Human Biomonitoring of Environmental Chemicals pot

And as early as the 1890s, factory their blood and urine screened to fore­ stall ilie elevated levels that produced acute lead poisoning.. Today, it is relatively doses for hundreds of c

Human Biomonitoring of Environmental

Chemicals

Measuring chemicals in human tissues is the "gold standard"

for assessing people's exposure to pollution

K e n S e xton , Larry L Needham and James L Pirkle

What chemicals in your daily ro ­

tin e s h o uld yo u b e m os t co n ­

ce rn ed about? Th e vo latile organi c

co mp o und s fr o m yo ur ca rp e t ? Th e ex­

haust fumes on the road to work? The

pes ti ci d e r es idu es in th e a ppl e in y our

lund,? Most of us are exposed to low

levels of tho sands of toxic chemicals

every day H ow c an a p erso n -o r a n a­

ti n-decide which substances sh uld

be controlled most rigoro sly?

One strategy is to go after the largest

so ur ces of pollution Th is approach ce r ­

tainly makes sense w hen those pollu­

t a nt s h ave o b v i o u s a nd w id es pr ea d

co n se qu e n ces, s u c h as w a r min g th e

globe, causing algal blooms, eroding the

ozone layer or killing off wildlife But

fo r p ro t ec tin g human h ea lth , this s trat e­

gy does n t serve so well, because the

lin k be tw ee n a g i v e n co mpolUld and its

biologic l effects can be difficult to

gauge For epidemiologists to correlate

e n v ir O ll me nt a p o llutant s w ith he a lth

problems, they need to know who has

been exposed and at what level

This knowledge is exceptio ally dif­

fi ult to gain when there is a lag be­

t wee n ex po s ur e and th e manif es t a t i o n

o f illn ess In s u c h c a ses, th e data ar e

se l d o m - if eve r - s uffici e nt to d e t e

-K f?II Se xt o ll is n professor of e ll u O llm e lltni sc i ­

e ll ces a t th e Ulli vers ity Of T exas Sc / wo f of Publ ic

H e alth , Br ow l/ su ifl R eg i o llal C ampl/ s, alld pa s t

p r esi d llt of th illt e matiollal Soc i e ty of Ex pos ur e

All a l ys i s (lSEA) iJ1r ry L N dham is Chief of the

O rgalli c Allalyti c al T ox i c olo gy Bral/ c h ill th e Na ­

tiolla/ C ellt e r for Ell v irolllll(?lltal H e alth of th e

Ce llt e r s f o r Di se a se COlltrol alld Pr eve lltioll

(C D C) alld the CIIrr e llt l S EA p n'S id e llt Jam es L

Pi r kl e is th Deput y Dir ec tor fo r Sci e ee at th e

C D C's Ell ui r O llm(?llt a l H e alth LAborat o ry S e ­

t O l" S addr ess i s Ull ive r it y of T e xa s S c h oo l of Pub­

li c Hmlt/I , Bro w l/ su ill Re g i o llal Campu s, RAH C

Bllildill g, 80 Fort Bro W lI , Br ow l/ su ill e, TX 78520

Illf e w t : kse x f Ol' @ ll f b e dll

min e th e pr e ci se age nt , th e d e t a s o f

contact and the full extent of the affect­

ed populati n Complicating matters,

th e s ci e ntif i c und e s a ndin g of the

m ec hani s m s of e x p os ur e, s u 1 a s h ow

v ari o u s co mpoWld s are ca rried throu g h

the air and changed alo g the way, is

o e n in co mpl e t e As a res ult, e pid e mi ­

ologists often find it difficult to estab­

lish cause-and-effect relati nships for

e n v ir o nm e ntall y indu ce d s i c kn ess e s

With o ut reli a bl e inf o rm a o n so m e pol ­

lutants may be wlfairly blamed, where­

a s oth e s e xe rt their dir e e ff ec t s w ithout

challenge Fortunately, there is h pe: a

m e th o d o f acc ur a t e l y m eas urin g n o t

o nl y co nta c t with , but a l so a b so rpti o n

o f t oxic c h e mic a l s fr o m , th e e n v iron ­

m e nt - human bi o m o nit o rin g

Is It in Me?

Eac h person 's risk of d eve l o pin g an e n ­

v ir o nm e nt a ll y r lat e d di sease, s u c h a s

ca n ce r , r es ult s fr o m a uni q e co mbin a­

ti n o f expos ur e ge n es, age, sex, nutri ­

ti n and lifestyle Science doesn't fully

und e s a nd ho w th ese var i a bl es int e ­

act, but exposure is clearly a key fac­

t o r Thu s, a fundam e nt a go al o f e n v i ­

ronm e ntal h e a lth p o lic y i s t o pr ev ent

(or at le st reduce) people taking in

chemicals that lead to any of the five

Ds-discomfort, ysfuncti n disabili­

ty, disease or death

E x p os ur e t o an e n v ir o nm e ntal

c h e mi ca l i s minimall y d e fined a s c on ­

t ac t w ith th e s kin , m o uth or n os tril s-a

m e an j n g tha t i ncl ud es breathin g, e at ­

ing and drinking For the purpos s of

a ssess in g ri s k , th e m os t im po rtant a t tribut es o f ex p os ur e a r e m ag nitud e (w h a t i s th e c on ce ntr a o n ?), dur a o n

(how lo g does contact last?), frequen­

cy (how often do exposures occur?)

a nd tim.in g ( at what age d o ex po s ur es

oc cur ?) The c alcu l at i on o f a ctua l ex po ­

s ur e a l so r quir es co mpl ex d e t ect i ve

work to discover all kinds of details,

including the chemical identity (for ex­

ample, the pesticide chlo rpyrifos),

s our ce ( n ea rb y agricultural u se), m e di­

um o f tran s port ( g round w at e ) and

ro ut e ( drinkin g c ontamin a t e d we ll wa ­

ter) Scientists must consider this infor­

ma ti n o n ex po s u re aga in s t t h e b ac k ­

ground of people's a tivity patterns,

eating and drinking habits, and lifestyle,

and they must also evaluate the influ­

e n ce of o th e r d1 e mic a ls in t h e a ir , water ,

beverages, food, dust and soil OveraU,

this is a daunting challenge

Hi s o r ica ll y, th ose scie ntist s w h o un ­

d e rt oo k s uch a co mpl ex t as k h ave r e­

li e d o n indir ec t m e th o d s: qu es t io n ­

n a ir es, di a ri es, int e v i ews, ce ntr a l iz ed

m o nit o rin g o f co mn1u l uty a ir o r wa t e ,

and a r eco rd of br o ad ac t i v it y p a tt e rn s

am o n g t h e p o pulati o n But th e r es ult s

were often disappointing Altho gh

th ese ci r um s tanti a appr oac h es ha ve

the advantages of practicality and fru­

ga li ty, th ey ca n also intr od u ce s ub s a n­

ti l un ce rt a in ty int o r es ultin g expos ur e

es tim a t es Tlti s s h o rt co min g muJtipli es

th e p o t e ntial for a fundam e nt a e rror ­

cla ss if y in g a p e s o n a s " n o t ex po se d "

wh e n h e or s h e ha s b ee n o r vice ve r sa

A second approach, the direct mea­

s ur e m e nt o f a n indi v idu a l 's e n v ir o n ­

m e nt , i s so m e tim es a poss ibili ty- f o r ex­

ample, a person might carry a portable

m o nit o r t o reco rd co nta c t wi th a ir bo rn e

chemicals Altho gh this technique of

f e s a n unequi v c al r ec ord o f c h e l n i c al

contact, it is technologically infe sible

o r p ro hibiti ve l y ex p e n s i ve t o m eas ur e

most pollutants this way Also, altho gh

su , monitors d cument exposure, they

tell nothing about the person's uptake

o f th ese a irb o rn e c h e mi ca l s h ow

much truly gets into his or her bo y,

w h i c h i s, o f c o ur s e , th e m os t r l eva nt

© 2004 Sigma Xi, Th e Sc ienti fic R esear c h Socie t y R e produ cti o n

38 Ame r ican Sc i e n t i s t , Vol u me 92 wi th pe nn iss i on only Con t act pe nn s@ a m sci.o r g

'::: \ - , ,

•

Bettmann / Corbis Figure 1 In Jul y 1945 , DDT wa s widel y (and mistakenly) hailed a s a progressive m e asur e to eradicate di s ease-bearing mo s quitoes without po s­

ing a ri sk to human health In thi s photo from a be ac h on Long I land , New York , a new in sec ticid e-s pra yi ng machine is test ed a s beachgoers

play in th e mist Althoug h thi s chemical contact is obvious, m any other s ource s of e n vironmenta l chemical exposure are more difficult to iden­ tify Human biomonitoring exami n es people's blood and urine t o evaJuate actual l ev els of more than a hundred substances

informatio n fo r assessing health risk

Fortwlately, technological ad vances in

biomed i ci n e a nd a n alyt i cal che m istry

now make it possible to get exactly tills

info rm a on Biolllo nit oring meaSUTes

the actual levels of suspected environ­

fluids This third approach has come to

be ilie "gold standard" for assessing ex­

posure to chemicals

Blood (and Urine) Will Tell

Bio m o nitorin g is not n ew It has its roots

in ilie analysis of biological sanlples for

markers for vario u s pharmaceutical

compounds and occ upati o nal che mi ­

cals, efforts that sought to prevent the

substances A1tllOugh it had a different

www.americanscientis t org

first applied about 130 years ago when

who were being treated with large dos­

es of salicylic acid (ilie precursor of as­

pirin) And as early as the 1890s, factory

their blood and urine screened to fore­

stall ilie elevated levels that produced

acute lead poisoning

The se i n ves ti ga t o r s soo n lea rn ed

th at ch e mic al As a r es u l t, th.i s measure

didn't help much in predicting the

risks of lead poisoning However, they did find that the amount of a com­

pound tl,at crosses the b dy's bound­

a ri es {ca ll e d the i.nt e rnal or absorbed

dose, or sometimes ilie body burden)

has considerable value for estinlating

the risk to health Today, it is relatively

doses for hundreds of chemicals by

looking for biomarkers of exposure in

access ibl e human ti ss u es a nd flui ds, in ­

cl udin g sa li va, seme n, urine , sp utum,

(all of which can be collected readily),

follicular fluid, adipose tissue and

into the body) Although procedures to collect any of the first set would, tech­

ni ca U y, be considered "nonin vasive,"

tural, psychological and social factors

So obtai nin g t h e ri ght m ater ial can

2004 J anuary- F ebruary 39

• • •

••

exposure assessment

emission source

•

•

1

•

potential dose

~

absorption barrier

.­

internal dose

adverse effect

•

Figure 2 Which toxicant i s morc dangerous ? Because of th e mu l tip l e s ep s through w h ich an en­

vironmental chemica l mu s t pas s before it become s a po t entia l h ealth thr ea t , th e answe r i s n ot al­

ways clear Here, t o icant 1 is more abundant in the e nviron m en t , ut th e specific propert i es of the

chemical may mean th at it pos es less medica l risk than ano th er compound Different methods of

exposure assessment can eva luat e each of these s tep s, but biomarker analysis , which m eas ur es in­

te rnal do ses of s pecific s ub sta nc es, provides th e m os t r e levant information for human h e alth

for th ose o f u s in th e bi o monitorin g for the presence of biological markers

field, it's never necessary to collect all of exposure-generally the targeted

of those samples- blood and urine are c h emica l , it s prim a r y m e tab o lit es or

typically sufficient These are analyzed th e pr od uct s of it s r eac ti n wi th cer t ain

40 Amer i ca n Scie nt ist, Volume 92

natural compounds in the body, such

as pro t ei n s

Choosing the appropriate tissue or fluid for biological monitoring is based

primarily on the chemical and p ysical pro erties of the ch mical of interest

so m e c h e mi ca l s includin g di ox in s,

polychlorinated biphenyls and organo­ chlorine pesticides have lo g biological

years) because they are sequestered in fatty tissues They are thus said to be

su h as organ phosphate pesticides and volatile organic compounds, which

phobic), have relatively short biological

r esidence tim es (ho ur s o r days) a nd

tend to be metabolized rapidly and ex­

cre ted in the urin e

also playa key role in detemlining the

best biological specimen for analysis

as a dioxin, remains present in blood for

a much lo ger period (years) than does

a nonpersi s t e nt co mpound s u c h as ben­

zene (h urs), but dioxin does n t form

benzene does For these reasons, persis­

tent chemicals are typically measured in

blood, and n npersistent c emicals are

meas u red in urine (as soo n a ft e r expo­

sure if the analy cal methods are suffi­ ciently sensitive-and they usually are

low levels parts-per-billio , parts-per­

small sample, say, 10 milliliters or less Clearly, the sensitivity of the analysis

is important in chOOSi n g w hat t o m ea­

sure-but it's not everything Other is­

s ue s mu s t be co nsid e red before th e re­

sults can be considered meaningful

a m o unt s o f targ e t c h emica l s, an inves­

br oa d questi o ns: How i s t h e m eas ur e­

ment related to the magnitude, dura­

t i o n , f requency a nd timin g of ex po­

s ur e? H ow do s ub se qu e nt pro cesses

within the body-;;uch as absorptio ,

di s tributi o n , metab o sm and exc r e­

ti n - influ e nc e th e t argeted biomark­

er? And is this particular marker spe­

ind ka te an e nti re cla ss of s ub s tan ces?

Because the science underpinning

human biomonitoring has improved

significantly in recent years, these ques­

tions are n ow eas i er t o answer The

r ap id adva nc e n e nt i n knowledge o f

what the body does to chemicals that

are inhaled, ingested or absorbed

through the skin has led to better inter­

pretation of the range of conce ntrations

for various biomarkers And the num ­

ber of testable compounds has in­

creased dramatically: Sensitive and spe­

cific bi oma rk ers are ava ilab l e f or man y

e n v i ro nm e nt a l c h e mi cals, including

metals, dioxins, furans, polychlorinated

biphenyls, pesticides, volatile organic

compounds, phthalates, phytoestrogens

and e nvironmental t obacco smoke As

research continues, the list will surely

co ntinue t o grow

Exposure mId Uptake

B i omo nit o rin g has m any advan t ages

ove r traditional methods For exa mple ,

biological s.unples reveal the integrated

effects of repeated contact Also, this

approach documents all routes of expo­

s ur e- inhalation, ab so rption thr o u g h

the skin and ingestion, including hand­

to-mouth tra nsfer by children Such

specimens also reflect the modifying in­

fluences of physiology, ioavailability

and bioaccumulation , which can mag­

nify the concentrations of so me envi­

ronmenta l chemica l s enough to raise

them above the detection threshold

Perhaps most importantly, these tests

can help establish correlati ns between

expos ur e and s ub seq u e nt illn ess in in ­

dividuals-which is often the key ob­

serva tion in proving whether or n ot a

link exists

A great strength of biomonitoring is

th a t it pro v ides Wlequivocal evidence

that both exposure and uptake have tak­

e n p l ace In some cases these d a ta can

confinn the findings of traditional expo­

s u re estirnates For exam pl e, in 1 979, res­

idents of Triana , A l abama, were noti­

fied that fish from a nearby creek had

forty times more DDT than the allow­

able limit, even though the local DDT

manufacturing plant had been inactive

since 1 971 The announcement was es­

pecially co n ce rnin g because m a n y p eo­

ple in that area caught and ate the fish

regularly In response to this discovery,

the Centers for Disease Control and

Prevention (CDC) constructed an eval­

uation based on DDT co n ce ntrations in

fish and the amount of fish eaten per

week This es tim a t e ind eed co rrelated

with levels of DDT and its metab lites,

www.ame ri canscientist.org

food soi V dust water levels levels levels air

level of toxicant

lung , intest i ne a n d ' i

excretion skin absorption rates

metabolism accumulation

j

Figure 3 Traditional esti mat es of human exposure have to account for man y variables , in· eluding so m e that demand assumptions about factors that are poorly und ers tood Th e r esu lt is often uncertain

human tissues

or fluids personal

~

emission

~

accuracy

Figure 4 Exposure to enviro nm e ntal c h e mi ca l s c an be assessed in several ways Genera ll y, th e accuracy and cost vary togeth er Monitoring emission sources is the l east expe n sive and l east accurate means of d e t e rminin g human exposure, whereas biomarker m eas ur e m e nt is m o re

c o s tly but a l so h igh l y informat i ve for that person

2004 J anuary-February 41

Figure 5 At its Environmental Health Laboratory , CDC scientists use several types of high­

r eso lution mass spe c trometry to analyze human tissue and fluid samples The equipment

shown here is being used to measur e dioxin le ve ls in a sample of blood se rum (Photograph

co urtesy of James L Pirkle.)

DOE and DOD, in the blood of Triana

r es id e nt s In a s imilar s t o r y that un­

folded in U,e late 1980s, chemical-plant

workers i n New Jersey and Missouri

discovened that they had been exposed

t o dioxin-contaminated compou nd s up

to U,e early 1970s They had come into

con t act wi th th e di ox in in var i o u s

ways- breathing it , swa ll ow in g it and

taking it in through the skin Despite

the comp l exi ti es of th e ir int e ac tion

w ith this dangerous s ub stance-a nd

the tim e int erva l s in ce expos ur e-a

to calculate the duration of potential

expos ur e was able t o acc ur ate l y es ti ­

m a t e int e rnal doses This finding was

confirmed by the correlation of these

r es ults with th e co n ce ntr atio n of djo x­

ins in their blood

H av in g information abo ut expos ur e

alld uptake is more than a pro forma de­

tail: There are many cases in w hich tra­

ditional estimates of exposure (q u es­

tionnaires, proximity t o so ur ces,

e n v ironm e nta l co n cen tr a tion s, co n ­

s truct e d sce nario s) are n o t cor r lated

with measured b i o mark ers F or exam­

ple, from 1962 to 1971, the U.s Air

"Agent Orange" in Vietnam Many ser­

vice members who participated in that

operation touched or breathed the her­

bicide, potentially exposing themselves

42 Amer ica n Sc ienti st, Volume 92

to high levels of dioxin The Air Force

fir s t es tinlated th e risk t o so ldi ers using

a sce na r i o approac h, w hich included the average dioxin co n centra ti n in

Agent Orange, the number of gallons

used during a soldier's tour of duty, and the frequency and duration of p0­

tential contact based on job descriptiOll

Despite a considerable scientific effort

that went into these predicti ns, CDC

studies in the late 1980s proved that

none of th e exposure estimates were

levels of dioxin in at-risk troops A sub­

seq u e nt investigation of personnel

with the highest dioxin levels did iden­

tify some patterns that explained their

in c eased con tact- for exam pl e, s mall ­

statu red e nli s t e d m e n o ft e n climbed int o the c h e nlic a l tanks to clea n ou t

residual Agent Orange

A more striking example of the val­

ue of biomonitoring came in the mid­

1970s wh n the United States elected

to start phasing out leaded gasoline

Prior t o t h i s deci s ion , traditional m od­

els h d suggested that eliminating lead

in gasoline would have only a slight ef­

fect on people's uptake of that metal

However, biomonitoring data from the

Nutr iti on Examination Survey re­

vealed that from 1976 to 1980 (as un­

leaded fuel was first introduced and

mately 55 percent) there was a parallel

decline in the amo lmt of lead coursing

thro gh the veins of the U.S popula­

ti n Overall, average blood concent r a­

tio s decreased from about 16 to less

than 10 micrograms of lead per deciliter of blood These data demon­

s tr ated the effectiveness of removing lead from gasoline, and th ey were a

dominant factor in the decision by the

(EPA) to remove lead from gasoline

more rapidly-a task that was effec­

tively complete by 1991 Today, the av­

ulation is l ess than 2 micrograms per

deciliter

Exposure Disclosure

The study that revealed the tight con­

nection between U,e lead in people's gas

tanks and the lead in their blood was

mounted by the CDC, which conducts

the National Health and Nutrition Ex­ amination Surveys (NHANES for

c he micals were measured as part of

gan measuring blood lead levels in the

ter the Food and Drug Administration

voiced concerns about possibl e expo­

sures from eating food stored in lead­

soldered callS, which turned out to be a

gasoline As part of NHANES II , the

EPA tested for certain persistent pesti­ cides in people's blood and n npersis­ tent pesticides or their metabolites in

urine After an eight-year hiatus,

that iteration, the COC measured lead

and cadmium and began testing for co­

tinine, th e major metabolite of nicotine,

in blood Additionally, U,e CDC began a

separate pilot program to measure new

compolmds, testing for trace amounts

of 32 volatile organic chemicals in blood

and 12 pesticides or their metabolites in

urine from approximately 1,000 of the NHANES III participants

Then came a n o th er l o n g gap in cov­

erage But thankfully, in 1999, NHANES

became a continu o u s survey of the

non institutionalized U.s population

(It is thought that excluding members

of iso l ated organizations, such as mili­

tary personnel, college students and

prisoners, provides a better c oss-sec­

ti on of America.) In th e cu rr e nt design,

Identifying priority

exposures Out of thousands

of chemicals, which are the most

dangerous? Biomarkers can help set

priorities for

public health

and regulatory C

follow-up

1

Identifying at-risk

can distinguish exposure differences among

racial, geographic or socioeconomic groups

Providing integrated

dose measurements

Biomarker analysis provides

direct assay of

integrates exposure from all sources

even ones that are hard

Recognizing time trends in

biomarkers in the population shows how body burdens of chemicals vary from season to season, year to year and decade to decade

•

Establishing reference

A blood test shows that you've been exposed to some chemical Should you

be worried? Your doctor can't tell without data from people with little or no exposure

Evaluating exposure prevention efforts

Our government is entrusted with reducing people's exposure to environmental chemicals Do th ey succeed? Before-and-after

biomarker tests can tell

1

to measure

Fig ur e 6 Wh e n u se d t o es tabli s h levels of hum a n chemical exposure, biomonitoring h as s i x m a jor u ses that ca n help to pr o tect publi c h ea lth

110

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Figure 7 Leaded gaso l in e began to be phased out in the 1970s Although the predicted e ffect on blood lead was minimal , actual lead exposur e

in gasoline (l e ft) Blood l e ad and gas lead continued to fo ll ow nearly identical decrease s up to 1990 At the same time, a series of studie s on l e ad

a n e w n a tional s ampl e i s coll e ct e d

every two years Altho gh some other

studies have locused on specific popu­

l a ti o n s o r on m o r e r es tri c t e d dat a,

tion and collection of biological sam­

they do n t necessa rily h ve high or

ip a nt s are ex amin e d annu a lly fr o m 1 5

Reporting For Duty

Nationa l Report on Hum a n E x posure

to Environmental Ch micals, which in­

A second report was published in Jan­

i es u s ed biomonitorin g t o pro v ide an

on go ing a ss e sm e nt o f ex po s ure t o a

o s studies of workplace exposure, lor

exa mpl e, had rai se d co n ce rns about

m eas ur e d in a r e pr ese ntativ e slice o f

the U.s p pulatio

The inventory of tested substances in

the second CDC re ort includes lead,

m e c ur y, c admium and oth e r metals ;

p rsistent (organochlorine-based) and

cides and other pesticides; pest repel­

diox ins, furans and po l ychlorinated

biphe yls; and phytoestrogens Results

port is that it provides refere ce ranges

for exposure among the gen ral U.S population If people are concerned

that they may have b en excessively

ex po s ed to an en v ironnl e ntal chemical,

they can compare their biomarker lev­

els to those standards These reference

r a n ges a re imm e n se l y b e n e ficial to

public-h alth scientists who must de­

need foUow-up action Ifa era e levels

among the c o h ort are s imilar t o tho s e

of the g n ral public, then the group's

ex p os ur e i s unlikel y t o c au se uniqu e

problems On the other hand, if levels

are substantiaUy hig er than national

ul at ion s that may be more vulnerable to ex ·

exa mpl e , p , p'-DDE , a long-lasting metabolite

can-Americans compared with the general

the l owest among this group , indicating that

ond Nationa l Report on Human Exposure to

Environmental Chemicals , published in 2003

(NHANES III) , 1988-1991

n o rm s, e pidemiol o gi s t s c an co nfirm

ca r e a s appr o priat e Th e r f e e n ce

r a n ges pr ov id e indire c t fin a n cia l a d ­

700

ai :g: 600

We

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;:: CI

Cii CI 400

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0> :Jl

2 00

100 L -' ' -' ' =~ _

0 5

0 4

0.3

0 2

0 1 -' -' ' -' -' - -'- ­

3 0

5

0 1 1 0 10 100

se rum co t nin e ( ng / mL )

1000

vantages too, because distinguishing

c mmon from unusu l chemical con­

tact helps direct resources to the most­

pertinent exposure situatio s

The overarching purpose of these re­

ports is to help scientists, physicians

and health officials to prevent, reduce

and treat e virOlIDlenta y induced ill­

nesses However, some caution must be

exercised in interpreting the findings: It

is important to remember that detect­

ing a ch mical in a person's blood or

urine does n t by itself mean that the

exposure causes disease Separate sci­

entific studies in animals and hum ans

are required to d termine wh.ich levels

are likely to do harm For most chenu­

cals, toxicologists simply d n't have

this informa o

But even if scientists are n t s ur e of

the overall level of risk they can make

con rete statements about wh ther sit­

u ti ns are getting better or worse The

latest CDC re ort, in addition to listing

current biomarker levels in the popula­

to , lso highlights some interesting

exposure trends glean d from earlier

NHANES findings For example from

1991 to 1994,4.4 percent of children be­

tween the ages of o e and five had lev­

els of blood lead greater than or equaJ

to 10 micrograms p r deciliter, the Fed­

eral acti n level By the second collec­

tion period (1999 and 2000), only 2.2

percent of this age group exceeded this

thresh ld Tim decrease suggests that

efforts to reduce lead exposure for chil­

dren have been successful It also serves

as a reminder that some children in­

clu ing th ose li ing in homes with

lead-based p int or lead-contaminated

dust, remain at unacceptably high risk

The last report also indicates a hope­

ful trend in the exposure to environ­

mental to acco smo e, as shown by

tests for the biomarker cotinine in the

blood of n nsmo ers Median leveJs of

cotinine fell more than 70 percent in

rou hly a decade-that is, b tween the

second (1988 to 1991) and third (1999

and 2000) p rio s of data collectio

This drop provides objective evide ce

of reduced exposure to environmental

to acco smo e for the gen ral U.s pop­

ula o Nevertheless, the fact that more

than half of American youth continue

to be exposed to en ironmental to acco

smo e remains a public-h alth concern

The CDC pla s to release future re­

port that document their biomonitor

ing efforts every two years In the next

editio , they will also add the findings

from sep rate studies of special popu­

www ame r ican s cien t s t o r g

Figur e 9 U.S population cl e arly segregates into smokers and nonsmokers based on the lev e l of

c otinine in blood The working th.reshold for distingui s hing the two groups i s ]O nanogram s

per millilit e r of blood serum Among nonsmok e r s , the highest values of cotinine w e re found

in children under 12 , and th e y were strongly reflective of the number of s mokers in the home

Th e data a r e from NHANES JII , 1988-199]

lations, su h as the la orers who apply

pesti ides to crops, p ople living near

hazardo s-waste sites and workers in

lead smelters, all of which are likely to

have hig er-tha -average exposures to

certain e vironmental c emicals

Annual Check-Up With Biomarkers?

As the 21st century unfolds, the CDC

surveys and other well-designed bio­

monitoring studies will continue to build an understanding of people's ex­

posure to toxic e vironmental chemi­

cals No etheless, these data will not

o viate the need to collect other kinds

of relevant informatio - to monitor

sources of pollutio , to conduct sur­ veys of toxic substances in the enviro ­

ment and to study human a tivities and behaviors that contribute to e po­

sure More ver, further research in tox­

icology and epidenuology is necessary

b fore sp cialists can interpret the

health Significance of exposure bio­

markers for most environmental chem­

icals Particularly as d tecti n methods

improve-enabling investigators to

rneasure lower concentratio s of more

c emicals from sma er samples at less cost-scientific understanding of what

the body does to the ch nucal (and vice

versa) must keep pace If this effort is

successful, a full screen of exposure

biomarkers may be a part of every

routine physical exam in the n t­

too-distant future

Bibliography DeCaprio , A P 1997 Bioma r kers : comi n g of age for enviro nm en t a l ealt h and r i s k as­ sess m e n t Ell v irolllll e lltal Sc i e ce & T e e/molo­

gy 31 : 1 837- 1 848

Men d elso hn , M L , j P Pee t ers an d M J N o r mand y, ed s 1995 Bi o m a r ke r s alld Occ upa­

ti o ll a l Healtll: P rogress an d P erspec ti ves Was h ­

i ng t on , IX : j oseph He n ry Press

M e nd e lsohn , M L , L C Mohr and j P Peeters , ed s 1998 B mark e r s: Med ic al and

W o r k pla ce App l c ati o ll Was hing t o , D C:

j osep h He nr y P ress

Need h am , L L., an d K Sex t on 20C10 Assessing

c h dre n 's expos u re t o h a ardo u s environ­

me n ta l c hem i ca l s: An ove r view o f se l ec t ed research c ha ll e n ges a n d c omp l e x i ties /our­ lIal of Expos ur e Anal ysis alld Etf v iroll1" e lltal Epid e mi o l og y 1 0 (Pa rt 2 ) :6 1 1-629

N e edham , L L , D C Patter so n J r , V W

B urse , D C P a scha l , W E T urner and R H

H ill , Jr 1996 R efe ren ce ra nge data for as­ sessing ex po s ur e t o selec t ed e n viron m e nta l

t ox i c an t s To x i c l o y alld Illdu s tria l H e aflll

12 : 507 - 513

Pi r k l e, J L , E J Sampson , L L Need h am , D G

Patt e rson , J r , an d O L Ash l e y 1 995 Using bio l ogica l mon itoring to assess h u man expo­

s u r e t o p r io r ity tox i can t s Ell v irollm e llt a l

H ltll P erspec t ves 1 03 ( s u pplement 3): 4 5-48

F o r relevant Web lin ks, co n s ult thi s

i ss ue o f Americ a " Sc i e llt is O l/Iill e :

http ·//w ww a metican SC i e ntj s ! m:g I

I SS u eTOC/ i ss ye / S21

2004 j an u ary- F eb ru ary 45