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### Document

Number: 

# 31 ) II-C-2

Docket Number: 

# A-83-2 2

Printed 4/16/20089:12:07AM

Sheet 31 of 97P. 2

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. / > >-P 3 - 2 - \ UNITE D STATE S ENVIRONMENTA L PROTECTIO N AGENC Y JT , C - 2

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? ^R Z ? Offic e o f Ai r Qualit y Plannin g an d Standard s { SyT*~J Researc h Triangl e Park , Nort h Carolin a 2771 1

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3 RECEIVEO^ Tn M

ENVIRONMENTAL PROTECTIO N

AGENC Y 

### JU L 

### 1 2 198

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Dr . Pau l Koti nCENTRA L DOCKE T 450 5 Sout hYosemit e SECTIO N
Denver , Colorad o 8023 7
Dea r Dr . Kotin : Enclose dfo r you r review an d commen t i s th e staff' s identificatio n an ddiscussio no f th e majo r issue s raise da t th e Septembe r 14-15 , 198 3 Clea nAi r Scientifi c Advisor y Committe e (CASAC ) Ris k Assessmen t Subcommitte e meeting . I

nadditio nt o describin g th e majo r issues , w e provide dresponse s and/o r outline dwha t effort s hav e bee nundertake nsinc e th e meetin g t o addres s th e question s raised . Th e principa l purpos e o f th e enclosur e i s t o mak e sur e tha t w e hav e properl y characterize dth e Subcommittee' s comment s an d hav e identifie d majo r area s o f concer ns o they ca nb e properl y

addresse ddurin g th e developmen t o f th e lea dris k assessmen t program . I f w e hav e inadvertentl y misinterprete dcomment s mad e a t th e meetin g o r omitte dan y importan t issues , pleas e le t u s know a s soona s possible . W e o f cours e wil l mak e al l suc hcorrespondenc e availabl e t o othe r member s o f th e Subcommitte e a s wel l a s th e publi c (uponrequest ) s o everyon e wil l b e kep t informed . Pleas e direc t an

y comment s yo u ma y

hav e t o Tom

McCurdy . I f yo u hav e an y questions , pleas e fee l fre e t o cal l To m a t (919 ) 541-5655 . Inaddition , I woul dlik e t o thank Subcommitte e member s fo r participatin g i nou r Septembe r meeting , and especiall y appreciat e Dr . Anit a Curran' s fin e jo bo f chairin g th e meetin g i nyou r absence . We loo k forwar dt o hearin g fro m yo uo nthes e matters . Sincerel y

yours , /•* / Josep hPadget t Directo r Strategie s an

d Ai r Standard s Divisio n Enclosur e

cc : Subcommitte e Member sP. 3

AMBIEN T STANDARD S BRANC H STAF F IDENTIFICATIO NAN D DISCUSSIO N O F ISSUE S RAISE D A T TH E SEPTEMBE R 14-15 , 198 3 MEETIN G O F TH E CLEANAI R SCIENTIFI C ADVISOR Y COMMITTE E SUBCOMMITTE E O N RIS K ASSESSMEN T

Introductio n AS B staf f reviewe d th e unedite d two-volum e transcrip t o f th e Subcommitte e meetin g receive d fro mM.P
. Curri n an d Associates , cour t reporters
. Staf f ha s groupe d th e variou s issue s and concern s raise d b ySubcommitte e member s concernin g th e lea d ris k assessmen t effor t int o fou r majo r categories , a s liste d below

. Th e followin g discussio n i s intende d t o foste r a dialogu e betwee n EP A staf f and intereste d partie s o n a n appropriat e methodolog yfo r assessmen t o f healt h risk s pose d b yexposur e t o airborn e lead

. In additio n t o summarizin g issue s raise d b yth e Subcommittee , w e hav e sough t t o respon d t o th e majo r concern s expresse d and t o clarif ypoint s abou t whic h som e misunderstandin g wa s apparen t a t th e meeting

. I n som e cases , ou r comment s reflec t staf f view s o n a topic , suc h a s guaranteein g anonymit yo f th e expert' s probabilisti c judgment s and no t forcin g convergenc e o f differen t expert' s judgments

. In othe r cases , w e simpl yagre e wit h a Subcommitte e member' s commen t o r explor e alternative s fo r implementin g a recommendation

.

Comment s regardin g thi s staf f discussio n shoul d b e addresse d to : Thoma s McCurd y Ambien t Standard s Branc h U.S
. Environmenta l Protectio n Agenc y MD-1 2 Researc h Triangl e Park , N.C

. 2771 1 (919 ) 541-565 5 (FTS ) 629-565 5 A l l writte n communication s wil l becom e par t o f th e publi crecor d regardin g th e lea d nationa l ambien t ai rqualit ystandar d (NAAQS) review

. Al l verba l comment s wil l b e summarize d an d als o wil l becom e par t o f th e publi crecord

. Anyon e intereste d i n inspectin g th e publi crecor d o n th e lea d ai rstandar d review , ma

yse e o rcop ymateria l i n Docke t #A-83-2 2 availabl e at : Centra l Docke t Sectio n U.S

. Environmenta l Protectio n Agency 40 1 M Street , S

W Washington , D.C

. 2046 0- ^

Tabl e o f Issue s Addresse d
Issu e Pag e 1 . Rol e o f th e lea dris k assessmen t i nth e lea dNAAQ S review . 2
2 . Th e us e o f exper t judgmen t i nassessin g healt hrisk . 4 3 . Technica l problem s specifi c t o a lea dris k assessment . 1 0
4 . Genera l issues . 2 4

1 . Rol e o f th e Lea dRis k Assessmen t i nth e Lea dNAAQ S Review . Thes e issue s ar e relativel y non-controversia l an dreall y

involv e Subcommitte e membe r question s mor e tha nanythin g else .
a . QUESTION : Wha t rol e wil l th e lea dris k assessmen t pla y i nth e lea d NAAQ S revie w

effort ?
RESPONSE : Thi s poin t wa s addresse di npar t b y Bo bKella m

i nhi s presentatio n t o th e Subcommitte e (Vo l I. , p . 23 2 ff) . I t wa s als o addresse di na mor e genera l wa y

b y Tom McCurd y (Vo l I. , p . 2 4 ff) . Th e ris k assessmen t generate s healt hris k (probability ) estimate s associate dwit halternativ e ai r standard s an dassesse s th e natur e an dseverit y

o f possibl e advers e healt hconsequence s i f the y wer e t o occur . Th e probabilisti c approac hi s a nexplici t wa y

o f incorporatin g existin g knowledg e andmajo r uncertaintie s int o modelin g wha t advers e healt heffect s migh t resul t from alternativ e ai r standards , give nal l o f th e non-ai r exposure s see nb y childre nandothers . Th e ris k assessmen t permit s a mor e meaningfu l an dexplici t treatmen t o f th e margi no f safet y issue , providin g a mean s fo r equatin g a nadequat e margi no f safet y wit ha polic y decisio nconcernin g wha t constitute s a nacceptabl e leve l o f ris k fo r lead . Thi s decision , o f course , require s tha t ris k estimate s b e provided . (Not e tha t w e distinguis hbetwee nris k assessmen t andris k evaluation ; w e ar e undertakin g a ris k assessmen t onl y fo r lead . A

forma l ris k evaluatio nprobabl y wil l no t b e don e a s par t o f thi s exercise. ) Result s o f th e lea dris k assessmen t wil l possibl y b e use di ntw o majo r ways . First , ris k estimate s woul db e use di ndevelopin g andassessin g th e "rang e o f interest " fo r possibl e alternativ e ai r standard s tha t i s define di n th e OAQP S "Staf f Paper. " Second , the y woul dbecom e par t o f th e rational e fo r selectio no f th e standard , specificall y tha t par t o f th e rational e focuse don judgin g wha t constitute s anadequat e margi no f safety . Thi s rational e appear s i nth e Federa l Registe r notic e accompanyin g a propose do r promulgate dNAAQS .



# JP. 5

b . QUESTION : Wha t rol e wil l th e CASA C Subcommitte e o nRis k Assessmen t

play i nth e lea dNAAQ S review ?
RESPONSE : Th e Subcommitte e i s bein g aske dt o advis e OAQP S o nth e conduc t o f th e lea dris k assessmen t effort , includin g suc hthing s a s desig no f th e projec t plan , expert s t o b e consulted , developmen t o f th e encodin g protocol , andstructurin g o f th e variou s componen t model s comprisin g th e tota l effort . Th e Subcommitte e als o i s par t o f CASAC' s revie w o f th e lea dcriteri a document , th e staf f paper , andsome o f th e majo r supportin g analyse s (e.g. , exposur e analysis) .

2 . Issue s relate dt o th e us e o f exper t judgmen t i nassessin g healt hrisk . Ther e wa s muc hdiscussio na t th e meetin g o nth e us e o f exper t judgment s i nth e planne dris k assessment . Muc ho f i t wa s genera l i nnature , applyin g t o al l effort s usin g forma l exper t encodin g t o explicitl y addres s majo r uncertaintie s inth e dat a base . Thes e genera l issues , a s wel l a s issue s specificall y

addressin g th e lea deffort , ar e discusse dbelow . Sinc e ther e i s substantia l overla pamon g th e issues , th e breakdowni s somewha t artificial .
a . COMMENT : Margi no f safet y consideration s shoul db e separate da s muc ha s possibl e from

th e ris k assessmen t effort , especiall y th e exper t encodin g part , s o a s t o no t "compound " th e margi no f safety . RESPONSE : Whil e staf f woul dno t stat e th e issu e i nth e abov e manner , w e agre e wit hth e comment . T o us , wha t standar dwoul dprovid e a nadequat e margi no f safet y

i s obviousl y

a valu e judgmen t tha t EP A policymaker s shoul d make . Suc hpolic y

consideration s shoul dpla y n o par t i na ris k assessmen t effort , whic hi s analyti c i nnature . Addressin g andattemptin g t o minimiz e strategi c andunintentiona l motivationa l bia s i s a standar dpar t o f th e probabilit y

encodin g process . Buildin g "margin s o f safety " int o judgment s woul db e a bia s i non e directio njus t a s judgin g degre e o f scientifi c confirmatio ninstea do f probabilit y woul db e a bia s i nth e other . Ever y effor t wil l b e mad e t o minimiz e bia s i neithe r direction . On e neve r know s fo r sur e i nan y give ncas e whethe r al l motivationa l and cognitiv e biase s hav e bee neliminated . Thi s i s on e o f severa l reason s i t i s desirabl e t o us e a balance dsampl e o f expert s rathe r tha njus t one . Th e staf f i s awar e o f th e type s o f problem s tha t ca naris e withi nanenterpris e whic hha s inherentl y subjectiv e aspects , bu t emphasize s tha t th e bas e o f compariso ni s a les s systemati c approac hwit hth e sam e subjectiv e aspects , no t anunattainabl e objectiv e ideal . Mor e informatio nregardin g debiasin g i s containe di nDrs . McNamee' s andWallsten' s presentation s a t th e meetin g (Vol . I , p . 6 5 f f andp . 17 0 ff) .

b . ISSUE : An

y techniqu e tha t relie s o nopinion s o f expert s i s heavil y influence db

y th e expert s chosen . (Or , a s anothe r Subcommitte e membe r pu t it , th e neutralit y

o f judgment s t o be obtaine dfrom th e expert s i s questionable. )P. 6

RESPONSE : W e agree . I t i s unfortunat e tha t ris k assessmen t i s no t a n entirel y

objectiv e matter . Th e importan t thin g i s tha t th e approac helicit s th e righ t kind s o f judgment s from som e o f th e bes t peopl e t o mak e the m an d make s us e o f the m

i nth e appropriat e manner .
W e generall y

us e th e ter m

'judgment ' rathe r tha nth e ter m 'opinion ' fo r a reason . Th e connotationa l differenc e i s important . Reasone dprobabilit y judgment s whic hincorporat e bot hth e availabl e knowledg e andth e remainin g uncertainty , obtaine dvi a teste delicitatio ntechnique s shoul dno t b e equate d wit h"opinions " (or poin t estimat e "guesses" ) althoug hopinion s ente r vi a th e reasonin g proces s whic hsuc hjudgment s ar e made . Probabilit y languag e i s a flexible , ye t precise , languag e inwhic hth e stat e o f information , suc ha s i t ma y be , i s represente di nth e mos t usefu l way .
AS B staf f andmanagemen t recogniz e tha t th e Agenc y shoul dobtai na representativ e samplin g o f th e entir e spectrum o f scientifi c though t onan uncertai ntopi c i nth e lea dris k assessmen t effort . Thi s include s al l aspect s o f th e effort , andno t jus t thos e component s focuse dondose-respons e relationship s o r onphysiologica l interactio namon g body lea dpools . However , ther e ar e definit e practica l limit s t o ho w muc hw e ca ndo . (Se e Issu e 2. d below. )

T o obtai na diversit y o f scientifi c view s o na particula r healt heffect , AS B staf f plan s t o continu e it s revie w o f th e lea dcriteri a document , consul t wit hECA O staf f workin g onit , an dtal k wit hCASA C Subcommitte e member s t o identif y

expert s wh o hol ddifferin g view s onth e scientifi c evidenc e suggestin g a neffect . Fo r eac hhealt heffec t categor y tha t wil l b e addresse di nth e ris k assessment , w e wil l the nstructur e a lis t o f expert s representin g th e rang e o f full y

informe dviews . Thi s lis t wil l b e pare dt o matc hresource s availabl e fo r encoding . (Some "extra " peopl e ma y b e include di ncas e som e expert s ar e unavailabl e a t th e tim e o f encoding. ) Generally , internationa l trave l wil l b e avoide di nth e encodin g effor t du e t o resourc e limits . Th e pare dlis t o f expert s t o b e encode dwil l b e presente dt o th e CASA C Subcommitte e i na publi c meetin g t o allo w al l intereste dpartie s t o revie w andcommen t upo nou r selectio nof experts . Whil e ultimat e responsibilit y fo r selectin g expert s rest s wit hEPA , w e woul dlik e th e Subcommitte e t o determin e whethe r o r no t w e hav e include da reasonabl e spectrum andbalanc e o f scientifi c views . No t encodin g al l view s ona topi c doe s no t undermin e th e approach ; a n omissio nma y

narro w th e ban do f ris k estimate s tha t wil l ultimatel y com e ou t of th e exercise . Thi s i s particularl y tru e i f anextrem e view i s no t encoded .

c . COMMENT : Th e assessmen t obtaine dfrom anexper t i s markedl y influence d b y th e wa y

i nwhic hquestion s ar e asked . RESPONSE : Th e exten t t o whic hthi s i s tru e i s unknown . However , th e exten t t o whic hth e encodin g protoco l itsel f affect s importan t judgment s deserve s clos e scrutiny . Sinc e th e exper t als o wil l hav e th e protoco l prio r t o hi s o r he r session , th e exper t become s a self-monito r o f th e approach .P. 7

Th e Subcommitte e andth e intereste dpubli c a t large wil l hav e ampl e opportunit y t o revie w

andcommen t upo nth e encodin g protocol .

d . ISSUE : Th e numbe r o f expert s t o b e encode di s to o small . OAQP S need s mor e tha nthre e expert s pe r topi c t o obtai na usefu l rang e o f judgment s regardin g mos t leadissues . RESPONSE : A s AS B staf f agree da t th e meeting , i t i s desirabl e t o encod e mor e experts . However , eac hencodin g require s resource s whic har e limited . Eac hencodin g sessio nrequire s a t leas t on e traine dprobabilit y assesso r and a technica l assistan t t o conduc t th e sessio nan drecor dinformation . Th e session s ar e long , an dn o mor e tha non e exper t a day ca nb e encode db

y on e "team. " Sinc e expert s ar e geographicall y dispersed , considerabl e trave l i s require ds o i t i s unlikel y tha t mor e tha ntw o expert s ca nb e encode dpe r wee k pe r team . Inaddition , logistic s o f th e effor t ar e enormous . Encodin g session s ar e onl y par t o f th e process . Preparatio ntim e i s require db

y eac hencodin g team . Protocol s an dtrainin g material s hav e t o b e developed , pre-testin g ha s t o b e done , an drevision s hav e t o b e made . Al l o f thi s i s tim e consumin g andexpensive . Curren t resource s availabl e t o AS B fo r th e lea dencodin g effor t ar e estimate dt o b e sufficien t fo r a maximum o f 3 0 encodin g sessions . (Fo r mor e discussio no f thi s point , se e Issu e 4. a below. ) W e ha doriginall y planne do

nencodin g 1 5 expert s twic e o na t mos t fiv e healt hend-point s (or thre e expert s pe r end-point) . We di dno t anticipat e a nee dfo r extensiv e encodin g fo r th e exposur e an dphysiologica l component s o f th e ris k assessmen t effort . (W

e ha dplanne dt o represen t some o f th e mos t significan t uncertai n aspect s o f thes e two component s vi a a combinatio no f staf f wor k an dphon e call s t o experts) . Give nth e Subcommittee' s comment s regardin g th e exposur e an dphysiologica l models , however , i t i s apparen t tha t encodin g i nthes e area s i s needed . Inth e absenc e o f additiona l fund s fo r th e lea dris k assessmen t effort , undertakin g encodin g fo r th e othe r tw o component s wil l requir e a reallocatio n o f th e 3 0 encodin g sessions . Non e o f th e reallocatio noption s ar e particularl y attractive . Thre e tha t immediatel y com e t o min dare : 1 . reduc e th e numbe r o f healt hend-point s t o b e addressed . (Th e Subcommitte e ha s alread y mad e suc ha recommendation , bu t se e th e discussio nbelow

o f Issue 3.b. )
2 . reduc e th e numbe r o f expert s encode do nan y on e end-point . 3 . eliminat e th e secon dencodin g sessio nfo r a nexper t fo r al l o r some o f th e end-points . Perhap s a combinatio no f thes e strategie s ca nb e use dt o develo pa mor e expansiv e bu t stil l viabl e encodin g effort . W e thin k i t i s importan t t o formall y an dexplicitl y

addres s th e large uncertaintie s inheren t i nth eP. 8

curren t stat e o f informatio n o n lead

. AS B staf f welcome s suggestion s fro m th e Subcommitte e o n ho ww e ca n bes t us e th e encodin g resource s availabl e fo r thi s project

.

e . ISSUE : Th e numbe r o f expert s t o b e encode d o n a topi c shoul d var y dependin g upo n th e diversit yo f view s i n th e scientifi c communit yo r upo n th e significanc e o r magnitud e o f subsequen t healt h effects

. RESPONSE : W e distinguis h thi s issu e fro m th e preceedin g on e i n tha t th e numbe r o f expert s t o b e encode d o n an ytopi c conceivabl ycoul d b e mor e o r les s tha n thre e i f a n "importance " criterio n i s used

. AS B staf f agree s wit h th e commen t i n genera l an d wil l tak e i t int o consideratio n whe n allocatin g resources ,

f

. COMMENT : Eac h exper t i s s o narro wtechnicall ytha t he r o r hi s judgment s becom e relativel yvalueles s beyon d th e technica l sense . RESPONSE : W e wil l no t b e askin g fo r synopti c informatio n fro ma n expert
. W e hop e t o elici t th e expert' s judgment s concernin g a focuse d scientifi c o r technica l matte r tha t i s inherentl yuncertain

. W e believ e tha t th e bes t plac e t o obtai n thi s informatio n i s fro m a n exper t o n th e topic

. W e wil l synthesiz e a particula r expert' s judgment s wit h othe r judgment s vi a mathematica l models

. No individua l exper t i s expecte d t o provid e globa l judgments

. And , a s stresse d abov e i n staff' s respons e t o Issu e 2.a , w e d o no t wan t socia l valu e judgment s fro ma n exper t a s par t o f thi s exercise

. Iti s importan t t o recogniz e tha t i f a lea d ris k assessmen t wer e no t done , a t som e poin t i n th e lea d NAAQ S revie wproces s someon e (probabl yth e proverbia l "faceles s bureaucrat" ) woul d hav e t o mak e implici t o r explici t decision s o n mos t o f th e issue s t o b e addresse d i n encodin g sessions

. I f expert s ar e involved , bu t i n th e a d ho c an d informa l manne r a s the yar e now , the n th e decision-makin g rational e i s difficul t t o documen t and explai n t o th e public

.

g . COMMENT : OAQP S shoul d tal k t o expert s befor e i t structure s th e variou s models

. Thi s wil l allo wstaf f t o determin e wha t i s know n abou t th e proble ms o tha t realisti c model s ca n b e developed

. RESPONSE : W e agree . A s Subcommitte e member s wh o attende d th e meetin g know , AS B staf f wer e no t allowe d t o substantivel ydiscus s th e lea d ris k assessmen t effor t wit h non-EP Ascientist s workin g o n o r reviewin g th e lea d criteri a documen t unti l publi c releas e o f tha t document

. Whil e w e di d revie wth e relevan t literature , thi s certainl yconstraine d wha t w e wer e abl e t o d o i n structurin g ou r variou s componen t model s sinc e mos t lea d expert s ar e contributor s t o o r ar e workin g o n th e CD
. Wit h releas e o f th e draf t C D i n October , w e hav e begu n a modes t effor t t o discus s mode l structurin g issue s wit h variou s experts
. Thi s effor t wil l expan d i n th e nea r future

. I n addition , and a s wa s suggested , w eP. 9

7
wil l b e usin g Subcommitte e member s a s a "clearinghouse " fo r suggestion s onwh o w e shoul dcontac t o nparticula r mode l buildin g issues . I f an y Subcommitte e membe r woul dlik e t o sugges t expert s o nmodel-bui 1 din g that w e shoul dconsul t with , pleas e contac t To m McCurdy . (NOTE : Thre e exposur e expert s wer e recommende dt o u s a t th e meeting : Drs . Spengler , Moschandreas , andFugas . W e wil l b e contactin g thes e andothe r individual s shortly . Fo r th e record , however , w e hav e ha dcontac t wit hth e firs t tw o expert s andar e familia r wit hth e wor k o f al l three. )

h . COMMENT : Th e bes t wa y t o obtai ninformatio nfrom expert s i s t o develo p anoveral l strateg y fo r obtainin g neede dinput s andadap t i t t o eac hexper t dependin g upo nth e circumstances . I f th e proble m i s over-structured , OAQP S wil l mis s som e specific s andopportunitie s that aris e durin g th e process . RESPONSE : AS B staf f agre e i ngenera l wit hth e comment , howeve r som e discussio ni s warrante dregardin g flexibilit y o f th e mode l structure , especiall y

a t differen t stage s i nth e ris k assessmen t process . Ou r desir e i s t o b e a s flexibl e a s possibl e bu t ther e ar e thre e type s o f contraint s onhow flexibl e w e ca nbe . On e constrain t concern s th e inheren t logi c o f ou r situation , anothe r concern s th e goldfis hbow l natur e o f th e NAAQ S settin g process , anda thir dderive s from ou r limite dresources . Thes e constraint s ar e discusse dbelow . Ou r overal l strateg y fo r obtainin g informatio nfrom expert s i s t o firs t involv e the m

i ninformall y

structurin g th e variou s model s neede di n th e assessmen t an

di nidentifyin g wha t kind s o f judgment s ar e mos t easil y mad e b y lea dexperts . W e the nwan t t o formall y encod e expert s onth e form o f functiona l relation s and/o r onvalue s fo r particula r variable s i n th e relations . Durin g th e encodin g session s w e pla nt o recor dandlate r presen t an

y observation s th e expert s car e t o make . I f tw o round s o f encodin g ar e undertaken , th e abov e wil l b e repeate d(an dperhap s som e mode l restructurin g wil l als o b e accomplished) . Finally , expert s wil l revie w andcommen t upo noutput s o f th e ris k assessmen t project . Wit hrespec t t o th e constraints , ther e ar e certai nrelationship s tha t nee dt o b e capture di nassessin g risk s associate dwit halternativ e NAAQS . A s w e se e it , assurin g that thes e relationship s ar e incorporate dint o th e ris k mode l i na logica l anddefensibl e manne r i s on e o f th e majo r responsibilitie s o f a nanalys t i nth e assessmen t effort . Thus , onc e a mode l structur e i s derived—wit hexper t assistance , o f course — i t canno t b e change darbitraril y t o fi t anexpert' s views . Thus , ther e i s a limi t t o ho w flexibl e ananalys t ca nb e wit hrespec t t o mode l structure . Usin g mor e tha non e mode l woul dincreas e flexibility , bu t thi s i s probabl y infeasibl e du e t o resourc e limitations . B y expandin g andlengthenin g th e proces s o f interactio nwit hvariou s expert s w e coul dprobabl y increas e consensu s amon g expert s t o b e encode dconcernin g th e bes t compromis e model . (W

e mea nconsensu s onth e mode l andhenc e oninput s t o b e encode d- no t onprobabilit y

judgment s themselves. ) However , availabl e resource s constrai nth e exten t o f consensu s buildin g w e ca nfeasibl y undertake . (Se e th e discussio no f Issu e 4. a onp . 2 4 fo r anelaboration. )P.1 0

8 Finally , ther e ar e specia l circumstance s surroundin g mos t NAAQ S standard settin g effort s tha t usuall y reduc e th e amoun t o f flexibilit y availabl e t o us . Th e mos t importan t on e from ou r experienc e i nsettin g NAAQ S i s th e nee d t o extensivel y

documen t fo r judicia l revie w purpose s wha t factor s wer e considere d i nth e decision-makin g process . Thi s accountabilit y mandat e als o applie s t o th e encodin g process , i f on e i s undertaken . Th e nee dfo r accountabilit y and th e desir e t o avoi dan y appearanc e o f manipulatio no f expert s b y EP A o r it s contractor s force s u s int o a les s flexibl e postur e tha nmigh t occu r i na non-regulator y

setting . It result s i na fixe dlis t o f expert s t o b e encode d anda "public " protoco l availabl e fo r revie w prio r t o th e encodings . Inth e conduc t o f th e lea dNAAQ S ris k assessmen t effort , AS B andit s contractor s wil l b e a s flexibl e a s possibl e withi nth e constraint s note dabove .

i . ISSUE : Shoul dth e encode ddistribution s b e attribute dt o specifi c experts ?
RESPONSE : Th e Subcommitte e itsel f wa s divide donthi s issue . Som e member s though t tha t ever y distributio nshoul db e identifie dwit ha particula r expert ; othe r member s though t tha t anonymit y wa s appropriate . ASB' s pla nwa s t o no t identif y eac hencode ddistributio nwit ha nexpert , unles s anexper t desire dit . Ou r preferenc e wa s t o simpl y labe l eac h curv e a s A , B , C , etc . Th e expert' s reasonin g behin dhe r o r hi s encode d judgment s als o woul dals o b e presented . I naddition , w e planne dt o includ e a lis t o f al l expert s participatin g i nth e study , identifie db y healt heffec t category . Thus , intereste dreader s woul dkno w wh o wa s encode dona particula r healt hendpoin t (o r exposur e mode l variable , etc. ) bu t woul dno t b e tol dexactl y wh o provide da particula r encoding . Som e Subcommitte e member s wante dexplici t identificatio ni norde r t o promot e accountability . Th e gis t o f thei r argumen t wa s tha t expert s shoul d b e willin g t o defen dthei r judgments . I f the y cannot , o r i f the y

wer e no t comfortabl e bein g a participan t i nth e encodin g process , th e expert s shoul dno t participate . Othe r Subcommitte e member s though t tha t suc hidentificatio nwoul dhav e a "chillin g effect " onth e expert' s cando r andonpersuadin g man y expert s t o participate . The y

fel t tha t whil e scientist s andothe r expert s shoul db e hel daccountabl e fo r thei r scientifi c conclusions , thi s reasonin g di dno t appl y t o encode djudgmenta l probabilit y distributions , whic har e judgment s base donth e availabl e evidence , no t scientifi c conclusions . AS B staf f think s tha t labelin g eac hdistributio nwit hanexpert' s nam e migh t unnecessaril y

burde nsom e o f th e expert s wit ha concer nabou t ho w thei r judgment s wil l b e receive db y variou s parties . We nee dth e bes t judgment s possible , andexterna l pressur e ca nonl y wor k agains t tha t aim . I t i s commo n understandin g tha t anonymit y generall y

enhance s candor . Th e argumen t tha t anonymit y

woul ddecreas e th e chanc e fo r tota l cando r seem s muc hweake r t o us . I f ever y distributio ni s attribute dt o anexpert , some expert s ma y no t participat e i nth e exercis e onth e ground s tha t participatio nwoul dlea dt o involvemen t i na protracte dpubli c "discussion " (or , mor e likely , a heate dP.1 1

debate ) o f th e merit s o f eac hencode dpoin t i nth e expert' s distribution . Neithe r th e aren a no r th e subjec t matte r woul db e scientific , andmany scientist s simpl y woul dno t wan t t o b e involve di nsuc ha debate . Check s andbalance s onmanipulatio no f th e expert' s distribution s hav e bee nmentione dearlier . (Se e Issu e 2.c. ) Inaddition , th e rational e behin deac h majo r encode ddistributio nwil l b e provide dalon g wit hth e dat a s o that reader s ca njudg e fo r themselve s i f th e distributio nmake s sens e (i.e. , i s base dupo na fai r revie w o f th e scientifi c evidenc e an di s internall y consistent) , Thes e check s shoul db e sufficien t t o avoi dmakin g anindividual' s probabilit y judgement s th e focu s o f publi c debate . Despit e it s merits , however , ther e remain s th e lega l questio no f whethe r o r no t EP A ca nguarante e anonymit y o f encode dexpert s o r mak e us e o f th e resultin g encode ddistribution s i na NAAQ S ris k assessmen t withou t attributin g the m t o thei r source . EPA' s Offic e o f Genera l Counse l (OGC ) i s currentl y investigatin g thi s issu e andwil l mak e a recommendatio nt o AS B onhow t o proceed . Thei r recommendatio nwil l b e mad e availabl e t o th e Subcommitte e upo nreceip t b y AS B staff .

j . ISSUE : Exper t judgmen t shoul dno t b e aggregate dint o a combined , o r single , distribution . RESPONSE : AS B staf f agrees . Forcin g th e expert s t o converg e o r averagin g th e experts ' result s obscure s situation s wher e variou s researcher s ma y hav e fundamentall y

differen t point s o f view an djudgment s concernin g th e phenomeno n bein g encoded . Staf f agree s wit hsom e Subcommitte e member s tha t th e EPA Administrato r shoul db e give nthi s informatio n(a s wel l a s th e reason s behin d suc hdisparat e views) . Inaddition , th e "spread " amon g expert s provide s a vivi drepresentatio no f th e subjectivit y involve di nrepresentin g uncertaint y associate dwit ha variabl e o r relationshi pbein g analyzed . Th e Administrato r andpubli c shoul db e presente dwit hthi s informatio na s well . W e als o agre e wit hsom e Subcommitte e member s tha t i t i s usefu l t o hav e som e typ e o f feedbac k amon g th e experts , _r f tw o round s o f encodin g ar e done . Thi s feedbac k woul dconsis t o f showin g th e previou s round' s encoding s alon g wit h anexpert' s reasonin g fo r hi s o r he r distribution . Thi s typ e o f feedbac k woul dhav e valu e i nthat i t woul dhel pexpert s becom e awar e o f othe r possibl e perspective s andjudgments . Thi s doe s no t mean , however , tha t AS B staf f think s that a forma l Delph i approac hshoul db e use dt o promot e interactio namon g experts . W e hav e n o plan s t o us e th e Delph i o r othe r forma l processe s designe dt o promot e grou p consensus .

k . ISSUE : Expert s shoul db e confine dt o materia l reviewe di nth e criteri a documen t fo r th e base s o f thei r judgments . RESPONSE : Th e expert s wil l b e encourage dt o b e full y familia r wit h relevan t materia l i nth e criteri a documen t (CD) . Fo r bot hlega l reason s andP.1 2

1 0

reason s havin g t o d o wit h ou r vie wo f ho wris k assessment s ar e bes t done , w e thin k i t i s importan t tha t scientifi c assessmen t o f th e stat e o f knowledg e give n i n th e relevan t criteri a documen t b e th e scientifi c basi s o f th e probabilisti c ris k assessment
. Hence , t o thi s exten t w e agre e wit h th e comment
. However , a s variou s meetin g attendee s recognized , i t i s als o importan t t o b e realisti c abou t th e natur e o f probabilisti c judgments

. Eve n thoug h the y ar e base d o n a give n scientifi c assessmen t o f a dat a bas e the yca n als o b e influence d b

yothe r things

. Thi s include s th e expert' s training , history , temperament , backgroun d reading , and wha t h e o r sh e know s abou t ongoin g o r recentl ycomplete d research

. W e canno t simultaneousl yas k a n exper t t o giv e hi s o r he r bes t probabilisti c judgmen t whil e constrainin g th e exper t t o a particula r scientifi c assessment
. Probabilit yjudgment s and scientifi c assessmen t judgment s ar e relate d bu t differen t i n importan t ways . I t ma ymak e sens e t o undertak e a scientifi c assessmen t o f a give n prescribe d dat a base , bu t i t i s probabl yimpossibl e t o mak e a probabilit yjudgmen t tha t i s influence d onl yb ya prescribe d dat a base

. Pleas e not e tha t eac h exper t wil l b e encourage d t o refe r t o th e criteri a documen t i f i t woul d hel p durin g th e encodin g procedure

. Doin g thi s allow s th e expert s t o refres h thei r memorie s o n specifi c issues

. I n short , AS B staf f certainl yagree s that , interprete d realistically , th e criteri a documen t woul d provid e th e basi s fo r th e ris k assessment
.

3

. Technica l issue s tha t ar e specifi c t o lead

. Th e Subcommitte e raise d a numbe r o f issue s relatin g t o th e technica l feasibilit yo f undertakin g a ris k assessmen t o f alternativ e ai r lea d standards

. Mos t o f th e Subcommittee' s concern s wer e focuse d o n th e exposur e modeling componen t o f th e ris k assessment
. However , issue s wer e raise d abou t mos t components
. Thi s Sectio n proceed s fro mth e genera l t o th e specific , and withi n th e specifi c issue s part , fro mexposur e t o dose-respons e issues

.
a . ISSUE : Lea d i s to o comple x a n issu e t o adequatel yanalyz e vi a a forma l ris k assessmen t method

. (Specifi c complexitie s ar e note d below. )
RESPONSE : Th e abov e statemen t wa s a them e voice d repeatedl yi n th e two-da ymeeting

. I n respons e t o thi s issue , AS B staf f submit s th e followin g excerp t fro ma lette r t o Dr
. Bernar d Goldstei n fro mJosep h Padget t date d Ma y4 , 1983

.

o o g I n th e past , yo u hav e expresse d concer n tha t lea d migh t b e t controversia l a pollutan t fo r EPA' s firs t attemp t a t incorporat e forma l ris k assessmen t int o th e NAAQ S standard-settin g process . I agre e tha t ther e i s a grea t dea l o f difficult ysurroundin g th e evaluatio n an d interpretatio n o f certai n healt h effect s attribute dP.1 3

1 1
t o ambien t lea dexposures . Centra l nervou s syste m impact s ar e a cas e i npoint . However , a s yo uknow , thi s i s th e cas e wit hmos t o f ou r NAAQ S pollutants ; lea di s no t uniqu e i ntha t respect . We fee l tha t th e inheren t uncertaint y surroundin g lea dhealt h effect s make s lea da particularl y goo dchoic e fo r doin g a probabilisti c ris k assessmen t o f alternativ e NAAQS . Ou r propose d metho dwil l explicitl y mode l thi s uncertaint y s o tha t th e impac t o f a wea k informatio nbas e o nth e estimatio no f healt hrisk s i s clearl y delineated . Th e methodolog y als o permit s compariso no f healt hrisk s fo r many possibl e advers e healt heffect s o f ambien t lead . Inthi s manner , th e controvers y ca nb e pu t int o perspective . Th e quantitativ e descriptio no f uncertaint y associate dwit hal l o f th e healt heffect s categorie s wil l allo w a mor e rigorou s evaluatio no f th e impact s o f alternativ e lea dai r standards . (However , a s yo uknow , th e lea dris k assessmen t effor t wil l no t includ e a forma l ris k evaluatio neffor t a t thi s time . Th e quantitativ e integratio no f ris k estimate s int o a forma l evaluatio n metho dt o furthe r ai ddecision-makin g mus t awai t anothe r time. )

Al l o f thes e virtue s aside , a s w e mentione da t th e meeting , i f th e Subcommitte e feel s tha t ther e ar e insurmountabl e problem s associate dwit h th e conduc t o f a ris k assessmen t fo r lea do r i f insufficien t progres s i s made , we wil l discontinu e th e effort .

b . ISSUE : Argonn e presente da lis t o f si xhealt hendpoint s tha t coul d b e use di nth e ris k assessment . Fo r thre e o f th e en dpoints : rena l function , immunologica l reactions , and reproductive/developmenta l effect s ther e ar e littl e dat a but , the y indicat e advers e response s onl y a t relativel y

hig hexposur e levels . Therefore , thes e thre e endpoint s shoul db e droppe dfrom th e assessmen t effort . RESPONSE : Th e endpoint s presente db y Argonn e wer e fo r illustrativ e purpose s andd o no t necessaril y represen t healt heffect s tha t AS B wil l includ e i nth e assessment . Evidenc e summarize di nth e criteri a documen t indicate s varyin g degree s o f uncertaint y associate dwit hth e entir e spectrum

o f healt hresponse s t o lea dexposure . Whil e th e Sub Committee' s advic e t o delet e from consideratio nthos e effect s whic hhav e bee nobserve dt o occu r i norgan s andothe r system s i nchildre na t relativel y hig hlevel s i s helpful , i t i s importan t t o not e tha t knowledg e i s incomplet e andinconclusive , andth e possibilit y o f mor e genera l toxi c effect s canno t b e rule dout . Thi s seem s particularl y tru e fo r data , mostl y from anima l investigations , onalteration s i nfeta l physiolog y andmetabolis m an dpost-nata l delay s i nneurobehaviora l development . Attemptin g t o characteriz e uncertaintie s associate dwit hsuc heffect s i s th e inten t o f th e ris k assessment . W e ar e currentl y

developin g anencodin g protoco l fo r lead' s interferenc e wit hhemebiosynthesi s anderythropoieti c effects . Thi s protoco l wil l b e initiall y

reviewe db

y appropriat e expert s (e.g. , hematologists) , selecte dP. M

1 2 wit h th e hel p o f criteri a documen t author s an d consultants

. W e pla n o n the n sendin g th e protoco l t o Subcommitte e member s fo rthei rrevie wprio r t o ou rnex t meeting

.

c
. ISSUE : Ther e ar e numerou s problem s wit h th e propose d lea d NAAQ S exposur e mode l (lead-NEM)

. Variou s Subcommitte e member s raise d th e followin g issue s concernin g th e propose d lead-NEM

. I n som e cases , w e grou p ou rrespons e t o severa l issues

. ISSU E cl : Ther e i s n o goo d larg e se t o f ai rqualit ydat a tha t i s available , useable , o rbelievable , especiall yi n term s o f th e tim e resolutio n o f exposur e propose d i n th e lead-NEM

. Dat a canno t b e "manufactured " fro m th e l-in- 6 day s samplin g o f 24-hou rai rlea d level s tha t i s suitabl e fo r analyzin g hourl yo reve n dail yai rlea d exposures
.
ISSU E c.2 : Ai rlea d monitorin g station s ar e i n th e wron g plac e fo restimatin g huma n exposures
.
ISSU E c.3 : Ther e ar e n o monitorin g dat a availabl e t o accoun t fo rtw o factor s tha t affec t ai rlea d exposures : th e variatio n i n chemica l compositio n o f lea d particle s an d th e variatio n i n particl e size

.
I n response , w

e agre e tha t ai rdat a ar e lacking , d o no t full yrepresen t huma n exposures , an d ar e no t wel l describe d a s t o particl e siz e o rchemica l composition

. W

e wil l utiliz e tim e serie s analysi s t o fil l i n missin g value s an d us e th e neighborhoo d type , microenvironmen t concepts , an d availabl e praticl e size/compositio n dat a t o bette rrelate.ambien t monitorin g dat a t o th e typ e o f ai rlea d see n i n huma n habitats*

. Lea d i s no t uniqu e i n havin g thes e shortcomings ; al l NAAQ S ai rqualit yinformatio n i s deficien t i n a t leas t som e o f th e way s mentioned

. Staf f ha s reviewe d al l lea d ai rdat a i n EPA' s SAROA D system

. Fro m th e hundred s o f urba n area s havin g dat a meetin g EPA' s acceptanc e criteri a fo r completeness , w

e picke d 1 0 area s meetin g certai n populatio n siz e an d geographi ccriteri a tha t ha d th e bes t data

. Fo rth e mos t part , ambien t lea d i s monitore d fo ron e 24-hou rperio d ever ysi xdays

. Thi s i s n o differen t tha n particulat e matter , fo rwhic h w e hav e alread ydevelope d a NAAQ S exposur e model

. T o obtai n a ful l se t o f dail y values , w

e fil l i n missin g dat a usin g time-serie s analyti ctechniques

. Thi s data-supplementin g approac h ha s bee n use d o n al l NAAQ S pollutant s analyze d t o date

. W

e woul d no t attemp t t o develo p one-hou rdat a fro m 24-hou r data

. W

e ha d n o plan s t o d o thi s fo rlead , althoug h tha t poin t probabl y wa s no t made clea ra t th e meeting

. W e ar e currentl ydoin g a detaile d analysi s o f lea d dat a havin g nearl y complet e annua l dat a set s o f 24-hou rdata

. Th e Cit yo f Philadelphi a ha s a t leas t tw o station s reportin g on e o rmore year s o f complet e dail y average d data

. Apparently , ther e ar e a fe wothe rsite s wit h th e sam eP.1 5

1 3 typ e o f information . W e ar e als o conductin g statistica l analyse s o f th e feasibilit y

o f replicatin g th e origina l dat a distributio nwit hvariou s random sample s o f l-day-in- 6 dat a sets . W e ar e als o comparin g thes e sample ddat a set s supplemente db y filled-i ntim e serie s dat a wit hth e ra w dat a se t t o tes t ho

w wel l filled-i ndat a replicat e ra w data . Thes e analyse s ar e bein g don e b y PEDC o unde r contrac t t o us . Writte nresult s wil l b e sen t t o th e Subcommitte e a s soo na s w e receiv e them . Othe r dat a problem s relate dt o th e us e o f monitore ddat a mentione db y th e Subcommitte e wer e know nt o us , suc ha s th e comple xai r flow andturbulenc e pattern s characteristi c o f cities . Thi s make s i t difficul t t o relat e monito r reading s t o ambien t level s i nlocalize dho t spo t conditions , suc ha s i nstree t canyons . W e wil l attempt , however , t o us e availabl e informatio ncontaine di n th e criteri a documen t onlead' s vertica l andhorizonta l dispersio nove r tim e withi nurba nsetting s andonre-entrainmen t o f roa ddus t t o develo ptransformatio n factor s necessar y

t o mor e accuratel y

estimat e potentia l exposure s t o airborn e lead . Concer nwa s raise da t th e meetin g regardin g th e lac k o f attentio nw e gav e t o lea dparticl e siz e distributio nan dchemica l compositio no f airborn e lead . Bot ho f thes e factor s influenc e mobilit y i nth e environment , solubility , an

dth e likelihoo dtha t a ninhale do r ingeste dparticl e wil l b e retaine dandabsorbed . Urba nlea dparticle s ar e predominantl y fin e mod e aerosols , wit ha mas s media nequivalen t diamete r consistentl y withi na rang e o f 0.2 3 t o 0.3 0 y

m (Robinso nandLudwig , 1969 ; Stephen s et

_al_. , 1978 , 1980 , 1982) . Lea daerosol s collecte dnea r stationar y source s tendt o b e large r (Landriga net_ aj_. , 1975) , althoug hth e likelihoo do f thei r depositio n int o bloo dexchang e region s o f th e respirator y trac t o r int o th e gu t vi a th e mucociliar y

escalato r may

b e a s higha s fo r fin e particles . Inorgani c lea demitte dfro

m automobile s andpoin t source s a s lea dhalide s an doxide s appear s t o convert t o lea dsulfate s (Te r Haa r andBayard , 1976 ; Biggin s and Harrison , 1978 , 1979 ; Dzuba y andStevens , 1973) . Organi c lea dcompound s (generall y

unmeasured ) ar e photoreactiv e andthei r presenc e i nurba natmospher e i s transitor y

(Harriso net

_ a_l_. , 1979 ; Skogerboe , 1975) . We ha dplanne dt o adjus t th e lea dmonito r dat a vi a transformatio n factor s (albei t base do nlimite dinformation ) i norde r t o account fo r th e variation s i nlea dparticl e siz e andchemica l composition . Thes e adjustments , alon g wit hothe r considerations , wil l be mor e full y discusse d i na preliminar y

AS B staf f review

o f informatio nrelevan t t o th e exposur e mode l tha t wil l b e sen t t o yo ui nth e nex t few week s fo r revie w

and comment . W e fee l compelle dt o us e monitorin g dat a a s th e base s o f NAAQ S analyse s fo r bot hinstitutiona l andlega l reasons . Attainmen t o f a NAAQ S standar d i s determine db

y wha t monitor s sample , no t wha t occur s i nmicroenvironment s use db y peopl e o r b

y wha t peopl e ar e actuall y expose dto . Implementatio n an dcontro l program s ar e develope ds o tha t ai r qualit y a t th e "critical " monito r (just ) meet s anapplicabl e standard . Ai r qualit y experience db

y peopl e may

o r may no t b e bette r tha nwha t i s officiall y recorded . Sinc e attainmen t i s predicate dupo nmonito r readings , w e mus t wor k fro m monitorin g data . Otherwise , w e canno t analyz e th e operationa l impac t o f wha t i t mean s t o jus t attai na

nalternativ e ambien t ai r standard . Thus , predicatin g ou r analyse s upo nmonitorin g dat a i s a logica l constrain t give nou r current regulator y

philosophy

rathe r tha na matte r o f choice .P.1 6

1 4
Th e questio nthe nbecomes , ho w d o yo ubes t represen t huma nexposure s t o airborn e pollutant s wit hambien t monitorin g data ? Th e NE M approac hi s on e wa y o f makin g tha t representation . W e hav e n o illusion s tha t ou r exposur e estimate s precisel y reflec t realit y

andpredic t actua l exposures . Thi s i s wh y

w e wan t t o undertak e probabilisti c exposur e analyses . W e d o thin k tha t estimate s base do nNE M wil l b e reasonabl e anda s goo da s ca nb e mad e give nth e dat a bas e andresource s availabl e fo r analysis . Th e explicitnes s o f ou r formulatio nallow s u s t o mak e correction s a s neede di nvariou s component s o f th e NEM

model , a s wa s don e successfull y i nth e carbo nmonoxid e versio no f NEM . T o be abl e t o correc t fo r new information , however , mean s tha t yo uhav e t o buil di nth e necessar y flexibilit y

from th e beginning . This , b y necessity , result s i na comple xmode l wit hlot s o f component s andvariable s (man y o f whic hzer o ou t i nth e end) .

ISSU E c.4 : Ther e ar e to o many cohor t group s propose dt o b e used ; man y group s wil l hav e n o childre ni nthem .
A s note di nth e previou s discussio no f Issue s c.l-c.3 , w e agre e tha t man y

cohor t group s ma y

hav e n o childre ni nthem . Infact , w e welcom e thi s occurrenc e a s i t reduce s compute r ru ntim e considerably . Al l previou s application s o f NEM ha dcohor t group s tha t wer e eventuall y no t used , bu t thi s fac t wa s no t know ni nadvanc e o f performin g preliminar y analyses . Al l cohor t group s ar e ther e fo r a reason . Fo r lead , th e group s ar e define dprimaril y

o nth e basi s o f suspecte ddifference s inrespons e characteristic s t o leadexposure . However , practica l consideration s als o pla y a role . Sinc e cohor t dat a generall y com e from

U.S . Censu s Burea ufiles , i t i s ofte nnecessar y t o adop t thei r distinctions . (Ther e i s n o othe r typ e o f informatio navailabl e tha t i s applicabl e nationwide. ) Thus , ther e i s som e balancin g o f divers e criteri a tha t ha s t o occu r i nsettin g u pcohor t groups .

ISSU E c.5 : Som e part s o f th e mode l hav e t o b e collapse d(suggestion : us e onl y 3 childre ncohort s b y ag e categor y

rathe r tha n7) ; othe r part s ma y hav e t o b e expanded . W e hav e n o proble m

wit hthi s suggestion . W e ha dconsidere dmakin g a simila r reductio nprio r t o th e meeting . I t doe s mak e ou r analysi s mor e manageable . However , sai dreductio nshoul donl y b e mad e i f i t make s sens e from

anexposur e pattern , physiologica l impact , o r healt hendpoin t viewpoint . W e solici t andwelcom e furthe r inpu t from th e Subcommitte e on preferre dcohor t categorie s andth e rational e fo r thei r selection . (Havin g fewe r cohor t group s doe s sav e u s compute r runmoney . Th e saving s ar e minimal , however , wit hrespec t t o fil e set-up . Ou r procedur e i s highl y automate dandth e numbe r o f categorie s use ddoe s no t affec t fil e developmen t cost s significantly. )

ISSU E c.6 : Ai r lea dlevel s i nurba narea s d o no t correlat e wel l wit htrend s i ngasolin e lead . Traffi c densit y i s no t a goo dindicato r o f lea dfallou t fro m moto r vehicl e traffi c (citin g anEP A repor t oncorrelatio nanalyse s i n Dalla s o r Houston) .P.1 7

1 5
W e agre e wit hth e firs t par t o f thi s comment . Ambien t lea dcome s from bot hprimar y

source s (moto r vehicl e emissions , poin t sourc e emissions ) an dsecondar y

source s (re-entraine ddusts , soil) . W e wer e no t plannin g t o us e gasolin e lea dlevel s inou r analysis , sinc e ou r wor k i s base don monitore ddat a a s note dabove . (Or , i nth e cas e o f poin t sources , on diffusio nmodelin g o f lea demissions. )
W e d o no t agre e wit hth e secon dpar t o f th e comment , however . A significan t correlatio nbetwee nlea dconcentratio ni nstree t dus t and roadsid e soil s andtraffi c densit y ha s bee nfoun d(Rolf e et

_aj_ , 1977 ; Quarle s et

_a_U , 1974 ; Wheele r an dRolfe , 1979) . Thes e andothe r studie s wil l b e use di nderivin g appropriat e relationship s betwee nai r lea dand soi l anddus t lea dlevel s t o approximat e thes e pathway s o f lea dexposure .

ISSU E c.7 : Housin g typ e shoul db e considere di nth e exposur e mode l a s wel l a s housin g age . From th e lea dpain t viewpoint , ol dhousin g i non e cit y i s ofte nver y

differen t tha nol dhousin g i nanothe r du e t o wal l coverin g practices . (Th e exampl e give nwa s wal l pape r us e i nPhiladelphi a vs . pain t us e i nChicago. )

ISSU E c.8 : Househol dcleanlines s i s anothe r facto r tha t affect s lea d exposure ; thi s i s correlate dwit hsocio-economi c standing . T o ge t a handl e o

nthi s issu e (an

drelate dexposur e issues) , tal k wit hmanager s o f lead-poisonin g preventio nprograms . Inrespons e t o Issue s c. 7 an dc.8 , w e understan dtha t indoo r lea di s partl y a functio no f th e item s mentione dandintende dt o us e tw o variable s a s surrogate s fo r them : pre-195 0 housin g expresse da s a percentage , an d averag e famil y

incom e expresse da s th e percentag e o f familie s belo w th e officia l povert y

line . Alternativ e possibl e surrogate s d o exist . (Wal l pape r us e dat a wil l b e a problem , however . U.S . Censu s dat a ar e no t availabl e onthi s item. ) W e wil l investigat e furthe r th e Subcommittee' s suggestion s expresse di nth e tw o comments , includin g contactin g lea d poisonin g progra m

official s i ncitie s lik e Chicag o andPhildelphia .

ISSU E c.9 : Th e exposur e modelin g effor t shoul db e base dupo nmateria l containe di nth e lea dcriteri a document . Staf f agre e andfull y inten dt o bas e exposur e modelin g wor k o n materia l containe di nth e criteri a documen t (CD) . Al l o f th e transformatio n factor s use di nth e mode l ar e base dona revie w o f studie s containe di n th e CD . Th e sam e i s tru e fo r othe r mode l variables , suc ha s non-ai r route s o f lea duptak e andmicroenvironmen t additiv e factor s (use dt o accoun t fo r lea dgenerate di na location , no t relate dt o ambien t lea d levels) .P.1 8



### 1 6

T o provid e th e Subcommitte e wit hanimpressio no f th e exten t t o whic h AS B tie s it s exposur e mode l t o th e CD , w e enclos e tw o workin g memo s from PEDC o discussin g variou s issue s andrelatin g the m t o variou s page s i nth e draf t lea dCD . Ther e ar e othe r memo s o nth e subjec t tha t w e wil l mak e availabl e t o th e Subcommitte e i f i t s o desires . Th e enclose dmemo s are :
1 . "Route s o f Lea dUptake. " T . Johnso nt o T . McCurdy , Octobe r 13 , 1982 . 2 . "Lea dUptak e Rate s b y Source. " T . Johnso nt o T . Feagan s an d T . McCurdy , Jul y

5 , 1983 .

ISSU E c.10 : AS B shoul drevie w othe r lea dexposur e modelin g wor k t o se e wha t ha s bee ndon e i nth e pas t (especiall y thos e effort s usin g simpl e techniques) . Staf f concu r an dhav e an dwil l agai nrevie w othe r lea dexposur e models . A s mentione dearlier , w e wil l als o tal k wit hlea dexposur e modelin g expert s o

nth e issue s note dabov e (an dbelow) .

ISSU E oil . AS B fi t a nexistin g mode l t o lea dinstea do f developin g a ne w model ; lea di s a uniqu e ai r pollutant , andAS B need s a uniqu e mode l fo r it .
W e fee l tha t th e NE M logi c an dstructur e i s applicabl e t o al l NAAQ S pollutants . Basically , i t relate s monitore dai r qualit y t o huma n microenvironments , account s fo r indoo r generate dai r pollutants , use s th e bes t informatio navailabl e onpopulatio nlocation , andaccount s fo r populatio n movement s throug htim e an dspace . Simulatio nrun s ca ntes t th e impac t o n output s o f alternativ e value s o f inpu t variable s o f interest . Inaddition , NEM i s structure dtowar ddoin g (bu t ha s no t t o dat e bee ns o used ) probabilisti c analyse s o f exposure s t o addres s uncertainty . Th e majo r ne w

factor s specifi c t o lea dtha t ar e no t alread y i nth e logi c o f NEM

ar e indirec t andnon-ai r route s o f exposure . W e hav e known from th e beginnin g tha t thes e route s woul dhav e t o b e explicitl y handle d i nth e lead-NEM . W e hav e devote dconsiderabl e tim e andthough t onincorporatin g non-ai r pathway s int o th e mode l bu t agre e tha t w e nee dt o spen da lo t mor e effor t i nthi s area . W e wil l attemp t t o incorporat e informatio no nal l majo r pathway s int o th e lea dexposur e model , andrepresen t th e mos t significan t uncertainties . W e recogniz e tha t w e di dno t communicat e ou r thinkin g o r progres s o nthes e issue s t o th e Subcommitte e ver y well . W e wil l attemp t t o d o s o a t th e nex t Subcommitte e meeting , an di nwritin g befor e that . We ar e conscientiousl y

reevaluatin g ou r entir e exposur e modelin g approac han d continu e t o lear nabou t lead ; hopefull y thi s wil l b e bette r communicate d i nth e future .P.1 9



### 1 7

ISSU E c.12 : AS B shoul d minimiz e non-ai r source s o f lea d i n th e modelin g effor t t o avoi d "excessiv e backgroun d noise " du e t o lead-base d paint , pica , etc
. Loo k a t th e "cleanest " cohort s only

.

ISSU E c.13 : Ther e i s to o muc h uncertaint yi n eac h o f th e componen t models ; ther e i s to o muc h disaggregatio n usin g an idealize d framewor k fo r whic h n o dat a exist s t o eithe r d o th e analysi s o r t o evaluat e plausibilit yo f th e mode l itself

. Ther e ar e n o dat a t o verif yth e model

.

ISSU E c.14 : Ther e ar e to o manycompartment s i n th e mode l tha t ar e no t neede d t o estimat e th e impac t tha t differen t ai r lea d level s hav e o n children' s health

. D o awa ywit h unessential s a t firs t and ad d compartment s a s neede d t o addres s questio n a s the yarise

. (O r a s anothe r Subcommitte e pu t it : NE M i s a n "over-archin g conceptualization " tha t i s bein g force

fi t t o th e science. )
AS B staff' s respons e t o thes e thre e Subcommitte e comment s build s upo n ou r previou s discussion

. W e se e th e thre e comment s a s reflectin g th e scientifi c perspectiv e o f understandin g phenomena , wherea s w e fee l compelle d b

yth e ver ynatur e o f th e exercis e t o adop t th e analyti c perspective

. Commen t 1 2 reflect s th e scientifi c vie wo f experimenta l design , wher e confoundin g variable s ar e controlle d s o tha t relationship s o f interes t ar e isolated

. W e use , rathe r tha n generate , an yrelevan t informatio n tha t ha s bee n generate d b ywel l designe d experiment s o r b yth e applicatio n o f statistica l procedure s tha t contro l a s wel l a s possibl e (usuall yno t ver ywell ) fo r extraneou s influence s o f nonexperimenta l data

. Ou r rol e i s no t t o generat e suc h informatio n bu t rathe r t o us e whateve r informatio n i s availabl e a t th e tim e a decisio n mus t b e mad e t o asses s th e differenc e meetin g alternativ e P b standard s woul d mak e i n healt h risk s incurred

. Non-ai r source s o f P b contribut e t o th e level s tha t caus e thi s ris k a s wel l a s ai r sources . In othe r word s w e woul d commi t th e fallac yo f attributin g a singl e caus e t o a phenomen a fo r whic h ther e ar e multipl e cause s i f w e wer e t o minimiz e non-ai r source s o f P b i n th e modelin g effort

. Th e resultin g ris k assessmen t woul d b e logicall yunsoun d and therefor e ten d t o produc e misleadin g outputs
. Comment s c.1 3 an d c.1 4 hav e bee n addresse d i n par t i n th e respons e above

. W e thin k a lo t o f disaggregatio n i s needed , especiall ya t first , i n orde r t o properl ystructur e a comple x situation

. I n addition , i t i s usuall y easie r t o aggregat e i n modelin g tha n t o decompos e afte r a structur e i s finalized

. Lac k o f dat a t o adequatel ydefin e a variabl e i s on e goo d reaso n t o aggregate
. Wit h eac h aggregation , however , on e les s uncertai n facto r remain s tha t ca n b e addresse d explicitly

. On e les s variabl e als o remain s tha t ca n b e exercise d i n orde r t o determin e wha t impac t varyin g i t ha s o n mode l outputs
. Fro mou r pas t experience , w e ca n anticipat e th e followin g kind s o f question s regardin g lea d exposures . I f variable s d o no t exis t i n th e mode l t o addres s them , w e ar e remis s a s analysts

.P.2 0



### 1 8

Dietar y lea dmake s upa significan t portio no f tota l lea dingeste d b y th e typica l child . Wha t i s th e distributio no f dietar y lead use di nth e model , how i s th e relationshi pbetwee nairborn e an d dietar y lea dlevel s derived , andwha t impac t doe s dietar y lea d hav e o nelevate dbloo dlea dlevel s whe nalternativ e lea dNAAQ S ar e jus t attained ?

2 . I f smelter s reduce dthei r emission s b y 50 % (o r some othe r proportion ) o naverage , wha t i s th e estimate dimpac t o nbloo dlea ddistribution s i nchildre nles s tha nsi xyear s ol dwh o liv e i nsmelte r communities ? Wha t migh t i t b e afte r te nyears , whe ndus t an dsoi l lea dlevel s ar e subsequentl y

reduced ? Staf f anticipate s tha t many question s lik e thes e wil l b e raise ddurin g th e lea dNAAQ S review . W e wan t t o b e abl e t o formall y addres s them . T o d o so , we probabl y

nee da comple xmodel . A s mentione da t th e meeting , ther e i s now

a n"inescapabl e demand " fo r exposur e modelin g o f NAAQ S pollutants . Thi s poin t wa s echoe db y on e o f th e Subcommitte e member s in Commen t c.1 5 (below) , andstaf f concur . A s mentioned , w e ar e reviewin g th e entir e exposur e mode l (a s wel l a s othe r modelin g components ) i norde r t o simplif y wher e possible . However , th e Subcommitte e shoul db e awar e tha t ther e i s a stron g counterforc e towar dcomplexity—no t fo r it s ow nsake , bu t becaus e i t i s i nth e onl y wa y t o analyz e issue s tha t industrial andenvironmenta l reviewer s o f ou r wor k ar e a s wel l a s EP A managemen t intereste din . I f th e underlyin g dat a bas e i s highl y

uncertain , thi s wil l b e reflecte di nou r results .

ISSU E c.15 . Al l problem s aside , yo ustil l "hav e t o com e upwit hexposur e estimates " o f airborn e lea dt o analyz e ai r lea dstandards . W e agree .

d . ISSUE : Th e Subcommitte e though t tha t ther e wer e a numbe r o f problem s associate dwit hth e propose dus e o f a Rabinowitz-typ e o f compartmenta l mode l t o analyz e distributio nandkinetic s o f lea di nchildren . Comment s referre dt o th e following :

ISSU E d.l . Withou t develope dphysiologica l model s o nchildren , th e exercis e i s doomed . Ther e ar e many limitation s associate dwit husin g model s develope dfo r adult s t o childre nbecaus e o f difference s relate dt o lea d metabolism . Amon g thes e difference s ar e th e greate r gastrointestina l absorptio nandretentio nrate s i nchildre no f ingeste dlead , andth e rapi dgrowt ho f tissue s i nth e developin g chil dan dthu s increase dtransfe r rate s betwee nbod

y compartment .P.2 1



### 1 9

ISSU E d.2 . Th e Rabinowit z et

_ a\_. wor k i s goo dbu t i t wa s don e o nadult s only . Th e pathwa y

constant s ar e muc hdifferen t fo r adult s tha nfo r children . Perhap s recen t primat e dat a ma y hel pi naddressin g th e adul t vs . childre nmetabolis m issue . Perhap s huma nautops y studie s ma y

b e anothe r sourc e o f compartmen t lea dlevel s a t differin g ages .

ISSU E d.3 . Th e relationshi pbetwee nabsorbe dlea dandbon e lea di s non linear . I t i s no t a first-orde r process . RESPONSE : A s th e criteri a documen t notes , "i nyoun g children , bloo dlea d i s muchles s a reliabl e indicator " o f tota l body burde nbecaus e o f thei r larg e labil e pool s o f sof t tissu e an dbon e lea d(CD , p . 10-28) . Thus , thei r bloo dlea dlevel s reflec t recen t a s wel l a s pas t exposures . Mathematica l description s o f physiologica l lea dkinetic s tha t ar e bein g considere dfo r ou r mode l allo w a quantitativ e understandin g o f th e sequenc e o f change s i nlevel s o f lea di nvariou s body pool s andtissues . Thi s i s essentia l t o estimatin g andinterpretin g change s i nbloo dlea ddistributio n associate dwit halternativ e ai r lea dstandards , give npas t ai r an dnon a i r exposures . Hopefully , availabl e model s suc ha s Rabinowitz' s ca nb e use do r modifie dfo r thi s purpose . Whateve r mode l i s develope dwil l no t b e an y mor e comple xtha nnecessary . Th e Ph.D . dissertatio no nlea duptak e andbiokinetic s i ninfan t and juvenil e primate s give nt o AS B staf f b y Dr . Lippman npromise s t o yiel d importan t information . Staf f wil l investigat e th e usefulnes s o f huma n autops y studie s i nprovidin g AS B wit hcompartmenta l lea dinformatio ni n children . Whil e relationshi pbetwee nbloo dlea dandai r lea d(Hammon de t al. , 1980) , die t (Unite dKingdo m Centra l Directorat e o nEnvironmenta l Pollution , 1982 ) an dta pdrinkin g wate r (Sherloc k e1*

_ al_. , 1982 ) ar e al l non-linea r i n mathematica l form , mos t o f th e availabbl e compartmenta l mode l o f lea d metabolis m

ar e governe db

y a syste m

o f linea r first-orde r differentia l equation s wit hconstan t fractiona l transfe r coefficient s Holtzman , 1978 ; Rabinowit z e t al. , 1976 ; Batschele t et

_a]_. , 1979) . Ther e i s evidence , however , tha t non-linea r kineti c mechanism s exis t betwee n toxicologicall y

activ e lea dan dth e bloo dlea dpoo l including : partiall y rate-limite dgu t absorptio no f lea d(Aungs t et

_al_. , 1982) ; rate-limite d an dsite-limite dkinetic s i nth e distributio no f lea dbetwee nplasm a an d erythrcyt e pool s (D e Silva , 1981) ; increase durinar y excretio no f lea d (Chamberlai net

_aj_. , 1974) ; increase dtissu e absorptio no f bloo dlea d (Indraprasi t et

_aj_. , 1974) . Increase dmobilizatio no f lea dstore di nth e Skelton , especiall y

durin g childhood , and ; transpor t o f lea dthroug hbon e tissue s b

y proces s (Barry l 1982) . Marcu s (1983 , i npress ) formall y teste d non-linea r model s fo r severa l o f thes e mechanism s anddi dno t fin d significantl y

superio r prediction s o f bloo dkinetic s ove r linea r models .P.2 2



### 2 0

I t i s clea r tha t understandin g non-linea r mechanism s fo r lea dkinetic s i nma nrequire s fa r mor e detaile dexperiment s tha nhav e t o dat e bee n carrie dout . AS B wil l continu e t o asses s th e availabl e literatur e t o addres s th e problem s raise db

y Subcommitte e member s i nthis , a s wel l a s othe r area s o f physiologica l modeling . We wil l als o tal k t o relevan t expert s abou t th e possibilit y

o f modifyin g th e Rabinowit z mode l s o i t ca nb e use dfo r children , give nal l o f th e problem s note db y th e Subcommittee . W e wil l rela y ou r finding s t o th e Subcommitte e a s soo na s possible . I t shoul db e note dtha t i f w e hav e n o acceptabl e wa y o f relatin g ai r an dothe r medi a lea dexposure s t o bloo d(o r bone ) lead , ther e i s littl e sens e i ndevelopin g dose-respons e relationships . I norde r t o d o a lea d ris k assessmen t thi s relationshi pmus t b e represented . Th e subjec t are a i s obviousl y

ver y importan t t o th e entir e assessmen t effort . Wha t woul db e acceptable ? AS B staf f wishe s tha t a scientificall y vali dmode l wa s availabl e t o jus t "plu g in " andobtai nphysiologica l impac t estimate s associate dwit halternativ e lea dai r standards . Thi s i s no t th e situation , obviously . What , then , i s th e alternativ e t o physiologica l modeling ? I f ther e i s none , ou r onl y optio nseem s t o b e t o us e th e bes t informatio navailabl e andexplicityl y represen t majo r uncertaintie s i nou r procedure . Again , staf f i s intereste di nreceivin g Subcommitte e inpu t onthi s issue .

ISSU E d.4 . OAQP S shoul dd o researc ho nhow wel l th e Rabinowit z mode l compare s t o dat a onchildren . RESPONSE : OAQP S i s no t th e organizatio nwithi nEP A tha t woul dd o th e researc hsuggested . AS B wil l conve y th e recommendatio nt o th e appropriat e grou pi nEPA' s Researc handDevelopmen t Office .

ISSU E d.5 . Ther e ar e to o man y compartment s i nth e lea dphysiologica l model . AS B shoul deliminat e non-essentia l compartment s initiall y andaddthe m

a s needed . Th e onl y

compartmen t fo r whic ha goo ddat a bas e exist s i s bloo d lea dandsinc e bloo dlea di s known , ther e i s n o nee dt o comput e it . RESPONSE : Staf f concur s wit hth e concep t tha t th e physiologica l mode l no t hav e an

y mor e compartment s beyon dthos e necessar y t o "understand " an d describ e th e distributio nandequilibriu m dynamic s o f th e lea dbody burden . A s th e Subcommitte e i s aware , bloo dlea dlevel s are a functio n o f recen t lea dexposure s a s wel l a s pas t lea dexposures . T o estimat e wha t change s occu r i nbloo dlea ddistribution s o f childre nwhe na nalternativ e ai r lea dstandar di s jus t attaine drequire s u s t o mode l majo r functiona l relation s amon g body

pool s o f lead . Hopefully , th e Rabinowit z mode l ca n b e use do r modifie dfo r thi s purpose . Tha t model , o r an y other , wil l no t b e an y mor e comple xtha nneede dt o d o th e job .P.2 3



### 2 1

I t shoul db e note dthat some Subcommitte e member s di dno t fee l that th e mode l containe dto o man y compartments . The y note dthat th e documente d transfe r o f lea damon g compartment s andth e influenc e o f tota l body burde n o f lea do

nth e absorptio nanddistributio no f newl y introduce dlead , argu e fo r a mode l that sufficientl y addresse s thi s dynami c situation . AS B staf f concur . A subcommitte e membe r als o commente dthat modelin g bloo dlea dwa s unnecessar y

give nth e wealt ho f bloo dlea ddata . W e d o hav e bloo dlea d dat a tha t wil l b e use dt o th e fulles t exten t possible . At th e minimum , i t wil l b e use dt o chec k bloo dlea ddistribution s estimate dvi a th e physiologica l model . Th e sam e i s tru e o f an y bon e lea ddata , o r she d teet hdat a (i f suc ha compartmen t appear s i nth e model) , that ar e available . Staf f wil l mak e a concerte deffor t t o obtai nal l relevan t dat a o nbody lea ddistributions . However , havin g bloo dandothe r tissu e lea ddat a i s no t sufficien t fo r standard-settin g purposes . Often , exposur e informatio nassociate d wit hbloo dlea ddat a i s lacking , an danexposure-physiologica l link canno t b e made . I

naddition , bloo dlea ddat a ar e no t associate dwit hth e hypothetica l situatio no f just attainin g a nambien t ai r standard . Thus , suc hdat a d o no t provid e anunderstandin g o f ho w bloo dlea dlevel s ma y chang e ove r tim e i na sensitiv e populatio ngrou pexperiencin g ai r lea d level s expecte da t attainmen t (give nvariou s assumption s abou t lea d exposur e du e t o non-ai r routes) .

ISSU E d.6 . Modele doutput s fro m th e compartmenta l mode l shoul db e compare d t o bloo dlea dinformatio ntha t i s availabl e i nselecte dcities . (However , on e Subcommitte e membe r note dtha t bloo dlea ddat a i s no t a goo dsurrogat e fo r tota l lea dexposur e a s bloo dlea dlevel s chang e to o rapidly. )
RESPONSE : Thi s issu e ha s bee naddresse di nth e previou s discussion . Staf f wil l compar e ou r estimate dbloo dlea ddistribution s wit havailabl e data . W e agre e tha t bloo dlea ddat a d o no t provid e th e entir e pictur e concernin g tota l lea dexposure , especiall y fo r lon g tim e periods . Fo r thi s reaso nw e hav e propose dth e us e o f a compartmenta l mode l o f lea d poo l interactio na s th e basi s fo r ou r physiologica l impact s procedure .

e . ISSUE : Th e Subcommitte e ha dfew comment s regardin g th e dose-respons e portio no f th e lea dris k assessmen t project . Som e o f th e Subcommittee' s discussio no f thi s portio nrelate dt o outpu t measure s (discusse dbelow ) o r t o healt hendpoint s (discusse dabov e a t 3b) . Subcommitte e concern s regardin g th e propose dplanne ddose-respons e effor t wer e focuse donth e probabilit y

surfac e an

dsensitiv e populatio ngrou p"cutpoint " concept s presente db

y Argonn e Nationa l Laboratory . Thes e concern s were :P.2 4



### 2 2

ISSU E e.l

. Th e ide a o f developin g individua l dose-respons e function s fo r differen t "cutpoints " i n th e sensitiv e populatio n grou p i s th e F/ B formulation

.

ISSU E e.2

. Athre e dimensiona l dose-respons e relationshi p i s to o complex

. Slic e i t dow n t o 2 s o tha t expert s ca n b e comfortabl e tha t th e judgmen t wil l b e properl ycommunicated

. RESPONSE : Th e firs t commen t concern s Argonne' s proposa l t o generat e a probabilit ysurfac e b yencodin g healt h expert s at , say , th e first , fifth , tenth , twenty-fift h etc
. percentile s fo r th e mos t sensitiv e grou p (children)

. Thi s approach , whil e firs t formulate d b yTo mFeagan s an d Dr
. Biller , i s no t a n ide a peculia r t o a particula r approac h t o ris k assessment
. Rather , i t capture s th e logi c o f th e situatio n w e mus t dea l with : namely , tha t th e shap e and locatio n o f relevan t dose-respons e relationship s ar e uncertai n and tha t thi s uncertaint yaffect s risk s t o th e mor e sensitiv e member s o f th e mos t sensitiv e groups . W e mus t dea l wit h thi s inheren t logi c a t OAQPS , a s w e hav e i n th e past , whethe r w e d o a forma l ris k assessmen t o r not
. A s th e member s o f th e Subcommitte e know , empirica l evidenc e show s tha t no t al l sensitiv e peopl e respon d t o a pollutan t i n th e sam e way . Som e sensitiv e peopl e ar e no t a s sensitiv e a s others

. Neithe r thi s fac t no r th e uncertaint ytha t exist s abou t th e shap e an d locatio n o f resultan t dose-respons e relationship s ca n b e ignored

. I t i s clea r fro mth e legislativ e histor yo f th e Clea n Ai r Ac t and it s amendment s tha t a NAAQ S shoul d protec t almos t al l member s o f th e mos t sensitiv e grou p agains t advers e healt h effect s wit h a n adequat e margi n o f safet y(Senat e Committe e o n Publi c Work s ALegislative , Histor yo f th e Clea n Ai r Ac t Amendment s o f 1970 ; seria l 93-1 8 (1974))

. (A s a n aside , bot h C O report s presente d a t th e meetin g treate d th e sensitiv e populatio n grou p a s a homogeneou s categor yo f peopl e and thi s wa s a fundamenta l proble mwit h thei r approaches

. I n bot h case s i t resulte d i n logicall yindefensibl e ris k numbers. )
AS B staf f believe s that , a s wel l a s headcoun t ris k measures , a ris k measur e tha t wil l giv e ris k estimate s fo r type s o f individual s a t variou s percentil e "cutpoints " o f th e mos t sensitiv e group i s required

. Whic h percentil e cutpoint s woul d b e focuse d o n i s a polic ychoice , o f course , tha t AS B staf f doe s no t make

. Onc e encoding s hav e bee n obtaine d fo r a se t o f cutpoint s tha t spa n th e mos t sensitivv e group , ris k estimate s fo r cutpoint s chose n b

ypolicy-maker s ar e calculabl e b yinterpolation

. Th e Subcommittee' s secon d commen t concern s whethe r a 3-dimensiona l dose-respons e surfac e i s to o comple x fo r expert s t o wor k with

. Dr
. Wallsten' s researc h indicate s tha t healt h expert s ca n understan d an d wor k wit h 3-dimensiona l surfaces

. A s Drs
. Whitfiel d and Wallste n indicate d a t th e meetin g (Vol

. II , p . 12 1 ff) , th e thre e surface s ar e obtaine d conditionall y o n on e dimensio n s o tha t a n exper t onl yha s t o dea l wit h tw o dimension s a t an yon e time

.P.2 5



### 23

I naddition , w e submi t tha t thre e dimension s ar e necessar y fo r a probabilisti c assessment . By definition , tw o dimension s ar e dos e (expresse d i nphysical units ) andrespons e (usuall y expresse da s a percen t of th e expose dgrou ptha t respond s t o some specifie dhealt heffec t level) . Th e uncertaint y

concernin g wha t th e tru e dose-respons e relationshi pi s fo r th e grou pbein g analyze dresult s from th e fac t tha t no t al l person s wer e investigate dno r wer e al l possibl e exposur e condition s take nint o account . T o addres s uncertaint y i nth e populatio ndose-respons e relationship , w e wil l encod e expert s t o obtai nthei r probabilisti c judgment s regardin g respons e rat e fo r th e populatio ngive na particula r dos e (o r dos e give na specifie drespons e rate) . Thes e probabilisti c judgment s consitute s th e * thir ddimension . Withou t the m yo uhav e t o assum e a particula r dose-respons e curve . W e d o no t thin k tha t anapproac htha t ignore s uncertaint y i nth e dose-respons e relationshi pi s th e wa y t o conduc t a ris k assessmen t o f alternativ e ambien t ai r standard s whos e mai npurpos e i s t o formall y dea l wit hsignifican t uncertaintie s s o tha t policymaker s ca nmos t meaningfull y decid e whic hstandard , i nthei r judgment , provide s a nadequat e margi nof safety . Durin g th e C O ris k assessmen t metho ddevelopmen t project , Woodwar d andClyd e Consultant s (WCC ) develope da three-dimensiona l dose-respons e relationshi pfo r thre e majo r carbo nmonoxid e healt heffects . (SR I di d not. ) Fo r th e additiona l angin a attac k effect s category , WC C develope d th e probabilit y

dimensio nb

y fittin g a norma l distributio naroun dth e log-odd s dose-respons e relationshi ptha t th e firm derive dfrom

encode d exper t data . WC C assume dtha t th e mea no f th e fitte dnorma l distributio n wa s th e sam e a s th e mea nof th e lo g odd s regressio nmode l (-3.6 5 + 3.1 1 I n(COHb) ) wit ha standar ddeviatio no f 0.50 , whic hcam e from encode d data . A

simila r procedur e wa s use dt o accoun t fo r uncertaint y regardin g dose-respons e relationship s fo r th e othe r tw o majo r healt heffect s o f CO . Whil e AS B doe s no t necessaril y agre e wit hho w

WC C derive dth e probabilisti c dimensio ni nit s work , th e firm showe dtha t i t ca nb e done--a s di d Dr . Wallsten .
Ou r conclusion , then , i s tha t a 3-dimensiona l surfac e i s bot hfeasibl e anddesirabl e fo r probabilisti c analyse s of uncertai ndose-respons e relationships . W e solici t Subcommitte e commen t onthi s conclusion .

4 . Genera l Issue s Thes e issue s d o no t fi t wel l int o an y of th e previou s categories . The y involv e outpu t measure s andAS B analyti c resources .

a . COMMENT : AS B shoul dexpen dmor e resource s t o undertak e th e lea d ris k assessment . Th e economi c impact s o f a lea dNAAQ S warran t spendin g sufficien t resource s onth e pollutant . RESPONSE : OAQP S wil l b e expendin g onth e orde r of $750,00 0 onth e lea dris k assessmen t effort . Thi s figur e include s th e contractua l wor k wit hArgonn e Nationa l Laborator y (an dit s consultant s andsubcontractors) ;P.2 6



### 2 4

ai r qualit y

dat a analysi s andfil e developmen t wor k b y PEDCo ; par t o f Dr . BiTier' s contractura l wor k wit hStrategie s andAi r Standard s Divisio n(SASD) ; exposur e modelin g compute r charge s a t EPA' s Nationa l Compute r Center ; par t o f th e poin t sourc e modelin g wor k b y GC A Technology ; and'in-hous e staf f time . Thi s figur e represent s a sizabl e amoun t o f SASD' s analysi s budge t fo r NAAQ S pollutants . Beside s lead , tha t budge t mus t b e divide damon g ozone , particulat e matter , sulfu r dioxide , nitroge ndioxide , andcarbo nmonoxide- ' th e pollutant s tha t ar e currentl y bein g reviewed . Thes e pollutant s hav e a societa l economi c impac t a t leas t a s larg e a s lead . SASD' s budge t fo r regulator y analyse s i s determine da t highe r level s o f EP A management . NAAQ S review s compet e wit hman y othe r program s fo r resources . Unde r ou r curren t budget , providin g additiona l fund s fo r lea d ris k assessmen t activitie s (suc ha s mor e encoding ) ma y mea ntha t th e regulator y

analysi s budge t fo r on e o f th e othe r NAAQ S pollutant s wil l hav e t o b e reduced . Th e zero-sum natur e o f th e competitio nfo r availabl e resource s require s u s t o sta y withi nou r ris k assessmen t budge t i f a t al l possible .

b . COMMENT : Th e outpu t measure s use di nth e lea dris k assessmen t effor t shoul dinclud e prevalenc e type s o f measures . Impac t onbot hALA- D andprotoporphyri ni nth e sensitiv e grou pshoul db e use da s outpu t measure s o f th e physiologica l model . .'•'' . v * : '" '
RESPONSE : Staf f agre e onbot hcounts . W e pla nt o provid e people occurrence s outpu t measure s a s wel l a s th e numbe r o f peopl e affected . W e inten dt o us e change s i nerythrocyt e protoporphyri nlevel s a s an outpu t measur e sinc e i t doe s reflec t somewha t longe r ter m exposure s tha n doe s bloo dlead . Th e us e o f ALA- D inhibitio nwil l b e considere da s well . Bot ho f thes e indice s ar e als o bein g considere da s possibl e healt h endpoint s i nth e ris k assessment .