PHILADELPHIA — Although the Centers for Disease Control and Prevention set a blood lead level of 10 mcg/dL or higher as the threshold for concern in children in 1991 and reaffirmed it in 2005, many experts agree that levels below that also are dangerous.
“Kids have adverse effects at levels below 10 mcg/dL, but it's hard to pinpoint a specific level where you can say that adverse effects stop,” Dr. Carla Campbell said at a conference sponsored by the Mid-Atlantic Center for Children's Health and the Environment.
“But the lower you get below 10 mcg/dL, the more error you have, [and] the more likely children are to be misclassified,” which led to retention of the 10 mcg/dL cutoff, said Dr. Campbell, a specialist in pediatric environmental and public health at Drexel University, Philadelphia, who chaired the CDC's advisory committee that produced the agency's 2005 report.
In November 2007, a new report by the same group, the CDC's Advisory Committee on Childhood Lead Poisoning Prevention, recommended that blood lead testing be done on all children, and that for a child whose level “is approaching 10 mcg/dL, more frequent blood screening (more than annually) might be appropriate, particularly if the child is aged less than 2 years old, was tested at the start of warm weather when blood lead levels tend to increase, or is at high risk for lead exposures” (MMWR 2007;56[RR-8]:1–14).
A review published last May was more explicit: The level of 10 mcg/dL “has no special biological significance and certainly should not be interpreted as safe,” wrote David C. Bellinger, Ph.D., a professor of neurology at Harvard University, Boston (PLoS Med. 2008;5:e115).
The growing concern about levels below 10 mcg/dL led to a novel lead-control program in Washington. The nonprofit Lead Safe D.C. program, sponsored by the National Nursing Centers Consortium, launched a program aimed at reaching every child in the District of Columbia with a blood lead level of 5 mcg/dL or higher, Harrison Newton said at the meeting. Young children with high blood lead levels are identified in the District through a municipal mandate that requires all children to get tested for blood lead at least twice before they're 2 years old.
Once affected children are identified, their homes are visited by community outreach workers who encourage families to take steps to reduce the lead hazard. Cleaning kits are distributed to the families, said Mr. Newton, program director for Lead Safe D.C.
Blood lead levels in U.S. children began to plummet starting in 1978 when lead paint was discontinued. This was followed by the elimination of lead-containing solder in food cans and the phasing out of leaded gasoline. According to the CDC's 2007 report, 1.6% of children aged 1–5 years had blood lead levels of 10 mcg/dL or higher in 1999–2002, and the average level in all children this age was 1.9 mcg/dL. In contrast, during 1976–1980, about 88% of children this age had blood lead levels at or above 10 mcg/dL, and the mean level was 15 mcg/dL.
The major current sources of lead poisoning in children are paint chips and dust in housing that retains old leaded paint, and in water that passes through old pipes, Jianhong Liu, Ph.D. said. These sources mean that substantial disparities in lead exposure exist in the United States, with the highest levels seen in children who live in old housing.
For example, in 2005 the average blood lead level among all U.S. children aged 5 years and under was about 2 mcg/dL, but it was about 6 mcg/dL for children in Chicago and 14 mcg/dL for children in Philadelphia, said Dr. Liu, of the Center for Public Health Initiatives at the University of Pennsylvania, Philadelphia.
An x-ray of both knees of a child with lead poisoning shows dense metaphyseal bands involving distal femurs, proximal tibias, and proximal fibulas. ©LearningRadiology.com