By Kelly A. Reynolds, MSPH, Ph.D.
Cocaine, marijuana, heroine, ecstasy, PCP, and Adderall all represent one of six major categories of common illicit drug use. With a mere $12 (USD) and a cup of urine, you can determine a person’s recent use of all these drugs collectively. Spring for another $40, however, and monitor an individual’s drug use over a period of months with the collection and analysis of hair samples. Collection of biological samples for monitoring drug use (i.e., biomonitoring) is a common practice today for employers wanting to ensure a drug-free-workplace, particularly for employees in high-risk occupations or positions of responsibility. In addition, the media is full of stories related to sport teams testing players for performance enhancing steroids and illegal drugs.
By now, you are probably wondering how this information relates to water quality and purification – it’s all in the biomonitoring. The development of clinical test methods for illicit drug use, or other biomarkers of toxicant exposures, has lead to improvements in the field of exposure assessment. Today, each individual’s biological record can be used to determine exposure to hazards in the environment, including drinking water. When combined with questionnaire information and environmental monitoring data, scientists have a more accurate assessment of what we are exposed to and when those exposures occurred.
Practicalities of biomonitoring
Biomarkers are defined as any biological sample (i.e., enzymes, cells, saliva, sweat, urine, blood, tissue, hair or nails) that change in a measurable way when exposed to pollutants. These responses may occur at the molecular, biochemical or cellular level in organisms. The level of response is often quantitative, allowing for a measure of the magnitude of an organisms exposure. How long contaminants can be detected in biological samples depends on a variety of factors that are inherent to the host, contaminant or the environment. For example weight, body fat, metabolism, health status, urine pH, etc., can all affect the distribution, dilution and degradation of toxicants. Coarse hair tends to accumulate toxicants more efficiently. The duration and magnitude of the exposure also affects detection periods in biological samples. Thus the dose/detection relationship does not necessarily increase at the same rate. In general, however, target contaminants persist in hair and nail samples for months (1-6 months, but typically three months) compared to hours to days for blood and urine samples. This allows the researcher to determine exposure over a much greater period of time.
Sampling hair and nails is a lot less invasive than collection of urine and blood samples. Thus, compliance is often higher for volunteer study participation. In addition, collection of hair and nails rarely requires the privacy needs of excreta. This has been important in illicit drug testing where patients have come up with very creative ways to deceive the analyst by substituting, diluting or otherwise tampering with urine samples. (FYI- test labs have very sophisticated means now for tracking tampered samples). A downside to hair collection is that some people don’t have much on their heads. This is generally not a problem as hair can be taken from just about any site on the body, including the face, underarms, arms, legs and even from private regions. A further downside is the amount of hair needed- between 60 and 120 strands. On average, hair grows at a rate of about a half-inch per month. Theoretically, the longer the hair, the greater the exposure history available, however, the closer the strand is to the scalp, the more concentrated the toxicants. Thus, most drug test laboratories only test the first 1-2 inches, representing approximately 90 days of exposure. Labs testing for arsenic report an historical evaluation of up to a year of exposures.
Similar to hair biomarker samples, nails provide a longer-term toxicant exposure assessment. Usually clippings are taken from all 10 fingers or toes and the sample extract combined during the laboratory analysis. One of the problems identified with hair and nail exposure assessment is that target contaminants could be present on the exterior surfaces of the biomarker. Although arsenic tends to be tightly bound to the keratin of hair and nails, not all sources are internal, given that the toxicant can be present in air, soil and even personal care products (i.e., soap, shampoo). External contamination from water contacts via bathing and showering can mislead exposure assessments that assume biomarker concentrations result from ingestion or inhalation intake routes.
Building the exposure database
For more than 30 years, the US Centers for Disease Control and Prevention’s (CDC) Environmental Health Sciences Laboratory (EHSL) at NCEH has been using biomonitoring to determine human exposures to environmental chemicals.1 This information is valuable for risk assessment because it measures actual amounts within people, and not just the potential for exposure based on environmental monitoring data. EHSL continues working to build a database of human exposures to more than 300 toxicants.2 This internationally recognized program provides important information for epidemiological studies that can lead to a better understanding of how such exposures relate to human health effects. According to the EHSL website, the laboratory is able to test for important environmental toxicants such as lead, cadmium, mercury, uranium, thorium, and chromium; and environmental tobacco smoke; in addition to multiple dioxins and furans; polychlorinated biphenyls and polycyclic aromatic hydrocarbons.
Specific to drinking water, EHSL can routinely monitor biomarkers for methyl tert-butyl ether (MTBE); trihalomethanes (THM) from DBPs in water; pesticides: VOCs; mercury and cadmium. Recent studies of biomonitoring for drinking water contaminant exposures include a survey of selenium and arsenic in hair and toenails.3,4 While no one really knows what a safe level of arsenic is in hair or toenails, these studies show a statistically significant correlation between targeted biomarkers and environmental contamination levels. Another study of cadmium and lead in toenails and hair was published in 2005 where environmental exposure routes and food consumption patterns were differentially correlated to contaminant levels in biomarkers. This latter study is an example of how population surveys (i.e., epidemiological studies) can be used to determine the relative contribution of various exposure routes of contaminants found in biological samples. Biomarkers can also help us to understand what happens to toxicants in the body. Monitoring changes in the chemical form of arsenic in different biological samples, for example, may provide insights into human metabolic responses.
While biomarkers can be very useful to enhance the science of exposure assessment, we must be careful not to overestimate their accuracy. Measurements can be highly variable and given that they are an average reading, may either over or under estimate exposures. Future studies are needed to link biomarker information with other exposure assessment databases to fully evaluate the reliability of the biomarker data for predicting human health risks.
- CDC. National Biomonitoring Program. http://www.cdc.gov/biomonitoring/ ↑
- CDC. Fourth National Report on Human Exposure to Environmental Chemicals. Department of Health and Human Services. http://www.cdc.gov/exposurereport/pdf/FourthReport.pdf ↑
- Gault, AG, HAL Rowland, JM Charnock et al., 2008. Arsenic in hair and nails of individuals exposed to groundwaters in Kadal province, Cambodia. Science of the Total Environment. 393: 168-176. ↑
- Slotnick, MJ and JO Nriagu. 2006. Validity of human nails as a biomarker of arsenic and selenium exposure: A review. Environmental Research. 102: 125-139. ↑
About the author
Dr. Kelly A. Reynolds is an associate professor at the University of Arizona College of Public Health. She holds a Master of Science degree in public health (MSPH) from the University of South Florida and a doctorate in microbiology from the University of Arizona. Reynolds has been a member of the WC&P Technical Review Committee since 1997. She can be reached via email at [email protected].