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# <vEP A Unite d State s Environmenta l Protectio n Agency Offic e o f Ai rQualit yEPA-450/2-89-01 1 Plannin g gn d Standard s ^ Jun e 198 9 ResearchTnangl e Par k N C 2771 1 Ai r 

# REVIEW O F TH E NATIONA L AMBIEN T AI R QUALIT

Y STANDARD S FO R LEAD : EXPOSUR E ANALYSI S METHODOLOG Y AN D VALIDATIO N 

# OAQP S STAF F REPOR T£3
_



### Thi s repor t ha s bee nreviewe dby th e Offic e o f Ai r Qualit y Plannin g an

d Standards , U.S . Environmenta l Protectio nAgency, , an dapprove dfo r publication . Mentio no f trad e name s o r commercia l product s i s no t intende dt o constitut e endorsemen t o r recommendatio nfo r use .P. 4

REVIEW O F TH E NATIONA L AMBIEN T AI ROUALIT YSTANDARD S FO RLEAD : EXPOSUR E ANALYSI S METHODOLOG YAND VALIDATIO N

OAOP S STAF F REPOR T

Ai r Oualit y

Manayemen t Divisio n Offic e o f Ai r Qualit y Plannin y

an dStandard s U.S . Environmenta l Protectio nAyenc y Researc hTrianyl e Park , N.C . 2771 1

Jun e 198 9P. 5

1 1 

### Acknowledgment s Thi s staf f pape r i s th e produc t o f th e Offic e o f Ai r Qualit y Plannin g an

d Standards . Th e principa l autho r i s Jef f Cohen , wit h assistanc e fromAlla n Marcus , Donn a Sledge , Dav e McLamb , Gai l Brion , an

d John Haines
. Technica l contribution s wer e provide d b y Ne w Yor k Universit yMedica l Center , PE I Associates , Inc. , an d Allianc e Technologie s Corporation
. Th e repor t incorporate s comment s fromOAQPS , th e Offic e o f Researc h an d Development , th e Offic e o f Drinkin g Water , th e Offic e o f Policy , Planning , an d Evaluation , an

d th e Offic e o f Genera l Counse l withi n EP Aan d wa s formall yreviewe d b ya subcommitte e o f th e Clea n Ai r Scientifi c Advisor yCommittee
. Helpfu l comment s wer e als o submitte d b ya numbe r o f independen t scientist s an d b yrepresentative s o f th e U.S . Center s fo r Diseas e Control , th e Lea d Industrie s Association , th e Canadia n Departmen t o f Healt h an d Welfare , th e Canadia n Ministr y o f th e Environment , an d th e Californi a Departmen t o f Healt h Services
. _• • Th e author s wis h t o than k Trici a Holland , Teres a demons , an d Virgini a Wyat t fo r excellenc e i n wor d processin g an d numerou s othe r task s an

d Dic k Atherto n fo r graphic s assistance
.



### tfiP. 6
m TABL E O F CONTENT S Pag e
v
v vi i I- l Lis t o f Figure s Lis t o f Table s Executiv e Summar y I . Introductio n II . Lea dExposure : Multimedi a Consideration s II- l
A . Airborn e Lea d11- 3 B . Lea di nSoi l 11- 5 C . Lea di

nDus t II- 9 D . Lea di

nth e Die t . E . Lea di

nWate r F . Lea dinPain t III . Estimatin g Lea dExposure s an d Bloo dLea dLevel s A . Alternativ e Modelin g Approache s 11-1 2 11-1 3 11-1 4 III- l III- l
111- 2 B . Calculatin g Bloo dLea dDistribution s Aroun dPredicte d Mean s IV . Integrate dLea dUptake/Biokineti c Mode l IV- 1 A . Estimate s o f Lea dUptak e IV- 3 B . Uptak e an

d Bloo dLea dConcentration s IV- 6 V . Statistica l Relationship s Betwee nBloo dLea dan d Airborn e Lead : Us e i

nDisaggregat e an

d Aggregat e Model s ..... . V- l A . Disaggregat e Mode l V- 3 B . Aggregat e Mode l V-1 4 VI . Validatio no f Integrate dLea dUptake/Biokineti c Exposur e Mode l VI- 1 A

. Validatio n Usin g Eas t Helen a Dat a ... . VI- 2 B

. Applicatio n o f Uptake/Biokineti cMode l t o Othe rDat a Set s VI-1 2 C

. Conclusion s VI-1 7P. 7

I V

TABL E OF CONTENT S (Continued )
Pay e
VII . Conclusion s an dApplication s o f Lea dExposur e Modelin g VII- 1 Appendi xA . Estimate s o f Lea dUptak e A- l Appendi xB . Estimatio no f th e Relationshi pBetwee nSoil , Dust ,

an dAmbien t Lea dB- l Appendi xC . Estimatin g 199 0 Baselin e Bloo dLea dAverage s C- l Appendi xD . CASA C Closur e Repor t D- 1 Reference sP. 8

LIS T O F FIGURE S

Numbe r 2- 1
2- 2
4- 1
6- 1



### 6- 2 Titl e

Principa l Pathway s o f Huma nExposur e t o Lea d an dSubsequen t Physiologica l Distributio n. . . . ooo o Trend s i

nMaximum

Quarterl y

Lea dConcentration s fo r Variou s Monito r Type s oooooooooooooo o o o o Summar y o f Relationship s Betwee nDail y Lea dUptak e an dBloo dLea dfo r Differen t Ay e Group s 

### Pa^ e
II- 2
II- 6
IV-1 7 Compariso n o f Distributio n o f Measure d Bloo d Lead Level s i n Children , 1- 5 year s o f Age , Livin g Withi n 2.2 5 mile s o f E.Helen a Smelte rvs . Level s Predicte d b yUptake/Biokineti c rlOQ G I ^KUl l D j o o o o o o o o o o o o o o o o o o o o o o o » 1" 0 Compariso n o f Distributio n o f Measure d Bloo d Lea d Level s i n Children , 1- 5 year s o f Age , Livin g Withi n 2.2 5 mile s o f E.Helen a Smelte rvs . Level s Predicte d b yUptake/Biokineti c nOU c 1 \l\U nw ] o o o o o o o o o o o o o o o o o.o o o o o o V 1" 3

LIS T OF TABLE S
Numbe r 

### 2- 1
2- 2
3- 1 3- 2
4- 1 Titl e

Typica l Lea dConcentration s i nVariou s Exposur e
rlGv i tdoooooooo . ooooooooooooooooo o Frequenc y

Distribution s o f Maximum Quarterl y

Lea d Concentration s b

y Typ e o f Sit e . ooooooooooo o Compariso no f Estimate dGSD s Acros s Severa l Studie s o o o Illustrativ e Bloo d Lead Distribution s Assumin g Differen t Mea n Bloo d Lead s and Geometri cStandar d Deviation s . . « Estimate d 1990 Averag e Lea d Intak e an d Uptake i n 2-Yea r Childre n Unde rAverag e Ai rLea d Levels , 'OOOOOOOOO O 11- 2
11- 6 II1- 6

III- 8

IV- 4_ _P. 9 v i 4- 2 Predicte d Equilibrate d Bloo d Lea d Level s Ove rTim e Amon g

Childre n wit h Constan t Lea d Uptake s . ......... . . IV-1 5 5- 1 Disaggregat e Mode l o f Contribution s fro m Variou s Medi a t o 199 0

Media n Bloo d Lea d Level s o f U.S , Childre n ( 2 Year s o f Age) : Backgroun d Level s an d Incrementa l Contribution s fro m Air

. . . V- 9 5- 2 Bloo d Lead/Ai rLea d Slope s i n Childre n fo rDifferen t Aye s

an d CXpU5UP€ 5 OOOOOOOOOOOOOOOOOOOOOO O V "I D 6- 1 Compariso n o f Inteyrate d Lea d Uptake/Biokineti cMode l

Prediction s t o 198 3 Measurement s i n Eas t Helen a ...,, . VI- 6 6- 2 Children' s Bloo d Lea d Level s Measure d i n Omaha , 1971-197 7

Vs , Integrate d Uptake/Biokineti cMode l Predictions

. ... . VI-1 4 6= 3 Children' s Bloo d Lea d Level s Measure d i n Silve rValley ,

Idah o 1974-197 5 Vs , Integrate d Uptake/Biokineti cMode l

r ic U I v * t l Ull j o o o o o o o o o o o o o o o o o o o o o o o o V 1"1 D A- l Age-Specifi cEstimat e o f Tota l Dietar yLea d Intak e fo r
i3JU"I7J O oooooooooooooooooooooooo o rt—J A- 2 Tota l Dietar yLea d Intak e fo r1978-198 3 fo rFiv e Ag e

Group s o f Childre n ................... . A- 5 A- 3 Summar

yo f Environmenta l Lea d Measurement s fro m Variou s Poin t Sourc e Location s .... . ........... . . A- 8 A- 4 Long-Ter m Relationship s Betwee n Dust , Soi l an d Ambien t
H i I L- C u U ooooooooooooooooooooooooo o - r\ ~ 10 , A- 5 Estimatin g Short-Ter m Response s i n Equilibriu m Soi l an d

Dus t Lea d Level s fro m Change s i n Ambien t Ai rLea d A-1 3 B- l Environmenta l Lea d Concentration s i n Omaha , Nebraska

. , . . B- 6 B- 2 Linea rMode l Paramete rEstimate s fo rAir : Soi l an d Dus t

Lea d Relat i UnSlllU^ o o o o O 0 o o o o o o o o o o o o o o o D~ 0 B- 3 Averag e Dus t an d Soi l Lea d vs . Ai r Lea d Relationship s U j r l»UV*dl#lU n o o o o o o o o o o o o o o o o o o o o o o o o D —O C- l Selecte d 197 8 Bloo d Lea d Level s from NHANE S I I .... . . C- 2 C° 2 Predicte d Change s i n Averag e Bloo d Lea d Level s Associate d wit hGasolin e Lead.Trend , ................ . C- 6 C- 3 Trend s i n Dietar y

Lea d Intake: Tota l Intak e (an d Atmospheri c Contributions) . ............... . C- 8 C- 4 Adjustment s t o 197 8 Mea nBloo d Lea d Level s fo r Dietar y L 6 3 0 KGQU C U l OllSooooooooooooooooooooo o U~ l 1 t C- 5 Derivatio n o f 199 0 "Baseline " Averag e Bloo d Lea d Level s . . C-1 4 C- 6 Maternal:Chil d Bloo d Lea d Concentration s an d Ratio s ... . C-1 6P.1 0

• a i rf'^*' " •' v i i
EXECUTIVElSUMMAR

Y

Fo rit s revie wo f th e Nationa l Ambien t Ai rQualit yStandard s (NAAQS ) fo r lead , EP Ai s assessin g healt h risk s associate d wit h lea d exposure , particularl y nea rstationar ysource s o f atmospheri clea d emission s (e.g. , lea d smelters) , unde ralternativ e regulator yscenarios

. Acritica l elemen t i n thi s proces s wil l be a

n exposur e analysi s wherebybloo d lea d level s ar e estimate d amon g population s expose d unde ralternativ e lea d regulation s i n th e future

. Thi s repor t summarize s relevan t informatio n o n lea d exposur e an d present s th e modelin g methodologie s tha t th e staf f believe s shoul d b e considere d fo rth e lea d NAAQ S exposur e analysis

. Result s o f validatin g on e o f thes e methodologie s ar e als o presented

. Thi s repor t does no t discus s healt h effect s associate d wit h lead , o r th e implication s o f differen t level s o f lea d exposure . Tha t informatio n i s reviewe d i n th e criteri a documen t and wil l be integrate d int o a separat e staf f pape ralon g wit h result s o f exposur e analyse s tha t emplo yth e methodologie s describe d here

. Th e followin g discussio n highlight s th e majo rpoint s an d conclusion s discusse d i n thi s paper . Multipl e Pathway

s o f Exposur e Huma n exposur e t o lea d occur s throug h multipl e pathways , an d ca n be o trace dprimaril y

t o leadi

npain t pigments , solde r i ncanne dfood s an

d plumbing , an

d atmospheri c emission s fro m moto r vehicle s an

d stationar y

lea d
sources . Althoug hairborn e leadi s a principa l startin g poin t o f environmenta l contamination , ora l intak e o f deposite datmospheri c leadi s ofte nth e primar y identifiabl e facto r predictin g th e bloo dlea do f youn g children . Th e principa l pathway s o f huma nexposur e ca nbe see ninFigur e 1 .P.1 1

vii i

Figur e 1 . PRINCIPAL PATHWAY S O F HUMA NEXPOSUR E T O LEA

D AN D SUBSEQUEN

T PHYSIOLOGICA

L DISTRIBUTION .

Oownwar dTrend s inLea dExposur e Lea dcontaminatio no f th e huma nenvironmen t ha s bee noccurrin g fo r thousand s o f year s sinc e it s many use s bega nt o b e discovered . Widespread , globa l dispersio no f lea dwa s greatl y accelerate dbeginnin g inth e 1920' s wit hit s introductio na s a nanti-knoc k compoun di ngasoline . U

p unti l recently , approximatel y 90 % o f airborn e leadi nthe U.S . wa s du e t o automotiv e emissions . Us e o f leadi ngasolin e ha s decline db y aoou t 90 % sinc e 1978 ; thi s trendwil l continu e a s complianc e wit hth e 198 6 gasolin e phasedownstandar di s complete dan d a s th e flee t o f lead-burnin g car s shrinks . Thi s trendha s bee nparallele db y a majo r reductio ni

n ambien t ai r leadlevels , whic hno w averag e betwee n0. 1 an d 0. 3 ug/m ^ i

n mos t U.S . citie s withou t leadpoin t sources . Th e reductio ninatmospheri c lead , combine dwit hth e gradua l phaseou t
o f lea dsolde r incanne dfoo dmanufacturin g an d th e ba no f lea dsolde r i nP.1 2
i x plumbin g ha

s resulte d i n a significant*dec l ih e i n dietar ylea d intake

. Fo rexample , i t i s estimate d tha t fro m 1978 t o 1985 , averag e dietar ylea d intak e i n a 2-yea rchil d droppe d fro m 52. 9 microgram s (Mg ) pe rda yt o 10. 4 pg/day

. Thi s tren d i s expecte d t o continue

. Thes e recen t change s i n nationwid e exposur e an d expecte d futur e trends , a

s wel l a

s contribution s fro m th e othe rai ran d non-ai rsource s o f lea d exposur e (e.g. , drinkin g water , contaminate d soils ) ar e importan t components o f th e methodologie s describe d i n thi s report
. Th e ai rlea d contribution s includ e bot h direc t inhalatio n o f lea d particle s an d indirec t exposur e throug h ingestio n o f lea d i n dus t an d i n soil

. Lead-base d paint , however , wil l continu e t o b e th e majo rsourc e o f high-dos e lea d exposur e and symptomati cTea d poisonin g fo rchildre n i n th e U.S

. fo ryear s t o come . Hig h exposure s t o lea d i n olde rhousin g wit h deterioratin g o reve n intac t lead-painte d surface s (vi a chalkin g o r weathering ) wil l no t be significantl yinfluence d b yan ychange s i n atmospheri c lea d emissions

. Becaus e childre n excessivel yexpose d t o lead-base d pain t canno t be expecte d t o be protecte d b yan ylea d NAAQS, no matte rho wstringent , the ywil l no t be include d i n th e exposur e analyse s describe d i n thi s report
. Availabl e dat a ar e presente d t o demonstrat e ho wsuc h estimate s coul d b e generated

. Comprehensive o plan s fo rsaf e an d effectiv e remova l o rcontainmen t o f lea d painte d surface s fro m ol d housin g need t o b e develope d and implemented

. Focu s on Poin t Source s Th e focu s o f th e exposur e modelin g approache s describe d i n thi s report , and th e overal l lea d NAAQ S review , i s o n stationar ylea d source s suc h a s primar yand secondar ylea d smelter s and batter yplants

. Althoug h suc h source s hav

e contribute d littl e t o th e overal l pollutio n loa d acros sPJ3

_

large , regiona l areas , fallou t fro m thes e source s ca n b e sever e o n a loca l scale

. Ambien t lea d level s aroun d suc h poin t source s var ydependin g o n distance , topography , win d spee d an d direction , plan t operatin g parameters , emission s controls , particl e size s an d depositio n rates , etc
. Dat a Limitation s Preclud e Quantitativ e Estimate s fo rAl l Sensitiv e Sub-Group s T o asses s th e healt h risk s associate d wit h alternativ e ai rlea d standards , i t i s necessaryt o estimat e th e bloo d lea d (PbB ) level s tha t woul d b e distribute d i n th e population s o f concer n unde rvariou s ai r lea d concentrations

. Youn g children , pregnan t wome n (a s exposur e surrogate s fo rth e fetus) , an d middle-age d men , ar e identifie d a s particularl y susceptibl e t o lead-relate d risks

. Quantitativ e estimate s o f bloo d lea d distribution s unde ralternativ e standard s wil l b e mad e onl yfo ryoun g childre n and middle-age d men . Feta l exposur e t o lead , i n most cases , ca n b e expecte d t o b e dominate d bymaterna l bon e lea d store s fro m pas t exposures . Therefore , accuratel y predictin g futur e change s i n feta l bloo d lea d level s woul d requir e estimate s o f materna l lea d burde n an d informatio n o n ho wbon e lea d store s woul d b e mobilize d an d transferre d acros s th e placenta

. Althoug h i t i s likel y tha t ther e i s extensiv e mobilizatio n o f lead , lik e calcium , durin g period s o f physiologica l stress 0 suc h a s pregnancy , ther e ar e n o biokineti cdat a t o quantif ythi s dynami cprocess . I n th e absence o f suc h data , no attemp t wil l b e mad

e t o estimat e feta l lea d exposure s associate d wit h materna l Pb B level s unde ralternativ e standards

. Give n th e sensitivit yo f th e fetu s an d neonate , however , potentia l risk s associate d wit h pre - an d neo nata l exposure s wil l b e o f majo remphasi s i n th e overal l lea d NAAQ S assessment
.P. M

x i Olde r wome nma y

als o b e at increase dris k du e t o releas e o f bon e lea dafte r menopaus e du e t o th e processe s o f osteoporosis . A 1ac k
o f biokineti c informatio no npost-menopausa l demineralizatio npreclude s quantitativ e estimatio no f bloo dlea dchange s unde r alternativ e lea d NAAQ S fo r thes e individual s a s well . Averag e Estimate s Predicte db y Exposur e Model s Wil l b e Combine dWit h Empirica l Estimate s o f Varianc e t o Calculat e Bloo dLea dDistribution s Thi s pape r present s thre e approache s tha t ca nb e use dt o estimat e th e impac t o f inhale dan dingeste dlea daerosol s an dcompound s onPbB level s distribute di

npopulation s livin g nea r lea dpoin t sources . Becaus e mos t o f th e dat a inpu t t o thes e model s ar e yenerall y averag e estimates , al l three-model s firs t estimat e Pb B level s interm s o f populatio nmea n levels . Give nth e significan t behaviora l an dbiologica l variabilit y withi npopulations , an dth e importanc e o f highl y expose dindividual s withi n th e populatio na t risk , i t i s necessar y t o determin e th e entir e bloo d lea ddistributio ncorrespondin g t o a give nmea nPbB . Thi s allows , fo r example , percentage s o f th e populatio nexpecte dt o exceed . PbB level s o f
concer nt o b e ascertained. - Becaus e Pb B level s ar e typicall y distribute d lognormally , i t i s possibl e t o calculat e percentile s o f a bloo dlea d distributio narounda give nmea nPb B leve l b y usin g th e geometri c standar d deviatio n(GSD ) o f tha t population' s bloo dlea ddistribution . Severa l epidemiologica l studie s hav e indicate dtha t th e lo g value s
o f measure dindividua l PbB level s i na uniforml y

expose dpopulatio nar e normall y distribute dwit ha variation , includin g analytica l variation , rangin g betwee n1, 3 an d1,4 . Fo r purpose s o f predictin g futur e exposures , a rang e o f GS D value s o f 1.30-1.5 3 ha s bee ndocumente dfo r childre n livin g nea r lea dpoin t sources , an dth e midpoin t o f 1.4 2 wil l b e assume d

asmP.1 5
x i i

a s a reasonabl e bes t estimate

. AGS D valu e o f 1.3 7 derive d fro m th e NHANE S I I surve ywil l b e use d fo radults

. Th e thre e model s ar e summarize d below

. Uptake/Biokineti cModel : Applicabl e t o Childre n fro m Birt h Th e firs t modelin g approac h presente d i s th e uptake/biokineti c mode l whic h use s measure d rate s o f absorption , o r"uptake " o f lea d throug h differen t pathways (e.g. , inhalation , ingestion ) fro m experimenta l studie s togethe rwit h availabl e mathematica l ("biokinetic" ) model s fro m lea d balanc e studie s t o projec t eithe rtota l bod yburde n o rth e amount o f lea d i n an yo f th e presume d "physiological " kineti ccompartment s (e.g. , blood , sof t tissue , bone ) a t an ytime

. Th e mode l i s thereb ycapabl e o f reflectin g "non-equilibrium " lea d exposures . I t ha s bee n develope d a t thi s tim e onl y fo ryoun g children

. Th e mode l i s base d o n age-specifi cair , soil , dust , food , an d wate r lea d intakes , an d o n age-specifi cabsorptio n factors

. Bloo d lea d an d tissu e lea d distributio n fro m absorbe d lea d i s describe d b ya linea r pharmacokineti cmode l whos e parameter s chang e wit h age . The ai rlea d concentration s aroun d a poin t sourc e ca n b e estimate d fro m historica l dat a o n emission s an d site-specifi cinformatio n abou t meteorologica l dispersio n parameters
. T

o addres s situation s whe n thi s informatio n i s no t known , a s i n th e cas e o f assessin g futur e NAAQ S scenarios , a methodolog ywa s develope d t o estimat e th e associate d soi l an d househol d dus t lea d concentration s usin g relationship s derive d fro m availabl e dat a fro m a wid e rang e o f poin t sourc e areas . Thi s approac h allow s estimatio n o f effect s o n soi l and dus t lea d o f historica l change s o rpropose d change s i n ai rlea d levels

. Dietar ylea d intak e estimate s ar e derive d fro m historica l an d curren t dat a an d futur e projection s o f th e Multipl e Sourc e Food Model , originall yP.1 6 xii i develope d i n th e 198 6 criteri a document , an d update d t o includ e mor e recen t information

. Becaus e th e biokineti cmode l assume s linea rrate s o f lea d transfe r betwee n tissues , i t i s limite d t o predictin g low-moderat e leve l exposure s (i.e. , PbB < 25-3 0 ug/deciliter , o rpg/dl)

. Th e model' s mathematica l assumption s an d numerica l parameters , however , combin e plausibl e biologica l hypotheses , anima l experimenta l data , an d result s o f observationa l studies

. Further, , i t allow s explici t projection s o f futur e lea d concentration s i n variou s medi a an d i n tur n ca n estimat e th e impact s o f thes e differen t change s o n differen t ag e group s o f children

. I t i s thi s flexibilit ytha t make s th e integrate d uptake/biokineti cmode l adaptabl e fo ra wid e rany e o f predictiv e exposur e assessments , an d whyi t wa s th e focu s o f th e validatio n exercise s describe d i n thi s paper . Aggregat e Ai rLea d Model : Applicabl e t o Youn g Childre n Th e secon d approach , referre d t o a s an "aggregate " model , use s a directl yapplie d mathematica l relationshi p betwee n ai rlea d an d bloo d lea d derive d fro m communit yepidemiologica l studie s tha t include s bot h direc t inhalatio n exposur e an d indirec t exposure s vi a secondar ydepositio n processes . Thi s approac h require s an implici t assumptio n tha t dus t an d soi l lea d concentration s ar e approximatel yi n equilibriu m wit h ai rlea d levels , an d tha t th e presen t ai rlea d exposure s reflec t historica l levels

. Thi s mode l als o require s estimate d contribution s t o children' s bloo d fro m non-ai rsource s o f lea d exposure , whic h ar e derive d fo rcurren t an d futur e year s base d o n suc h nationwid e dat a a s gasolin e usage , dietar y patterns , dietar ylea d concentrations , an d bloo d lea d surveys . Becaus e aggregate d ai rlead:bloo d lea d relationship s ar e no t availabl e fo radults , an d sinc e th e importanc e o f indirec t ora l exposure s t o deposite d atmospheri cP.1 7 

### xi v

leadi s relativel y

mino r amon g adults , thi s approac hi s limite dt o youn g children . Thi s typ e o f mode l i s bes t use do na sit e specifi c basi s du e t o th e larg e numbe r o f confounder s an dcovariate s suc has industria l exposure , ag e o f housing , an dsocia l conditions . A summar y o f ke y studie s usefu l i

nderivin g aggregat e bloo dlead/ai r lea dslope s fo r childre ni s included , alon g wit ha plausibl e rang e fo r thes e slope s (3- 5 p g lead/d l bloo dpe r u

g lead/cubi c mete r o f air) . Disaggregat e Ai r Lea dModel : Applicabl e t o Childre nan dAdult s Th e thir dapproach , referre dt o as a "disaggregate " model , i s a hybri do f th e firs t two tha t combine s separat e empirica l relationship s from multipl e regressio nmodel s betwee nbloo dlea dan dleadintak e from air , food , water , dust , an dsoi l lea dsources . Thi s model.wa s presente d inth e 198 6 criteri a documen t an di s update dher e t o includ e mor e recen t data . A

numbe r o f experimenta l exposur e an depidemiologica l studies , i n whic hsuc hdat a wer e availabl e ar e discussed . • I nthi s model , ther e i s a nimplici t assumptio ntha t th e soi l an d dus t lea dlevel s measure da t som e time reflec t earlie r exposures , s o tha t th e Pb B level s estimate dar e essentiall y a t equilibrium

an dno t jus t reflectin g som e recen t chang e o r event . Th e mos t plausibl e disaggregat e relationship , o r "slope " betwee n inhale dai r lea dan

dchildren' s bloo dlead , derive dfrom analysi s o f 3 poin t sourc e studies , i s 1.9 7 pg/d l pe r py/m3 . Th e averag e inhalatio n slop e fo r adult s derive dfrom th e mos t reliabl e experimenta l an depidemiolog y studie s i s 1. 4 pg/d l pe r pg/m3 . A facto r o f 1. 3 i s applie dt o accoun t fo r th e resorptio no f lea dfrom bon e i nadult s an

da slop e o f 1. 8 pg/d l pe r pg/m3 i s derived . Th e slop e value s use dinth e "disaggregate " mode lP.1 8
•>r a-x^.r^-A;

. X V

ar e ingeneral , consisten t with.thos e derive dfrom th e "uptake / biokinetic " model . Uptake/Biokineti c Mode l Validation s Successful ; Othe r Application s Shoul dProcee dwit hCautio n Result s o f severa l validatio nexercise s utilizin g th e uptake/biokineti c mode l comparin g predicte dan dobserve dbloo dlea dlevel s ar e presente d i nthi s paper . Th e mos t detaile danalysi s wa s performe dwit hdat a gathere d
aroun dth e smelte r i

nEas t Helena , Montana . Tw o type s o f validatio neffort s
wer e undertake nwit hthi s dat a set : 1 ) inth e firs t effort , th e bes t historica l dat a regardin g suc hmode l parameter s a s measure dair , yar dsoil , an dhousehol ddus t lea dexposur e estimate s wer e used ; 2 ) i nth e secon d validatio neffort , predicte dlevel s o f ai r (usin g dispersio nmodelin g tha t accounte dfo r fugitiv e emission s an dbackgroun dcontributions) , an dsoi l
an ddus t (usin g generalize drelationship s derive dfrom empirica l analyse s
o f a wid e rang e o f poin t sourc e data ) wer e use dt o estimat e Pb B levels . Th e latte r wor k wa s undertake nt o determin e ho w wel l th e mode l behave d whe nactua l measurement s o f necessar y inpu t dat a ar e no t available . Thi s
wa s necessar y

s o tha t th e reliabilit y o f th e mode l coul db e assesse dfo r polic y analysi s purpose s whe nles s tha nful l informatio ni s availabl e t o us e wit hth e model . Result s o f th e differen t Eas t Helen a validation s indicat e goo dconcordanc e betwee nobserve dan dpredicte daverag e Pb B level s i nchildre nlivin g nea r th e smelter . Th e difference s observe d
wer e no t statisticall y significant . Les s extensiv e validatio nexercise s onothe r publishe ddat a ar e reporte d i nthi s pape r t o tes t th e uptake/biokineti c mode l at othe r U.S . location s
an dtime s includin g Omaha , Nebraska , fro m 197 1 t o 197 7 an

dSilve r Valley , Idaho , i n1974-1975 . I

nthes e othe r validations , th e mode l performe dP.1 9

X V I
reasonabl ywel l i n predictin g averag e Pb B level s belo w25-3 5 pg/dl

. A s expecte d a t highe rexposur e levels , th e linea rmode l underestimate d actua l exposures . Give n th e man

yuncertaintie s i n th e inpu t dat a an d th e biologica l variabilit ytha t canno t b e incorporated , th e result s o f th e validatio n exercise s presente d revea l tha t th e lea d uptake/biokineti cmode l perform s quit e wel l i n predictin g mea n bloo d lea d concentration s i n childre n livin g nea rpoin t source s o f lea d a t exposur e level s o f curren t relevance

. Usin g thi s methodology , alon g wit h th e approac h t o estimat e lognorma l bloo d lea d distribution s usin g empirically-derive d GSDs , exposur e analyse s o f childhoo d population s livin g nea rstationar ylea d source s (i.e. , "cas e studies" ) wil l b e prepared

. Bloo d lea d distribution s fo rmiddle-age d me n i n thes e area s wil l als o b e estimate d usin g th e disaggregat e approach

. Result s o f thes e analyse s wil l b e incorporate d int o th e staf f pape rt o bette rinfor m th e Administrato ro n th e impact s o f alternativ e lea d NAAQS

. Th e uptake/biokineti cmodel 0 ca n als o b e a usefu l too l i n estimatin g PbB level s i n childre n livin g wit h differen t lea d hazards , suc h a s heavil y contaminate d soil s fro m historica l depositio n nea rmajo rurba n roadway s o rclose d smelter s o rmines

. Ongoin g regulator yeffort s b ydifferen t component s o f EP

At o contro l concentration s o f lea d i n air , wate ran d soi l hav e create d a significan t nee d t o mode l bloo d lea d concentration s tha t delineate s specifi croute s o f multi-medi a lea d exposure . Th e "uptake/biokinetic " mode l adequatel yprovide s suc h specificit yfo r youn g children

. Furthe rrefinement s ar e underwa yt o includ e non-linearitie s i n absorptio n rate s an d biokinetics

. Unti l then , th e mode l i s limite d t o estimatin g relativel ylo wt o moderat e exposure s an d shoul d b e use d wit h cautio n i n othe rapplications

.P.2 0

REVIE W O F TH E NATIONA L AMRIEN T AI RQUALIT YSTANDARD S FORLEAD : Exposur e Analysi s Methodolog y an dValidatio n
I. . INTRODUCTIO N EP A i s assessin g healt hrisk s associate dwit hlea dexposure , especiall y
nea r stationar y

source s o f atmospheri c lea demission s (e.g. , lea dsmelters) , unde r alternativ e regulator y scenario s fo r it s revie w o f th e Nationa l Ambien t Ai r Qualit y

Standard s (NAAQS ) fo r lead . Th e scientifi c an d technica l informatio nonlea dha s bee nreviewe di nEPA' s "Ai r Qualit y Criteri a fo r Lead " (EPA , 1986) . A "staf f paper" , i

nfina l preparation , wil l evaluat e an

dinterpre t th e mos t relevan t o f tha t informatio nt o hel p th e Administrato r inselectin g th e averagin g times , forms , an dlevel s fo r th e primar y

an dsecondar y

standards. * A

critica l elemen t i

nthi s proces s wil l b e a

nexposur e analysi s whereb y bloo dlea dlevel s ar e estimate d
amon g population s expose dunde r alternativ e lea dNAAQ S i nth e future . Thi s repor t summarize s relevan t informatio no nlea dexposur e and . present s th e modelin g methodologie s tha t th e staf f believe s shoul db e con sidere dfo r th e lea dNAAQ S exposur e analysis . Result s o f validatin g on e
o f thes e methodologie s ar e als o presented . Usin g methodologie s describe d
an dvalidate di

nthi s report , exposur e analyse s o f population s livin g nea r stationar y

lea dsource s (i.e. , "cas e studies" ) ar e bein g prepared . Result s
o f thes e analyse s wil l b e incorporate dint o th e staf f pape r alon y wit hth e overal l healt hris k assessment . Th e staf f wil l us e result s o f th e cas e studie s t o bette r inform th e Administrato r onth e impact s o f alternativ e lea dNAAQS .

*Th e curren t primar y

standar dfo r lea d(t o protec t publi c health ) i s 1. 5 microgram s pe r cubi c mete r (pg/m-^) , maximum arithmeti c mea naverage dove r a calenda r quarter . Th e secondar y standar d(t o protec t publi c welfare ) i s identica l t o th e primar y standard .1- 2

Normally , materia l o f thi s typ e woul db e incorporate dint o th e staf f paper . Du e t o th e comple xnatur e o f leadexposur e analysis , w e chos e t o plac e thi s materia l i na separat e repor t t o achiev e a mor e thoroug h revie w an dals o t o facilitat e othe r application s o f lea dexposur e analyse s unrelate dt o th e NAAQ S review . Thi s repor t shoul dthe nb e considere da s
a supplemen t t o th e OAQP S staf f paper . I t i s intende dfo r thos e reader s familia r wit hth e technica l informatio ncontaine di nth e criteri a documen t (hereafte r referre dt o a s "CD") . Thi s repor t doe s no t discus s healt h effect s associate dwit hleado r th e implication s o f differen t level s o f leadexposure . Tha t informatio ni s reviewe di nth e criteri a documen t an d wil l b e integrate di nth e staf f pape r wit hresult s o f th e exposur e analysis . Thi s paper , a s wil l b e don e wit hth e staf f paper , ha s bee ncirculate dfo r revie w b y th e Clea nAi r Scienc e Advisor y Committe e (CASAC ) an dth e public . A cop y o f th e closur e lette r from th e CASA C sub-committe e tha t reviewe d th e Augus t 198 8 draf t repor t i s containe din-Appendi xD „ Th e approac huse di

nthi s pape r i s t o asses s an dintegrat e exposure relate dinformatio nderive dfrom th e criteri a documen t review tha t th e staf f believe s shoul db e considere di nth e review

o f th e primar y

lead NAAQS . SectionI I present s relevan t feature s o f huma nexposur e t o atmospheri c an

dnon-atmospheri c source s o f leadthroug hvariou s pathways . SectionII I introduce s differen t approache s t o estimat e th e impac t o f alternativ e ai r leadlevel s o nlea dbody

burden s among differen t populations , Section s I

V an dV discus s the methodologie s o f thes e differen t approache s i ndetail . Sectio nV I present s result s o f validatio nexercise s usin g th e uptake/biokineti c model . Sectio nVI I discusse s som e application s o f th e modelin g approache s describe di nthi s repor t inadditio nt o thei r rol e i n th e review

o f the lea dNAAQS .P.2 2

- •* ? •' * • - ^ i$.J'''•'- ••-''
- .' ' '
II . LEA D EXPOSURE : MULTIMEDI A CONSIDERATION S T o asses s th e risk s associate dwit halternativ e lea dNAAQS , i t i s necessar y t o understan dth e influenc e exerte db y atmospheri c lea do

nth e tota l lea d exposur e o f th e population(s ) o f concer nthroug hvariou s exposur e pathways . Relevan t dat a onthes e pathway s an dth e relationship s betwee nai r lea dan d lea di nothe r medi a ar e summarize di nthi s section . Th e goa l o f th e exposur e assessment s presente dinthi s repor t i s t o addres s aggregat e lea dabsorptio n fro m man y pathway s fo r population s livin g nea r stationar y lea dsource s tha t wil l b e affecte db

y alternativ e lea dNAAQS . Muc ho f th e methodoloyy presente d
canals o b e applie dt o othe r population s wit hdifferen t exposur e profiles . Exposur e situation s (othe r thanoperatin y stationar y

leadfacilities ) dominate d b y single , intense , and/o r intermitten t source s ar e no t include dfo r lac k o f adequat e data , and/o r becaus e an y lea dNAAQ S woul dhave little , i f any , pro tectiv e effec t fo r thos e situations . The y includ e mos t significantly , hig hpain t lea dexposur e (se e Subsectio nII. F below ) an doccupationa l exposures . (Indirec t exposure s o f childre nt o occupationa l dust s tracke dhome b y workin g parent s
ar e implicitl y

include di

nth e modeling) . Othe r miscellaneou s intermitten t
source s no t addresse dher e includ e variou s consume r product s (e.g. , leachin g
o f lead-glaze dpottery) , an dhousehol dactivitie s o r hobbies , suc has staine d glas s constructio nan dremova l o f leadpain t soldering . Se e Sectio n7.3. 2 o f the C D fo r a mor e complet e discussio no f thes e kind s o f exposur e sources . Th e source s an

dpathway s o f huma nleadexposur e ar e diayramme din Figur e 2- 1 an

dtypica l level s o f lea dindifferen t medi a t o whic hU.S . population s ar e expose dar e presente di nTabl e 2-1 . Huma nexposur e t o lea d
ca nb e trace dprimaril y t o lea dinpain t pigments , solde r incanne dfood s an d plumbing , as wel l a s t o atmospheri c lead . Althouyhairborn e lea di s a principa l startin g poin t o f environmenta l contamination , ora l intak e o f deposite datmospheri c leadi s ofte nthe primar y identifiabl e facto r predictin gH- 2

VI R KIONI V . PtCt t UNIMl l Figur e 2-1 . PRINCIPAL PATHWAY S O F HUMA NEXPOSUR E T O LEA

D AN D SUBSEQUEN

T PHYSIOLOGICA

L DISTRIBUTION . ADAPTE D FROM CD , FIGUR E 7-1 .

Mediu m TABL E 2-1 . TYPICA L LEA O CONCENTRATION

S I N VARIOUS EXPOSUR E MEDI A
Rura ] Are a Urba n Are a Nea r Poin t Source(s) a Reference s Ambien t Ai r (ug/m-3)' >
Indoo r Ai r (pg/m-3 )

Soi l (ppm )

Stree t Oust (ppm) d
Hous e Oust (ppm) d

Typica l Food s (ppm ) Wate r (pg/1 )
Paint * 0. 1
0.0 3 •0.0 8

S - 3 0

80 - 13 0 (90 ) 5 0 •SO O (300 )

0.00 2 - 0. 8 5 - 75 pg/ L

< 1 - > 5 mg/cm ? 0. 1 - 0. 3

0.0 3 - 0. 2

3 0 - 450 0

10 0 - 5,00 0 (1500 ) 5 0 - 3.00 0 (1000 )

Sam e Sam e
Sam e 0. 3 - 3. 0
0. 2 - 2. 4

_
15 0 - 15,00 0
(25,000 )
10 0 - 20,00 0 (10,000 )

Sam e Sam e
Sam e Faoro , 198 8
Se e Footnot e c

CO , Tabl e 7-11 ; Mielk e e t al. ; 1983 ; LaBell e e t al. . 1987 ; Se e Tabl e A- 3 Nriagu , 1978 ; CO , Tabl e 7-2 6 U.S . EPA , 1977 ; Landriga n e t al. , 1975 ; Mors e e t al. , 1979 ; Anql e an d Mclntire . 197 9 Fleqe l e t al. . 198 8 Briskin , 198 8
Billic k

an d Gray , 197 8
••"Withi n 2- 5 k

m o f source s includin g primar y an d secondar y lea d smelters , batter y plants . ^Represent s quarterl y average s monitore d i n 1986 .
c Rang e o f indoor/outdoo r ratio s use d (0. 3 - 0.8 ) fro m CD , Tabl e 7- 6 excep t nea r pofn t source s ttfier e larg e particle s pre dominat e an d infiltratio n int o home s i s low , rati o appear s t o be close r t o 0. 3 (Cohe n an d Cohen , 1980) . ^Value s i n parenthese s represen t estimate s provide d i n C O (Table s 7-1 8 an d 7-20 ) a s typica l averages . e Sinc e ther e ma

y b e severa l layer s o f lead-base d pain t o n a give n surface , absolut e concentratio n o f lea d i s les s usefu l tha n my/cm 2

. Survey s b y HU D i n Pittsburg h showe d tha t mor

e tha n 70 * o f pre-194 0 dwellin g unit s an d 20 * o f post 196 0 unit s had a t leas t on e surfac e wit h mor e tha n 1. 5 mq/cm 2 lea d pain t (NAS , 1980) .P.2 4 

### II- 3
th e bloo d lea d o f youn g children

. Jjigh e .corre l ation s hav e bee n foun d betwee n children' s bloo d lea d an d th e lea d conten t o f househol d dust , playgroun d dust , mouthin g behavior , lea d o n children' s hands , an d househol d cleanlines s (Sayr e e t al. , 1974 ; Bake re t al. , 1977 ; Charne ye t al. , 1980 ; Roel s e t al. , 1980 , Yanke l e t al. , 1977 ; Angl e e t al. , 1979 ; Walte re t al. , 1980 ; Brunekree f e t al. , 1981 ; Qua h e t al. , 1982 ; Bellinge re t al. , 1986 ; Bornschei n e t al. , 1986 ; Schillin g an d Bain , 1988)

. Larg e scal e isotopi cstudie s provid e stron g evidenc e tha t ai rlea d ha s a rapi d an d measurabl e effec t o n ingeste d lead , eve n i n adul t population s a t lo wlevel s o f ai rlea d (Facchett i
e t al. , 1985)

. I t i s necessary , therefore , t o attemp t t o quantif yho w atmospheri cemission s ca n influenc e human exposure , no t onl ythroug h direc t inhalatio n o f lead-containin g particles , bu t throug h ingestio n o f lea d deposite d ont o soil , dusts , vegetation , an d othe renvironmenta l surfaces

. Unti l recently , betwee n 85-90 % o f airborn e lea d i n th e U.S

. originate d fro m gasolin e combustion , wit h mos t o f th e remainde rfro m stationar yindustria l processe s suc h a

s primar yan d secondar ylea d smelting , batter yplants , an d combustio n o f oil , coal , wast e oi l an d municipa l waste
. Becaus e o f th e accelerate d reductio n o f th e lea d conten t i n gasolin e an d th e continuin g phaseou t o f olde rlead-burnin g vehicles , concer n regardin g lea d emission s int o th e ambien t ai ri s shiftin g almos t exclusivel yt o relativel yconfine d
area s surroundin g significan t stationar ysource s o f lea d an d thi s paper' s focu s wil l b e o n estimatin g exposure s an d risk s i n thos e locales

. A

. Airborn e Lea d 1

. Physical , Chemica l an d Spatia l Characteristic s Ambien t ai rlea d level s resul t fro m curren t industria l emissions , lead-contaminate d roa d an d wind-blow n dust , automotiv e exhaust , an d soli d wast e combustion

. Th e industria l contributio n include s point , fugitiv eII- 4

process , an

dmaterial s handlin g emission s fro m leadmining , smelting , an d
recover y operation s a s wel l a s variou s fabricatio nan dmanufacturin g processes . Curren t contribution s fro m road s an

dothe r fugitiv e dus t source s var y wit h locatio nan

dth e influenc e o f historicall y contaminate dsoil . I ngeneral , abou t 50 % o f .automotive leademission s deposit s withi na few hundre dmeter s o f majo r roadway s (Daine s e t al. , 1970 ; Huntzicke r e t al. , 1975 ; Ingall s an dGarbe , 1982) , whil e th e remainin g particle s ar e smal l enoug ht o remai nairborn e an dca ntrave l hundred s o r thousand s o f kilometers . Thi s long-distanc e transpor t likel y account s fo r th e surfac e contaminatio n
o f pola r glaciers , oceans , an dothe r remot e location s aroundth e glob e (Settl e an

dPatterson , 1982) . I ncontras t t o automobil e exhaust , atmospheri c leademission s from industria l plant s tha t proces s lea dan dit s product s hav e contribute dlittl e t o th e overal l pollutio nloadacros s large , regiona l area s althoug hfallou t from thes e source s ca nb e sever e o na loca l scale . Th e trajectorie s o f atmospheri c emission s from industria l source s vary wit hwin dspee dan

d direction . Hig hconcentration s aroundlea dsmelter s an dothe r majo r emitter s canb e dominate db y fugitiv e emissions , predominatel y mad e u po f larg e [> 7 micrometer s (pm) ] lea dparticle s resultin g fro m material s handling , furnac e upsets , an dfurnac e chargin g an dtappin g operation s (Landriga ne t al. , 1975 ; Jennet t e t al. , 1977 ; Batty e e t al. , 198b) . Stac k an dven t emission s ca nals o produc e significan t an dfrequen t shor t distanc e impacts , especiall y incomple xterrai no r aroundolde r facilitie s (Iaccarino , 1988) . Beyon dth e immediat e are a ( « 2 km ) o f lead stationar y

sources , proces s emission s from stacks , predominatel y a s lea d sulfate s an

doxide s wit ha siz e rang e betwee n1 an d1 0 pm , becom e th e majo r sourc e o f leadi

nsoil s an

dai r (Dor ne t al. , 1976 ; Roel s e t al. , 1980 ; Davidso nan

dOsborn , 1984) .P.26

_ 11- 5 2

. Ambien t Concentration s A s indicate d i n th e C D (Sectio n 7.2.1 ) an d EP A(1989) , ai rlea d level s i n urba n area s an d nea rpoin t source s hav e bee n markedl yreduce d sinc e 197 7 b yth e us e o f unleade d gasolin e i n ne wcar s equippe d wit h catalyti cconverters , th e gradua l phaseou t o f olde rlead-burnin g cars , th e lead-in-gasolin e phasedow n program , an d stead yreduction s i n emission s fro m stationar ysource s i n complianc e wit h stat e implementatio n plan s towar d attainmen t o f th e lea d an d particulat e matte rNAAQ S an d partl y becaus e o f decrease d industria l production

. Tota l atmospheri clea d emission s droppe d 94

% betwee n 197 8 an d 1987 ; gasolin e lea d us e droppe d b y90 % ove rtha t perio d an d industria l sourc e emission s droppe d b yove rone-hal f (EPA , 1989)

. Recen t (1980-1986 ) ai rqualit ydat a fo rbot h poin t source-oriente d site s (predominantl y"SLAMS " sites) , roadsid e site s ("NAMS" , micro-scale ) an d othe r site s (middle-scale , neighborhood) , ar e summarize d i n Tabl e 2- 2 (Battye , 1988)

. B

y1986 , th e onl yquarterl yaverag e concentration s ove r1. 5 pg/m 3
wer e recorde d a t monitor s nea rstationar ysources . Twelv e countie s i n th e U.S

. reporte d quarterl yaverage s abov e 1. 5 pg/m 3 i n th e 1986-198 7 period ; 1 3 mor e wer e o n th e margi n o f exceedin g th e NAAQ S bu t eithe rha d inadequat e numbers o f sample s o rwer e slightl ybelo wth e standar d level

. Trend s i n maximu m quarterl yaverage s between " 198 0 an d 198 6 ar e o illustrate dinFigur e 2-2 . Eve nmor e dramati c decline s ar e eviden t i ndat a confine dt o roadsid e monitorin g (se e Battye , 198 8 and . EPA , 1989) . B . Lea di

nSoi l Th e natura l occurrenc e o f leadinth e earth' s crus t averaye s 5-5 0 p g lead/ g soi l invariou s soils * (CD , p . 7-28) , althoug hsoil s nea r

*0n e pg/ g i s equivalen t t o on e par t pe r millio no r 1 ppm .P.2 7 II- 6
TAHL E 2-2 . FREQUENC Y DISTRIBUTIO N

Sit e type/tim e f- r am e 198 0 throug n 198 6 A l l monitors 0 NAMSC SLAM S Microscal e roadside d Middl e scal e Neighborhoo d scal e 198 6 onl y Al l monitor s NAM S SLAM S Microscal e roadsid e Middl e scal e Neighborhoo d scal e 198 7 onl y Al l monitor s NAM S SLAM S Percentag e o f O F MAXIMUM QUARTERL

Y (•jg/m3) d

site s i n ranqe s (concentration s <0. 5
77. 5 78. 9 73. 4 24. 1 45. 7 68. 7
93. 0 97. 5 92. 9 1U0. 0 100. 0 94. 4
93. 0 97. 4 93. 1 0.5-1. 0

15. 4 17. 2 16. 7 37. 9 47. 1 24. 3
2. 5 1. 3 2. 2 0. 0 0. 0 0. 0
2. 8 0. 0 2. 3 1.0-1. 5

3. 2 4. 7 2. 8 25. 9 7. 1 7. 0
1. 2 1. 3 0. 9 U. O 0. 0 O. U
1. 7 1. 3 1. 7 concentra t i n uq/m^ ) 1.5-2. 0
1. 5 1. 1 1. 7 10. 3 U. U O. U
1. 6 0. 0 1. 3 U. O 0. 0 5. 6
0. 4 0. 0 0. 0 AI R LEA

O CONCENTRATION

S

io n >2. U
2. 3 U. 2 3. 4 1.7 - U. O U. U
1. 8 O. U 2. 7 U. O O. U 0. 0
2. 0 1. 3 2. 9 Mean
0.3 9 0.4 1 U.3 8 U.7 4 U.4 6 0.3 7
U.1 7 0.1 4 U.2 1 0.1 8 U.1 2 0.1 4
0.2 0 0.2 0 0.2 0 "lumbe r o f

site year s 3,27 9 47 1 1,15 8 5 8 7 U 11 5
51 4 79 22 6 9 9 1 8
45 8 7 8 175

d 0at a are fro m th e SAROA O an d AIR S systems an

d represen t th e numoe r o f site-year s fo r whic h th e maximu

m quarterl y concentratio n fal l withi n th e designate d ranges . T o D e included , a vali d site-yea r mus t hav e a t leas t thre e quarter s o f dat a wit h a t leas t observation s pe r quarter. -

ion s pe r quarte r ^Include s site s previousl y classifie d int o categorie s (e.g . mee t an y o f th e curren t definitions . "urban" ) tha t d o no t

C NAM S refer s t o th e Nationa l Ambien t Monitorin g Statio n network , whil e SLAM S refer s to th e Stat e an

d Loca l Ambien

t Monitorin g Statio n network . Eacn o f these tw

o network

s include s bot h roadsid e an d poin t sourc

e monitors ; however , i n th e cas e o f lead , th e NAM

S networ k tend s t o focu s o

n roadsid e sites , whil e th e SLAM S networ k

incorporate s mor

e poin t sources an

d othe r specia l purpos e monitors . ^Microscal e site s wer e withi n 5-l b meter

s fro m a majo r roadway . Middl e scal e site s had-furthe r setback

s an d defin e concentration s u p t o severa l cit y blocks . Neighborhoo d scal e site s defin e concentration s i n mor e extended area

s o f unifor m lan d us

e withi n dtie s (0.5- 4 km 2 ) . Afte r 1986 , dat a collectio n a t these site s stopped . Source : Batty e (1988) .

r o S 0 0 3 Z o $ H Z w u z o u

> • < • J CC H tC < ZS or 1 - 0. 9 -
o.a- 0. 7 - 0. 6 - 0. 5 - 0. 4 - 0. 3 - 0. 2 - 0. 1 - 0 - , \ \' —

\\ 

# v-v^--^ ^ ^~^-~ ^ ^ tr 

### ^Z^ m 

### ~~~~~J^\

—i— i - i i i aAL L $ NAM S
" A SLAM

S *

i 1 I" ' 7 9 8 1 v 8 3 Yea r 8 5 8 7 FIGUR E 2-2 . TREND S INMAXIMU M QUARTERL Y AI R LEA D CONCENTRATION S FOR VARIOU S MONITO R SITES , BAfTY E (1988) .P.2 8
II- 7

naturall y

occurrin g outcrop s ca nreach?severa l hundre dppm . Urba nsoil s
ar e contaminate db

y lea dfrom

a combinatio no f automotiv e an dpoin t sourc e depositio na s wel l a s from lea di npain t o

nindoo r an

doutdoo r surfaces . Elevate dsoi l lea dconcentration s (a s hig ha s 200 0 ppm ) hav e bee nfoun d withi n1 0 fee t o f woo dfram e house s painte dwit hlead-base dpain t (Te r Haa r
an dAronow , 1974) . Accumulation s o f lea dinsoil s (an ddusts ) aroun dbric k
o r ston e structure s hav e als o bee nfound , an dca nb e partiall y

attribute d t o washof f lea dcollecte do nroofs , ledges , an dexterio r wall s (Wheele r an d Rolfe , 1979) , an

dpossibl y

t o a naerodynami c effec t o f th e structure s o n depositio no f lea dfrom nearby.sources . Recen t dat a from Baltimor e (Mielk e
e t al. , 1983 ) an

di nan daroundChicay o an d"downstate " Illinoi s (LaBell e
e t al. , 1987 ) indicat e tha t lea daccumulate s i nsoi l awa

y fro m painte d structure s an

dknow nindustria l lea dsources , i na patter na t leas t partiall y relate dt o traffi c activit y an ddistanc e from

nearby roads . Th e uppe r layer * o f roadsid e soil s may contai ndeposite datmospheri c leadi nconcentration s o f 1 0 t o 50 0 pp m i nexces s o f natura l level s withi n 1 0 meter s o f th e roadbed , beyon dwhic hconcentration s declin e abruptly , dependin g o

ntraffi c densit y

an dvolum e an

dvehicl e spee d(Pag e an dGanje , 1970 ; Mott o etal. , 1970 ; Quarle s e t al , 1974 ; Wheele r an dRolfe , 1979 ; Pierso nan

dBrachaczek , 1976 ; Mielk e e t al. , 1983 ; LaBell e e t al. , 1987) . Soi l lea dconcentration s i na sampl e o f cit y

park s hav e als o bee nreporte d t o b e high , rangin g from 20 0 t o 330 0 pp

m (Cho w e t al. , 1975 ; Zimdah l an d Hassett , 1977) .

*Becaus e o f th e vertica l gradien t o f lea di nsoi l (i.e. , lea dconcentratio n decrease s wit hsoi l depth) , th e technique s use di nsamplin g soil s influenc e th e lea dconcentration s found . Inthi s report , soi l lea ddat a refe r t o th e uppe r 1- 5 centimete r layer , whic hi s th e mos t relevan t fo r potentia l intak e b

y children .P.2 9
II- 8 Topsoi l lea d concentration s aroun d variou s lea d poin t source s generall y decreas e exponentiall ywithi n a 3-1 0 k m radiu s fro m 100-60,00 0 pp m dow n t o backgroun d level s (Yanke l e t al. , 1977 ; Schmit t e t al. , 1979 ; Roel s e t al. , 1978 ; Dieme l e t al. , 1981 ; Fugas , 1977)

. However , elevate d soi l lea d level s hav e eve n bee n foun d a t distance s exceedin g 20-2 5 k m fro m som e smelter s (Wixson , 1978)

. Limite d dat a indicat e tha t lea d i n soi l nea r primar yan d secondar ylea d smelter s occur s a s lea d oxides , sulfide , sulfate , an d elementa l lea d (Olso n an d Skogerboe , 1975 ; Corri n an d Natusch , 1977)

. Muc h o f th e lea d i n th e atmospher e i s deposite d o n terrestria l surface s wher e i t i s retaine d i n organi ccomplexe s o radsorbe d t o hydrou s iro n oxide s nea rth e soi l surfac e (CD , p . 7-31)

. Th e abilit yo f soi l t o immobiliz e lea d largel ydepend s o n soi l pH an d organi cconten t (i.e. , fulvi cand

. humi c substances)

. Man

yU.S

. soils ' appea rt o hav e a larg e capacit yt o bin d lea d wit h onl ya smal l fractio n dissolve d i n soi l moistur e wher e i t i s availabl e fo rplan t uptake

. Th e environmenta l impac t o f lea d o n th e biot a o f terrestria l
an d aquati cecosystem s i s discusse d i n Chapte r6 o f th e CD

. Improvement s i n ai rqualit yd o no t necessaril yinvolv e reduction s i n soi l lea d a t th e sam e rate
. Th e decontaminatio n o f th e environmen t i s a ver ycomple xan d slo wprocess , particularl yfo rsoi l lea d whic h has bee n show n t o remai n a t elevated.level s severa l year s afte rlea d manufacturin g plant s hav e cease d operatin g (Prpic-Maji ce t al. , 1984)

. Whil e lea d i n soi l i s relativel yimmobile , i t stil l ma yente rth e foo d chain , b e ingeste d directly , b e mobilize d b ymechanica l force s suc h a s gardening , o rma yb e redisperse d int o th e ai ran d resuspende d int o wate rb ywin d scatterin g o f soi l particle s an d dust.

. Consequently , population s livin g i n area s wit h historica l accumulation s o f lea d i n soi l ma ycontinu e t o b e expose d t o lea d fo rindefinit e period s despit e effectiv e control s o f atmospheri cemissions

.P.3 0

- ' '• • ' ; j ! 

### II- 9

C . Lea di

nDus t -••-.•• Dus t i s a norma l componen t o f th e home (i.e. , "hous e dust" ) a s wel l a s th e outdoo r environmen t wher e i t canb e foun do nsidewalks , playgrounds , driveways , an

dothe r hardsurfaces . Anthropogeni c material s deposite don thes e outdoo r surface s wil l b e referredt o a s "stree t dusts" . I naddition , th e very toplaye r o f soil s (includin g lea f litter ) t o whic hpeople , particularl y children , com e i

ndirec t contact , ar e considere di nth e criteri a documen t t o b e "soil " dusts" . Bot hhous e dus t an

dstreet/soi l dus t contai nlea dfro m atmospheri c deposition , "natural " soil , an dpain t chips . A s wit hroadsid e soil , significan t correlation s betwee nlea dconcentration s instree t dus t an dth e proximit y an ddensit y

o f traffi c hav e bee nfoun d(Rolf e e t al. , 1977 ; Lauan dWony , 1982) . Concentration s o f lea dindust s o nplaygrounds , streets , an dsoi l surface s als o increas e wit hhighe r ai r lea dconcentration s an dwit hproximit y t o stationar y

lead.source s (Roel s e t al. , 1980 ; Brunekree f e t al. , 1981 ; Yanke l e t al. , 1977) . A s summarize db y Nriag u(1978) , stree t dust s from differen t U.S . citie s containe dbetwee n30 0 an d18,00 0 pp

m lead . A

survey o f stree t dust s in7 7 midwester ncitie s showe da naverag e lea dconten t o f - 1,63 6 pp m i nresidentia l neighborhood s an d2,41 3 pp

m incommercia l an

d industria l area s (NAS , 1980) . Limite dchemica l analyse s o f roadsid e soil s an ddust s fro

m U.S . citie s foun dlea dpredominatel y a s sulfate , alon g wit h mino r amount s o f oxid e an dhalid e salt s (Olso nan dSkogerboe , 1975 ; Corri n an dNatusch , 1977) . Pavemen t dust , stree t dust , gutte r debris , an dhousehol d dus t sample s contai nmostl y larg e lea dparticle s rangin g betwee n4 0 an d 100 0 p m (Pierso nan

dBrachaczek , 1976 ; Sturge s an dHarrison , 1985 ; Dugga n an dInskip , 1985) . Highe r lea dconcentration s ar e usuall y foun di nth e smalle r size dfractions . Th e concentratio nina sampl e o f stree t dus tP.3 1

11-1 0 sieve da t 10 0 pm , fo r example , i s usuall y a t leas t tw

o t o fou r time s greate r tha ntha t i

nth e sam e sampl e sieve da t 1,00 0 p m (Dugga nan

dInskip , 1985 )
an d76 % o f th e composit e weigh t o f hous e dus t wa s measure di nparticle s smalle r tha n14 9 p

m (Qu e He e e t al. , 1985) . Thi s i s significan t give n tha t th e bioavailabilit y o f soi l leadtend s t o increas e wit hdecreasin g particl e siz e (Barltro pan dMeek , 1979) . Inaddition , preliminar y wor k indicate s tha t smalle r particle s (<100-25 0 pm ) readil y adher e t o finger s
an dare thu s likel y

t o b e ingeste d(Dugga nan dInski p1985 ; Qu e He e e t al. , 1985) . Unlik e lea dtha t i s incorporate dint o soil , lea di nsurfac e dusts , bot hindoor s an

doutdoors , i s mobil e an dca nb e expecte dt o respon dove r time t o a muc hgreate r degre e t o change s i natmospheri c lea demissions . Airborn e lea ddeposite donstreets , sidewalk s an ddriveway s i s subjec t t o distributio nb

y win dan

dwater . Windblownparticle s associate dwit h dus t are.ap t t o b e redeposite dwithi nth e urba nenvironmen t b y th e comple x win dcurrent s cause db y building s an

d stree t canyons . Followin g th e installatio no r supplementatio no f emissio ncontrol s a t lea dpoin t sources , an dsignifican t improvement s inai r lea dquality , significan t drop s i n concentration s o f lea dinplaygroun ddust , surfac e dus t onsoil , an di n hous e dus t hav e beenobserve dwithi n1 t o 2 year s (Mors e e t al. , 1979 ; Prpic-Maji c e t al. , 1984) . Anothe r study foun da wea k correlatio nbetwee n dus t lea dsample s collecte dtw o month s apar t inth e sam e house s inWale s (Davie s e t al. , 1985) . Th e author s note dtha t thi s i s consisten t wit hth e suggestio ntha t externa l influences , e.g. , soil , ar e importan t fo r dus t lea dan ddifference s inweathe r o r seaso ncoul dinfluenc e th e amoun t o f soi l brough t int o th e hous e an dthereby

caus e short-ter m

change s indus t composition . Thi s illustrate s agai nth e potentia l responsivenes s o f hous e dus t lea dlevel s t o change s inai r quality .__________________^_^___

_P.32
_ 11-1 1
Ther e i s som e evidenc e t o suggest , tha t thi s sam e relationshi papplie s innon-poin t sourc e area s an d tha t lea dinsurfac e dust s shoul ddeclin e
a s a resul t o f th e declin e i ngasolin e lea demissions . A surve y o f rainwashe darea s i

nth e U.K . an

d Ne w Zealan dfoun dtha t th e norma l acidit y o f rai n(p

H betwee n4 an

d 5 ) wa s insufficien t t o completel y dissolv e
an dtranspor t lea dparticles , an d tha t residu e nea r street s pose s a healt h hazar dt o childre nwh o ar e pron e t o inges t stree t dust s (Da y e t al. , 1979) . However , Laxe nan

d Harriso n(1977 ) foun dtha t a ligh t rainfal l ( 2 t o 3
mm ) i s sufficien t t o remov e 90 % o f th e lea dfrom th e roa dsurface , mainl y t o surroundin g soi l an d t o waterways . Furthermore , base do ndepositio n fluxe s arounda majo r roadwa y ove r a yea r an

d concentration s o f lea di nth e
roaddrainag e water , Harriso ne t al . (1985 ) estimate dtha t remova l o f lea d i nrunof f water s exceed s tha t deposite donth e roadsides . Th e rat e o f
remova l o f lea dfrom

stree t dust s i s als o dependen t onth e frequenc y an d efficienc y

o f stree t cleanin g operations. ' I t appear s reasonabl e t o expec t tha t wit hdeclinin g input , lea dconcentration s i nstree t an

d househol d° dust s wil l als o dro pdu e t o precipitation , wind , stree t an d hous e cleaning . Survey s o f a divers e se t o f home s indicat e a wid e rang e o f hous e dus t lea d level s betwee n1 0 an d 35,00 0 pp

m (EPA , 1977 ; Harrison , 1979 ; Angl e an d Mclntire , 1979 ; Thornto ne t al. , 1985 ; Clar k e t al. , 1985 ) an d a s hig ha s 100,00 0 pp

m withi n2 k

m o f a smelte r (Landriga ne t al. , 1975) . Lea dlevel s i nhous e dus t ca nvary considerabl y

dependin g o

nhous e cleanin g practices , a s demonstrate db

y Charne y e t al. , (1983) , a s wel l a s o nth e presenc e an

d conditio no f lead-base dpainte dsurfaces , th e presenc e o f cigarett e smoke , th e amoun t o f dus t an d soi l blow

nint o o r carrie dint o th e hous e onclothin g
an dshoe s (especiall y

o nthos e occupationali y expose dt o lead ) an d pets , indoo r source s o f lea dothe r tha npain t (e.g. , soldering) , th e permeabilit y11-1 2

o f th e home t o outdoo r ai r (whic hca nvary wit hseason) , an

d outdoo r con centration s o f ai r lead . Lea d concentration s i nhous e dus t ar e als o dependen t
o nothe r constituent s i nth e dus t an

d i t i s therefor e importan t t o conside r th e tota l amoun t o f leade d dus t a s wel l a s dus t lea d concentration . T o asses s th e impac t o f atmospheri c lea d o nchildren' s tota l exposure , i t i s necessar y

t o estimat e th e contribution s o f differen t ai r lea d level s t o outdoo r an

d indoo r soil/dus t lea d level s a s wel l a s th e amoun t o f dir t a chil d ma y

ingest , bot hinadvertantl y an d deliberately . Thes e issue s ar e addresse d inth e modelin g approache s presente d inSection s I V an d V . D . Lea d inth e Die t Th e ingestio no f foo d i s a majo r componen t o f mos t individuals ' tota l lea d uptake , althoug hth e relativ e contributio ni s a functio no f thei r age , an d th e siz e an

d typ e o f diet . Th e occurrenc e o f lea d inth e die t ma y b e
a resul t p f a ) natura l source s o f lead; b ) depositio no f airborn e lea d particle s ont o crops , forage , feed , soils , an d water ; an

d c ) th e harvesting , processing , transportation , packaging , preparation , an d storag e o f foo d durin g w°nic hlea d
ca nb e introduce d a t ever y stag e eithe r b

y atmospheri c depositio no r throug h metalli c contamination , particularl y from plumbin g o r solde r i ncans . Recen t studie s o

nlea d conten t o f variou s foods , bot hbefor e an d afte r processing , packaging , an d preparation , an

d o nfoo d consumptio npattern s inth e U.S. , provid e informatio nondietar y lea d intake s fo r differen t population s (Beloia nan d McDowell , 1981 ; Wolni k e t al. , 1983 ; Nationa l Foo d Processor s Associations , 1982 ; Pennington , 1983 ; U.S . FDA , 1983 , 1984) . Usin g thes e dat a fo r 1982-83 , a "Multipl e Sourc e Foo d Model " wa s develope d inth e C D tha t apportion s lea d i n"typical " chil d an d adul t diet s t o th e followin g sources : natura l soi l lead , direc t atmospheri c lea d adde d t o foo d crop s befor e harves t an d durin g processing , indirec t atmospheri c lea dP.3 4 11-1 3 tha t has bee n incorporate d i n soils , lea d i n solde rfro m foo d can s an d drinkin g water , an d lea d whos e origi n canno t b e determine d a t presen t (CD , Sectio n 7.3.1.2)

. Th e mode l wa s validate d byusin g th e sam e parameter s alon g wit h mor e recen t foo d dat a fro m 198 4 an d 198 b t o successfull ypredic t continuin g decline s i n dietar ylea d intake

. Fo rexample , dietar ylea d intak e fo ra 2-yea rol d chil d ha s droppe d fro m abou t 45-5 0 pg/da yi n 197 8 t o a n estimate d 13. 1 pg/da yi n 1985 ; comparabl e decline s (fro m 45-5 0 pg/da yt o 15-2 0 pg/day ) hav e bee n see n i n differen t adul t population s sinc e 198 2 (Flege l e t al. , 1988. ) Eve n greate rreduction s ha d bee n achieve d i n th e earl y t o mid-1970' s (CD , p . 7-49)

. Thes e trend s ar e attributabl e t o th e drasti c reductio n i n gasolin e lea d emission s an d th e voluntar yphaseou t o f lead-soldere d
can s b yU.S

. manufacturer s sinc e th e 1970's

. Thi s downward shif t i s expecte d t o continu e u p unti l th e earl y1990' s a s lea d fro m bot h thes e source s drop s further

. Th e method s b ywhic h estimate s o f dietar ylea d intak e fro m th e Multipl e Sourc e Foo d Mode l ar e derive d an d applie d t o modelin g tota l lea d exposur e ar e discusse d i n Appendi xAan d Sectio n V

. E

. Lea d i n Wate r Lea d i s a natural , usuall ywery minor , constituen t o f surfac e an d yroun d waters
. Atmospheri clea d ca n ente raquati csystem s throug h direc t fallou t o r i n surfac e runof f a s suspende d particle s o radsorbe d t o soi l particles

. Unde r mos t condition s (pH , temperature , alkalinity) , lea d form s insolubl e salt s an d precipitate s t o sediments , whic h probabl yaccount s fo rth e lo wlea d conten t o f U.S

. surfac e wate rsupplies ; th e averag e concentratio n rangin g betwee n 3 an d 4 microgram s P

b pe rlite rwate r(pg/L ) (NAS , 1980)

. I n contrast , lea d level s i n household , school , an d offic e buildin g drinkin g wate rca n b e muc h highe rdu e t o plumbin g corrosio n an d subsequen t leachin g o f lead , rangin g betwee n 1 0 an d 3 0 pg/ 1 o n average . Th e combinatio n o f corrosiv e (i.e. , sof t o racidic ) wate ran d lea d pipe s o rlea d soldere dP.3 5

11-1 4 joint s i n distributio n system s o rhouses create s localize d zone s o f hig h lea d concentration s u p t o 380 pg/ 1 (Wort h e t al. , 1981)

. Th e combinatio n o f ne wsolde r an d corrosiv e wate rca n resul t i n concentration s commonlyove r1000 mg/L

. I n \ general , level s ar e highes t i n sample s o f ho t and/o rstagnan t "firs t draw " water
. Drinkin g Wate ri s a majo rsourc e o f lea d exposur e fo rman yinfant s whil e the y ar e dependen t o n bab yformula s durin g thei rfirs t year , a s wel l a

s fo ryoun g children

. Th e 1986 Saf e Drinkin g Wate rAmendment s banne d th e us e o f lea d solde ro r flu xan d lead-bearin g pipe s an d fittings , t o b e implemente d an d enforce d b yth e State s b yJun e 1988

. I n Augus t 1988 , EPA' s Offic e o f Drinkin yWate rpropose d revisin g th e existin g lea d standar d o f 5 0 pg/ L t o 5 pg/L , measure d a t th e entr ypoin t t o th e distributio n syste m o rth e treatmen t plant , wit h a "no-actio n level " averag e o f 1 0 pg/L , measure d a t th e hom e tap
. Estimate d contribution s tha t natural , atmospheric , an d solde rlea d mak e t o tota l lea d exposur e vi a drinkin g wate ran d tota l die t ar e addresse d i n th e modelin g approache s presente d i n Section s I V an d V

. F

. Lead i n Pain t

Ingestio n o f lead-containin g pain t i s considere d t o b e th e most frequen t caus e o f sever e lea d intoxicatio n amon g childre n (Chisolm , 1984 ; CDC , 1985)

. Significan t correlation s hav e bee n foun d betwee n th e quantit yan d conditio n o f lea d painte d surface s i n home s an d bloo d an d feca l lea d level s i n inne rcit ychildre n i (Urban , 1976 ; CD , pp . 11-15 6 t o 11-160)

. Significan t difference s i n bloo d lea d ! level s hav

e bee n foun d i n relatio n t o housin g conditio n amon g childre n a

s youn ya

s nin e monthsj wit h highes t level s i n childre n livin g i n deterioratin g pre-Worl d Wa rI I housing , intermediat e level s i n well-maintaine d an d rehabilitate d olde r i housing , an d lowes t level s i n childre n i n publi chousin g an d newe runit s fre e o f j lea d pain t (Clar k

e t al. , 1985)

. Othe rinvestigation s indicat e tha t i n additio n t o peelin g lead-base d paints , "intact " lead-base d pain t contribute s t o elevate d bloo d lea d level s i n childre n vi a chalkin g o rweatherin g (Gilber t e t a>. ,_ . ._^

. P.36

_ 11-15^^"'""' " "" '

1979 ; Galk e e t al. , 1975 ) o rca n b e exposed-t o childre n wh o chewo rgna wupo n th e surfaces

. Furthe rrisk s ar e associate d wit h conventiona l pain t remova l technique s (i.e. , sanding , burnin g hea t guns ) whic h ca n generat e concentration s o f fin e lea d dus t u p t o 100-100,00 0 pg/m 3 (NIBS , 1988 ; Inski p an d Atterbury , 1983)

. Unde rth e 197 1 Lead-Base d Pain t Poisonin g Preventio n Act , whic h has sinc e bee n amended , th e Departmen t o f Housin g an d Urba n Developmen t has . regulator yan d researc h responsibilitie s fo reliminatin g th e hazard s o f lead-base d pain t poisonin g i n federall yfunde d housing

. I n 1977 , th e Consume rProduc t Safet yCommissio n banne d househol d pain t (includin g to y an d furnitur e paint ) containin g more tha n 0.06 % lea d a s hazardous

. Thi s wa s a n importan t ste p bu t i t doe s no t affec t hazard s pose d b ylead-base d paint s alread ypresen t o n ol d housin g surfaces

. Prio rt o 1940 , som e interio r paint s containe d mor e tha n 50 % (500,00 0 ppm ) lead

. Us e o f lea d pigmen t paint s decline d slowl ybetwee n 194 0 an d th e lat e 1960' s afte rwhic h i t decline d a t a rapi d rat e (NAS , 1972)

. Pop e (1986a ) estimate s tha t i n 1980 , th e interio rand/o rexterio rsurface s o f betwee n 21. 5 an d 47. 3 millio n household s i n th e U.S. , mostl ybuil t befor e 1960 , containe d greate rtha n 0. 7 mg/cm ^

lea d i n painte d surfaces , a leve l considere d hazardou s t o youn g childre n b yth e Center s fo rDiseas e Contro l (CDC)

. Betwee n 6. 2 an d 13. 6 millio n childre n unde rth e ag e o f 7 ar e estimate d t o hav e reside d i n lead-base d painte d housin g i n 198 0 (Pope , 1986a)

. Eve n i f coate d wit h low-leve l leade d paint , th e underlyin g layer s o f lead^-base d pain t i n olde rhome s represen t a larg e reservoi ro f lea d exposur e i n children , particularl yi f ther e i s peelin g paint , broke n o rcracke d plaster , o rhole s i n th e walls

. Th e numbe ro f lead-base d painte d home s wit h thes e deterioratin g condition s (i.e. , "unsound" ) i s estimate d t o hav e bee n betwee n 800,00 0 t o 2. 9 millio n

### n-1 6

i n 198 0 wit h approximatel y235,00 0 t o 842,00 0 childre n unde rag e 7 livin g i n suc h home

s (Pope , 1986a)

. Lead-base d pain t continue s t o b e th e majo rsourc e o f high-dos e lea d exposur e an d symptomati clea d poisonin g fo rchildre n i n th e U.S

. (Chisolm , 1971 ; CDC , 1985) , an d i t appear s tha t exposur e t o lead-base d pain t wil l continu e t o b e a proble m fo rdecade s t o com e (Schneide ran d Lavenhar , 1986)

. Betwee n 197 3 an d 1980 , onl y10 % o f pre-194 0 housin g unit s and.5 % o f housin g unit s built.i n th e 1940' s had bee n remove d fro m ou rnation' s housin g stoc k b ydemolition , disaster , o rb yothe rmean s suc h a s conversio n t o commercia l spac e (Burea u o f th e Census , 1983)

. Les s tha n hal f o f thes e remove d unit s wer e locate d i n centra l cit yarea s wher e lea d poisonin g i s mos t prevalent

. I n addition , poo rurba n familie s ofte n hav e n o choic e bu t t o liv e i n poorl ymaintaine d olde rhousing , give n tha t th e vas t majorit yo f
ne whousin g unit s create d fro m 197 3 t o 198 0 i s locate d outsid e o f centra l cit yarea s an d tha t acut e shortage s o f moder n an d lead-free , lo wincom e renta l unit s exis t i n man ycitie s (Farfel , 1985)

. Man yrura l familie s ar e als o afflicte d wit h a lea d pain t ris k sinc e abou t 41 % o f rura l housin g i s "substandard " (ATSDR , p . VI-15)

. Hig h exposure s t o childre n livin g i n olde rhousin g wit h flakin g o r intac t lead-base d pain t wil l no t b e significantl yinfluence d b yan ychange s i n atmospheri clea d emissions

. Childre n wit h pic a fo rpain t chip s o r other s livin g i n deterioratin g lead-base d painte d home s wh o ar e excessivel y expose d t o pain t lead-contaminate d dus t throug h norma l han d t o mout h activit y canno t b e expecte d t o b e protecte d b yan ylea d NAAQ S n o matte rho

wstringent

. Fo rthi s reaso n an d becaus e exposur e t o pain t lea d i s s o highl yvariable , n o attemp t wil l b e mad e her e t o quantitativel yestimat e exposure s o f childre n wh o ar e excessivel yexpose d t o lead-base d pain t unde rvariou s ai rlea dP.3 8 11-1 7
levels , a s i s don e fo r othe r exposureamedia . Som e o f th e availabl e data , althoug hsparse , ar e discusse da t th e endo f Appendi xA t o demonstrat e ho

w som e estimate s coul db e generated . Despit e th e smal l amoun t o f data , an dth e grea t variabilit y

inpain t lea dexposures , i t i s clea r tha t an y exposure s
an dbloo dlea dlevel s predicte dfo r childre nunde r variou s ai r lea dlevel s usin g th e approache s inSectio nII I wil l b e significantl y highe r fo r childre n wit hhig hpain t lea dexposure . Comprehensiv e plan s fo r saf e an deffectiv e
remova l o r containmen t o f lea dpainte dsurface s from ol dhousin g nee dt o b e develope dan

dimplemented , otherwis e pediatri c plumbis m wil l persis t unti l
muc ho f th e presen t housin g stoc k i s completel y rehabilitate do r demolishe d (Chisolm , 1986) . Preventin g excessiv e exposur e t o existin g source s o f lea d inan daroun dhousin g mus t b e addresse db y a nappropriat e combinatio no f legislation , housin g cod e inspectio nan denforcement , financia l incentives , parental education , an dothe r programs .P.3 9

III . ESTIMATIN GLEAD EXPOSURE S AND BLOO D LEAD LEVEL S A . Alternativ e Modelin g Approache s T o asses s th e healt hrisk s associate dwit halternativ e ai r lea d standards , i t i s necessar y t o estimat e th e bloo dlea d(PbB).level s tha t woul db e distribute dinth e population(s ) o f concer nunde r variou s ai r lea d concentrations . [Th e amoun t o f lea dmeasure di nwhol e bloo di s a

ninde xo f th e rapidl y

diffusibl e fractio no f th e tota l body burde no f absorbe dlea d
an di s generall y

use da s th e dosage , o r inde xo f exposure , i ninvestigatin g th e variou s huma nhealt heffect s associate dwit hlead. ] Lea dexposur e occur s throug hmultipl e medi a bu t unfortunately , longitudina l assessment s o f simultaneou s multi-medi a exposure s hav e no t ye t bee nmade . Potentiall y usefu l longitudina l analyse s are no w bein g carrie dou t a s par t o f th e Cincinnat i Lea dProgra m Projec t (Clar k e t al. , 1987) . Thre e approache s
ar e examine dher e tha t ca nb e use dt o estimat e o r predic t th e impac t o f inhale d
an dingeste dlea daerosol s an dcompound s onth e bod y burde no f lea da s indexe d b y bloo dlead . Thes e approache s ar e presente di ndetai l inSection s I V an d V fo r consideratio nfo r usin g one , two , o r al l thre e i nassessiny

th e protectio nprovide db y alternativ e lea dNAAQS . Th e firs t approach , discusse di nSectio nIV , i s t o us e measure drate s
o f absorption , o r "uptake " o f leadthroug hdifferen t pathway s (e.gT , inhalatio n
an dingestion ) fro

m experimenta l studie s togethe r wit havailabl e mathematica l ("biokinetic" ) model s fro m lea dbalanc e studie s t o projec t eithe r total , body burde no r th e amoun t o f lea di nan y o f th e presume d"physiological " kineti c compartment s (e.g. , blood , sof t tissue , bone ) a t an y time . Th e secon dapproach , referre dt o a s a n"aggregate " model , i s t o directl y appl y a mathematica l relationshi pbetwee nai r lea dan dbloo dlea d derive dfrom

communit y

epidemiologica l studie s tha t reflect s bot hdirec tII1- 2

inhalatio nexposur e an dindirec t exposure s vi a secondar y depositio npro cesses . Th e thir dapproach , referre dt o a s a "disaggregate " model , i s a hybri do f th e firs t tw o inwhic hseparat e empirica l relationship s betwee n bloo dlea dan

dlea dintak e from

lea dinair , food , water , dust , an dsoil , availabl e from

experimenta l exposur e an depidemiologica l studie s o f differen t populations , ar e applie dt o lea dconcentratio nestimate s i ndifferen t media . Th e natur e o f th e relationship s detecte dbetwee nlea dconcentration s inbloo dan

dvariou s environmenta l media , an dth e merit s an

dlimitation s in usin g empirica l relationship s t o represen t lea dexposur e throug hmultipl e pathway s inthes e latte r tw o approaches , wil l b e discusse dinSectio nV . B . Calculatin g Bloo dLea dDistribution s Aroun dPredicte dMean s Becaus e mos t o f th e dat a inpu t t o thes e model s ar e generall y averay e estimates , al l thre e model s estimat e PbB level s interm s o f populatio nmea n levels . Th e distributio no f Pb B level s inU.S * childre ni s broa dbecaus e ther e i s a distributio no f exposure s thos e childre nface , a distributio no f behavio r pattern s tha t affec t th e uptak e o f tha t exposure , an da distributio n
o f biologica l absorptio nan dexcretio nrates . Fo r purpose s o f settin g a lea dNAAQS , i t i s necessar y t o determin e th e bloo dlea ddistributio n
acros s a define dpopulatio ngrou pcorrespondin g t o a give nmea nPb B fo r tha t grou ps o that , fo r example , percentage s o f individual s exceedin g Pb B level s o f concer nca nb e ascertained . Determinin g suc hdistribution s i s a n attemp t t o accoun t fo r th e significan t behaviora l an dbiologica l variabilit y withi npopulations . I t i s th e grou po f individual s wit hth e potentiall y greates t advers e respons e t o an y give nlea dexposur e tha t ar e o f greates t
concer ninestablishin g a primar y lea dNAAQS . Consisten t wit hmeasurement s o f othe r metal s intissue s o f huma n populations , th e distributio no f Pb B level s fo r an y relativel y

homogeneou s111-^ 3 ; P.4 1

populatio n closel yfollow s a lognormal,distributio n (CD , Sectio n 11.3.4)

. . Alognorma l distributio n i s completel yspecifie d b yit s geometri cmean an d geometri cstandar d deviation

. I t i s possible , therefore , t o calculat e percentile s o f a bloo d lea d distributio n (e.g. , media n o r9 9 percentile )
aroun d a mean PbB leve l b yusin g th e geometri cstandar d deviatio n (GSD) o f tha t population' s bloo d lea d distribution

. Severa l epidemiologica l studie s hav e indicate d tha t th e lo g value s o f measure d individua l Pb B level s i n a uniforml yexpose d populatio n ar e normall ydistribute d wit h a variation , includin g analytica l variation , rangin g betwee n 1. 3 an d 1.4 , whe n expresse d
a s a GS D (Teppe ran d Levin , 1975 ; Aza re t al. , 1975 ; Billic k e t al. , 1979)

. Th e NHANE

S I I stud yprovide s th e bes t availabl e dat a o n nationwid e bloo d lea d level s i n term s o f qualit ycontro l an d sampl e size

. I n regressio n analyse s o f thes e data , Schwart z (1985a ) estimate d a GS D o f 1.42 8 fo ryoun g childre n age d 6 month s t o 5 years , afte rremovin g th e varianc e i n PbB level s attributabl e t o ai rlea d exposur e b yadjustin g ever yindividual' s PbB leve l t o wha t i t woul d b e a t zer o ai rlead , whil e allowin g fo rvariation s i n backgroun d non-ai rlea d exposure . Afte rexcludin g fro m th e analysi s childre n wit h PbB level s abov e 4 0 pg/dl , wh o woul d no t b e expecte d t o b e substantiall yaffecte d b ychange s i n th e lea d NAAQ

S (fo rexample , becaus e o f highe rtha n averag e pic a activit y o rexcessivel yhig h exposure s t o lea d i n paint) , Schwart z (1985b ) reapplie d th e sam e techniqu e an d calculate d a GS D o f 1.419

. Thus , a GS D withou t attributio n o f an ysourc e o f lea d exposur e excep t gasolin e lea d an d industria l ai rlea d emission s ma yb e take n a

s a rounded-of f valu e o f approximatel y 1.4 2 fo rth e NHANE

S I I populatio n o f childre n (CD , p . 11-31)

. Give n tha t th e focu s o f thi s exposur e analysi s i s o n population s livin g nea rlea d poin t source s wher e bloo d lea d variabilit yma yb e differen t compare d

W M IP.4 2 III- 4

t o th e tota l mi xo f U.S

. children , a separat e assessmen t o f bloo d lea d GSD' s fo rsuc h population s i s presente d here

. Publishe d statistic s o f PbB sample s nea rvariou s lea d poin t source s hav e bee n assemble d an d analyze d i n Cohe n (1986 ) an d Marcu s (1988a)

. Th e GSD s calculate d fro m thes e point
source/bloo d lea d survey s ar e liste d i n Tabl e 3-1 , alon g wit h th e NHANE S I I GS D fo rchildren

. T

o differen t degrees , th e primar yorigi n o f non-biologica l variatio n i n lea d exposur e fo rthes e poin t sourc e population s wa s th e smelter , especiall yi n th e Roel s an d Yanke l studie s conducte d whe n smelte remission s wer e considerabl yhigher

. I t i s possibl e tha t childre n wit h exposur e t o a single , intens e sourc e o f lea d ma yhav e relativel ylo wvariabilit y (essentiall yonl ydu e t o intrinsi cbiologi cvariability ) wit h a hig h
mean bloo d lead

. Th e mos t recen t stud yindicate s a large rvarianc e a t relativel ylowe rexposur e level s nea rth e Montan a smelte rsurveye d i n 1983 , suggestin g tha t multipl e origin s wit h separat e variabilit yma yb e presen t rathe rtha n a singl e predominan t sourc e o f variabilit yi n lea d exposur e (Marcus , 1988a)

. Th e selectio n o f a GS D valu e t o mode l population s livin g nea rvariou s lea d poin t source s i n th e futur e depend s o n assumption s regardin g varianc e i n exposur e i n th e future

. Perhap s th e mos t relevan t dat a ar e fro m th e 198 3 E

. Helena , Montan a stud ysinc e the yreflec t th e mos t contemporar yconditions

. I t ca n b e expecte d tha t eve n fo rthi s population , however , tota l lea d exposur e wil l hav e droppe d substantiall yb y1990 , th e startin g poin t o f ou rexposur e analyses

. Thi s i s attributabl e t o recen t an d continuin g downwar d trend s i n lea d level s i n canne d foods , th e nationwid e ba n o n lea d solde ri n ne wconstructio n an d plumbin g repairs , th e lead-in-gasplin e phasedown , an d perhap s increasin g ' publi cawarenes s regardin g th e danger s o f lea d exposur e an d effectiv e avoidanc e measures . Al l o f thes e change s shoul d resul t i n no t onl ylowe rmea n baselin e•'!•'"*-,&• ; «T * , III- 5

TABL E 3-1 . COMPARISO NOF,ESTIMATE D GSD s ACROS S SEVERA L STUDIE S P.4 3

' I

Population/Referenc e Mean Pb B (ug/dl ) Estimate d GSD 1 NHANE S I I - tota l mi xo f childre n 1- 5 year s ol d (Schwartz , 1986b ) 11-yea rold s livin g nea rBelgia n primar ylea d smelte r(Roel s e t al. , 1980 ) 1- 9 yea rold s livin g nea rIdah o primar ylea d smelte r(Yanke l e t al. , 1977 )

1- 5 yea rolds , livin g nea rMontan a primar ylea d smelte r(CDC , 1983 ) 1- 5 yea rold s livin g i n 3 Missour i smelter , town s (Bake re t al. , 1977 ) 16. 0

21. 7

56. 5

1- 5 yea rolds , closes t t o 3 non-ferrou s 15. 6 smelter s i n U.S

. (Hartwel l e t al. , (median ) 1983 ) 

### 9. 4
16. 2 1.4 2

1.2 9

1.3 2

1.3 9

1.5 3
1.5 7

iGS D calculation s describe d i n Cohe n (1986 ) an d i n Marcu s (1988a) .P.4 4

III- 6
Pb B levels , bu t perhap s mor e importantly , infewe r hig hleve l exposur e situation s an

dtherefor e les s varianc e i nPbB level s tha nexiste din1983 . Quantifyin g suc ha

neffec t t o estimat e a futur e GS D valu e i s difficult . I t i s likely , however , tha t futur e reduction s i nbaselin e "non-poin t source " lea dexposure s wil l resul t ina reductio ni nexposur e varianc e s o tha t th e bloo dlea dGS D wil l b e mor e reflectiv e o f intrinsi c biologi c variance , suc h
a s tha t foun dinth e Roel s an dYanke l studies . Althoug hthes e latte r studie s wer e conducte ddurin g time s o f muc hhighe r exposures , th e exposure s
wer e dominate db

y hig hsmelte r emission s an dsoil/dus t contamination , resultin g i

nrelativel y

lo w PbB variability . Fo r purpose s o f modelin g futur e exposure s amon g childre nlivin g nea r differen t lea dpoin t sources , a rang e o f GS D value s canb e considered : a lowe r boun do f approximatel y 1.3 0 derive dfrom

th e Yanke l e t al . an dRoel s e t al . studie s an da nuppe r boun d GS D valu e o f 1.5 3 derive dfrom th e 198 3 CD C stud

y o f E . Helena , Montan a children . Th e midpoin t o f thi s rang e i s 1.42 , whic hcoincidentall y i s identica l t o th e NHANE S I I GS D estimate . Unti l additiona l dat a ar e available , a rang e o f 1.30-1.5 3 wil l therefor e b e assume dfo r childre nlivin g nea r leadpoin t source s a s a reasonabl e rang e o f GS D values , an dth e midpoin t o f .1.4 2 wil l b e assume da s a reasonabl e bes t estimate . I nth e cas e study

exposur e -analyses , the large r an dmor e conservativ e GS D o f 1.5 3 wil l b e teste di n sensitivit y

analysis . Sinc e bloo dlea destimate s wil l als o b e mad e fo r middle-age dmen , GS D value s fo r adul t bloo dlea ddistribution s ar e needed . Ther e i s littl e informatio nonadul t bloo dlea dGSD s from poin t sourc e studies . Th e mos t complet e dat a bas e i s clearl y fro m NHANE S II , whic hha s bee n analyze dinth e C D t o yiel da rang e o f GS D values , dependin g onrac e an d plac e o f residence , betwee n1.3 4 an d1.3 9 fo r adul t wome nan dbetwee nIII- 7

1.3 7 an d1.4 0 fo r adul t me n(CD ^ Tabl e ,11-9) ; Give nth e uncertaintie s i n extrapolatin g thes e range s t o adul t population s livin g nea r poin t source s unde r futur e exposur e scenarios , a midpoin t valu e o f 1.3 7 wil l b e chose na s
a reasonabl e estimat e fo r bot hadul t me nan dwomen . Analytica l variatio nwhic hexist s inan y measuremen t ha s a

nimpac t
o nth e bia s an

dprecisio no f statistica l estimate s suc ha s th e GSD s derive d fro m th e studie s discusse dhere . Fo r thi s reason , i t i s importan t t o recogniz e th e magnitud e o f analytica l variatio ninbloo dlea dmeasurement s du e t o measuremen t variatio n(i.e. , betwee nmeasurement s ru nat th e sam e time ) an dvariatio ncreate db y analyzin g bloo dsample s at differen t time s (CD , p . 11-29) . Usin g GSD s adjuste di nsuc ha way , althoug hprovidin g a
mor e accurat e characterizatio no f a give nbloo dlea ddistribution , ma y no t b e appropriat e fo r thi s assessmen t becaus e th e healt heffect s studie s tha t wil l b e use dt o defin e dose-respons e relationship s di dno t correc t thei r Pb B measurement s fo r analytica l variance . Thes e studies , lik e NHANE S I I
an dth e poin t sourc e epidemiologica l surveys , generall y employe dth e bes t avai l abl e measuremen t technique s an dqualit y

control . Usin g "corrected " GSD s t o predic t th e distributio no f children' s Pb B level s arounda mea n populatio nPbB , an

dthe nmatchin g thos e predicte dPb B level s wit h"uncorrected " Pb B levels 0 derive dfrom healt hstudie s inorde r t o asses s th e risk s associate d wit htha t populatio nmea nPbB , woul dresul t i na somewha t biase dassessment . Therefore , th e rang e o f GSD s presente dabov e tha t ar e no t correcte dfo r analytica l varianc e wil l b e use di nfurthe r calculations . Tabl e 3- 2 present s bloo dlea ddistribution s associate dwit hsampl e populatio nmea nPb B level s calculate dusin g th e GS D value s derive dabove .P.4 6

III- 8
Thes e distribution s wer e calculate d usin g th e formul a give n t o describ e
a lognorma l distributio n (Yanke l e t al. , 1977) : PbB = GM(GSD) * where : G M = geometri c mea n PbB GS D = geometri c standar d deviatio n
z = th e numbe r o f standar d deviation s Pb B = valu e o f PbB a t z standar d deviation s

TABL E 3-2 . ILLUSTRATIVE BLOO D LEA D DISTRIBUTION S ASSUMING DIFFERENT MEA

NBLOO D LEAD S AN

D GEOMETRI C STANDARD DEVIATION S
Geometri c Percentil e 

### GS D
1.3 7 Mea n



### Pb B


### 4 5 6 7 90t h



### 6. 0 7. 5 9. 0 10. 5 95t h



### 6. 7 8. 4 10. 1 11. 7 99t h



### 8. 3 10. 4 12. 5 14. 6 99.5t h



### 9. 0 11. 3 13. 5 15. 8

J.4 2 4 6. 3 7. 1 9. 0 9. 9

5 7. 8 8. 9 11. 3 12. 3 6 9. 4 10. 7 13. 6 14. 8 7 11. 0 12. 5 15. 8 17. 3P.4 7

IV . INTEGRATE D LEA

D UPTAKE/BIOKINETI C MODE L Th e "uptake/biokinetic " modelin g approac hattempt s t o accoun t fo r th e following : a ) th e amoun t o f lea di nth e bod

y at an y on e time i s th e produc t
o f dynami c interaction s o f partiall y offsettin g processe s o f absorption , distribution , storage , mobilization , an dexcretion ; b ) thes e processe s vary wit hth e rout e an

drat e o f exposure , a person' s age , nutritiona l an dhealt h status , an

dbaselin e exposure; , c ) uptak e fro m al l source s b

y al l absorption route s ca nbe separatel y modeled , thu s providin g a nestimat e o f th e relativ e importanc e o f atmospheri c lea dexposure , eithe r directl y o r indirectly , t o tota l body

burden ; an

dd ) pas t an

dfutur e trend s inenvironmenta l lead level s du e t o differen t contro l effort s an dregulation s ar e importan t determinant s o f projecte dexposures . Ther e hav e bee nsevera l studie s measurin g th e intake , uptake , an d metabolis m

o f lea dinadul t mal e volunteers , fro m whic hbalanc e scheme s hav e bee nconstructe d(Kehoe , 1961 ; Chamberlai ne t al. , 1978 , Rabinowit z e t al. , 1976 , 1977) . B

y makin g estimate s abou t lea dintake s an dvariou s metaboli c factors , balanc e scheme s canbe constructe dfo r differen t group s wit h differen t exposure s t o leadt o asses s th e importanc e o f specifi c exposur e factor s unde r variabl e condition s (e.g. , alternativ e lea dNAAQS , phaseou t
o f leadi

nsoldere dcan s an

dingasoline) . Pre-schoo l ag e childre n(£ 6 year s old) , pregnan t wome n(a s exposur e surrogate s fo r th e fetus) , an d adul t me n(40-5 9 year s o f age ) ar e specifie di nth e CD a s particularl y sensitiv e t o lead . O f thes e groups , childre nbetwee n2 an d3 year s ol d exhibit , i

ngeneral , th e highes t bloo dleadlevel s (Mahaffe y e t al. , 1982 ; Billic k e t al. , 1979) , mos t likel y du e t o thei r greate r hand-to-mout h activit y a s wel l a s t o variou s metaboli c processe s (Harley an dKneip, . 1985) . T o predic t exposur e impact s o f alternativ e ai r lea dstandards , mode l balanc e scheme s hav e bee ndevise dfo r childre nage d0- 6 year s an d
ar e discusse dbelow .



### a a_P.4 8
IV- 2

A lac k o f adequat e biokineti c dat a fo r pregnan t female s prevent s suc h modelin g fo r th e fetus . I naddition , accurat e biokineti c modelin g o f th e sensitiv e populatio no f adul t male s woul drequir e a t leas t 4 0 year s o f cumulativ e exposur e inputs . Suc huptak e modelin g woul db e difficul t give n th e grea t variabilit y inexposur e historie s amon g U.S . adult s an dth e paucit y
o f data . Exposur e modelin g fo r purpose s o f ris k estimatio nfo r adults , discusse dinSectio nV.A. , wil l rel y oncombinin g air : bloo dlea d"disaggregated " relationship s wit hestimate dbaselin e "non-air " bloo dlea dlevels . A discussio no f lead' s absorption , excretion , retention , an ddistributio n withi nth e body

unde r differen t exposur e an dphysiologica l condition s i s
necessar y

backgroun dt o the uptake/biokineti c model , an di s provide din Chapte r 1 0 o f th e CD . A s wil l b e furthe r discussed , applicatio no f thi s
o r an y lea dexposur e mode l mus t recogniz e th e limitation s o f th e availabl e dat a an dth e significan t variabilit y amon g population s i nthei r behavioral , exposure , an

dphysiologica l characteristics . Fo r presen t purposes , th e childre nt o b e considere di nth e mode l d o no t includ e th e whol e U.S . population ; they compris e group s wit hcontrastin g exposure s t o lead , som e o f them extreme , i norde r t o illustrat e th e variation s inlea dexposur e an dabsorptio n
aroun dlea dpoin t source s unde r differen t scenarios . Sectio nIV. A present s methodologie s t o estimat e averag e dail y lea duptake-fro m

al l exposur e
source s unde r alternativ e ai r lea dlevels . Sectio nIV. B present s methodologie s t o relat e thes e estimate s o f lea duptak e t o average , steady-stat e bloo d lea dlevels . Althoug hthi s approac hpredict s hypothetica l outcome s an d th e absolut e number s shoul dno t b e use duncritically , th e mode l doe s striv e t o us e th e availabl e data , wit hal l it s limitations , t o the'fulles t exten t possibl e t o provid e a usefu l too l i neventuall y distinguishin g th e healt h impact s o f alternativ e lea dNAAQS .

### IV- 3

A

. Estimate s o f Lea d Uptake Th e metho d employe d t o estimat e th e degre e t o whic h eac h environmenta l sourc e o f lea d contribute s t o a child' s tota l dail ylea d uptak e i s base d o n th e distributio n o f ambien t ai rlea d level s tha t woul d b e allowabl e o r expecte d unde reac h standar d considered

. Probable exposur e condition s wit h respec t t o othe rexposur e medi a suc h a s foo d and dust , an d averag e biologica l absorptio n rate s fo reac h exposur e rout e ar e als o specified

. Th e metho d consist s o f a four-ste p process : 1 ) definitio n o f ambien t concentration s o f lea d fo rmajo rexposur e source s (i.e. , air , food , water , soil , dust) ; 2 ) determinatio n o f dail ylea d intak e accordin g t o th e relationship : I , - C

i • [Pb] 1 where I- j i s th e dail ylea d intak e fro m source , i , C- j i s th e ingestio n o r inhalatio n (i.e. , consumption ) pe rda yo f eac h lea d sourc e i an d [Pb]- j i s th e concentratio n o f lea d i n eac h sourc e i ; 3 ) calculatio n o f th e amount o f lea d absorbe d fro m eac h exposur e sourc e i :
M . 3 T. < > a • u i x i M i - wher e U- j i s lea d uptake fo reac h exposur e sourc e i , I Ti s th e dail ylea d intak e fro m eac h sourc e i , an d A- j i s th e percen t absorptio n o f lead , vi a th e appropriat e exposur e rout e fo rth e particula rsource ; an d 4 ) calculatio n o f th e tota l lea d uptak e fro m al l sources , U u : % = ( ^

-AT ) Th e wa ydail ylea d uptake woul d be calculate d i s illustrate d i n Tabl e 4.- 1 fo r2-yea rol d childre n livin g nea r(withi n 2- 5 km ) a lea d poin t source . Detail s o f th e mode l parameter s and th e line-by-lin e estimates , alon g wit hTABL E 4-1 . ESTIMATE D 199 0 AVERAG E LEAD INTAK E AN D UPTAK E I N2-YEA R OL D CHILDRE N UNDE R AVERAG E AI R LEAD LEVELS 1 0.2 5 pg/m 3 0. 5 pg/m 3 0.7 5 pg/m 3 1. 0 pg/m 3 1.2 5 pg/m 3 l. S pg/m 3 1 . Outdoo r ai r lea d (pg/m 3 ) 2 . Indoo r ai r lea d (pg/m 3 ) 3 . Tim e spen t outdoor s (hours/day ) 4 . Tim e weighte d averag e (pg/m 3 ) 5 . Volum e o f ai r respire d (m 3 /day ) 6 . Lea d Intak e fro mai r (pg/day ) 7 . % deposition/absorptio n in lung s 8 . Tota l lead uptak e fro mlung s (pg/day ) 9 . Dietar yLea d Consumptio n (pg/day ) a ) fro msolde r o r othe r metal s b ) atmospheri c lea d c ) natura l lead , indirec t atmos
pheric , undetermine d source s 10 . % absorptio n i n gu t 11 . Dietar ylea d uptak e (pg/day ) 12 . Stree t dust/soi l lea d (pg/g ) 13 . Indoo r dus t lea d (pg/g ) 14 . Tim e weighte d averag e (pg/g ) 15 . Amoun t o f dir t ingeste d (g/day ) 16 . Lea d intak e fro mdir t (pg/day ) 17 . % dir t lea d absorptio n in gu t 18 . Lea d uptak e fro mdir t (pg/day ) 19 . Tota l lead uptak e fro mlun g an d gu t (pg/day ) 0.2 5 

### .0 8 2- 4 .09-.1 1 

### 4- 5 0.4-0. 6 

### 4 2 0.2-0. 3



### 5. 6 1. 2 3. 6 42-5 3 4.4-5. 5 

### 18 1 27 1 241-25 6 .08-.13 5 19.3-34. 6 

### 2 5 4.8-8. 6 9.4-14. 4 

### 0. 5

0.1 5 

### 2- 4 .18-.2 1 

### 4- 5 0.7-1. 1 

### 4 2 0.3-0. 5



### 5. 6 1. 2 3. 6 42-5 3 4.4-5. 5 

### 30 8 48 2 424-45 3 .08-.13 5 33.9-61. 2 

### 2 5 8.5-15. 3 13.2-21. 3 0.7 5

0.2 3 

### 2- 4 .27-.3 2 

### 4- 5 1.1-1. 6 

### 4 2 0.5-0. 7



### 5. 6 1. 2 3. 6 42-5 3 4.4-5. 5 

### 43 6 69 3 607-65 0 .08-.13 5 48.6-87. 8 2 5 . 12.1-21. 9 17.0-28. 1 

### 1. 0

0. 3 2- 4 .36-.4 2 

### 4- 5 1.4-2. 1 

### 4 2 0.6-0. 9



### 5. 6 1. 2 3. 6 42-5 3 4.4-5. 5 

### 56 3 90 4 790-84 7 .08-.13 5 63.2-114. 3 

### 2 5 15.8-28. 6 20.8-35. 0 1.2 5

0.3 8 

### 2- 4 .45-.5 4 

### 4- 5 1.8-2. 7 

### 4 2 0.8-1. 1



### 5. 6 1. 2 3. 6 42-5 3 4.4-5. 5 

### 69 1 111 5 974-104 4 .08-.13 5 77.9-140. 9 

### 2 5 19.5-35. 2 24.7-41. 8 

### 1. 5

0.4 5 

### 2- 4 .54-.6 3 

### 4- 5 2.2-3. 2 

### 4 2 0.9-1. 3



### 5. 6 1. 2 3. 6 42-5 3 4.4-5. 5 

### 81 8 132 6 1157-124 1 .08-.13 5 92.5-167. 6 

### 2 5 23.1-41. 9 28.4-48. 7
Assumption s an

d calculation s ar e describe d i n Appendi x Ab yro w number . Refer s t o childre n livin g nea r on e o r mor e lea d poin t source s an

d unaffecte d b

ylea d paint
. Childre n livin g i n typica l urba n o r rura l environment s remot e fro mlea d poin t source s ca n b e modele d usin g th e sam e uptak e calcu l at'ipn s an d substitutin g paramete r value s wher e difference s ar e note d i n Appendi x A .P.5 1
' IV- 5 limitation s o f th e availabl e dat a base , ar e discusse di nAppendi xA . Fo r comparativ e purposes , childre nlivin g i narea s generall y

unaffecte db

y stationar y

lea demission s ca nals o b e modele dusin g mos t o f th e sam e paramete r values ; exception s (indoor/outdoo r particle dpenetratio nrates , respirator y depositio nrates ) ar e note di nAppendi xA . Dus t an d soi l lea dlevel s associate dwit hgive nai r lea dconcentration s woul ddiffe r substantiall y betwee npoin t an

d non-poin t sourc e areas ; thi s to o i s briefl y discusse d i nAppendi xA . Th e followin g point s ar e importan t t o conside r wit hregar d t o th e uptak e calculation s i nth e table : 1 ) th e calculation s d o no t represen t population-wid e exposur e scenario s unde r alternativ e standards , onl y exposur e fo r th e specifie dai r lea dconcentrations . Ambien t lea dlevel s aroun da poin t
sourc e meetin g a give nlea dNAAQ S var y dependin g ondistance , topoyraphy , loca l meteorolog y

relate dt o pollutan t transpor t an d diffusion , plan t operatin g parameters , emission s controls , particl e size s an d depositio nrates , etc . Ai r qualit y

dispersio nmodelin g tha t account s fo r thes e factor s wil l b e use d inth e actua l cas e study analyse s t o assig nai r lea dconcentration s unde r o alternativ e standard s t o differen t "receptor " point s wher e peopl e liv e aroun d th e lea d poin t sources ; 2 ) th e estimate s i n th e tabl e appl yt o 2-yea rol d childre n t o illustrat e th e perio d o f maximu m exposure . Bloo d lea d level s estimate d b yth e biokineti cmode l (discusse d below ) accoun t fo raccumulatin g exposur e throughou t childhood , no t jus t a singl e year . I t i s necessary , therefore , t o mak

e age-specifi cexposur e estimate s tha t reflec t change s i n behavio ran d metabolis m a s a chil d ages . Age-specifi cexposur e estimate s ar e als o discusse d i n detai l i n Appendi xA ; an d 3 ) th e genera l type s o f exposur e environment s considere d her e d o no t includ e olde rhome s wit h lead-base d pain t hazards

. Suc h condition s ar e discusse d a t th e en d o f Appendi xAt o illustrat e th e severit yo f lead-pain t hazard s compare d t o othe rexposures .IV- 6

B . Uptak e an

dBloo dLea dConcentratio n T o estimat e bloo dlea d(PbB ) level s unde r differen t exposur e scenarios , severa l differen t kind s o f studie s ca nb e use dt o deriv e a relationshi p betwee nabsorbe dlead(or leaduptake ) an dbloo dlead . Availabl e studie s includ e populatio nsurvey s i nwhic hth e bloo dlea dconcentratio no f individual s o r group s i s correlate dwit hmeasure dlea dconcentration s i n air , food , water , soil , o r dust ; experiment s i nwhic hvolunteer s ar e expose d t o controlle dai r leadconcentration s an dthei r PbB level s measured , and ; lea dbalanc e studie s o f individual s wit hmeasure dlea dintakes . Th e mos t relevan t experimenta l studie s including , fo r comparativ e purposes , thos e o n adults , ar e discusse dher e alon g wit hdescription s o f th e analyse s use d t o deriv e uptake/Pb B relationships . Relationshi pbetwee nbloo dlea dan d environmenta l lea dconcentration s fro m populatio nsurvey s ar e discusse das par t o f th e aggregat e an ddisaggregat e model s i nSectionV . 1 . Dietar y

Lea dIngestio nStudie s in * Infant s Studie s tha t have measure ddietar y leadintak e concurrentl y wit h Pb B level s amon g infant s an dtoddler s ar e compare di nth e criteri a documen t (CD , Tabl e 11-49) . Althoug hprecis e estimate s o f dietar y lea dconsumptio n
canno t b e made , thes e studie s (U.K . Centra l Directorate , 1982 ; Lace y
e t al. , 1985 ; Sherloc k e t al. , 1982 ; Ry ue t al. , 1983 ) hav e severa l advantayes : 1 ) carefu l contro l an danalysi s o f dietar y intake ; 2 ) minima l leadexposur e t o source s othe r tha nth e die t a s th e stud y populatio n(infants ) i s relativel y immobile ; an

d3 ) intake/bloo dleadrelationship s canb e use dt o estimat e th e impac t o f tota l lea dexposur e (i.e. , from al l sources ) o

nbloo dlea d becaus e trace r studie s (Chamberlai ne t al. , 1978 ; Rabinowit z e t al. , 1976 ) show no difference s i

nth e distributio no f lea dt o tissue s whethe r take nup from lun g o r gut .P.5 3 

### IV- 7
Bot h th e U.K

. Centra l Directorat e an d th e Sherloc k e t al

. studie s involve d infant s wit h relativel yhig h PbB level s an d hig h intakes

. I t i s wel l documente d tha t th e relationshi p betwee n PbB an d lea d uptak e fro m an y sourc e i s approximatel ylinea ra t lo wintak e level s bu t "flatten s out " at , hig h intak e level s (CD , Section s 11. 2 an d 11.3)

. Becaus e th e PbB level s ( < 2 0 pg/dl ) an d lea d intake s o f th e Ry u infant s ar e more relevant , th e criteri a documen t conclude s tha t th e slop e fro m thi s stud y(0.1 6 pg/d l pe r pg/da ylea d intake ) i s th e bes t availabl e estimat e (CO , p . 11-129)

. Th e infant s i n th e Ry u e t al

. (1983 ) stud yabsorbe d substantia l quantitie s o f lea d fro m formul a o rwhol e mil k i n lead-solder d cans . Eve n lea d a t muc h lowe rlevel s fro m formul a i n glas s bottle s achieve d a n apparen t bloo d lea d equilibriu m postnatally

. Reanalyse s o f th e Ry u e t al

. dat a b yMarcu s (1989 ) suggeste d a large rslope , abou t 0.2 4 pg/d l pe rpg/da ylea d intak e i n formul a an d milk

. Usin g non-linea ran d piecewis e linea rmodel s t o examin e PbB-dietar y lea d slope s a t highe rintak e levels , Marcu s (1989 ) reanalyze d th e Ry u e t a l

. data , a

s wel l a

s dat a o n Scottis h infant s (Lace ye t al. , 1985 ) an d schoo l childre n (Laxe n e t al. , 1987 ) expose d acros s a wid e rang e o f wate r lea d levels

. Becaus e th e diet s amon g th e infant s i n th e Lace ye t al

. stud y wer e predominantl yliquid , th e derive d wate rlead/bloo d lea d relationshi p i s considere d a surrogat e t o predic t th e contributio n o f tota l die t t o bloo d lea d levels

. Apiecewis e linea rmode l fitte d th e dat a abou t a s wel l a s a cube-roo t o rsquare-roo t model , wit h a PbB/wate rPb slop e fro m th e Lace ye t al

. stud yo n infant s o f 0.25 4 pg/d l pe rpg/ L fo rwate rlea d level s belo w1 6 pg/L , an d a muc h lowe rslop e o f 0.042 6 abov e tha t inflectio n point ; afte rpartia l lin g ou t th e effect s o f hous e dus t lead , th e Laxe n e t al

. school-childre n ha d a PbB/wate rP b slop e o f 0.16 1 pg/d l pe rpg/ L fo rwate r

### IV- 8

lea d level s belo w1 5 pg/L , an d a 0.031 8 slop e abov e tha t leve l (Marcus , 1989)

. I f th e slope s fro m Lace ye t al

. an d Laxe n e t al

. ar e converte d t o uptak e slope s b yassumin g 1 L/ d wate rconsumption , the n th e thre e absorptio n coefficient s (0.2 4 fro m Ry u e t al. , 0.25 4 fro m Lace ye t al. , 0.16 1 fro m Laxe n e t al. ) ar e reasonabl yconsisten t fo rlo wlevel s o f dietar ylea d intake

. Furthermore , give n th e difference s amon g th e thre e stud ypopulation s an d thei rexposur e situations , th e abov e result s ar e strikingl yconsisten t i n term s o f th e shap e o f th e dose-respons e relationship , th e locatio n o f th e inflectio n point , an d th e magnitud e o f th e difference s abov e an d belo wtha t point

. Th e highe rslop e foun d fo rth e Lace ye t al

. infant s compare d t o th e Laxe n e t a l

. schoo l childre n i s expecte d give n th e reductio n i n lea d gu t absorptio n rate s wit h age . Th e uptak e o f lea d fro m die t depend s no t onl yo n th e ag e o f th e child , bu t als o possibl yo n th e chemica l an d physica l for m o f th e lead , an d o n othe rcomponent s o f die t tha t affec t lea d absorption

. Muc h lowe r coefficient s ma

yb e appropriat e fo radult s an d fo rolde rchildre n wh o onl y inges t lea d wit h meals ; eve n highe rcoefficient s ma yb e appropriat e fo r lea d absorbe d b y\/ery youn g childre n who consum e lea d betwee n meal s an d wh o hav e nutritiona l deficiencie s tha t facilitat e lea d absorption

. Th e lowe rslop e a t hig h level s o f wate rlea d o rdietar ylea d uptak e probabl yrepresent s othe rfactor s tha t reduc e absorption , e.g. , much o f th e "excessive " dietar ylea d intak e ma yoccu rdurin g meal s an d i s thu s much les s bioavailable

. Ther e i s reasonabl e consistenc yamon g thes e high-uptak e slopes : 0.042 6 fro m Lace ye t al

. infants ; 0.031 8 fro m Laxe n e t al

. schoo l children ; an d 0.03 2 fro m th e Sherloc k an d Cool s studie s fo radult s (se e below)

. Uncertaint yabou t th e change-ove rbetwee n high-absorptio n an d low
absorptio n case s probabl yreflect s incomplt e informatio n abou t th e foo d an d wate rconsumptio n pattern s an d othe rdietar yfactors

. Fo rpresent-da yP.5 5 •~*$.-?4A.~"~'• ' ' IV- 9
U.S

. dietar ylea d exposure , th e steepe rslope s ar e likel yt o b e more accurate
. Th e result s fro m th e Ry u e t al

. an d Lace ye t al

. studie s wil l b e use d t o represen t th e infan t dose-respons e relationship : th e midpoin t o f th e slope s (0.1 6 an d 0.254 , i.e. , 0.207 ) estimate d fo rlo wexposur e level s (i.e. , < 1 6 pg/L) , an d th e Lace ye t al

. slop e o f 0,02 6 fo rhighe rexposur e levels

. Assumin g th e sam e lea d concentratio n i n tota l die t wher e th e slop e flatten s out , th e wate rlea d "threshold " leve l fro m th e Scottis h studie s o f approximatel y1 6 pg/ L (o r1 6 pg/Kg ) ca n b e converte d t o a correspondin g dietar yintak e leve l b y multiplyin g b yth e averag e dietar yintak e fo ra n infant

. Th e C O cite s a dietar y intak e rat e o f 1.50 2 Kg/da yfo ra 2-yea rol d chil d (Tabl e 7-15 ) an d a rat e o f 1. 0 Kg/da ywil l b e assune d fo rth e infant

. Th e resultin g leve l o f 1 6 pg/da y wil l b e use d a s th e inflectio n poin t i n applyin g th e slope s fro m Ry u e t al

. an d Lace ye t al

. (0.20 7 an d 0.026)

. Becaus e lea d ^£t.a;ke/Pb B relationship s ar e o f interest , thes e slope s wil l b e combine d wit h th e midpoin t o f gastrointestina l absorptio n rate s (42-53% ) cite d fo rinfant s i n th e CD , t o illustrat e th e relationshi p betwee n bloo d lea d and*dail ylea d uptak e fo rinfant s a t th e en d o f thi s section

. Abaselin e (i.e. , non-air ) PbB o f 4 pg/d l wil l b e assumed , base d o n recen t studie s o f PbB level s an d lea d intak e i n Bosto n an d Cincinnat i infant s (Rabinowit z e t al. , 1986 ; Succo p e t al. , 1987)

.

2 ° littlerJJl*£k&-JStUdlfes:-JtHL^lliiLt i Th e relationshi p betwee n bloo d lea d an d foo d and/o rwate rlea d level s ha s bee n examine d fo radult s i n bot h experimenta l studie s i n Wiic h controlle d dietar ysupplement s were administere d t o volunteers , an d duplicat e die t studies

. Again , severa l studie s indicat e non-linea rbloo d lea d response s a t hig h exposure s bu t a linea rrelationshi p a t relativel ylo wintak e level s ( < 10 0 pg/day , o r< 3 0 pg/d l PbB)

.IV-1 0

Tw o studie s identifie d i n Tabl e 11-4 9 an d 11-5 0 o f th e C D appea rmost usefu l i n estimatin g a dietar ylead/bloo d lea d relationshi p chiefl ybecaus e o f thei rrelativel ylarg e sampl e size s an d contro l ove rconfoundin g factors : Sherloc k e t al

. (1982) , a duplicat e die t stud yo f 3 1 mother s (an d thei rchildren ) fro m Ayr , Scotland ; an d Cool s e t al

. (1976 ) i n whic h 1 1 subject s an d 1 0 control s were studie d fo rbloo d lea d respons e t o ora l dosage s o f lea d acetate
. Th e latte rstud ywa

s a n extensio n o f th e Stui k (1974 ) experiment , result s of.whic h wil l no t b e use d her e becaus e response s were no t followe d lon g enoug h fo rbloo d lea d t o equilibrate

. Th e weighte d mea n o f th e slope s reporte d i n th e C D fo rth e Sherloc k

an d Cool s studie s i s 0.03 2 pg/d l increas e i n bloo d lea d pe r pg/da yintake , whic h i s a facto ro f 5- 6 time s lowe rtha n th e comparabl e slop e estimate d fo rinfant s a t lo wexposur e levels

. Agastrointestina l absorptio n facto ro f 0.15 , cite d i n th e C D fo radults , wil l b e applie d t o thi s intak e slop e t o deriv e a bloo d lead/uptak e relationship

. Abaselin e Pb B leve l o f 4 pg/d l wil l b e assume d fo radult s base d on . projection s describe d i n Appendi xC

. Th e sam e patter n o f non-linea rabsorptio n see n i n childre n wil l b e assume d fo r adult s an d a slop e o f .00 9 pg/d l pe rpg/da ywil l b e use d fo rlevel s abov e approximatel y4

0 pg/day , whic h correspond s t o a n inflectio n poin t o f 1 5 pg/k g lea d i n diet , multiplie d b ya n approximat e dietar yintak e o f 2.8 9 kg/da yfo r middle-age d me

n (CD , Tabl e 7-15)

. 3

. Applicatio n o f Chamberlai n an d Heard Analysi s o f Adul t Exposur e Dat a A n attemp t t o relat e bloo d lea d an d absorbe d lea d wa s mad e b yChamberlai n an d Heard (1981 ) usin g epidemiologica l an d clinica l dat a o n adul t me n (William s e t al. , 1969 ; Kehoe , 1961 ; Nordman , 19.75 ; Zurl o an d Grif f ini , 1973 ; Fuga

s an d Saric , 1979)

. Tota l dietar yan d airborn e lea d uptake wa s estimate d usin g calculation s simila rt o thos e presente d i n th e integrate d lea d uptak e mode l i n Sectio n IV.A

. Th e followin g assumption s give n i n Chamberlai n e t al. , (1978 ) were used : a ) a fraction , 0.55 , o f th e uptak eP.5 7
IV-1 1 become s attache d t o re d bloo d eelIs i b ) th e biologica l half-lif e o f lea d i n bloo d i s 1 8 days ; c ) a factor , 1.3 , i s t o b e allowe d fo rlong-ter m resorptio n an d re-entr yint o bloo d o f som e o f th e lea d whic h i s store d i n bone ; an d d ) th e mass o f bloo d i s 540 0 grams . Wit h thes e assumptions , Chamberlai n an d Hear d calculate d th e followin g relationship :
APbB = 0.5 5 x1 8 x1. 3 = 0.3 4 pg/d l pe rpg/da y AUptak e 54 " x0.69 3 Thi s relationshi p i s comparabl e t o tha t derive d fro m th e Cool s an d Sherloc k

studie s afte rgastrointestina l absorptio n i s accounte d for

. Give n uncertaintie s abou t som e o f th e studie s analyze d b yChamberlai n an d Hear d regardin g exposur e level s an d qualit ycontrol , an d becaus e o f th e hig h exposur e levels , thi s slop e i s presente d her e onl yfo rcomparative , purpose s an d wil l no t b e use d further

. 4

. Lea d Balanc e Studies : Compartmenta l Model s T o demonstrat e a causa l relationshi p betwee n lea d i n th e bod yan d a biologica l change , i t woul d b e idea l t o kno wth e amoun t o f lea d presen t a t th e sit e an d tim e o f th e effect

. Fo rinstance , i f lea d i s suspecte d t o induc e neuropsychologica l changes , a measur e o f th e lea d leve l presen t i n nerv e cell s whe n th e chang e occurre d woul d b e desirable

. Livin g tissue s ca n rarel yb e sampled , an d dat a obtaine d a t necrops ycanno t revea l th e variation s i n exposur e throughou t th e individual' s life

. Fo ranalytica l simplicity , tissue s ca n b e groupe d togethe ro n th e basi s o f lea d distributio n characteristic s an d bod yburden s o f lea d represente d a s a limite d numbe ro f distinct , homogenous , an d well-mixe d pool s o rphysiologica l compartment s wit h simila rkineti cproperties

. Mathematica l biokineti cmodel s hav e bee n fitte d to , dat a obtaine d i n long-ter m balanc e studie s an d t o lea d isotop e trace rexperiment s tha t estimat e th e rate s o f inpu t to , transfe rbetween ,P.5 8

IV-1 2

an dexcretio nfro

m th e differen t compartment s (Rabinowit z e t al. , 1976 , 1977 ; Batschele t e t al. , 1979 ; Bernard , 1977 ; Mallo n1983 ; Harle y an d Kneip , 1985 ; Marcus , 1985a,b,c) . Difference s inth e predictiv e lea dmodel s hav e bee ndiscusse db y Bernar d(1977) , Batschele t e t al . (1979 ) an dHammon d
e t al . (1981) . Model s ar e show nschematicall y

inthe C D (Figure s 10- 3 an d 10-4) . Th e choic e o f pool s o r leve l o f aggregatio nina mode l depend s o nth e availabl e experimenta l data , th e appropriat e tim e scale , an

dth e pre dictiv e use s o f th e analysis , an di s a compromis e betwee naccurac y an d simplicity . Fo r example , bloo dcanb e broke ndow nint o plasm a an

derythrocyte s
an dthe nfurthe r int o plasm a protein-boun dlead , diffusibl e lead , extracellula r flui dlead , an

derythrocyt e proteins . Sof t tissue s can.b e broke ndow nint o brai n(hippocampus , medulla , etc.) , kidneys , liver , hair , an ds o on . Th e hardtissu e pool s canb e separate dint o compac t (cortical. ) an dcancellou s (trabecular ) bones , an dteeth ; withi neac ho f these , separat e component s
may b e neede dt o mode l distinc t diffusio ntim e scale s (Marcus , 1985a,c) . Becaus e the skeleta l syste m i nyoun g childre ni s rapidl y developin g an

di s bot hlarg e an

dkineticall y

active , i t i s especiall y importan t t o mode l bon e lea dinchildren . Unti l suc hrefinement s ar e furthe r tested , a relativel y simpl e 3- 5 poo l mode l provide s a nadequat e framewor k fo r predictin g lea d distribution s i

nchildren . Thes e model s ar e helpfu l inpredictin g tota l bod y burde no r equilibrium level s o f lea dove r time inan y o f th e presume dkineti c compartment s unde r differen t exposur e conditions . Th e basi c assumptio no f th e model s i s tha t th e mas s o f lea dineac ho f th e compartment s change s accordin g t o a syste m
o f couple dfirst-orde r linea r differentia l equation s wit hconstan t fractiona l transfe r rates . Suc hmodel s predic t tha t whe nth e lea dintak e change s fromP.5 9
IV-1 3

on e constan t leve l t o another , ther e is"a I directl y

proportiona l chang e i n th e mas s o f lea di

neac hcompartmen t an dth e attainmen t o f a new equilibrium . Th e rate s an

dmagnitude s o f thes e change s ar e dependen t upo nth e rate s o f leadfluxinth e tissue s an dca ntheoreticall y

b e calculate dfrom

a compartmenta l mode l o f th e appropriat e parameters . Suppor t fo r a first , orde r kineti c mode l fo r lea dmetabolis m

i s demonstrate db

y calculations , usin g firs t orde r model s
o f sof t tissu e an

dbon e concentration s o f lead , an dothe r element s (calciu m strontium , radium) , tha t fi t huma nmeasurement s as wel l a s b y usin g mor e comple xmodel s (Johnso nan dMyers , 1981 ; Mallon , 1983) . A four-compartmen t biokineti c mode l o f lea dmetabolis m ha s bee ndevelope d fro m dat a obtaine di

ncontrolle dsingl e dos e an dchroni c lea dexposure s o f infan t ( 9 months ) an

djuvenil e (2 2 months ) baboon s (Mallon , 1983 ; Knei pe t al. , 1983) . Dynami c bloo dmeasurement s an dsteady stat e bloo dan

dorga n lea dmeasurement s wer e closel y fitte dt o predic t concentration s o f lea d i nblood , liver , an

dkidney , an

dbon e (th e fou r compartment s i nwhic h95 %
o f tota l bod

y leadi s contained ) (Hear dan dChamberlain , 1984) . Huma n metabolis m

an dgrowt hpattern s wer e applie di na compute r simulatio no f th e mode l tha t wa s the nsuccessfull y validate dusin g huma nautops y data . Th e mode l parameter s wer e revise dusin g measure dmetaboli c dat a fo r eac horga n(e.g. , bon e turnove r rates ) fo r childre nan dwer e use dt o simulat e orga nlea dburden s an dconcentration s inchildre nwit hconstan t leadexposure s from

birt h(Harley

an dKneip , 1985) . Althoug hcomplet e mode l validatio ni s no t possible , th e revise dmode l i s consisten t wit hexperi menta l dat a onbloo dleadaccumulatio nfollowin g dietar y lea duptak e amon g infant s (Ziegle r e t al. , 1978) , an dskeleta l lea daccumulatio nfollowin g controlle dexposure s i nadult s (Hear dan

dChamberlain , 1984) . Give nE£Q
_
IV-1 4 th e availabl e data , th e mode l appear s t o provid e th e bes t estimate s o f Pb B level s i

nchildre nwit hcontinuou s lea duptak e ove r time . Tabl e 4- 2 present s PbB level s predicte db y th e mode l fo r mal e childre n unde r differen t exposures , o r leaduptak e levels . Th e value s inTabl e 4- 2 includ e a

nadjustmen t fo r th e propagatio no f materna l leaddurin g pregnanc y tha t persist s throughou t childhood . Thi s adjustmen t wa s don e usin g anothe r kineti c mode l fi t t o bloo dlea ddat a collecte dlongtudinall y i nyoun g children , from birt ht o 2 7 month s (Succo pe t al. , 1987 ) an d assumin g a baselin e materna l PbB leve l o f 4 pg/d l (se e SectionC.6) . Th e followin g equatio nadapte dfro m Succu pe t al . wa s used : dPbB t = PbB 0 (e " a * ) where : dPbB t = adde dbloo dlea dincremen t propagate dfrom materna l PbB a t • time t ; PbB 0 = baselin e materna l Pb B ( 4 pg/dl) ; an dth e rat e constan t a = 0.072 . Th e rat e constan t a = 0.07 2 mo - 1 correspond s t o a mea nresidenc e time
o f 1 / a =1 4 months , o r a half-lif e o f ln(2) / a = 1 0 months . Thi s almos t certainl y

represent s resorptio no f tha t fractio no f prenata l leadburde n sequestere di

nth e neonata l skeleta l tissues . Th e apparen t mea nresidenc e time o f leadinbloo di ninfant s i s much.shorte r (se e Sectio nV.A.5) . o N o difference s were foun d b ytfi e biokineti cmode l betwee n th e sexe s excep t a t olde rages , an d predicte d Pb B level s were highes t amon g 2- 3 yea r olds , consisten t wit h result s o f NHANE S II , th e Ne

wYor k Cit yscreenin g progra m (Billic k

e t al. , 1979) , an d ongoin g longitudina l stud y(McMichae l e t al. , 1986)

. Thes e result s wil l b e applie d t o estimate s o f th e integrate d lea d uptak e mode l t o estimat e children' s Pb B level s unde ralternativ e ai rlea d levels

. I t i s importan t t o not e tha t thi s equilibriu m bloo d lea d mode l i s linea ri n tota l lea d uptak e a t eac h age . Thi s i s a necessar yconsequenc e o fP.6 1
_i-»mIV-1 5

TABL E 4-2 . PREDICTE D EQUILIBRATE D BLOO D LEA D LEVEL S (pg/dl ) OVERTIM E AMON GCHILDRE N WIT H CONSTAN T LEA

D UPTAKES 3 Lea dUptak e (pg/day ) Ag e 1 2 3 4 5 6 7 8 9 1 0 1 0

3. 0 4. 9 4. 6 4. 5 4. 4 4. 4 4. 2 3. 4 2. 3 2. 6 2 0

'57 9 9. 0 8. 2 8. 2 7. 9 7. 8 7. 4 5. 9 4. 6 5. 2 3 0

8. 9 13. 0 11. 9 11. 8 U. 4 U. 3 10. 7 8. 3 6. 9 7. 8 4 0

11. 9 17. 1 15. 5 15. 4 14. 9 14. 7 13. 9 10. 8 9. 3 10. 4 5 0 

### TT. 8 21. 1 19. 2 19. 0 18. 4 18. 2 17. 2 13. 3 U. 6 13. 0 6 0 

### TT. 8 24. 2 22. 0 21. 8 21. 0 20. 7 19. 5 14. 9 13. 9 15. 6 7 0

20. 8 28. 3 25. 6 25. 4 24. 5 24. 2 22. 8 17. 4 16. 2 18. 2 8 0

23. 8 32. 3 29. 3 29. 0 28. 0 27. 6 26. 0 19. 9 18. 5 20. 8

a Fro m Harle yan d Knei p (1985 ) afte raccountin g fo rpropagatio n o f materna l bloo d lea d durin g pregnanc y(se e text)

.IV-1 6

th e linea rpharmacokineti cmode l assume d b yHarle yan d Knei p (CD , Appendi x 11-A)

. Th e uptake/biokineti cmode l i s thu s logicall yconsisten t wit h aggregat e an d disaggregat e linea rtotal-uptak e model s discusse d i n th e 

### followin y

sections . Figur e 4- 1 compare s th e relationship s betwee n lea d uptak e an d bloo d lea d derive d fro m th e variou s studie s o n infant s an d adults

. Despit e th e divers e natur e o f th e populations , stud ydesigns , an d methodologies , ther e i s a fai r degre e o f consistenc yi n th e relationships

. Eac h stud yfoun d tha t a linea r functio n provide d a s goo d a fit , i f no t better , tha n othe rnon-linea rform s a t th e relativel ylo wexposur e level s investigated

. Som e experimenta l an d epi
demiologica l evidenc e suggest s however , tha t th e relationshi p betwee n lea d concentration s i n tissue s an d cumulativ e lea d intak e i s onl yapproximatel y linea ra t lo wlevel s o f intake , an d tha t successiv e increment s i n intak e o r exposur e resul t i n progressivel ysmalle rcontribution s t o bloo d lea d concen tration s (Aza re t al. , 1975 ; Moore , 1977 ; Gross , 1981 ; Sherloc k e t al. , 1982)

. Th e curve s draw n i n Figur e 4- 1 fo rinfant s an d adult s d o i n fac t includ e smalle r slope s fo rlea d uptak e value s abov e 20-4 0 pg/day

. Thi s curvilinea r relationshi p ma

yb e du e t o increase d rena l clearanc e wit h highe rbloo d lea d (Gross , 1981) , distributiona l non-linearitie s du e t o difference s i n lea d bindin g site s i n differen t tissue s (Hammon d e t al. , 1981 ; Marcus , 1985b ; Manton , 1985) , and/o rt o a sizeabl e poo l o f mobil e lea d i n bon e maintaine d
mor e o rles s independentl yo f uptak e (Rabinowit z e t al. , 1977 ; Chamberlain , 1983)

. I t appear s however , tha t non e o f th e mechanism s introduc e significan t non-linearitie s a t bloo d lea d level s belo w3 0 pg/d l (Marcus , 1984 , 1985a,c ; Chamberlain , 1983 ) an d tha t a linea rmathematica l mode l i s vali d fo rrelativel y lo wt o moderat e lea d exposure s (CD , p . 10-31 , Appdx

. UA-2)

. A s discusse d above , a t level s abov e 30-4 0 pg/dl , bloo d lea d ma yb e a n inadequat e inde x

## BLOO D LEA D (ug/dl ) 3 0

2 5 -
2 0 -

„.....••"•• • ,*••——•*•" 

### RYU/LACE Y SHERLOCK/COOL S HARLE Y Sc

KNEI P

4 0 6 0 

## LEA D UPTAK E (ug/day ) 8 0 

### 10 0

FIGUR E 4-1 , Sununar

yo f Relationship s Betwee n Dail yLead Uptak e an d Bloo d Lead fo r Differen t Ag e Groups , Derive d fro ma ) Ry

u e t al . (1983 ) an

d Laceye t al . (1985 ) Studie s o n Infants ; b ) Sherloc k e t al . (1982 ) an d Cool s e t al . (1976 ) Studie s o n Adults ; an d c ) Harle yan

d Knei p (1985 ) Biokineti c Mode l wit h Estimate s fo r 2- 3 yea r ol d childre n illustrated
. < .P.6 4
IV-1 8
fo rtissu e lea d burden s i n man ychildre n (Piomell i e t al. , 1984 ) an d linea r model s ar e likel yt o los e thei rpredictiv e power . Fo rthi s reason , tn e relationship s depicte d i n Figur e 4- 1 ar e truncate d a t 30 pg/dl

. T o estimat e Pb B level s abov

e 30 pg/dl , whic h i s no wabov e th e Pb

B leve l o f health-relate d concer n fo rchildren , us e o f non-linea rmodel s discusse d i n th e criteri a documen t woul d be require d (CD , Appendi x11.B)

. Th e compartmenta l biokineti cmode l o f lea d metabolis m develope d b yMallo n (1983 ) and Knei p e t al.

. (1983) , an d revise d fo rchildre n b yHarle yan d Knei p (1985) , relie d o n a broa d arra yo f experimenta l an d observationa l measurements o f mammalia n metabolis m an d growt h patterns , and ha s bee n successfull y validate d usin g availabl e huma n experimenta l an d autops ydata

. A s i s th e cas e fo ran

ymathematica l model , ther e ar e inheren t limitation s ari d associate d uncertainties

. Becaus e thi s mode l i s base d o n th e most comprehensiv e dat a availabl e an d ha

s bee n develope d specificall yt o predic t orga n lea d concen tration s ove rtim e i n youn g childre n wit h continuou s lea d uptake , i t appears tha t th e output s o f th e Harle yan d Knei p (1985 ) biokineti cmode l ar e th e most appropriat e t o predic t Pb B levels , i n childre n usin g th e integrate d lea d uptake estimate s presente d i n Sectio n IV. Aan d Appendi xA

. Pb B level s calculate d fro m th e conjunctio n o f th e integrate d lea d uptak e an d biokineti c model s wil l b e presente d i n th e staf f pape rdescribe d i n th e Introductio n (alon g wit h estimate s usin g othe rmodelin g approache s tha t ar e discusse d later ) i n orde rt o estimat e potentia l healt h impact s unde ralternativ e ai r lea d levels

. Methodologie s fo rcalculatin g children' s an d adul t bloo d lea d level s dat a unde ralternativ e standard s usin g othe rdat a an d othe rmodelin g approache s wil l b e discusse d i n Sectio n V

.P.6 5

V . STATISTICA L RELATIONSHIP S BETWEEN;BLOO D LEAD AND AIRBORN E LEAD : US E I N DISAGGREGAT E AND AGGREGAT E MODEL S Thi s sectio naddresse s tw o othe r method s o f determinin g th e contributio n
o f ai r lea dt o tota l exposur e an dth e potentia l healt himpact s associate d wit halternativ e ai r lea dlevels . Th e previou s sectio nexamine dth e re lationship s betwee nbloo dlea di nchildre nan

destimate dlevel s o f lea d uptak e from

th e air , housedust , outdoo r soi l an ddust , an

ddiet . Th e tw

o approache s presente dher e develo pa direc t relationshi pbetwee nai r lea d
an dbloo dlea dfrom

variou s experimenta l an dcommunit y

o r epidemiologica l studies : 1 ) a disaggregat e mode l i nwhic htota l exposur e t o ai r lea di s assesse db

y separatel y

analyzin g th e relationshi pbetwee nbloo dlea dan d inhale dai r lead , versu s th e associate dchange s i nbloo dlea da s a resul t
o f exposur e t o lea dtha t ha s deposite dont o soil , dust , food , an dwater ; an d2 ) a naggregat e mode l inwhic ha singl e variable , ai r lead , serve s
a s a ninde xfo r lea dexposur e throug hothe r medi a affecte db y integrate d atmospheri c lea ddeposition . o o Experimenta l studie s includ e thos e i nwhic hadul t volunteer s hav e bee nexpose dt o controlle dlevel s o f laborator y generate dlea daerosols . Becaus e intak e o f ai r lea dthroug hth e die t an ddus t wa s probabl y

minima l fo r th e adul t subject s i nthes e experiments , these - studie s underestimat e th e dose-respons e relationship s tha t woul db e see namon g childre nwit h change s i

nai r lea d(Angl e e t al. , 1985) . Epidemiologica l (i.e. , community ) studie s provid e correlation s betwee nai r lea dan dbloo dlea di

ndifferen t population s o f childre nan dadult s unde r varyin g condition s o f lead , from curren t o r previou s atmospheri c fallou t an dothe r sources , an

dyiel ddose respons e relationship s a t mor e relevan t exposur e levels .P.6 6
V- 2

Becaus e o f th e simultaneou s presenc e o f lea dinmultipl e medi a wit hdifferen t time profiles , th e assessmen t an dus e o f thes e studie s i s no t alway s direct . A s inan y attemp t t o mode l lea dexposure , possibl e confoundin g variable s tha t influenc e Pb B level s bu t whic har e no t relate d t o ai r lea dmeasurement s (e.g. , lea dinpaint , canne dfoo dan dplumbing , socioeconomi c status , parenta l care , housin g an dplay conditions , calciu

m intake ) canno t alway s be disentangled . Contro l fo r confounder s ca nbe achieve db

y comparin g population s tha t diffe r onl y inthei r exposur e t o airborne-derive dlead , althoug hidentifyin g suc hgroup s ha s bee ndifficult . Anothe r possibilit y

i s t o perfor m

a multivariat e statistica l analysi s in whic hadjustment s ar e mad e fo r som e o r al l o f th e confounder s befor e calculatin g th e bloo dlead/ai r lea drelationship . Thi s require s informatio nonth e valu e o f eac hconfounde r fo r eac hindividual , whic hi s als o difficul t t o estimate . Inth e cas e o f lead , severa l confounder s ten dt o wor k inth e
sam e directio na s ai r lead" , e.g. , elevate dexposur e an dunfavorabl e socia l condition s ofte nar e bot hconcentrate di ncentra l cities . Consequently , whe nstatistica l adjustmen t i s incomplete , th e relationshi pbetwee nai r lea dan dbloo dleadwil l likel y be inflated . Adjustmen t fo r a confoundin g variabl e ma y resul t inal l o. f th e share dvarianc e betwee n confounde r an

dexposur e variabl e bein g attribute dt o th e confounder ; thi s ca n inevitabl y

leadt o underestimatio no f th e "true " impac t o f th e exposur e variabl e (Rutter , 1983) . Incharacterizin g goo dstudie s o f ai r lead/bloo d lea drelationships , severa l reviewer s (e.g. , Hammon de t al. , 1981 ; Brunekreef , 1984) , a s wel l a s th e CD , discus s key factor s tha t shoul dbe considered . Thes e includ e a well-define dstudy population , a goo dmeasur e o f individua l exposure , measuremen t o f bloo dlea dwit hadequat e qualit y control , a statistica l analysi s mode l tha t i s biologicall y plausibl e an

dconsisten t wit hth e data ,: , a -V i •&}{}• -: -"•!•:'••*': ' V- 3 :

an dcontro l o r measuremen t o f importan t covariate s (CD , p . 11-63) . Th e studie s identifie dinth e CD , an d highlighte dhere , addres s thes e factor s sufficientl y

tp establis hmeaningfu l relationships . A . Disaggregat e Mode l 1 . Ai r Lead/Bloo dLea dRelationship s i nAdult s Becaus e th e relationshi pbetwee nbloo dlea dan d environmenta l exposur e i s nonlinea r acros s th e rang e o f potentia l exposure , bu t approximatel y linea r
a t lowe r level s (CD , p . 11-65) , th e focu s her e i s onstudie s o f adult s with ou t excessiv e occupationa l o r persona l exposure . Longitudina l studie s in whic hchange s i

nbloo dlea dwer e measure dinadul t volunteers - expose dt o controlle dlevel s o f laborator y generate daerosols , insom e case s wit h isotopi c lea dtracer , ar e summarize di nTabl e 11-4 0 o f th e CD . Dat a fro m th e mos t relevan t studie s hav e bee nreanalyze di nth e C D t o yiel dbloo d leadai r lea d"slopes " (S) , wher e 3 measure s th e chang e inbloo dlea d expecte dfo r a uni t chang e i nai r lead . A s note di

nth e CD , th e bloo dlea dinhalatio nslop e estimate s vary appreciabl y

fro m on e subjec t t o anothe r i nth e experimenta l studies , an d fro m on e stud

y t o another . Th e weighte dslop e an d standar derro r estimate s fro m th e Griffi nstud

y (1.7 5 +

_0.35 ) wer e combine dwit hthos e calculate d similarl y

fo r th e Rabinowit z study (2.1 4 +^0.47) , an

d th e Keho e study (1.2 5
_ + 0.35) , yieldin g a poole dweighte dslop e estimat e o f 1.6 4 +/0.2 2 (CD , pp . 11-9 9 t o 11-102) . Excludin g th e subject s i nth e Keho e study expose d t o ver y highai r lea dlevel s (u p t o 3 6 pg/m-^) , result s ina naverag e slop e o f approximatel y

1. 9 pg/d l pe r pg/m^ . Severa l deficiencie s i nth e individua l studie s ar e discusse dinth e C D suc ha s uncontrolle do r unmeasure dai r lea dexposure s outsid e th eV- 4

chamber s o rdifficultie s i n determinin g non-inhalatio n bloo d lea d baselin e level s (CD , p . 11-101)

. Furthermore , thes e experimenta l inhalatio n studie s ma yunderestimat e th e overal l impac t o f airborn e lea d (vi a depositio n an d incorporatio n ove rtim e int o soils , dusts , water , foo d chain)

. Thi s i s much les s o f a problem , however , i n predictin g change s i n adul t lea d exposur e i n th e future , compare d t o children

. Fo rexample , althoug h slightl y elevate d adul t bloo d lea d level s hav e bee n observe d i n area s o f hig h lea d contaminatio n (Barltro p e t al. , 1975 ; Gallache re t al. , 1984 ; Rabinowit z e t al. , 1985) , adult s d o no t inges t significan t amount s o f dir t an d (unles s unde rfastin g conditions) , normall yd o no t absor b ingeste d lea d a t th e sam e rat e a s children

. Th e cross-sectiona l relationshi p betwee n bloo d lea d an d ai rlea d i n adult s ha s bee n examine d i n severa l populatio n studies

. Aza re t al

. (1975 ) studie d fiv e group s o f men (ca b driver s an d offic e workers ) who carrie d persona l ai rlea d monitor s an d whos e non-ai rlea d exposure s (water , smoking )
wer e als o measure d ove ra 24-hou rperiod

. Severa l alternativ e geometri c mean regression s hav e bee n calculated , includin g linea ran d non-linea r model s assumin g differen t non-ai rcontribution s t o bloo d lead , an d estimation s o f th e effec t o f endogenou s lea d store d i n th e skeleto n usin g ag e a s a surrogat e measur e o f cumulativ e exposure . Non e o f th e fitte d model s ar e significantl ydifferen t statisticall y(CD , p . 11-81 ) wit h a poole d slop e estimat e o f 1.3 2 +0.3 8 pg/d l pe rpg/m 3 (CD , p . 11-105)

. Althoug h th e othe rpopulatio n studie s typicall yuse d les s accurat e measure s o f individua l exposure s (e.g. , Teppe ran d Levin , 1975 ; Nordman , 1975 ; Johnso n e t al. , 1975) , th e rang e o f slop e estimate s (1.0-2.0 ) i s comparabl e t o th e Aza re t a l

. an d experimenta l inhalatio n result s (Snee , 1981 ; se e CD , p . 11-98)

.P.6 9 V- 5 Althoug h th e studie s differe d i n co-variable s measured , populations , exposur e conditions , etc. , th e mos t reliabl e an d relevan t studie s consistentl y yiel d inhalatio n slop e value s typicall yi n th e rang e o f 1.3-2. 0 pg/d l pe rpg/m 3 , wit h a weighte d averag e slop e o f 1.4

. Th e abov e slop e estimate s ar e derive d fro m studie s i n whic h exposur e t o ai rlea d wa s assesse d ove rdays , weeks , o rmonth s an d ar e base d o n th e assumptio n tha t a n equilibriu m leve l o f bloo d lea d i s achieve d withi n a fewmonth s afte rexposur e begins

. Thi s i s onl yapproximatel ytrue , sinc e som e o f th e absorbe d lea d tha t accumulate s i n th e skeleto n deposit s i n th e spong ytrabecula rbone s (e.g. , rib , vertebrae ) wher e i t ma

yb e resorbe d int o th e bloo d stream
. A n additiona l facto r therefore , shoul d b e allowe d fo rpossibl e re-entr yo f lea d int o th e bloo d transferre d fro m bon e o rothe rlong-ter m storag e (Chamberlain , 1983)

. Base d o n isotopi crati o an d radiolabe l trace rstudie s O n adults , Chamberlai n e t al

. (1978 ) estimate d thi s factor , t o b e 1.3

. Simila rexperiment s late r indicate d tha t abou t 20 % (i.e. , a facto ro f 1.2 ) o f a n adul t male' s bloo d lea d i s fro m bon e lea d resorptio n (Chamberlain , 1985)

. Re-entr yint o bloo d
o f store d lea d i s likel yt o b e lowe ri n childre n becaus e o f th e rapi d growth , hig h rat e o f turnove ran d smalle rreservoi ro f lea d i n thei rskeleta l systems
. Whil e n o adjustmen t fo rbon e resorptio n wil l b e mad e fo rchildren' s slopes , i t appear s reasonabl e t o appl ya facto ro f 1. 3 t o th e bloo d lead/ai r lea d inhalatio n slop e o f 1. 4 derive d abov e fo radults , yieldin g a slop e estimat e o f abou t 1. 8 pg/d l pe rpg/m 3

. 2

. Estimatin g Futur e Adul t Bloo d Lea d Average s Tw o adul t population s ar e identifie d a s especiall ysensitiv e t o lead : middle-age d males , 40-5 9 year s o f age ; an d pregnan t women , a s exposure , surrogate s fo rfetuse s (se e CD , Section s 13.7. 2 an d 13.7.3)

. Olde rwomen ma yals o b e a t increase d ris k du e t o mobilizatio n o f bon e lea d afte rmenopaus e du e t o th e processe s o f osteoporosi s (Silbergel d an d Schwartz , 1987)

.

aBB IP.7 0 V- 6 Approximatel y95

% o f adul t bod ylea d burde n i s sequestere d i n bon e an d thi s accumulatio n ca n maintai n elevate d bloo d lea d level s year s afte rhig h exposure s hav e ende d (CD , p . 10-23)

. I n mos t cases , feta l exposur e t o lea d
ca n b e expecte d t o b e dominate d b ymaterna l bon e lea d store s fro m pas t exposure s which , i n th e U.S. , wer e muc h highe rtha n curren t levels

. Accuratel ypredictin g futur e change s i n feta l bloo d lea d level s woul d requir e estimate s o f materna l lea d burde n an d informatio n o n ho wbon e lea d store s woul d b e transferre d acros s th e placenta

. Althoug h i t i s likel y tha t ther e i s extensiv e mobilizatio n o f lead , lik e calcium , durin g period s o f physiologica l stres s suc h a s pregnancy , ther e ar e n o biokineti cdat a t o quantif ythi s dynami cprocess . I n th e absenc e o f suc h data , n o attemp t wil l b e mad e t o estimat e feta l lea d exposure s associate d wit h materna l PbB level s unde ralternativ e standards

. Give n th e sensitivit yo f th e fetus , however , potentia l risk s associate d wit h prenata l exposure s wil l b e o f majo remphasi s i n th e overal l lea d NAAQ S assessment
. Give n a backgroun d o r"baseline " bloo d lea d estimat e representin g non-ai r lea d adul t exposures , an d a n averag e disaggregate d bloo d lead : ai rlea d relationship , th e followin g simpl e equatio n ca n b e use d t o predic t bloo d lea d mean s fo radul t mal e population s i n ou rcas e studies : 7 = y 0 + 1.8 A wher e 7 = mean bloo d lea d (pg/dl ) y 0 = non-ai rbackgroun d bloo d lea d (pg/dl) , an d A= averag e ai rlea d (pg/m 3 ) Estimate s o f non-ai r"background " bloo d lea d leve l contribution s fo rdifferen t adul t population s tha t wil l b e use d i n th e 1990-9 6 cas e studie s ar e derive d i n Appendi xC

. Othe rissue s involve d i n estimatin g feta l PbB level s ar e als o discusse d there

.P.7 1 V- 7 •
3 . Ai r Lead/Bloo dLea dRelationship s i nChildre n Thre e populatio nstudie s o f childre nlivin g nea r leadpoin t source s i nwhic hcovariate s wer e controlle d(e.g. , age , sex , dus t exposure ) wer e extensivel y

analyze dinth e C D fo r th e mos t usefu l an drelevan t estimate s o f inhalatio nslopes : Angl e an dMclntire , 197 9 ( 3 • 1.9 2 £0.60) ; Roel s e t al. , 1980( 3 = 2.4 6 +_0.58) ; an dYanke l e t al. , 1977/Walte r e t al. , 198 0 ( 3 = 1.5 3 £0.064) . Th e media nslop e o f th e thre e studie s i s 1.9 7 (CD , p . U-189) ; it s applicatio nfo r us e i nth e disaggregat e mode l i s discusse dbelow . 4 . Estimatin g Children' s Bloo dLea dLevel s Usin g Disaggregat e Mode l Th e relationshi pbetwee nbloo dlea dan ddirec t inhalatio no f airborn e lea dprovide s informatio nusefu l fo r change s i nai r leado

na time scal e o f onl y severa l month s (CD , p . U-189) . Ove r time , suspende dlea di s deposite d
an dincorporate dint o soil , dust , an dwater , an

denter s th e foo dchain . - Sinc e prio r an

dcurren t atmospheri c fallou t directl y modif y th e dail y burde no f ingeste dlead , large r change s i nbloo dlea dwoul db e predicte di f th e associate dchange s i nth e surfac e depositio no f leadwer e accounte dfor , rathe r tha nsimpl y

inhale dai r lead(Angl e e t al. , 1984) . T o accoun t fo r th e simultaneou s presenc e o f leadi nmultipl e environmenta l media , th e C D ha s analyze dth e separat e mathematica l relationship s betwee nbloo dleadan d dietary , soil , an

ddus t lea d(describe di ndetai l i

nChapte r 11,4) . Usin g representativ e value s fo r lea dconcentration s i nthes e media , thes e relation ship s wer e applie di

na furthe r analysi s presente dinth e C D (CD , Tabl e 13-6 ) as awa y

t o estimat e proportiona l input s t o tota l bloo dlea dlevel s inU.S . children . A

simila r disaggregat e mode l wa s develope db y Angl e an

d Mclntir e (1979 ) an

dAngl e e t al . (1984 ) i nformin g a

nintegrate dlea dex posur e functio nfrom

measurement s o f lea dinair , soil , an dhous e dus t an

d relatin g tha t t o Pb B level s o f childre nlivin g i nvariou s area s o f Omaha .

S HV- 8

Th e disaggregat e mode l develope d inth e CD , intende d t o represen t th e the n"curren t (i.e. , 1983-84 ) exposur e picture, " i s adapte d her e in Tabl e 5- 1 fo r differen t ai r lea d level s an d backgroun d level s o f lea d in food , water , dust , an d soil , expecte d in1990 . Th e estimate s ar e mea n Pb B level s fo r 2-yea r ol d children ; comparabl e analyse s fo r othe r age s o f childre nca nb e don e usin g th e age-specifi c estimate s o f dietar y lea d intak e presente d inAppendi xA . Calculation s an d assumption s use d inderivin g th e estimate s ar e summarize d i nfootnote s t o th e tabl e an d ar e simila r t o thos e describe d inTabl e 13- 6 o f th e CD . Th e followin g change s wer e mad e fo r th e presen t analysis : 1 ) Estimate d level s o f dietar y lea d intak e fo r childre nin199 0 wer e substitute d fo r th e estimate s fo r 1983-8 4 use d i nth e CD . Th e 199 0 pro jections , describe d i nAppendi xA , ar e base d o nth e Multipl e Sourc e Foo d Mode l develope d i

nth e C D an

d use s mor e recen t dat a o nth e downwar d trend s infoo d an

d water ; 2 ) Soi l an

d housedus t lea d concentration s associate d wit hdifferen t ai r lea d level s ar e estimate d base d o nth e long-ter m

relationship s derive d from regressio nanalyse s o f dat a collecte d from concurren t measurement s o f air , soil , and/o r dus t lea d concentration s a t abou t 4 5 lea d poin t sourc e location s (se e Tabl e A-4) . Thes e sam e relationship s ar e bein g use d t o estimat e surfac e soi l an d indoo r dus t lea d level s inth e uptak e biokineti c model . I

ncontrast , soi l an d dus t lea d concentrations , unde r differen t ai r lea d level s wer e estimate d inTabl e 13- 6 o f th e C D b y interpolatio no f dat a from th e Angl e e t al . (1984 ) study . Thi s study i s bu t on e o f man y dat a set s include d inth e aforementione d regressio nanalysi s describe d i n Appendi xB .P.7 3


### V-9

TABL E 5-1 . DISAGGREGAT E MODE L O F CONTRIBUTION S FROM VARIOU S MEDI A T O 199 0 MEA

N BLOO D LEAD LEVEL S (pg/dl ) O F U.S . CHILDRE N ( 2 YEAR S O F AGE) : BACKGROUN D LEVEL S AND INCREMENTA L

CONTRIBUTION S FRO

M AIR 1

Sourc e Backgroun d - nonai r foo d an d water ^ Dust 3 Subtota l Background-Ai r Foo d an d Water * Ingeste d Dus t (wit h P b deposite d fro m air) ^ Inhale d air 6 Tota l 0.2 5
1. 5 0. 1 

### T T
0. 2 1. 0
0. 5 3. 3 0. 5

1. 5 0. 1 

## •r a 0. 2 1. 7
1. 0 4. 5 Ai rLea d

0.7 5
1. 5 0. 1 

# ra 0. 2 2. 5
1. 5 5. 8 (pg/m 3 )

1. 0
1. 5 0. 1 

## ra 0. 2 3. 2
2. 0 7. 2 1.2 5

1. 5 0. 1 

# ra 0. 2 4. 0
2. 5 8. 3 1. 5

1. 5 0. 1 

### U F
0. 2 4. 7
3. 0 9. 5
Adapte dfro

m Tabl e 13- 6 o f CD . ^Estimate ddietar y

intak e o f non-ai r P bi n199 0 (fro

m Cohen , 1988a,b ; Appendi xA ) 9. 2 pg/day

x0.1 6 pg/d l pe r pg/day (fro m Ry u e t al. , 198 3 an

d Laxe ne t al:. , 198 7 as re-analyze db y Marcus , 1989) . 3 Fro m CD , Chapte r 7 , 1/1 0 dus t no t atmospheric . Usin g Angl e e t al . (1984 ) "lo w area " fo r soi l an

d hous e dus t level s an d media nregressio ncoefficient s fro m Star k e t al . (1982) : (1/10 ) x(9 7 pg/ g x0.0022 ) + (32 4 pg/ g x0.0018) . *A s i n2 above , bu t usin g 1. 2 pg/day fo r dietar y

intak e o f atmospheri c lead . Derive dfo r componen t o f backgroun dPbi nfoo dfro

m pas t depositio nfrom ai r ont o soi l an

d int o othe r medi a leadin g int o humanfoo dchain . degressio nequation s o f Star k e t al . (1982 ) use dalong wit hlevel s o f soi l dus t an

d hous e dus t predicte db y regressio nanalyse s o f collecte dpoin t sourc e environmenta l data , describe di nAppendi xB . Fo r example , th e mea nsoi l an dhous e dus t lea dconcentration s associate dwit h1. 0 pg/m 3 i nai r ar e approximatel y

63 0 pp m an d 103 5 ppm , respectively . Th e effec t o

nbloo dlea dwoul dbe : (63 0 x0.0022 ) + (103 5 x0.0018 ) = 3. 2 pg/d l pe r pg/m 3 . 6 Usin g th e media ninhalatio nslop e o f 1.9 7 pg/d l pe r pg/m 3 fro m th e CD , p . U-189 .•V-1 0 3 ) Th e soi l an d dust/bloo d lea d regressio n coefficient s use d t o comput e soi l an d housedus t contribution s t o bloo d lea d ar e fro m th e C D analysi s o f th e Star k

e t al

. (1982 ) stud yan d ar e describe d i n th e C D a s th e mos t reasonabl e media n estimate s (pp

. 11-151 , U-191)

. Th e coefficient s use d i n Tabl e 13- 6 o f th e C D ar e fro m th e Angl e e t al

. (1984 ) stud yan d represen t uppe rboun d values

. I t mus t b e emphasize d tha t th e bloo d lea d estimate s presente d i n Tabl e 5- 1 represen t populatio n mea n Pb B level s an d ar e illustrativ e only

. T o asses s healt h risk s associate d wit h suc h ai rlea d exposures , i t woul d b e necessar yt o calculat e Pb B distribution s aroun d thes e mean levels , a s discusse d earlie ri n Sectio n III.B

. Th e uncertaint yi n predictin g mean bloo d lea d usin g th e disaggregat e mode l ca n b e estimate d i n principl e sinc e standar d error s associate d wit h th e ai rPb:Pb B slope s ar e availabl e (CD , p . U-105)

. Th e difference s amon g th e slop e estimate s fro m differen t studie s ca n b e ascribe d t o man yfactor s includin g difference s i n stud ypopulations , lea d bioavailabilty , an d t o statistica l artifacts , e.g. , th e attenuatio n o f slope s attributabl e t o environ
menta l measuremen t uncertaintie s (Fuller , 1987)

. Difference s i n estimate d standar d error s o f th e regressio n coefficient s reflec t sampl e size , rang e o f value s o f environmenta l variable s i n th e sample , an d contro l o f othe r source s o f variability

. Acomposit e slop e coul d b e estimate d a s a weighte d averag e wit h weight s inversel yproportiona l t o th e variance s fo reac h o f th e slopes

. Tota l varianc e woul d appropriatel yinclud e bot h within-stud y an d between-stud yvariatio n an d therefor e al l th e variance s an d covariance s o f th e paramete restimate s woul d hav e t o b e calculate d i n a serie s o f iterations

. Althoug h suc h analysi s coul d b e conducted , i t was decide d tha t th e informatio n abou t uncertaint yo f predicte d mean bloo d lea d adde d b y thi s complicate d procedur e woul d no t b e significant , especiall yi n vie wV - l 1 / • :
o f th e larg e uncertaintie s abou t the-for m o f th e dose-respons e model , th e judgmenta l selectio n o f ke ystudies , an d th e contribution s fro m non-ai r source s o f lead

. Sinc e completio n o f th e 198 6 CD , severa l finding s hav e becom e availabl e tha t supplemen t previou s conclusions

. Unpublishe d analysi s b yJohnso n an d Wijnber g (1988 ) o f th e 198 3 stud yo f youn g childre n livin g nea rth e Eas t Helen a smelte r(CDC , 1983 ) estimat e slope s fo rbot h bloo d lead-soi l lea d
an d bloo d lead-dus t lea d o f approximatel y1. 4 pg/d l pe r100 0 ppm . Thi s analysi s adopte d modelin g use d b yEP Ai n th e C

D t o fi t othe rsimila rstudie s an d adjuste d fo rnumerou s covariate s includin g children' s age , ai rlead , dus t and/o rsoi l lea d dependin g o n analysis , poo rqualit ylea d painte d housing , smoking , an d secondar yoccupationa l exposure . A s indicate d i n man

yo f th e studies , th e dus t lea d slop e i s simila rt o th e soi l lea d slope , suggestin g tha t soi l ma ycontribut e bot h directl yan d indirectl yt o blood

. Suc h hypothese s regardin g cause-effec t response s o f bloo d lea d t o earlie rexposure s hav e bee n explore d i n recen t longitudina l studie s o n bloo d lea d an d developmenta l indicator s i n Cincinnat i (Bornschei n e t al. , 1985 , 1986 ) an d Bosto n (Rabinowit z e t al. , 1985 ; Bellinge re t al. , 1987 ) children

. Th e Cincinnat i dat a se t wa s analyze d b ystructura l equatio n method s (Bentler , 1980 ) fo rrelationship s betwee n exterio rsurfac e scrapings , dus t lead , an d bloo d lead

. Unfortunately , th e result s ar e expresse d a s a . linea requatio n i n logarithm s o f th e environmenta l variables , an d th e standardize d regressio n coefficient s are no t directl yinterpretabl e a s overal l slope s fo rsoi l o rdus t lea d give n th e publishe d informatio n (Born
schei n e t al. , 1986)

. Th e analyse s o f th e Bosto n dat a use d a somewhat differen t technique — rando m effect s model s fo rlongitudina l dat a (Ware , 1985)

. Unfortunately ,V-1 2

soi l lea d dat a wer

e no t sample d longitudinally

. Ther e wer e repea t measurements fo rblood , dust , ai ran d wate rlead

. Th e 18-mont h bloo d lea d regressio n mode l reporte d b yRabinowit z e t al

. (1985 ) use d th e logarith m o f th e yar d soi l lea d measuremen t a s a predictor , s

o tha t th e reporte d slop e i s no t directl ycomparabl e t o thos e cite d i n th e CD

. However , th e slope s a t severa l concentration s ar e simila rt o thos e cite d i n th e CD : 8 pg/d l pe r 100 0 pp m soi l lea d whe

n soi l lea d = 10 0 ppm , 1. 6 pg/d l pe r1000 pp n soi l lea d whe n soi l lea d = 500 ppm , an d 0. 8 pg/d l pe r1000 pp m whe n soi l lea d = 100 0 ppm . Subsequen t analyse s o f thi s populatio n usin g composit e bloo d lea d average s betwee n 6 an d 24 month s (an d a mea n soi l lea d leve l o f 700 ppm ) yielde d a slop e o f 0. 9 pg/d l pe r1000 pp m soi l lead , varyin g fro m 0. 6 t o 1. 6 accordin g t o th e reporte d amount o f mouthin g b yth e childre n (Rabinowit z an d Bellinger , 1988)

. Becaus e th e Bosto n stud ygrou p di d no t generall yliv e i n crowde d conditions , i n home s wit h deterioratin g leade d paint , o rhave nutritiona l deficiencies , thei rresult s ma yno t be directl yapplicabl e t o childre n a t highe rrisk

.

^fokfnet.f cJ^ode f Th e disaggregate d air , soil , an d dus t lea d "slopes " use d her e ar e plausibl yconsisten t wit h th e uptake/biokineti cmode l parameters
. T o sho w this , w e us e th e well-know n relationshi p (e.g. , Rabinowit z e t al." , 1976 ) betwee n bloo d lea d increments , dPbB , an d lea d intak e increments , dPbl ; dPb B = dPb l * (mea

n residenc e tim e i n bloo d pool) / (volum e o f distributio n i n bloo d pool ) Fo ra two-yea rol d child , th e Harley-Knei p mode l predict s a mea n residenc e tim e i n th e bloo d poo l o f abou t 8 days , i.e. , a bloo d lea d hal f lif e o f 8

* 0.69 3 = 5.6 days , consisten t wit h Duggan' s (1983 ) estimat e o f 4- 6P.7 7

• • a •! ; • Aiyap jiff*--"' "' ' : ' ' > i V-1 3 days . Th e bloo dleadpoo l i s muc hJarge r tha nth e bloo dlea dvolume , includin g accessibl e part s o f th e sof t tissues , bon e an d bon e marrow , an

d extracellula r fluid . Rabinowit z e t al . (1976 ) estimate s tha t th e volum e
o f thi s poo l i

nadul t volunteer s wa s 7. 5 - 10. 8 K g (o r approximatel y 70-10 0 dl) , almos t twic e th e adul t bloo dvolume . Thus , a facto r o f 2 i s
use dt o calculat e th e tota l volum e o f availabl e bloo dlea ddistributio ni n th e equatio nbelow . Sinc e th e bloo dvolum e i ninfant s (abou t 12 % o f body weight ) i s proportionatel y greate r tha ni nadult s (abou t 8 % o f body weight) , w e wil l assume th e bloo dvolum e i n1- 5 yea r ol d childre ni s abou t 10 % o f body weight , adjuste dfo r whol e bloo ddensit y o f 1.0 6 kg/1 . Thus , th e volume o f distributio ni na 1 0 k

g chil d(abou t 2 year s old ) i s take na s about : 2 * 0.1 0 * 1 0 k.y/(1.0 6 kg/1 ) = 2 1 = 2 0 dl . Assumin g tha t th e tota l amoun t o f dir t consumed , C , i s abou t 0. 1 g/day , o f whic h a fractio n a = 0.25 , approximately , i s absorbe d (se e Appendi xA.17) , th e leade d dir t i s partitione d a s som e fractio n p o f soi l
an d 1 - p o f interio rhous e dust. * Thus : dPb l = c* a * ( p * Pb S + ( 1 - p ) * PbD ) Assumin g p = 0. 5 i.e

. equa l soi l an d dus t access , dPb B = (0. 1 g/d ) * (0.25 ) * (0. 5 Pb S + 0. 5 * PbD ) * 8d/2 0 d l

= 0.00 5 Pb

S + 0.00 5 Pb

D Thu s th e soi l lea d vs . bloo d lea d an d th e dus t lea d vs . bloo d lea d slope s ar e bot h predicte d t o b e abou t 0.00 5 pg/d l pe rppm . Avariet yo f factor s ma yb e responsibl e fo rth e somewhat smalle r empirica l slop e estimates , typicall yabou t 0.00 2 (se e above)

. Eve n thoug h th e individua l househol d Pb S an d PbD level s ar e availabl e i n som e studies , thes e ar e no t necessaril yth e exac t exposur e covariates , bu t onl ysurrogat e measure s o f dir t lea d exposure . I t i s wel l.RJ&-

V-1 4
know ntha t exposur e measuremen t "error " tend s t o flatte no r attenuat e regressio nslope s i

ndose-respons e studie s (e.g. , Pickles , 1982 ; Fuller , 1987 ; Brunekree f e t al. , 1987) . Further , specificatio no f th e constant s (e.g. , a < 0.2 5 o r C < 10 0 mg/d ) coul dals o reduc e th e predicte dslopes . Th e agreemen t i s nonetheles s impressive . Th e ai r lea dslop e i s similarl y calculated . Fro

m Tabl e 4.1 , th e poin t
sourc e uptak e at 1. 0 pg/m 3 i s 0. 6 - 0. 9 pg/d , thu s Pb B = (0. 6 - 0.9 ) * Pb A * 8d/2 0 dl

= (0.2 4 - 0.36 ) Pb

A Th e estimate ddirec t inhalatio nslop e o f 0.2 4 - 0.3 6 i s muc hsmalle r thanha s bee ncite dfo r empirica l disaggregat e studies . Thes e discrepancie s hav e bee npreviousl y

note di

nMarcu s (1988b ) ina nanalysi s o f Eas t Helen a data . Th e difference s betwee nth e uptake/biokineti c mode l apparen t PbD slop e an

dth e disaggregat e regressio nslop e (0.0034 1 vs . 0.00151) , apparen t Pb S slope s (0.0019 9 vs . 0.00102) , an dapparen t Pb

A slope s (0.6 3
vs . 1.08 ) wer e i

nth e sam e direction . I t i s possibl e tha t th e empirica l multipl e regressio nstudie s hav e misallocate dth e varianc e i nlog(PbB) , attributin g to o littl e effec t t o soi l an ddus t ingestion . W e canno t determin e whethe r thes e ar e artifact s o f th e multipl e regressio nmode l o r o f th e uptake/biokineti c simulatio nmodel . Nevertheless , th e slop e value s use di n the disaggregat e mode l ar e i ngenera l consisten t wit hth e uptake/biokineti c model . B . Aggregat e Mode l 1 . Ai r Lead/Bloo dLea dRelationshi p I nth e disaggregat e modelin g approach , "inhalation " slope s ar e derive d fro m epidemiologica l studie s b y makin g adjustment s fo r measure dindirec tP.7 9
V-1 5
ai r exposur e variable s (e.g. , hous e dlis' t lead) . Thes e inhalatio nslope s ar e the ncombine dwit hseparat e slope s fo r othe r exposur e medi a (e.g. , dust , food , water ) t o arriv e a t a nintegrate dlea dexposur e function . Wit hth e exceptio no f Angl e an dMclntir e (1979) , th e communit y studie s from

whic h inhalatio nslope s hav e bee nderive dhav e no t simultaneousl y measure dlea d inmor e tha ntw

o o r thre e media . Consequently , th e integrate dlea dexposur e functio ni s necessaril y base do

ndat a from

multipl e studie s involvin g differen t populations , exposur e conditions , measuremen t techniques , etc . A nalternativ e metho do f calculatin g th e effec t o f change s i nai r lea do

n children' s bloo dlea di s t o analyz e individua l communit y studie s inwhic h reliabl e "unadjusted " bloo dlead/ai r lea drelationship s canb e derive dsuc h tha t th e impac t o f bot hdirec t (inhaled ) an dindirec t (vi a dust , soil , etc. ) contribution s o f ai r leadar e combined , o r aggregated , inon e variabl e (i.e. , ai r lead) . Thi s approac hha s th e advantag e ove r disaggregat e modelin g (usin g th e adjuste d"inhalation " slope ) i ntha t th e tota l impac t o f atmospheri c lea do nchildren' s exposur e i s bette r capture dsinc e sinc e ai r lea dlevels , i ngeneral , ar e causall y relate dt o othe r importan t exposur e variable s suc h
a s han dan dhousehol ddus t lea d(Brunekreef , 1984) . Th e populatio nstudie s wit hidentifiabl e ai r monitorin g method s an d reliabl e bloo dlea ddat a are . summarize dinTabl e 11-3 6 o f th e CD . Non e o f th e studie s include dadul t populations . Sinc e adult s d o no t typicall y inges t muc hdeposite dlea danyway , th e aggregat e modelin g approac hwil l b e limite dt o youn g children . I nTabl e 5-2 , th e calculate d3 value s fo r eac h study ar e presente daccordin g t o th e bloo dlea dlevels , ages , an dtyp e o f locatio no f th e investigate dchildren . Differen t statistica l analyse s o f thes e studie s hav e resulte di na rang e o f possibl e value s fo r th e bloo d

aaTabl e 5-2 . BLOO D LEAD/AI RLEA D SLOPES 1 I

N CHILDRE N

FO RDIFFEREN T AGE S AN D EXPOSURE S Typ e o f Locatio n(Study ) Bloo d Lea d (yg/dl) / Ag e (years ) Urba nNea r Poin t Source(s ) <25/l- 7 8.5a» b(Brunekree f e t al. , 1983 ) 3.6-4.0 * (Zielhui s e t al. , 1979 ; Brunekree f e t al. , 1981 ) <25/l-1 8 0. 6 (Angl e an d 0.66 * (Brunekr 0 eef , 198 4

1.9 2 Mclntire ; 1979 ; 2.10 * fro m Angl e an d 4.4 0 CD) Mclntire , 1979 )
<25/10-1 5 - 2.4 6 (C D fro m Roel s e t al

. 1976 ) 5.3 a (Roel s e t al

. 1980 ) « 5.9-9.8 a » D (Brunekreef , 198 4 fro m Roel s

e t al. , 1976 , 1978 , 1980 )
>25/0- 9 2. 9 (Billic k e t al. , 1979 , 1980 ; 1.07-1.5 2 (Yanke l e t al. , 1977 ; Walte re t al. , , L Nathanso n an d Nudleman , 1980 ) 1980 ; Snee , 1982b ; CD ) °* 2.4-3.3 a (Brunekreef , 198 4 fro m Yanke l e t al. ,

1977 )
>25/l-1 8 - • 2.6-3.7 ^ (Landriga n e t al

. 1975 ; Mors e e t al. , 1977 ) 4.6 a (Brunekreef , 198 4 fro m Roel s e t al. , 1976 , 1978 , 1980 ) ^Slope s ar e i n unit s o f p g lead/d l bloo d pe rp g lead/m 3 air

. a "Aggregate " slope s derive d fro m grou p comparison s o rmultipl e regressio n analyse s tha t wer e unadjuste d fo rsoi l o r dus t lead , thereb yattemptin g t o accoun t fo rinfluenc e o f deposite d atmospheri clea d throug h thes e exposur e routes
. Remainin g slope s represen t relationship s betwee n bloo d lea d an d ai rlea d du e solel yt o direc t inhalatio n whic h hav e bee n calculate d b yadjustin g fo rth e influenc e o f soi l and/o rdus t lead

. ^Us e o f low-volum e particulat e sampler s likel yunderestimate d ai rlea d exposures , an d overestimate d th e 3 value , especiall ynea rpoin t sourc e wher e larg e particle s predominate

.P.8 1 V- l 7

lead/ai r lea drelationshi p(3) . Unadjuste d(i.e. , aggregate ) relationship s
ar e presente di

nadditio nt o adjuste d(i.e. , disaggregate ) relationship s derive dfrom

regressio nanalyses , th e latte r whic hrefe r t o th e bloo d lead/ai r lea drelationship s du e t o direc t inhalatio nexposure . Relativel y

wid e range s o f 3 value s ar e observe dfo r industria l an d urba narea s a t lo

w an dhighPb B level s an dfo r al l age s o f children . Th e apparen t trendtoward s smalle r slope s wit hincreasin g Pb B level s i s consisten t wit hfinding s withi nsom e studie s (Angl e an dMclntire , 1979 ; Roel s e t al. , 1980 ) an dothe r observation s o f curvilinea r bloo dlead/exposur e relationship s (Aza r e t al. , 1975 ; Moor e e t al. , 1977 ; Gross , 1981 ; Sherloc k e t al. , 1982 ; Hammon de t al. , 1981) . A s discussed , th e C D determine dtha t th e disaggregat e inhalatio n slope s derive dfrom

th e studie s b

y Angl e an

dMclntire , Roel s e t al. , an d Yanke l e t al . ar e th e mos t reliabl e give nthei r overal l quality . Aggregat e analyse s o f thes e data , eithe r b y Brunekee f (1984 ) o r th e origina l author s (Roel s e t al. , 1980 ) illustrat e th e significan t declin e i nair:bloo dlea d slop e whe nadjustment s ar e mad e fo r factor s tha t covar y wit hai r lea d(e.g. , soi l an dhous e dus t lead) , an dthe.dependenc e o f thes e slope s onexposur e levels . Fo r example , Brunekree f (1984 ) segregate dth e Roel s e t al . dat a
an dcompare dgroup s wit hlarg e difference s i nexposur e (i.e. , < 1 k m from smelte r vs . urban/rural ; 3 B 5.9 ) group s wit hsmal l difference s a t hig h exposur e level s (i.e. , < 1 k m vs . 2. 5 k

m from smelter ; 3 s 3 4.6 ) an dgroup s wit hsmal l difference s inexposure s a t lo w level s (i.e. , 2. 5 k m from smelter/urba nvs . urban/rural ; 3 a 9.8) . A s i nth e Brunekree f e t al . (1983 ) study , th e us e o f low-volum e sampler s ma y hav e underestimate dai r lea d exposures , an

doverestimate dth e 3 value , especiall y fo r thos e childre n
nea r th e smelte r wher e larg e particle s predominate . Th e slop e ma y b eP.8 2

V-1 8

underestimate dfo r youn g children , however , sinc e thi s study onl y sample d childre nolde r tha n1 0 year s o f age . I t i s importan t t o not e severa l additiona l studie s an danalyse s tha t
ma y provid e equall y

relevan t an

dusefu l informatio nfo r purpose s o f estimatin g
a naggregat e bloo dlead/ai r leadslope . Thes e studie s (Brunekree f e t al. , 1983 ; Zielhui s e t al . 1979 ; Brunekree f e t al. , 1981 ) use dwell-define d study population s (childre nyounge r tha n1 0 yrs . old ; PbB level s belo w 2 5 pg/dl) . employe davailabl e qualit y contro l procedure s fo r bloo dlea danalysis , an dmeasure do r controlle dfo r importan t covariate s (se e CD , Tabl e 11-36) . Severa l specifi c comment s shoul db e mad e regardin g thes e studies : 1 . Th e serie s o f studie s reporte db y Zielhui s e t al . (1979 ) an d Brunekree f e t al . (1981 ) include dmany environmenta l measurement s (lea di n ambien t an

dindoo r .air , lea dindustfal l indoor s an doutdoors , soil , streetdust , floordust , tapwater , an ddustines s o f homes ) an dregressio n analyse s t o determin e th e impac t o f differen t variable s onPbB level s (i.e. , th e abov e environmenta l indice s as wel l as distanc e from th e smelter , parenta l education , ag e o f th e child , mouthin g activity , an dcleanlines s o f th e child) . Venou s bloo dleadsample s wer e analyze db y standar dtechnique s an d althoug hinformatio noninterlaborator y comparison s i s no t give ninth e origina l study , qualit y contro l participatio ni s reporte db y on e o f th e investigator s i

na subsequen t revie w (Brunekreef , 1984) . Ai r leadwa s
measure da t tw

o site s 0. 2 an

d0. 4 k m from th e smelte r i

n197 6 an

din1977 . Th e level s inTabl e 5- 2 wer e take nfrom Brunekree f (1984 ) an drepresen t thos e measure da t 0. 4 k m fro m th e smelter . Ai r lea dwa s measure da t 6 site s continuousl y

fo r 2 month s in1978 . Brunekree f (1984 ) estimate s 3 = 4. 0 fo r 197 6 b

y assumin g a differenc e o f 2. 0 pg/m 3 inaverag e ai r leadexposur e level s betwee nth e 2- 3 yea r ol dchildre nwit hth e highes tP.8 3

V-1 9

an dlowes t Pb B levels . Afte r adjustmen t fo r parenta l education , th e bloo d lea ddifferenc e o f abou t 8 pg/d l decrease dt o 7. 2 ug/dl , resultin g i n
a slightl y

lowe r 3 estimat e (3.6) . Fo r 1977 , a differenc e o f 1. 0 yg/m 3
wa s assume dfo r ai r lea dexposur e level s betwee nsmelte r an dcontro l childre n age d2- 3 year s wh o ha dPb B level s o f 18. 2 an d14. 6 pg/dl , respectively , agai n resultin g ina 3 o f 3.6 . In1978 , onl y childre nlivin g betwee n0. 4 an d1. 0 k m o f th e smelte r wer e sample dan dai r level s di dno t correlat e wit hbloo d lea dwithi nthi s population . Thus , no direc t estimat e o f 3 ca nb e derived , althoug hsoil , lea dan dindoo r an

doutdoo r dus t lead , an dtherefore , accumulate d lea ddeposition , accounte dfo r a significan t fractio no f th e varianc e i n PbB level s (Brunekree f e t al. , 1981) . 2 . Th e mor e recen t study b y Brunekree f e t al . (1983 ) o nDutc hcit y

an d suburba nchildre nmeasure dvenou s bloo d(whic hwa s analyze da s p-ar t o f th e Europea nCommunit y laborator y

qualit y

contro l program ) an dmany environmenta l an

dsocia l variable s an dpotentia l confounder s (lea di n drinkin g water , soil , stree t an dplaygroun ddust , han ddust , indoo r dust , mouthin g behavior , dietar y intakes , parenta l educatio nan doccupation , ag e
o f home , etc) . The . very hig h3 valu e (8.5 ) derive db y Brunekree f (1984 )
eve nafte r adjustmen t ina multipl e regressio nanalysi s fo r si xo f th e confounders , ma y

b e relate dt o a

nunderestimatio no f ambien t ai r lea d level s du e t o th e fac t tha t lo w volum e Britis hSmok e ai r monitor s wer e employed , incontras t t o th e hi-vo l sampler s use di nmos t othe r studies . Th e exten t o f inflatio ni nth e estimate dslop e a s a resul t o f an y underestimate d ai r lea dleve l i s uncertain . Brunekree f (1984 ) note s howeve r tha t eve ni f thi s bia s i s accounte dfor , th e differenc e i nurba nan

dsuburba nai r lea d level s wa s probabl y

no t large r tha n0. 2 yg/m 3 . Th e contras t i nlea d depositio nbetwee nth e area s wa s significan t (i.e. , 64 3 vs . 22 0 mg/m2/day) ,V-2 0

indicatin g tha t ongoin g lea dpollutio naccounte dfo r a goo ddea l o f th e difference s inPb B levels , althoug hvariation s inhistorica l emission s can
no t b e entirel y

rule dout . Th e relativel y lo w PbB level s inthi s study ( a 8-1 3 ug/dl ) coul db e anothe r partia l explanatio no f th e hig h3 estimates , give ntha t othe r studie s use dt o deriv e 3 include dchildre nwit hPb B level s
onaverag e close r to , an dabove , 3 0 ug/dl . A t thi s point , th e bloo d lead/lea dintak e relationshi pi s estimate dt o leve l off ; belo w 3 0 ug/dl , • thi s relationshi pappear s t o b e approximatel y linea r (CD , p . 11-104) . Th e remainin g slope s liste dinTabl e 5- 2 ar e base dondat a from childre n whos e PbB levels , a s som e i nYanke l e t al . (1977) , exceede d2 5 pg/dl . A s discusse di

nth e CD , th e relationshi pbetwee nlea duptak e an dPbB level s abov e abou t 3 0 pg/d l appear s t o b e non-linea r (CD , p . 10-31) . Becaus e PbB level s abov e 25-3 0 pg/d l excee dthos e wher e health-relate dconcern s ar e triggere d(se e CD , Chapte r 13) , thes e slope s ar e les s relevan t t o th e presen t review . Insummary , th e analyse s usin g th e aggregat e approac hassume th e
same sourc e fo r mos t lea di nair , soil , an

dhousedust , an

dtha t adjustmen t o f PbB level s fo r soi l o r dus t lea dt o yiel da ninhalatio nslope , under estimate s th e "true " impac t o f atmospheri c lea donPbB levels . A rang e o f 3 value s canb e estimate dfrom a ) additional , an

dapparentl y

relevant , studie s
no t use dt o deriv e inhalatio nslope s inth e C D (i.e. , Zielhui s e t al. , 1979 ; Brunekree f e t al. , 1981 , 1983 ) an db ) aggregat e analyse s tha t includ e bot hdirec t (inhalation ) an dindirec t (vi a soil , dust , etc. ) ai r lea d contribution s i

nth e ke y

"inhalatio nslope " studie s cite dinth e criteri a document . Althoug hfa r fro m conclusive , thes e studie s an danalyse s sugges t
a rang e o f possibl e bloo dlead/ai r lea daggregat e slope s inth e rang e o f 2P.8 5 V-2 1
t o 1 0 fo ryoung , moderatel yexpose d childre n wit h th e mos t reliabl e slope s fallin g betwee n 3 an d 5 (CD , p . 11-104)

. 2

. Predictin g Children' s Bloo d Lea d Level s Usin g Aggregat e Mode l T o predic t PbB level s associate d wit h alternativ e ai rlea d level s usin g thes e aggregat e slopes , i t i s necessar yt o estimat e th e contributio n t o tota l lea d exposur e fro m source s no t affecte d b ya propose d ai rqualit y standard , fo rexample , lead-soldere d foo d cans , lea d i n plumbing , an d lead-base d paint

. I t shoul d b e note d tha t b yusin g measure d lea d concen tration s i n dus t fro m a wid e rang e o f location s an d conditions , th e integrate d uptak e mode l discusse d i n th e previou s sectio n implicitl yinclude s averay e contribution s t o tota l exposur e fro m lead-base d paint , bu t exclude s fro m th e analysi s hig h leve l exposure s associate d wit h deteriorate d lead-base d painte d housing

. Severa l difficultie s aris e i n attemptin g t o explicitl yestimat e exposure s fro m non-ai rsource s o f lead : 1 ) Wit h th e exceptio n o f non-ai rlea d i n diet , fe wstudie s provid e detaile d informatio n o n th e relativ e contributio n o f variou s source s t o children' s PbB level s i n th e U.S

. Estimate s mus t b e mad e b yinferenc e fro m earlie rsurve ydata ; an d 2 ) Becaus e non-ai rcontribution s t o PbB level s probabl yvar ywidel y i n spac e an d tim e among children , a singl e estimat e fo rth e average , cas e ma yresul t i n a lea d NAAQ S tha t i s no t protectiv e fo ral l children

. [Thi s ca n b e expected , fo rexample , fo rchildre n wh o regularl yinges t lead-base d paint. ] Conversely , complianc e wit h th e ai rstandar d wil l provid e extr a protectio n i n area s wher e lea d fro m non-ai rsource s i s belo wth e average .P.8 6

V-2 2 I n settin g th e 197 8 lea d NAAQS , th e Agencyestimate d tha t non-ai r source s o f lea d contribute d 1 2 pg/d l o n averag e t o children' s PbB levels

. Sinc e then , significan t reduction s i n PbB level s hav e occurred , attributabl e no t onl yt o decline s i n atmospheri clea d emission s bu t t o th e gradua l conversio n b ymanufacturer s t o non-lea d soldere d cans , i n som e case s reductio n i n th e numbe ro f old , lead-painte d homes , cleane rworkin g conditions , an d b yparent s an d publi chealt h agencie s t o minimiz e children' s lea d exposure . Furthe rdecline s i n lea d exposur e ca n b e expecte d a s thes e trend s continu e an d lea d exposur e fro m drinkin g wate rdrops , du e t o increase d awarenes s a s a resul t o f widespread , mandate d publi cnotifications , th e 198 6 Saf e Drinkin g Wate rAc t bannin g th e us e o f lea d solde ran d pipe s i n ne

wconstructio n an d plumbin g repairs , an d t o reduction s i n wate r corrosivit yb ypubli cwate rsupplier s a s complianc e wit h th e revise d nationa l wate rregulation s fo rlea d begins

. Th e mos t recent , an d well-conducted , nationwid e surve yo f children' s PbB level s wa s th e Secon d Nationa l Healt h an d Nutritio n Evaluatio n Surve y(NHANE S II ) o f 197 6 t o 1980

. Appendi xC describe s analyse s tha t a ) start s wit h th e averag e PbB leve l fo rchildre n fro m 1978 , th e midpoin t o f th e NHANE S I I survey , an d b ) estimate s a 199 0 Pb B averag e b y adjustin g th e 197 8 valu e t o accoun t fo rth e importan t changes , summarize d below , i n lea d exposur e tha t hav e recentl yoccurre d an d tha t "ca n b e expecte d t o continue : 1

. Us e o f lea d i n gasolin e ha s decline d b yabou t 9 0 percen t sinc e 1978 ; thi s tren d wil l continu e u p throug h 1990-9 2 a s complianc e wit h th e lea d i n gasolin e standar d i s complete d an d a s th e flee t o f lead-burnin g car s shrinks

. A

s observe d durin g th e NHANE S I I surve yperio d (se e CD , Sectio n 11.3.6) , th e continue d dramati cdeclin e i n gasolin e lea d emission s i s predicte d t o paralle l a majo rshif t i n Pb B levels

.P.8 7

•.<•V-2 3 2

. Asignifican t reductio n i n dietar ylea d intak e has occurre d sinc e th e lat e 1970's , an d thi s tren d wil l continu e a s atmospheri clea d emission s an d depositio n an d th e us e o f lead-soldere d cans , continu e t o decline

. Th e derive d rang e o f mean PbB level s fo rchildre n expecte d i n 199 0 (4. 2 - 5. 2 pg/dl ) reflect s change s tha t hav e occurre d sinc e 1978 , an d tha t ar e expecte d t o continue , i n gasolin e lea d emission s an d depositio n an d canne d foo d technology

. An yothe rchange s tha t ar e mor e difficul t t o quantif yar e als o probabl yo f lesse rimportanc e fo rth e bul k o f th e population

. Fo r example , change s fo rchildre n livin g i n lead-painte d housin g ha s no t bee n significan t o n a broa d scale

. Thi s rang e o f 199 0 "baseline " averag e estimate s represent s th e mean PbB level s tha t woul d b e expecte d i n 199 0 i n U.S

. childre n no t expose d t o atmospheri clea d fro m lea d poin t source s directl yo rindirectly , base d o n th e dat a an d assumption s presente d above

. Anothe rmetho d t o estimate.children' s mean "non-air " PbB i s t o us e availabl e dat a o n typica l backgroun d level s o f lea d i n food , water , dust , an d soi l ingeste d b yU.S , childre n an d the.relationshi p betwee n lea d take n u p throug h thes e medi a an d children' s PbB levels

. Tabl e 13- 6 o f th e criteri a documen t use s suc h dat a i n calculatin g a mean PbB o f 4.4 2 pg/d l t o b e expecte d a t an ai rlea d leve l o f zero . Althoug h thi s valu e wa s calculate d base d o n 1983-8 4 FD Adat a o n lea d i n food , i t i s interestin g tha t i t i s withi n th e rang e describe d above

. Thi s rang e ca n b e use d i n th e aggregat e mode l approac h t o estimat e range s o f mean bloo d lea d level s unde r alternativ e ai rlea d exposure s i n th e followin g equation : mean PbB = (4. 2 - 5. 2 pg/dl ) + ( 3 t o 5 pg/d l pe rpg/m 3 ) Ai rP b I t mus t b e emphasize d tha t thes e estimate s fo rnon-ai rcontribution s t o averag e PbB level s represen t averag e values

. Man ychildre n ma

yb e a t ris k fo rsignificantl yhighe rlea d exposure s tha t canno t b e prevente d b yatmospheri cP.8 8

V-2 4
emissio n controls

. I n particular , thes e includ e childre n wh o liv e i n deteriorate d o rrecentl yresurface d lead-painte d housin g wh o deliberatel yo r inadvertentl yinges t pain t dus t throug h norma l mouthin g activities , childre n expose d t o hig h drinkin g wate rlea d level s fro m erodin g lea d pipe s o r solder s i n distributio n systems , childre n o f parent s wh o wor k i n lead-relate d industrie s an d ar e expose d t o lea d dus t tha t i s subsequentl ycarrie d hom e o n clothing , o rchildre n livin g nea rlea d smelter s an d othe rpoin t source s where historica l accumulation s o f lea d ar e excessive

. I t i s importan t tha t othe rregulator yagencie s an d publi chealt h programs , includin g othe rEP A components , responsibl e fo rminimizin g children' s lea d exposure s fro m non ai rsources , o rfro m historica l accumulation s o f atmospheri clea d deposition , maintai n o rincrease , where necessary , thei refforts

.P.8 9

VI . VALIDATIO N

O F INTEGRATE D LEAD UPTAKE/BIOKINETI C EXPOSUR E MODE L
Whil e al l thre e modelin g approache s identifie di nSectio nII I ar e usefu l i nassessin g th e relativ e protectio nafforde dby differen t lea dNAAQS , th e aggregat e an ddisaggregat e bloo dlead-ai r leadmodel s ar e intende dt o b e "equilibrium " models . However , w e kno w tha t ther e i s a grea t dea l o f variatio ni npas t an dpresen t exposure s t o lea dfro m variou s
source s an

dpathways . O f th e three , th e uptake/biokineti c mode l ca nbes t estimat e th e change s over tim e o f bloo dleadt o change s i nenvironmenta l lea di nrapidl y

developin g youn g children . A genera l descriptio no f th e mode l i s provide di nSectio nI V and Appendi xA . Averag e dail y uptak e fo r youn g childre ni s calculate dunde r condition s specifie di nterm s o f ambien t ai r lea dlevels , soi l an ddus t lea dlevel s tha t correspon dt o bot hhistorica l an dcurren t atmospheri c lead emissions , an

ddietar y

leadlevel s fro

m bot hwate r an

dfood . Additiona l exposure s t o pain t leadca nbe adde dbu t ar e no t i nth e presen t exercis e give nth e hig hdegre e o f variability , an dth e inadequat e dat a bas e (se e sectio nII.F) . Bloo dlead(PbB ) level s i npopulation s o f youn g children , wh o
ar e th e mos t expose dan dhighl y

susceptibl e t o lead , ar e estimate dove r tim e base do ntota l dail y

leaduptak e usin g a biokineti c compartmenta l model . Parameter s suc ha s indoo r ai r leadexposure , tim e spen t indoor s
vs . outdoors , absorptio nrate s throug hth e lung o r gastrointestina l tract , an damoun t o f dir t tha t childre ntypicall y inges t throug hhand-to-mout h activity , ar e estimate dfro m availabl e dat a i nth e literature , a s summarize d i nAppendi xA . Inthi s chapter , result s o f severa l validatio nexercise s wher e predicte d
an dobserve dbloo dlead s wer e compare dar e presented . Th e mos t detaile d analysi s wa s performe dwit hdat a gathere daroun da smelte r i nEas t Helena ,VI- 2

Montana . Tw o type s o f validatio neffort s wer e undertake nwit hthi s dat a set : 1 ) i nth e firs t effort , th e bes t dat a regardin g suc hmode l parameter s
a s observe dair , soil , anddus t lea dexposur e estimate s wer e used ; 2 ) i nth e
secon dvalidatio neffort , predicte dlevel s o f air , soi l an ddus t level s wer e
use dt o estimat e Pb B levels . Th e latte r wor k wa s undertake nt o determin e ho w wel l th e mode l behave dwhe nactua l measurement s o f necessar y inpu t dat a
ar e no t available . Thi s wa s necessar y s o tha t th e reliabilit y o f th e mode l coul db e assesse dfo r polic y analysi s purpose s whe nles s tha nful l informatio n i s availabl e t o us e wit hth e model . Also , presente di nthi s sectio nare validatio nexercise s usin g observe dbloo dlea destimate s i nlocation s othe r tha nEas t Helena . Whil e les s effor t wa s undertake ni nthes e exercises , the y nonetheles s provid e additiona l informatio no nth e reliabilit y

o f th e mode l andprovid e insigh t regardin g th e sensitivit y o f th e mode l result s t o uncertaintie s inth e inpu t data . Give nth e man y uncertaintie s i nth e inpu t dat a and th e biologica l variabilit y tha t canno t b e incorporated , th e result s o f th e validatio nexercise s presente dbelo w revea l tha t th e lea d uptake/biokineti c mode l perform s quit e wel l i npredictin g mea nbloo dlead concentration s i nchildre nlivin g nea r poin t source s o f lead . A . Validatio nUsin g 198 3 Eas t Helen a Dat a Th e dat a se t considere dfirs t i s base do na 198 3 stud y i nwhic hth e Montan a Departmen t o f Healt han dEnvironmenta l Science s (MDHES ) an dth e Center s fo r Diseas e Contro l (CDC) , incooperatio nwit hEPA , measure d bloo dleadlevel s inapproximatel y 40 0 childre nage s 1- 5 livin g aroun d th e ASARC O lea dsmelte r i nEas t Helena . Th e lea dconten t o f soi l an d dust s aroun dan

di nindividua l home s wa s measured . Airborn e leadwa s
measure dbefor e anddurin g th e surve y a t 8 sites . Thre e stud y area s wer e designate daccordin g t o thei r distance s fro m th e smelter : Are a 1 , withi nP.9 1

VI- 3 1 mil e o f th e smelter ; Are a 2 , 1-2.2 5 mile s fro m th e smelter ; Are a 3 , mor e tha n 5 mile s fro m th e smelter

. Th e validatio n exercise s include d childre n fro m Area s 1 an d 2 only

. I n orde rt o estimat e 198 3 PbB level s i n th e Eas t Helen a childre n s o the y coul d b e matche d agains t th e measure d PbB levels , exposur e profile s wer e generate d extendin g a s fa rbac k a s 1978 , dependin g o n th e children' s ag e i n 198 3 an d thei rresidentia l location

. Afive-yea rdescriptio n o f monthl y ambien t ai rlea d concentration s throughou t th e stud yare a wa s generate d usin g th e Industria l Sourc e Complex-Long-Ter m (ISC-LT ) dispersio n mode l base d o n a i rlea d concentrations , sourc e samplin g dat a o f smelte remissions , an d loca l meteorologica l data , an d accountin g fo rdr yatmospheri cdeposition

. Are a an d year-specifi cestimate s o f backgroun d lea d contribution s (i.e. , mobil e sources , re-entraine d soil , loca l mino rpoin t sources ) were als o include d t o accoun t fo rtota l ambien t exposure . Onl yon e site , abou t 1/4 mil e fro m th e smelter , provide d sufficientl ycomplet e ai rqualit ydat a ove rth e perio d 1978-198 3 tha t coul d b e considere d representativ e o f populatio n exposur e i n th e vicinit y o f th e monito ralthoug h ai rlea d dat a were availabl e fro m monitor s i n te n othe rlocation s aroun d Eas t Helena

. Atota l o f 15 8 monthl yaverag e lea d reading s were availabl e fro m thes e monitor s betwee n 198 0 an d 1983

. Thes e average s wer e compare d wit h predicte d ai rlea d concentration s fro m th e ISC-L T dispersio n model

. A

s woul d b e expecte d wit h a dispersio n mode l usin g limite d meteorologica l data , th e mode l predicte d n o more tha n 37 % o f th e month-to-mont h variabilit y i n monito rreadings

. However , simpl e linea rregressio n predictin g monitore d reading s a s a functio n o f a constan t an d IS C predictions , indicate d tha t reasonabl yaccurat e estimate s o f ai rqualit ywer e made wit h th e IS C model : th e constan t wa

s withi n th e rang e o f th e estimate d backgroun d concentration s an d
wa s statisticall ysignificant , and ; th e coefficien t fo rth e IS C predictio n variabl e wa

s no t significantl ydifferen t fro m 1.0

.P.9 2

VI- 4
Estimate s o f soi l an d dus t lea d concentration s wer e als o obtaine d usin g tw o methodologies

. I n th e firs t case , home-specifi cobserve d value s fo r soi l an d dus t lea d wer e used

. I n th e secon d case , soi l an d dus t lea d estimate s wer e made usin g model s develope d b yMcLam b (1988 ) an d Marcu s (1988c ) tha t describ e soi l an d dus t lea d a s a functio n o f ambien t lead

. (Fo ra descriptio n o f thes e models , se e Appendi xB)

. Th e latte rapproac h wa s deeme d necessar yt o determin e ho wwel l th e mode l predict s whe n ful l informatio n o n mode l input s i s no t available

. (Thi s i s indee d th e usua l situatio n whe n th e mode l i s use d t o asses s th e impact s o f alternativ e regulator yprogram s o n mean bloo d lead s o f a populatio n o f children. ) Age-specifi cexposur e parameter s use d a s inpu t t o th e uptak e mode l
ar e describe d i n Appendi xA

. Estimate s o f dietar ylea d intak e fo rdifferen t ag e group s betwee n 197 8 an d 1983 , liste d i n Tabl e A-2 , wer e calculate d throug h applicatio n o f th e Multipl e Sourc e Foo d Mode l develope d i n Chapte r7
o f th e CD

. Th e latte rmode l use s year-specifi cFD Adat a o n foo d lea d conten t (i.e. , marke t baske t surveys ) an d age-specifi cdat a o n dietar ypattern s throughou t childhoo d an d ha s sinc e bee n validate d usin g recen t 1984-8 5 dat a (Flege l e t al. , 1988)

. Th e contributio n o f drinkin g wate rt o dietar y lea d exposur e wa

s estimate d fo ra n averag e ta p wate rlea d concentratio n o f 1 2 pg/1 , whic h wa s th e leve l reporte d fo rth e Stat e o f Montan a i n 1983

. Th e criteri a fo rvalidatio n nee d t o b e carefull ydefined

. Ther e i s a grea t dea l o f individua l variabilit yi n PbB levels , eve n wit h availabl e estimate s o f lea d concentration s i n exposur e pathway s suc h as air , dust , an d soi l

. Th e variabilit yi s attributabl e t o individua l biologica l variation , t o unknow n factor s mediatin g exposur e suc h as frequenc yo f hand-mout h contact , an d t o othe runattribute d source s o f lead

. Eve n wit h goo d environmenta l data , th e fractio n o f varianc e i n th e logarith m o f bloo d lea d tha t i s accounte dP.9 3

• f '.{j-S?
- ''•!•'•

' ': ' - ' ' !
VI- 5 fo rb ya n optima l tota l uptak e regressio n mode l (multipl e R^ ) rarel yexceed s 30%

. Fo rth e Eas t Helen a data , R ^ = 0.2 8 i n th e bes t fittin g model s (Johnso n an d Wijnberg , 1988)

. Thus , i t doe s no t see m fruitfu l t o us e th e individua l predicte d PbB level s a s a criterio n fo rmode l validation

. W e use d th e mor e realisti cgoa l o f matchin g th e geometri cmean PbB fo rchildre n i n a larg e neighborhoo d tha t wa s moderatel yhomogeneou s wit h respec t t o exposure . Amore globa l validatio n involve s comparin g th e cumulativ e distributio n functio n o f observe d Pb B wit h tha t o f th e individua l Pb R estimate s fro m th e uptake/biokineti cmodel

. Thes e comparison s fro m th e differen t validatio n run s ar e summarize d i n Tabl e 6-1

. Th e simulation s were al l ru n a t tw o levels , on e wit h al l parameter s se t t o th e lowe rbound s fo ruptak e parameter s i n Appendi xA , an d th e secon d wit h al l parameter s set-t o th e uppe rboun d level s i n Appendi xA

. Th e midpoin t o f th e all-lowe ran d all-uppe rboun d Pb R estimates , i.e. , th e simpl e mean wa

s foun d t o b e th e bes t predictor

. I n mode l ru n A , onl yob-sjerved

_value s fo rair , soi l an d dus t inpu t dat a wer e used

. Thi s dat a se t wa s limite d t o th e 2 8 observation s nea rth e smelte rwhere a n ambien t monito rwa s withi n a fe wblock s o f th e homes

. Mode l ru n B include s observation s o n 29 9 children

. Thi s expande d dat a se t wa

s obtaine d b yusin g dispersio n modelin g technique s t o estimat e bloc k specifi cambien t exposur e estimates. 1 Comparison s betwee n run s A.an d R illustrat e tha t accurat e PbB reduction s resul t fro m usin g eithe robserve d

1 Asimila rvalidatio n exercis e wa s conducte d previousl ywher e averag e PbB level s predicte d b yth e uptake/biokineti cmode l fo rdifferen t censu s tract s were compare d t o measure d PbB level s i n 1- 5 yea rolds , livin g nea r tw o secondar ylea d smelter s an d i n a referenc e area , i n Dallas

. Result s were usefu l i n indicatin g tha t greate rrefinemen t i n th e spatia l scal e woul d b e necessar yi n accuratel ymodelin g hig h exposur e situations

. Fo rth e Eas t Helen a analysis , an d i n subsequen t case-stud ymodeling , th e highes t degre e o f spatia l refinemen t possibl e (i->e. , cit yblock s o r bloc k groups ) i s used

.TABL E 6-1 . COMPARISON OF INTEGRATE D LEAD UPTAKE/BIOKINETI C MODE L PREDICTION S T O 198 3 MEASUREMENT S I N EAS T HELEN

A
Mode l Ru n Population 3 Pb Ai rQualit y Dust/Soi l Lea d Predicte d vs . Measure d Averag e Bloo d Lead 0 an d GSD C 2 8 childre n livin g i n are a 1 aroun d singl e a i rmonito rwit h vali d dat a 8 9 Are a 1 an d 21 0 Are a 2 Childre n

8 9 Are a 1 an d 21 0 Are a 2 Childre n Measure d a t monito r approx . 1/

4 mil e fro m smelte r Contributio n fro m smelte ranissio n estimate d b ydis
- persio n mode l (loca l meteorolog ydata ) loca l backgroun d P

b level s (e.g. , aut o anissions , fugitiv e dusts ) estimate d fro m 198 2 sourc e apportionmen t stud y Same a s fo rRu n B excep t tha t dis
- persio n modelin g use d meteoroloyica l dat a fro m a nearb y airpor t Measure d i n an d outsid e individua l homes
Measure d i n an d outsid e individua l homes

Estimate d fro m generalize d air : soil/dus t P

b relationship s fro m regressio n analyse s o f availabl e dat a i n literatur e 16. 3 vs . 16. 5 pg/dl * 1.4 2 vs . 1.4 9

9. 3 vs . 9. 3 pg/dl * 1.6 1 vs . 1.5 9

i O N 9. 5 vs . 9. 3 pg/dl * 1.6 7 vs . 1.5 9

Note : Dietar yP

b exposur e estimate d fo ral l mode l run s base d o n year-specifi canalyse s o f 1980' s FD Afoo d concentratio n dat a an d foo d consumptio n dat a fro m Penningto n (1983 , 1986) , an d U.S.D.A

. Nationwid e Foo d Consumptio n Survey , 1977-78

. a Area s as define d i n th e tex t b Geometri cmean s c Geometri cStandar d Deviatio n *A1 1 difference s statisticall yinsignificant ; t-test s o f difference s o f mean s assumin g lognorma l bloo d lea d distributio n an d non-equa l variances

. lea d

XI

- c oP.9 5
VI- 7

o r estimate dambien t ai r data. : Ru nC , lik e ru nB , ha s 29 9 observations . However , i

nth e latte r mode l run , observe dmeasure s o f household-specifi c soi l an ddus t lea dar e replace dwit hestimate s obtaine dfro m equation s tha t explai nsoi l an

ddus t lea dlevel s a s function s o f ambien t lea d(se e Appendi xB) . Also , whil e mode l ru nC use s dispersio nmode l estimate s
o f ambien t concentrations , as doe s mode l ru nB , th e sourc e o f meteorologica l dat a i s different : RunB use s loca l meteorologica l data , an dru nC use s airpor t data . Thi s differenc e allow s run s B an dC result s t o b e compare d t o asses s ho

w sensitiv e bloo dlea destimate s ar e t o les s location-specifi c meteorologica l dat a as wel l as t o estimate dsoi l an ddus t Pbconcentrations . Figure s 6- 1 an

d6- 2 compar e th e bloo dlea ddistribution s predicte db y Run s B an

dC , respectively , wit hth e actua l 198 3 measurement s o f Eas t Helen a children . I t i s importan t t o emphasiz e tha t th e model , becaus e o f th e availabl e inpu t data , i s designe dt o predic t mea npopulatio nresponse s an dno t individua l Pb B levels . Individual s wit hgreate r tha naverag e response s i nth e uppe r tai l o f th e distributio ncompris e th e populatio no f concern , however . A s discusse di

nSectio nIII.B. , th e respons e o f th e mos t affecte dindividual s wil l b e estimate di

ncase-stud y

analyse s b

y calculatin g th e lognorma l distributio n
arounda give nmea nPb B leve l usin g empirically-derive destimate s o f PbB variance . Th e degre e o f protectio nunde r a give nexposur e scenari o wii l k e characterize db

y th e fractio no f childre nwit hPb B belo w some leve l o f concern . Th e result s o f th e Eas t Helen a validatio nar e show nfo r individua l childre n i nFigure s 6- 1 an

d6-2 , withou t th e applicatio no f a GSD . Th e fraction , o r percentage , protecte di s o nth e vertica l axi s an dth e potentia l leve l o f
concer ni s onth e horizonta l axis . A s ca nb e see nb y thes e figures , an

din scatte r plot s o f individua l predicte dvs . observe dPb B level s (no t shown) , ther e i s significan t individua l variatio na t highe r level s du e t o extr a variabilit y

no t include di

nth e model . Thes e figure s reinforc e th e presumptio nP.9 6

VI- 8

10 0

9 0 -

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## z U J o c c U l Q . 8 0

7 0 -
6 0

5 0 -
4 0 -
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### i O - MOOE L ESTIMAT E

•- OBSERVE D

1 1 1 1 1 -111

~

1 0 2 0 3 0 4 0

BLOO D LEA D CONCENTRATION , ug/d l S O 6 0

FIGUR E 6-1 . COMPARISO N O F DISTRIBUTIO N

O F MEASURE D BLOO D LEA D LEVEL S IN CHILDREN , 1- 5 YEAR S O F AGE , LIVINGWITHI N 2.2 5 MILE S O F E . HELEN A LEAD SMELTE RVS . LEVEL S PREDICTE D BYUPTAKE/BIOKINETI C MODEL . MEASURE D SOI L AND DUS T LEAD LEVEL S WER E INCLUDE D I N ESTIMATINGUPTAK E LEVELS . (RU N B )P.9 7

VI-9" "

10 0 r
9 0

U J 8 0
70
60

z U J s o o c c 4 0
30
20
1 0 . tTT^^^^^T^^U T

O = MODE L ESTIMAT E O - OBSERVE D

1 0 20 3 0 4 0

BLOO D LEA D CONCENTRATION , ^g/d l 5 0



### FIGUR E 6=2 . COMPARISO N O F DISTRIBUTIO N

O F MEASURE D BLOO D LEAD LEVEL S I N CHILDREN , 1= 5 YEAR S O F AGE , LIVINGWITHI N 2.2 5 MILE S O F E , HELEN A LEAD SMELTE RVS , LEVEL S PREDICTE D B YUPTAKE/RWKINETI C MODEL , ESTIMATE D SOI L AN D DUS T LEA

D LEVEL S FROM

GENERALIZE D RELATIONSHIP S WER E INCLUDE D I N ESTIMATINGUPTAK E LEVELS , (RU N C )P.9 8

VI-1 0

tha t th e "importation " o f empirically-derive dPbB varianc e i s necessar y t o full y captur e variability . Thes e figure s als o show tha t th e model , a s designed , give s a usefu l estimat e o f th e mea nresponse . Usin g th e approac h discusse dpreviousl y o f a ) firs t estimatin g populatio nmea nPbB usin g th e uptake/biokineti c mode l an db ) the ncalculatin g th e Pb B distributio nusin g
a nempirically-derive dGS D (i nthi s cas e 1.53 ; se e Tabl e 3-2) , th e modele d PbB distributio nwoul db e nearl y identica l t o th e observe ddistributio nsinc e th e predicte dmea ni s s o clos e t o th e observed . Suc hcomparison s ar e no t illustrate dher e simpl y becaus e th e difference s woul db e virtuall y indistinguishable . I nconclusion , generall y satisfactor y

result s wer e obtaine dfo r predictin g geometri c mea nPb B levels . Mode l ru nA canb e considere da "pure " validatio nru

ntha t use s th e bes t inpu t dat a availabl e t o predic t
mea nbloo dlead s whic hcanb e compare dt o mea nobserve dbloo dleads . Mode l run s B an

dC wer e necessar y

validation s sinc e exac t populatio n locations , loca l meteorology , an dsoi l an

ddus t lea ddat a wil l r'arel y b e availabl e fo r poin t sourc e area s wher e th e mode l wil l b e use dfo r polic y analysis . Therefore , RunC canb e considere da "generalize dmethodology " fo r "export " o r applicatio nt o othe r study areas . Althoug hth e difference s betwee nobserve dan dpredicte dmea nPbB level s
ar e no t statisticall y significant , pos t ho c calibratio no f th e mode l t o remov e
an y difference s wa s considere d(Marcu s an dHoltzman , 1988) . Bot hlinea r
an dnonlinea r model s wer e examine dan di t wa s foun dtha t calibrate d model s (includin g age-dependen t ones ) improve dpredictiv e abilit y o f th e mode l onl y

marginally . On e alternativ e i s t o simpl y subtrac t th e differenc e betwee nobserve dan

dpredicte dPb B level s inth e generalize dmethodolog y Ru nC ( =0. 2 pg/dl ) o r us e a multiplicativ e facto r (th e latte r probabl y
mor e appropriat e give nth e lognormalit y o f th e Pb B distribution) . Suc haP.9 9

VI-1 1 calibratio nbase donth e result s o f a single , albei t larg e an ddetailed , validatio nma y

b e inappropriate , especiall y considerin g th e uncertaintie s inheren t i nsuc hmodelin g exercise s (e.g. , a "positive " calibratio nma y b e neede di na differen t location) . Give nthes e uncertainties , n o p_os_ t hoc

_ calibratio no f cas e stud y exposur e estimate s i s currentl y bein g propose dalthoug hsuc ha nadjustmen t coul deasil y b e accommodate di f decide dupon . Severa l sensitivit y

run s wer e mad e i norde r t o "fine-tune " variou s parameter s fo r whic hdat a ar e incomplet e suc ha s age-specifi c dir t consumptio nrate s an

dgu t absorptio nrate s fo r ingeste dlead . Fo r example , i nestimatin g th e rat e by whic hingeste dlea di s absorbed , th e criteri a documen t identifie s man y factor s tha t hav e t o b e considered , amon g the m person' s age , physiologica l status , medium fo r th e lea d(e.g. , foodvs . pain t o r "dirt") , coinciden t ingestio no f othe r element s i nfood(e.g. , calcium ) whic hcompet e wit hlea dfo r intestina l absorptio nsites,.an dth e non-linea r relationshi pbetwee n o lea dintak e an

dbloo dlea d(du e fo r exampl e t o a saturabl e gu t absorptio npathway) . Difference s ma y als o b e attributabl e t o physica l o r chemica l difference s inbioavailabilit y o f depositio nfro

m smelte r emissions , o r t o th e highe r rat e o f intak e i nthes e area s compare d t o typica l situations . — I nfact , ther e ar e reason s t o believ e tha t suc hdifference s ma y exis t i nEas t Helena . Th e lead-bearin g particle s tha t are deposite dnea r th e smelte r hav e a highe r proportio no f large r particle s fro m fugitiv e emission s (e.g. , erosio nfro

m tailing s piles , loadin g operations ) wherea s th e mor e distan t deposit s ar e predominantl y smalle r particle s fro m stac k emissions . Anothe r facto r i s tha t parent s o f childre nwh o live dclose r t o th e smelte r (e.g. , Are a 1 ) ma y

hav e bee nmor e sensitize dt o leadexposur e an dthu s tende dt o contro l acces s t o leade dsoi l an ddus t mor e tha nparent s i nP.10 0

VI-1 2

Are a 2 . Ther e ma y

als o hav e bee ndifference s du e t o nutritiona l factors. ) T o tes t this , w

e ranth e mode l wit h20 % gu t absorptio no f dir t leadinAre a 1
and30 % absorptio ni nAre a 2 . Two additiona l run s wer e mad e inwhic hth e same absorptio nfactor , eithe r 25 % o r 30% , wa s use dfo r bot hareas . Area-specifi c result s o f th e 20 % (Are a 1 ) / 30 % (Are a 2 ) mode l wer e no t significantl y differen t fro

m th e observe dgeometri c means . Likewise , usin g a 25 % absorptio nfacto r fo r bot h
area s yielde dno significan t differenc e betwee npredicte dan dobserve d geometri c mean s fo r th e overal l stud y area . Result s usin g th e 30 % rat e cite di nth e C D base do nindirec t chemica l an danima l experiment s wer e
no t a s concordant . Becaus e o f th e programmin g complexitie s tha t woul db e introduce di f dua l absorptio nrate s wer e use dinal l othe r application s
o f th e model , a 25 % absorptio nrat e i s chose nfo r genera l us e sinc e i t yielde dadequat e overal l results . A s indicate dinSectio nIII , th e mode l shoul db e regarde da s vali dfo r estimatin g mea nresponse s an di t doe s appea r tha t withth e correc t rang e o f soi l an ddus t leadinputs , th e mode l adequatel y predict s th e geometri c mea n
o f th e observe ddistribution . Estimatio no f th e highe r percentile s o f th e PbB distributio nrequire s application , t o th e geometri c mean , o f a GS D from , fo r example , NHANE S I I o r exposur e survey s arounddifferen t poin t sources . B . Applicatio no f Uptake/Biokineti c Mode l t o Othe r Dat a Set s Ther e ar e othe r publishe ddat a t o tes t th e uptake/biokineti c mode l
a t othe r U.S . location s an dtimes . On e dat a se t wa s collecte di nOmaha , Nebraska , fro

m 197 1 t o 197 7 (Angl e an dMclntire , 1979 ; Angl e e t al. , 1984) . Anothe r dat a se t wa s collecte dthroughou t Silve r Valley , Idaho , i n 1974-197 5 an

di s describe di nYanke l e t al . (1977) , an dWalte r e t al . (1980 ) wit hadditiona l informatio ngive ninth e CD .