National Health and Nutrition Examination Survey

Pyrethroid pesticides are synthetic analogues of pyrethrins, used to control a range of insects in residential, commercial and agricultural settings, and they may be applied on animals to control insect infestation. Pyrethroid insecticides are among the most common active ingredients in commercially available insect sprays and are also used as structural termiticides. Permethrin is used in skin lotions and shampoos as a medical treatment for lice and scabies. Pyrethroid insecticides do not persist in the environment because they are rapidly degraded within days to months. Human metabolism of pyrethroids occurs rapidly, and metabolites are eliminated in urine and bile over several days. Two of the urinary metabolites measured are unique to specific pyrethroids: 4-fluoro-3-phenoxyacetic acid from cyfluthrin and cis-3-(2,2-dibromovinyl)-2,2-dimethylcyclopropane carboxylic acid from deltamethrin. The other urinary metabolites can result from exposure to any of several pyrethroid insecticides. Because pyrethroid insecticides are widely used in the U.S. population, measuring urinary pyrethroid metabolites is important to evaluate human exposure and potential for health effects.

Of the two herbicides measured in urine, 2,4-dichlorophenoxyacetic acid (2,4-D) and 2,4,5-trichlorophenoxyacetic acid (2,4,5-T), only 2,4-D is currently registered for use in the U.S. 2,4-D is widely used to control broadleaf weeds in residential, agricultural, and aquatic environments. It degrades in soil over days to weeks and is rarely detected in ground waters. 2,4-D is not metabolized by humans and is eliminated unchanged and rapidly in the urine. Because 2,4-D is widely used in the U.S., measuring urinary 2,4-D is important to evaluate human exposure and potential for health effects.

The specific organophosphorus insecticides with urinary metabolites measured are chlorpyrifos and chlorpyrifos-methyl (3,5,6-trichloro-2-pyridinol or TCPy), diazinon (2,-isopropyl-4-methyl-6-hydroxypyrimidine or IMPY), malathion (malathion dicarboxylic acid or MDA), and methyl and ethyl parathion (para-nitrophenol or PNP). Chlorpyrifos and malathion are widely used in residential and agricultural insect control, and chlorpyrifos-methyl and diazinon are restricted to agricultural applications only. Methyl parathion has extremely limited agricultural use, and ethyl parathion is no longer registered for use in the U.S. Each of these measured urinary metabolites can also result from environmental degradation of the parent organophosphorus insecticide. Human metabolism of these organophosphorus insecticides results in the specific metabolites named above, dialkylphosphate metabolites, and other metabolites, all which are eliminated in urine over a few days. Detecting any of these urinary metabolites in a person’s urine may indicate exposure to the specific organophosphorus insecticide or to the environmental breakdown product or both. Because several of these insecticides are widely used in the U.S., measuring these urinary organophosphate insecticide metabolites is important to evaluate human exposure and potential for health effects.

Participants aged 6 years and older who met the subsample requirements.

The approach followed is a modification of previous methodology (Beeson et al. 1999; Olsson et al. 2004). The target analytes are extracted and concentrated from the urine matrix using an automated solid phase extraction system. Selective separation of the analytes is achieved using high-performance liquid chromatography with a gradient elution program. Sensitive detection of the analytes is performed by a triple quadrupole mass spectrometer with a heated electrospray ionization source (Davis et al. 2013). Analytes are identified using the specific m/z ion transition, the retention time and the ion ratio of the quantification and confirmation m/z ion transitions. Isotopically labeled internal standards are used for precise and accurate quantification. This method can be used to assess human exposure to select non-persistent pesticides by measuring their metabolites in urine. It does not directly test for any disease.

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/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 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.

NCEH developed and distributed a quality control protocol for all the laboratories which outlined the Westgard rules used when running NHANES specimens. Any problems encountered during shipping or receipt of specimens, instrument calibration, reagents, and any special considerations are submitted to NCHS and Westat. Summary statistics for each control pool, QC graphs, 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 specifications outlined by Westgard (1981).

Subsample weights

Measures of urinary Pyrethroids, Herbicides, and OP Metabolites 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 2003-2004 data files using the unique survey participant identifier SEQN.

Detection Limits

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 detection limit divided by the square root of 2 is the value that is provided for results that are below the limit of detection.

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