Children who live near toxic waste sites in lower- and middle-income countries such as India, Indonesia, and The Philippines may experience higher blood lead levels, resulting in a loss of IQ points and a higher incidence of mental retardation, according to a study presented today at the Pediatric Academic Societies (PAS) annual meeting in Washington, D.C.

"This study is important because, to our knowledge, the burden of disease from these toxic waste sites has never been calculated before," said Dr. Kevin Chatham-Stephens, M.D., from the Icahn School of Medicine at Mount Sinai and lead author of the study.

Researchers measured lead levels in soil and drinking water at 200 toxic waste sites in 31 countries and then estimated the blood lead levels in 779,989 children who were potentially exposed to lead from these sites in 2010. The blood lead levels ranged from 1.5 to 104 µg/dL, with an average of 21µg/dL in children ages four years and younger.

"The average blood lead level in an American child is approximately 1.3 µg/dL," said Dr. Chatham-Stephens. Currently, blood lead levels higher than 5 μg/dL in children (10 μg/dL in adults) is considered by the Centers for Disease Control and Prevention (CDC) to be lead poisoning, a definition that does not require the presence of symptoms.

According to Dr. Chatham-Stephens, these higher blood lead levels in children living near toxic waste sites could result in an estimated loss of five to eight IQ points per child and an incidence of mild mental retardation in six out of every 1,000 children. The condition of mental retardation is defined as having an IQ below 70.

"On a global level, this analysis highlights the importance of assigning more public health resources to identify, evaluate and remediate lead-contaminated toxic waste sites in these countries," said Philip Landrigan, M.D., Dean for Global Health at the Icahn School of Medicine at Mount Sinai and one of the authors of the study. "In order to prevent further detrimental effects on neurodevelopment in children, these countries should create programs to identify toxic wastes and reduce lead exposure."

In the U.S., the mean blood lead level in children has declined over time. In the late 1970s, the median blood lead level of U.S. preschool children was 15 μg/dl, and 88 percent of children had a level exceeding 10 μg/dl. Between 1976 and 1980, 780,000 children aged one to six years old had blood lead concentrations of 30 micrograms/L or above.

The CDC guideline as to what is considered to be an undue level of lead absorption has continuously decreased over the latter half of the twentieth century from a permissible high of 50-60 μg/dl in the 1960s and early 1970s.

Lead-based paints were banned for use in housing in 1978. Houses containing some lead-based paint remain an issue even today as deterioration of old paint can cause problems. Approximately 24 million housing units have deteriorated lead-based paint and elevated levels of lead-contaminated house dust.

"Lead has serious, long-term health consequences," said Dr. Chatham-Stephens, whose work contributed to the study "The Pediatric Burden of Disease from Lead Exposure at Toxic Waste Sites in Low and Middle Income Countries in 2010," a joint research partnership between Mount Sinai and the Blacksmith Institute.