Executive Summary

Background

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 by measuring chemicals in people's blood and urine, also called biomonitoring. The Fourth National Report on Human Exposure to Environmental Chemicals (Fourth Report) presents exposure data for 212 environmental chemicals for the civilian, noninstitutionalized U.S. population. This Fourth Report includes results from 2003–2004, as well as data from 1999–2000 and 2001–2002 as reported in the Second and Third National Report on Human Exposure to Environmental Chemicals.

To obtain data for this Fourth Report, the Centers for Disease Control and Prevention (CDC)'s Environmental Health Laboratory at the National Center for Environmental Health measured chemicals or their metabolites in blood and urine from a random sample of participants from the National Health and Nutrition Examination Survey (NHANES). CDC's National Center for Health Statistics conducts NHANES, which is a series of surveys on the health status, health-related behaviors, and nutrition of the U.S. population. Since 1999, NHANES has been conducted in continuous two-year survey cycles.

For the National Exposure Report, an environmental chemical refers to a chemical compound or chemical element present in air, water, food, soil, dust, or other environmental media, such as consumer products. Blood and urine levels reflect the amount of the chemical that actually gets into the body from the environment. Either the chemical or its metabolite is measured. A metabolite is a substance produced when body tissues chemically alter the original compound.

The Fourth Report includes results for 75 chemicals measured for the first time in the U.S. population. These 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; and
• some additions to chemical groups previously measured.

A complete listing of the 75 new chemicals is given in What's New. A full listing of all the chemicals included in the Fourth Report is available at http://www.cdc.gov/exposurereport/pdf/NER_Chemical_List.pdf.

Public Health Uses of the Fourth Report

The Fourth Report provides unique exposure information to scientists, physicians, and health officials to help prevent effects that may result from exposure to environmental chemicals. Specific public health uses of the exposure information in the Fourth Report are to:

• determine which chemicals get into Americans' bodies and at what concentrations;
• determine what proportion of the population has levels above those associated with adverse health effects for chemicals with a known toxicity level;
• establish reference values that can be used by physicians and scientists to determine whether a person or group has an unusually high exposure;
• assess the effectiveness of public health efforts to reduce exposure of Americans to specific chemicals and track levels over time;
• determine whether exposure levels are higher among minorities, children, women of childbearing age, or other special groups; and
• direct priorities for research on human health effects from exposure.

Interpreting the Data

The presence of an environmental chemical in people's blood or urine does not mean that it will cause effects or disease. The toxicity of a chemical is related to its dose or concentration, in addition to a person's individual susceptibility. Small amounts may be of no health consequence, whereas larger amounts may cause adverse health effects. Research studies, separate from the National Exposure Report, are required to determine the levels of a chemical that may cause health effects and the levels that are not a significant health concern. For some chemicals, such as lead, research studies provide a good understanding of health risks associated with various blood levels. For most of the environmental chemicals included in the Fourth Report, more research is needed to determine whether exposure at the levels reported is a cause for health concern. CDC conducts and provides biomonitoring measurements for this type of research in collaboration with other agencies and institutions.

The Fourth Report presents data that provides estimates of exposure for the civilian, noninstitutionalized U.S. population. The current survey design does not permit CDC to estimate exposure on a state-by-state or city-by-city basis. For example, CDC cannot extract a subset of data and examine levels of blood lead that represent a state population.

Key Highlights and Findings

First-Time Exposure Information for the U.S. Population Provided for 75 Chemicals

The Fourth Report, for the first time, provides population reference values in blood and urine, including 95^th percentile levels, for 75 chemicals. The 95^th percentile level means that 95% of the population has concentrations below that level. Public health officials use such reference values to determine whether groups of people are experiencing an exposure that is unusual compared with an exposure experienced by the rest of the population.

To provide scientists and public health officials these new data quickly, CDC published much of this exposure information on new chemicals in separate scientific peer-reviewed publications before the Fourth Report was released. Abstracts and links to full-text articles are available at http://www.cdc.gov/exposurereport/.

Widespread Exposure to Some Industrial Chemicals

Findings in the Fourth Report indicate widespread exposure to some commonly used industrial chemicals.

• Polybrominated diphenyl ethers are fire retardants used in certain manufactured products. These accumulate in the environment and in human fat tissue. One type of polybrominated diphenyl ether, BDE-47, was found in the serum of nearly all of the NHANES participants.
• Bisphenol A (BPA), a component of epoxy resins and polycarbonates, may have potential reproductive toxicity. General population exposure to BPA may occur through ingestion of foods in contact with BPA-containing materials. CDC scientists found bisphenol A in more than 90% of the urine samples representative of the U.S. population.
• Another example of widespread human exposure included several of the perfluorinated chemicals. One of these chemicals, perfluorooctanoic acid (PFOA), was a byproduct of the synthesis of other perfluorinated chemicals and was a synthesis aid in the manufacture of a commonly used polymer, polytetrafluoroethylene, which is used to create heat-resistant non-stick coatings in cookware. Most participants had measurable levels of this environmental contaminant.

Ongoing Progress in Reducing Blood Lead Levels in Children

Progress is being made in reducing children's blood lead levels. New data on blood lead levels in children aged 1 to 5 years enable estimates of the number of children with elevated levels (that is, levels greater than or equal to 10 micrograms per deciliter [µg/dL]). Figure 1 shows how the percentage of blood lead levels in children has declined since the late 1970s. For example, for the period 1999–2004, 1.4% of children aged 1 to 5 years had elevated blood lead levels, the smallest percentage of any of the prior survey periods.

These data document that public health efforts to reduce the number of children with elevated blood lead levels in the general population continue to be successful. However, the Fourth Report also notes that other data sources show that special populations of children at high risk for lead exposure (for example, children living in homes containing lead-based paint or lead-contaminated dust) have higher rates of elevated blood lead levels and remain a major public health concern.

First Available Exposure Data on Mercury in the U.S. Population

For the first time, the Fourth Report characterizes mercury exposure of the U.S. population aged 1 year and older. Previous National Exposure Reports presented mercury levels for children 1–5 years old and women 16–49 years old. Total blood mercury levels are primarily composed of one type of mercury, methyl mercury, which enters the body mainly from dietary seafood sources. Findings in the Fourth Report show that total blood mercury levels increase with age for all groups and begin to decline after the fifth decade of life. Compared to older women of childbearing age, younger women have higher birth rates and lower mercury levels (see Figure 2).

Eight Different Species and Metabolites of Arsenic Measured

By using special laboratory methods, CDC researchers measured total arsenic and seven other forms of arsenic in the urine of NHANES participants for the first time. Some of the forms of arsenic measured are metabolites of inorganic arsenic and others are less toxic species that are formed in the environment. By differentiating these types of arsenic exposure, the Fourth Report helps scientists understand which forms of arsenic are important to human health.

First-Time Assessment of Acrylamide Exposure in the U.S. Population

Acrylamide is formed when foods containing carbohydrates are cooked at high temperatures (e.g., French fries) and as a byproduct of tobacco smoke. Most people are exposed to acrylamide through the diet and from smoking. Because acrylamide is a reactive chemical, it can bind to proteins. These reaction products are called adducts. CDC's Environmental Health Laboratory developed a new method to measure acrylamide and its metabolite, glycidamide, as adducts of hemoglobin, a major blood protein. This measure reflects the dose of acrylamide and glycidamide over the previous several months of intake. The data in the Fourth Report show that acrylamide exposure is extremely common in the U.S. population.

Perchlorate and Thyroid Function

The chemical perchlorate is both naturally occurring and manmade and is used to manufacture fireworks, explosives, flares, and rocket propellant. For decades, scientists have known that large medical doses of perchlorate affect thyroid function. Low-level exposure to perchlorate from the environment has been under investigation by many scientists in recent years. The Fourth Report shows that all NHANES participants have detectable perchlorate in their urine and provides reference values for urinary perchlorate levels (see Table 1). This knowledge helps scientists target the levels of human exposure for future study.

Exposure to Cadmium

Recent research studies show that urine cadmium levels as low as 1 microgram per gram of creatinine in people may be associated with subtle markers of effects on the kidney and with an increased risk for low bone-mineral density. The Fourth Report shows that about 5% of the U.S. population aged 20 years and older has urinary cadmium levels at or near these levels. Cigarette smoking is the most likely source for these higher cadmium levels. These findings should promote further research on the public health consequences of cadmium in people.

Reduced Exposure to Environmental Tobacco Smoke

Environmental tobacco smoke (ETS) has significant health effects on cardiovascular and respiratory disease. Cotinine is a metabolite of nicotine, and for nonsmokers, levels of cotinine in people's blood tracks exposure to ETS. In the past 15 years, data show that blood cotinine levels for nonsmokers in the US population have decreased about 70%, indicating that public health interventions to reduce ETS exposure have been successful.

U.S. Population's Exposure to Volatile Organic Compounds

People are exposed every day to volatile chemicals in the air we breathe. The Fourth Report provides measurements on 33 of these hydrocarbon and halohydrocarbon-type chemicals. One example is the gasoline additive methyl tert-butyl ether (MTBE). Exposure to this chemical can occur through the air we breathe or from contaminated water sources. A high percentage of the NHANES participants representing the U.S. population showed detectable levels of MTBE.

Selection of Chemicals for the Fourth Report

Chemicals presented in the Fourth Report were selected on the basis of scientific data that suggested exposure in the U.S. population; the seriousness of health effects known or suspected to result from exposure; the need to assess the efficacy of public health actions to reduce exposure to a chemical; the availability of a biomonitoring analytical method with adequate accuracy, precision, sensitivity, specificity, and speed; the availability of sufficient quantity of blood or urine samples; and the incremental analytical cost to perform the analyses. More information is available at http://www.cdc.gov/exposurereport/chemical_selection.html.

Plans for Future National Exposure Reports

CDC's goal is to make new biomonitoring exposure information available as soon as possible to the public and scientific community. To meet this goal, CDC periodically releases the National Exposure Report and also publishes biomonitoring exposure information in peer-reviewed publications. The National Exposure Report is cumulative, providing biomonitoring exposure data starting in 1999 through the latest available data at the time of the report release. Future plans include releasing data on additional chemicals and providing more information on exposure in population groups defined by age, sex, and race or ethnicity. Peer-reviewed journal articles published since the latest release of the National Exposure Report provide more recent and supplementary biomonitoring data for the U.S. population. These peer-reviewed publications typically also contain more extensive data analysis than that provided in the National Exposure Report.

For the most up-to-date biomonitoring information, users can view the National Exposure Report Web site (http://www.cdc.gov/exposurereport/), a one-stop source that contains the most recent version of the Report as well as the biomonitoring publications.

About CDC's Environmental Health Laboratory

By using advanced laboratory science and innovative techniques, CDC's Environmental Health Laboratory at the National Center for Environmental Health has been at the forefront of efforts to assess people's exposure to environmental chemicals. CDC's laboratory scientists have built on more than three decades of experience in measuring chemicals directly in people's blood or urine, a process known as biomonitoring. Biomonitoring measurements are the most health-relevant assessments of exposure because they measure the total amount of the chemical that actually gets into people from all environmental sources (e.g., air, soil, water, dust, or food). With a few exceptions, the concentration of the chemical in people provides the best exposure information for public health officials to evaluate the potential for adverse health effects.

¹Jones RL, Homa DM, Meyer PA, Brody DJ, Caldwell KL, Pirkle JL, Brown MJ. Trends in blood lead levels and blood lead testing among U.S. children aged 1 to 5 Years, 1988–2004. Pediatrics 2009 Mar;123(3):e376-e385.

²Caldwell KL, Mortensen ME, Jones RL, Caudill SP, Osterloh JD. Total blood mercury concentrations in the U.S. population: 1999–2006. Int J Hyg Environ Health 2009.