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Report on the Environment

Human Exposure to Environmental Contaminants

Other Human Exposure and Health Topics

What are the trends in exposure to environmental contaminants including across population subgroups and geographic regions?

Understanding the extent to which human populations are being exposed to environmental contaminants helps identify those contaminants of potential public health concern and populations who may be disproportionately exposed to contaminants or uniquely vulnerable. For example, children may have disproportionately heavy exposures to environmental contaminants because they drink more water, breathe more air, and eat more food per pound or kilogram of body weight than adults; further, children may be more vulnerable to some environmental contaminants depending on the stage of development during which exposure occurs.3,4 Evaluating exposure across certain race or ethnic groups, or other potentially susceptible subgroups, identifies possible variations in exposures. Tracking the levels of environmental contaminants in a population also enables an assessment of how exposures to those contaminants are changing in that population over time.

Referring back to the environmental public health paradigm, measurements of human exposure to environmental contaminants can be made in the ambient environment (air, water, land), at the point of human contact, or after contact and contaminant entry into the human body has occurred. In answering this question, the focus is on human biomonitoring, which involves the measurement of human tissues or excreta for direct or indirect evidence of exposure to chemical, biological, or radiological substances. The ambient contaminant measurements presented in the media chapters are not considered here, nor can they be directly linked with biomonitoring data presented to answer this question.

Historically, human exposure has been defined as the amount of a chemical, physical, or biological contaminant at the outer boundary of the body available for exchange or intake via inhalation, ingestion, or skin or eye contact.5 As such, human exposure to environmental contaminants has been estimated primarily through measurements of contaminant concentrations in air, water, or soil, combined with estimates of the frequency and duration of human contact with the contaminated media. These resulting exposure estimates have provided a valuable foundation for many of the regulatory and non-regulatory actions that have been taken to limit exposure to ambient contaminants. However, developments in data collection techniques and analytical methods have improved the capability to characterize human exposure via biomonitoring, which provides measurements of contaminants within the human body.

For a few environmental contaminants, particularly lead and some other metals, biomonitoring has been used for exposure characterization for a number of years. More recently, techniques for biomonitoring have been expanded to include many additional environmental contaminants. These measurements provide a tool that complements ambient measurements in characterizing human exposure to environmental contaminants. However, concentrations of environmental contaminants reported at a national level in blood, urine, or any other type of tissue cannot be used to extrapolate directly to a particular source.

The use of biological markers (or biomarkers) builds on the more traditional exposure assessment approach, providing more information on the extent to which a contaminant enters, remains, and acts in the body. Biomarker information attempts to determine the extent to which a contaminant is present in the body after entering through portals of entry such as the eyes, skin, stomach, intestines, or lungs. Given the complex set of factors that govern contaminants that are absorbed and distributed in the body, a direct measurement of the levels of a contaminant or related “marker” in the body offers more information about exposure than measured ambient levels alone.

In general, a biomarker reports the level of a substance or a marker (i.e., the product of an interaction between an agent and some target molecule or cell) present in samples collected from the body or produced by the body. Biomarkers of exposure measure concentrations of a contaminant, its metabolite(s), or reaction product(s) in the body fluids or tissue, most commonly blood or urine. Measurements can also be taken from a variety of other body compartments, such as feces, breast milk, hair, nails, exhaled air, and tissues obtained through biopsy or autopsy. The exposure measure used to answer this question focuses on biomarkers of exposure. Biomarkers of exposure do not predict whether biological alterations and potential health effect will result. Whether a particular exposure ultimately results in an adverse health outcome depends on a host of factors, as is described in the "Human Health Chapter Introduction".

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