WASHINGTON — The largest study of children's health ever undertaken in the U.S. started yesterday.

In an effort to learn more about the effects of pollution on American children, the National Children's Study will track up to 100,000 children's exposure to environmental factors from their first trimester before birth until they're at least 21.

Nearly a decade in the planning, the study has a component in Hawai'i, where the University of Hawai'i's John A. Burns School of Medicine will begin to recruit about 1,000 O'ahu families to take part. Dr. Beatriz Rodriguez is the local contact person.

"We are embarking on the road to discovering the preventable causes of the major chronic diseases that plague American children today," Dr. Philip Landrigan of the Mount Sinai School of Medicine, one of the lead researchers, said yesterday.

The National Children's Study tackles a major mystery: How does the environment — everything from a pregnant woman's diet to a child's exposure to various chemicals — interact with genetics to affect youngsters' health and development?

Information leading to advances in diagnosis and treatment for conditions such as autism, asthma, cerebral palsy and attention deficit disorder could be available in three to five years, said Dr. Peter Scheidt, the study's director. Plus, many adult diseases take root in childhood.

But while technology has finally advanced enough to separate multichemical and gene-environment interactions, research until now hasn't included enough children to show why some are more at risk than others. The hope is that the new study can identify both what's harmful and what's not.

The study is sponsored by the National Institutes of Health with support from the Centers for Disease Control and Prevention and the Environmental Protection Agency.

Pregnant women invited to take part in the study will be asked to commit themselves and their children to 38 hours of examinations in the first two years. After that, only the children will be examined every three years.

Participation in the study is limited to pregnant women living in specific areas selected by a mathematical model. Women can't volunteer, but they will be contacted by representatives of the study and given the option to participate. Those who participate will be paid.

RECRUITING BEGINS

This week and for the next 18 months, researchers will fan out in New York's dense and ethnically diverse borough of Queens plus the smaller, rural Duplin County, N.C., to find the first recruits: Women in early pregnancy or who are trying to conceive.

Those who agree to participate will give samples of their blood, hair and urine, let researchers test the water and dust in their homes, and undergo health interviews throughout pregnancy. Their babies' health will be tracked, with periodic exams and checks of their home environment in the first year of life and then about every three years afterward.

Sparsely populated Duplin County — where University of North Carolina-Chapel Hill researchers will cover 885 miles of road to recruit — is home to many large hog and turkey farms and their processing factories. Queens mixes a modern urban environment with decades-old industrial sites.

The first two locations chosen for the study are "worlds apart," said Dr. Barbara Entwisle, the principal investigator at the University of North Carolina-Chapel Hill. Queens is densely populated, while Duplin County, in eastern North Carolina, is "rural and proudly southern," she said.

Afterward, the trial study will expand nationwide to include up to 100,000 children from 105 diverse locations in an effort to represent environmental and demographic differences.

In April, scientists will begin recruiting in five more locations, in parts of California, Pennsylvania, Utah, South Dakota and Minnesota. The first locations are pilot-testing the study's initial steps, with nationwide enrollment set for summer 2010.

Among the big questions: When someone is genetically vulnerable to a disease like diabetes, are there early environmental exposures that push them over the edge? And does simple exposure to common compounds — such as plastics or pesticides found in people's urine — mean they were harmed? If so, are there key periods when exposure is riskiest?