Testing people for pollutants

But efforts to use the relatively new science of biomonitoring is not without criticism. Some experts say that information from biological samples could be used by insurance companies or in hiring to discriminate against people or communities. Other experts worry that a detailed accounting of what's in breast milk could cause some women to stop nursing their babies. Focusing on chemicals in breast milk, they say, might inadvertently suggest that breast-feeding is not safe.

Regardless, biomonitoring's time seems to have come. Technological advances have made it possible to detect a wider array of chemicals in the body at much lower levels than before. The federal Centers for Disease Control and Prevention launched a study two years ago to examine blood samples from 5,000 Americans, citing evidence that chemicals may be influencing rates of cancer, asthma, autism, birth defects and Parkinson's disease.

Such advances coincide with mounting concern about environmental links to breast cancer, in particular. Studies suggest that fewer than half of breast-cancer cases can be explained by known risk factors, such as genetic traits and reproductive patterns. American women today have a one in eight chance of developing the disease, up from one in 22 in the 1940s.

Leading cancer researchers have endorsed breast-milk biomonitoring as an important new direction in breast cancer research.

More than 85,000 synthetic chemicals have been introduced in the last 50 years for industrial, farming and other uses, yet more than 90% of them have not been tested for their effects on human health. However, studies have linked 46 chemicals to mammary tumors in animals, according to the National Toxicology Program.

Previous breast-milk biomonitoring studies, performed mostly in Europe, have detected more than 200 toxic substances in breast milk, including dioxins (industrial byproducts), DDT (a pesticide) and PCBs (chemicals used to make an array of products).

Two recent breast-milk biomonitoring studies showed high amounts of flame-retardant chemicals -- called polybrominated diphenyl ethers -- in U.S. women. Those relatively small-scale studies were conducted by the Environmental Working Group, a nonprofit organization, and the University of Texas, Houston.