The umbilical cord is quite literally a lifeline, connecting the fetus to the placenta. It passes oxygen and nutrients to the fetus through the umbilical vein, and accepts waste products from the fetus through the two umbilical arteries. In the placenta, capillaries branch from the umbilical vein and arteries. The capillaries are bathed in pools of the mother’s blood that collect in the placenta. Because the capillaries are in connective tissue, the blood they contain does not actually mix with the mother’s blood. But, through the process of diffusion, gases and nutrients can pass from the mother’s blood across the capillary walls to the fetus’s blood.

Scientists had long thought that the placenta prevented most environmental chemicals and pollutants to which the mother was exposed—through eating, breathing, and skin contact—from reaching the developing baby. However, recent studies show that umbilical cord blood carries not only essential gases and nutrients, but also industrial chemicals, pollutants, and pesticides.

Researchers at the Environmental Working Group, an environmental advocacy organization, and fellow nonprofit Commonweal, found an average of 200 industrial chemicals in the umbilical cord blood of a small sample of babies born in U.S. hospitals. The babies were chosen at random, and the umbilical cord blood was collected after the cords were cut. Researchers discovered that the cord blood contained pesticides, consumer product ingredients, and wastes from burning coal, gasoline, and garbage. Among the chemicals found were mercury, which can harm brain development and function; perfluorinated chemicals (PFCs), which are found in Teflon, Scotchgard, Stainmaster, and other protective coatings and have been linked to cancer and birth defects; polybrominated diphenyl ethers (PBDEs), which are flame retardants found in furniture, computers, and televisions and can affect brain development and the thyroid; and polychlorinated biphenyls (PCBs), industrial insulators and lubricants that were banned in the U.S. in 1976 for their toxicity.

Scientists have never studied the effects of exposure to this complex mix of chemicals. And because the babies tested in these studies were anonymous, researchers cannot follow up to see if their development has been affected. However, scientists know that chemical exposures in the womb or during infancy are a greater threat to health than exposures a person may experience later in life. This is because babies develop rapidly, are smaller than adults, and have underdeveloped defense mechanisms.

Currently, there is not enough data to link cord blood chemicals to developmental problems. However, some people argue that the government should not wait for a definitive conclusion because the risk to babies is so high. In other words, the government already has “sufficient cause” to limit the risk. This doctrine of sufficient cause, which is also known as the “precautionary principle,” has already led the plastics industry to stop producing baby bottles containing the controversial chemical Bisphenol A (BPA). Advocacy groups argue that the government must go further, reforming laws and policies to protect children from exposures to industrial chemicals. Such reforms, however, could entail huge costs for many industries, as well as consumers. And without proof of harm, one could argue there is no reason to remove hundreds of chemicals from production. The problem is controversial and will not be easily solved.

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