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The EPA does all it can to ensure that the identity of survey participants cannot be disclosed. All direct identifiers, as well as any characteristics that might lead to identifications, are omitted from the data. Any intentional identification or disclosure of a person or establishment violates the assurances of confidentiality given to the providers of the information. Therefore, users will (1) use the data in this study for statistical reporting and analysis only; (2) make no use of the identity of any person or establishment discovered inadvertently and will advise the HEDS Administrator of any such discovery; (3) will not link this data with individually identifiable data from other EPA or non-EPA data.

By using the data you signify your agreement to comply with the above-stated statutorily based requirements.

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The PAHs in Blanks data set contains the analytical results of measurements of up to 11 polynuclear aromatic hydrocarbons (PAHs) in 20 blank samples from 14 households. Measurements were made in blank samples of indoor air, dust, and soil. Blank samples were used to assess the potential for sample contamination during collection, storage, shipment, processing, and analysis. The samples were analyzed as part of the QA/QC protocols of the NHEXAS project. The target PAHs included anthracene (CAS #120-12-7), benzo(a)pyrene (CAS #50-32-8), chrysene (CAS #218-01-9), and phenanthrene (CAS #85-01-8). Keywords: quality assurance; blanks; PAHs.

The National Human Exposure Assessment Survey (NHEXAS) is a federal interagency research effort coordinated by the Environmental Protection Agency (EPA), Office of Research and Development (ORD). Phase I consists of demonstration/scoping studies using probability-based sampling designs. The studies collected household environmental and personal samples for chemical analysis, and questionnaires were administered. The NHEXAS Phase I Questionnaires were organized into six modules for simplicity in administration (to minimize respondent burden and maximize participation rates at each step) and for collecting information that can be temporally related to the exposure, concentration, and/or biological measurements collected in NHEXAS: Descriptive, Baseline, Technician, Follow-up, Time and Activity diary, and Dietary diary (and follow-up). The NHEXAS-Maryland study sampled residences determined by a proportion-based sample of Baltimore and four adjacent counties and measured metals, pesticides, and polynuclear aromatic hydrocarbons (PAHs). The study was conducted by Harvard University, Emory University, Johns Hopkins University, and Westat. Data collection occurred up to six times over one year for the participating households. Analytical results were obtained under strict QA/QC requirements during collection, processing, and final deposition into databases.

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Quality Assurance:

These data are the result of a probability-based sampling design specific to the population under study. Thus the data may or may not be representative of subsets of this study's population or of other populations. The study was designed to test certain hypotheses, which may limit its applicability for other purposes. When using these data it is important to consider the percentage of non-responses or non-detects and concentrations less than the detection limit as indicators of its usefulness for other purposes. The U.S. EPA accepts no liability for any errors or omissions in the results included in the data sets, associated information, and/or documentation.

Based on the output format selected by the user and the software into which the data set is imported, measurements and sampling weights may be zero-padded to the right of non-zero decimal digits. These zeroes are a function of the formatting process and the software's acceptance of that format and should not be construed as significant digits in the value. Measurement values are provided with four significant digits; sampling weights are provided with three decimal digits.

Records for samples or questionnaires not meeting chain of custody or QA requirements have not been included in this data set.