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OAR Box 1112 

Prepped by RyanDugan 

Document Number: 

18) ll-B-7 

Docket Number: 

A-83-22 

Printed 4/16/2008 9:12:06 AM Sheet 18 of 97 
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I X^mi I UNITED STATES ENVIRONMENTAL PROTECTION AGENCY 77 ^ n 

\~>** SEP A 1985 

SUBJECT: Modeling the blood lead distribution in children 

FROMi Joe l Schwartz 

Office of Policy Analysis 

To: Jeff Cohen 

Office of Air Quality Planning and Standards 

This memo is t o repor t the results of reapplying the 

technique s of my previou s memo on modeling the blood lead 

distributio n afte r taking int o account the CASAC's request to 

only conside r thos e children tha t can realisticall y be helped by 

an air quality standard. 

The implication of tha t statemen t was tha t CASAC felt that 

ther e were some children whose blood lead levels were s o high 

tha t change s in ai r lead would no t be important. It is not 

obvious what blood lead cutoff t o use . sinc e t o adequatel y define 

"help" we need t o know more about the doe s respons e relationship 

of lead than we do. For instance , reducing a child's blood lead 

leve l from 50ug/dl t o 40ug/dl will stil l leav e i t above any 

acceptabl e level , but tha t change may produce a s much health 

improvement fo r tha t child a s moving anothe r child from 25ug/dl 

t o 15ug/dl, and may produce more health improvement. It is 

certainl y possibl e tha t moving a child from 120ug/dl t o llOug/dl 

will produce no noticeabl e healt h improvement, and only major 

reduction s matte r a t tha t level . Picking the point a t which that 

occurs is mostly an exercis e in judgment. 

Moreover, the implications of changing log blood lead while 

leaving the GSD fixed is tha t change s in blood lead are 

proportionate . That is, a change tha t reduce s a child's blood 

lead from 25 to 20 ug/dl would be expected to reduce a child 

a t 50 ug/dl t o 40ug/dl. It is ver y likely that the health 

benefit of the latte r equals or exceed s the healt h benefit of 

the former. The constan t proportionat e reduction implicit in 

the lognormal distributio n has suppor t in biology (beside s the 

obvious suppor t tha t the distributio n is in fac t lognormal). 

The children with high blood lead levels ar e more likely to 

include thos e with highe r than averag e gu t absorptio n rates. 

and higher than averag e pica activity . Seducing ai r 

contamination of dir t and dust by 10% should produce a 10% 

reduction in thei r absorptio n from tha t media, just a s i t does 

f o r the low absorptio n and low pica children. However, that 

will result in a greate r absolute decrease. 

If we interpre t the CASAC statemen t t o only exclude thos e 

children fo r whom ther e will be no noticeabl e improvement, than 

i t would be reasonabl e t o exclude only thos e children above 70 

ug/dl. All of our NHANES analyse s have excluded al l indivic' 
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with blood lead levels over 70 ug/dl, so my previous memo covers 

that case. 

On the other hand, we might interpret the CASAC comment to 

mean that if children are a t blood lead levels where we cannot 

substantially affec t the number of children a t those levels, that 

we should therefor e ignore them for the airlead standard; Again, 

we need to decide what such a level is. In our analysis of the 

NHANES data we performed logisti c regressions of the probability 

of children being above various levels as a function of gasoline 

lead, a major source of air emissions. Gasoline lead was a 

statisticall y significant predictor of blood lead levels being 

above 35 ug/dl, s o the upper cutoff for impact of airlead must be 

higher than that. The lowest reasonable number is 40 ug/dl, so I 

used that in the next se t of runs. 

I excluded all children over 40 ug/dl and removed the 

effec t of gasoline lead broadening the distribution by adjusting 

everyone's blood lead to zero gasoline lead. I then dropped the 

gsd by 15% of the fall produced by removing the broadening due 

to gasoline lead to account for the 15% of NHANES airlead that 

was not gasoline lead. Excluding children over 40ug/dl gives a 

gsd in log space of .3502, compared to .360 a t zero airlead with 

the children over 40 ug/dl but below 70 ug/dl included. The 

comparable gsd's in normal space are 1.419 excluding the 

children above 40 ug/dl and 1.42 8 including them. This is 

the range that seems most appropriate.