Table of Contents

Component Description

Polychlorinated biphenyls (PCBs) are a class of chlorinated aromatic hydrocarbon chemicals that once were used as heat-exchanger, transformer, and hydraulic fluids, and as additives to paints, oils, joint caulking, and floor tiles. The different types of PCBs are known as congeners, which are compounds that are distinguished by the number of chlorine atoms and their location on the biphenyl structure. Peak production occurred in the early 1970s, and production was banned in the U.S. after 1979. More than 1.5 million pounds of PCBs were manufactured in the U.S. prior to 1977. Concern about these chemicals continues because of their persistence in the environment and accumulation in wildlife and the animal food chain. PCBs enter the food chain by various routes, including migration into food from external sources, contamination of animal feeds, and accumulation in the fatty tissues of animals. PCBs are found a higher concentrations in fatty foods, (e.g., dairy products and fish), and food is the main source of exposure for the general population. PCBs can be transferred from mother to infant via breast milk. Exposure to these chemicals nearly always occurs as mixtures rather than individual PCB congeners.

Eligible Sample

Study participants aged 3 years and older from NHANES 2001 - 2002 with stored serum available to prepare pooled samples.

Description of Laboratory Methodology

Twenty nine non-dioxin-like polychlorinated biphenyls were measured in serum by gas chromatography/isotope-dilution high-resolution mass spectrometry (GC/ID-HRMS). The analytical method for PCBs is described in Sjodin et al., 2004 and Barr et al., 2003. Reported results met the Division of Laboratory Sciences’ quality control and quality assurance performance criteria for accuracy and precision (similar to specifications outlined by Westgard, 1981).

Data Processing and Editing

Specimens were processed, stored, and shipped to DLS, NCEH, CDC (Atlanta, Georgia). The analytical approach used, including data processing is described in detail in Sjodin, et al (2004). Reported results met the Division of Laboratory Sciences’ quality control and quality assurance performance criteria for accuracy and precision (similar to specifications outlined by Westgard, 1981).

Laboratory Quality Assurance and Monitoring

The NHANES quality assurance and quality control (QA/QC) protocols meet the 1988 Clinical Laboratory Improvement Act mandates. Detailed QA/QC instructions are discussed in the NHANES Laboratory/Medical Technologists Procedures Manual (LPM).

Read the General Documentation on Laboratory Data file for detailed QA/QC protocols. The analytical methods are described in the Description of the Laboratory Methodology section.

Analytic Notes

The sampling scheme for NHANES 2001–2002, a complex multistage area probability design, included 11,039 persons. Data were collected through household interviews and through standardized physical examinations conducted in mobile examination centers. On the basis of self-reported data, a composite race/ethnicity variable helped define three major racial/ethnic groups: non-Hispanic blacks, non-Hispanic whites, and Mexican Americans. Informed consent was obtained from all study participants. Serum samples used to prepare pools for analysis were selected from those obtained by venipuncture from 2150 participants, a random one-third subsample of people 12 years of age and older from NHANES 2001-2002 and representative of the U.S. general population for this age range. A total of 1,832 individual serum samples were used to prepare the 54 pooled serum samples analyzed for this subset of NHANES 2001-2002.

After collection of samples, serum specimens were divided into aliquots and were stored cold (2–4°C) or frozen until they were shipped on dry ice to CDC’s National Center for Environmental Health (NCEH). Serum samples were stored frozen after receipt at NCEH at –70°C until analyzed. The 2,150 individual serum samples available were categorized in 24 demographic groups (Table 1), each representing a combination of race/ethnicity, gender, and age (12–19 years, 20–39 years, 40–59 years, and 60 years and older). The number of samples available, the number of these samples that were usable, and the number of pools formed in each demographic group are presented in Table 1. On the basis of the number of individual serum samples per demographic group, multiple pools were available for 14 demographic groups, and one pool was available for 10 demographic groups (Table 1). To ensure that no individual sample overly influenced the pooled results, all serum samples included in any one pool (25.5 mL each) were of equal volume (i.e., each individual sample contributed 750 μL). Most pools included 34 individual serum samples that were randomly selected. Only 31 individual serum samples were available, however, for the pool representing non-Hispanic black men 60 years of age or older. In addition, one of the two pools representing Mexican American men between 20 and 39 years of age consisted of only 33 individual specimens. 

In addition, residual serum from 3–11 year old NHANES 2001–2002 participants, previously analyzed for cotinine, a marker of environmental tobacco smoke, was used to create pools representing 3-5 year old and 6-11 year old participants. The 1049 individual samples available were categorized in 12 demographic groups, each representing a combination of race/ethnicity, sex, and age (3–5 years and 6–11 years). A total of 937 randomly selected individual samples were used to prepare 24 pools (two per demographic group). The number of samples available, the number of these samples that were usable, and the number of pools formed in each demographic group are presented in Table 1. To ensure that no individual sample overly influenced the pooled results, all samples included in any one pool were of equal volume (i.e., 0.5 mL). Eleven of the individual serum samples from non-Hispanic black females 3–5 years of age contributed <0.5 mL. Each pool included 21 (3–5 year old) or 57 (6–11 year old) individual samples randomly selected (Table 1).

Table 1. Number of individual serum samples available, number of usable samples, and number of pools formed from NHANES 2001–2002 participants per demographic group.

serum samples available

Guidelines for Working with Pooled-Samples from NHANES 2001-2002
Because the samples constituting the pools originated from NHANES 2001-2002, which was designed to be representative of the non-institutionalized US population, the pooled results should provide good coverage of the US population. We cannot be assured, however, that estimates based on the pooled samples are unbiased for at least two reasons: 1) the sampling weight information was lost when the samples were pooled because each pool consists of equal volumes of each sample in the pool; and 2) the measured value for a pooled sample (consisting of individual samples that tend to be log-normally distributed) is comparable to an arithmetic average of log-normal results and thus represents a biased estimate of the central tendency (geometric mean or median) of the samples making up the pool. Also, because samples were pooled across the design cells of the original NHANES sampling design, it is not possible to obtain unbiased estimates of standard errors. These bias and standard error issues are being addressed in later NHANES surveys involving pooled samples. 

Pooled-Sample weights
The sampling weight information was lost when the samples were pooled because each pool consists of equal volumes of each sample in the pool. 

Variance estimation
The sampling scheme for NHANES 2001–2002 is a complex multistage, probability sampling design that selects participants who are representative of the civilian, non-institutionalized U.S. population. Over-sampling of certain population subgroups is done to increase the reliability and precision of health status indicator estimates for those groups. For PCBs, instead of using the full NHANES sample, a random one-third subsample of NHANES participants was used. Curtin et al. (2012) provide documentation of the construction of sampling weights for this one-third subsample. Also, because of the use of stratified multistage selection, incorporation of the sampling design is needed to calculate sampling variances (NCHS, 1994). These variances cannot be calculated for NHANES 2001-2002 pooled sample estimates, however, because samples were pooled across the design cells of the original NHANES 2001-2002 sampling design.

Links to NHANES Data Files
Although this pooled-sample data file cannot be directly linked to other NHANES 2001-2002 data files, it does contain demographic information (RIAGENDR, RIDRAETN, and RIDAGGRP) for each pooled-sample.

Variables in the data file
Each variable in the data file is given in Table 2 with its definition. The definition used for the numeric constant for categorical variables is given in the column: Definition of Categorical Variables.

The NHANES abbreviation used for each analyte measured with the IUPAC name is given in Table 3. The code “XYZ” in the variable names “ADJUSTED_RESULT_XYZ” and “RESULT_COMMENT_XYZ” as defined in Table 2 corresponds to the Value of the “NHANES code” in Table 3.

Table 2. NHANES Code, Common Abbreviation and IUPAC Name for each analyte reported
Variable Description Definition of Categorical Variables
POOLID Pool identification number n/a
RIAGENDR Gender of subjects in pool 1 = Male
2 = Female
RIDRAETN Race / Ethnicity of subjects in pool 1 = Non-Hispanic White (NHW)
2 = Non-Hispanic Black (NHB)
3 = Mexican American (MA)
RIDAGGRP Age group of subjects in pool -1 = 3-5 Year old
0 = 6-11 Year old
1 = 12-19 Year old
2 = 20-39 Year old
3 = 40-59 Year old
4 = >60 Years old
RIANSMP Number of samples pool n/a
ADJUSTED_RESULT_XYZ Reported Concentration (ng/g lipid). "XYZ" in the variable name corresponds to the NHANES abbreviation for each analyte. n/a
RESULT_COMMENT_XYZ Code for measured concentration. "XYZ" in the variable name corresponds to the NHANES abreviation for each analyte 0 = Detectable Result
30 = Non-Reportable Result
37 = Result having a concentration below the limit of detection.
The value for the variable "ADJUSTED_RESULT_XYZ" for this analyte corresponds to the limit of detection divided with the square root of 2.

 

Table 3. NHANES Code, Common Abbreviation and IUPAC Name for each analyte reported
NHANES CODE Common Abbreviation IUPAC Name
28 PCB28 2,4,4'-Trichlorobiphenyl
52 PCB52 2,2',5,5'-Tetrachlorobiphenyl
49 PCB49 2,2',4,5'-Tetrachloro biphenyl
44 PCB44 2,2'3,5'-Tetrachloro biphenyl
74 PCB74 2,4,4',5-Tetrachlorobiphenyl
66 PCB66 2,3',4,4'-Tetrachlorobiphenyl
101 PCB101 2,2',4,5,5'-Pentachlorobiphenyl
99 PCB99 2,2',4,4',5-Pentachlorobiphenyl
87 PCB87 2,2’,3,4,5’-Pentachlorobiphenyl
110 PCB110 2,3,3’,4’,6-Pentachlorobiphenyl
151 PCB151 2,2’,3,5,5’,6-Hexachlorobiphenyl
149 PCB149 2,2’,3,4’,5’,6-Hexachlorobiphenyl
146 PCB146 2,2',3,4',5,5'-Hexachlorobiphenyl
153 PCB153 2,2',4,4',5,5'-Hexachlorobiphenyl
138 PCB138-158 2,2',3,4,4',5' and 2,3,3’,4,4’,6-Hexachlorobiphenyl
128 PCB128 2,2',3,3',4,4'-Hexachlorobiphenyl
178 PCB178 2,2',3,3',5,5',6-Heptachlorobiphenyl
187 PCB187 2,2',3,4',5,5',6-Heptachlorobiphenyl
183 PCB183 2,2',3,4,4',5',6-Heptachlorobiphenyl
177 PCB177 2,2',3,3',4,5',6'-Heptachlorobiphenyl
172 PCB172 2,2',3,3',4,5,5'-Heptachlorobiphenyl
180 PCB180 2,2',3,4,4',5,5'-Heptachlorobiphenyl
170 PCB170 2,2',3,3',4,4',5-Heptachlorobiphenyl
199 PCB199 2,2’,3,3’,4,5,5’,6-Octachlorobiphenyl
196 PCB196-203 2,2’,3,3’,4,4’,5,6’ and 2,2’,3,4,4’,5,5’,6-Octachlorobiphenyl
195 PCB195 2,2’,3,3’,4,4’,5,6-Octachlorobiphenyl
194 PCB194 2,2’,3,3’,4,4’,5,5’-Octachlorobiphenyl
206 PCB206 2,2’,3,3’,4,4’,5,5’,6-Nonachlorobiphenyl
209 PCB209 2,2',3,3',4,4',5,5',6,6'-Decachloro biphenyl

References

Codebook and Frequencies

POOLID - Pool ID number

Variable Name:
POOLID
SAS Label:
Pool ID number
English Text:
Pool ID number
Target:
Both males and females 3 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
. Missing 0 0

RIAGENDR - Gender

Variable Name:
RIAGENDR
SAS Label:
Gender
English Text:
Gender
Target:
Both males and females 3 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
1 Male 38 38
2 Female 40 78
. Missing 0 78

RIDRAETN - Ethnicity

Variable Name:
RIDRAETN
SAS Label:
Ethnicity
English Text:
Ethnicity
Target:
Both males and females 3 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
1 Non-Hispanic White 35 35
2 Non-Hispanic Black 20 55
3 Mexican American 23 78
. Missing 0 78

RIDAGGRP - Age Group

Variable Name:
RIDAGGRP
SAS Label:
Age Group
English Text:
Age Group
Target:
Both males and females 3 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
0 6 Yrs. to 11 Yrs. 12 12
1 12 Yrs. to 19 Yrs. 19 31
2 20 Yrs. to 39 Yrs. 13 44
3 40 Yrs. to 59Yrs. 10 54
4 60 Yrs. to 150 Yrs. 12 66
-1 3 Yrs. to 5 Yrs. 12 78
. Missing 0 78

RIANSMP - Number of samples included in Pool

Variable Name:
RIANSMP
SAS Label:
Number of samples included in Pool
English Text:
Number of samples included in Pool
Target:
Both males and females 3 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
21 to 57 Range of Values 78 78
. Missing 0 78

SS028 - PCB28

Variable Name:
SS028
SAS Label:
PCB28
English Text:
PCB28
Target:
Both males and females 3 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
0.7 to 6.3 Range of Values 77 77
. Missing 1 78

SS044 - PCB44

Variable Name:
SS044
SAS Label:
PCB44
English Text:
PCB44
Target:
Both males and females 3 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
0.1 to 0.7 Range of Values 77 77
. Missing 1 78

SS049 - PCB49

Variable Name:
SS049
SAS Label:
PCB49
English Text:
PCB49
Target:
Both males and females 3 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
0.2 to 0.5 Range of Values 77 77
. Missing 1 78

SS052 - PCB52

Variable Name:
SS052
SAS Label:
PCB52
English Text:
PCB52
Target:
Both males and females 3 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
0.2 to 0.9 Range of Values 77 77
. Missing 1 78

SS066 - PCB66

Variable Name:
SS066
SAS Label:
PCB66
English Text:
PCB66
Target:
Both males and females 3 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
0.3 to 2.8 Range of Values 78 78
. Missing 0 78

SS074 - PCB74

Variable Name:
SS074
SAS Label:
PCB74
English Text:
PCB74
Target:
Both males and females 3 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
1 to 24.7 Range of Values 78 78
. Missing 0 78

SS087 - PCB87

Variable Name:
SS087
SAS Label:
PCB87
English Text:
PCB87
Target:
Both males and females 3 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
0.3 to 0.9 Range of Values 78 78
. Missing 0 78

SS099 - PCB99

Variable Name:
SS099
SAS Label:
PCB99
English Text:
PCB99
Target:
Both males and females 3 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
1 to 16.2 Range of Values 78 78
. Missing 0 78

SS101 - PCB101

Variable Name:
SS101
SAS Label:
PCB101
English Text:
PCB101
Target:
Both males and females 3 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
0.1 to 1.1 Range of Values 78 78
. Missing 0 78

SS110 - PCB110

Variable Name:
SS110
SAS Label:
PCB110
English Text:
PCB110
Target:
Both males and females 3 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
0.1 to 0.8 Range of Values 78 78
. Missing 0 78

SS128 - PCB128

Variable Name:
SS128
SAS Label:
PCB128
English Text:
PCB128
Target:
Both males and females 3 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
0.2 to 0.9 Range of Values 78 78
. Missing 0 78

SS138 - PCB138-158

Variable Name:
SS138
SAS Label:
PCB138-158
English Text:
PCB138-158
Target:
Both males and females 3 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
2.6 to 71.1 Range of Values 78 78
. Missing 0 78

SS146 - PCB146

Variable Name:
SS146
SAS Label:
PCB146
English Text:
PCB146
Target:
Both males and females 3 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
0.4 to 15.6 Range of Values 78 78
. Missing 0 78

SS149 - PCB149

Variable Name:
SS149
SAS Label:
PCB149
English Text:
PCB149
Target:
Both males and females 3 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
0.2 to 0.8 Range of Values 78 78
. Missing 0 78

SS151 - PCB151

Variable Name:
SS151
SAS Label:
PCB151
English Text:
PCB151
Target:
Both males and females 3 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
0.3 to 0.9 Range of Values 78 78
. Missing 0 78

SS153 - PCB153

Variable Name:
SS153
SAS Label:
PCB153
English Text:
PCB153
Target:
Both males and females 3 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
3.3 to 118.6 Range of Values 78 78
. Missing 0 78

SS170 - PCB170

Variable Name:
SS170
SAS Label:
PCB170
English Text:
PCB170
Target:
Both males and females 3 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
0.9 to 32.1 Range of Values 78 78
. Missing 0 78

SS172 - PCB172

Variable Name:
SS172
SAS Label:
PCB172
English Text:
PCB172
Target:
Both males and females 3 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
0.4 to 4.8 Range of Values 78 78
. Missing 0 78

SS177 - PCB177

Variable Name:
SS177
SAS Label:
PCB177
English Text:
PCB177
Target:
Both males and females 3 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
0.3 to 5.6 Range of Values 78 78
. Missing 0 78

SS178 - PCB178

Variable Name:
SS178
SAS Label:
PCB178
English Text:
PCB178
Target:
Both males and females 3 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
0.4 to 7.5 Range of Values 78 78
. Missing 0 78

SS180 - PCB180

Variable Name:
SS180
SAS Label:
PCB180
English Text:
PCB180
Target:
Both males and females 3 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
1.9 to 100.6 Range of Values 78 78
. Missing 0 78

SS183 - PCB183

Variable Name:
SS183
SAS Label:
PCB183
English Text:
PCB183
Target:
Both males and females 3 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
0.3 to 9 Range of Values 78 78
. Missing 0 78

SS187 - PCB187

Variable Name:
SS187
SAS Label:
PCB187
English Text:
PCB187
Target:
Both males and females 3 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
0.5 to 35.4 Range of Values 78 78
. Missing 0 78

SS194 - PCB194

Variable Name:
SS194
SAS Label:
PCB194
English Text:
PCB194
Target:
Both males and females 3 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
0.4 to 22.7 Range of Values 78 78
. Missing 0 78

SS195 - PCB195

Variable Name:
SS195
SAS Label:
PCB195
English Text:
PCB195
Target:
Both males and females 3 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
0.3 to 4.1 Range of Values 78 78
. Missing 0 78

SS196 - PCB196-203

Variable Name:
SS196
SAS Label:
PCB196-203
English Text:
PCB196-203
Target:
Both males and females 3 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
0.4 to 20.1 Range of Values 78 78
. Missing 0 78

SS199 - PCB199

Variable Name:
SS199
SAS Label:
PCB199
English Text:
PCB199
Target:
Both males and females 3 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
0.4 to 23.7 Range of Values 78 78
. Missing 0 78

SS206 - PCB206

Variable Name:
SS206
SAS Label:
PCB206
English Text:
PCB206
Target:
Both males and females 3 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
0.4 to 15.1 Range of Values 78 78
. Missing 0 78

SS209 - PCB209

Variable Name:
SS209
SAS Label:
PCB209
English Text:
PCB209
Target:
Both males and females 3 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
0.3 to 16.4 Range of Values 78 78
. Missing 0 78