Table of Contents

Component Description

Organophosphate (OP) pesticides are used in both residential and agricultural settings in the United States. OP pesticides include malathion, diazinon, chlorpyrifos, Guthion® (azinphosmethyl), malathion, parathion, and many others. All OP pesticides have a common mode of toxicity because they are competitive inhibitors of acetylcholinesterase, the enzyme responsible for deacetylation of the neurotransmitter acetylcholine (Koelle G.B., 1994; Gompertz D., 1996). Unfortunately, the toxic effects of OP pesticides are not unique to insects; high doses can similarly affect wildlife and people.

OP pesticides were among the first of the U.S. Environmental Protection Agency (EPA)-registered pesticides whose food tolerances were reassessed (EPA, 2017), due to their common mode of toxicity and potential adverse effects in vulnerable populations, such as children.

Most of the organophosphate pesticides registered for use in the United States by the EPA are O, O-dimethyl, or O-diethyl substituted, which metabolize to dialkylphosphate (DAP) metabolites. The six common DAP metabolites (Dimethylphosphate, Diethylphosphate, Dimethylthiophosphate, Dimethyldithiophosphate, Diethylthiophosphate, and Diethyldithiophosphate) do not retain any of the structure unique to the pesticides from which they were derived, so it is impossible to identify individual pesticides from these metabolites. However, because these metabolites are common to the majority of OP pesticides, they can provide invaluable information about cumulative exposure to the OP class.

Eligible Sample

All examined participants aged 3 to 5 years and a one-third subsample of examined participants aged 6 years and older were eligible.

Description of Laboratory Methodology

The method uses solid phase extraction (SPE) coupled with isotope dilution-ultrahigh performance liquid chromatography (UHPLC)-tandem mass spectrometry (Jayatilaka N.K., et. al., 2017). The method relies on an enzymatic hydrolysis of urinary conjugates, automated off-line SPE to pre-concentrate the target compounds while minimizing urine matrix potential interferences to increase the overall sensitivity and specificity. The deconjugated target analytes in the urine extract are separated on an UHPLC system with reversed phase chromatography and quantified by isotope dilution tandem mass spectrometry.

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, and lab site for this component in the NHANES 2017-2018 cycle.

Laboratory Method Files

Organophosphate Insecticides- Dialkyl Phosphate Metabolites (OPD) (March 2022)

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, Atlanta, GA for analysis.

Detailed instructions on specimen collection and processing are discussed in the NHANES Laboratory Procedures Manual (LPM). Vials were stored under appropriate frozen (–30°C) conditions until they were shipped to the Division of Laboratory Sciences for testing.

The NHANES quality control and quality assurance protocols (QA/QC) meet the 1988 Clinical Laboratory Improvement Amendments 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 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 during “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 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 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’ 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

Refer to the 2017-2018 Laboratory Data Overview for general information on NHANES laboratory data.

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.

Subsample Weights

Organophosphate Pesticides - Dialkyl Phosphate Metabolites were measured in a one-third subsample of participants 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 2017-2018 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).

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 limit was constant for the analyte in the data set. Two variables are provided for this analyte. The variable name ending in “LC” (ex., URDOP1LC) 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 the analyte with analytic results below the lower limit of detection (URDOP1LC=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]). The variable prefixed URX (ex., URXOP1) provides the analytic result for that analyte.

The lower limit of detection (LLOD, in ng/mL) for Organophosphate Pesticides - Dialkyl Phosphate Metabolites:

Variable Name

Analyte Description

LLOD

URXOP1

Dimethylphosphate (ng/mL)

0.1

URXOP2

Diethylphosphate (ng/mL)

0.1

URXOP3

Dimethylthiophosphate (ng/mL)

0.1

URXOP4

Diethylthiophosphate (ng/mL)

0.1

URXOP5

Dimethyldithiophosphate (ng/mL)

0.1

URXOP6

Diethyldithiophosphate (ng/mL)

0.1

References

Codebook and Frequencies

SEQN - Respondent sequence number

Variable Name:
SEQN
SAS Label:
Respondent sequence number
English Text:
Respondent sequence number.
Target:
Both males and females 3 YEARS - 150 YEARS

WTSB2YR - Environmental Subsample B Weights

Variable Name:
WTSB2YR
SAS Label:
Environmental Subsample B Weights
English Text:
Environmental Subsample B Weights
Target:
Both males and females 3 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
3829.845402 to 1395405.4654 Range of Values 2851 2851
0 Participants 6+ years with no lab specimen 135 2986
. Missing 0 2986

URXOP1 - Dimethylphosphate (ng/mL)

Variable Name:
URXOP1
SAS Label:
Dimethylphosphate (ng/mL)
English Text:
Dimethylphosphate (ng/mL)
Target:
Both males and females 3 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
0.0707 to 622 Range of Values 2801 2801
. Missing 185 2986

URDOP1LC - Dimethylphosphate Comment Code

Variable Name:
URDOP1LC
SAS Label:
Dimethylphosphate Comment Code
English Text:
Dimethylphosphate Comment Code
Target:
Both males and females 3 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
0 At or above the detection limit 2712 2712
1 Below lower detection limit 89 2801
. Missing 185 2986

URXOP2 - Diethylphosphate (ng/mL)

Variable Name:
URXOP2
SAS Label:
Diethylphosphate (ng/mL)
English Text:
Diethylphosphate (ng/mL)
Target:
Both males and females 3 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
0.0707 to 252 Range of Values 2804 2804
. Missing 182 2986

URDOP2LC - Diethylphosphate Comment Code

Variable Name:
URDOP2LC
SAS Label:
Diethylphosphate Comment Code
English Text:
Diethylphosphate Comment Code
Target:
Both males and females 3 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
0 At or above the detection limit 2792 2792
1 Below lower detection limit 12 2804
. Missing 182 2986

URXOP3 - Dimethylthiophosphate (ng/mL)

Variable Name:
URXOP3
SAS Label:
Dimethylthiophosphate (ng/mL)
English Text:
Dimethylthiophosphate (ng/mL)
Target:
Both males and females 3 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
0.0707 to 355 Range of Values 2800 2800
. Missing 186 2986

URDOP3LC - Dimethylthiophosphate Comment Code

Variable Name:
URDOP3LC
SAS Label:
Dimethylthiophosphate Comment Code
English Text:
Dimethylthiophosphate Comment Code
Target:
Both males and females 3 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
0 At or above the detection limit 2540 2540
1 Below lower detection limit 260 2800
. Missing 186 2986

URXOP4 - Diethylthiophosphate (ng/mL)

Variable Name:
URXOP4
SAS Label:
Diethylthiophosphate (ng/mL)
English Text:
Diethylthiophosphate (ng/mL)
Target:
Both males and females 3 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
0.0707 to 34 Range of Values 2796 2796
. Missing 190 2986

URDOP4LC - Diethylthiophosphate Comment Code

Variable Name:
URDOP4LC
SAS Label:
Diethylthiophosphate Comment Code
English Text:
Diethylthiophosphate Comment Code
Target:
Both males and females 3 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
0 At or above the detection limit 1646 1646
1 Below lower detection limit 1150 2796
. Missing 190 2986

URXOP5 - Dimethyldithiophosphate (ng/mL)

Variable Name:
URXOP5
SAS Label:
Dimethyldithiophosphate (ng/mL)
English Text:
Dimethyldithiophosphate (ng/mL)
Target:
Both males and females 3 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
0.0707 to 175 Range of Values 2804 2804
. Missing 182 2986

URDOP5LC - Dimethyldithiophosphate Comment Code

Variable Name:
URDOP5LC
SAS Label:
Dimethyldithiophosphate Comment Code
English Text:
Dimethyldithiophosphate Comment Code
Target:
Both males and females 3 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
0 At or above the detection limit 1476 1476
1 Below lower detection limit 1328 2804
. Missing 182 2986

URXOP6 - Diethyldithiophosphate (ng/mL)

Variable Name:
URXOP6
SAS Label:
Diethyldithiophosphate (ng/mL)
English Text:
Diethyldithiophosphate (ng/mL)
Target:
Both males and females 3 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
0.0707 to 1.27 Range of Values 2804 2804
. Missing 182 2986

URDOP6LC - Diethyldithiophosphate Comment Code

Variable Name:
URDOP6LC
SAS Label:
Diethyldithiophosphate Comment Code
English Text:
Diethyldithiophosphate Comment Code
Target:
Both males and females 3 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
0 At or above the detection limit 111 111
1 Below lower detection limit 2693 2804
. Missing 182 2986