National Human Adipose Tissue Survey (Nhats)
The U.S. Environmental Protection Agency (EPA)'s National Human Monitoring Program (NHMP), established by the U.S. Public Health Service in 1967, used an exposure-based approach to assess human exposure to toxic substances. Its primary component was the National Human Adipose Tissue Survey (NHATS), an annual survey conducted from 1970 to 1989 to collect and chemically analyze human adipose tissue specimens for the presence of toxic chemicals.
Objectives of the NHATS survey were to estimate baseline levels and trends of exposure to toxic chemicals for the U.S. population and selected subpopulations.
Samples were collected via a statistically-based survey sampling design to obtain a national sample of adipose tissue donors from among cadavers and surgical patients for three age groups:
- 0-14 years,
- 15-44 years,
- 45+ years.
In this design, the 48 conterminous states were partitioned into the nine U.S. Census divisions, and tissue donors were selected from randomly-selected Metropolitan Statistical Areas (called MSAs) within each Census division. The MSAs were selected with probabilities proportional to their populations, ensuring that the more-populated regions of the country were appropriately represented in the sample. As much as possible, the same MSAs were used from one survey to another to allow for time trends to be more precisely estimated.History/Chronology:
- 1970- 1981, 1983 Tissue samples collected from individual donors were analyzed to estimate concentrations of selected organochlorine pesticides and the extent to which polychlorinated biphenyls (PCBs) were detected within each survey. For multiresidue analysis of pesticides, a modified Mills, Onley and Gaither analytical method was used, while packed column gas chromatography with electron capture detection (PGC/ECD) was used to quantify levels of various organochlorine pesticides and the presence of PCBs.
- 1982,1984,1986 These surveys were conducted using the list of target chemicals expanded to include additional semivolatile and volatile organic compounds (e.g., organochlorine pesticides, aromatics, PCBs, chlorobenzenes, phosphates, and phthalates) of interest under the Toxic Substances Control Act (TSCA)
- 1982, 1987 The tissue samples collected in the these surveys were analyzed for polychlorinated dibenzo-p-dioxins and dibenzofuran congeners. For these surveys, high resolution gas chromatography with mass spectrometry (HRGC/MS) was performed on composites, or samples consisting of mixtures of tissue samples from multiple donors. Composite sampling designs were employed and statistical methods were developed to allow analytical results from composite samples to be used in estimating concentration levels for individuals in the U.S. population.
Because many of the chemicals monitored by NHATS were lipophilic chemicals, lipid-adjusted body burden concentration levels are stored in the NHATS database. That is, the measured wet weight of each tissue sample was divided by the sample's percent extractable lipid content prior to the calculation of the concentration level. EPA has used NHATS data in a number of ways to characterize population exposures to a wide range of toxic substances.Other Sources:
This document has been reviewed in accordance with U.S. Environmental Protection Agency policy and approved for publication. Mention of trade names or commercial products does not constitute endorsement or recommendation for use.
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