Exposure to Environmental Contaminants
What are the trends in human exposure to environmental contaminants?
Importance of Monitoring Human Exposure
Trends in human exposure are important for several reasons:
- Understanding the extent to which human populations are being exposed to environmental contaminants helps identify:
- Contaminants of potential public health concern.
- Population subgroups (e.g., by age, race, ethnicity) 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. They may also be more vulnerable to some environmental contaminants at certain stages of development.1,2
- Contaminants of potential public health concern.
- Tracking the levels of environmental contaminants in a population enables assessment of how exposures to those contaminants are changing in that population over time.
Measures of Human Exposure
Different approaches are used to measure or estimate exposure, each with advantages and disadvantages. These approaches include ambient concentration measurements, exposure modeling, personal monitoring, and biomonitoring.
- Ambient concentrations: Measurement of ambient concentrations provides information about how much of a contaminant is present in the environment (air, water, or soil), but not how much of the contaminant humans actually come in contact with. In some cases, ambient concentrations may be modeled or estimated rather than measured.
This type of exposure estimate has provided a valuable foundation for many of the regulatory and non-regulatory actions that have been taken to limit exposure to ambient contaminants. Measurements of ambient concentrations of contaminants are presented in Air, Water, and Land indicators, but cannot be directly linked with the biomonitoring indicators presented to address the ROE exposure question.
- Exposure modeling: Exposure models estimate exposure by combining information about environmental contaminant concentrations with information about people's activities and locations (e.g., time spent working, exercising outdoors, sleeping, shopping) to account for the contact with contaminants. This approach requires data on contaminant levels where people live, work, and play, as well as knowledge of their day-to-day activities.
- Personal monitoring: With personal monitoring, an individual wears a monitoring device during normal day-to-day activities. Personal monitoring provides valuable insights into the source of contaminants to which people are being exposed. It is most commonly used in workplaces.
A challenge with personal monitoring (as with biomonitoring) is ensuring that the extent of sampling is sufficient to be representative of the population being studied. No national-scale personal monitoring data are available.
- Biomonitoring: Biomonitoring measures how much of a contaminant—or its metabolite(s) or reaction product(s), referred to as “biomarkers”—are present in the human body. Measurements are most commonly made in blood or urine, but can also be taken from a variety of other body compartments, such as feces, breast milk, hair, nails, and exhaled air, as well as tissues obtained through biopsy or autopsy.
Several environmental contaminants, including heavy metals, some pesticides, and other persistent organic pollutants, can accumulate in the body. Biomonitoring has been used to characterize exposure to lead and some other metals for a number of years. More recently, advances in biomonitoring have enabled measurement of many other environmental contaminants.
ROE Indicators
The ROE presents seven human biomonitoring indicators to address the ROE exposure question: Blood Cadmium, Serum Cotinine, Blood Lead, Blood Mercury, Serum Persistent Organic Pollutants, Urinary Pesticides, and Urinary Phthalates.
By directly measuring contaminants or their biomarkers in human fluids or tissues, biomonitoring takes into account the complex set of physiologic and metabolic factors that govern how contaminants are absorbed and distributed within the body.
These indicators (which rely on data from the Centers for Disease Control and Prevention's [CDC's] National Health and Nutrition Examination Survey [NHANES]) provide an overall representation of the levels of selected contaminants, or metabolites of contaminants, in human blood and urine across the U.S. population. Measurable levels of many of these contaminants appear in at least some subset of the populations tested. Together, these indicators enhance understanding of the extent to which exposure to individual substances has occurred on a national scale.
Although ROE biomonitoring indicators show the relative amounts of environmental contaminants in people and in subpopulations over time, by themselves, biomarkers of exposure do not:
- Provide information about the contaminant source.
- Predict whether the presence of the contaminant in the body will result in biological alterations or harmful health effects, either acting alone or in combination with other contaminants.
- Provide information on when, where, and how exposure occurred. For example, lead in children's blood may come from exposure to airborne sources, contaminated water or food, or contaminated soil or dust.
- Explain possible differences among some subpopulations.
Also, there are still many contaminants for which no biomonitoring indicators exist, and others that are simply not feasible to analyze using current technology or data collection methods. These include radon, most criteria air pollutants (e.g., ozone, nitrogen dioxide, carbon monoxide, particulate matter), and biological agents (e.g., molds, certain infectious agents such as bacteria or viruses, dust mites). In many cases, biomonitoring for these contaminants is either cost-prohibitive or not yet technologically feasible.
Biomonitoring methods are constantly evolving, so exposure indicators may be added over time as data become available. For example, as part of its ongoing National Health and Nutrition Examination Survey (NHANES), CDC continues to add environmental contaminants to its biomonitoring efforts. EPA anticipates adding several contaminants to the ROE biomonitoring indicator suite in future years.
In addition, other exposure measurements for which no national-scale indicators currently exist, such as personal inhalation monitoring, along with data from CDC's Environmental Public Health Tracking Program, may offer future indicators to help answer this ROE question.
References
[1] Landrigan, P.J., C.A. Kimmel, A. Correa, and B. Eskenazi. 2004. Children's health and the environment: Public health issues and challenges for risk assessment. Environ. Health Perspect. 112(2):257-265.
[2] World Health Organization. 2006. Principles for evaluating health risks in children associated with exposure to chemicals. Environmental Health Criteria 237.