Research Study Rejects CDC and WHO "Safe" Lead Exposure Levels
Study Indicates Children Suffer More Damage Below Current "Safe" Level
Thursday, April 17, 2003
In a groundbreaking study published in the April 17 edition of the New England Journal of Medicine, researchers have concluded that the current "safe" lead level of 10 micrograms of lead per deciliter endorsed by the Centers for Disease Control and Prevention and the World Health Organization is not safe, and in fact, significant damage is caused to children with lead blood levels below 10 micrograms. These findings underscore the importance of lead exposure prevention and suggest that more U.S. children may be adversely affected by environmental lead than previously estimated.
The University of Rochester Medical Center was one of four organizations participating in the study funded by the National Institute of Environmental Health Sciences. Scientists measured blood level concentrations in 172 Rochester, N.Y. children at 6, 12,18, 24, 36, 48 and 60 months of age, and also administered the Stanford-Binet Intelligence Scale along with other tests to measure behavioral development, including memory, planning and problem solving, and attentional flexibility.
Results showed that blood lead levels of 10 micrograms of lead per deciliter, previously considered safe, are associated with greater declines in IQ scores than those additionally caused by further elevations above 10 ug/dl. That is a 7.4 point decline in IQ was associated with blood lead values up to 10 ug per deciliter while each further increase of an additional 10 ug per decilter was associated with a 4.6 point decrease in IQ. In addition, all lead exposed children showed some degree of behavioral dysfunction in memory, planning and problem solving and attentional flexibility.
"The major message here is that kids who are exposed to lead sustain the most damage early on in their exposure, so that in effect, there is NO safe lead exposure level," Deborah A. Cory-Slechta, Ph.D., director of the University of Rochester Medical Center's Environmental Health Sciences Center. "This data is a clear call for implementing a strong lead prevention policy.
While this study did not explore the reason behind lower lead levels causing more serious damage, there is evidence that suggests higher concentrations of heavy metals enhance cellular defense, thereby lessening the rate at which additional damage occurs.
The lead author of the paper is Richard L. Canfield, Ph.D., of Cornell University. The Children's Hospital Medical Center in Cincinnati also participated in the study.
Approximately 434,000 U.S. children aged 1-5 years have blood lead levels greater than 10 micrograms of lead per deciliter of blood. According to a CGR report issued in May 2002, approximately 24% of Rochester kids are poisoned. Because lead poisoning often occurs with no obvious symptoms, it frequently goes unrecognized, leading to learning disabilities, behavioral problems, and, at very high levels, seizures, coma, and even death.
The major source of lead exposure among U.S. children is lead-based paint and lead-contaminated dust found in deteriorating buildings. While lead-based paints were banned for use in housing in 1978, approximately 24 million housing units in the United States have deteriorated leaded paint and elevated levels of lead-contaminated house dust. More than 4 million of these dwellings are homes to one or more young children.
Children from all social and economic levels can be affected by lead poisoning, although children living at or below the poverty line who live in older housing are at greatest risk. Children of some racial and ethnic groups living in older housing are disproportionately affected by lead. For example, 22% of black children and 13% of Mexican-American children living in housing built before 1946 have elevated blood lead levels compared with 6% of white children living in comparable types of housing.
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