Chapter 13 Lead Exposure and Poisoning
ETIOLOGY
Why Is Exposure to Lead a Problem?
Lead is a neurodevelopmental toxin for the immature nervous system at even very low levels, and it has toxic effects for almost all other organ systems at higher levels. In the past, lead exposure was classified as “lead poisoning” because it was identified clinically only when high-level toxicity caused symptoms and organ failure. Now, most children identified with chronic lead exposure are asymptomatic. Adverse effects are now primarily identified in cognition, learning, and behavior among populations of affected children. Public policy in the United States and other countries has markedly reduced commercial use of lead, with a resultant reduction of environmental contamination. Public health efforts have promoted routine screening for lead exposure. The Centers for Disease Control and Prevention (CDC) has a Web site devoted to lead exposure: www.cdc.gov/lead/.
What Are the Sources of Lead?
Dust derived from deteriorating lead-based paint is currently the most important source of environmental lead in the United States. Exposure to environmental lead historically has resulted from its use in products such as paint, pottery glaze, gasoline, water pipes, inks, and pigments. Lead has even found its way into foods, such as candy in Mexico. Although lead was banned as a component of interior paint in the 1960s and from exterior house paint in 1978, lead-based paint remains on interior and exterior walls of most homes built before 1978. As this paint ages and wears, it contaminates house dust and soil, contributing to the risk of lead exposure. Renovation of old housing is a particular hazard for children because the resulting dust increases the likelihood of inhalation and ingestion of lead. Modern housing standards have replaced lead water pipes with copper and plastic, but many communities still have lead water mains. Lead was phased out as a gasoline additive starting in the late 1970s but was only completely banned in 1995. Other, less common sources of lead exposure include the following:
Clothing worn by parents who work in lead-related industries such as battery plants, smelters, or recycling (see http://www.cdc.gov/niosh/topics/lead)
Hobbies such as making stained glass, ammunition loading, fishing weights, jewelry making
Imported toys and jewelry (www.cdc.gov/nceh/lead/faq/toys.htm)
Candy imported from Mexico (see www.ocregister.com/multimedia/lead/)
How Is Exposure to Lead Defined and Identified?
Excessive accumulation of lead in the body is defined by an elevated blood lead level (BLL). There is no BLL threshold below which lead can be said to be safe, but BLL ≥ 10 μg/dl is currently used to identify a child who has excessive lead exposure. This BLL triggers environmental clean-up and close monitoring of the affected child. In the past, “lead poisoning” was a symptomatic outcome of lead toxicity. As recently as 1970, the diagnosis of excessive lead exposure required a BLL of ≥ 65 μg/dl. The level for diagnosis then decreased steadily as the effects of lead toxicity became better understood: ≥ 40 μg/dl in 1971, ≥ 30 μg/dl in 1975, and ≥ 25 μg/dl in 1985. The level was lowered to ≥ 10 μg/dl in 1991, because it had become apparent that adverse cognitive effects occurred at BLL between 10 and 20 μg/dl, even though no obvious “lead poisoning” symptoms could be identified. More recently, evidence of a toxic effect at even lower levels has been identified and efforts are underway to further define this risk.
How Common Are Elevated Lead Levels?
Nearly 500,000 children in the United States currently have blood lead levels ≥ 10 μg/dl, and more than 10 of every 100,000 employed adults have BLL ≥ 25 μg/dl. Although symptomatic lead poisoning has declined greatly in the United States over the past 30 years, lead exposure remains an important public health concern because the metal is still present in old housing and in many different types of work sites. Lead exposure is especially common in most of the developing world, which means that physicians who care for immigrants and adopted children must be aware of the problem.
How Does a Child Become Exposed to Lead?
Children from 6 months to 3 years of age have the highest risk for exposure to lead because their developmental progression includes crawling, exploration, and hand-to-mouth activity, all of which put them in proximity to lead in the environment. Mouthing of objects and sucking on hands introduce lead into the child’s gastrointestinal tract. Pica, the consumption of nonfood items, is the behavior most associated with continuous, high-level lead ingestion. Inhalation of lead-containing dust, especially when a home is being renovated, can result in absorption across the respiratory mucosa and cause very high lead levels. Young children absorb up to 50% of lead that is either ingested or inhaled, but little is spontaneously excreted. Even low-level exposure can result in a large lead burden if it continues over many years.
Stay updated, free articles. Join our Telegram channel
Full access? Get Clinical Tree
