Component Description
Volatile Organic
Compounds and Trihalomethanes/MTBE (Whole Blood)
Volatile organic
compounds (VOCs) are a large group of chemicals that have been used as
solvents, degreasers, and cleaning agents in industry and consumer products.
Many of the VOCs were found to contaminate ground water and drinking water
sources. Because of human health concerns, these VOCs have been banned or
restricted from most uses.
Halogenated
solvents are VOCs consisting of a hydrocarbon chain or one hydrocarbon
substituted with one or more chlorine or bromine atoms. Most of these chemicals
are used as degreasers and solvents in various products, such as paint. In the
past, 1,1,1-trichloroethane was used as a dry-cleaning agent, insect fumigant,
and solvent in consumer products. Methylene chloride, tetrachloroethene, and
trichloroethene are other VOCs that were widely used in the past.
Benzene, toluene, ethylbenzene, xylene, and styrene, collectively referred to as BTEXS, are components of
tobacco smoke. Along with 2,5-dimethylfuran, these VOCs are usually detected in
the blood of cigarette smokers at higher levels than in non-smokers.
Chlorobenzene (monochlorobenzene) and the three dichlorobenzenes are
halogenated aromatic hydrocarbons primarily used in industrial and chemical
synthetic processes. Chlorobenzene has been used to produce DDT, phenol, and
nitrobenzene. The dichlorobenzenes are also chemical intermediates in the
synthesis of dyes, pesticides, and other industrial products.
1,4-Dichlorobenzene (para-dichlorobenzene) is used also as a moth repellent and
as a deodorizer. Disinfection by-products (DBP), including bromodichloromethane,
dibromochloromethane, bromoform, and chloroform are formed when chlorine
interacts with natural organic materials found in water. Primary sources of
DBPs are chlorinated drinking water and recreational water bodies, such as
swimming pools.
The prevalence of
disinfection by-products in drinking water supplies has raised concerns about
possible adverse health effects from chronic exposure to these potentially
carcinogenic compounds. Methyl-tert-butyl ether (MTBE) was used as an additive
to replace lead in gasoline, but its use was banned after widespread ground
water contamination was discovered.
Inhalation is the
most common VOC route of exposure in the general population, including indoor
sources such as paints, adhesives, cleaning solutions, and aerosolized
insecticide sprays; industries producing these solvents; and contaminated waste
disposal sites. Drinking water may contribute to exposure when underground
drinking water supplies are contaminated. After they are absorbed in the body,
VOCs are rapidly eliminated in exhaled breath, or may be rapidly metabolized
and eliminated in the urine.
Eligible Sample
Examined
participants aged 12 years and older from a one-half sample were eligible.
Description of Laboratory Methodology
An automated
analytical method was developed using capillary gas chromatography (GC) and
mass spectrometry (MS) with selected-ion monitoring (SIM) detection and
isotope-dilution. This method quantifies levels of individual VOCs and
Trihalomethanes (THMs) and methyl tert-butyl ether (MTBE) in whole blood to
low-parts-per-trillion range. Because non-occupationally exposed individuals
have blood VOC concentrations within this range, this method is applicable for
determining these quantities and investigating cases of sustained or recent
low-level exposure.
Refer to the
Laboratory Method Files section for a detailed description of the laboratory
methods used.
There were no
changes to the lab method, lab equipment, or lab site for this component in the
NHANES August 2021-August 2023 cycle.
Laboratory Method Files
Volatile Organic Compounds (VOCs) & Trihalomethanes/MTBE Laboratory Procedure Manual
(September 2025)
Laboratory Quality Assurance and Monitoring
Whole blood
specimens were processed, stored, and shipped to Division of Laboratory
Sciences, National Center for Environmental Health, Centers for Disease Control
and Prevention, Atlanta, GA for analysis.
Detailed
instructions on specimen collection and processing are discussed in the NHANES Laboratory Procedures Manual (LPM). Vials are stored under appropriate refrigerated (2-8°C) conditions until
they are shipped to National Center for Environmental Health for testing.
The NHANES quality
assurance and quality control (QA/QC) protocols meet the 1988 Clinical
Laboratory Improvement Amendment mandates. Detailed QA/QC instructions are
discussed in the NHANES LPM.
Mobile Examination
Centers (MECs)
Laboratory team performance is monitored using several techniques. NCHS and
contract consultants use a structured competency assessment evaluation during
visits to evaluate both the quality of the laboratory work and the QC
procedures. Each laboratory staff member is observed for equipment operation,
specimen collection and preparation; testing procedures and constructive
feedback are given to each staff member. Formal retraining sessions are
conducted annually to ensure that required skill levels were maintained.
Analytical
Laboratories
NHANES uses
several methods to monitor the quality of the analyses performed by the
contract laboratories. In the MEC, these methods include performing blind split
samples collected on “dry run” sessions. In addition, contract laboratories
randomly perform repeat testing on 2% of all specimens.
NCHS developed and
distributed a QC protocol for all CDC and contract laboratories, which outlined
the use of Westgard rules (Westgard et. al., 1981) when testing NHANES
specimens. Progress reports containing any problems encountered during shipping
or receipt of specimens, summary statistics for each control pool, QC graphs,
instrument calibration, reagents, and any special considerations are submitted
to NCHS quarterly. The reports are reviewed for trends or shifts in the data.
The laboratories are required to explain any identified areas of concern.
All QC procedures
recommended by the manufacturers were followed. Reported results for all assays
meet the Division of Laboratory Services’ QA/QC performance criteria for
accuracy and precision, similar to the Westgard rules (Caudill et. al., 2008).
Data Processing and Editing
The data were reviewed. Incomplete data or improbable values were sent to the performing laboratory for confirmation.
Analytic Notes
There are over 800
laboratory tests performed on NHANES participants. However, not all participants
provided biospecimens or enough volume for all the tests to be performed.
Analyst should
evaluate the extent of missing data in the dataset related to the outcome of
interest as well as any predictor variables used in the analyses to determine
whether additional re-weighting for item non-response is necessary.
Please refer to the NHANES Analytic Guidelines and the on-line NHANES Tutorial for details on the use of sample
weights and analytic issues.
Volatile Toxicant
Questionnaire
A volatile toxicant questionnaire (VTQ) was administered on the mobile
examination center (MEC), by trained interviewers, using the Computer-Assisted
Personal Interview (CAPI) system. The VTQ section includes data about the participant’s
home, activities, amount of time spent in various locations, and exposure to
different chemicals over the past 48 hours. This questionnaire data can be used
in conjunction with the VOC laboratory dataset and found in the Volatile
Toxicant Data File in the NHANES August 2021 – August 2023
Questionnaire Data section.
Subsample Weights
Whole blood VOCs
were measured in a one-half subsample of participants 12 years and older.
Special sample weights are required to analyze these data properly. Specific
sample weights for this subsample are included in this data file and should be
used when analyzing these data.
Demographic and
Other Related Variables
The analysis of
NHANES laboratory data must be conducted using the appropriate survey design
and demographic variables. The NHANES
August 2021-August 2023 Demographics File contains demographic data,
health indicators, and other related information collected during household
interviews as well as the sample design variables. The recommended procedure
for variance estimation requires use of stratum and PSU variables (SDMVSTRA and
SDMVPSU, respectively) in the demographic data file.
The Fasting Questionnaire File includes auxiliary information such as fasting status, length of fast and the
time of venipuncture.
This laboratory
data file can be linked to the other NHANES data files using the unique survey
participant identifier (i.e., SEQN).
Detection limits
The detection
limits were constant for all of the analytes in the data set. Two variables are
provided for each of these analytes. The variable name ending in “LC” (ex.,
LBD2DFLC) indicates whether the result was below the limit of detection: “0”
means that the result was at or above the limit of detection, “1” indicates
that the result was below the limit of detection. The other variable prefixed LBX
(ex., LBX2DF) provides the analytic result for that analyte. For analytes with analytic results below the
lower limit of detection (ex., LBD2DFLC=1), an imputed fill value was placed in
the analyte results field. This value is the lower limit of detection divided
by square root of 2 (LLOD/sqrt [2]).
Lower
Limit of Detection (LLOD, in ng/mL) for Whole Blood VOCs:
| VARIABLE NAME |
SAS LABEL |
LLOD |
| LBX2DF |
Blood 2,5-Dimethylfuran (ng/mL) |
0.0110 |
| LBXV06 |
Blood Hexane (ng/mL) |
0.122 |
| LBXV07N |
Blood Heptane (ng/mL) |
0.100 |
| LBXV08N |
Blood Octane (ng/mL) |
0.100 |
| LBXV1D |
Blood 1,2-Dichlorobenzene (ng/mL) |
0.0250 |
| LBXV2A |
Blood 1,2-Dichloroethane (ng/mL) |
0.0100 |
| LBXV3B |
Blood 1,3-Dichlorobenzene (ng/mL) |
0.0250 |
| LBXV4C |
Blood Tetrachloroethene (ng/mL) |
0.0480 |
| LBXVAPN |
Blood a-pinene (ng/mL) |
0.0200 |
| LBXVBF |
Blood Bromoform (ng/mL) |
0.0080 |
| LBXVBM |
Blood Bromodichloromethane (ng/mL) |
0.0060 |
| LBXVBZ |
Blood Benzene (ng/mL) |
0.0240 |
| LBXVBZN |
Blood Benzonitrile (ng/mL) |
0.150 |
| LBXVC6 |
Blood Cyclohexane (ng/mL) |
0.0200 |
| LBXVCB |
Blood Chlorobenzene (ng/mL) |
0.0110 |
| LBXVCF |
Blood Chloroform (ng/mL) |
0.0080 |
| LBXVCM |
Blood Dibromochloromethane (ng/mL) |
0.0050 |
| LBXVCT |
Blood Carbon Tetrachloride (ng/mL) |
0.0050 |
| LBXVDB |
Blood 1,4-Dichlorobenzene (ng/mL) |
0.0400 |
| LBXVDEE |
Blood Diethyl Ether (ng/mL) |
0.0400 |
| LBXVEA |
Blood Ethyl Acetate (ng/mL) |
0.158 |
| LBXVEB |
Blood Ethylbenzene (ng/mL) |
0.0240 |
| LBXVEC |
Blood Chloroethane (ng/mL) |
0.0450 |
| LBXVFN |
Blood Furan (ng/mL) |
0.0250 |
| LBXVIBN |
Blood Isobutyronitrile (ng/mL) |
0.0400 |
| LBXVIPB |
Blood Isopropylbenzene (ng/mL) |
0.0400 |
| LBXVMC |
Blood Methylene Chloride (ng/mL) |
0.250 |
| LBXVMCP |
Blood Methylcyclopentane (ng/mL) |
0.0200 |
| LBXVME |
Blood MTBE (ng/mL) |
0.0100 |
| LBXVMIK |
Blood Methyl Isobutyl Ketone (ng/mL) |
0.100 |
| LBXVOX |
Blood o-Xylene (ng/mL) |
0.0240 |
| LBXVST |
Blood Styrene (ng/mL) |
0.0300 |
| LBXVTC |
Blood Trichloroethene (ng/mL) |
0.0120 |
| LBXVTE |
Blood 1,1,1-Trichloroethane (ng/mL) |
0.0100 |
| LBXVTHF |
Blood Tetrahydrofuran (ng/mL) |
0.125 |
| LBXVTO |
Blood Toluene (ng/mL) |
0.0250 |
| LBXVTP |
Blood 1,2,3-Trichloropropane (ng/mL) |
0.0400 |
| LBXVXY |
Blood m-/p-Xylene (ng/mL) |
0.0340 |