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Summar yo f Preliminar yStaf f Conclusion s an d Recommendation s o nth e Primar yStandar d Th e majo r staf f conclusion s and recommendation s mad e i nSectio nVII , A- C ar e briefl ysummarize d below : 1 ) Th e quarterl yaveragin g perio d use d fo r th e curren t lea d standar d allow s significantl yelevate d monthl yaverag e concentrations , and repeate d monthl yexcursion s abov e a quarterl ystandar d leve l ma yproduc e Pb B level s elevate d ove r thos e tha t woul d b e predicte d unles s th e standar d wa s exceeded . Becaus e suc helevation s ma yb e associate d wit hsom e increase d healt hrisk , th e staf f recommend s tha t consideratio nb e give nt o a monthl yaverag e sinc e i t woul d b e mor e protectiv e o f children' s healt htha nth e curren t quarterl ystandard . Guidanc e i s requeste d fro mCASA C o nwhethe r th e adde d protectio nprovide d b ya chang e t o a monthl ystandar d woul d warran t a revisio no f th e curren t quarterl yaveragin g period . Th e staff'als o request' s commen t o nwhethe r th e availabl e informatio nsuggest s th e nee d fo r a n averagin g perio d les s tha na month . Shoul d a monthl yaverag e lea d NAAQ S b e chosen , i t woul d b e necessar yt o revis e th e curren t on e i nsi xda yai r lea d samplin g schedule . Analyse s ar e underwa yt o determin e th e mos t appropriat e samplin g schedule s unde r a monthl ystandard . 2 ) Th e primar ylea d NAAQ S shoul d b e expresse d i na statistica l for m rathe r tha nth e curren t deterministi c form . Th e decisio no nth e statistica l approac ht o b e adopted , wit hpossibl ymor e frequen t sampling , shoul d b e mad e i nconjunctio nwit hestablishin g a leve l fo r th e standard . 3 ) Lea d affect s man ydifferen t orga nsystem s and biochemical/physiologica l processe s acros s a wid e rang e o f exposur e levels . Thes e effect s rang e fro mbiochemica l change s i nenerg ymetabolism , neurotransmission , and bloo dP. 3

enzym e activit ydetectabl e a t very lo wdosage s wit hn o apparen t threshol d o na subcellular-molecula r level , t o severe , irreversibl e centra l nervou s syste mdamag e manifeste d b ymenta l retardation , encephalopath yand possibl y deat ha t Pb B level s abov e 80-10 0 ug/dl . 4 ) Base d o nrecen t studies , th e Pb B leve l o f 3 0 ug/d l use d a s th e maximu m safe.leve l fo r a nindividua l chil d i nsettin g th e 197 8 lea d NAAQ S contain s littl e o r n o margi no f safet yfor . childre nfro msevera l advers e healt h effects . Base do na nassessmen t o f th e availabl e healt heffect s data , th e staf f conclude s tha t a chil d wit ha Pb B o f 25-3 0 ug/d l i s a t ris k o f signifi

can t alteration s i nhem e synthesi s (a s indicate d b yelevate d EP) , depressio n i nvitami nD metabolism , an d possibl yneurobehaviora l disturbances , whic h collectivel yma yrepresen t impaire d functionin g an d deplete d reserv e capacitie s o f man ydifferen t tissue s an d organs . Belo w25-3 0 ug/dl , th e ris k as sociate d wit hobserve d reduction s i nhem e and vitami nD hormon e synthesis , a s wel l a s altere dbrai nwav e activit yan d smal l decrement s i ncognitiv e functio nan dbehavio r hav e no t bee nfull ydetermined . Th e CD C ha s revise d th e Pb B leve l use d t o identif ychildre nwit hexcessiv e lea d exposur e i nth e lea d poisonin g preventio nscreenin g progra m fro m3 0 t o 2 5 ug/dl , a medica l "intervention " leve l tha t represent s a compromis e betwee nth e amoun t o f tolerabl e ris k andth e practica l limit s o f effectivel yimplementin g th e existin g screenin g program . Th e staf f conclude s tha t a Pb B fo r a nindividua l chil d o f 2 5 ug/d l appear s t o contai nlittl e o r n o margi no f safet yfro m significan t risk s o f multi-orga nimpairment s an d possibl e neurologica l dysfunction . 5 ) Fairl yconsisten t result s wer e provide db yth e thre e modelin g approache s use d t o estimat e Pb B level s amon g childre nunde r alternativ e ai r lea d concentration s assume d t o b e maintaine d a t constan t levels : th e integrate dP. 4

lea d uptake/biokineti c model , th e aggregat e epidemiologica l bloo d lead/ai r lea d slop e approach , an d th e disaggregat e epidemiologica l approac hpresente d i nth e criteri a document . Calculation s wer e performe d o nth e assumptio n tha t th e geometri c standar d deviatio n(GSD ) fo r th e chil d populatio ni s constan t an d i nth e rang e o f 1.3 4 t o 1.3 9 a s cite d i nth e CD . Base d o n thi s .premise , al l thre e model s predicte d tha t i norde r t o preven t 99.5 % o f childre nfro m

exceedin g 2 5 pg/dl , a nai r lea d leve l constantl ya t attainmen t n o highe r tha nth e curren t standar d leve l woul d b e required , and possibl y n o highe r tha n0.7 5 pg/m 3 , dependin g o nth e assumption s and calculation s use d i nth e differen t models . Shoul d a Pb B o f 2 0 pg/d l b e determine d t o b e th e maximu macceptabl e saf e Pb B leve l an d assumin g a goa l o f 99.5 % protection , GSD s betwee n1.3 4 an d1.39 , and anai r leve l tha t i s constantl ymaintained , the na leve l n o highe r tha n0.5-0.7 5 pg/m 3 woul d b e require d - unles s th e leas t conservativ e aggregat e epidemiologica l mode l alon e i s considered , i n whic hcase , a leve l o f 1.2 5 pg/m 3 ma yb e sufficient . Aleve l that , i s maintaine d a t 0. 5 pg/m 3 , and possibl ya s lo wa s 0.2 5 pg/m 3 , woul d b e require d t o preven t 99.5 % o f childre nfro mexceedin g Pb B level s abov e 1 5 pg/dl , dependin g o nwhic hmode l i s considered , an dassumin g a constan t GS D betwee n 1 .3 4 an d 1.39 . Calculation s wer e als o performe d base d o na differen t characterizatio n o f th e tai l en do f th e distributio no f children' s Pb B levels . Thi s alternativ e statistica l approac hindicate s tha t somewha t differen t averag e ai r lea d level s woul d b e require d fo r equivalen t healt hprotectio nusin g th e sam e thre e exposur e modelin g approaches . Fo r example , th e criteri a documen t "disaggregate " mode l estimate s tha t a t a naverag e ai r lea d leve l o f 0. 5 pg/m 3 , th e populatio nmea nPb B leve l amon g childre nwoul d b e approximatel y 8. 5 pg/d l whic hcorrespond s t o keepin g 99.5 % o f childre nfro mexceedin g aP. 5

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Pb B leve l o f 18. 1 o r 19. 9 pg/d l (dependin g o nwhic hGS D i s assumed) . I n

contrast , accordin g t o result s usin g th e alternativ e statistica l approac h (whic hi s base do na logisti c regressio nanalysi s o f NHANE S I I data) , a populatio nmea nPb B leve l o f 8. 7 pg/d l woul d correspon d t o preventin g 99.5 % o f childre nfro m

exceedin g a Pb B leve l o f 2 5 pg/dl . Furthe r informatio nan d CASA C guidanc e i s sough t on : a ) whethe r thes e modelin g approache s ar e vali d give nth e availabl e dat a an d ho wthe yca nb e improved ; b ) appropriat e value s o f specifi c parameter s withi nth e variou s models , e.g. , blood/ai r lea d slope , non-ai r Pb B contribution ; an d c ) th e appropriat e statistica l techniqu e t o characteriz e th e tai l en d o f th e bloo d lea d distributio nunde r alternativ e ai r lea d level s a s predicte d b yth e variou s models , i.e. , shoul d a "constant " GS D b e use d t o represen t th e entir e distributio no f children' s bloo d lea d level s (and i f so , wha t th e appropriat e GS D valu e is) , o r whethe r th e alternativ e approac hbase d o n logisti c regressio nanalysi s o f NHANE S I I dat a woul d b e animprovement .