What exactly is biomonitoring?

Biomonitoring is a scientific technique for assessing human exposures to natural and synthetic chemicals, based on sampling and analysis of an individual's tissues and fluids. While blood, urine, breast milk and expelled air are most commonly measured, hair, nails, fat, bone and other tissues may also be sampled. This technique takes advantage of the knowledge that chemicals that have entered the human body leave markers reflecting this exposure. The marker may be the chemical itself. It may also be a breakdown product of the chemical or some change in the body that is a result of the action of the chemical on the individual. For example, alterations in the levels of certain enzymes or other proteins may serve as markers; so too might modifications of normal body processes, such as the transfer of oxygen to tissues.

The levels of natural and synthetic chemicals detected through biomonitoring are sometimes referred to as body burdens. This is a misleading term in that it suggests that the detection of a substance always means that it is causing adverse effects. However, biomonitoring only measures exposure; it does not provide information about toxicity or risk. Indeed, many natural chemicals, such as the metal manganese, found in tissues and fluids are essential for the proper functioning of the human body.

Perhaps the most important strength of biomonitoring is that it is the only technique that can provide a direct measure of the exposure of human individuals and populations. However, because it requires a great deal of resources, only a relatively small number of individuals and compounds can be monitored. This, in turn, limits the amount and applicability of the analytical data collected.

In the absence of biomonitoring, exposure assessments are performed indirectly -- based on a combination of: (1) measurements of concentrations of chemicals in the environment, e.g., soil, water, or food, and (2) estimates of human behaviors, e.g., food consumption or time spent at various activities. This indirect approach has several drawbacks. First, environmental analyses are typically limited in both space and time, i.e., concentrations are known for only limited numbers of places at a few times. Second, human behaviors are quite variable and this adds significantly to the uncertainties in the calculations. Due to these limitations, it is difficult to know how accurately such indirect assessments reflect human exposures.

In addition to being a direct measure, biomonitoring has the advantage that it integrates, or adds together, exposures from multiple sources, e.g., air, water, and food, to provide a reflection of total exposure. Thus, it is a measure of total exposure by all routes and from all sources. This strength of biomonitoring can also be seen as a limitation, because this automatic integration over routes and sources means that it is not possible to determine the relative contributions of individual sources, e.g., fish consumption, to the total exposure. Another limitation is that biomonitoring only provides exposure information at one point in time. Thus, this technique cannot provide information about the time course of exposure, that is, whether it occurred as a result of one simple exposure, multiple independent exposures over a long period of time, continuous exposure over time or some combination of these.

Because of these limitations, biomonitoring by itself cannot provide information about either the likelihood or magnitude of future exposures. This is true even if a series of fluid and/or tissue measurements are performed over a significant time period, because a number of factors, e.g., possible changes in environmental concentrations, can influence the measured levels.