Human Biomonitoring of Environmental Chemicals

Human Biomonitoring of Environmental Chemicals Measuring chemicals in human tissues is the "gold standard" for assessing people's exposure to pollution Ken Sexton, Larry L. Needham and James L. Pirkle hat chemicals in your d aily rou mine the precise agent, the details of sure also requires complex detective W tine should you be most con contact and the full extent of the affect work to discover all kinds of d etails, ce rn ed about? Th e vo latile orga ni c ed population. Complicating matters, incl uding the chemical identity (for ex compounds from your ca rpet? The ex th e scie ntific unde rstanding of the ample, the pesticide chl o rpy rifos), haust fumes on the road to work? The mechanisms of exposure, sud1 as how source (nearby agricultural use), medi pesti cide residues in the apple in your various compoWlds are ca rried through um o f transport (ground water) and lund ,? Most of us are exposed to low the air and changed along the way, is route (drinking contaminated well wa levels of thousands of toxic chemicals oft en incomplete. As a result, epidemi ter). Scientists must consid er this infor every day. How can a person-or a na ologists oft en find it difficult to estab ma tion on exposure against the back tion-decide which substances should lish cause-and-effect relationships for ground of people's acti vity patterns, be controlled most rigorously? environmentally induced sickn esses. eating and drinking habits, and lifestyle, One strategy is to go after the largest With out reliable information some pol and they must also evaluate the influ sources of pollution. This approach cer lutants may be wlfairly blamed, where ence of other d1emicals in the air, water, tainly makes sense when those pollu as others exert their dire effects w ithout beverages, food , dust and soil . OveraU, tants have obvious and w id espread cha llenge. Fortunately, there is hope: a this is a daunting challenge. consequences, such as warming th e method of accurately measuring not Historica ll y, those scientists w ho un globe, causing algal blooms, eroding the only contact with, but also absorption dertook such a complex task have re ozone layer or killing off wildlife. But of toxic chemicals from, the environ li ed on indirect me th ods: question for protecting human hea lth, this strate ment- human biomonitoring. naires, diaries, interviews, centralized gy does not serve so well, because the monitoring of comn1uluty air or water, link between a given compolUld and its Is It in Me? and a record of broad activity patterns bio logical effects can be difficult to Each person's risk of developing an en among the population. But th e results gauge. For epidemiologists to correlate vironmentall y related disease, such as were o ft en disappo inting. Although envirOllmental po llutants w ith health cancer, results from a unique combina these ci rcumstantial approaches have problems, they need to know who has tion of exposure.. genes, age, sex, nutri the ad vantages of practicality and fru been exposed and at what level. ti on and lifestyle. Science doesn't fully gali ty, th ey can also introduce substan This knowledge is exceptionally dif understand how these variabl es inter tial uncertainty into resulting exposure fi cult to gain when there is a lag be act, but exposure is cl ea rl y a key fac estimates. Tltis shortcoming muJtiplies tween exposure and the manifestation tor. Thus, a fundamental goal of envi the potential for a fundamental error of illness. In such cases, th e data are ronmental health policy is to prevent classifying a person as "not exposed" seldom- if ever- sufficient to deter- (or at least reduce) people taking in when he or she has been or vice versa. chemicals that lead to any of the fi ve A second approach, the direct mea Kf?II Sextoll is n professor of ell uirOllmelltni sci Ds-discomfort, dysfuncti on, disabili surement of an individual's environ ellces at the Ulliversity Of Texas Sc/wo f of Public ty, disease or d eath. ment, is sometimes a possibility-for ex Health, Browl/suifle Regiollal Campl/s, alld past Exposure to an e nv ironmental ample, a person might ca rry a portable presidellt of the illtematiollal Soc iety of Exposure chemi ca l is minimally defined as con monitor to record contact with airborne Allalysis (lSEA) . iJ1rry L. Needham is Chief of the tact w ith the skin , mouth or nostrils-a chemi cals. Al though this technique of Orgallic Allalytical Toxicology Bral/ch ill the Na meanjng tha t includes breathing, eat fers an unequivocal record of cheln ical tiolla/ Cellter fo r Ellvirolllll(?lltal Health of the ing and drinking. For the purposes of contact, it is technologica lly infeasible Cellters for Disease COlltrol alld Prevelltioll assessing risk, the most im portant at or prohibitively expensive to measure (CDC) alld the CIIrrellt lSEA pn'Sidellt . James L. tributes of exposure are magnitude most pollutants this way. Also, although Pirkle is the Deputy Director fo r Sciellee at the CDC's ElluirOllm(?lltal Health LAboratory. Sex (what is the concentrati on?), duration sud , monitors document exposure, they tOl" S address is Ull iversity of Texas School of Pub (how long does contact last?), frequen tell nothing about the person's uptake lic Hmlt/I , Browl/suille Regiollal Campus, RAHC cy (how o ft en d o exposures occur?) o f these airborn e che mi ca ls- how Bllildillg, 80 Fort BroWlI , Browl/suille, TX 78520 . and tim.in g (at what age do exposures much truly gets into his or her body, Illfer/ wt: ksexfOl'@ll fb.edll occur?). The calculation of actual expo w hich is, of course, th e most relevant © 2004 Sigma Xi, The Scienti fic Research Society. Reproduction 38 American Scientist, Vol ume 92 with pennission only. Contact [email protected]. '::: \ -. , , . • • .. Bettmann/ Corbis Figure 1. In July 1945, DDT was widely (and mistakenly) hailed as a progressive measure to eradicate disease-bearing mosquitoes without pos ing a ri sk to human health. In this photo from a beach on Long Island, New York, a new insecticide-spraying machine is tested as beachgoers play in the mist. Although this chemical contact is obvious, many other sources of environmental chemical exposure are more difficult to iden tify. Human biomonitoring examines people's blood and urine to evaJuate actual levels of more than a hundred substances. information for assessing health risk. first applied about 130 years ago when dose, or sometimes ilie body burden) Fortwlately, technological ad vances in doctors mon..itored the amount of sali has considerable value for estinlating biomedicine and analytical chemistry cyluri c acid in the urine of rheunlatics the risk to health. Today, it is relatively now make it possible to get exactly tills who were being treated with large dos afford able to m easure the absorbed information. Biolllonitoring meaSUTes es of salicyli c acid (ilie precursor of as doses for hu ndreds of chemicals by the actual levels of suspected environ pirin). And as early as the 1890s, fa ctory looking for biomarkers of exposure in mental chemicals in hwnan tissues and workers who were exposed to lead had accessible human tissues and fluids, in fluids. This third approach has come to their blood and urine screened to fore cluding saliva, semen, urine, sputum, be ilie "gold standard" for assessing ex stall ilie elevated levels that produced hair, feces, breast milk. and fingernails posure to chemicals. acute lead poisoning. (all of w hich can be coll ected readily), These investi ga tors soon lea rn ed and blood, lung tissue, bone marrow, Blood (and Urine) Will Tell that the degree of contact with a sub follicula r fluid, adipose tissue a nd Biomonitoring is not new. It has its roots stance doesn't necessarily determine blood vessels (which require incursion in ilie analysis of biological sanlples for the biologically relevant exposure to into the body). Although procedures to markers for various pharmaceutical that ch emical. As a result, th.i s measure coll ect any of the first set would, tech compounds and occupational chemi didn't help much in predicting the nica Uy, be considered "noninvasive," cals, efforts that sought to prevent the risks of lead poisoning. H owever, they in fact, that categorization rests on cul harmful accumulati on of dangerous did find that the a mount of a com tural, psychological and social factors. substances. A1tllOugh it had a different pound tl,at crosses the body's bound So obtaining the ri ght material can name at the time, the general idea was aries {ca ll ed the i.nternal or absorbed sometimes be awkward. Fortunately www.americanscientist.org 2004 January-February 39 natural compounds in the body, such exposure assessment as protei ns. Choosing the appropriate tissue or oXlcan toxicant 2 fluid fo r biological monitoring is based primarily on the chemical and physical properties of the chemical of interest and, in some cases, th e time interval emission since th e last exposure. For example, source some chemica ls including diox in s, polychlorinated biphenyls and organo chlorine pesticides have long biological resid ence times in the body (months or years) because they are sequestered in fatty tissues. They are thus said to be fat-l oving or, to use the proper term, • • l lipophilic. By contrast, other chemicals • • • pathway --- such as organophosphate pesticides • • . ~ • •• and volatile organic compounds, which • don' t accumulate in fats (being li po phobic), have relatively short biological residence times (hours or days) and tend to be metabolized rapidly and ex creted in the urine.

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