Biomonitoring: A Primer for Nurses

Overview In March of 2001, the Centers for Disease Control and Prevention [CDC] released the first National Report on Human Exposure to Environmental Chemicals. In this report, CDC published the levels of 27 selected environmental chemicals in human tissues [mainly blood and urine]. Using techniques known as biomonitoring, the CDC is able to measure environmental chemicals in the human body, specifically in blood, urine, serum, saliva, or other tissues. On January 31, 2003, the CDC released its second national report, which contains summary exposure data for 116 chemicals in blood and/or urine.

Nurses may wonder, and patients may ask, "What do the new exposure data mean?" The Nurses Leadership Council has developed the following Q & A for nurses to help them understand biomonitoring and to be ready to answer patients' questions.

What is biomonitoring?

Biomonitoring is the measurement of specific substances in the human body, usually through the analysis of blood, urine, milk or other tissue samples. Using biomonitoring, researchers can identify the physical evidence of a current or past exposure to a particular substance. Evidence may include (1) trace concentrations of the substance itself, and (2) the presence of metabolites formed when the original substance is broken down and processed for elimination.

Typically, biomonitoring is based on an appropriately designed study to answer a specific question or hypothesis. The study design takes into consideration the types of sample, sample collection methods and handling requirements, and eligibility of volunteers to provide samples of fluid and/or tissue at any given time. Samples are then analyzed using CDC-validated analytical methods to measure trace concentrations of a predetermined set of naturally occurring and/or manmade substances that may be present in the body. The detection of a substance simply indicates that an exposure occurred sometime before the sample was obtained.

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How accurate is biomonitoring in measuring exposure to determine evidence of a current or past exposure? Are there known problems with the methods of measurement?

CDC has developed and validated new, highly sensitive and specific, analytical methods to assure the accurate measurement of the environmental chemicals in its laboratory. CDC uses the most sophisticated laboratory equipment.

As with all analytical methods, the level of detection depends upon having sufficient sample for the test. CDC has found some environmental chemicals below its level of detection. In these cases, CDC can either develop another test method or take larger samples so that the chemical can be found.

CDC can say only that an environmental chemical is either present or absent in blood or urine at the time samples are drawn. It cannot say whether an exposure is from long ago or just yesterday. Other research is needed to make that assessment.

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What data did the CDC release in the National Exposure Report?

As a public health agency, CDC conducts a national health survey of the U.S. population periodically under its National Health and Nutrition Examination Survey [NHANES] program. Starting in 1999, CDC began to collect data on selected environmental chemical substances in human blood and urine to determine national exposure levels. In January 2003, CDC released the combined exposure data from its 1999 and 2000 sampling programs. By combining the 1999 and 2000 data, CDC indicates that it will have enough information to present the data as a glimpse of national exposure representative of the U.S. population and also to present the data by certain demographic groupings [e.g., age, gender, and race/ethnicity.]

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What do the CDC data represent?

The CDC designed its ongoing biomonitoring study to better understand background levels of substances in the general U.S. population. This research is helping CDC and other scientists to:

• Establish average exposure levels among Americans;
• Establish and compare biomonitoring data across subgroups by age, sex, and race/ethnicity to determine if certain groups of people have higher levels of exposure;
• Measure trends in exposure over time;
• Set priorities for additional research; and
• Verify the efficacy of selected pollution controls and other public health policy measures.

In the first National Exposure Report [March, 2001], CDC was able to document reductions in exposure to environmental tobacco smoke in the general U.S. population by monitoring human levels of cotinine - a metabolite of nicotine. Using these data, CDC confirmed that smoking controls have been effective in reducing exposure to nicotine among non-smokers. As biomonitoring technology continues to advance, more information is being made available to help scientists and policy makers enhance public health.

Additionally, the first National Exposure Report showed that the geometric mean blood lead levels for children aged 1-5 years decreased between 1991-1994. This demonstrates the success of public health efforts to decrease the exposure of children to lead and highlights the continued need for intervention within special populations of children at high risk.

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Can the CDC data be used to identify any "hot spots" of concern?

CDC's biomonitoring data provide a national "reference" range for the general U.S. population. A "reference" range is a range of concentrations for environmental chemicals that CDC has detected in the blood and/or urine of most US residents. To establish this "reference range" CDC wanted to sample people who did not have any extraordinary exposure. Thus, people with occupational exposure were not included in the study. Once "reference" ranges are established, physicians and scientists can determine whether a person or group has had an unusually high exposure.

Because the CDC collected samples from a small number of locations across the U.S., CDC cautions that these biomonitoring data cannot be broken into geographical subgroups representing states or smaller area. Therefore, "reference ranges" can be thought of as the background exposure levels for the general U.S. population¹. Over time, as CDC gathers more data from other studies, these background levels will be confirmed.

In addition, the CDC data do not identify the source[s] of environmental chemicals or the direct exposure route(s) for any individual patient.

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How can nurses help patients understand the data from CDC?

Nurses may think of the CDC biomonitoring data as providing a snapshot for the general population of the range of exposure to the CDC-sampled chemicals. The CDC biomonitoring data cannot be used to infer any specific exposure for any individual patient because each person's exposure history will be different. Once CDC collects sufficient data to establish "reference" ranges, nurses will be able to evaluate whether their patients have had an unusually high exposure.

Further research is needed to determine if environmental chemicals at measured levels present any clinically-relevant impact or any adverse health effect. CDC officials caution that, "just because people have an environmental chemical in their blood or urine does not mean that the chemical causes disease."²

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Should individual patients be tested?

Unless there are unusual circumstances, testing for chemical levels in individual patients is not done at this time. If a patient wants to be tested for specific chemicals, samples must be collected and analyzed using the CDC protocols. Only then can individual patient data can be compared to the CDC data to indicate where the individual patient might fall relative to the "reference range." For any specific health evaluation, additional information is needed to put patient-specific data into perspective. Again, CDC officials caution that "just because people have an environmental chemical in their blood or urine does not mean that the chemical causes disease."³

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How do environmental chemicals enter our bodies?

The human body is made of thousands of chemical substances, such as vitamins, nutrients, proteins, and hormones, which are essential to life. While some of these chemical substances are generated within our bodies, others are absorbed by eating, drinking, breathing and through dermal contact with our surroundings.

Throughout our lives, humans and other organisms are continually exposed to environmental chemicals: some are naturally occurring (e.g., those from air, water and soil or produced by plants, animals and natural events, such as forest fires and volcanoes) and others are manmade (e.g., pharmaceuticals, soaps, disinfectants, auto exhaust and other pollution, etc.)

Although scientists have long understood that our bodies absorb substances from our environments, today's technology allows researchers to detect and measure extraordinarily low levels in human blood and urine samples.

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What do CDC biomonitoring data tell us about human exposure?

Before biomonitoring technology was developed, scientists could only roughly estimate the potential exposure of humans to substances in air, water, soil and food. Today, biomonitoring sampling and analytical technologies can provide information on concentrations of chemical substances in blood or urine at a specific point in time. Using biomonitoring data, scientists today can conclude that an exposure has taken place at some point prior to obtaining the sample. CDC is collecting these data so that it can establish "reference" ranges of exposure to environmental chemicals so that future health evaluations will be improved.

Exposure to a chemical does not imply that negative health effects will result. CDC underscored this point by stating, "Just because people have an environmental chemical in their blood or urine does not mean that the chemical causes disease."⁴

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What does biomonitoring tell us about levels of exposure?

While biomonitoring data can confirm that an exposure to an environmental chemical substance has occurred, they do not provide information about:

• The source(s) of an exposure: Was the person exposed through diet, air, medical treatment, pollution, etc.?
• How long a substance has been in the body: Was it a single large exposure, multiple smaller exposures or a combination? Did the exposure(s) occur recently or further back in time?
• What effect, if any, a substance may have on human health: What are the potential health effects? Are they positive or negative? At what levels or concentrations would you expect to see changes in health?

Biomonitoring data can only quantify exposure if the relationship can be established between the amount of a substance with which a person comes into contact and concentrations of that substance (or its metabolites) in the human body.

Converting biomonitoring data into meaningful estimates for an exposure assessment requires additional studies to identify factors such as the contact between an individual and a concentration of a substance over a defined period of time as well as the interaction of that substance within the body (e.g., absorption, distribution, metabolism and excretion).

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Should people be concerned when biomonitoring studies measure chemicals that have not been previously detected?

Scientists have made gigantic leaps in advancing the quality of analytical technologies, including those used in biomonitoring. Today, scientists are able to detect greater numbers of environmental chemicals and to measure them at smaller and smaller concentrations in the body than ever before. Consequently, the measurement and reporting of a particular environmental chemical for the first time does not necessarily mean that this chemical is new to our bodies. It may mean that advancements in analytical technology now allow the detection of previously undetected levels. Likewise, the initial measurement does not allow any interpretation of trends in levels of exposure. It simply means that scientists have developed better analytical methods for studying human exposures.

Scientists are able to measure chemicals in blood and urine at trace concentrations as small as parts per million, parts per billion, and even parts per trillion. CDC's National Report on Human Exposure to Environmental Chemicals typically reports measurements in units of micrograms per liter, often expressed as µg/L. One microgram equals one millionth of a gram. One microgram in one liter represents a concentration of one part per billion (ppb).

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Can biomonitoring data help public health officials and scientists evaluate risks to human health?

Biomonitoring studies provide only one element in developing a complete picture of risk: the confirmation that an exposure has occurred. A complete picture of human risk requires the scientific risk assessment process, a complex process that requires input from many areas of expertise. There are four major components of a scientific risk assessment:

• Hazard Identification: A description of the potential health effects associated with a particular substance.
• Exposure Assessment: Estimations of the quantity of a substance to which a person has come in contact with over a defined period of time. It includes measurements or estimations of the intensity, frequency and duration of exposure to a substance.
• Dose-Response Assessment: A determination of the relationship between a dose of a substance and a specific biological response.
• Risk Characterization: The integration of all previous components to estimate the likelihood of health effects due to exposure under a defined set of conditions.

Biomonitoring data take some of the guesswork out of the Exposure Assessment phase of a scientific risk evaluation. In addition to biomonitoring data, scientists need information about the most likely route of exposure (e.g., air, food, water, skin), the concentrations of substances in these media, and how our bodies absorb, metabolize, and excrete these substances to accurately construct an exposure assessment.

The following diagram illustrates the information that CDC is currently collecting in comparison to other data. Environmental samples include samples of food, water and air to identify the types and amounts of environmental chemicals present. However, to better estimate actual exposure, CDC is sampling human blood and/or urine to identify the internal dose. While useful to clarify if an environmental chemical was actually absorbed in the body, added information about impact and possible clinical effects are needed. Research studies are needed to answer specific questions about the significance of these blood and/or urine levels collected by CDC. Disease registries are useful to capture information about disease statistics and additional information from other research studies is needed to examine whether there is a relationship between the levels of environmental chemicals in human fluids/tissues and health status.

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Where can I find additional information?

CDC offers the following articles, which describe biomonitoring in more detail, including how chemicals get into the body and how chemicals are measured in the body.

• CDC, National Report on Human Exposure to Environmental Chemicals, NCEH Pub. No. 01-0379, Atlanta, Ga., March 2001. Also found at www.cdc.gov/nceh/dls/report.
• Pirkle JL, Needham LL, Sexton K. Improving exposure assessment by monitoring human tissues for toxic chemicals. J Exp Anal Environ Epidemiol 1995;5:405-24. downloadable PDF file
• Sampson EJ, Needham LL, Pirkle JL, Hannon WH, Miller DT, Patterson DG, et al. Technical and scientific developments in exposure marker methodology. Clin Chem 1994:40(7):1376-84. downloadable PDF file