Lead (Pb)

Exposure Sources

The toxicity of Pb to humans has been known for over 2,000 years, and is not disputed. The general population may be exposed to Pb in ambient air, foods, drinking water, soil, and dust. Pb has also been found in a variety of other consumer products including storage batteries, solders, pottery glazes, leaded crystal glassware, cosmetics, hair dyes, jewelry, gun shot and ammunition, relic fishing sinkers, tire weights, imported children’s toys, and traditional or folk remedies. For adults, exposure to levels of Pb is usually associated with occupational exposures. For children, exposure to high levels of Pb is associated with living in areas contaminated by Pb (e.g., soil or indoor dust in older homes with Pb-based paint). Older homes with lead pipes have been a source of high lead exposure due to high lead levels in drinking water.

Health Effects

Toxic effects of Pb have been observed in every organ system that has been rigorously studied. The most extensively studied health outcomes are neurological, renal, cardiovascular, hematological, immunological, reproductive, and developmental effects. Neurological effects of Pb are of greatest concern because effects are observed in infants and children and may result in life-long decrements in neurological function. Infants may be born with a Pb burden derived from maternal transfer in utero and subsequently can continue to absorb maternal Pb from ingestion of breast milk. Children are also more vulnerable because of behaviors that increase ingestion of Pb surface dusts (e.g., hand-to-mouth activity) and because gastrointestinal absorption of ingested Pb is higher in children compared to adults, possibly due to a combination of physiological differences and differences in diet and nutrition.

In adult males and females reproductive effects, such as damage to sperm and alterations in hormone production have been noted.

Toxicokinetics

• Following inhalation of organic lead, approximately 60–80% of lead deposited in the airway is absorbed.
• Gastrointestinal absorption of inorganic lead is influenced by the physiological state of the exposed individual and the species of the lead compound.
• Gastrointestinal absorption of lead is higher in children (40–50%) than in adults (3–10%). The presence of food in the gastrointestinal tract decreases absorption.
• Absorption of lead from soil is less than that of dissolved lead but is similarly depressed by meals (26% fasted; 2.5% when ingested with a meal).
• In adults, about 94% of the total amount of lead in the body is contained in the bones and teeth versus about 73% in children.
• Lead remains in bones for decades and in blood for months.
• Independent of the route of exposure, absorbed lead is excreted primarily in urine and feces.

Biomarkers

• The analysis of lead in whole blood is an accurate method of assessing a recent exposure. The Centers for Disease Control and Prevention (CDC) reference value is 5 µg/dL.
• Bone lead measurements are an indicator of cumulative exposure.
• Measurements of hair lead levels have been used to assess chronic lead exposure. Hair lead concentrations resemble bone levels.
• Measurements of urinary (before and after chelation treatment) are used to assess lead exposure.

Environmental Testing

• Soil: The natural lead content of soil typically ranges from 15 to 20 µg/g. However, lead levels in the top layers of soil vary widely due to deposition and accumulation of atmospheric particulates from anthropogenic sources.
• Water: Lead levels in surface and groundwater can vary widely, depending on geography. The European Scientific Committee on Health and Environmental Risks (SCHER) and WHO (World Health Organization) have set a maximum contaminant level of 10 µg/L for lead in drinking water.

Reference

Agency for Toxic Substances and Disease Registry (ATSDR). 2020. Toxicological Profile for Lead. Atlanta, GA: U.S. Department of Health and Human Services, Public Health Service