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EPA-Expo-Box (A Toolbox for Exposure Assessors)

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Exposure Reconstruction
(Biomonitoring and Reverse Dosimetry)

Biomonitoring

Biomonitoring is the act of measuring the concentration of chemicals, their metabolites, or their byproducts in:

Biomonitoring measures the actual levels of chemicals, metabolites, or byproducts in the body.

  • Tissues, such as skin and hair
  • Body fluids, such as blood, saliva, semen, and breast milk
  • Excreta, such as urine and feces, or
  • Exhaled air

(CDC, 2009; Hays et al., 2007).

Biomonitoring data can be used to infer human exposure from multiple pathways and sources. In addition, such measurements will reflect the effects of external factors, such as disease state, exposure to other environmental pollutants, dietary habits, access to health care and other social factors, and other daily activities, including smoking or exercise habits. These external factors can influence both the extent of exposure for individuals or a population and their biological response to exposure (NRC, 2006; Sexton et al., 2004).

Biomonitoring

There are advantages and limitations associated with biomonitoring.

Biomonitoring Advantages Biomonitoring Limitations
Measures aggregate and cumulative exposure (i.e., all sources, all routes, all pathways) Not source- or pathway-specific
Reflects uptake and accumulation Requires permissions for collection of human specimens
Might be able to correlate internal dose with observed health effects Difficult to interpret potential health risks
  Can be costly

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NHANES

The National Health and Nutrition Examination Survey (NHANES), conducted by the Centers for Disease Control (CDC), provides a large data set of biomonitoring data that is “designed to assess the health and nutritional status of adults and children in the United States”. NHANES interviews and physical examinations are conducted continuously with information gathered from approximately 5,000 people each year. Interviews are used to gather information about topics including demographics, diet and exercise habits, and housing characteristics. Physical examinations, including blood and urine samples, a cardiovascular fitness test, and dental and vision examinations, are conducted by trained medical professionals. NHANES findings are the basis for national averages and distributions for measurements like height, weight, and blood pressure (CDC, 2009).

The chemical-specific biomonitoring data collected through NHANES are available for direct download from the NHANES website. Summaries of the results are published in a series of reports referred collectively as the National Report on Human Exposure to Environmental Chemicals. NHANES data have been used to:

  • Characterize body burdens,
  • Determine populations with increased body burdens,
  • Identify exposure levels in populations of concern,
  • Establish reference or background values and identify unusually high exposures,
  • Assess efforts to reduce exposure and trends over time,
  • Direct research priorities, and
  • Connect exposure to body burden.

The National Report on Human Exposure to Environmental Chemicals currently includes information on 246 chemicals and these data are stratified by age, race, and sex (CDC, 2012, 2009). Because data are gathered periodically and across large population segments, trends in body burdens of chemicals for specific subpopulations can be analyzed. Health status information has also been used along with the biomonitoring data to investigate potential relationships between chemical exposure and diseases (CDC, 2009).

In general, survey data on health status, family history, and behaviors like smoking and physical activity can be combined with data from blood and urine samples to explore relationships between exposure, external factors, and resulting body burdens. Researchers can also use health and behavior data to determine which exposure pathways are most relevant for specific chemicals based on the types and amounts of chemicals that appear in biomonitoring samples (CDC, 2009).

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Other Sources

NHANES is the most comprehensive source for human biomonitoring data in the United States. Other sources of biomonitoring data include the National Institute of Health’s (NIH) National Children’s Study, the German Environmental Survey (GerES), the German Environmental Specimen Bank (ESB), and the Canadian Health Measures Survey (CHMS).

The NIH’s National Children’s Study is an ongoing effort, and, with at least 100,000 children participating across the United States, it is the largest long-term study of children’s health and development. In addition to monitoring health outcomes like birth defects, autism, learning disabilities, and asthma, other information that can be used to characterize potential exposure, including housing characteristics, chemical exposure, gene-environment interactions, and access to healthcare, will be recorded. Researchers collect blood, urine, breast milk, meconium, nail, and hair samples from the children and their mothers over the course of the study and measure biomarkers for exposure to pesticides, metals, volatile organic compounds, and other chemicals.

The German Environmental Survey (GerES) is a representative population study to examine the exposure of Germany's general population to environmental contaminants. Four GerES surveys have been conducted since 1985. The most recent survey, the German Environmental Survey for Children (GerES IV), was conducted from 2003 to 2006 and collected information from 18,000 children including measurements of blood and urine concentrations of neurotoxins (e.g., Pb, Hg), carcinogens (e.g., VOCs, PAHs, Arsenic), and other substances (e.g., PCBs).

In addition to GerES, Germany’s Federal Environment Agency (Umweltbundesamt) conducts other health-related monitoring including maintenance of the Environmental Specimen Bank, which archives human samples of blood, blood plasma, urine, saliva, and hair to allow scientists to track the deposits of chemicals in humans as well as their distribution and transformation. The Human Biomonitoring Commission, established in 1992 by the Federal Health Office and the Federal Environment Agency, seeks to clarify fundamental and practical issues related to human biomonitoring.

The Canadian Health Measures Survey (CHMS) began in 2007 as an effort by the Canadian government to collect information about the health and lifestyles of Canadians. Its structure and survey methods parallel NHANES in that interviews and physical examinations are used to gather information for CHMS. In addition to physical measurements, blood and urine samples, information on nutrition, health status, lifestyle, demographics, and socioeconomics, CHMS is also collecting indoor air measurements and monitoring activity patterns for some study participants.

Other Sources of Biomonitoring Data

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Tools

Resources available to risk assessors that provide information and guidance on the use of biomonitoring data include the Handbook for Use of Data from NHANES and the Biomarkers Database. The National Research Council’s (NRC’s) book titled Human Biomonitoring for Environmental chemicals also provides general information on how biomarker data are analyzed and used in exposure assessment.

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