National Health and Nutrition Examination Survey

Biomonitoring of urinary environmental phenols and parabens is used to determine their prevalence in humans and the relevance of human exposure in public health. The sources of human exposure to these phenolic compounds include industrial pollution, pesticide use, food and bottled water, and personal care products. Specifically, bisphenol A (BPA) is used in the manufacture of polycarbonate plastics and epoxy resins, which have been used in baby bottles, as protective coatings on food containers, and as composites and sealants in dentistry.

Alkylphenols such as 4-tert-octylphenol, are used in the manufacture of nonionic surfactants used in detergents. Phenols are also used as sunscreen agents for skin protection, and as UV filters in cosmetic products and plastics to improve stability (e.g., benzophenone-3 [BP-3]), or used as bactericides (e.g., triclosan) in soap and other personal care products.

Parabens are short alkyl chain esters of para-hydroxybenzoic acid (PHBA) that are widely used as preservatives in pharmaceuticals, cosmetics and in such personal care products as shampoos, hair and shaving products, facial and skin cleansers, and lotions. Parabens also occur naturally in some foods, including specific fruit juices and wine. After parabens are absorbed in the body, they are rapidly hydroyzed and then conjugated to glucuronide or sulfate and eliminated in the urine. Measurement of urinary environmental phenols and parabens is useful to assess recent human exposure.

Participants aged 6 years and older who met the subsample requirements

Bisphenol A (BPA) and Alkylphenols (APs) have been previously measured in biological matrixes by using gas chromatography (GC) or high performance liquid chromatography (HPLC) coupled with different detection techniques. To achieve enhanced sensitivity and selectivity, the phenols have been derivatized to alkyl or acyl derivatives before GC-mass spectrometry (GC/MS) analysis. We have developed a sensitive method for measuring BPA, 4-tert-octylphenol (tOP), benzophenone-3 (BP-3), one chlorophenols triclosan, and four parabens. The method uses solid phase extraction (SPE) coupled on-line to HPLC and tandem mass spectrometry (MS/MS). With the use of isotopically labeled internal standards, the detection limits in 100 μL of urine are 0.1-2 nanograms per milliliter (ng/mL), sufficient for measuring urinary levels of phenols in non-occupationally exposed subjects.

Urine specimens are processed, stored, and shipped to the Division of Environmental Health 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/Medical Technologists Procedures Manual (LPM). Vials are stored under appropriate frozen (–20°C) conditions until they are shipped to National Center for Environmental Health for testing.

Mobile Examination Centers (MECs)

Laboratory team performance is monitored using several techniques. NCHS and contract consultants use a structured quality assurance evaluation during unscheduled visits to evaluate both the quality of the laboratory work and the quality-control procedures. Each laboratory staff person is observed for equipment operation, specimen collection and preparation; testing procedures and constructive feedback are given to each staff. Formal retraining sessions are conducted annually to ensure that required skill levels were maintained.

The NHANES QA/QC protocols meet the 1988 Clinical Laboratory Improvement Act mandates. Detailed QA/QC instructions are discussed in the NHANES LPM.

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 2.0% of all specimens.

NCHS developed and distributed a quality control protocol for all the contract laboratories which outlined the Westgard rules used 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 and Westat 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 Environmental Health Laboratory Sciences’ quality control and quality assurance performance criteria for accuracy and precision (similar to specifications outlined by Westgard (1981).

Subsample weights

Measures of urinary environmental phenols and parabens were measured in a one third subsample of persons 6 years and over.  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.

Variance estimation

The analysis of NHANES laboratory data must be conducted with the key survey design and basic demographic variables. The NHANES 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.

Links to NHANES Data Files

This laboratory data file can be linked to the other NHANES data files using the unique survey participant identifier 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 named URD___LC indicates whether the result was below the limit of detection. There are two values: “0” and “1””. “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 named URX___ provides the analytic result for that analyte.

The lower limit of detection for the environmental phenols (bisphenol A (BPA) and alkylphenols (APs)) is: 

Please refer to the Analytic Guidelines for further details on the use of sample weights and other analytic issues.