Posted 07/28/2006

USC researchers find unusually high levels of arsenic in some South Carolina neighborhoods

Unusually high levels of arsenic have been found in some South Carolina neighborhoods where University of South Carolina researchers are studying possible links between chemical exposure during pregnancy and mental retardation.

Describing the early findings as “surprising,” researcher Marjorie Aelion said the levels are “higher than the EPA standard for residential areas.”

Arsenic is one of a number of toxic chemicals suspected of having a role in causing mental retardation, said Aelion, who is part of an interdisciplinary team from the Arnold School of Public Health and the School of Medicine.

Using data from Medicaid administrative data files the research team is identifying geographical clusters of children identified with developmental delay or mental retardation. When a cluster is found the researchers test soil samples from the area looking for unusual concentrations of chemicals.

The study is supported by a $1.4 million grant from the National Institutes of Health. It involves 152,000 children born in South Carolina between 1996 and 2001.  Because the state has such a high Medicaid enrollment, that is about half of the total number of births for those years, it is an excellent environment for this type of study.

Aelion, an expert in environmental contamination, is a professor in the Department of Environmental Health Sciences. Others on the team are Suzanne McDermott, a professor in the Department of Family and Preventive Medicine at the Medical School and Andrew Lawson, an expert in spatio-environmental epidemiology and a professor in the Department of Epidemiology and Biostatistics.

Heavy metals such as mercury and lead have been linked to mental retardation, said McDermott, but the team is looking at other less-studied elements – arsenic, copper, chromium, beryllium, antimony, cadmium, barium and manganese -- because of their potential to cause harm to a developing brain.

Since the 1960s scientists have been unable to identify more than 50 percent of the causes of mental retardation.

 “That means for half of the cases of mental retardation we can’t tell parents what caused it. It just happens. And that seems to be a perfect situation for an epidemiologist to figure out some more causes,” said McDermott.

Soil is the focus of the study because contaminants from the air and the water settle in the soil, said McDermott. “What you find is that soil is a very good indicator of what’s in the environment.”

The Medicaid data can track the addresses of women through their pregnancies. The scientists selected the 1996-2001 period so they could follow the group forward to the present in order to see if their Medicaid billing records have a code for developmental delay or mental retardation.  Only a small proportion of mental retardation is identified at birth so these diagnoses are made throughout early childhood.

The team has funding for three years of research with an opportunity to competitively bid for two additional years if results are promising.

For that reason, the team has decided to concentrate on the more heavily industrialized half of the state from the Midlands to the mountains.  If the NIH approves two additional years the team will investigate the coast and the Coastal Plain where the water table is much higher, the geology is different and agriculture chemicals are widely used.

Although the team has access to databases that identify industrial locations and toxic dump sites, McDermott said the team is not interested in drawing maps but in identifying chemicals and linking exposure to mental retardation.

“You may live near a (chemical) site, but someone may be using the same chemical in their hobby room and it’s just as dangerous to them,” McDermott said.