Routes of exposure to lead

Ingestion of dust, soil, water or lead items

Ingestion is the most common route of exposure to lead in children and adults not occupationally exposed. Specifically, oral ingestion of lead-based paint, lead-containing dust, and lead-contaminated soil has been shown to be the primary route of lead exposure in children. In pre-school children, normal hand-to-mouth behavior leads to lead ingestion through placing hands, toys and other objects and dust or soil on those objects into their mouths, posing a serious threat to those children living in a contaminated environment with lead in soil, household dust and paint (Juberg, Kleiman, and Kwon 1997; NSW EPA 2003).

The primary site of absorption of lead in children is the gastrointestinal tract, with children absorbing up to 50% of the lead they ingest, about five times as much as adults. The extent and rate of gastrointestinal absorption are influenced by physiological states of the exposed individual (e.g., age, fasting, nutritional calcium and iron status) and physicochemical characteristics of the medium ingested (e.g., particle size, mineralogy, solubility, and lead species). No feedback mechanism causes a decrease in the absorption of ingested lead once levels become elevated (ATSDR 2002; Wisconsin Dept of Health 2004).

Children or pregnant women with pica, an eating disorder typically defined as the persistant eating of nonnutritive substances for a period of at least one month at any ages in which this behavior is developmentally inappropriate, are at even greater risk as they may consume up to 20 grams of soil per day as well as other inanimate objects that may or may not contain lead, such as clay, dirt, sand, stones, pebbles, hair, feces, lead, laundry starch, plastic, ice, fingernails, paper, paint chips, coal, chalk, wood, plaster, and burnt matches (Ellis 2002). Research suggests that pica occurs in 25-33% of young children and 1-6 % of preschool children. Pregnant women may absorb much greater quantities of ingested lead, more closely approximating the 50% absorption rate of children (Ellis 2002; NSW EPA 2003).

Inhalation of dust or aerosols

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Dermal / Injection (not significant)

Absorption of lead through the skin is minimal. Though the skin is able to absorb certain organic lead compounds, such as tetraethyl lead found in petrol and recent research suggests inorganic lead compounds (e.g., lead nitrate, lead acetate and lead oxide) can also be absorbed in very small quantities, lead poisoning in children through dermal exposure is rare, primarily because children’s contact with these elements is limited (Wisconsin Dept of Health 2004). As a blood lead tests is the most common detection method, additional research is needed on led testing methods. Skin absorption may also pose a threat to workers in the construction trades and paint industry that are less likely to wear protective clothing to prevent lead dust from adhering to their skin (ATSDR 2002; NSW EPA 2003).