Definition: Biomonitoring is the process of measuring chemicals in people’s bodies.
Classification: Tool and technique for human study
Over the past decade, the direct measurement of environmental chemicals and their breakdown products (metabolites) in human tissues and fluids – a technique known as biomonitoring – has enhanced our understanding of individual exposures to environmental factors. These chemicals can be measured in people’s blood, urine, hair and saliva (Angerer, 2006). Several of the chemicals of greatest concern in connection with effects on future disease incidence—including most endocrine-disrupting compounds—are lipophilic (fat-loving) and may be found in fat tissue including the extensive fat tissue found in breasts, as well as in the milk of lactating mothers (Anderson, 2000; Shen 2007).
Monitoring excretion (urine samples), circulation (blood samples) or salivary levels of chemicals can be fairly straight-forward, and can be done reliably and repeated over time. Some chemicals are best measured in urine, such as those that are metabolized and excreted quickly (like bisphenol A). For these chemicals, multiple measures over time may provide the best picture of an individual’s exposure. Other chemicals, such as those that persist and bioaccumulate in the body (like PCBs or PFCs) are best measured in blood. In some cases, metabolites persist in the body much longer than the parent compound, as is the case with DDT, whose metabolite DDE lingers for decades.
Measurement of chemicals in breast tissue, or in fat, is impractical and risky, and it poses ethical concerns. Nevertheless, fat and biopsy samples containing both natural estrogens and lipophilic endocrine disruptors can be removed at the time of surgeries of both breast cancer patients and patients undergoing other types of breast surgery (Siddiqui, 2005). Reliable measurement of chemicals in placental tissue or cord blood at the time of birth, or meconium and breast milk after delivery, can give non-invasive information about fetal and perinatal exposures to chemicals at critical times during childhood development (Shen, 2007).
An issue that has become increasingly important for researchers and study participants alike, is addressing the rights of participants to be informed of the results of biomonitoring studies using samples from their own bodies. While scientist traditionally do not share data with scientific study participants, an increasing number of biomonitoring studies use the Community Based Participant Research (CBPR) model (Morello-Frosch, 2009) in which participants are informed of study results. This model is allowing scientists to break the traditional boundaries between themselves and study participants, and to inform participants of their individual results, larger findings of the study, and the implications for personal and environmental health.
The U.S. Centers for Disease Control and Prevention’s Fourth National Report on Human Exposure to Environmental Chemicals (CDC, 2009) measured 212 different chemicals in the blood and urine samples of approximately 2,400 adults participating in the National Health and Nutritional Examination Survey (NHANES), which has a much larger overall sample size. It presents data on chemicals, one at a time, related to the proportion of individuals with detectable levels of particular chemicals and the ranges of the levels detected. This study is repeated every other year, allowing for longitudinal (across time) understanding of exposures and body burdens in representative samples from across the nation (though it is important to note that different people participate in the study each year).
Further analyses of the large national NHANES data over time reveals important information about possible associations between various demographic factors and accumulated body burden of chemicals of concern (Aylward, 2013). For example, examination of socioeconomic status and NHANES results over the decade of 2001-2010 revealed that higher socioeconomic status was associated with higher body burdens of about half the chemicals tested, while lower status tended to be associated with higher concentrations of the other half (Tyrell, 2013). Because the various chemicals tend to sort into different types of sources (for example, industrial pollution vs. household products), data like this can help support appropriate public policy initiatives that target specific chemicals, their sources, and people’s capacity to control their exposures.
Recognizing that fetal and early-life exposures to toxicants may be particularly implicated in predisposing people to many diseases, longitudinal studies in both the United States (Belanger, 2013) and Europe (Gehring, 2013) are taking repeated samples over time from mothers and fetuses, and then from the children after their births and into childhood. Other smaller-scale longitudinal studies, like those of the Breast Cancer and Environment Research Program, focus on girls’ body burdens of toxicants associated with pubertal development (a risk factor for later life breast cancer).
As compared with both short- and long-term assessment of environmental pollution of particular geographical sites, which aggregates pollution across areas where many people live, biomonitoring allows scientists to examine exposures at the individual level. This analysis allows for the assessment of an individual’s integrated and cumulative exposures to multiple chemicals, even as the person is moving across geographical borders as they go home, to school, to work and generally navigate through their communities (Angerer, 2006). Monitoring excretion (urine samples), circulation (blood samples), or salivary levels of chemicals can be fairly straight-forward, and can be done reliably and repeated over time (Siddiqui, 2005).
One important trade-off that must be considered in current biomonitoring studies is the choice between measuring single or limited numbers of chemicals in large numbers of samples versus getting richer profiles of body burdens of environmental chemicals in smaller samples. This decision may be guided by the aims of a particular study.
Although biomonitoring data are excellent indicators of people’s exposures to various environmental compounds, the data do not necessarily identify the sources or duration of exposure (Morello-Frosch, 2009). And unless samples are evaluated at various critical times over the lifespan, it is difficult to evaluate links between exposures and risk for diseases like breast cancer that develop with a long latency between early exposures and ultimate diagnosis.