DURHAM, N.C. (AP) -- A new center at Duke University will become the first to study why more babies are born premature or underweight in the South than elsewhere in the nation.

These conditions, which contribute to infant mortality, had been declining but in recent years have started to increase in the region.

A $7.7 million grant from the U.S. Environmental Protection Agency will pay for the five-year study, which will focus on what role environment, genes and socioeconomic status play in these births. It's the largest EPA grant ever awarded for a children's research center.

Exposure to substances such as mercury, lead and pesticides, as well as stress, the health of the mother, and genetic predisposition can contribute to the unhealthy births, said Marie Lynn Miranda, an associate research professor and director of the new Southern Center on Environmentally Driven Disparities in Birth Outcomes, which was announced Tuesday.

The rate of premature births and low birth rates vary among racial groups, she said, adding that while these rates are well-documented, researchers need more information on why they occur.

"These inequalities are especially pronounced in the American South," Miranda said. "It's not just a difference in income and socioeconomic status. There's more going on."

In the U.S., 18 percent of babies born to black women are premature, Miranda said. Comparatively, the rate is 12 percent among Hispanic babies and 11 percent among white babies. In North Carolina, 15 percent of black babies are born prematurely, compared to 11 percent for whites and 8.5 percent for Hispanics.

The infant mortality rate also is higher in North Carolina. The rate among minorities was 14.9 deaths per 1,000 births in 2005, more than double the rate for children born to white parents.

Language, environment, and learning all contribute to the health of children, and researchers hope to raise awareness about the importance of these factors.

"Children crawl on the floor, putting everything in their mouths, increasing their exposure to contaminants," said Stephen Johnson, administrator of the U.S. Environmental Protection Agency. "By promoting children's health research, we are working to provide a healthier start for every child born in America."

The project, a subsidiary of Duke's Children's Environmental Health Initiative, will include a review of 15 years' worth of data on live births in North Carolina. Researchers will compare the information with data on social and environmental variables, Miranda said.

Researchers also will collect data on 1,200 to 1,500 women who go to the Lincoln Community Health Center or Duke Hospital's obstetrics clinic for care, Miranda said. The women who volunteer to participate will be asked to fill out psychological questionnaires and give blood samples to be used for chemical and genetic tests.

Reducing premature births could improve the health of these children later in life, Miranda said, noting that premature births often result in obesity, heart disease and diabetes in adults.

"If we get it wrong in the beginning," she said, "there is a whole cascade of health effects that individuals grow up with."

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