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LEAD

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Lead is a highly toxic metal, and exposure to it can produce a wide range of adverse health effects.1,2 It is a soft, pliable metal that resists corrosion and when ingested, has a sweet taste.3,4 Lead is a ubiquitous environmental containment found in water and soil.1 The most common cause of childhood lead poisoning is ingestion of lead-containing paint chips or lead-contaminated dust as a result of normal hand-to-mouth activity.5,6 Until 1978, lead was commonly used in paints to provide pigment and color stability. Other potential sources include ingestion of drinking water, soil, and food.7 According to the US Department of Housing and Urban Development (HUD), about 25% of the nation’s current housing stock—some 24 million homes—still contains significant lead-based paint hazards.8 Although lead paint that is intact does not pose an immediate concern, lead paint that is deteriorating or is disturbed during repair or renovation activities creates a hazard. There is new evidence that lead poisoning is harmful at blood levels that were once thought safe.9-11 The effects of sustained exposure, such as learning disabilities have been observed in children with lead levels as low as 5 μg/dL, with no evidence of a threshold.11 In 2012, the Centers for Disease Control and Prevention (CDC) revised the definition of lead toxicity and lowered the “normal” blood lead level value to below 5 μg/dL.12

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Lead poisoning was once a disease of poor or minority children living in older housing in the inner cities.13 Unfortunately, the number of at-risk groups has expanded as families from all strata inadvertently expose their children through home renovation activities.14 Gender differences also exist, and males appear to be more affected than females for any given exposure source or amount.15

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TOXICOKINETICS

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Lead ingestion is the primary route of exposure for children, whose gut absorbs 45% to 50% of a lead dose, compared with 10% to 15% in adults.16 After absorption occurs, the amount of lead entering the bloodstream is dependent on several factors: the amount or concentration of lead in the specific medium; the physicochemical characteristics of the lead compound; and specific host factors such as age, nutritional status, and fasting conditions. Once absorbed, 99% of lead binds to erythrocytes, and the remaining 1% is free to diffuse into soft tissues and bone, where it equilibrates with blood lead.17 In the body, the total lead burden can be divided into four compartments: blood (half-life 35 days), soft tissue (half-life 40 days), and the trabecular (half-life 3 to 4 years) and cortical components (half-life 16 to 20 years) of bone. Lead that is deposited in hair, teeth, nails, and bones is tightly bound and not felt to be harmful.

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In terms of lead’s toxicity, the most notable effect is seen in the heme synthetic pathway. Lead inhibits ...

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