The Northeast Census Region historically had high
percentages exceeding both 1 and 3 ppm; however, in recent yea
this difference has disappeared. Non-whites had great
percentages exceeding 3 ppm than did whites.
The baseline levels given in Table 3.1-6 for 1981 i
1983 indicate a considerable decline in the percentage
individuals having PCB levels greater than 1 ppm. Th
corresponds to a similar drop in the percentage of PCB leve
exceeding 3 ppm cited in an earlier report by Lucas et.al. (
and confirmed in this report by Tables A. 29 and A. 30. Not
however, from Tables A.29 and A.30 that the percentage of samp]
individuals having detectable levels of PCBs has increased to ]
percent for the 1981 and 1983 fiscal years.
3.2 Ti»e Trend Analyses
The investigation of trends involves the estimation
changes in residue level distributions over time. Specifica:
this involves the comparison over time of residue distribut:
-------
25
TABLE 3.1-6. COMPARISON OP PCB BASELINE LEVELS FOR 1981
AND 1983 AGAINST ALL TEARS COMBINED
Estimated Percent Greater than 1 ppm
All Tears
Subpopulation Combined 1981 1983 -
Age (in years):
0-14
15-44
45+
Sex:
Male
Female
Race :
White
Non-White
Census Region:
Northeast
North Central
South
West
Entire Nation
12.3
32.2
39.3
32.9
25.1
28.4
32.4
37.1
26.5
27.2
24.8
28.9
12.1
16.1
23.7
17.7
17.4
15.0
31.5
12.2
18.9
17.8
21.3
17.5
3.1
3.6
9.9
10.9
0.3
6.0
1.9
2.4
10.2
4.9
3.5
5.5
-------
I
26
t
characteristics. Since the distribution of individual residi
I levels is skewed, it is useful to address a number of differei
1 distribution characteristics to adequately describe the chang<
in residue levels.
The population average amount and median (50
percentile) are both measures of central tendency th
' characterize the "typical" residue level. The percentage
t
detectable levels and percentage of quantifiable leve
characterize the prevalences of a toxic compound while the upp
percentiles of a distribution characterize the extreme values.
The estimation of time trends and their differenc
across geographic and demographic subpopulations are based on t
use of a statistical model. The model expresses the assumed fo
of the relationship between the residue level characterist
under investigation and the temporal, geographic and deraograph
factors of interest. Details concerning the various forms
models used in this study are given in Appendix 8.
This report presents estimates of national trends for
variety of different population characteristics. The natior
trends represent weighted averages over the differe
subpopulations to give a single estimated trend for the enti
U.S.
This report also presents separate trends for t
individual subpopulations. The subpopulation trends i
presented only for two population characteristics considered
be the most important and meaningful: percentage of individue
having detectable levels and the median levels. For statistic
reasons the median was considered to be more appropriate than 1
average level. The skewness of the residue distribution ma)
the statistical analysis more valid when based on averages
log-transformed data, which then correspond to an analysis
medians when transformed back to the original data scale (ppm).
The following sections present a summary of the ma;
results for each of the three compounds of interest: 6-BHC, H<
and PCBs. The effects of the fiscal years 1981 and 1983 on
-------
29
• u
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30
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27
estimated trends are of particular interest since the data for
these years have been updated to include additional information
since the last statistical analysis of the NHATS data.
3.2.1 Tiae Trend Estimates for 0-BBC
Plots of national time trend estimates for 6-BHC are
given in Figures 3.2-1 through 3.2-4 for the different residue
distribution characteristics of interest. The estimated trend
given in each figure is represented by the dashed line while the
•olid lines represent 95 percent confidence bands for the trend.
The individual plotted points correspond to point estimates
computed separately from the data for each fiscal year. The
points provide a comparison of how well the estimated trend
describes the actual changes in levels across the fiscal years.
The national trends for 6-BHC indicate the following:
• The percentage of individuals having
detectable levels of 6-BHC has remained
fairly constant near 100 percent
• The percentage of individuals having
quantifiable levels is decreasing
• The average 6-BHC level is declining from
an estimated level of 0.45 ppm in 1970 to
about 0.16 since 1981
• The median level is also estimated to be
decreasing
Summarizing the results for the national trends, it
appears that the percentage of the population having at least a
detectable level of 6-BHC is remaining near 100 -percent.
However, the actual levels of e-BHC are decreasing. Further
information concerning the estimated model coefficients and
associated significance levels are given in Table B.2 in Appendix
B.
-------
28
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32
I
I
Figures 3.2-5 through 3.2-8 present the estimated
trends for the different demographic and geographic
subpopulations for the percentage of individuals having
detectable levels of g-BRC. Figures 3.2-9 through 3.2-12 present
) the trend estimates for the median level of B-BHC. The plotted
trends correspond to predicted values generated from statistical
! models described in Table B.8. For further details concerning how
the trend plots were generated, see Appendix B.
. For the percentage of individuals having detectable
levels of B-BHC the comparison of trends across the different
subpopulations reveal there are no practical differences. The
only statistical differences involve the absolute levels across
the age groups; there are no statistically significant trenc
differences.
Analysis of trends for the median level of 8-BHC
indicate the following results:
• The time trends are significantly
different across the age groups. The
medians are declining for all three age
groups, however, the youngest age group
has declined less since the levels were
already lower than the other older groups.
• There is no significant difference in the
time trends or the absolute levels between
the two race groups
• There is no significant difference in the
time trends between sexes but there is a
difference in the absolute level between
sexes (females tend to have slightly
higher levels)
• There are no significant differences in
time trends among the four census regions;
however, there are differences in the
absolute levels among the regions. The
South Region has the highest levels.
-------
33
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!
3.2.2 Time Trend Estimates for HCB
• Plots of national estimates of time trends, 95 percent
. confidence bands, and individual point estimates for HCB are
j given in Figures 3.2-13 through 3.2-16 for several population
residue characteristics. The results indicate:
• The percentage of individuals having
detectable levels of HCB has remained near
100 percent
• There is no signficant trend in the
percentage of individuals having quanti-
fiable levels
e The trends for both the average and median
levels of HCB indicate a statistically
significant quadratic trend; however, the
actual changes in levels are minimal with
the exception of about a .01 ppm drop in
1983.
Summarizing the national trends for HCB, the prevalence
of RCB in the population is remaining near 100 percent and the
actual levels have remained relatively constant with the
exception of a drop in 1983. Information concerning the estimated
model coefficients and the associated statistical significance
levels are given in Table B.3 in Appendix B.
Figures 3.2-17 through 3.2-20 present the estimated
time trends for the different demographic and geographic groups
for the percentage of individuals having detectable RCB levels.
Figures 3.2-21 through 3.2-24 present the estimated trends for
the median levels. The statistical models used to estimate the
trends presented in these figures are described in Table B.9 in
Appendix B.
The comparison of RCB trends indicate there are no
significant differences among any of the subpopulations with
respect to the percentage of individuals having detectable levels
of HCB. For the median levels, comparison of the subpopulations
indicates the following results:
-------
42
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I
1
• The time trends are different across the
age groups; the "0-14 yrs" age group
levels have remained fairly constant while
the other groups (particularly the oldest
group) had elevated levels for several
years during the late seventies
• There is no significant difference in time
trends or absolute levels between the two
race groups
• There is no significant difference in time
trends between the sexes; however, there
is a difference in the absolute levels
(males have higher levels)
• There are no significant differences in
time trends across the census regions;
however, there are differences in the
absolute levels. The West Region has the
highest levels.
3.2.3 Time Trend Estimates for PCBs
Since the data for PCBs indicate only the residue leve
range to which a tissue specimen belongs, the results presente
here correspond to the population percentages of individual
estimated to have PCB levels exceeding specific values.
An earlier NHATS report by Lucas et.al (3) indicate
that the estimated population percentage of individuals havin
total PCB levels greater than 3 ppm had fallen to near zero
Figure 3.2-25 indicates that additional data collected since the
also confirms this finding. The emphasis in this study therefor
involved the estimation of the percentage of individuals havin
PCB levels greater than 1 ppm. Figure 3.2-26 presents th
estimated trend for the percentage of PCB levels exceeding 1 ppm
This indicates a significant decreasing trend from a high valu
near 50 percent in 1972 to a low value near 9 percent in 1983.
Although the PCB amounts are decreasing, the percentag
of individuals having detectable levels is increasing up to
1983 value near 100 percent. Figure 3.2-27 presents a plot of th
estimated time trend for the percentage of individuals havir
-------
55
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58
detectable PCS levels. Information concerning the estimated trenc
model coefficients and their associated significance levels ii
presented in Table B.4 in Appendix B.
Figures 3.2-28 through 3.2-31 present the estimate<
trends for "percent detected" across the different d*mographi<
and geographic subpopulations. These comparisons indicate
significant trend differences only across the age groups. The "0
14 years" group has generally had lower levels but a greate
increasing trend.
Figures 3.2-32 through 3.2-35 present the estimate
trend comparisons for the percentage of individuals having PC
levels greater than 1 ppm. Comparison of the subpopulation
indicate the following results:
«
• There are significant differences in time
trends across the age groups; the trend
for the "0-14 yrs" age group leveled off
during the late seventies. The sharp
increase in trend indicated in Figure 3.2-
32 for the recent years is an artifact due
to the curve fitting for the earlier
years. Such an increase is not indicated
in the actual data for these years.
• There is no significant difference in
trends between the race groups; however,
there is a difference in absolute levels
(non-whites have higher levels)
• There is no significant difference in time .
trends between the sexes; however, there
is a difference in absolute levels (males
have higher levels)
• There are no significant differences in
time trends across the census regions;
however, there are differences in the
absolute levels. The Northeast Region has
the highest levels.
Figures 3.2-36 through 3.2-39 present the comparison <
trends across the various demographic and geograph
subpopulations for the percentage of individuals having F
levels exceeding 3 ppm. The results indicate the following:
-------
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There are trend differences among the age
groups; the levels for the "0-14 yrs"
group have always been low while the other
groups had elevated levels during the
middle and late seventies. Following the
passage of regulations limiting the
production of PCBs, the levels have since
declined so that all age groups now have
very few individuals with levels exceeding
3 ppm.
There is no trend difference between
whites and nonwhites. However, non-whites
have higher absolute levels.
There is no trend difference between males
and females. However, males have higher
absolute levels.
There are trend differences among the
different census regions; the Northeast
Census Region had a much larger percentage
of individuals exceeding 3 ppm in the
middle seventies. since the PCB
regulations have been enacted, the levels
have since declined to the point where
very few individuals have levels exceeding
3 ppm.
-------
72
4.0 REFERENCES
(1) Bolt MM 1977. SURREGR: Standard errors of regressi
coefficients from sample survey data. Research friang
Institute, Research Triangle Park, NC 27709. . -
(2) Lucas RM, Erickson MD, and Williams SR 1980. PCB Resid
Levels in Human Adipose Tissue: A Statistic
Evaluation by Racial Grouping. Prepared by t
Research Triangle Institute for the Office of Tox
Substances, U.S. Environmental Protection Agenc
Washington, DC EPA/13-79-015.
(3) Lucas RM, lannaechione VG, and Melroy DK 1982. "Polychl
rinated Biphenyls in Human Adipose Tissue and Mother
Milk." Report to the Office of Toxic Substances, U.
Environmental Protection Agency by the Resear
Triangle Institute, Research Triangle Park,. NC 2770
RTI/1864/50-03F.
(4) Lucas RM, Melroy DK and I miner man FW 1983. National Adipo
Tissue Survey Statistical Analysis File. Report to t
Office of Toxic Substances, U.S. Environment
Protection Agency by the Research Triangle Institut
Research Triangle Park, NC 27709. RTI/1789/00-01F.
(5) Mack GA, Leczynski B, Chu, A and Mohadjer, L 1984. "Surv
Design for the National Human Adipose Tissue Survey
prepared by Battelle's Columbus Laboratories a
Westat, Inc., for the Office of Toxic Substances, U.
Environmental Protection Agency, Washington D.
20460.
(6) Shah BV 1979. SESUDAAN: Standard errors program for co:
puting of standardized rates from sample survey dat
Research Triangle Institute, Research Triangle Park, 1
27709. RTI/1789/00-01F.
(7) Johnson, NL and Kotz S 1980. "Continuous Univariate Distr
butions - I Distributions in Statistics*, John WiL
and Sons, New York, NY.
-------
APPENDIX A
ESTIMATED BASELINE RESIDUE LEVELS
FOR INDIVIDUAL FISCAL TEARS
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APPENDIX B
STATISTICAL APPROACH TO THE ESTIMATION
OF POPULATION TIKE TRENDS
-------
B.I STATISTICAL MODELS
«
The Analysis of time trends and their differences
across subpopulations require the use of statistical models. The
model for any given characteristic of the residue, level
distribution expresses the functional form of the relationship
between the characteristic of interest and the "predictor
variables" thought to affect it: time (fiscal year), age, race,
sex and geographic region (census region). The model provides the
mathematical framework needed to investigate and interpret
observed relationships in the collected data. The assumed model
includes unknown coefficients (parameters) whose values are
estimated from the observed data by using linear regression
techniques. The results of the regression analysis provide:
(1) A mathematical equation that expresses
the best relationship (of the assumed
model form) for predicting residue
levels as a function of time and the
geographic and demographic
characteristics associated with the
given subpopulation.
(2) Estimates of the unknown coefficients
and the magnitudes of the possible
errors associated with these coefficient
estimates. This information is used to
assess whether or not a given factor
(e.g., time, census region) has a
statistically significant influence on
the population residue levels and
indicates the possible range of its
influence.
Due to the multi-stage sampling design used to collect
the NRATS data, the regression analyses .required special
adjustments (e.g., implemented in the computer program SURREGR
(1)) to address the correlation structure inherent in the
collected data. This allowed proper estimates to be made for the
standard errors of the coefficients, thus providing for valid
assessments to be made of the influence of each factor on the
observed residue levels.
-------
B-2
B.2 APPROACH TO THE TIME TREND MODELING
Two types of trend models were used in th
statistical analyses. The first type involved the estimation of
single time trend to represent the entire nation with-respect t
the population residue distribution characteristic of interest
The second type involved the investigation of differences i
trends across the geographic and demographic subpopulations. I
the following sections the approach to modeling is discuss*
separately for each type.
B.2.1 National Time Trends
For each compound analyzed, national time trends wei
estimated for several different characteristics of the populatic
residue level distribution. For 6-BHC and HCB these included:
e Percentage of population having a detect-
able level of the compound
• Percentage of population have a quantifi-
able level of the compound
• Population average residue amount
e Population median
Since the collected data for PCBs were categorical :
nature, different characteristics were addressed in the P<
trends. These were:
e Percentage of the population having
detectable levels of PCBs
e Percentage of the population having PCB
levels exceeding 1 ppm, and
e Percentage of the population having PCB
levels exceeding 3 ppm.
-------
B-3
The model used for each compound and population
characteristic had the form:
Y - BQ + BI(FY-FY) + B2(FY-FT)2 + £, - (B.I)
where:
Y represents the observed value of the
residue level characteristic of interest for
a specimen collected during the given fiscal
year (FY)
(FY-FY) denotes the linear part of the time
trend centered at the midpoint of the study
period
(FY-FY)2 represents the quadratic part of the
time trend centered at the midpoint of the
study period
BQ, Bi_ and B2 are unknown coefficients that
are estimated from the observed data, and
E denotes the total contribution of all other
factors affecting the residue level other
than those included in the model.
The definition of the response variable Y depends on
the population characteristic being addressed. The definitions
for Y are summarized here.
Population Average Residue Amount:
Y « the specimens's observed residue level
Population Median:
Y « Logarithm (base 10) of the observed
residue level
Note
The analysis for the median was performed by estimating
the average level for the distribution of logarithms (base
10) of the original data and then transforming the result
into an estimate of the median for the original
distribution (7).
-------
B-4
Population Percentage Raving Detectable Levels:
0, if the observed residue level is
below the level of detection for the
analytical measurement process (See
Table B.I)
y «
1, if the observed value is above the
level of detection
Population Percentage having quantifiable levels:
0, if the observed residue level is
below the level of quantification for
the analytical measurement process
(see Table B.I)
y »
1, if the observed value is above the
level of quantification
TABLE B.I. APPROXIMATE LEVELS OF DETECTION AND LEVELS OF
QUANTIFICATION FOR THE COMPOUNDS &-BHC,
HCB, AND PCBs
Definition of Value e-BHC HCB PCBs
Level of Detection* (ppn) .02 .0033 1.0
Level of Quantification** (ppm) .07 .01
* These values correspond to concentration levels that yield
signal-to-noise ratios of approximately three. This implies
that the probability of declaring detection of a chemical in
sample that has none is less than 1 percent.
** These values correspond to concentration levels that yield
signal-to-noise ratios of approximately ten. This implies
that the percent relative error in estimating concentrations
at or greater than this value is 10 percent or less.
Each of the models for the different characteristi
and compounds was fit to the observed data using the comput
software called SURREGR (1). The estimated values for t
coefficients and their associated statistical significance leve
are given in Tables B.2 through B.4.
-------
B-5
33
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B-8
B.2.2 Investigation of Time Trend Differences Across
Subpopulations
The investigation of time trend differences aero:
Subpopulations was limited to two population characteristics f<
B-SRC and RGB:
• Percentage of the population having
detectable levels of the compound, and
e Population median.
For PCBs three characteristics were addressed:
• Percentage of the population having
detectable levels of PCBs
• Percentage of the population having PCB
levels exceeding 1 ppm, and
• Percentage of the population having PCB
levels exceeding 3 ppir.
A complex statistical model was used for each compou
to express the residue characteristic as a function of time a
the Subpopulations of interest. The form of the model is giv
by:
Y = BO + Bi(FY-FY) * B2(FY-FY)2 + AGE * SEX + RACE + C
* (FY-FY)*(AGE+RAC£+SEX-K:R) (B.
+ (FY-FY)2*(AGE+RACE+SEX+CR),
where:
Y represents the residue distribution char-
acteristic of interest
AGE, RACE, SEX and CR denote the main effects
due to the different demographic and
geographic Subpopulations
(FY-FY)*(AGE+RACE+SEX*CR) denotes the inter-
actions of the linear part of the time trend
with the different Subpopulations, and
-------
B-9
(FY-FY)2*(AGE+RACE+SEX+CR) denotes the inter-
actions of the quadratic part of the time
trend with the subpopulations.
The statistical significance of an interaction involving fiscal
year indicates that the tine trends are different "fcor the
associated subpopulations. Significance of a main effect
indicates a difference in absolute levels across the subpopula-
tions associated with that aain effect.
The regression techniques used in statistical model
fitting require the assumption that the distribution of specimen
residue levels is normally distributed. This assumption, however,
is more closely satisfied for the logarithms (base 10) of the
residue level data since the actual residue distribution is
skewed. For this reason the comparison of subpopulation trends
for the median levels of B-BHC and HC8 were based on the log-
transformed data. The statistical model (Equation B.2) was used
to obtain trend estimates based on the log-transformed data.
These trends were then transformed back into trend estimates for
the median of the distribution of actual residue levels.
The results of fitting the observed data to the given
model are presented in Tables B.5 through B.7. These tables
present the significance levels for the effects of each model
corresponding to the different compounds and response variables.
The time trend estimates and plots for the various
geographic and demographic subpopulations were generated by using
predicted values from a reduced model derived from Equation B.2.
The reduced model included only the statistically significant
model effects in Equation B.2 that were associated with fiscal
year and the geographic or demographic factor being compared in
the trend plot. For each response variable and compound the
estimated coefficients for the reduced models are presented in
Tables B.8 - B.10.
-------
B-10
TABLE B.5. SIGNIFICANCE LEVELS FOR THE MODEL EFFECTS
ASSOCIATED WITH THE COMPARISON OF 0-BBC
TRENDS ACROSS SUBPOPDLATIONS
Significance Levels
Effect
Age Group
Race Group
Sex
Census Region
Fiscal Year-Linear
Fiscal Year by Age Group
Interaction
Fiscal Year by Race Group
Interaction
Fiscal Year by Sex Interaction
Fiscal Year by Census Region
Interaction
Fiscal Year-Quadratic
Fiscal Year-Quadratic by Age
Group Interaction
Fiscal Year Quadratic by Race
Group Interaction
Fiscal Tear Quadratic by Sex
Interaction
Fiscal Year Quadratic by Census
Region Interaction
Percent
Detected
Model
.0016
.4551
.2084
.2612
NT***
.1077
.2341
.6562
.3727
NT***
.1033
.2751
.9476
.3880
Average Log*
Amount Model
NT**
.0676
.0416
.0000
NT***
.0002
.3626
.0523
.3628
NT***
.0000
.3798
.7526
.8512
* Used in the analysis of trends for the median.
** The effect is not testable due to the significance of a
related interaction effect.
*** Not testable doe to the parameterization used to define the
model.
-------
B-ll
TABLE B.6.
SIGNIFICANCE LEVELS FOR THE MODEL EFFECTS
ASSOCIATED WITH THE COMPARISON OF HCB TRENDS
ACROSS SDBPOPOLATXORS
Effect
Age Group
Race Group
Sex
Census Region
Fiscal Year-Linear
Fiscal Year by Age Group
Interaction
Fiscal Year by Race Group
Interaction
Fiscal Year by Sex Interaction
Fiscal Year by Census Region
Interaction
Fiscal Year-Quadratic
Fiscal Year-Quadratic by Age
Group Interaction
Fiscal Year Quadratic by Race
Group Interaction
Fiscal Year Quadratic by Sex
Interaction
Fiscal Year Quadratic by Census
Region Interaction
Significance Levels"
Percent
Detected Average Log*
Model Amount Model
.0973 NT**
.1181 .8135
.9108 .0006
.0988 .0000
NT*** NT***
.0806 .0010
.1132 .1058
.2360 .5545
.2555 .1250
NT*** NT***
.3413 .0264 •
.0918 .€854
.5965 .7747
.9113 .5852
* Used in the analysis of trends for the median.
** The effect is not testable due to the significance of a
related interaction effect.
*** Not testable due to the parameterization used to define the
model.
-------
B-12
TABLE B.7.
SIGNIFICANCE LEVELS FOR THE MODEL EFFECTS
ASSOCIATED WITH THE COMPARISON OF FCB
TRENDS ACROSS SDBPOPULATIONS
Siqnificance Levels
Percent Percent GT
Detected 1 PPM
Effect Model Model
Age Group
Race Group
Sex
Census Region
Fiscal Year-Linear
Fiscal Year by Age Group
Interaction
Fiscal Year by Race Group
Interaction
Fiscal Year by Sex Interaction
Fiscal Year by Census Region
Interaction
Fiscal Year-Quadratic
Fiscal Year-Quadratic by Age
Group Interaction
Fiscal Tear Quadratic by Race
Group Interaction
Fiscal Tear Quadratic by Sex
Interaction
Fiscal Tear Quadratic by Census
Region Interaction
NT*
.4140
.7548
.8013
NT**
.0346
.1324
.5806
.7610
NT**
.3028
.1B84
.5244
.6265
NT*
.0001
.0002
.0021
NT**
.0018
.5278
.2554
.3210
NT**
.0046
.0730
.6472
.3521
Percent GT
3 PPM
Model
.0000
.0010
.0080
.0029
NT**
.2220
.3324
.5858
.6052
NT**
.0003
.1252
.3227
.0537
* The effect of is not testable due to the significance of
a related interaction effect.
** Not testable due to the parameterization used to define
the model.
-------
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-------
HEWT DOCUMENTATION ».,«*>•" «o «.
PAGE 560/5-85-025
Baseline Estimates and Time Trends for Beta-benzene Hexachlorlde
Hexachlorobenzene, and Polychlorinated Blphenyls 1n Human
AH inn, A Ti«u* 1970-1983
Gregory A. Mack* and Ley la Mohadjer2
». NI^KKMH 0*i»ni»t»» turn* •»• tttrun
*Battelle Columbus Division 2ne$tat, Inc.
SOS King Avenue 1650 Research Boulevard
Columbus. Ohio 43201 Rockville, Maryland 20850
U.S. Environmental Protection Agency
Office of Toxic Substances. Design and Development Branch
401 N Street. S.U.
Washinaton, D.C. 20460
«. MHWMTt MMMW, IN
9/30/85 (Date o
•.
NHATSisT-tr
Work Asslgnmer
c, 68-01-6721
«
!&> TfW it •wt A Mn*
Final Report
14.
It AMtrMt (Urn* WO ••*•»)
The National Human Adipose Tissue Survey (NHATS) 1s an on-going annual pr
collect and chemically analyze adipose tissue specimens from a representative
sample of autopsied cadavers and surgical patients. The objective of the
Is to estimate baseline levels and time trends for the presence of toxic <
In the adipose tissue of the U.S. population. This report presents the re
a statistical analysis conducted on three specific chemicals: Beta-benzene hexi
(6-BHC), hexachlorobenzene (HCB), and polychlorinated biphenyls (RGBs). The
are based on NHATS data collected between 1970 and 1983.
The results Include baseline estimates of the percentages of the populatlo
detectable levels of these compounds 1n their adipose tissue as well as <
of the mean and median levels. Estimates are given separately for various dei
groups and geographic regions of the country as well as national estimates.
Results of the analysis indicate that nearly 100 percent of the populat
detectable levels of these compounds in their adipose tissue. However, tti
levels of these compounds are either decreasing or remaining nearly constant.
17. OMvnwM A/i»ir»i» a. Oncnpur*
COtATT
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-------
B-ll
TABLE B.6.
SIGNIFICANCE LEVELS FOR THE MODEL EFFECTS
ASSOCIATED WITH THE COMPARISON OF HCB TRENDS
ACROSS SDBPOPDLATIORS
Effect
Age Group
Race Group
Sex
Census Region
Fiscal Year-Linear
Fiscal Year by Age Group
Interaction
Fiscal Year by Race Group
Interaction
Fiscal Year by Sex Interaction
Fiscal Year by Census Region
Interaction
Fiscal Year-Quadratic
Fiscal Year-Quadratic by Age
Group Interaction
Fiscal Year Quadratic by Race
Group Interaction
Fiscal Year Quadratic by Sex
Interaction
Fiscal Year Quadratic by Census
Region Interaction
Significance Levels"
Percent
Detected Average Log*
Model Amount Model
.0973 ITT**
.1181 .8135
.9108 .0006
.0988 .0000
NT*** NT***
.0806 .0010
.1132 .1058
.2360 .5545
.2555 .1250
NT*** NT***
.3413 .0264 •
.0918 .€854
.5965 .7747
.9113 .5852
* Used in the analysis of trends for the median.
** The effect is not testable due to the significance of a
related interaction effect.
*** Not testable due to the parameterization used to define the
model.
-------
B-12
TABLE B.7. SIGNIFICANCE LEVELS FOR THE MODEL EFFECTS
ASSOCIATED WITH THE COMPARISON OF PCB
TRENDS ACROSS SUBPOPULATIONS
Siqnificance Levels
Percent Percent GT
Detected 1 PPM
Effect Model Model
Age Group
Race Group
Sex
Census Region
Fiscal Year-Linear
Fiscal Year by Age Group
Interaction
Fiscal Year by Race Group
Interaction
Fiscal Year by Sex Interaction
Fiscal Year by Census Region
Interaction
Fiscal Year-Quadratic
Fiscal Year-Quadratic by Age
Group Interaction
Fiscal Year Quadratic by Race
Group Interaction
Fiscal Tear Quadratic by Sex
Interaction
Fiscal Tear Quadratic by Census
Region Interaction
NT*
.4140
.7548
.8013
NT**
.0346
.1324
.5806
.7610
NT**
.3028
.1884
.5244
.6265
NT*
.0001
.0002
.0021
NT**
.0018
.5278
.2554
.3210
NT**
.0046
.0730
.6472
.3521
Percent GT
3 PPM
Model
.0000
.0010
.0080
.0029
NT**
.2220
.3324
.5858
.6052
NT**
.0003
.1252
.3227
.0537
* The effect of is not testable due to the significance of
a related interaction effect.
** Not testable due to the parameterization used to define
the model.
-------
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