Working to prevent lead poisoning in children: Getting the lead out

Environmental lead exposure and poisoning are preventable. Unfortunately, they remain a serious public health risk, and children are the most vulnerable. Although mortality is low because of screening and the aggressive use of chelating agents, morbidity is still significant.2

Most exposures to lead are caused by inorganic lead entering the body through inhalation of dust or fumes or swallowing when eating or drinking. Lead can also be absorbed transdermally, although this is not a common route of exposure for children in a household setting. Industrial exposure, where lead dust accumulates on clothing, hair, and skin; pica; use of folk remedies and imported cosmetics, such as kohl; or use of imported ceramic serving dishes can increase the risks. Lead poisoning in women can be transferred to the fetus in utero because lead crosses the placenta; it can also be transferred through breast-feeding. Lead that is not excreted initially is distributed into the blood, soft tissues, and bones.

Children aged 9 months to 6 years are at greatest risk of lead exposure. Children have more hand-to-mouth behaviors, and rapid growth and absorption make them more susceptible than adults to the effects of lead. Children who live in older substandard housing in urban areas—particularly houses built before 1978, when lead-based paint was banned—are at greatest risk. In addition, older homes are more likely to have leaded pipes, brass fittings and solder, and vinyl mini-blinds, all of which contain lead. Chipping and peeling paint can contaminate dust and soil. Living and playing near industrial sites also expose children to lead contaminants. Despite measures to reduce housing-related lead exposure, lead-paint hazards are present in an estimated 24 million homes, 1.2 million of which are occupied by low-income families with children younger than 6 years.3 Children living in poverty are also more likely to have poor diets, further placing them at risk. One randomized community-based trial found no significant difference in children's BLLs at the end of the year, even with intensive case management that includes home visits and education. These findings suggest that safe housing, rather than environmental exposure reduction, is necessary once the BLLs are elevated.4

Adults with jobs or hobbies that use lead can put the children who live with them at risk. Nationally, 95% of adult lead exposures are occupational,5 and exposed adults are predominantly men. Occupations such as painting, housing renovation, automotive repair, ceramic production, bridge construction and repair, jewelry making, building demolition, scrap metal recovery, and foundry operations may expose persons to lead products. Certain avocations, such as furniture stripping, stained-glass making, welding, making bullets, use of firearms in an indoor firing range, and making or using fishing sinkers, also pose a risk.

The CDC tracks BLLs in children through the National Health and Nutrition Examination Survey and surveillance data from state and local health departments. BLLs in children have declined considerably, largely as a result of education and policies that curtail lead contamination in the environment, such as the elimination of leaded gasoline in the United States and safe housing initiatives.5-7 BLLs of 40 µg/dL were not unusual in the 1970s. Currently, average BLLs range from 2 to 4 µg/dL.8

Overall, the prevalence of elevated BLL in the US population aged 1 year and older was 0.7% for 1999-2002, 68% lower than the prevalence reported in the 1991-1994 survey.6 During the 1999-2002 survey, prevalence of elevated BLL was highest (1.6%) among children aged 1 to 5 years. This indicates approximately 310,000 US children aged 1 to 5 years had a BLL higher than 10 µg/dL, the level at which the CDC recommends intervention and the American Academy of Pediatrics (AAP) defines lead poisoning.2 African- American children may be disproportionately affected because of socioeconomic conditions. Although surveys have found a lower prevalence of elevated BLL among black non- Hispanic children associated with more recently built homes, these children remain at greater risk of developing lead poisoning. During 1999-2002, a higher percentage of non-Hispanic blacks and Mexican Americans had an elevated BLL (1.4% and 1.5%, respectively) than did non-Hispanic whites (0.5%).6 Among children aged 1 to 5 years, non-Hispanic blacks had the highest prevalence of elevated BLL (3.1%). Intensified efforts are needed to meet the 2010 goal of lowering BLLs to less than 10 µg/dL.

NEUROLOGIC AND COGNITIVE EFFECTS

The CDC Advisory Committee on Childhood Lead Poisoning Prevention reviewed the scientific literature regarding the adverse health effects associated with a BLL below 10 µg/dL.7 This review included 23 published reports on intelligence quotient (IQ) and cognitive index outcomes and 12 publications related to other outcomes. The Committee found an inverse association between BLL and cognitive function, with no evidence of a weaker association in populations with lower levels of elevated BLL. Thus, the Committee concluded a causal relationship between lead exposure and impaired cognitive function was likely. In one prospective study published in 2008, children were followed from age 6 months to 6 years, and IQ was assessed based on the Wechsler Preschool and Primary Scale of Intelligence–Revised.9 Compared with children with a BLL below 5 µg/dL, those with a BLL of 5.5 to 9.9 µg/dL scored 4.9 points lower on the full-scale IQ test. Thus, findings from this cohort study suggest intellectual function can be impaired at concentrations below the current defined level for elevated BLL. This is consistent with an earlier study published in 2003 that found a 4.6-point reduction in IQ at ages 3 and 5 years for every 10 µg/dL increase in average BLL concentration.10 The effects were even greater for a given change in lead concentration in children with a BLL below 10 µg/dL than in children with a higher BLL. A 2005 international pooled analysis study also found an association between a change in lead concentration and intellectual deficits among children with a BLL below 7.5 µg/dL.11 In addition, abnormalities in verbal comprehension and expression and auditory abilities can occur.5 A study that examined the relationship between exposure to tobacco smoke and exposure to environmental lead concluded that both are risk factors for attention-deficit/hyperactivity disorder in children.12 Other studies have suggested long-term negative health outcomes, such as teen pregnancy and tobacco use, may be associated with childhood lead poisoning.13