Component Description
Phthalates are a group of chemicals used to make plastics more flexible and
harder to break. They are often called plasticizers. Some phthalates are used as
solvents (dissolving agents) for other materials. They are used in many
products, such as vinyl flooring, adhesives, detergents, lubricating oils,
automotive plastics, plastic clothes (raincoats), and personal-care products
(soaps, shampoos, hair sprays, and nail polishes). Phthalates are used widely in
polyvinyl chloride plastics, which are used to make products such as plastic
packaging film and sheets, garden hoses, inflatable toys, blood-storage
containers, and medical tubing. 1,2-cyclohexane dicarboxylic acid, diisononyl
ester (DINCH) is used as a replacement of some high molecular weight phthalates.
Once phthalates or DINCH enter a person's body, they are converted into
breakdown products (metabolites) that pass out quickly in urine. Biomeasures of
phthalates and phthalates alternatives in humans are necessary to evaluate
potential human health effects from exposure to these chemicals.
Eligible Sample
All examined participants aged 3 to 5 years were eligible and participants
aged 6 years and older from a one-third subsample were eligible.
Description of Laboratory
Methodology
The test principle utilizes high performance liquid
chromatography-electrospray ionization-tandem mass spectrometry (HPLC-ESI-MS/MS)
for the quantitative detection in urine of the following metabolites: monoethyl
phthalate (MEP), monobutyl phthalate (MBP), mono-isobutyl phthalate (MiBP),
mono(3-carboxypropyl) phthalate (MCPP), mono(2-ethylhexyl) phthalate (MEHP),
monobenzyl phthalate (MBzP), monoisononyl phthalate (MNP),
mono(2-ethyl-5-oxohexyl) phthalate (MEOHP), mono(2-ethyl-5-hydroxyhexyl)
phthalate (MEHHP), mono(2-ethyl-5-carboxypentyl) phthalate (MECPP),
monocarboxyoctyl phthalate (MCOP), monocarboxynonyl phthalate (MCNP), and
cyclohexane-1,2-dicarboxylic acid-mono (hydroxy-isononyl) ester (MHNCH) (Silva,
et al., 2007). Urine samples are processed using enzymatic deconjugation of the
glucuronidated metabolites followed by on-line solid phase extraction (SPE)
coupled with reversed phase HPLC-ESI-MS/MS. Assay precision is improved by
incorporating isotopically labeled internal standards of the phthalate
metabolites and MHNCH. In addition, 4-methyl umbelliferyl glucuronide is used to
monitor deconjugation efficiency. This selective method allows for rapid
detection of metabolites of commonly used phthalates and DINCH in human urine
with limits of detection in the low ng/mL range.
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 2015-2016 cycle.
Laboratory Method Files
Phthalates and Phthalate Alternative Metabolites
(October 2018)
Laboratory Quality
Assurance and Monitoring
Urine specimens are processed, stored, and shipped to the Division of
Laboratory Sciences, National Center for Environmental Health, Centers for
Disease Control and Prevention for analysis.
Detailed specimen collection and processing instructions are discussed in the
NHANES Laboratory
Procedures Manual (LPM). Specimen vials are stored under appropriate frozen
(–20°C) conditions until they are shipped to the National Center for
Environmental Health for testing.
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 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
quality-control 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 are 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 quality control protocol for all CDC and
contract laboratories, which outlined the use of Westgard rules (Westgard, et
al., 1981) when running 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
by NCHS 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 Sciences’ quality control
and quality assurance 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
Refer to the 2015-2016
Laboratory Data Overview for general information on NHANES laboratory
data.
Subsample Weights
Urinary metals were measured in a full sample of
participants ages 3-5 and a one third subsample of persons 6 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 2015-2016
Demographic Data File contains demographic and 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.
Starting in the 2015-2016 NHANES cycle, the variable URXUCR (urine
creatinine) will not be reported in this file. URXUCR can be found in the data
file titled Albumin & Creatinine - Urine.
This laboratory data file can be linked to the other NHANES data files using
the unique survey participant identifier SEQN.
Starting in the 2015-2016 NHANES cycle, the variable URXUCR (urine
creatinine) will not be reported in this file. URXUCR can be found in the data
file titled “Albumin & Creatinine – Urine”.
Detection Limits
The detection limits were constant for the analytes in the
data set. Two variables are provided for each of these analytes. The variable
named ending in “LC” (ex., URDCNPLC) indicates whether the result was below the
limit of detection: the value “0” means that the result was at or above the
limit of detection, “1” indicates that the result was below the limit of
detection. For analytes with analytic results below the lower limit of detection
(ex., URDCNPLC=1), an imputed fill value was placed in the analyte results
field. This value is the lower limit of detection divided by the square root of
2 (LLOD/sqrt [2]). The other variable prefixed URX (ex., URXCNP) provides the
analytic result for the analyte.
The
lower limit of detection (LLOD, in ng/mL) for the phthalates and plasticizers
metabolites:
| VARIABLE NAME |
SAS LABEL |
LLOD |
| URXCNP |
Mono(carboxyisononyl) phthalate (ng/mL) |
0.2 |
| URXCOP |
Mono(carboxyisoctyl) phthalate (ng/mL) |
0.3 |
| URXECP |
Mono-2-ethyl-5-carboxypentyl phthalate (ng/mL) |
0.4 |
| URXHIBP |
MHIBP phthalate (ng/mL) |
0.4 |
| URXMBP |
Mono-n-butyl phthalate (ng/mL) |
0.4 |
| URXMC1 |
Mono-(3-carboxypropyl) phthalate (ng/mL) |
0.4 |
| URXMCOH |
MCOCH phthalate (ng/mL) |
0.5 |
| URXMEP |
Mono-ethyl phthalate (ng/mL) |
1.2 |
| URXMHBP |
Mono-3-hydroxy-n-butyl phthalate (ng/mL) |
0.4 |
| URXMHH |
Mono-(2-ethyl-5-hydroxyhexyl) phthalate (ng/mL) |
0.4 |
| URXMHNC |
Cyclohexane 1,2-dicarboxylic acid monohydroxy isononyl ester
(ng/mL) |
0.4 |
| URXMHP |
Mono-(2-ethyl)-hexyl phthalate (ng/mL) |
0.8 |
| URXMIB |
Mono-isobutyl phthalate (ng/mL) |
0.8 |
| URXMNP |
Mono-isononyl phthalate (ng/mL) |
0.9 |
| URXMOH |
Mono-(2-ethyl-5-oxohexyl) phthalate (ng/mL) |
0.2 |
| URXMZP |
Mono-benzyl phthalate (ng/mL) |
0.3 |
Please refer to the NHANES Analytic Guidelines and the on-line NHANES Tutorial for
further details on the use of sample weights and other analytic
issues.