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The document summarizes current knowledge about the relationships between airborne lead and consequent effects on man and his environment. The effects that have been observed to occur when airborne lead has reached or exceeded specific levels for time periods constitute the central criteria on which EPA will base a national ambient air quality standard for lead. Although this document deals mainly with airborne lead, it also outlines other environmental routes of exposure to lead and gives approximations of the relative contributions to human exposure of the respective routes. In man, lead primarily affects red blood cells, the central and peripheral nervous systems, soft tissues, such as liver and kidney, and bone; the latter ultimately sequesters 95% of the body's lead burden. Significant biological indices of exposure to lead include microgram quantities of lead and of erythrocyte protoporphyrin (EP) per deciliter of blood (micrograms/dl). Adverse effects range from elevated EP and mild anemia at 20 to 40 micrograms/dl--through gastrointestinal, renal, and hepatic pathologies--to severe neurobehavioral impairment at > 80 to 120 micrograms/dl, sometimes culminating at those levels in convulsions and abrupt death. Preschool children and developing fetuses are the populations at greatest risk.
U.S. EPA. Air Quality Criteria for Lead (1977). U.S. Environmental Protection Agency, Washington, D.C., EPA/600/8-77/017 (NTIS PB280411), 1977.