(New York Times News Service) - With her 7-week-old baby nursing at her breast, Dr. Sandra Steingraber spoke at a conference held recently in New York to address an important issue: the presence of low levels of chemical residues in breast milk.

Steingraber, an ecologist and a visiting assistant professor at Cornell University's program on breast cancer and environmental risk factors, described breast-feeding as "a very exquisite communion between myself and my child" - but also a transfer of chemicals.

She and the other experts who gathered at the New York Academy of Medicine for the conference on Oct. 5, "Chemical Contaminants in Breast Milk: Impact on Children's Health," agreed that it was not known if the chemicals that turned up in human breast milk were harmful, and they did not want to make women afraid to breast-feed.

Many studies show that breast-fed babies are healthier and do better developmentally than those who are given formula.

"We are making a very clear and unequivocal affirmation that those of us in the medical community are all absolutely convinced that breast milk is without question the very best form of nutrition for human infants," said Dr. Philip Landrigan, director of the Center for Children's Health and the Environment at the Mount Sinai School of Medicine, which organized the conference.

But, Landrigan said: "Because pediatricians and others are so anxious to promote breast-feeding, they've been reluctant to confront the fact that breast milk is not as good as it could be and as it used to be. It has become very clear to the medical community that over the past 25 to 30 years, a number of toxic chemicals have found their way into breast milk - PCBs, DDT, solvents and heavy metals."

People absorb environmental chemicals from polluted air and contaminated foods - fish and animal products in particular.

Because chemicals like polychlorinated biphenyls (PCBs), dioxin and dichlorodiphenyl dichloroethene (DDE), a breakdown product of DDT, are fat soluble, they are not readily excreted from the body.

Instead, they attach to fat cells, where they may stay for a lifetime. But if a woman breast-feeds her child, these fat cells are activated to produce milk. The contaminants, clinging to the fat, go directly into the milk.

A woman can shift 20 percent of her total body burden of contaminants into her infant in the first six months of breast-feeding, Steingraber said.

Few studies have examined whether the breast milk of the average American woman contains high enough levels of contaminants to harm infants.

"We do know that for women with PCBs at the high end of the range in the American population, their babies have reduced IQ, and loss of some psychological and verbal skills," Landrigan said. "We do know that babies are vulnerable. We know that very complex processes of growth and development are occurring which create windows of opportunity for damage."

The few studies on the long-term effects of pollutants in breast milk that have been done, however, show conflicting results. Experts agree that more research is needed.

"The United States should be embarrassed by the lack of research in this country on this critically important issue," said Dr. Gina Solomon, a senior scientist at the Natural Resources Defense Council, based in San Francisco. "In comparison, some European countries have systematic monitoring year after year of levels of contaminants in breast milk."

At the conference, Dr. Peter Scheidt said the National Institutes of Health was starting a large study to examine the effects of many types of environmental exposures on children, including contaminants in breast milk.

The study, which will include 100,000 babies enrolled while they are still in the womb, is expected to be started in a few years.

On a positive note, Solomon reported that levels of PCBs, DDT and dioxins in breast milk have gone down in Western countries, largely because of bans or strict regulatory controls on these chemicals. But, she said, a relatively new type of contaminant, polybrominated diphenyl ethers (PBDEs), which are used as flame retardants in computers, furniture, upholstery, plastic casings and other consumer products, are increasing exponentially in breast milk. Levels are still low now, but if the use of PBDEs are not limited, levels are expected to rise to potentially dangerous levels, Solomon said.

Another researcher reported that some studies showed that women who had high levels of DDE, the DDT breakdown product, had more difficulty breast-feeding than others.

"We did see a strong effect of DDE, with women who had the least amount of DDE breast-feeding for 36 weeks on average compared to nine weeks in the highest group," said Dr. Walter Rogan, epidemiologist at the National Institutes for Environmental Health Sciences.

Steingraber said, "We should be asking how can we get environmental contaminants out of breast milk."

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