Because of their behavior and physiology, children are more affected by exposure to lead than are adults.

• Children absorb more ingested lead than do adults.
• Children generally ingest lead-contaminated soil and house dust at higher rates than adults because of mouthing and hand-to-mouth behaviors.
• Children who exhibit pica, a compulsive hand-to-mouth behavior and repeated eating of nonfood items, are at greatest risk.
• Children have a higher breathing rate than adults, breathing in a greater volume of air per pound.
• Being shorter than adults are, children are more likely to breathe lead-contaminated dust and soil as well as fumes close to the ground.
• In addition, the percent of lead absorbed in the gut, especially in an empty stomach, is estimated to be as much as five to 10 times greater in infants and young children than in adults. (Alexander et al. 1974; Chamberlain et al. 1978; James et al. 1985; Ziegler et al. 1978 as cited in ATSDR 1999)
• Gastrointestinal absorption of lead in children is increased by iron, calcium, zinc, and ascorbate deficiency. (Mahaffey et al. 1990 as cited in AAP 1993)

Children are more sensitive than adults are to elevated BLLs. Children's developing brains and nervous system (and other organ systems) are very sensitive to lead.

Childhood lead exposure has been associated with

• higher absenteeism in high school
• lower class rank
• poorer vocabulary and grammatical reasoning scores
• longer reaction time
• poorer hand-eye coordination (AAP, 1993)
• The incomplete development of the blood-brain barrier in fetuses and in very young children (up to 36 months of age) increases the risk of lead's entry into the developing nervous system, which can result in prolonged or permanent neurobehavioral disorders.
• Children's renal, endocrine, and hematological systems may also be adversely affected by lead exposure.

There is no known threshold exposure level (as indicated by BLLs) for many of these effects. No blood lead threshold for adverse health effects has been identifies in children.

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