Introduction

Today almost everyone is exposed to environmental lead. Exposure to lead and lead chemicals can occur through inhalation, ingestion and dermal contact.

• Most human exposure to lead occurs through ingestion or inhalation.
• In the U.S. the public is not likely to encounter lead that readily enters the human body through the skin (dermal exposure), as leaded gasoline additives are no longer used.
• Lead exposure is a global issue. Lead mining and lead smelting are common in many countries, where children and adults can receive substantial lead exposure from sources uncommon today in the U.S. (Kaul et al. 1999; Rothenberg et al. 1994; Litvak et al. 1999; López-Carrillo et al. 1996; Wasserman et al. 1997). Most countries will have phased out use of leaded gasoline by 2007.

Ingestion

Lead exposure in the general population (including children) occurs primarily through ingestion, although inhalation also contributes to lead body burden and may be the major contributor for workers in lead-related occupations.

• Lead paint is the major source of lead exposure for children. (AAP 1993; ATSDR 2005) As lead paint deteriorates, peels, chips, or is removed (e.g., by renovation), or pulverizes due to friction (e.g., in windowsills, steps and doors), house dust and surrounding soil may become contaminated. Lead then enters the body through normal hand-to-mouth activity. (Sayre et al. 1974 as cited in AAP 1993)
• Ingestion of contaminated food, water or alcohol may be significant for some populations. In addition, ingesting certain home remedy medicines may expose people to lead or lead compounds. (See Where Is Lead Found?).

Inhalation

• Inhalation is the second major pathway of exposure. Almost all inhaled lead is absorbed into the body, whereas from 20% to 70% of ingested lead is absorbed (with children generally absorbing a higher percentage than adults do) (ATSDR 2005). (See What Are the Physiologic Effects of Lead Exposure?).
• Since leaded gasoline additives were phased out beginning in the 1970s, and control measures were implemented in industries, which have reduced air emissions, inhalation is no longer the major exposure pathway for the general population in the U.S.
• In some foreign countries, however, leaded gasoline is still used, and the resulting emissions pose a major public health threat.
• Inhalation may be the primary route of exposure to some workers in industries that involve lead.
• Inhalation may be the primary route of exposure for adults involved in home renovation activities.

Dermal

Dermal exposure plays a role for exposure to organic lead among workers, but is not considered a significant pathway for the general population.

• Organic lead may be absorbed directly through the skin.
• Organic lead (tetramethyllead) is more likely to be absorbed through the skin than inorganic lead.
• Dermal exposure is most likely among people who work with lead.

Endogenous Exposure

Endogenous exposure to lead may contribute significantly to an individual's current blood lead level, and of particular risk to the developing fetus (see What are the physiologic effects of lead?).

• Once absorbed into the body, lead may be stored for long periods in mineralizing tissue (i.e., teeth and bones).
• The stored lead may be released again into the bloodstream, especially in times of calcium stress (e.g., pregnancy, lactation, osteoporosis), or calcium deficiency.

Progress Check