P. 1



# OAR Box 1126 Prepped by Ollie Stewart



# Document

Number: 

# 122)11-1-33 6
Docket Number: 

# A-83-2 2

Printed 4/18/2008 9:58:26

AM Sheet 122 of 182

# Psycho-Socia l Factors , Lea d Exposure , ___andI 9

•AMM^^^: :•.'•••-J'

•-.-••:. ;!;.--.<v.- ; .'• „ •.•• • Th e histor y o f researc h o n lea d i s instructive . Th e effect s o f lea d encephalopath y o n menta l retardatio n an d deficit s i n moto r functio n hav e bee n know n fo r centuries . Th e amoun to f ambien tlea d i n th e environmen tincrease d sharpl y wit h th e adven to f th e Industria l Revolutio n i n th e nineteent h century , s o tha tno w th e averag e bloo d lea d leve l considere d acceptabl e i n a highl y industrialize d natio n lik e th e U.S . ma y b e u p t o 3 0 M-gM l (U.S . Environmenta l Protectio n Agenc y (EPA) , 1986) . Thi s i s seve n time s a s hig h a s averag e bloo d lea d level s i n Nepal , a n acculturate d bu tnonindustrialized , societ y (Piomell i e tal. , 1980) . Nevertheless , concer n ove r asymptomati c lea d exposur e withou tth e sign s o f encephalopath y bega n onl y abou t5 0 year s ago , whe n th e sociopolitica l climat e se tth e stag e fo r concer n abou toverpopulation , abus e o f natural resources , an d environmenta l poUution . Lea d the n becam e th e prototyp e fo r researc h o n man y environmenta l poUutants . Researc h emphasi s focuse d o n advers e healt h effects , tha tis , lea d toxicit y o n orga n system s of

th e body . Experimenta l prospectiv e researc h wa s perforc e don e primaril y o n laborator y animals . Huma n researc h focuse d o n medicall y oriente d epidemiologica l studie s tha tattempte d t o locat e source s o f

exposure , at-ris k populations , an d environmenta l ecologica l condition s tha tcoul d b e use d t o se tstandard s fo r publi c policy . Th e mai n questio n addresse d b y thi s researc h wa s finding th e threshol d leve l o f lea d

1 No w a tth e Nisonge r Center , Ohi o Stat e University . 1 No w a tChape l HU I Pediatric

s PA. , Nort

h Carolina . Acknowledgements . W

e wis h to acknowledg e NIEH S Grant#flM tEP A Gran t CR809992-01-9 ; USPH

S Gran t""HI" " to th e Chil d Developmen tResearc h Institute ; •B^tf-MPaa-n-prt^^W

n th e Divisio n fo

r Disorder

s o f Developmen tand Learning, wher e th e childre n wer e evaluated . Thank

s ar e als o du e t

o th e Departmento

f Pediatrics , Nort

h Carolin a Memoria

l Hospita

l and th

e Healt h Effect s Researc

h Laboratorie

s o f th e Environmenta

l Protectio n Agency fo

r thei r countles s example s o f suppor tand collaboration in thes e projects . 97' « £ "' • '•'•' 

# '"'•'"t: ••Arf?-:•-•

"?•;•••



# • • vA ? ~

- 1 : - ''''•-. ;^;;v.rfS&fcfife^v«%v.Jd.a ' ; J.-H 

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# feife%<

•.^ ; S 3 To«I C SUBSTANCE S 

### burde n i n th e bod y tha

tsignal s a

n unacceptabl

e ris k for retardatio

n o f cognitive an d adaptive behavior, a s measure d b y intelligenc

e tests , an d for minima l brai n dysfunction (MBD) , a s exemplifie d b y hyperactivity, attentio n deficitdisorders , fine motor skills , reactio n time , etc . LEA D EXPOSUR

E LEVEL S A vas tbody o

f clinical , epidemiological , an d experimenta

l dat a ha s accumulate

d ove r recen

tdecade s to sho w tha

tyoung children, particularl y preschoolers , ar

e mos ta trisk fo r th e adverse effect

s o f lea d (Nationa

l Academ y o f Science s (NAS) , 1980 ; U.S . EPA , 1986) . Th

e basi s for thi

s risk-effectrelationship ha s it s genesi s i n bot

h th e physiologica

l statu s o f th e developin g chil d an

d th e relationship o

f the chil d t o a given exposur

e setting . Youn

g children , a s developin g organisms , hav e metaboli

c characteristic

s quit e distinc tfro m th e adul

thuma n an d thes e difference

s ar e suc h tha tthe y augu r a deleteriou s outcome when a genera l toxican t suc h a s lea d i s introduce

d int o th e picture . Fo

r example , childre

n hav e a n incompletely develope d blood-brai n barrie r t o movemen

to f lea d t o th e centra l nervou s system . Secondly , demands o f rapi d growt h requir e nutrien tassimilation rate

s tha toften resul

ti n deficiencie

s in thes e factors, on e resulto

f whic h i s tha tlea d absorption and/o

r retentio n i s enhance

d (Mahaffe y & Michaelson , 1980 ; NAS , 1976 ; NAS , 1980 ; U.S . EPA , 1986) . Childre n ar e als o fundamentall

y distinc tfro m adult s wit h respec tt o exposur e status . First

, childre n assimilat

e lea d i n food an d wate r a ta higher rat e tha n d o adult

s o n a body-weigh to

r surface-are

a basis (NAS , 1980) , absor

b a greate

r fractio n o f th e ingeste d element

, an d retai n a greate r portion o

f th e absorbe

d amoun t(Alexander

, Delves , & Clayton

, 1972 ; Ziegler, Edwards , Jensen, Mahaffey, & Fomon, 1978) . Secondly , i n crawlin g babies th e ingestio n o

f nonfoo d items , suc

h a s lea d contaminate

d dus tand soil , normall

y occur s a s par to f nonna l behavio r suc h a s mouthing activity . I

n olde r childre n wh o frequentl

y engag e in rough-andtumble outdoo r play , lea

d i n dus to r soil i s transferre d t o thei r hand s an d t o food they hol d i n thei r hands , an

d i s thus eventuaU

y ingested . I

n a settin g where ther

e i s significan

tcontaminatio

n o f dustan d soil , this rout

e ma y dominat e th e dietar

y pathways (Nationa

l Academ y o f Sciences , 1976

, 1980) . Fro m a historica

l perspective , iti s quit

e clea r tha tthe acceptabl

e leve l o f exposur e o f children t

o lea d an d ou r understandin

g o f th e natur e o f th e advers e effect

s engendered hav

e bee n undergoing constan tchange. Wit

h respectt o exposure , concer

n ha s shifte d fro m suc h evidenc e o f interna l (o r systemic) exposur

e a s bloo d lea d values o

f 6 0 ug/d l an d highe r t o value s considerabl

y belo w this . I

n it s 197 8 statemen

to n lea d poisoning i

n young chUdre n (U.S . Center

s fo r Diseas e Contro

l (CDC) , 1978) , an

d directe d to PSYCHO-SOCIA L FACTOO S « 9



### . ^TM~ -^~,i»f«»

d variou s ris k categories , th e pediatri c community , the CDC artoc u ute a - , bloo d 

### fead whe n predicate d upo n a n initia l action level oi * i* » d agai n t o 

### 2 5 Ireatmen tshoul d begin . ^^tog^ J | rotectio n 

### Ug/d l (U.S . CDC

, 1985) . Simila

r y th e U&**TM> base d o n 

### Agenc y establishe

d a n ambien t-'"JXo f

ea d expos e i n chUdren, wha tth e agenc y too k t o b e acceptabl

e level s o i ie - r whic h wer e belo w th e older value o

f 6 0 W^ 1 

### : { 

### ^ , consti 

### tute s Th e compellin

g rational e behin d a rethinkingM * wlu

i ^ societ y acceptabl

e level s o

f P^ « ^^tiat o concern constellatio

n o f subclinical

o rmor e *"*'%X ^ exposur e levels , o n hav e bee n th e effect s o f lead , reporte

d a trathe r ^P ° rf

hera l 

### hem e biosynthesis , erythropoiesis , an d bot n c 

### " \ 1980- NAS , nervou s syste m function

s (Moore, Mered.t

h * Gold 

### ~[£TM^ ' " & 1980 ; Needlema

n U Landrigan

, 1981 ; Piomelli , »*J X Davidow , 1982 ; U.S . EPA

, 1977) . I ti s th e issu e o

f lea d neurotoxicit

y a tlo w levels o f exposur e tha ti s th e centra

l focu s ol 

### f u 

### ^ t r 

### '^T L r w m S I n th e updat e o f the EP A documentAirQ M 

### '\ Cnt 

### TMt Z»So*c EPA . 1986), w e reviewe d 2 0 o f th e bes tknow n stud.* i o the-eurotox * effect s o f lo w level s o f lea d exposure where th e <*^ **£**££*£ symptom s o f lea d encephalopathy . Tabl

e 1 show s som e o

f th e weaknesse s and/o r inconsistencie

s o f thes e studies : „«^»« , „ f i M 

### d 1. WhU e severa l studie s sho w statistically significan teffect s o f lead exposur e o n I Q testperformance, th e grou p effect s ar e usuaU y sma U tha t is/les s tha n 6 I Q points , whic

h i s nea r th e standard erro

r fo r *es e tarts. (ClinicaU y significan

tI Q effect s woul d b e nearer to 1

5 I Q PTM*-*«• * on e standar d deviation. ) Th

e I Q test , like othe r standardized V>V*TM*TM performanc

e test s (fin e motor, reaction time , perceptual-moto r * W ^ b e to o blun ta n instrumen

tt o reliably tap subtl e neurobehaviora l effect s o t moderat e lea d exposure . . . 2 Onl y a fe w studie s use d a standardize d ratin g scal e to

r hyperactivity

. However, fe

w significanteffects o

f asymptomati c lea

d exposur e wer e found . Ou

r grou p als o foun d n o effec to n chUdre

n ag e 12-7 2 months . (MUar

, Schroeder, Mushak , & Boone , 1981. ) 3 . Neurologica

l examinations yielde d fe w lea d effect s belo w 40 »ig/dl . Apparently

, mor e sensitiv e neurometric measure s ar e needed . Ou

r group (Otto, Benignus , MuUer

, & Barton, 1981 ) demonstrate d significan t amplitud e change s in slo w wav e potential s o f childre n age d 12-4 7 m 

### °TMTML wit h 6-59 (ig/dl , whU

e thi s effec

tdi d no tappea r i n older chUdre n (48-/ 5 mos.) . . . . . 

### 4 . N o stud y ha s evaluated children' s intelligen to r socia l behavio r base d o n a theoretica

l hypothesi s a s t o th e natur e o f th e cognitive , attentions , an

d perceptual-motor deficits thathav e ofte n bee n found o n I Q test s an d attentio n defici tquestionnaires .P. 4



# - • !'W$^'J'£m7''i'-J.&i •^^l a #/•••? ? JJ. '.-J 

# \J$W4- : 

# -; K - .

TABL E 1 Summar y o f Studie s o n Neurobehaviora l Functions o

f Lead-Expose

d Children *



## ..,„,. . Populatio n •tudte d N^povx p Clink-typ e Stadi a o f

Cfeildrca wit h Hij b Lea d Level * delaBurdean d Cha m (1972 )

d « to Buid tand

Rumm o (1974) ; Rummo r l al . <1979 )

KttokflTO ) Inne r dt y

^ (Ridunond , VA )

Follow-u p urn * subject )

Inne r dr y (Providence , RI

)

Inne r dt y (Ne w Haven , CT) C-7 2 Pb-7 0

C-6 7 Pb-7 0

C-4 5 Pb,-1 5 Pt»-2 0

C-2 5 Pb-2 « HfU

ltstifis,jr r (range !

4. 0 4. 0

7- 8 7- <

3.8(4-8 ) 5. 6 5. 6

2.7(1.1-8.3 ) 2.8(1.0-5.1 ) Bloo d had , W/d l (rang e o e ± S.D. I

r 58O0-100) -

PbT-lHi^/ 1 2Q2|ig/g

D(»8 ) 61(17 ) M(»13 ) 88(x41 )

38(30-55 ) 8 1 (58-137 ) rtychooietri c tcst i employe d

I Q (Stanford Binet ) Rn c moto r Cro u moto r Concep tformatio n Behavio r profil e WB C Ful l Stal e I Q Vettall Q Performance I Q Bender.Ge--.tal

t Readin g Spellin g Arithmeti c Goodenough-Harri a draw tea t Auditory voca

l aaaoc . Tactil e recognitio n Behavio r profil e McCarth y Scale! : Gen . cognitiv e Verba l Perceptua

l Quantitativ e Memor y Moto r Paren trating ! Neurologi c even t Denve r Developmental : Gra u moto r Fine moto r Languag e Score : % aubnonnal :

Scor e % aubnonnal: '

C 9 3 4 6 4 8 4 5 47 52 8 Norm 1.00 1.00 - 1.00 - 7/1 2 Sunmar y o f mult a
C 9 4 2 6 7 10 1 0

27 7 1 1
1 3 3 3 Pb , 9 4 4 9 4 4 4 6 5 2 1 0 meaaure e al g C 1.0 2 .8 2 .8 2 P

b 8 9 4 5 1 6 15 3 0 8 7

4 9 1 2 16
3 1 15 2 5
8 8
4 1 4 3 5 0 10 differe n P b 1.06 .81 " .73 - Pb . 77 3 5 3 6 IS level , o f aignlfi cance'- '

<.0 5 N.S . N.S . <0 1
.0 1 N.S . .0 1 N.S . N.S . N.S . .0 1 .0 5 .00 1
<0 1 <0 5

<0 1

N.S . •<.0 1 •<.0 1 

## %.&'.



# wi<yr

vVftft' j



### •R*' -

•&r !S5!H. i a??Jt"r. :'-• 

# m - - T.a^aft-a.a •a.-:1*:JlS. - ! 

### •JU

TABL E 1 Summar y o f Studie s o n Neurobehaviora l Functions o

f Uad-Expose d Children * (Continued)

Summar y o f mult a Referenc e Ko-ok.i. l (1977 ) Populatio n atudie d Inne r city (Rochciter , NY ) Wfmf C-3 6 Pb-3 1 Ag e a t teeting,y r (range ) 3.6(1.9-5.6 ) 3.611.7-5.4) Bloo d Uad ,

(rang e o r ± S.D. ) 28(11-40 ) 80(61-200 ) Ptychometn- c tee u employe d I Q Equivalent : Socia l Spatia l Spoke n vocal l n to-cooiprehcnaio n Visua l attentio n Auditory memor

y Sinelt---- r Are a Studie e Landriganetal . (1975 )

McNei l etal . (1975 )

Datelin e (1977

) Smelte r are

a (E l Paao . TX)

Smelte r are

a (E l Paao , TX

)

Smelte r ate

a (Mar-cheater . UK

) C-7 8 Pb-4 6

a-" 3 7 ! (1.8-18 ) Pb-10 1 9 1 <4 0 WIS C Ful l Scal e IQ 1 40-6 8 WPPS

1 Ful l Scal

e IQ * WIS C + WPPS

I Combine d WIS C * WPPS

I Subecalea

Mod.Fb-2 3 HiPb-2 4 4.7(4.1-5.6 )

4.8(4.2-5.4 ) 29(14-39 )

58(4043 )

28(18-35 ) 44(36-64 ) Neurologi c tearin g

McCarth y Genera l Cognitnr e WISC- W A E Ful l Scal

e I Q Oaeretak y Moto r Leve l Californi a Pertonalit

y Frooti g Perceptua l Quotien t Finger-Thumb Appoeitio n Griffith ! Menta l Dev . Froatig Viaua

l Perceptio n PegboardTca

t Dominan t han d Nondominan t han d 9 3 IC C C 9 3 9 1 9 3 9

0 9 3 P b 8 9 8 6 8 8 C > P b o n 13/1 4 acale

a 7/1 4 Kale ! aig C > Pb o n 1/ 8 teit i aig . C 8 2 8 9 10 1 . differen t 7/ 8 teat a differen t P b 8 1 8 7 9 7 C > Pb , 6/1 0 itctn e 10 0 2 7 Mod . 10 8 14. 3 17.5 19. 5 10

3 2 9 Hig h 10 2 11. 8 17. 3 19. 8 Levelao f aignifi -
>.1 0 <.! 0 >.1 0 >.1 0 >.1 0 >.1 0
N.S . N.S .

N.S . N.S . N.S . •e0.0 5 N.S . N.S . N.S . N.S . N.S . N.S .P. 5

TABL E 1 Summar y o f Studie s o n Neurobehaviora l Functions of

Lead-Expose

d Children * (Continued )

(range ) Bloo d lead ,

pg/d l (rangto r tS.D. )
Wlnnckt , Hrdina . Stnettcrarc a 4 Bnxkhau s (Durjberg , FRC ) (1982 )

Per-in o and Inne r Qt y LowPb-5 0 Emhar t(197<) " (Ne w York

, KY ) Mod.Fb-3 0 FbT-2.4ppm * Germa n WB C Ful

l Scal e PbT-9.2pp m Verba l I Q N o Pb B Perfonnancel Q Bende r Gettal tTea

t Standard Neurologica l Test a Conner * Teache r Rating !

Follow-u p »

J subjccti

Genera l Populatio n Studi o Needlema n e tal . Urban (1979) - (Boston , MA ) LowPb-3 1 Mod.Pb-3 2 10-3 0 40-7 0

2 1 (*4 ) 32(*3 )

PbT^lOppm 1 ' > 2 0 pp m McCarth

y Scale r Gen . cognitiv e Verba l Perceptua

l Quantitativ e

McCarth y Scale r Gen . cognitiv e Verba l Perceptua

l Quantitativ e
Readin g teets Conner * teache r ratinga Vark w experimental test *
WB C Pu D Scal e I Q Verball Q Perfonnancel Q Seashor e Rhyth m Te* t Toke n Tea

t Sentenc e Repetitio n Tet t Delaye d Reactio n Tun e Teache r Rating * c 12 2 13 0 13 0 17. 2 2. 7 ? Lo w 9 0 4 4 4 4 4 8 4 5 46 Lo w 9 4 t s 4 3 4 3 4 4 4 9 P

b 11 7 12 4 12 3 19. 6 7. 2 ? Mod . 8 0 3 9 3 7 4 4 4 2 42 Mod . 8 2 4 1 4 0 3 8 3 9 4 6 No t Reporte d No t Reporte d Not Reporte

d
106. 6 103. 9 100. 7 21. 6 24. 8 12. 6 102. 1 99. 3 104. 9 19. 4 23. 6 11. 3 C > Pbon3/ 4 Uodt a 

# s

c : • /

-•wB>W*»v -

Summaiy TABL E 1 o f Studie s o n Neurobehaviora l Functions o

f Lead-Expose

d
Populatio n •tudle d Ag e a t teettafry r (range ) ^ 4 1

n o r ±S.D. )

McBrideetal . (1982)

Yul e e tal . (1981 )

Yul e etal . (19M ) Urt»nfeuburba n Lo w ft - >10 0

(Sydney , Australia ) Mod . Pb - >10O

Urban (London , UK

) Grou p 1 - 3

4 Grou p I-* 8 Group 3-4 9 Crou p 4-3 5 2- 9 ug/d l 19-2 9 g/d l

8.8* (7-10 ) 11.6(11-12 ) 14. 5 (1V16 ) 1M(1M »

Sam e subject

a i n Yut e etal . (1981 )

Yul e an d Lanadow

n Urba n (1963) ; Yule (London , UK ) e tal . (1983 ) teet a employe d Children ' (Continued)

Stan-nar y o f reattlt a
Peabod y Pictur e Vocab . Tet t Rn e Moto rTrackin g Pegboar d Tappin g Te* t Bea m Wal k Standin g Balanc e Rutte rActivit y Scal e W1SC- RPu n Scal e I Q Verba l I Q Performanc e I Q Verno n Spellin g Tea t Verno n Mat h Te w Neal e Readin g Accuracy * Nea k Readin g Compre. k
Needlema n Teache r Rating s Conner * Teache r Rating * Rutte rTeache r Rating* , includin g •Qwractivtty*'facto r
WBC-RPu D Scal e Verba l I Q Performanc e I Q Neal e Readin g Accurac y Ntil tReadin g Comprehensio n Vcmor tSpellin g Verno n Mat h Group : Lo w -10 5 Mod . -10 4 C > Pb 1/

4 comperiaon a -2 0 -3 0

- 5 -2 0 -3 1

- 4 C < Pb I M comperiaona -1. 9 1 2 10 3 10

3 10 1 10

1 10 6 0

3 10 4 9

8 97 9

7 12 1 11 0 11 7 11 0 1 2 1-5 3 1.3

4 -2. 1 3 9 6 9 S 96 9 2 93 9 6 9 5 3 2.4 S 4 96 9 4 9 9 8 9 95 8 9 8 8 4 2.63 N.S . -C0.0 5 N.S . N.S . N.S . -C0.0 5 N.S . .00 7 .04 3 .10 2 .00 1 N.S . .00 1 .00 1 .09 6 (4/1 1 Hem s tig . different ) .2 6 .3 7 (3/4 factor * aig . a tp <.0S ) (2/2 6 item s tig . a

tpS-05 ) (5/2 6 item * diffe ra t.05<p<.10 ) 6% 4 % 20 % 17 % Lo w 10 7 10 4 10 8 Hin h 10 5 10 3 10 6.- • -XM . u , • .-r f

t-f • , '.-'.'< ' •A.-.. , ..:-*.i ; ? -a-, ' 

### PJ L

TABL E 1 Summar y o f Studie s o n Neurobehaviora l Functions o

f Lead-Expose

d Children " (Continued )
Populatio n studie d N/grou p Aj e • ! tating, j r (range ) Bloo d lead ,

HSM 1 (rang e o r xS.D. ) tcat a employe d Stmutar ^ o f rcanlt a
Smit h etal . (1983 ) Urba

n (London , UK

) HI-15 5

Mad-10 3 Low-14 5

Urba n (Bim-Jnghim . UK

) PM>8. 0 PbT-5-3. 5 Pb T <2. 5 (Al l i n ug/g ) SPM-13. 1 ug/d l

15.5(6-30 ) WBC-RPuB Scal e

Verba l I Q Perfonnancel Q Wor d Readin g Tea

t Seaahore Rhythm Tea

t Viaua l Sequential Memor

y Sentenc e Memor

y Shep e Copyin g Mathctnab a Mean Viaua

l RT(aea ) Cmn m Teache r Rating

a Britid i Abilit

y Scale . Namin g Recal l Comprvhenaio n Recognitio n I Q Stanford-BinetItem s Shape * Block * Bead * Playroo m Activit

y Lo

w 10 7 10 3 10 8 4 5 2 1 2 0 9 1 4 1 6 .3 7 1 1 Me

d 10 5 10 3 10 6 4 2 2 0 1 9 9 1 4 1 5 .3 7 1 1 Hig h 10 5 10 3 10 6 40 2 0 20 9 1 4 1 5 .3 9 1 3

Smelte r are

a (Sto&urg , FRC) PbT:6.16ppm » PbB : 14. 3 ug/d l



### m i i i iiiumi immtat0mmsH0nmm m

TABL E 1 Summar y o f Studie s o n Neurobehaviora l Functions o

f Lead-Expose

d Children ' (Continued)
Populatio n aMdla d Ag e a t tearing , ) T trasge l
Wtnnesaetal . (1984 ) Smelte r are a (Nocdenham . FRC)

• Abbreviation ! C-contro l aubiectl P b - leed-e.poie d eubjecta . N.S . - nonaignificant(p>.05) ; PbT-toot h lead ; WIS C - Wechele r Intelligenc e Scal e lo r Children ; WPPS I - Wechaler IWoo l and Prim. TM Scal e o l IMeUg-m c RT-ReKtio n Tone . ---Sgnltanc e Wvet a .. . tho - foun d aiu . p-urialing ou tconfoundin g covamte.JUnn.t y cop»pon>hyrintad . wa . TMTeZ ^ -Som e wit h po*, TM ndM^ c finding, .ugg«tin g ..*•• » rtpoaur , i n «« . < X 4M 0 *g/dl . -IWn tofeach^ p .conn , -bord.rt,n«r-.«»p«, - -detam.. - 0 , Tbnonn.1 - 'U- d fo . child TM ove r 5 y« n o f «. . X M fo

r child TM und. , 5 y» » o f .g. . 'Mai n tneaaur . , » tkntm . tad (PbT) . Dm.-tad . -^^-^^W^Mon. . •Blood lead level , lake n 9-1 2 month , prio r t o icing , non e .bov . 33 «MI . 'Dat a no tcomct-r f lo r age . ton.^o^» b y Endur , conecrm g te mMhodol- ^ prthm . m oioo u ... o r v * j . di d M MbMnhat . aignificanl difference , betwee n control .n d Pb-opoee d childre n indicate d I n U u tw o column , t o th e ngh t(te e Z%r^^!^7^ Z Zt£ £ Z m-hodo^ l prob, TM i n e*» r pubbd- d .iuly » connmw d Ignihcn , «*

—b«w« „ «ud y g^p . indict * i n U. ttw o righthand column , fo r WIS C I

Q Ma treault . (M e chapte r text) .

# Y' v 

# 7'< J-^^M-W-

| - •??-: ( i ' '•r-xi.'J^r^fa-^V.at.a J » - V •.^•.- -



## ^ p " :?,'. I.QiZ:, 

# m^

. ' \4> ?Ssfa&

<

10 6 Toxi c SUBSTANCES 

### 5
. Epidemiologica

l studie s hav e no t

followedu p o n thes e childre n t o evaluat e th e cumulativ e clinica l effects o f leadexposure o r

reversibilit

y upo n removal o

f lea dfro mhis/he r hom e environment
. 6
. Th e long-termclinica

l neurotoxi c effects o

f moderate leadexposure o n children' s developmen t largely remai n to b e investigated
. 7
. Epidemiologica

l studie s tha t

hav e bee n don e poin t

t o th e presenc e o f ahazar dcause db y leadan dth e nee dfo r guideline s to regulate exposur e i n th e general population
. Bu t the y ar e o

f limite dhel p i

n predictin g th e outcome o

f individual s wit

h specific deficit s tha t

var y along continuou s behavioral dimension s interactin g wit h socia l an ddevelopmen

ta l factors
. RESEARC H DIFFICULTIE S Biologica l Indice s I n additio n t o th e above , ther e ar e some general , pervasiv e difficultie s i n lea dresearch
. Th e firs t i s th e highl y controversial issu e o f th e bes t biologica l inde x o f internal , o r

systemic , exposur e t o lead
. A growin g dat a bas e dealin g wit

h lea dtoxicokinetic s provide s some useful guide s i n considerin g achoic e o

f exposur e index
. Bloo dleadmeasurement , t o th e exten t that i t ca n b e accurately determine di n agive n laboratory , i s dependen t fo r it s usefulnes s o n th e natur e o f th e exposur e bein g sustaine dby th e stud y population
. Lea d absorbe dint o th e bloodstreami s cleare dfro mbloo dt o tissue s o n th e orde r o f week s o r several month s (Chamberlain , Heard , Little , Newton , Wells , & Wiffen , 1978 ; Rabinowitz , Wetherill , & Kopple , 1977)
. Hence , i t i s mos t usefu l wit

h chroni c elevate dexposur e an dles s s o wit h episodi c bout s o f lea dintake
. Measuremen t o f leadin a n accessible , accumulatin g matri x suc h a s she ddentitio n pushe s back th e exposure perio dt o years , but thi s measur e i s by it s natur e retrospectiv e (se e Needleman e t al. , 1979)
. On e analyze s she ddentitio n t o ascertai n whethe r leadexposure occurred, rathe r

dia n i s occurring. Hence , whil e dentitio n analysi s i s more appropriat e in definin g aggregat e exposur e an dit s relationshi p t o health measures , i t doe s no t provid e ausefu l regulatory metri c fo r monitorin g lea

dexposure i n rea

l tim e o r concurren t

leadintake versu s chang e i n outcome measure assessment
. I n th e absenc e o f availabl e method s fo

r in situ measuremen t o f lea di n childre n durin g thei r mos t vulnerabl e stag e o

f development , th e bes t compromis e seem s t o b e serial bloo dlea dmeasurements , fo

r example , quarterly
. Such seria

l measurement s would , o f course , increas e th e reliabilit y o f usin g bloo dleada s th e exposur e inde x becaus e increase s i n 

# f 

# s&m

PSYCHO-SOCIA L FACTOR S 10 7 

### chroni c exposur

e woul db e ascertainabl e whil e th e occurrenc e o f episodi c intak e o f larg e amount s o

f lea dwoul db e mor e likel y t o b e capture di n laborator y analysi s wit

h frequent sampling
. Exposur e indicator s tha

t directl y reflec t

abiologica

l lesio n ar e als o o

f valu e whe n take

n i n tande mwit

h bloo dlea dvalue s (CDC , 1978)
. A t present , th e indicator

o f mos t utility o f thi s typ e i s free erythrocyt e protoporphyri n (FEP) , ahem e precurso r whos e elevatio n i s relate dmor e t o chroni c tha

n t o episodi c exposure . Socia l Factor s The secon dchaUeng e i s agrowin g understandin g o f an dconcer n ove r th e interrelationship s amon g socia l factors , lead , an dchil dIQ
. The contributio n o

f maternal inteUigenc e t o th e child' s intelligenc e mus t als o b e evaluate din carefull y controUe dstudie s o

f lea deffect s o n intelligence
. Hebe

r (1970 ) foundahig h concordanc e betwee n materna l an dchil dinteUigence
. A majorit y o f th e childre n wit h IQ s i n th e retarde d rang e hav e mother s wit

h IQ s o f les s tha n 80
. H e als o foun dadeclin e i n I Q rang e fo r lowe r socioeconomic statu s (SES ) chUdren wit h increasin g age . Fo r mother s wit

h IQ s les s than 80 , th e percentag e o f thei r childre n wit h IQ s les s than 8

0 increase dfrom20

% fo r age s unde r

6 year s o f ag e t o 90 % fo r thos e ove

r 13
. I f mother s o

f leadexpose dchUdre n hav e IQ s les s tha n 80 , the n inteUectua

l difference s previousl y attribute dt o lea dmigh t als o b e explaine dby materna

l IQ
. Mos t studie s hav e attempte dt o contro l fo r possibl e covariate s (Tabl e 2) suc h a s socia

l class , age , maternal IQ , pica , an dparents ' attitud e towar d education , bu t

no t fo r th e qualit y o f th e caregivin g environment
. Studie s examining th e relationshi p betwee n socioeconomi c statu s an d intelligenc e an dacademi c achievemen t hav e yielde dmixe dresults. I n a meta-analysi s o

f 20 0 studie s relatin g SES t o academi c achievement
. Whit e (1982 ) foun dtha t hom e atmospher e correlate dt o amuc h highe r degre e wit h academi c achievemen

t tha n an y othe r

combinatio n o

f SE S indicators
. The mor e important

variable s wer e th e childrearin g practice s an d stimulatio n o

f learnin g a

t hom e an dschool , an dno t parents ' occupation , income , or

education
. I

n general , SES seem s t o b e abroa dbut crud e measure o f factors suc h a s caregivin g practices , resources , etc. , tha t may b e bette r examinedindividuaUy
. Th e Influenc e o f

Caregivin g Th e result s o

f previou s researc h hav e suggeste dtha t there migh t

b e deficiencies in the caregiving environment o f chUdren wh o evidenc e increase d •\ f



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•'••''"•'•'' 10 8 TOXI C SUISTANCS S TABL E 2 Evaluatio n o f

Contro l o f

Confoundin g Variable s o f th e Twent y Majo r Studie s o n Lo w t o Moderat e Bloo d Lea d Level s i n ChUdre n

Poaaibl a Confoundin g Variabtee ControUe d (Indicate d b y + Blin d Hom e Ma i Ag e Pic

a Evil . Envir . Rac e I Q SE S Exposu R Hiitoi y d e laBurd e & Choat e (1972) Kotok(1972 ) Lansdownetal
. (1974) Perin o & Emhar t

(1974) d e laBurd e & Choat e (1975 ) Landriga n etal
. (1975 ) McNei l etal
. (1975 ) Kotoketal
. (1977 ) Ratcliff e (1977 ) Needlema n etal
. (1979 )
. . Rummoetal
. (1979 ) Emhar t etal
. (1981 ) Yul e etal
. (1981,1984 ) McBrideetal
. (1982 ) Winneke , Hrdina , & Brockhaus(1982 ) Haive y etal
. (1983 ) Smit h etal
. (1983 ) Winnek e etal
. (1983 ) Yul e etal
. (1983 ) Winnek e & Kraeme r

(1984)



### lea d burden (Chatterje

e & Gettman, 1972 ; Lansdown , Sheperd , Clayton , Delves , Graham

, & Turner

, 1974 ; MilUcan

, Lourie, & Layman

, 1956 ; Rennert , Weiner, & Madden , 1970 ; Rummo , Routh, Rummo, & Brown, 1979) . Milar , Schroeder, Mushak

, Dolcourt , an d Gran t(1980 ) compare d two group s o f chUdren , 12-3 0 month s o

f ag e an d 31-7 8 months o

f age , showin g increased lea

d burden wit

h a sampl e o f chUdre n matche d fo r age , sex , an d socioeconomi c status , butshowing n o evidence o

f increase d lea d burden . Th e qualit

y o f th e caregivin

g environmen

to f thes e childre

n was assesse d wit

h th e Home Observatio

n fo r Measuremen

to f th e Environmen t(HOME ) Inventor

y develope d b

y CaldweU

, Heider, an

d Kapla n (1966 ) A measur

e o f materna l intelligenc

e was als o obtained . Fo

r younger childre n i n th e sample , significan tdeficit s in materna

l I Q an d quaUt y o f th e caregiving environmen twer e associate

d wit h increase d lea d burden . Subscale s o f th e HOM

E Inventor

y dealin g wit h emotiona

l an d verba l responsivit

y o f th e mothe

r and materna

l involvemen

twit h th e chil

d showe d significan

tdeficiencies i n th

e caregivin

g environmen

to f th e chUdre n wit h increased lea

d burden. Fo

r olde r chUdren

, the HOM

E PsrcHoSociA tFACTOK S 10 9 

### Inventor y als o showe d deficiencies i n th e caregiving environmentwith increase d lea d burden, bu

tth e differences were statisticaU y no t significant . Researc h ha s onl y recentl y begu n t o documentth e powerful influences o

f the earl y caregivin

g environmento n subsequen tdevelop men to f the duld . Studie

s b y Bradle y and Caldwe

U (1976a, b ) use d th e HOM E Inventor

y t o identif y factor s in th e chUd' s environmen tdurin g th e firsttw o year

s o f lif e tha tar e relate d to menta

l testperformanc

e a t3 6 an d 5 4 months o

f age . Tw o o f th e subscales o

f th e HOM

E Inventor

y tha twer e strongl y relate d t o late r inteUectua

l developmentwer e emotional an d verba l responsivity o

f the mothe

r and materna

l involvemen twit

h th e child . These ar

e th e tw o subscale s identified b

y Mila r e tal . (1980

) showin g significan tdeficiencie

s i n the environmen

to f chUdre n wit h increase d lead burden . Traditionally, th

e interpretatio

n o f th e researc

h o n lea d effect

s i n human s ha s bee n tha tincrease d lea d burden directl

y results i n deficit

s i n cognitiv e functioning. However, alternativ e hypothese s ar

e equaU y plausible . First

, th e result s o f Mila r etal . (1980

) sugges tth e possibilit

y tha t deficit s foun d in chUdre

n expose d to lea d ma

y b e a direc

tresul to f deficiencie s i n th e caregivin

g environmentand ma

y no tb e related t o lea d a tall . Th e researc h o f Bradle y an d Caldwe U (1976a , b ) tend s t o support this conclusion . Second , i ti s possible tha

tdeficiencies i n the caregivin g environmen t ar e responsible fo

r increase d lea d burden an

d tha tth e deficiencie s ar

e caused b y lead . A chil

d i n a n environmentwhere lea d i s available woul d b e muc h mor e Ukel y t o inges tsignifican

tamounts o

f lea d i f lef t unsupervise

d b y his/he r caregiver

. The poo r caregivin g environmen tma y b e a n anteceden

tt o th e lea d ingestion , bu tthe neurotoxi c effect s o f lea d ma y b e responsibl

e fo robserve d deficit s i n cognitiv e functioning . This situation ma

y b e analogous to malnutrition i n chUdren . Severe malnutri tion ca n lea d t o cognitive deficit

s (Dobbing , 1970) , bu tCraviot o and DeUcardie (1972

) hav e als o documente d tha

taspect s o

f th e caregivin

g environmen

tma y plac e chUdre n a tris k fo rmalnutrition . A thir d hypothesi s i s tha

tth e caregiving environmen tan d lea d combin e to affec tinteUectua

l developmen tadversely . Thi s woul d b e simila r t o the relationshi

p foun d b y Werner

, Honzik , an d Smit

h (1968 ) between perinata

l complication

s an d later psychologica

l development . A

t 2 0 months o

f ag e I Q difference

s betwee n chUdre

n wit h an d without perinata l complication

s wer e only 5- 7 points fo

rchUdre n from a favorabl

e socia l background ; bu

tfo r infant s livin g i n a lo w socioeconomic environment

, th e I Q difference

s range d from 19-3 7 points . Apparently , perinata l insul tan d th e quaUt y o f th e child' s environmentbot h affecte d development. Similarly

, eve n wit h lo w lead levels , w e migh tanticipat e a

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### combine d effec to f SES , materna

l IQ , th e caretakin

g environment

, inadequat e nutrition , an d lead , eac h o f whic h b y itsel f i s no tsignificant

, bu twhe n combine d wit

h the other

s pose s a cumulativ

e risk o f handicaps in th e developmen to

f cognitive an

d adaptiv e behavior. TH E DEVELOPMENTA

L PERSPECTIV

E Th e epidemiological studie s presente d earUe r o n the toxicolog

y o f lea d have bee n ver

y valuable fo

r dealin g wit h the acut

e effect s o f lea d exposure , bu

tthe y hav e bee n onl

y modestl y helpfu l i n addressing it

s chroni c effects . A developmenta l perspective , i n addition t o defining who i s a trisk , wha ti s wrong , an

d how the diseas e ca

n b e corrected , als o ask

s whatth e cumulativ e risks o n functionin g a ta late r age ar e withi n one' s ecologica l context~an

d ho w thes e advers

e effect s ca n b e compensated for

, reversed , or a

tleas tminimized . Focusing investigativ e effort s o n younger populations ha s othe r advantages whe n on e considers tha tpossible neurologica

l insultresultin

g from lea d takes place withi n a developmenta l context. Samerof

f an d Chandle r (1975 ) pointe d ou

ttha ttha teven serious insult

s suc h a s anoxi a and prematurit

y often have transien

teffects . I

f th e exposure t o lea

d occurre d man y years before , a robus

tdefici tma y notstill b e presen

t becaus e o f the reversibilit

y o f effects . The

y als o pointed ou

ttha tthe severit y o f effec tcoul d b e lessene d b

y a favorable home environment. I n addition , during th e firsttwo year s o f life , brai n growt h i s ver y rapi d an d th e brai n i s mor e vulnerable t

o insult(Dobbing, 1970) . The possibUit y o f differentia l effect s o f lead dependento n the ag e a texposure ha s no tbee

n carefull y investigated . Th e majorit y o f chUdre n evaluate

d i n studie s investigatin g possible subclinica l effect s o f lea d were mor

e tha n five year

s old . I tha s bee n documented (CDC , 1978

) tha tchUdre n between 1 an

d 3 year s o f ag e ar e mos tsusceptibl e t o lead poisoning . Th e subsequen

tevaluation o

f chUdre n tw o o r mor e years afte

r exposur

e t o lea d make s i tdifficul tt o retrospectively determine th e exten tan d duratio n o f a cluld' s lea

d exposure . B

y studyin g younge r population s o f chUdren , th e influenc

e o f uncontroUe

d an d unknown event

s affectin g developmenti s reduce d becaus e o f the recenc

y o f th e lea d exposure . B y addin g th e developmenta l perspectiv

e an d recognizing th e ethica

l Umitation s o f doin g prospective lea

d studie s o n chUdren

, i tseem s tha

t lea d investigators shoul d tak e a lesso n fro

m relate d fields Uk

e nutrition. Decades o

f researc h attempt s in nutritio

n hav e faile d to clarif y a causa l relationship betwee n malnutritio n an d specifi c psychologica

l developmen ta l variable s in chUdre

n (Read, 1982) . A s wit

h malnutrition, itma

y b e PSYOCO-SOOA L FACTOD S 11 1



### impossible t

o isolat e the causa

l effect s o f lea d independen to

f th e social conditions i n whic

h the y occur. Perhap s w e shoul d mov e beyon d th e assumption tha

tther e i s a direc

tcausal relationshi p betwee n lea d exposure , altere

d brai n development , an d impaire d behaviora l function ing an d focu s instea

d on : (a ) mor e systemati c analysi s o

f th e way s i n whic h th e child' s lea

d exposure , socia

l environment , an d earl

y experience interac ti n jointl y to influenc

e th e cours e o

f hi s psychological develop ment , wit h mor e precise assessmen to f

lea d exposur e an d behaviora l development ; (b

) a fulle r understandin g o

f th e mechanism s throug h whic h lea d exposur

e ma y affec tinteUectua

l an d adaptive behavio r development ; an

d (c ) evaluation o

f th e effectivenes s o f

systemati c effort

s t o preven tor reverse the detrimenta l consequence s o f

earl y lea d exposure . This latte rstrateg y has bee n pursue d b y studie s tha thave trie

d to evaluat e th e effect

s o f lea d chelation therap y (se e Rutter , 1980, fo rreview). W e too k a simila rstrateg y wit h a longitudinal an d cross-sectiona l stud y o f th e inteUectual, social , an d neurobehaviora l developmen to

f preschoo l chUdre n expose d to lo w (10-3 0 (ig/dl ) or moderat e (30-6 0 (ig/dl) bloo

d lea d levels . W e asked tw o questions : (a

) Doe s cross-sectional compariso n sho w a significan

tinteractio

n between age an d bloo d lea d levels , betwee n age •an d typ e o f exposur e (occupationa

l vs . nonoccupational) , o

rbetwee n ag e an d th e importan

tbehavior covariate

s o f lea d exposure (socioeconomi c status , materna

l IQ , an d quaUt y o f th e caregivin g environment) ; an d (b)
, Upo n regular five-yearreevaluations , i s ther e a chang e in thes e children' s inteUectual, social , an

d neurobehaviora

l developnesn ttha

tca n b e related t o curren tbloo d level s o

r to cumulativ

e previou s Woo

d lea d level s afte

r removal o

f lea d from thei

rhom e environments ? GENERA L METHODOLOG Y Population s Sample d Severa l source s wer e utilize d t o recrui tsubject s fo r thi s project . Thes e source s included : (a

) referrals from th e statewid e Earl y and Periodi c Screening, Diagnosis , an

d Treatmen

t(EPSDT ) Program ; (b ) referral

s from loca l lea d screenin

g program

s i n Wake , Lencor , an d Ne w Hanove r counties , an

d (c ) direc trecruitmen

to f chUdre n from, families employe d o r residin g nea rlead-relate

d industries . Direc

tcontact , recruitment, an d schedulin g o f subject s wer e don e b y th e PatientCoordinato r through local o r count y healt h department

s unde r th e aegi s of

th e Nort

h Carolina Statewid e Lea d Screenin g Advisor y Committee . A . descriptio n wa s sen tt o al l count y healt h department

s t o infor m them , o f

th e objective s an d resources o

f th e researc h projec tan d to encourag s referral

s a s ne w case s^fiS**--**^ 8 ".a-a ti J, TT*^*" i '•M?^?; ' V-W^V*^ * V - 

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11 2 Toxi c SUBSTANCE S

o f elevate dPb B level s ar e discovered
. Description s of recruitmen t

source s foUow
. EPSDT Program Th e Nort h Carolin aEPSD T Progam , implemente dunde r Titl e XI X of th e Socia l Securit y Ac t (Medicai dLaw) , provide dgenera l medica l screenin g fo r

lowe r incom e families
. A

U Medicai deligibl e famile s wer e informe dtha t

screenin g i s avaUable , bu t participatio n i n th e EPSD T progra mwa s voluntary
. Screenin g wa s performe db y count y healt h department s an dloca l well-bab y clinics
. On e componen t o f th e screenin g progra mwa s alead

poisoning test

performe dbetwee n 1 2 an d6 0 month s o f age . Thi s tes t

determine dth e free erythrocyt e protoporphyri n (FEP ) leve l usin g ahematofluorimete r an dcapillar y bloo dsampl e (fingerprick)
. I f th e leve l o f FEP , ameasur e o f

hem e synthesis , wa s greate r tha n 5 0 p-g/dl , a venipunctur e bloo dsampl e wa s draw n an dsen t t o th e Nort h Carolin a Divisio n o f

Healt h Service s (NCDHS ) fo r bloo dlea danalysis
. I

f th e Pb B level s wer e > 5 0 ug/dl , chUdre n wer e referredt o appropriat e medica l facUitie s fo r

chelatio n treatmen t

t o reduc e Pb B levels
. I f Pb B level s wer e betwee n 3 0 an d5 0 (ig/dl , th e count y healt h departmen t wa s instructe dt o sen dperiodi c bloo dsample s t o th e stat e la b t o monito r Pb B levels
. A hom e visi t tea mwa s als o sen t

t o identif

y th e sourc e o f

lea dan dt o initiat e appropriat e abatemen t procedure s t o eliminat e th e sourc e o f contamina

tion. A flo w diagra mo f th e screening , treatment , an dabatemen t procedure s implemente di n Wak e Count y i s show n i n Figur e 1
. NCDH S provide ddat afro mscreenin g probe s b y th e Environmenta l Epidemiolog y Branc h fo r th e purpos e o f

determinin g th e frequenc y o f occurrenc e o f

elevate dFEP/Pb B case s b y count y durin g 198 1 an dpreviou s years . Thi s procedur e permitte dth e identificatio n o f "ho t spots " fo r

stud y purpose s an dth e evaluatio n o f count y complianc e wit h th e EPSD T P b screenin g program . A lis t o f potentia l subject s fo r

th e propose dstudie s wa s als o obtaine di n thi s manner . Availabl e dat afromNCDH S record s include dbirthdates , sex , race , county , FEP , PbB , an dth e dat e tha t th e bloo dsampl e wa s draw n fromeac h child
. Contac t wit h individua l familie s wa s arrange dan dcoordinate dthroug h count y o r loca l healt h agencie s participatin g i n th e EPSD T Program
. NCDH S ha s perfome dabou t 10,00 0 Pb B analyse s durin g eac h o f th e pas t five years . Elevate dPbB s hav e bee n foun di n 1-12 % o f

th e sample s analyze dfromth e screenin g probes
. Th e highes t incidence s wer e foun di n Lenoi r an dNe w Hanove r

counties , whic h wer e selecte dfo r on e o f ou r studies
. Local Screening Programs P b screenin g i n mos t

area s o f

Nort h Carolin ai s carrie dou t a s a n optiona l par t

o f th e EPSD T Program
. Lenoir , Cabarrus , Ne w Hanover , PSYCHO-SOCIA I FACTOR S 11 3
SCREENIN G PBOCEDUB K

FIGUR E 1
. Screenin g procedure s for th e Ua dScreenin g Program
.

an dWak e Counties , however , hav e organize daggressiv e screening , intervention , an dabatemen t program s i n response t o recent outbreak s o f P b poisonin g i n thes e areas . Subject s fo r ou r earl y studie s wer e referre d primaril y b y th e Wak e Count y Healt h Departmen t an dw e continue dt o stud y thes e chUdren
. W e als o studie dchUdre n frommor e remote part s o f th e stat e b y mean s of

amobU e laborator y i n Lenoi r an dNe w Hanove r counties
. Pb-Industry Target

Populations A variet y o f

majo r P b industrie s ar e locate di n Nort h Carolina
. Childre n whos e parent s wor k i n thes e industrie s constitut e adiscret e populatio n wit h increase dris k o f lea dpoisoning
. Permissio n wa s obtaine d to continu e th e stud y of chUdre n fro mfamiUe s employe db y on e o f thes e P b industries
. Abou t

ha U o f th e subject s wh o participate di n ou r initia l stud y wer e obtaine dfromthi s source . Thes e chUdre n constitute dalarg e par t o f th e five-year

foUow-u p study
. I t

shoul db e note dtha t

th e stud y populatio n consiste do f aself-selecte dsampl e fro mth e lowe r incom e segmen t of th e genera l population ; w e felt tha t concentratio n o n th e lowe r incom e grou p wa s appropriat e i n thi s projec t becaus e lea dpoisonin g i s mos t prevalen t

i n thi s targe t

grou p (se e U.S
. EPA , 1977 , 1986)
. 

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yi^ i

li d TOXI C SUOSTANCE S 

### Experimenta l Desig n an d Statistical Methodolog y Thes e wer

e no texperimenta

l studies , butrathe

r used a cross-sectiona

l observationa

l epidemiologi c design . N o manipulatio n o f independent variable s was made . I

n other words , w e assume d fo r purposes o

f hypothesi s testing a rando m sample representativ

e o f chUdre n Ukel y to b e considered fo

r screening fo

r lea d exposur e i n th e EPSD

T population . Th e principa

l approac h t o analysi s involved multiple regression modellin g wit

h ag e and Pb B a s predictor

s fo r Centra l Nervous Syste

m (CNS ) outcomes . Whe

n considering I

Q a s th e outcome , th e regressio n model s controUe

d fo r age , SES, Home Environmen tScore, an

d materna l IQ . Th e genera l strateg y fb r determining th e bes tmode l paraUele d th e approac h o f Kleinbaum, Kupper

, an d Morgenste

m (1982) . Lea d Analysi s Procedure s A n essentia

l par to f toxicolog y researc h i s the assessmento

f the amoun to f a toxi c substanc

e presenti n a give n system . I n thi s research, bloo d lea d leve l was th e ke

y predictor variabl

e unde r study . Measurements o f blood lea

d and lea d i n hous e pain

tand hous e dus twer

e th e responsibUity o

f the Heav

y Metals Analysi s Laboratory , Departmen

to f Pathology , Universit

y o f Nort h Carolin a a tChape l HU I (UNC-Chape

l HUI) . The laborator

y ha d a variet

y o f trac e analytica

l equipment

, including atomic absorptin

g spectrometer

s (AAS ) tha

tpermi tbot h flam e and flameless atomi

c absorptio

n analysis . Lead in Blood Th e Delve s Cu

p micr o procedur

e (Delves , 1970

) wit h th e modificatio

n by Edige r an d Colema n (1972 ) wa s employe d fo

r whol e blood (an

d plasma ) lead determinations . Th

e Delve s Cup procedur

e was selected o n th e basi s o

f speed , minima

l sample manipulation , an d concomitan

tlo w contamination risk an

d a goo d "trac

k record" in ou

r hands an

d i n othe r laboratories . Speed was a critica l facto r becaus e o

f the larg e volume blood analysi s requirement

s an d relativ e instabUit

y o f blood . Direc

tinsertion o

f bloo d sample s int

o Delves Cup s foUowe

d by drying , preignition , an d atomization o

f th e containe

d lea d i s rapi d and relatively free from contamination problems . A numbe r o f interlaborator

y method compariso

n studie s hav e shown th e Delve s Cu p micr o procedur

e t o b e a s goo d a s o r better tha n other atomi

c absorptio

n or nonatomic absorptio

n techniques . Furthermore, this procedur e i s use d b

y man y laboratorie

s in the CDC proficienc y screenin g program

. 

### •i-Uii

PSYCHO-SCCIAI . FACTOOS 11 5 

### Specia l precaution

s wer e take n t o minimize sample contaminatio n prio r t o analysis . A

U glasswar

e tha tcam e in contac

twit h sample s wa s washed an

d chemicall

y debride d o f meta l contaminant

s b y low-meta

l aci d washing foUowe

d b y repeate d deionize d wate

r rinsing . Reagents , solvent s fo r reagents , an

d othe rassa y material

s wer e selected fo

r ver y sma U o r undetectabl e meta

l contaminan

tcontent. Wit

h huma n subjects , bloo d was coUecte

d int o B- D low-lea d vacutaine

r tube s vi a puncture . QuaUt y contro l wa s maintaine

d b y bot h interna l an d externa l means . Frequen tpreparatio

n an d testing o

f aqueous an

d matrix-matche

d standards o

n a daU y o r weekl y basis was employed to asses s change s i n day-to-da y precisio n an d accuracy

. Externa l monitorin

g o f laborator

y performanc

e wa s achieve d b y participatio

n o f ou r laborator

y i n th e CDC s proficienc y testing fo

rbloo d lea d determination . Furthe

r methodolog y evaluation wa

s don e usin g certifie d blood samples o

f known metal contentan

d provide d eithe rb y a commercia

l sourc e (Kaulso n Laborato ries ) o r by the Ne w Yor

k Stat e Healt h Department

. I n the CDC program , thre e mont h bovin e sample s wer e airmaile

d t o our laborator

y an d analyzed an

d th e results forwarde

d to CDC. Ou

rresults were the n compare d bot h wit h overa U participan

tperformanc

e an d wit h th e mea n value s fo rth e reference laboratories . Ou r overa U performanc

e ha s bee n quit e goo d over th

e rang e o f blood lea

d level s encountered i n th e proficienc y survey . Instrumen tan d Tes tBatter y Developmen t This projec

tha d severa l uniqu e features : th e developmen to f a mobue neurotoxicit

y testing laborator

y tha tpermitte d th e assessmen to

f chUdre n i n remot e cachemen

tarea s wit h sophisticated behaviora

l an d electrophysi ological , measures ; a cooperativ e arrangemen

twit h federal , state , county , an d loca l healt h agencie s an d industr y tha tpermitted th e coordinated screening an

d assessmento

f a trisk chUdre

n acros s th e state ; an d a n opportunit

y t o obtai n valuabl e longitudina

l dat a o n th e long-ter

m effect s o f earl y P b exposur e o n neurobehaviora

l an d cognitiv e development . Thi s projec twas base

d o n a productiv

e collaboratio

n amon g the EPA, th e Universit y o f Nort h Carolin a Schoo l o f Medicine , th e Nort

h Carolin a Division o

f Healt h Services , an

d privat e industry . The addition o f a sophisticated mobil

e laborator

y fo r th e assessmen to

f exposur e signifi cantl y enhanced th e research capabUitie s o f th e team . Behaviora l an d medica l evaluations were carrie

d ou tb y professiona

l staf f from th e Division fo

r Disorder

s o f Developmen tan

d Learnin

g (DDDL) . DDD

L i s a clinica

l trainin g faciUt y tha ti s par to f th e Qui d

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# I 11 6 TOXI C SUISTANCE S 

### DevelopmentResearc

h Institut e an d Biologica

l Sciences Researc

h Cente r (BSRC ) a tth e Universit

y o f Nort h Carolina . Dail y Test

Protocol and Home Visit Collectio n o

f electrophysiologica

l dat a wa s done a

tDDD L o r i n th e field mobU

e laboratory. Demographic, psychometric, an d medica l dat a were obtained i

n a n auxiliar

y traile r o r in spac e provide d b y loca l healt h agencies . FamiUe s wer e see n fo r a testing protoco

l tha ttoo k approximatel

y fou r hours to complete . Informe d consentwas obtaine

d fro m th e parent(s) , wh o als o were asked to sig n a volunteer' s statement. A tth e tim e o f testing , th e examine

r wa s blin

d a s t o th e child' s lea

d exposure . A maximu m o f fou r chUdre n pe r da y could b e evaluated i n di e mobil e laboratory. Afte r evaluatio n da

y a hom e visitwas mad

e fo r severa l reasons . I

f behavior problems wer

e assume d t

o b e related to lea

d exposure , contro

l assessments o

f th e hom e environmen

twoul d hav

e t o b e mad e t o estimat e it s contribution t

o th e child' s hyperactivit

y o r an y other proble

m behavior

. Th e Caldwe U HOM E Inventor

y i s a standardize

d ratin g scale use d fo

r this purpose . Th

e home wa s evaluated a s a vehicl e fo r continued lea

d exposure ; th e lead , i

f discovered , ha

d t o b e removed by cleanin g supervise d b y the count

y healt h department

. Dustsamples from th e livin g roo m carpet , bedroom , and insid e the fron tdoo r wer

e obtaine d b y suctio n o n preweighe d glas s filters and analyze d fo r lea d by x-ra y fluorescenc

e usin g a portabl

e unit . Home wate

r suppl y wa s als o analyzed fo

r lea d b y AAS . Thes e analyses hav

e le d to clea

n u p o f severa l homes an

d a resultan

t reduction o

f Pb B level s o f the lead-exposed chUdre n (Mila r Sc Mushak

, 1982) . Once a

U th e clinica

l dat a wer e gathere d an d evaluated , the chUdre

n were reviewed a

ta staffin

g conferenc

e and an y problem

s discovered during evaluation , whether the y wer e lea d relate d o r not, wer e referre d t o th e appropriat

e loca l communit

y resource

s fo r foUow-up . ChUdre

n wit h Pb B > 5 0 M-g/d l and FE P > 19 0 jig/dl wer

e referred to a hospita

l fo r furthe r evaluatio n and treatmen

to f elevated lea

d levels . Medical, Psychometric, and Behavioral Measures Tabl e 3 summarize

s th e blood lea

d chemistr

y an d medical, electrophysi - ological , psychometric , behavioral , an d demographic measure

s tha twer e coUecte d fro m childre n and parent

s wh o participate

d i n thi s project

. Thes e measures were chose n t

o provide convergen

tinformatio

n from severa

l differen tperspective s in orde

r to elaborat

e mor e clearl y the subtle an

d comple x effect s o f asymptomatic lea

d exposur

e o n CN S development. PSVCHO-SOOAI . FACTOR S 11 7 TABL E 3 Summar y o f

Evaluation s
I
. Exposure Evaluation A
. Fantu s LeadPoisonin g Questionnair e B
. Bloodlea d(PbB) : flameless atomi c absorptio n spectrometr y C
. Fre e erythrocyt e protoporphyri n (FEP) II
. Medical

Evaluation A
. Medica

l history B
. Pediatri c neurological examinatio n C
. Growth : height , weight , hea dcircumferenc e D
. La b tests : BDS , WBC , RBC , Hgb , HCT , MCV , MCH , MCH C ID
. Electrophysiological

Evaluation A
. Slo w Cortical Potential s durin g Sensor y Conditionin g

. B
. Brainste mAuditory Evoke dPotential s C
. Pattern-Reversal Visua l Evoke dPotential s IV
. Psychometric-Behavioral Evaluation A
. Stanford-Binet

Intelligenc e Test—Revise d B
. Bayle y Scale s o f Infant Developmen t

(<3 0 mos . o f

age ) V
. Demographic Covariale Evaluation A . Maternal IQ : Ammon s Quic k Tes t o r Peabod y Pictur e Vocabular y Tes t Revise d B
. Socioeconomi c status : Hollingshea dTwo-Facto r Inde x C
. Qualit y o f caregivin g environment : Caldwell' s Hom e Observatio n fo r Measuremen t o f th e Environmen t D
. Chronologica

l ag e E
. Se x 

### Severa l test s wer e selected o n th e basi s o f guideline s tha

twere later adopte d a ta n Internationa

l Symposium o n Neurobehavioa l Methodology in Pediatri c Lea d Researc h hel d i n Cincinnat

i i n September , 1981 . Thes e guideUne s included : (a

) us e o f standardized , age-norme d test s wit h documente

d vaUdit y an d reUabUit y whe n avaUable ; (b ) us e o f experimenta

l measure s t o evaluat e area s o f function fo

r whic h standardize d measures ar e notavaUable ; an

d (c ) us e o f instrument

s wit h cross-cultura

l compariso n data . An extensiv

e medica l histoi y wa s take

n o n eac h chU d to rul e outa variet y o f problem s relate d t o menta l retardatio

n butno tattributabl

e to lead , an d t o evaluat e lea d exposure history . Th

e instrumentw e use d wa s the Lead Poisoning Study Questionnaire develope d a tth e Fantu

s Lea d Screenin g Clini c a tCoo k Count y Hospita

l in Chicago . Thi

s 28-page questionnair

e examine s pertinen tdemographi c history , prenata l history , clul d developmenta

l mUestones , pas tmedica l history , lea

d poisonin g symptomatology , dietar

y history , famU

y history , immunizations , Ulnesses , vita

l signs , an

d chelation therapy and sid e effects .

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# Jjfe;.J&*7^. •.nahfi&e&f.-'.iteL-zi*: SUDSTANCS S STUD Y I : COMPARISO N O F CHILDRE N OCCUPATIONALL Y AN D NONOCCUPATIONALL Y EXPOSE D T O LEA D Fro m 197 5 t o 1980 , w e conducte d a n interdisciplinar y lea d screenin g ' progra m a s par tof

a progra m projec tgran tfrom th e Nationa l Institut e of Environmenta l Healt h Science s (ES-01104) . Ou r strateg y wa s t o scree n a populatio n no tonl y wit h traditiona l psychometri c measures , bu tals o fo r subclinica l dos e related effect s o f lea d usin g direc tlongitudina l observa tions o f children' s behavior , fo r example , hom e observations , parent/chil d interactions , activit y level , an d slo w wav e brai n potential s tha tmigh tb e developmentaU y relate d t o subclinica l lea d level s an d th e children' s behavior . Suc h a strategy , wit h appropriat e design , migh taUo w a searc h fo r behaviora l threshol d effect s o f lea d whil e avoidin g th e criticism s o f previou s studies . A Nort h Carolin a Memoria l Hospita l cas e repor to f lea d poisonin g i n a famil y from Raleig h uncovere d a highl y stabl e an d cooperativ e populatio n associate d wit h a batter y factory i n Wak e County , wher e th e relative s wer e employed . Th e chUdre n wer e expose d t o lea d dus tbrough thom e an d deposite d i n th e hous e dus tan d i n th e carpets , whic h place d toddler s a tth e crawlin g stag e a trisk (Dolcourt , 1977 ; Dolcourt , Hamrick , OTuama , Wooten , & Baker , 1978) . Fro m 197 7 t o 1979 , w e evaluate d ove r 11 5 chUdren , 4 2 o f

who m wer e chUdre n o f employee s i n tha tplan tan d 104 o f who m me tcriteri a fo r study . W e continu e t o foUo w the m longitudinaUy . Method s Subjects On e hundre d an d fou r chUdre n i n Wak e Count y age d 1 0 month s t o 6 1/ 2 year s a tth e tim e o f

initia l testing s wh o me tinclusio n criteri a serve d a s subjects . The y wer e mostl y blac k (94% ) from lowe r socia l classes—tha tis , x=4. 5 o n th e Hollingshea d Two-Facto r Inde x (Hollingshead , 1957) . ChUdre n previousl y evidencin g CN S diseas e o r insul to r havin g undergon e chelatio n therap y fo r lea d poisonin g an d chUdren wit h ptediagnose d languag e dela y o r menta l retardatio n wer e exclude d from dat a analysis . Approximatel y hal f o f th e chUdre n wer e les s tha n 3 0 month s o f ag e an d hal f

^er e ove r 3 0 month s o f age . Hal f

o f th e subject s wer e EPSD T childre n an d hal f wer e chUdren of

batter y factor y worker s referre d from a loca l count y healt h departmen tt o th e lea d screenin g program a t Nort h Carolin a Memorial Hospita l a s par to f a statewid e screenin g program . PSYCHO-SOCIA L FACTOO

S 

### 11 9 Procedures Subject s wer e evaluate d a tDDD L i n th e protoco l describe d abov e i n General Mtthodolgy, excep ttha tth e onl y electrophysiologica l measure s the y received wer e Slo w Cortical Potential s durin g Sensor y Conditionin g (se e Ott o e tal. , 1981 , for a reporto f results). Result s an d Discussio n A preliminar

y forward stepwis e regression analysi s o f th e relationship o f lea d t o I Q an d 1 8 o

f th e covariate s showe d n o effec to f occupationa l exposure amon g th e presen tcohor to f chUdre n (Haw k & Schroeder , 1983) . Therefore , furthe r analysi s of occupationa l exposur e wa s droppe d an d th e numbe r o

f confoundin g variable s wa s reduced t o HOME , SES , materna l IQ , age , sex , tes t(Bayley versu s Stanford-Binet) , presenc e o f th e fathe r i n th e home , an d numbe r of siblings , i n orde r t o avoi d overcontro l an d Typ e I I errors . Th e mai n statistical mode l use d a multivariat e regression analysi s i n whic h a se tof

a U th e interactio n term s wa s teste d first. I f th e se twer e nonsignificant , a

U interaction s wer e droppe d fro m th e model . Th e secon d ste p wa s t o tes tth e mai n effect s o f th e confoundin g variables . FinaUy , th e tes tfo r th e mai n effect s of lea d wa s performed . An y significan tresultwa s the n furthe r reduce d i n a stepwis e manne r fo r individua l o r linea r combination s o f

variable s fo r inclusio n i n th e final mode l (Kleinbau m e t al. , 1982) . Th e mai n resultwa s tha tther e wa s a significan tlinea r relationship betwee n bloo d lea d leve l (rang e 6-5 9 ug/dl ) an d I Q (F = 7.689 ; d f 1 , 96 , p < .01 ) (Figur e 2). Non e o f th e interactio n term s no r an y o f th e quadrati c o r cubi c effect s wa s significant . O f th e confoundin g variable s onl y SE S wa s significan t(

F = 20.159 ; df

1 , 96 , p < 001 ) an d remaine d i n th e model . Nevertheless , th e mai n effec to f lea d o n I Q remained significant . Th e faUur

e of HOME , materna l IQ , an d ag e t o reac h significanc e a s the v ha d i n othe r studie s wa s Ukel y th e resul to f multicollinearit y wit h SES . Tabl e 4 show s thatth e intercorrelatio n o f thes e variable s wa s high . I t seem s tha twhicheve r o f thes e variable s enter s th e regression equatio n firsti s Ukel

y t o render th e effect s o f th e other s les s significant . Whil e SE S an d HOM E share d a grea tdea l o f variance , on e woul d ordinaril y expec ta direc tmeasur e o f

caregivin g environmen tUk e th e HOM E t o b e a mor e accurat e measur e tha n a n indirec ton e base d o n parenta l occupatio n an d educatio n Uk

e SES . Orde r o f

entr y o f multicoUinea r covariate s int o th e regression equatio n wa s importan ti n determinin g whic h wer e significan t an d whic h wer e not . W e wU I return t o th e matte r o f separatin g th e effect s o f socia l factor s o n th e relationship betwee n lea d an d I Q i n th e Study ill: Replication Study.

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10 5

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III I N = I0 4 r 2 =Q077,F(l,l02)=8.49 l p<0.04 6 IQ=97. 4 -0.34528{PbB )



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### 6 0 6 0
4 5 

### t
_ 6 1 2 1 8 2 4 3 0 3 6 4 2 4 8 5 4

INITIA L BLOO D LEA D LEVE L (yug/dl ) 

### FIGUR E 2
. Initia

l IQ a s afunctio

n o f initia l bloodlea

dlevel s o f childre n screene dfro m1977-1979
.

TABL E 4 Correlatio n Matri x o f Bloo dLea dLeve l an dChil dI Q (1977 ) and Comcomitan

t Variable s VARIABLES Bloo d lea d leve l (PbB ) Chil d I Q Caldwe U HOM E Materna l I Q (MatlQ ) Chronologica l ag e (CA ) 4 Se x Socioeconomi c statu s (SES ) Fathe rpresen t(FaPr ) Numbe ro tsibling s (Sibs ) Pb B
-.27 6 -.26 9 -.19 3 -.06 8 -.07 2 .18 3 -.01 0 .31 4 I Q

.45 1 .37 9 .25 4 .13 0 -.44 9 .16 5 -.28 4 HOM

E

.52 2 .08 9 .12 3 -.62 4 .43 3 -.20 2 Matl Q

.02 9 -.02 8 -.47 5 .17 8 -.17 7 C

A

.06 2 -.14 3 .16 1 .116 SE X

-.06 4 .05 4 -.00 3 SE S

-.49 5 .16 1 FaP

r

-.06 4 PSVCHO-SOOA I FACTOH S 12 1 

### STUD Y II : FIVE-YEA

R FOLLOW-U

P STUDY The basi c objective o

f thi s stud y (Schroeder , Hawk , Otto , Mushak , & Hicks , 1985) wa s to determin e whether asymptomati c lea dexposur e i n earl y childhoo dresultedi n residual altere dCN S functio n i n chUdre n when they reache dschoo l age . Ther e migh t b e laten t

o r cumulativ e effects , even thoug h their

bloo dlea dlevel s woul db e lowe r

becaus e the y hadgrow n ou t

o f th e toddle r

stage
. Method s Subjects Eight y o f th e 10 4 chUdre n fro mStud y I wer e locate dthroug h count y healt h departmen t

an dschoo l record s fiv

e year s later

i n 1983
. O

f th e 80 , 5 0 agree dto reevaluation
. Procedures ChUdre n wer e see n a t th e Wak e County Health Departmen t i n th e mobU e laborator y usin g th e same protoco l a s i n Stud y I , describe dunde r General Methodology, except

that th e hom e visi t

wa s not repeated
. Mos t

o f their bloo dlea dlevel s ha dcom

e dow n (Figur

e 3)
. Result s an d Discussio n The sam e logisti c backwar

dmultipl e regressio n analysi s wa s use da s in th e initia

l study excep t

that initial bloo dlea dleve l wa s use da s th e independen t

variable , curren t

bloo dlea dleve l wa s adde dt o th e Us t o f covariates , an dtes t

an dag e wer e droppe da s covariate s becaus e a U o f th e chUdre n receivedth e Stanford-Bine t I Q tes t thi s time
. Th e tw o lea dscore s were highly correlate d( r = 0.74) ; th e correlatio n o f initia l lea dt o foUow-u p I Q wa s als o significan

t ( r = 0.34 , p < .05)
. The main result

i n thi s stud y wa s tha t

i n th e regression analysi s lea d n o longe r ha dasignifican

t effec t afte r th e confoundin g variable s wer e adde dto th e mode l (

F < 1)
. Apparently , th e decUne i n leadlevels , whU e no t appreciably disturbin g th e relation o f socia l factor s t o lea

dan dIQ , di d negate lead' s relatio n t o I Q whe n confoundin g factor s wer e controUed
. Thi s wa s no t

cause db y self-selectio n bia s a t follow-up becaus e th e demographi c characteristic s o f th e familie s wh o participate dwer e ver y simila r t o thos e wh o di dnot
. I n conclusion , i n th e presen t cohor t o f mainl y lo w SE

S black famiUes , th e covarianc e matri x amon g socia l factor s an dth e relationshi p o f leadt o

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A&y: 12 2 Toxi c SUISTANCE S

O INITIA L BLOO D LEA D
• FIVE-YEA R BLOO D LEA D



### 5-1 0 11-2 0 21-3 0 31-4 0 41-5 0 51-6 0 61-7 0 BLOO D LEA D LEVEL S (pg/dl ) FIGUR E 3 . Frequenc

y distributio n of

bloo d lea d level s o f

chUdre n see n fro m 1977-1978 an d i n follow-u p fiv e year s later . I Q seeme d t o b e fairl y stabl e ove r a five-year period . SE S seeme d t o captur e muc h o f

th e varianc e related t o th e othe r covariate s becaus e of multicollinearit y wit h HOME , materna l IQ , an d age .

STUD Y III : REPLICATIO N STUD Y Th e primar y objective s of thi s stud y wer e t o replicat e th e previou s studie s i n a mor e homogenou s grou p (all-blac k lo w SE S chUdren age d 3- 7 years ) an d t o find th e bes tregressio n mode l base d o n both accuracy and precisio n tha tdescribe d th e relationship o f lea d an d I Q (Haw k e tal. , 1985) . Regressio n analyse s typicaUy eliminat e o r incorporat e control PSYCHO-SOCIA L FACTOR

S 12 3 variable s o n th e basi s of precision, tha tis , whethe r significan tadditiona l variatio n i n one' s outcom e variabl e i s explaine d b y addin g on e o r mor e contro l variable s t o th e mode l comprise d o f outcom e an d predicto r variables . Alternatively , a n unforce d backwar d regression woul d eliminat e al l variable s thatdo no taccoun tfo r a significan tamoun to f varianc e wit h th e outcom e variable . Precisio n i s concerne d wit h rando m error , tha tis , th e siz e o

f th e confidenc e interva l aroun d th e estimate d parameter , tha t can occu r whe n estimatin g effects . Confounding, o n th e othe r hand , i s concerne d with systemati c erro r tha tca n occu r whe n estimatin g effects . Confoundin g i s sai d to exis t(Kleinbau m e tal. , 1982 ) i f a meaningfuU y differen tinterpretatio n of th e relationship o f interes twi U result, dependin g o n whethe r a n extraneou s variabl e i s ignore d o r include d i n one' s dat a analysis . Confounding , then , i s concerne d wit h th e issu e o f validity , tha tis , whethe r on e ha s th e rightanswer . Kleinbau m e tal . (1982 ) suggeste d a n analog y to targetshooting : validit y (confounding ) i s concerne d wit h whethe r o r no ton e i s aimin g a tth e correc tbuU' s eye , whil e precisio n i s concerne d with individua l variatio n fro m sho tt o shot , give n th e actua l bidl' s ey e involved . Accordin g t o Kleinbau m e tal . (1982) , whil e bot h precisio n an d confoundin g mus tb e considere d an d incorporate d durin g th e modelin g process , for etiologi c question s (suc h a s th e question s addresse d i n thi s study ) confounding , o r validity , usuall y take s final precedenc e ove r precisio n i n th e determinatio n o f th e final model . Thes e issue s wer e addresse d i n th e replication. Method s Subjects Eight y blac k chUdre n age d 3- 7 wer e recruite d fro m hig h ris k neighborhood s i n Lenoi r an d Ne w Hanove r countie s i n cooperatio n wit h count y healt h agencie s an d th e Environmenta l Epidemiolog y Branc h (EEB ) o f

th e Nort h Carolin a Divisio n o f Healt h Services . Mos to f th e member s o f

th e Ne w Hanove r sampl e wer e enrolle d i n th e Headstar t Program . A Us to f

criteri a tha tdefine d th e eUgibUit y o f individua l chUdre n fo r inclusio n i n th e stud y wa s provide d t o referrin g healt h agencies . Eligibilit y criteri a ar e specifie d below . 1 . Ag e 2 . Rac e 3 . Healt h status/histor y 3- 7 year s Blac k Subject s coul d no thav e an y curren t acut e o r chroni c Ulnes s o r b e unde r medicatio n o f

an y sort . Perinata l his -

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a 12 4 Toxi c SUBSTANCE S

4
. Lea dexposur e histoi y

5
. Socioeconomi c statu s

6
. I Q tor y shoul db e fre e of complications
. Subject s shoul dno t

hav e an y histor y o

f neurobiologica l insults
. Chil dshoul db e asymptomati c an d neve r hav e receive dchelatio n therap y o r bee n treate dfo r

lea dpoisoning
. A rang e o f Pb B level s fro m5-6 0 p.g/d l wa s desired
. Onl y lo w incom e familie s define da s Clas s I V o r V (Hollingshea dScale ) wer e Included
. EPSD T famiUe s wer e in

clude di n thi s group . I n orde r t o exclud e an y chUdre n wh o wer e clearl y mentall y retarded, amini

mu msubjec t

I Q o f 6 0 wa s required. Procedures Th e sam e procedure s a s outline di n th e Genera l Methodolog y sectio n wer e performed
. Base do n th e results o f ou r previou s studies , covariate s i n th e presen t

stud y wer e restricte dt o HOME , SES , materna l IQ , age , an d gender
. Result s an d Discussio n O f th e 8 0 chUdre n screened , 7 5 me t th e inclusio n criteri aan dwer e use dfo r analysis
. Thei r

demographi c characteristic s ar e give n i n Tabl e 5
. Th e mea n socioeconomi c statu s o f thi s grou p wa s lowe r

tha n othe r

group s tha t w e hav e studied
. Also , th e lo w materna l inteUigenc e score s reflect th e

TABL E 5 Demographi c Characteristic s o f Childre n i n th e Replicatio n Stud y DEMOGRAPHI C CHARACTERISTIC S MEA N SCOR E S D RANG E Mea n bloo d lea d leve l (|tg/dl ) Hig h bloo d lea d leve l (jig/dl ) Mos trecen tbloo d lea d leve l (|ig/dl ) Mos trecentFE P (iig/dl ) - Hom e caregive r practice s (Bradle y fc Caldwell , 1976a , 1979b ) Materna l I Q (Dun n fc Dunn . 1981 ) Chronologica l ag e (mos. ) Socioeconomi c clas s (Hollingshea d Tvwj-Facto r Index ) 21.8 0 26.7 1 20.6 5 32.7 4 59.8 4 63.4 1 58.4 0 4.9 1 9.7 6 6.00-39.0 0

14.1 1 6.2O-56.0 0 9.7 3 6.20-47.4 0 14.0 3 8. 0 -193. 0 15.0 8 11.2 9 11.7 4 0.2 0 20-4 7

40-9 4 39-9 1 4- 5 PSYCHO-SOCIA I FACTOR S 12 5

ne w revise dnorm s fo r th e Peabod y Pictur e Vocabular y Test , Revise d (PPVT-R ) (Dun n & Dunn , 1981) , whic h ar e les s comparabl e t o th e mor e commo n adul t

inteUigenc e test s suc h a s th e Wechsle r Adul t InteUigenc e Scal e (WAIS) , bu t

whic h ar e perhap s mor e vaU dtha n th e Ammon s Quic k Test
. STATISTICA L ANALYSI S

STRATEG Y FO RASSESSIN G INTERACTIO N AN D CONFOUNDIN G O F SOCIA L

FACTOR S Th e mai n objectiv e of

th e statistica l analysi s strateg y wa s t o fin dth e mode l tha t

bes t describe dth e relationship betwee n lea dan dIQ
. Th e principa l approac h t o analysi s involve dmultipl e regressio n modelin g wit h bloo dlea dleve l a s apredicto r variable , chil dI Q a s th e outcom e variable , an dage , SES , HOM E score , gender , an dmaterna l I Q a s contro l variables
. Th e contro l variable s wer e restricte dt o thos e five tha t ha dprove n sigrufican t

i n ou r earlie r studie s i n orde r

t o reduc e Typ e I I error s cause db y overcontrol
. Typ e I error s wer e controUe db y focusin g o n on e confirma

tor y hypothesis-tha t

bloo dlea dlevel s woul db e significantl y relate dt o chU dIQ-whU e controUin g fo r SES , materna l IQ , HOM E (caregivin g environment) , gender , an dage . Explorator y analyse s wer e performe dt o findth e mos t

accurat e an dprecis e mode l tha t describe dth e relationshi p betwee n lea dan dI Q an dthei r covariates
. 

### Method s TT,e genera l strateg y fo r determinin g th e bes t

regressio n mode l wa s th e sam e hierarchica l logisti c modelin g strateg y o f Kleinbau me t

a l (1982 ) a s wa s use dbefore
. Thi s strateg y incorporate dth e assessmen t o f confoundmg , "Inaction , an dprecisio n int o th e selectio n o f variable s fo r th e final model
. A backwar dstepwis e multipl e regressio n approac h wa s use dmwhic h interaction s (Pb B x age , Pb B x SE S Pb B x MI O Pb B x HOME ) wer e teste dfirst followe db y th e se t

o f possibl e confoundin g covanat e effects , followe db y examinatio n o f mai n effect s of

lea dan dI Q Thi s approac h involve dtestin g fo r ase t o f variable s (e.g. , a

U th e S ^ T l e r n S h.' n "" a° Ver u " t6S t (Chun k

test > rathe r

*a n testin g fo r ^te^bil^o f

hS fi , ea< ^ f , e x P ' t 0 6nhanc e th e simplicit y 8 a n d interpretabUit y of

th e final model
. Test s tha t attaine dsienificanc e o r nea r sigmficanc e wer e the n foUowe db y stepdow n £ F££ Zynyvin^i-.a^fwittju^iy j

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12 6 Ton e SUISTANCI

B regression) test s t o identif y specifi c variable s tha tshoul d b e retaine d i n th e final mode l t o increas e it s precision . I f th e overa

U tes tresults wer e no t significant , thes e term s wer e droppe d fro m th e final model . However , simpl y usin g stepwis e regressio n t o obtai n a bes tregression mode l can lea d t o misleadin g interpretatio n o f dat a becaus e th e issu e o f confoundin g i s no tautomaticaU y addresse d b y suc h analyse s (Kleinbau m e tal. , 1982) . Explorator y analyse s wer e the n performe d t o find th e mos taccurate and precis e model . A variabl e (e.g. , age , SES , etc. ) determine d t o b e a nonconfounde r migh tstU l b e retained i n th e mode l t o increas e precision; tha tis , th e variabl e migh tsignificantl y contribut e t o th e tota l variability i n I Q ove r an d abov e wha ti s contribute d b y th e othe r variable s remaining i n th e model . Similarly , eve n thoug h confoundin g ma y b e presen twithi n a se to f variables , i tma y b e tha tsom e smaUer subse ti s a U tha ti s require d fo

r control , whU e providin g increase d precisio n i n estimatin g th e associatio n o f interest . Procedure s Findin g th e mode l tha tbes tdescribe d th e dat a i n term s o f bot h precisio n an d confoundin g wa s accomplishe d i n th e foUowin g way . A gold standard, tha tis , a baselin e o r standar d adjuste d estimat e o f association , wa s compare d wit h adjuste d estimate s of associatio n tha taccounte d for othe r combination s o f

th e extraneou s variables . Th e gol d standar d wa s th e mode l obtaine d i n th e backwar d regression analysi s tha tcontroUe d fo r a U interaction s bu tkep ta U th e contro l variable s i h th e model . A subse tof thes e variable s tha tgav e nearl y th e sam e adjuste d estimate s o f th e regressio n coefficien t(p ) fo r Pb B wa s the n a candidat e fo r selection . Th e firstmode l t o b e compare d t o thi s gol d standar d wa s obtaine d i n th e backwar d regressio n tha teliminate d contro l variable s i n term s of precisio n (findin g th e factor s tha texplaine d th e mos tvariabUit y i n th e dependen tvariable) . Thi s answere d th e questio n o f whethe r th e mos t precis e mode l wa s als o th e mos tvaU d model . I

f th e tw o model s wer e no t th e sam e (i.e. , th e mos tprecis e mode l wa s not th e mos tvaU d model) , othe r model s wer e chose n base d o n logic , prediction s fro m pas tUterature , an d examinatio n o f

th e step s o f

th e origina l backwar d elimination . Th e f l coefficient s obtaine d fro m thes e variou s genera l linea r model s wer e compare d t o th e gol d standar d an d thos e mos tsimila r wer e the n use d t o calculat e confidenc e interval s fo r eac h model . Th e formul a use d fo r thi s calculatio n wa s a s foUows : £ -1 - ( T 64 , .975 ) (Sfl) . Th e mode l wit h th e smaUes tconfidenc e interva l i s th e mode l wit h th e greates tprecision , that is , di e mos taccurat e an d precis e model . PSYCHO-SOOAI . FACTOR S 127 

### Result s an d Discussio n IQ Results Result s of

th e confirmator y univariat e analysi s o f th e relation o f currentbloo d lea d leve l t o I Q ar e show n i n th e summar y tabl e (Tabl e 6 ) below . Sinc e th e chun k tes tof interaction s an d contro l variable s wer e nonsignificant , eac h se twa s droppe d fro m th e model . Explorator y test s usin g maxima l (historicall y highes tleve l obtaine d fro m PubUc Healt h Departmen trecords ) an d mea n Pb B level s wer e als o don e t o furthe r clarif y th e effect . Tabl e 6 show s tha tther e wa s a ver y stron g negativ e linea r relationshi p betwee n bloo d lea d level s an d IQ , irrespectiv e o f whic h Pb B inde x wa s used . Result s o f test s fo r quadrati c an d cubi c component s wer e no tsignificant . Figur e 4 show s a smoot h Unear relationship betwee n th e highes t(47. 4 ug/dl ) an d th e lowes t(6. 3 p-g/dl ) bloo d lea d levels . Result s of

the Exploratory Analyses Althoug h th e multipl e regressio n analysi s fo r th e interactio n term s usin g th e overa

U chun k tes twa s no tsignificant , th e on e fo r contro l variable s approache d significance , suggestin g tha ta mor e accurat e an d precis e mode l coul d b e found . Furthermore , inspectio n o f Tabl e 7 show s that , whil e th e regressio n mode l wit h lea d an d I Q alon e (includin g n o covariates ) wa s th e mos tprecise , tha tis , ha d th e smaUestconfidenc e interval , th e coefficien tfo r lea d differe d considerabl y fro m tha to f th e gol d standard , tha tis , th e mode l tha tinclude d lead , IQ , SES , HOME , materna l IQ , age , an d gender . Therefore , stepdow n backwar d regressio n analyse s wer e performe d i n whic h eac h variabl e wa s considere d individuaUy . N o interactio n variable s wer e foun d t o b e significant , eve n whe n considere d individuaU y i n th e backwar d stepwis e regression . Whe n backwar d regression continue d usin g a U singl e independen tvariable s (e.g. , Pb B an d contro l variables ) wit h n o forcing , SE S wa s th e firstvariabl e t o b e eliminated , foUowe d b y age , gender , an d the n HOME , whU e materna l I Q TABL E 6 Summar y Table of th e Confirmator

y Analysi s o

f th e Relatio n of

Blood Lea

d & I Q Univariat

e F, p
EFFEC T USIN G CURRENT Pb B STANFORD-BINE T I Q TES T USING MEA

N Pb B USIN G HIGHES T Pb B Interaction s Contro l Ua dPb B R 0.55 , 0.7 4

1.82 , 01 2 12.31 , 0.000 8 0.144 1.01 , 0.4 2 1.86 , 0.1 1 10.08
. 0.00 2 0.12 1 1.34
. 0.2 6 1.76 , 0.1 3 10.55 , 0.001 8 0.12 6iVS' K

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c SUBSTANCE

S remaine d i n th e mode l wit h lead . Lea d an d maternal I Q wer e foun d t o b e significan tvariable s i n relationship t o chil d IQ . Thatis , th e mode l tha t include d onl y thos e variable s sharin g a significan tamoun to f varianc e wit h the ' dependen tvariabl e wa s th e mode l comprise d o f lea d an d materna l IQ . However , compariso n of th e coefficien tfo r lea d i n thi s mode l (IQ , lead , an d materna l IQ ) wit h th e gol d standar d (fro m th e stepwis e regression tha teliminate d al l interaction s bu tkep ta U singl e variables ) indicate d tha tther e wa s a discrepanc y betwee n thei r value s thatseeme d t o b e substantia l (Tabl e 7) . Therefore , othe r model s employin g differen t combination s o f

term s wer e examine d (IQ , PbB , SES , materna l IQ , HOME ; IQ , PbB , age , materna l IQ , HOME , gender ; IQ , PbB , materna l IQ , HOME ; IQ , PbB , materna l IQ , HOME , gender) . Similarit y o f thei r coefficient s fo r lea d t o tha tof th e gol d standar d wer e assesse d an d size s o f th e confidenc e interval s wer e calculate d fo r each . Th e mode l wit h th e smaUes tdifferenc e i n & coefficien tfo r lea d fro m tha to f th e gol d standar d tha tsti U maintaine d a sma

U confidenc e interva l wa s IQ , PbB , materna l IQ , HOME , an d gender . Thatis , th e mode l thatbes tcontroUe d fo r confoundin g wit h th e greates tprecisio n (i.e. , th e mos taccurat e an d



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## 1 5 2 0 2 5 3 0 3 5 4 0 4 5 5 0 

# BLOO D LEA D LEVE L (jig/dl ) FIGUR E 4 . Chil d I Q a s a functio n o f bloo d lea d level s of

childre n screened i n th e replicatio n study . PSYCHO-SOOAI . FACTOB S 12 9 precis e model ) containe d lead , materna l IQ , HOME , an d gender . Nevertheles s tw o othe r model s (IQ , PbB , age , gender , HOME , an d materna l IQ ; IQ , PbB , gender , HOME , an d materna l IQ ) gav e acceptabl e accuracy an d precision . A U th e model s i n Tabl e 7 wer e significan tbeyon d th e p<.0 1 level . Th e exploratory analyse s demonstrate d tw o importan tpoints : th e mos tprecis e regressio n mode l ma y no talway s b e th e mos taccurat e on e i n th e assessmen to

f confoundin g socia l factor s o n th e lead-I Q relation ; an d i f bot h precisio n an d accurac y ar e considered , the n HOM E environmen twa s mor e precis e an d accurat e tha n SE S i n th e populatio n studied . SE S i s a rathe r crud e measur e tha tma y no taccuratel y reflec tth e heterogeneit y o f caregivin g practice s amon g lowe r SE S familie s (Dietric h e tal. , 1985 ; Elardo , Bradley , & CaldweU , 1975 ; Ramey , Farran , & CampbeU , 1979 ; Whit e & Watts , 1973) . Indee d th e relatio n o f HOM E scor e t o SE S ma y b e differen tfo r differen tsocia l classes . Recently , BeUinger , Needleman , Leviton , Watemaux , Rabinowitz , an d Nichol s (1984 ) foun d tha tHOM E score s wer e positivel y relate d t o umbiUca l cor d bloo d lea d level s i n uppe r middl e an d uppe r clas s inne r city Bosto n families , jus tth e opposit e o f wha tha s bee n foun d wit h lowe r SE S families . Therefore , SE S an d HOM E ar e no tinterchangeabl e measures . Considerabl y mor e stud y o f thei r interrelationship s i s needed . Th e presen tstud y suggest s tha tassessment s
TABL E 7 Accurac y an d Precisio n o f Differen tModel s o f

Regressio n o f

Bloo d Lea d Level s o n I Q Includin g Differen tCombination s o f Variable s a s Candidate s fo r Contro l Variable s

CANDIDAT E SUBSET P COEFFICIENT * 93 % CONFIDENC E INTERVA L l$xit*i,mnsb»i 1 . Age,SES,Cender,HOME,MlQ.PbB,IQ * 2 . Age , Cender,HOME.MIQ.PbB.l Q 3 . SES , HOME.MlQ.PbB.l Q 4 . Cender,HOME,MIQ,PbB,IQ , 5 . HOME,MlQ.PbB,I Q 6 . MIQ.PbB.IQ 7 . PbB.l Q -0.25 4 -0.24 8 -0.28 2 -0.25 5 -0.27 3 -0.39 6 -0.45 6 0.049 "

0.05 1 0.02 1 0.04 3 0.02 6 -0.10 2 -0.19 6 -0.558- a

-0.54 8 -0.58 5 -0.55 4 -0.57 2 -0.63 7 -0.71 5 0.607 * 0.59 8 0.60 6 0.59 7 0.59 8 0.53 5 0.52 0 'Thi s i s th e f ) coefficien

tfb r lea d 'Lowe r bound o

f th e confidenc e interva

l c Uppe r bound o f

th e confidenc e interva

l ^Absolut e difference betwee n th e lowe r and uppe r bound s o f th e confidenc

e interva l •TT-i e baselin e model o r gold standard wit h al l control variable s include d Th e matc

h to th e gol d standard wit h leas tconfoundin g ( p coefficien tfo r lead tha

ti s closes tto tha

ti n th e gold

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### *% - .** * 13 0 Toxi c SUBSTANCE S
o f thei r precisio n and

accurac y ar e importan t criteri at o conside r

i n choosin g th e bes t

regression mode l fo r

lea dan dIQ
. GENERA L DISCUSSIO N Lea d Exposur e an dI Q i n Childre n Considerabl e controvers y exist s concernin g th e effect s of lo w t o moderat e P b exposur e o n cognitiv e function , a s indexe db y standar dI Q tests , i n chUdre n (U.S
. EPA , 1986)
. Result s o f th e repUcation stud y provid e ver y stron g evidenc e ( p < .001 ) i n youn g chUdre n o f acontinuou s linea r decreas e i n I Q (Stanford-Bine t Fu U Scale ) wit h increasin g bloo dlea dleve l acros s awid e rang e (5-4 7 p-g/dl)
. Thi s confirmator y findin g i s particularl y compellin g becaus e th e potentiall y confoundin g facto r of socioeconomi c statu s wa s effectivel y controUe db y selectin g aver y homogeneou s grou p o f chUdre n (mostl y SE S Clas s V)
. Result s o f

th e five-year

follow-u p stud y provide dfurthe r clarificatio n o f th e long-ter meffec t

o f P b exposur e o n IQ
. Initia l assessmen t o f thes e chUdre n age d1- 6 i n 1977-197 8 showe dth e sam e invers e linea r relationship o f

Pb B an dI Q a s foun di n th e repUcation study
. I n addition , adissociatio n o f

materna l an dchil dI Q (Perin o & Emhart , 1974 ) wa s foun d ( r = 0.058 ) i n chUdre n belo w 3 0 month s o f ag e wit h elevate dPb B level s ( a 3 0 tig/dl)
. Fiv e year s late r th e Pb B level s o f

al l chUdre n retestedha d droppe dt o £ 3 0 p.g/dl
. Afte r controllin g fo r

possibl e confoundin g variable s (SE S an dHOM E caregive r scores) , n o significan t

P b effec t o n I Q wa s apparen t

an dth e previousl y observe ddissociatio n o f materna l an d chU dI Q wa s n o longe r presen t ( r = 0.451)
. Thes e observation s sugges t tha t I Q decrement s associate dwit h undu e P b absorptio n i n th e lo w t o moderat e rang e ma y b e reversibl e i f appropriat e abatemen t

procedure s ar e take n t o reduc e bod y P b burden s i n youn g chUdren
. However , thes e chUdre n mus t

b e foUowe dint o adulthoo dt o seriousl y tes t thi s hypothesis
. Assessin g th e Effect s o f th e Caregivin g Environmen t an d Othe r Socia l Factor s I n a U o f th e presen t

studies , socioeconomi c status , materna l IQ , an d HOM E score s wer e highl y interrelated
. Th e combinatio n o f thes e thre e covariate s seem s t o b da t th e sourc e of

multipl e pathway s tha t affec t th e relationshi p betwee n lea dexposur e an dIQ
. I t seem s tha t

avariet y o f socia l factor s mus t

b e considere dfo r

agive n populatio n an dtha t a considerabl e amoun t

o f additiona l research wi U b e neede dbefor e th e piece s ca n a

U b e fittedint o th e mosai c tha t wil l yiel dacoheren t

pictur e of PSVCHO-SOCIA I FACTOI S 13 1 thes e interrelationships
. Belo w w e conside r som e o f

th e mai n interrela

tionships o

f th e socia l covariate s of lea dexposur e i n chUdren
. HOM E Score s I n th e curren t

researc h HOM E score s wer e consistentl y relatedt o materna l IQ , SES , an dpresenc e of th e fathe r

i n th e hom e (se e Tabl e 4)
. Thi s las t variabl e wa s als o highl y relatedt o SES
. Fathe r absenc e wa s probabl y mor e o

f asocioeconomi c variabl e i n tha t i t wa s relatedt o th e mother' s receiving publi c assistance
. A relatedeffec t wa s tha t

singl e mother s an dthei r

chUdre n ofte n Uve dwit h relative s a s par t o f a n extende dfamil y resourc e network
. Familie s wh o lacke dthes e othe r breadwinner s tende dt o b e mor e indigen t an dmor e sociaU y isolated
. Th e relatio n o

f HOM E score s t o bloo dlea dleve l als o seem s t o var y wit h age . Milar

e t al
. (1980 ) foun dasignifican t relationship o f

HOM E score s t o bloo dlea dlevel s an dBayle y MD I score s i n th e 11-3 0 mont h ag e range , bu t

no t i n th e 31-7 2 mont h range . Dietric h e t al
. (1985 ) found , i n a comparabl e inne r

cit y populatio n i n Cincinnati , asignifican t relationship o f neonata l umbilica l cor dbloo dlea dlevel s an dHOM E scores , whic h tende dt o increas e fro m1 t o 1 5 month s o f age . However , thi s i s jus t th e opposit e of

wha t Bellinge r

e t al
. (1984 ) foun di n a n uppe r middl e an d uppe r clas s whit e populatio n i n arenovate dinne r cit y Bosto n area . S o i t seem s tha t

ther e ma y b e acomple x ag e x SE S x rac e interactio n wit h HOM E score s tha t

ma y b e relatedt o exposur e t o lea dan dit s relationshi p toIQ
. Socioeconomic Status Doe s SE S protec t

o r compensat e fo r

developmenta l ris k

cause db y pre an dperinata l neurotoxi c insult s Uk e lea dexposure ? I n th e presen t experiments , an dcertainl y i n mos t of th e experiment s discusse di n Tabl e 1 , SE S tende dt o accoun t fo r agrea t dea l o f th e varianc e foun di n th e relationship betwee n lea dan dIQ
. However , a s discusse dabove , thi s seem s t o depen dgreatl y o n th e age , sex , an drac e o f th e populatio n studied
. SE S i s apassive , rathe r crud e measur e o f

caregivin g environ

ment
. Studie s b y Samerof f an dChandle r

(1975 ) indicat e tha t

SE S ca n indee dbuffe r

physiologica l insult s i n th e pre - an dperinata l period
. However , thi s ma y no t alway s b e th e case , give n th e natur e o f som e neurotoxi c risks
. Fo r

example , Bellinge r

e t al
. (1984 ) foun dapositiv e relationshi p betwee n HOM E scor e an dumbilica l cor dlea di n a n uppe r middl e an duppe r

clas s .whit e populatio n livin g i n anewl y renovated inne r cit y Bosto n area . Thus , i n thi s cas e hig h SE S place dchildre n a t a highe r ris k fo r lea dexposur e (fro mth e dus t fro mth e lea dpain t

o n ol d building s tha t

ha dbee n tor n dow n o r sandblasted)
. Further , caregivin g: ' -'M?:^'?^^ ^ •



### :!&*:• 13 2 Toxi c SUBSTANCE S 

### practice s pe r

s e may b e overshadowe di n suc h asettin g b y th e risk s associate dwit

h housin g environment s chosen a s aresult o f havin g ahigh socioeconomi c status
. O n th e othe r hand
. Whit

e (1982) , i n ameta-analysi s o f 20 0 studie s relatin g SE

S t o academi c achievement , foundtha t amuch highe r correlatio n betwee n hom e atmospher e an dacademi c achievement tha n i n an y othe r

combinatio n o

f SE S indicators
. The more importan t variable s wer e childrearin g practice s an dstimulatio n o f learnin g a t

home an da t school , an dno t

parents ' occupation , income , o r education
. ChUdre n livin g i n socially disadvantage dsetting s ma y hav e fewe

r opportunitie s fo

r suc h experiences , but

thi s doe s no t

automaticaU

y confe r advers e ris k

upo n them
. Rather , th e ris k seem s t o U

e i n th e combinatio n o

f HOME , SES , an dmaterna l IQ
. Maternal IQ I n th e presen f

studie s maternal I Q wa s highl y relate dt o HOM E scores , SES , an dchil dI Q i n Experiment s I , U , an dU I an dwit h bloo dlea

d leve l i n experimen t

H I (r = 0.314 , p < .007)
. There wa s agreat dea l o f heterogeneity amon g th e mother s o f th e chUdre

n i n th e curren t

studies , both i n inteUectua

l leve l an di n childrearin g practices
. Many o f th e mother s wer e ver

y conscientious , bu t

other s engage di n harsh disciplinar y practice s an dprovide donl y aminimu mo f stimulatio n fo

r thei r chUdren i n th e home
. HOME score s range dfrom20-8 7 i n Study Ul , fo r instanc e (see Tabl e 5)
. I n particular , th e mos t indigen t mother s displaye ddepression , showin g Uttl

e positiv e affec

t towar dthei r

chUdren
. Dietric h e t

al
. (1985 ) als o reported alac k

of emotiona l responsivit

y o f caregivers , whic h wa s relatedt o lac

k o f chil dsupervisio n an dt o lea dexposure . Maternal I Q may als o b e relate dt o neglec t o f chUdren' s nutritional needs
. I n th e presen t

studie s nutritio n wa s controUedb y excludin g fro m stud y thos e subject s with nutritiona l deficiencies , suc h a s iro n deficien

cies
. Bu ti n everyda y lif

e ther e are many way s i n whic h borderlin e nutritiona l deficiencie s ma y affec t leadexposure (Mila

r & Schroeder , 1983) : (a) b y servin g a s anutritiona l basi s fo r pic a(Snowdon , 1977) ; (b ) b y alterin g susceptibiUt

y t o lea dintoxicatio n becaus e o f deficiencie s i n iron , copper , chromium , zinc , calcium , an dVitami n D , a U o f whic h compete with lea dfo

r protei n bindin g site s (Mahaffe y & Michaelson , 1980) ; (c ) becaus e o

f persistenc e o

f mouthin g an dpic ao

f peopl e with menta l retardatio n o r

autis mint o adulthoo d(Danfor d& Huber , 1982)
. Multipl e Path s an d Expression s o f Neurotoxi c Effect s o f

Lea d Ther e ar e man y path s b y whic h socia l factor s ca

n affec t th e relationshi p betwee n lea

dan dIQ
. Certainly I Q i s by fa r th e mos t we U PSYCHO-SOCIA L FACTO-R S 13 3



### studie dneurotoxi c effec

t o f lea dexposure in chUdren
. However , ther e ar e othe r effect s o f lea dexposure , suc h a s fine motor , perceptual-motor , reaction time, sensory-neural , an devoke dan dslo w wav e potentia l electrophysiologica

l effects , whic h hav e als o bee n demonstrate dan dfor whic h th e effect

s o f socia l factor s hav e hardl y bee n studied
. Ther e ar e als o many other

stressfu l biologica

l effects o f lead , fo r example , hematological , nephrological , cardiovascular , endocrine , an dgastroenterologica l effects , whos e interactio n wit

h neurotoxi c effects hav e not bee n addresse da t

aU
. Such acomple

x vie w o f neurotoxicit

y renders i t

difficult t o stud y (Weiss , 1980)
. Indee dBornschei

n (1985 ) ha s criticize dtraditiona l main effects model s a s inadequate fo

r reflecting th e complexit

y o f huma n neurotoxi

city
. In hi s view , adynami c interactional longitudinal mode l a s Ulustrate d i n th e us e o

f structura l equation s i s preferable
. However , suc h model s wil l als o hav e t o cop e wit

h suc h source s o

f erro r a s sampling , attrition , history , maturation , differen

t tes t instrument s fo

r differen t ag e groups , statistica l regression, heterogeneit

y o f covariate s ove

r time , etc
. (Balte s & Nesselroade , 1979)
. Fo

r instance , SE

S migh t b e fairly stabl e ove r

time i n a lo w SE S grou p caugh

t i n th e povert

y cycle , bu t

quit e differen t

i n a n upwardl y mobU

e middl e clas s group . Such achang e migh t easU y affect th e relationshi p o

f lea dexposur e t o I Q over

time
. Nevertheless , longitudina l studie s wU

I Ukel y provide mor

e conclusiv e answer s t o th e man y question s concernin g th e neurotoxi c effect s o f leado n retardation o

f cognitiv e an d adaptiv e development
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### % :-f- •'-'•iajiJ^S**'*,* 1



### A<AA7m% A77')<:'•• 

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: 

# : : 

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