Trace metals have been associated with adverse health effects in occupational studies or laboratory studies, but have not been monitored in general population groups.
This method is used to achieve rapid and accurate quantifications of multiple elements of toxicological and nutritional interest. The method is sensitive and rapid enough to screen urine specimens from subjects suspected to be exposed to a number of important toxic elements, or to evaluate environmental or other nonoccupationally exposure to these same elements.
Participants aged 6 years and older, who met the subsample requirements, were eligible.
Description of Laboratory Methodology
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). Read the General Documentation on Laboratory Data file for detailed data processing and editing protocols.
Inductively coupled plasma-mass spectrometry (ICP-MS) is a multi-element analytical technique (Date AR, 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, plasma is created in which the predominant species are positive argon ions and electrons. The sample passes through a region of the plasma that has a temperature of 6000–8000 ºK. The thermal energy atomizes the sample and then ionizes the atoms. The ions, along with the argon, enter the mass spectrometer through an interface that separates the ICP from the mass spectrometer, which is operating at an atmospheric pressure of 10–5 torr. The mass spectrometer permits ions at each mass to be detected 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 first the intensity of the ions and then the concentration of the element. The ICP-MS method is used to measure the following 12 elements in urine: beryllium (Be), cobalt (Co), molybdenum (Mo), cadmium (Cd), antimony (Sb), cesium (Cs), barium (Ba), tungsten (W), platinum (Pt), thallium (TI), lead (Pb), and uranium (U). This method is based on the method by (Mulligan KJ, et al. 1990) Urine samples are diluted 1+9 with 2% (v/v), double-distilled, concentrated nitric acid containing both iridium (Ir) and rhodium (Rh) for multi-internal standardization. This procedure can be used for all 12 elements or for subsets of the 12 elements.
There were no changes (from the previous 2 years of NHANES) to equipment, lab methods or lab site.
Detailed instructions on specimen collection and processing can be found in the NHANES Laboratory/Medical Technologists Procedures Manual (LPM).
Data Processing and Editing
Read the General Documentation on Laboratory Data file for detailed data processing and editing protocols.The analytical methods are described in the Description of Laboratory Methodology section above.
Laboratory Quality Assurance and Monitoring
NHANES Survey Design:
The analysis of NHANES laboratory data must be conducted with the key survey design and basic demographic variables. The Demographic file contains: Status Variables providing core information on the survey participant including examination status, Recoded Demographic Variables including age, gender, race etc., and Interview and Examination Sample Weight Variables and Survey Design Variables. The Questionnaire Data Files contain socio-economic data, health indicators, and other related information collected during household interviews. The Phlebotomy Examination file includes auxiliary information on duration of fasting, the time of day of the venipuncture, and the conditions precluding venipuncture. The Demographic, Questionnaire and Phlebotomy Examination files may be linked to the laboratory data file using the unique survey participant identifier SEQN.
Urinary heavy metals 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.
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 2007-2008 data files using the unique survey participant identifier SEQN.
The detection limits were constant for all of the heavy metals in the data set.
Lower detection limits for the heavy metals in the data set.:
Urinary Barium= 0.12 µg/L
Urinary Beryllium= 0.072 µg/L
Urinary Cadmium= 0.042 µg/L
Urinary Cobalt= 0.041 µg/L
Urinary Cesium= .066 µg/L
Urinary Molybdenum= .92 µg/L
Urinary Lead= 0.10 µg/L
Urinary Platinum= 0.009 µg/L
Urinary Antimonry= 0.032 ug/L
Urinary Thallium= 0.015 ug/L
Urinary Tungsten= 0.021 ug/L
Urinary Uranium= 0.0017 ug/L
The variable named LBD__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. In cases where the result was below the limit of detection, the value for that variable is the detection limit divided by the square root of two.
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.