Opinion ID: 390180
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Heading: The Lead Criteria Document7

Text: 11 EPA released its Air Quality Criteria For Lead on December 14, 1977. 42 Fed.Reg. 63076, JA 1480. The document was prepared to reflect the current state of knowledge about lead specifically, those issues that are most relevant to establishing the objective scientific data base that will be used to recommend an air quality standard for lead that will adequately safeguard the public health. CD 1-1, JA 1105. Accordingly, the Criteria Document examined a large number of issues raised by the problem of lead in the environment. One of these was the effects of lead exposure on human health. The Criteria Document concluded that, among the major organ systems, the hematopoietic (blood-forming) and neurological systems are the areas of prime concern. CD 1-12, JA 1116. Its discussion of the effects of lead on these two organ systems is central to our review of the lead standards. 8 12 The Criteria Document identified a variety of effects of lead exposure on the blood-forming system. We will discuss only the effects that played an important role in the Administrator's analysis. Anemia, which can be caused by lead-induced deformation and destruction of erythrocytes (red blood cells) and decreased hemoglobin synthesis, 9 is often the earliest clinical manifestation of lead intoxication. CD 11-7, 11-8, 11-13, JA 1229-1230, 1235. Symptoms of anemia include pallor of the skin, shortness of breath, palpitations of the heart, and fatigability. 10 The Criteria Document concluded, after a review of various studies, that in children, a threshold level for anemia is about 40 u(g) Pb/dl, whereas the corresponding value for adults is about 50 ug Pb/dl. CD 11-13, JA 1235. (The concentration of lead in the blood is measured in micrograms of lead per deciliter of blood ug Pb/dl.) 13 The Criteria Document also examined other more subtle effects on the blood-forming system, associated with lower levels of lead exposure. The most pertinent of these subclinical 11 effects for purposes of these cases is lead-related elevation of erythrocyte protoporphyrin (EP elevation). 12 According to the Criteria Document, this phenomenon must, for a number of reasons, be regarded as an indication of an impairment of human health. CD 11-11, JA 1233. First, EP elevation indicates an impairment in the functioning of the mitochondria, the subcellular units which play a crucial role in the production of energy in the body, and in cellular respiration. CD 1-6, 11-11, 11-14, 13-5, JA 1110, 1233, 1236, 1335. Second, it indicates that lead exposure has begun to affect one of the basic biological functions of the body production of heme within the red blood cells. 13 Heme is critical to transporting oxygen to every cell in the body. Third, EP elevation may indicate that any reserve capacity there may be in the heme synthesis system has been reduced. CD 11-11, JA 1233. Finally, the Criteria Document noted that lead's interference with the process of heme synthesis in the blood may suggest that lead interferes with production of heme proteins in other organ systems, particularly the renal and neurological systems. CD 11-11, JA 1233. The Criteria Document reported that the threshold for EP elevation in children and women is at blood lead levels of 15-20 ug Pb/dl, and 25-30 ug Pb/dl in adult males. CD 13-8 (Table 13-2), JA 1338 (Table 13-2). While suggesting that some of the initial hematological effects of lead exposure may constitute relatively mild effects at low blood lead levels, the Criteria Document concluded that they nevertheless signal the onset of steadily intensifying adverse effects as blood lead elevations increase. Eventually, (these)    effects reach such magnitude that they are of clearcut medical significance as indicators of undue lead exposure. CD 1-13, JA 1117. The Criteria Document did not identify a particular blood lead level at which regulatory response was appropriate, but it did note with approval the 1975 guidelines issued by the Center For Disease Control, which use elevated EP at blood lead levels of 30 ug Pb/dl as the cut-off point in screening children for lead poisoning. CD 13-5, JA 1335. 14 The Criteria Document also examined the effects of lead exposure on the central nervous system. Among the most deleterious effects of lead poisoning are those associated with severe central nervous system damage at high exposure levels. The Criteria Document noted that neurological and behavioral deficits have long been known to be among the more serious effects of lead exposure, but it pointed out that there is disagreement about whether these effects are reversible, and about what exposure levels are necessary to produce specific deleterious effects. CD 11-14, JA 1236. Much of the impetus for the debate on these questions has been provided by the continual emergence of new information suggesting that lead exposure levels previously thought to be harmless actually cause significant neurological damage. Id. The more severe neurological effects of high level lead exposure are the clinical syndrome of lead encephalopathy. Early symptoms include dullness, restlessness, irritability, headaches, muscular tremor, hallucinations, and loss of memory. These symptoms rapidly progress (sometimes within 48 hours) to delirium, mania, convulsions, paralysis, coma, and death. Id. at 11-15, JA 1237. The Criteria Document expressed particular concern that the onset of these serious symptoms can be quite abrupt, even in the absence of prior overt or clinical symptoms of disease. Id. at 13-6, JA 1336. After a review of various studies, the Criteria Document concluded that the blood lead threshold for these neurological effects of high level exposure is 80-100 ug Pg/dl in children, and 100-200 ug Pb/dl in adults. Id. at 1-13, 11-18, 11-25, 13-6, JA 1117, 1240, 1247, 1336. 15 The Criteria Document also went on to consider the evidence on whether lower level lead exposures can affect the central nervous system, particularly in children. It acknowledged that the issue is unsettled and somewhat controversial, but it was able to conclude, after a careful review of various studies on the subject, 14 that a rather consistent pattern of impaired neural and cognitive functions appears to be associated with blood lead levels below those producing the overt symptomatology of lead encephalopathy. CD 1-7, JA 1111. The Criteria Document reported that (t)he blood lead levels at which neurobehavioral deficits occur in otherwise asymptomatic children appear to start at a range of 50 to 60 ug/dl, although some evidence tentatively suggests that such effects may occur at slightly lower levels for some children. Id. 15 16 In addition to examining the health effects of lead exposure, the Criteria Document also discussed other issues critical to the task of setting air quality standards for lead. One of these issues is the relationship between air lead exposure and blood lead levels a relationship commonly referred to as the air lead/blood lead ratio. The Criteria Document acknowledged that derivation of a functional relationship between air lead exposure and blood lead levels is made difficult by the fact that the relationship is not a linear one; rather, the ratio tends to increase as air lead levels are reduced, CD 12-24, JA 1311. The Document was nevertheless able to conclude, after a detailed examination of the relevant studies, CD 12-22 12-29, JA 1309-1316, that air lead/blood lead ratios fall within a range of 1:1 to 1:2 (ug Pb/m 3 air):(ug Pb/dl blood) at the levels of lead exposure generally encountered by the population, i.e., blood lead levels increase by between 1 and 2 ug Pb/dl of blood for every 1 ug Pb/m 3 of air. (Air lead content is measured in micrograms of lead per cubic meter of air ug Pb/m 3.) CD 12-38, JA 1325. The Criteria Document reported that the studies indicate that the ratio for children is at the upper end of this range or even slightly above it. Id. 17 Finally, the Criteria Document also examined the distribution of blood lead levels throughout the population, concluding that there is a significant variability in individual blood lead responses to any particular level of air lead exposure. It further found that this variability is consistent and predictable, and that the application of established statistical techniques to the distribution of individual blood lead levels would make it possible to predict what proportion of the population would be above or below any particular blood lead level at a given level of air lead exposure. 16 The Criteria Document looked into the question whether any sub-groups within the population are particularly vulnerable to the effects of lead exposure. It concluded that preschool-age children and pregnant women are particularly sensitive to lead exposure, the latter mainly because of the risk to the unborn child. CD 13-11 13-14, JA 1341-1344.