Lead Toxicology

Because of similar chemical properties, the body confuses lead with calcium when ingested and incorporates it into the bone marrow, nerve tissue, brain, and kidneys. The body never decomposes the lead into another, more easily tolerated substance, because lead is an element.

In children, symptoms of lead poisoning can include headaches, irritability, abdominal pain, vomiting, anemia, weight loss, poor attention span, noticeable learning difficulty, slowed speech development, and hyperactivity. In adults, symptoms of lead poisoning can include pain, numbness or tingling of the extremities, muscular weakness, headache, abdominal pain, memory loss, unsteady gait, pale skin, weight loss, vomiting, irritability, and anemia. Although adults are susceptible to the toxic effects of lead, children are at high risk due to the nature of a child's activities that involve the introduction of non-food items into their bodies. Lead poisoning is one of the most common preventable public health problems related to children today.

At low concentration lead can adversely affect the brain, the central nervous system, blood cells, and kidneys. Blood lead concentrations as low as 10 ug/dl can impair mental and physical development. Lead at high concentrations (80 ug/dl or above) can cause convulsions, coma, and death. The effects of lead exposure on unborn and young children can be severe. The effects of lead poisoning in children include reading and learning disabilities, delays in physical and mental development, shortened attention span, speech and language handicaps, lowered IQ, neurological deficits, behavior problems, mental retardation, kidney disease, heart disease, stroke, and death. Children are more vulnerable to lead exposure than adults since lead is more easily absorbed into growing bodies, and the tissues of small children are more sensitive to the damaging effects of lead. Children may have higher exposures since they are more likely to get lead dust on their hands and then put their fingers or other lead-contaminated objects into their mouths. If you suspect lead poisoning, consult your physician immediately. (reference 57)

Toxicokinetics

Elemental lead and inorganic lead compounds are absorbed through ingestion or inhalation. Pulmonary absorption is efficient, particularly if airborne lead particle diameters are 1 mm generally are completely absorbed by the alveoli. Gastrointestinal absorption of lead is less effective and depends on a number of factors. Lead absorption rates may increase with iron, zinc, and calcium deficiencies. Children are at the highest risk for toxicity because they absorb up to 50% percent of the amount of lead ingested, whereas adults absorb only about 10 to 20% percent. Transdermal absorption is minimal for inorganic lead. (reference)

Lead is absorbed into blood plasma, where it equilibrates rapidly with extracellular fluid, crosses membranes such as the blood-brain barrier and the placenta, and accumulates in soft and hard tissues. In the blood, around 95 to 99% of lead is sequestered in red cells, where it is bound to hemoglobin and other components. Lead deposition in erythrocytes and soft tissues is responsible for most of the toxic effects of the metal.

The half-life of lead differs for each of the compartments, ranging from 25–40 days in erythrocytes, 40 days in soft tissues, and as many as 28 years in bone. Bone lead accounts for more than 95 % of the lead burden in adults and 70% of the burden in children. Lead is commonly incorporated into rapidly growing bones, such as the tibia, femur, and radius, where it competes with calcium and may exert toxic effects on skeletal growth. Bone acts as a reservoir for lead in the same way that it acts as a reservoir for calcium. The body may mobilize its lead stores during periods of stress, fever, hyperthyroidism, prolonged immobilization, pregnancy, and lactation. Lead that is not retained by the body is excreted unchanged in urine (65–75 %) and in bile (25–30 %). Lead also appears in hair, nails, sweat, saliva, and breast milk.