Biomonitoring: Is body burden relevant to public health?

Abstract

Biomonitoring is the study of the presence and concentration of chemicals in humans usually by the measurement of blood, urine or breath (exhaled air). Properly conducted, these data provide a picture of the amount of a chemical or agent actually absorbed into the body for a specific period of time. This review provides a history of biomonitoring, as well as the limitations and potential benefits of these studies. Examples of the proper and possibly improper use of biomonitoring and the impact made on our society are provided. Reasons for having comprehensive national biomonitoring programs are summarized, along with the societal benefits and risks. A brief discussion of the history of the NHANES program and select results from the 2005 Report are presented. By 2010, it has been predicted that the Centers for Disease Control (CDC) will be monitoring nearly 1000 chemicals in persons from all regions of the nation. The measurement of chemicals and biomarkers has revolutionized the field of exposure assessment. Overall, we recommend an approach of careful interpretation, understanding that the data obtained are useful for establishing baseline information about exposure, rather than equating detection with risk. We present suggestions for contextualizing biomonitoring results in order to provide the public with the tools to distinguish genuine health risks from trivial ones.

Introduction

In its simplest terms, biomonitoring is the “assessment of internal dose by measuring the parent chemical or its metabolite or reaction product in human blood, urine, milk, saliva, adipose or other tissue,” (Needham, 2005) although biomonitoring of fish, birds and other wildlife is also frequently conducted. Although technically inaccurate, the concentration of any given chemical in human tissues or the total amount of a chemical in the body is sometimes referred to as the “body burden” of an individual. Virtually any tissue or fluid can be utilized for chemical analysis. However, for practical and ethical considerations, only a few types of samples, mainly blood and urine, are generally collected. In the workplace, the measurement of breath has been an indicator of exposure to volatile chemicals (including ethanol). Often, factors such as where the chemical is most likely to be found and the behavior and volatility of the chemical often dictate which types of human samples can be most easily analyzed (cf. Table 1).

Of course, people are exposed to thousands of natural and man-made chemicals, as well as their metabolites, every day. This exposure occurs from the air, from ingested food and water, as well as the multitude of consumer products that people come into contact with on a daily basis. Over the past 5 years, it has become increasingly clear that each of us has ingested, inhaled or absorbed a variety of these chemicals because many can be easily measured in the blood or urine of every American (CDC, 2005). Sampling and measuring these chemicals and other agents is called “biomonitoring” (DeCaprio, 1997, Metcalf and Orloff, 2004).

Properly conducted, biomonitoring data provide a picture of the amount of a chemical or agent actually absorbed into the body. Due to advancements in the field of analytical chemistry, it is now possible to detect extraordinarily low concentrations of environmental chemicals in human tissue. For example, dioxin is now routinely measured in blood at the low parts per trillion (ppt) level. Based on information from both toxicology and epidemiology studies, the majority of chemicals that are currently detected in biomonitoring programs of the general population are not expected to produce adverse health effects at the levels being reported (CDC, 2005). Of course, it is imperative to understand the characteristics of the chemical of interest in determining the best “biological matrix” to use in measuring human exposure. The pharmacokinetics of the chemical, e.g., the time needed for absorption, distribution, metabolism, and elimination (ADME) can provide critical information when deciding how and when to sample a chemical. For example, a chemical which is water soluble or whose metabolite is water soluble will frequently be eliminated quickly in urine or, if volatile, through the lungs (and in exhaled air). Those chemicals which are highly lipid soluble often have longer half lives and are often transported to “adipose tissue (for organic chemicals) and bone and teeth (for lead), where their concentrations are in equilibrium with those in blood and are slowly eliminated,” sometimes over days, months, years or decades (Needham et al., 2005, Paustenbach, 2000a, Paustenbach, 2000b).

Data from biomonitoring investigations are becoming more widely available and are frequently considered “newsworthy,” greatly heightening public interest in these investigations (CDC, 2005, San Mateo County, 2005, Williams, 2005; New York Times (DuPont PFOA), 2005). However, these data are often presented without proper context, which can lead people to the understandable, but erroneous, conclusion that the low levels of chemicals found in our tissues are harmful, simply by virtue of their presence. In other words, the public is currently having difficulty relating the significance of merely detecting a chemical versus when the concentration in blood or urine poses a genuine risk to their short-term or long-term health.

Many factors need to be considered before it is possible to determine if the detected levels of either a naturally occurring chemical in our food (such as arsenic) or a synthetic man-made chemical (such as polychlorinated biphenyl (PCB)) might pose a human health hazard. Reporting data without some type of explanation can frequently generate confusion and unnecessary anxiety. It is not very useful to say, for example, “Mary has 20 ppt of benzene in her blood.” For a few chemicals which are sometimes monitored in manufacturing workers, such as benzene, we can often properly characterize the health significance of the data. However, for most of the over 200 chemicals that are now being monitored by the Centers for Disease Control and Prevention (CDC) and other organizations, interpretation of the results is problematic. Fortunately, there is a good possibility that in the near future, we will be able to present biomonitoring data in a way that will be informative and perhaps helpful for improving public health. To use our previous example, it is likely that within a few years we will be able to say, “Mary has 20 ppt of benzene in her blood. This places her at about the 50th percentile for blood benzene levels for adults in the United States. It is believed that about 80% of the benzene in her body has come from miscellaneous exposure to chemicals in the environment (including diet and smoking) and the remainder is due to her own natural biological processes. The concentration measured in Mary is about 5% of the average level seen in groups of petroleum workers and these persons have not been shown to have an elevated incidence of benzene-related disease.” In our view, this would be the kind of risk communication that could well be beneficial to the public.