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OAR Box 1111 

Prepped by RyanDugan 

Document Number: 

- W ) I l-A-1b 

Docket Number: 

A-83-22 

Printed 4/15/2008 1:25:18 PM Sheet 107 of 118 
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Summary of Preliminary Staff Conclusions and Recommendations on the 

Primary Standard 

The major staff conclusions and recommendations made in Section VII, A-C 

are briefly summarized below: 

1) The quarterly averaging period used for the current lead standard 

allows significantly elevated monthly average concentrations, and repeated 

monthly excursions above a quarterly standard level may produce PbB levels 

elevated over those that would be predicted unless the standard was exceeded. 

Because such elevations may be associated with some increased health risk, 

the staff recommends that consideration be given to a monthly average 

since it would be more protective of children's health than the current 

quarterly standard. Guidance is requested from CASAC on whether the added 

protection provided by a change to a monthly standard would warrant a 

revision of the current quarterly averaging period. The staff'also request's 

comment on whether the available information suggests the need for an 

averaging period less than a month. Should a monthly average lead NAAQS be 

chosen, it would be necessary to revise the current one in six day air lead 

sampling schedule. Analyses are underway to determine the most appropriate 

sampling schedules under a monthly standard. 

2) The primary lead NAAQS should be expressed in a statistical form 

rather than the current deterministic form. The decision on the statistical 

approach to be adopted, with possibly more frequent sampling, should be 

made in conjunction with establishing a level for the standard. 

3) Lead affects many different organ systems and biochemical/physiological 

processes across a wide range of exposure levels. These effects range 

from biochemical changes in energy metabolism, neurotransmission, and blood 
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enzyme activity detectable at very low dosages with no apparent threshold 

on a subcellular-molecular level, to severe, irreversible central nervous 

system damage manifested by mental retardation, encephalopathy and possibly 

death at PbB levels above 80-100 ug/dl. 

4) Based on recent studies, the PbB level of 30 ug/dl used as the maximum 

safe.level for an individual child in setting the 1978 lead NAAQS contains 

little or no margin of safety for. children from several adverse health 

effects. Based on an assessment of the available health effects data, the 

staff concludes that a child with a PbB of 25-30 ug/dl is at risk of significant alterations in heme synthesis (as indicated by elevated EP), depression 

in vitamin D metabolism, and possibly neurobehavioral disturbances, which 

collectively may represent impaired functioning and depleted reserve capacities 

of many different tissues and organs. Below 25-30 ug/dl, the risk associated with observed reductions in heme and vitamin D hormone synthesis, 

as well as altered brain wave activity and small decrements in cognitive 

function and behavior have not been fully determined. The CDC has revised 

the PbB level used to identify children with excessive lead exposure in the 

lead poisoning prevention screening program from 30 to 25 ug/dl, a medical 

"intervention" level that represents a compromise between the amount of 

tolerable risk and the practical limits of effectively implementing the 

existing screening program. The staff concludes that a PbB for an individual 

child of 25 ug/dl appears to contain little or no margin of safety from 

significant risks of multi-organ impairments and possible neurological 

dysfunction. 

5) Fairly consistent results were provided by the three modeling 

approaches used to estimate PbB levels among children under alternative air 

lead concentrations assumed to be maintained at constant levels: the integrated 
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lead uptake/biokinetic model, the aggregate epidemiological blood lead/air 

lead slope approach, and the disaggregate epidemiological approach presented 

in the criteria document. Calculations were performed on the assumption 

that the geometric standard deviation (GSD) for the child population is 

constant and in the range of 1.34 to 1.39 as cited in the CD. Based on 

this .premise, all three models predicted that in order to prevent 99.5% 

of children from exceeding 25 pg/dl, an air lead level constantly at attainment 

no higher than the current standard level would be required, and possibly 

no higher than 0.75 pg/m3, depending on the assumptions and calculations 

used in the different models. Should a PbB of 20 pg/dl be determined to be 

the maximum acceptable safe PbB level and assuming a goal of 99.5% protection, 

GSDs between 1.34 and 1.39, and an air level that is constantly maintained, 

then a level no higher than 0.5-0.75 pg/m3 would be required - unless the 

least conservative aggregate epidemiological model alone is considered, in 

which case, a level of 1.25 pg/m3 may be sufficient. A level that, is 

maintained at 0.5 pg/m3, and possibly as low as 0.25 pg/m3, would be required 

to prevent 99.5% of children from exceeding PbB levels above 15 pg/dl, 

depending on which model is considered, and assuming a constant GSD between 

1 .34 and 1.39. 

Calculations were also performed based on a different characterization 

of the tail end of the distribution of children's PbB levels. This alternative 

statistical approach indicates that somewhat different average air lead 

levels would be required for equivalent health protection using the same 

three exposure modeling approaches. For example, the criteria document 

"disaggregate" model estimates that at an average air lead level of 0.5 

pg/m3, the population mean PbB level among children would be approximately 

8.5 pg/dl which corresponds to keeping 99.5% of children from exceeding a 
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PbB level of 18.1 or 19.9 pg/dl (depending on which GSD is assumed). In 

contrast, according to results using the alternative statistical approach 

(which is based on a logistic regression analysis of NHANES II data), a 

population mean PbB level of 8.7 pg/dl would correspond to preventing 99.5% 

of children from exceeding a PbB level of 25 pg/dl. 

Further information and CASAC guidance is sought on: a) whether these 

modeling approaches are valid given the available data and how they can be 

improved; b) appropriate values of specific parameters within the various 

models, e.g., blood/air lead slope, non-air PbB contribution; and c) the 

appropriate statistical technique to characterize the tail end of the blood 

lead distribution under alternative air lead levels as predicted by the 

various models, i.e., should a "constant" GSD be used to represent the 

entire distribution of children's blood lead levels (and if so, what the 

appropriate GSD value is), or whether the alternative approach based on 

logistic regression analysis of NHANES II data would be an improvement.