Opinion ID: 390180
Heading Depth: 2
Heading Rank: 2

Heading: The Proposed Standards

Text: 18 Simultaneously with the publication of the Lead Criteria Document on December 14, 1977, the Administrator proposed a national primary ambient air quality standard for lead of 1.5 ug Pb/m 3 monthly average. 42 Fed.Reg. 63076, JA 1480. He also proposed that the secondary air quality standard be set at the same level as the primary standard because the welfare effects associated with lead exposure did not warrant imposition of a stricter standard. 42 Fed.Reg. 63081-63082, JA 1485-1486. In the preamble to the proposed standards the Administrator explained the analysis EPA had employed in setting the standards. 19 The Administrator first pointed out that a number of factors complicate the task of setting air quality standards which will protect the population from the adverse health effects of lead exposure. First, some sub-groups within the population have a greater potential for, or are more susceptible to the effects of, lead exposure. Id. at 63077, JA 1481. Second, there are a variety of adverse health effects associated with various levels of lead exposure. Id. Third, the variability of individual responses to lead exposure, even within particular sub-groups of the population, would produce a range of blood lead levels at any given air lead level. Id. at 63079, JA 1483. Fourth, airborne lead is only one of a number of sources of lead exposure and the relative contribution from each source is difficult to quantify. Id. at 63080, JA 1484. Finally, the relationship between air lead exposure and blood lead levels is a complex one. Id. at 63079, JA 1483. 20 In response to the first problem the Administrator began by noting that protection of the most sensitive groups within the population had to be a major consideration in determining the level at which the air quality standards should be set. And he determined that children between the ages of 1 and 5 years are most sensitive to the effects of lead exposure both because the hematologic and neurologic effects associated with lead exposure occur in children at lower threshold levels than in adults, and because the habit of placing hands and other objects in the mouth subjects them to a greater risk of exposure. Id. at 63077-63078, JA 1481-1482. Next, the Administrator examined the various health effects of lead exposure and proposed that EP elevation should be considered the first adverse health effect of lead exposure because it indicates an impairment of cellular functions, and should be the pivotal health effect on which the lead standards are based. Id. at 63078, JA 1482. Accordingly, he proposed that the air lead standards be designed to prevent the occurrence of EP elevation in children. In order to accomplish this, and to address the problem of variable responses to lead exposure, the Administrator selected 15 ug Pb/dl, the lowest reported threshold blood lead level for EP elevation in children, as the target mean population blood lead level. 17 He reasoned that setting the target mean population blood lead level at the lowest reported threshold blood lead level for EP elevation would ensure that most of the target population would be kept below blood lead levels at which adverse health effects occur. Id. at 63078, JA 1483. The Administrator also discussed the alternative approaches of basing the standard on more severe effects such as anemia, or attempting to decide the actual level of EP elevation which represents an adverse effect on health, and then making an adjustment to allow a margin of safety. Id. He specifically invited comments on these alternative approaches. Id. Finally, the Administrator outlined another approach to calculating the target mean population blood lead level involving the use of statistical techniques discussed in the Criteria Document. Id. 18 21 Having selected a target mean population blood lead level, the Administrator's next step was to allow for the multiplicity of sources of lead exposure. He thus had to estimate the amount of blood lead that should be attributed to non-air sources. The Administrator admitted that any amount he selected could be no more than a theoretical national average, and on the basis of the evidence available he proposed that the lead standards should be based on the general assumption that 12 ug Pb/dl of blood lead should be attributed to non-air sources. Id. at 63080-63081, JA 1484-1485. Given the target mean population blood lead level of 15 ug Pb/dl and the assumed contribution from non-air sources of 12 ug Pb/dl, the maximum allowable contribution from ambient air is 3 ug Pb/dl. The final step in his analysis was to determine what air lead level would prevent the ambient air contribution to blood lead levels from exceeding 3 ug Pb/dl. This step required determining the relationship between air lead exposure and blood lead levels, i.e., the air lead/blood lead ratio. On the basis of the information in the Criteria Document, the Administrator selected a ratio of 1:2 as appropriate for calculating the effect of air lead exposure on blood lead levels in children. Id. at 63079, JA 1483. 22 Thereafter, calculation of the air quality standard was a mathematical exercise as shown in the following table. 23 1. Target mean blood lead level 15 ug Pb/dl 2. Assumed non-air contribution -12 ug Pb/dl ------------- 3. Allowable air contribution =3 ug Pb/dl 4. Permissible air lead concentration given assumed air lead/blood lead ratio 3 ug Pb/dl X 1 ug Pbm 3 air =1.5 ug Pb/m 3 ---------------- 2 ug Pb/dl blood 24 The Administrator concluded, on the basis of available information, that the averaging period for the lead standard should be a calendar month. Id. at 63081, JA 1485.