The biologic fate of inorganic lead in the human body is well known. Inorganic lead is not metabolized but is directly absorbed, distributed, and excreted.

Once in the blood, lead is distributed primarily among three compartments--blood, soft tissue (kidney, bone marrow, liver, and brain), and mineralizing tissue (bones and teeth).

Mineralizing tissue contains about 95% of the total body burden of lead in adults (ATSDR, 1990).

 In blood, 99% of the lead is associated with erythrocytes; the remaining 1% is in the plasma and is available for transport to the tissues.

In single-exposure studies with adults, lead has a half- life in blood of approximately 25 days; in soft tissue, about 40 days; and in the non-labile portion of bone, more than 25 years.

In bone there is both a labile component, which readily exchanges lead with the blood, and an inert pool. Lead in the inert pool poses a special risk because it is a potential endogenous source of lead. Because of these mobile lead stores, a person's PbB level can take several months or sometimes years to drop significantly, even after complete removal from the source of lead exposure (ATSDR, 1990).

 Lead exposure is one of the most common preventable poisonings of childhood. It is estimated that one out of every six children in the United States, or a total of over three million children, have blood levels in the toxic range. Lead is a potent poison that can affect individuals at any age. Children with developing bodies are especially vulnerable because their rapidly developing nervous systems are particularly sensitive to the effects of lead.

 Almost all children in the United States are exposed to lead. Common sources include lead paint and lead contained in water and soil. Over 50 million homes, including a majority of those built before 1980, contain lead-based paint.

 Exposure to lead can have a wide range of effects on a child's development and behavior. Even when exposed to small amounts of lead levels, children may appear inattentive, hyperactive and irritable. Children with greater lead levels may also have problems with learning and reading, delayed growth and hearing loss. At high levels, lead can cause permanent brain damage and even death.