National Health and Nutrition Examination Survey

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.

Examined participants aged 6 years and older from a one-third sample.

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 Procedures Manual (LPM).

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, 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), tungsten (W), tin(Sn), strontium(Sr), manganese(Mn) thallium (TI), lead (Pb), and uranium (U). This method is based on the method by (Mulligan, 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.

Refer to NHANES 2011-2012 Lab Methods for Antimony, Arsenic, Barium, Beryllium, Cadmium, Cesium, Cobalt, Lead, Manganese, Molybdenum, Platinum, Strontium, Thallium, Tin, Tungsten, and Uranium for detailed description of the laboratory method used.

The NHANES quality control and quality assurance protocols (QA/QC) meet the 1988 Clinical Laboratory Improvement Act mandates. Detailed QA/QC instructions are discussed in the NHANES Laboratory Procedures Manual (LPM).

The data were reviewed. Incomplete data or improbable values were sent to the performing laboratory for confirmation.

Refer to the 2011-2012 Laboratory Data Overview for general information on NHANES laboratory data.

Subsample Weights

Urinary heavy metals were measured in a one third subsample of persons 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.

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 heavy metals in the data set. 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. For analytes with analytic results below the lower limit of detection (i.e., URD___LC=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 lower limit of detection (LLOD, in µg/L) for the heavy metals in the data set:

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.