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Frequently Asked Questions

What is the National Exposure Report?

The National Report on Human Exposure to Environmental Chemicals (National Exposure Report) is a series of ongoing assessments of the U.S. population's exposure to environmental chemicals using biomonitoring. Biomonitoring is the direct assessment of people's exposure to chemicals by measuring the chemicals or their breakdown products (metabolites) in blood or urine.

For each chemical studied, scientists at CDC's Environmental Health Laboratory tested the blood or urine of people who took part in CDC's National Health and Nutrition Examination Survey (NHANES), an ongoing study of the civilian, non-institutionalized U.S. population. CDC's National Center for Health Statistics conducts NHANES. By looking for chemicals in blood or urine, researchers are better able to determine how much exposure people have to those chemicals.

The National Exposure Report provides unique exposure information to scientists, public health officials, and physicians. Knowing the levels of environmental chemicals in the U.S. population helps physicians and public health officials determine whether people have been exposed to higher levels of environmental chemicals. Exposure information can also help scientists plan and conduct research about these chemicals and their health effects.

The National Exposure Report does not provide health or toxicity information, state- or community-specific data, specific product or environmentally related information, or regulatory guidelines or recommendations.
 

What chemicals are included in the National Exposure Report?

CDC developed the National Exposure Report to address critical information gaps in environmental health. The Fourth Report builds on information contained in the First, Second, and Third Reports. The Fourth Report includes data on the U.S. population's exposure to 212 chemicals. Seventy five of these chemicals are measured for the first time. These new chemicals are in the following groups:

  • acrylamide and glycidamide adducts
  • arsenic species and metabolites
  • environmental phenols, including bisphenol A and triclosan
  • perchlorate
  • perfluorinated chemicals
  • polybrominated diphenyl ethers
  • volatile organic compounds
  • additions to chemical groups previously measured

A full listing of the chemicals included in the Fourth Report is available at http://www.cdc.gov/exposurereport/pdf/NER_Chemical_List.pdf.


What time periods does the Fourth Report cover?

The Fourth Report presents data obtained during the following survey periods 1999–2000, and 2001–2002 and 2003–2004.


What chemicals are measured in the 2003–2004 data but are not included in the Fourth Report?

Several groups of non-persistent pesticides that were reported for 1999–2002.Their 2003–2004 data are not yet ready. The Fourth Report contains the 1999–2002 data for these chemicals.

In addition, some new pesticides are being measured in the 2003–2004 data but are also not yet ready, including: Five additional specific organophosphorus insecticide metabolites, one pyrethroid metabolite, seven fungicides or metabolites, four atrazine metabolites, two herbicides, four plasma herbicides, twenty two substituted urea herbicides.

Data for some polycyclic aromatic hydrocarbon (PAH) metabolites are not included in the Fourth Report because improvements in analytical methods have found uncertainties in the measurements. For a full explanation of the PAHs excluded, please see Appendix C of the Fourth Report.

For information about how chemicals were chosen for inclusion in the Fourth Report, please see "How did CDC decide which chemicals to include in the Fourth Report?"


What chemicals are being measured for the first time in the Fourth Report?

The new chemicals that have been added to this release of the Report can be found at http://www.cdc.gov/exposurereport/pdf/NER_Chemical_List.pdf.


How was the release date for the Fourth Report determined?

The release date for the Fourth Report is set as the soonest possible date after laboratory analyses are completed and after government scientists and independent peer reviewers finish review of the Report content. As the Report expands to study an ever increasing number of chemicals, scientists require additional time for developing methods to analyze certain chemicals, and the number of chemicals means that the time required to ensure quality review of results also increases. Each successive edition of the National Exposure Report has included additional chemicals. The current release presents data on 212 chemicals, compared to just 27 for the First Report in 2001.

CDC has taken action to provide new data on chemicals as the laboratory results for these chemicals become available, not waiting on the Report release. For many of the chemicals, CDC publishes biomonitoring exposure information for the U.S. population in peer-reviewed publications very soon after they are completed. These articles (or links to the articles) are available http://www.cdc.gov/exposurereport/. This website is the best one-stop source for CDC's most recent biomonitoring exposure information.


Does CDC update information on U.S. population exposure between releases of the National Exposure Report?

For many of the chemicals, CDC publishes biomonitoring exposure information for the U.S. population in peer-reviewed publications very soon after they are completed—that is, not waiting for a new National Exposure Report. These articles (or links to the articles) are available at http://www.cdc.gov/exposurereport/. This Web site is the best one-stop source for CDC's most recent biomonitoring exposure information.


How can people see the Fourth Report?

The Fourth Report can be downloaded as a PDF document, or it can be searched and linked in its HTML form at http://www.cdc.gov/exposurereport/.


Why did CDC develop the National Exposure Report?

CDC first developed the Report to begin addressing a critical need for chemical exposure information for the U.S. population.


What are the public health uses of the Fourth Report?

The overall purpose of the Fourth Report is to provide unique exposure information to scientists, public health officials, and physicians. Specific uses of the Fourth Report are:

  • To provide scientists and researchers with levels of chemicals found in the U.S. population so that appropriate studies can be conducted to determine whether these levels pose a health risk.
  • For chemicals that have a known toxicity level, to identify the proportion of the U.S. population with levels above those toxicity levels.
  • To establish reference values that can be used by physicians and public health officials to determine whether a person has an unusually high level of an environmental chemical in his or her blood or urine.
  • To assess the effectiveness of public health efforts to reduce the exposure of the U.S. population to specific environmental chemicals (e.g., pesticides).
  • To determine whether levels of environmental chemicals are higher among special groups such as minorities, children, women of childbearing age, and the elderly.
  • To track, over time, trends in the levels of exposure of the U.S. population to environmental chemicals.

How will the Fourth Report inform future research?

By knowing the levels of chemicals in the U.S. population, researchers can study whether health effects occur at these levels. For chemicals that have measurable levels for much of the population, studying exposure levels helps researchers learn what groups of individuals are most at risk for having higher levels.

CDC's Environmental Health Laboratory at the National Center for Environmental Health collaborates with other federal agencies, academic institutions, governments, and other organizations on about 50 to 70 studies of exposure to environmental chemicals each year. These studies address (1) health effects resulting from exposure, (2) sources of exposure, and (3) how chemicals are processed in the body.


What does finding these levels in people's bodies mean? Are the levels dangerous?

Just because we can detect levels of an environmental chemical in a person's blood or urine does not necessarily mean that the chemical will cause effects or disease. Advances in analytical chemistry enable us to measure low levels of environmental chemicals in people, but separate studies of varying levels of exposure determine whether specific levels cause health effects.

For some chemicals, health threshold levels are better defined. For example, scientists have conducted extensive research on the human health effects of exposure to lead. CDC has published guidelines on preventing lead poisoning among children. These guidelines are based on lead levels in blood (see http://www.cdc.gov/nceh/lead/about/fedstrategy2000.pdf). As another example, CDC's National Tobacco Control Program (http://www.cdc.gov/tobacco/) is working to reduce the exposure of nonsmokers to environmental tobacco smoke. Measurements of serum cotinine track exposure to environmental tobacco smoke in nonsmokers. However, for many environmental chemicals, threshold levels are not known and more research is needed to assess health risks associated with the blood or urine levels of these chemicals documented in the Fourth Report.


What are the common sources of environmental exposure to the chemicals listed in the Fourth Report?

For most chemicals, people are exposed to low levels through foods or by breathing in air that contains the chemical. People can also be exposed by using products with chemicals in them or which have been stored in containers made with the chemicals.


How can people find out what their levels are? Can their doctors perform these tests? If not, can people send samples to CDC or some other laboratory to be tested?

For most of the chemicals listed in the Fourth Report, analyses are not readily available in commercial clinical laboratories. A physician may be able to test people's blood or urine for a few chemicals that have known health consequences, such as lead or mercury. If necessary, physicians can refer people for further evaluation to a medical specialist, such as a medical toxicologist or a physician who specializes in occupational and environmental medicine. CDC does not perform laboratory tests at the request of individuals. CDC does perform biomonitoring in 1) population groups being investigated by public health authorities for possible adverse health effects resulting from chemical exposure; 2) populations in public health surveys, such as NHANES; and 3) research studies of environmental chemical exposures.


Is CDC involved in other studies to determine the sources of and the health effects caused by these exposures?

Yes. CDC's Environmental Health Laboratory at the National Center for Environmental Health collaborates with other federal agencies, academic institutions, governments, and other organizations on about 50 to 70 studies of exposure to environmental chemicals each year.


What are other organizations doing to study these exposures?

The Agency for Toxic Substances and Disease Registry (ATSDR), the National Institutes of Health (particularly the National Institute of Environmental Health Sciences [NIEHS]), and the U.S. Environmental Protection Agency (EPA) sponsor research that addresses sources and effects of chemical exposures. People can get information online at these sites:


How did CDC decide which chemicals to include in the Fourth Report?

There are over 80,000 chemicals used in industry and commerce and there are several thousand high production volume chemicals. This means many chemicals have the potential to enter people's bodies. The Environmental Health Laboratory at CDC has extensive experience with public health evaluations in which biomonitoring was used for assessment of human chemical exposures; these chemicals have been included in the National Exposure Reports. CDC has also solicited suggestions for candidate chemicals from the public and other government agencies. Chemicals included in the National Exposure Reports have been selected based on: scientific data that suggested exposure in the U.S. population; the seriousness of health effects known or thought to result from some levels of exposure; the need to assess the efficacy of public health actions to reduce exposure to a chemical; the availability of an analytical method that is accurate, precise, sensitive, specific, and rapid; the availability of adequate blood or urine samples from the NHANES survey; and the analytical cost to perform the analysis. More information is available at http://www.cdc.gov/exposurereport/.


What statistical information is given for each chemical?

For each chemical, the Fourth Report presents descriptive statistics about the distribution of blood or urine levels of the chemical in the population. Statistics include geometric means and selected percentiles with confidence intervals. Percentiles provide additional information about the shape of the distribution. For all chemicals, the 50th, 75th, 90th, and 95th percentiles are presented. Data are presented for the total population as well as for population groups defined by age, sex, and race or ethnicity.


What methods did CDC use to analyze these chemicals? Where can I find more information about these chemicals?

To measure these chemicals or their metabolites in blood and urine, CDC's Environmental Health Laboratory used advanced analytical techniques, such as isotope dilution mass spectrometry, inductively coupled plasma mass spectrometry, and graphite furnace atomic absorption spectrometry. You can find information on the specific methods used in Appendix C of the Fourth Report.

For additional information about these chemicals, visit http://www.cdc.gov/biomonitoring/chemical_factsheets.html.


Why doesn't the Fourth Report include data on the states or local communities that are included in the survey?

NHANES is a national survey, not a regional or state-based survey, and thus is designed for survey findings to reflect the nation rather than individual counties or states. Producing accurate estimates at the state or local level would have required a much bigger and much different sample and would have limited CDC's ability to collect national data.


The Fourth Report includes data for Mexican Americans, non-Hispanic blacks, and non-Hispanic whites but not for other races or ethnic groups. Why?

No population group is excluded from participation in NHANES. However, sample sizes for some groups are too small for reliable estimates to be calculated. To produce reliable statistics for Mexican Americans and non-Hispanic blacks, the survey selects larger numbers of these two groups. The survey is not designed to select larger numbers for all groups.


Why doesn't the Fourth Report include data on all age groups?

NHANES examines people of all ages; however, the age groups may be limited for some chemicals based on criteria such as availability of blood or urine or the cost of the testing.


What is NHANES?

NHANES is a unique survey conducted by CDC's National Center for Health Statistics. NHANES collects data on the health of people living in the United States through interviews, direct physical examinations, and laboratory tests. For more information about NHANES, please visit http://www.cdc.gov/nchs/nhanes/about_nhanes.htm.

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