• Component Description
• Eligible Sample
• Description of Laboratory Methodology
• Laboratory Quality Assurance and Monitoring
• Data Processing and Editing
• Analytic Notes
• References
• Codebook
  • SEQN - Respondent sequence number
  • WTSSBJ2Y - Surplus specimen B 17-18 2 year weights
  • SSDONA - Dodecafluoro-3H-4,8-dioxanoate
  • SSDONAL - Dodecafluoro-3H-4,8-dioxanoate cmt cd
  • SSGENX - GenX
  • SSGENXL - GenX cmt cd
  • SSCLPF - Chlorohexadecafluorooxanonane sulfonate
  • SSCLPFL - Chlorohexadecafluorooxanonane sulfon cd
  • SSFHPS - Perfluoro-1-heptanesulfonate
  • SSFHPSL - Perfluoro-1-heptanesulfonate cmt cd
  • SSPFHA - Perfluorohexanoate
  • SSPFHAL - Perfluorohexanoate cmt cd

National Health and Nutrition Examination Survey

2017-2018 Data Documentation, Codebook, and Frequencies

Perfluoroalkyl and Polyfluoroalkyl Substances (Surplus) (SSPFAS_J)

Data File: SSPFAS_J.xpt

First Published: December 2020

Last Revised: April 2022

Component Description

Human exposure to per- and polyfluoroalkyl substances (PFAS) is a growing public health concern. PFAS encompass thousands of environmentally persistent man-made chemicals that have been used in industry and consumer products worldwide since the 1950s. These chemicals can be used in food packaging and many other household products, as well as aqueous firefighting foams (AFFF).  PFAS have been detected in air, soil, and water.

Exposure to a select number of PFAS in the United States is widespread as suggested by nearly universal detection of these chemicals in serum collected from NHANES participants (CDC, 2019). Changes in the manufacture of several of the PFAS included in NHANES since the early 2000s may result in a potential increased market use of other PFAS. Yet, the extent of exposure to these newer and alternative PFAS among the general U.S. population is rather limited and only based on the use of urine as a matrix (Calafat et al. 2019). To fill in this data gap, NCEH modified and validated an analytical method used at CDC for quantifying five additional PFAS in serum.

These additional PFAS are: dodecafluoro-3H-4,8-dioxanoate (DONA), tetrafluoro-2-(1,1,2,2,3,3,3-heptafluoropropoxy)-propanoate (GENX), 9-chlorohexadecafluoro-3-oxanonane-1-sulfonate (CLPF), perfluoro-1-heptanesulfonate (FHPS), and perfluorohexanoate (PFHA).

Eligible Sample

One-third subsample of participants aged 12+ years from NHANES 2017-2018 with stored serum (N=1,929).

Description of Laboratory Methodology

The method uses 50 µL serum and is based on a modification of an existing method developed to quantify PFAS in serum and urine (Kato et al. 2018).  Concentrations of PFAS are quantified by on online solid phase extraction (SPE) coupled to high performance liquid chromatography-isotope dilution tandem mass spectrometry (HPLC-MS/MS) using validated analytical approaches published in the peer-reviewed literature.  The limits of detection are in the sub-parts-per-billion (ng/mL) range. 

Laboratory Quality Assurance and Monitoring

The analytical measurements were conducted following strict quality control/quality assurance CLIA guidelines. Along with the study samples, each analytical run included high- and low-concentration quality control materials (QCs) and reagent blanks to assure the accuracy and reliability of the data. The concentrations of the high-concentration QCs and the low-concentration QCs, averaged to obtain one measurement of high-concentration QC and low-concentration QC for each run, were evaluated using standard statistical probability rules (Caudill et al. 2008).

Data Processing and Editing

Data were received after all analyses were complete. The data were not edited.
Data Access: All data are publicly available.

Analytic Notes

Detection Limits

The detection limits were constant for all of the analytes in the data set. Two variables are provided for each analyte. The variable name ending in “L” (ex., SSDONAL) 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 limit of detection (ex., SSDONAL=1), an imputed fill value was placed in the analyte results field. This value is the limit of detection divided by square root of 2 (LOD/√2). The other variable prefixed SS (ex., SSDONA) provides the analytic result for that analyte.

The limits of detection (LODs, in ng/mL) for DONA, GENX, CLPF, FHPS, and PFHA are 0.1.

Subsample Weights

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. Previous versions of this data file included a sample weight variable (WTSB2YR) but when observations were removed from this data file, a new sample weight was created, and a new sample weight variable was added to this data file (WTSSBJ2Y). 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.

References

• Calafat AM, Kato K, Hubbard K, Jia T, Botelho JC, Wong LY. Legacy and alternative per- and polyfluoroalkyl substances in the U.S. general population: Paired serum-urine data from the 2013-2014 National Health and Nutrition Examination Survey. Environ Int. 2019 Oct;131:105048.
  
• Caudill SP, Schleicher RL, Pirkle JL. (2008). Multi-rule quality control for the age-related eye disease study. Statist Med 27: 4094-4106.
  
• CDC. 2019. Fourth National Report on Human Exposure to Environmental Chemicals, Updated Tables, January 2019. Atlanta, GA:Centers for Disease Control and Prevention; National Center for Environmental Health; Division of Laboratory Sciences. Available: https://www.cdc.gov/exposurereport/pdf/FourthReport_UpdatedTables_Volume1_Jan2019-508.pdf [accessed Feb 14, 2020].
  
• Kato, K., Kalathil, A.A., Patel, A.M., Ye, X., Calafat, A.M., 2018. Per- and polyfluoroalkyl substances and fluorinated alternatives in urine and serum by on-line solid phase extraction-liquid chromatography-tandem mass spectrometry. Chemosphere 209, 338–345.
  

Codebook and Frequencies