Table of Contents

Locator Record

Title: Heavy Metals (L06HM_B )
Contact Number: 1-866-441-NCHS
Years of Content: 2001 - 2002
First Published: March, 2005
Revised: NA
Access Constraints: None
Use Constraints: None
Geographic Coverage: National
Subject:Heavy Metals
Record Source: NHANES 2001 - 2002
Survey Methodology: NHANES 2001 - 2002 is a stratified multistage probability sample of the civilian non-institutionalized population of the U.S.
Medium: NHANES Web site; SAS transport files

Component Description

Urinary Barium, Beryllium, Cadmium, Cobalt, Cesium, Molybdenum, Lead, Platinum, Antimony, Thallium, Tungsten, and Uranium

Trace metals have been associated with adverse health effects in occupational studies or laboratory studies, but have not been monitored in general population groups.

Information on levels of exposure to these compounds is essential to determine the need for regulatory mechanisms to reduce the levels of hazardous pollutants to which the general population is exposed and to establish population-based reference intervals for several potentially toxic metals.

Eligible Sample

Participants aged 6 years and older who met the subsample requirements and who did not meet any of the exclusion criteria composed the eligible sample.

Description of Laboratory Methodology

Urinary Barium, Beryllium, Cadmium, Cobalt, Cesium, Molybdenum, Lead, Platinum, Antimony, Thallium, Tungsten and Uranium

Inductively coupled plasma-mass spectrometry (ICP-MS) is a multi-element analytical technique (Date et al., 1989). Liquid samples are introduced into the ICP through a nebulizer and spray chamber carried by a flowing argon stream. By coupling radio frequency power into flowing argon, a plasma is created in which the predominant species are positive argon ions and electrons. The sample passes through a region of the plasma with a temperature of 6000–8000 K. The thermal energy atomizes the sample and then ionizes the atoms. The ions, along with the argon, enter the mass spectrometer through the interface that separates the ICP, which operates at atmospheric pressure, from the mass spectrometer, which operates at a pressure of 10–6 torr. The mass spectrometer permits detection of ions at each mass in rapid sequence, allowing individual isotopes of an element to be determined. Electrical signals resulting from the detection of the ions are processed into digital information that is used to indicate the intensity of the ions and subsequently the concentration of the element. A total of 15 elements, including Be, Mn, Co, Ni, Mo, Sn, Sb, Cs, Ba, W, Pt, Tl, and Pb are measured in urine by ICP-MS based on the method by Kevin J. Mulligan et al. (Franke et al., 1994) Urine samples are diluted 1+9 with 2% v/v double-distilled concentrated nitric acid (GFS Chemicals Inc., Columbus, OH) containing both iridium and rhodium for multi-internal standardization. This procedure may be used for all 15 elements or subsets of the 15 elements.

This method is used to achieve rapid and accurate quantification of multiple elements of toxicological and nutritional interest. The method is sensitive enough to be used to rapidly screen urine specimens from subjects suspected of exposure to a number of important toxic elements or to evaluate environmental or other non-occupational exposure to these same elements.

Special note regarding urine cadmium

Urine cadmium levels are corrected for interference from molybdenum oxide. The variable name for the corrected cadmium levels is URDUCD. The formula for the correction is:

URDUCD = URXUCD – [(0.00175* URXUMO) – 0.0136]

where URXUCD is the original value for the cadmium result.

Corrected values that are less than zero are recoded to equal zero. If the result for urine molybdenum is missing, then the result for the corrected cadmium result is also missing.

The corrected data set also includes a variable URDUCDLC to indicate which results were below the limit of detection. For results below the limit of detection, the corrected value was calculated using the detection limit for urinary cadmium divided by the square root of two (value = 0.04).

See below for further explanation of this correction:

Effect of Molybdenum Oxide on Urine Cadmium Results

The ICP-MS method for the determination of urine cadmium has not been corrected for a possible interference from molybdenum oxide, MoO. Because the historical Proficiency Testing (PT) results for urine Cd were well within expected ranges and no consistent bias was observed with these PT samples, including several years of challenges, it was thought that, at typical biological molybdenum levels and typical instrumental oxide levels, the interference would not be significant. Upon investigation with over 6000 NHANES samples analyzed, we were able to see a possible effect on the urine Cd results when the results for the urine Cd versus Mo concentration were plotted. This effect cannot be easily seen with a few hundred sample results. Upon further investigation, we determined that the historical NHANES urine Cd results were biased high. For example, a 1st order approximation of the effect of this interference was determined to be 0.33 μg/L (at the 50th percentile) for urine Cd without correcting for the MoO interference versus 0.19 μg/L with the correction. Therefore, we investigated how best to implement a revised analytical method to eliminate this interference. In addition, until DLS had received and implemented some new ICP-MS technology, we could not eliminate this interference using the traditional ICP-MS technologies. We have recently implemented this new technology (Dynamic Reaction Cell technology [DRC]) and have been able to develop a revised analytical method that allows for correction of this MoO interference.

A method comparison was performed using 208 samples that included the typical range of Cd and Mo concentrations in urine. The results are shown in Figure 1, where (Cd Std Method – Cd Corrected Method) is plotted versus the urine molybdenum concentration. CdStd Method is the non-DRC method and Cd Corrected Method is the DRC method. The best fit regression line had an r2 = 0.81 and is given by Equation (1):

(Cd Std Method - Cd Corrected Method) = 0.00175 (Mo) – 0.01360 (1)

Equation (2) is the adjustment equation used to correct the Standard Method results to the new Corrected method (the new DRC method).

Cd Corrected Method = Cd Std Method – (0.00175 * (Mo) + 0.01360 UCD Corrected Method
= UCd Std Method – (0.00175 * (UMO) + 0.01360 (2)

Data Processing and Editing

Automated data collection procedures for the survey were introduced in NHANES 1999. In the mobile examination centers (MECs) and analytical laboratories, data for the laboratory component is recorded directly onto a computerized data collection form. The system is centrally integrated and it allows for ongoing monitoring of much of the data. While the complete blood count and pregnancy analyses are performed in the MEC laboratory, most analyses are conducted elsewhere by approximately 21 laboratories across the United States.

Guidelines have been developed that provide standards for naming variables, filling missing values, and handling missing records. NCHS staff, assisted by contract staff, has developed data-editing specifications that check data sets for valid codes, ranges, and skip pattern consistencies and examine the consistency of values between interrelated variables. Comments have been reviewed and recoded. NCHS staff verifies extremely high and low values whenever possible, and numerous consistency checks are performed. Nonetheless, users should examine the range and frequency of values before analyzing data.

For laboratory tests with a lower detection limit, results below the lower detection limit are replaced with a value equal to the detection limit divided by the square root of two. This value has been created to help the user distinguish a nondetectable laboratory test result from a measured laboratory test result.

Laboratory Quality Assurance and Monitoring

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.

Analytic Notes

Urinary Barium, Beryllium, Cadmium, Cobalt, Cesium, Molybdenum, Lead, Platinum, Antimony, Thallium, Tungsten, and Uranium

Measures of this urinary multi-analyte profile are assessed in participants aged 6 years and over on a randomly selected 1/3 subsample. Specific sample weights for this subsample are included in this data file and should be used when analyzing these data. Read the Special Sample Weights for this Dataset section below before beginning analysis.

The dataset includes 2-year and 4-year subsample weights. The 4-year weights should be used if these 2001–2002 data are combined with 1999–2000 data. The 1999–2000 data files have been updated to include the subsample 4-year weights. The recommended procedure for variance estimation requires use of stratum and PSU variables (SDMVSTRA and SDMVPSU, respectively), which are included in the demographic data file for each data release. For further information, see the NHANES Analytic Guidelines, June 2004 version at: http://www.cdc.gov/nchs/data/nhanes/nhanes_general_guidelines_june_04.pdf.

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 6 YEARS - 150 YEARS

WTSHM2YR - Heavy Metal Subsample 2 Year Mec Weight

Variable Name:
WTSHM2YR
SAS Label:
Heavy Metal Subsample 2 Year Mec Weight
English Text:
Heavy Metal Subsample 2 Year Mec Weight
Target:
Both males and females 6 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
0 to 671114.86074 Range of Values 2804 2804
. Missing 0 2804

WTSHM4YR - Heavy Metal Subsample 4 Year Mec Weight

Variable Name:
WTSHM4YR
SAS Label:
Heavy Metal Subsample 4 Year Mec Weight
English Text:
Heavy Metal Subsample 4 Year Mec Weight
Target:
Both males and females 6 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
0 to 339040.61749 Range of Values 2804 2804
. Missing 0 2804

URXUCR - Creatinine, urine (mg/dL)

Variable Name:
URXUCR
SAS Label:
Creatinine, urine (mg/dL)
English Text:
Creatinine, urine (mg/dL)
Target:
Both males and females 6 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
8 to 699 Range of Values 2709 2709
. Missing 95 2804

URXUBA - Barium, urine (ng/mL)

Variable Name:
URXUBA
SAS Label:
Barium, urine (ng/mL)
English Text:
Barium, urine (ng/mL)
Target:
Both males and females 6 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
0.08 to 248.7 Range of Values 2690 2690
. Missing 114 2804

URXUBE - Beryllium, urine (ng/mL)

Variable Name:
URXUBE
SAS Label:
Beryllium, urine (ng/mL)
English Text:
Beryllium, urine (ng/mL)
Target:
Both males and females 6 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
0.09 to 0.2 Range of Values 2690 2690
. Missing 114 2804

URDUCD - Cadmium, urine (ng/mL)

Variable Name:
URDUCD
SAS Label:
Cadmium, urine (ng/mL)
English Text:
Cadmium, urine (ng/mL)
Target:
Both males and females 6 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
0 to 36.777475 Range of Values 2690 2690
. Missing 114 2804

URDUCDLC - Urinary cadmium comment code

Variable Name:
URDUCDLC
SAS Label:
Urinary cadmium comment code
English Text:
Urinary cadmium comment code
Target:
Both males and females 6 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
0 detectable result 2582 2582
1 below detectable result 108 2690
. Missing 114 2804

URXUCO - Cobalt, urine (ng/mL)

Variable Name:
URXUCO
SAS Label:
Cobalt, urine (ng/mL)
English Text:
Cobalt, urine (ng/mL)
Target:
Both males and females 6 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
0.05 to 38.68 Range of Values 2690 2690
. Missing 114 2804

URXUCS - Cesium, urine (ng/mL)

Variable Name:
URXUCS
SAS Label:
Cesium, urine (ng/mL)
English Text:
Cesium, urine (ng/mL)
Target:
Both males and females 6 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
0.1 to 363.48 Range of Values 2690 2690
. Missing 114 2804

URXUMO - Molybdenum, urine (ng/mL)

Variable Name:
URXUMO
SAS Label:
Molybdenum, urine (ng/mL)
English Text:
Molybdenum, urine (ng/mL)
Target:
Both males and females 6 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
0.57 to 614.5 Range of Values 2690 2690
. Missing 114 2804

URXUPB - Lead, urine (ng/mL)

Variable Name:
URXUPB
SAS Label:
Lead, urine (ng/mL)
English Text:
Lead, urine (ng/mL)
Target:
Both males and females 6 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
0.07 to 13.1 Range of Values 2690 2690
. Missing 114 2804

URXUPT - Platinum, urine (ng/mL)

Variable Name:
URXUPT
SAS Label:
Platinum, urine (ng/mL)
English Text:
Platinum, urine (ng/mL)
Target:
Both males and females 6 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
0.03 to 1177.46 Range of Values 2690 2690
. Missing 114 2804

URXUSB - Antimony, urine (ng/mL)

Variable Name:
URXUSB
SAS Label:
Antimony, urine (ng/mL)
English Text:
Antimony, urine (ng/mL)
Target:
Both males and females 6 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
0.03 to 4.9 Range of Values 2690 2690
. Missing 114 2804

URXUTL - Thallium, urine (ng/mL)

Variable Name:
URXUTL
SAS Label:
Thallium, urine (ng/mL)
English Text:
Thallium, urine (ng/mL)
Target:
Both males and females 6 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
0.01 to 2.82 Range of Values 2653 2653
. Missing 151 2804

URXUTU - Tungsten, urine (ng/mL)

Variable Name:
URXUTU
SAS Label:
Tungsten, urine (ng/mL)
English Text:
Tungsten, urine (ng/mL)
Target:
Both males and females 6 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
0.03 to 10.09 Range of Values 2652 2652
. Missing 152 2804

URXUUR - Uranium, urine (ng/mL)

Variable Name:
URXUUR
SAS Label:
Uranium, urine (ng/mL)
English Text:
Uranium, urine (ng/mL)
Target:
Both males and females 6 YEARS - 150 YEARS
Code or Value Value Description Count Cumulative Skip to Item
0.003 to 3.469 Range of Values 2690 2690
. Missing 114 2804