Our Stolen Futurea book by Theo Colborn, Dianne Dumanoski, and John Peterson Myers



An excerpt from Chapter 8, Here, There, and Everywhere



By strange coincidence, while Soto and Sonnenschein were chasing contamination in their lab, a similar drama was unfolding at the opposite end of the country at Stanford University School of Medicine in Palo Alto, California. In this case, too, the mystery estrogen was traced to plastic lab equipment but not to polystyrene products or to nonylphenol. The Stanford team found another estrogen mimic, bisphenol-A, which was leaching from an entirely different kind of plastic, polycarbonate. This plastic is used for lab flasks and for many consumer products such as the giant jugs used to bottle drinking water.

Here again, the discovery was accidental and one that occurred only because the scientists were conducting research with estrogen-sensitive cells. David Feldman, a professor of medicine, and his colleagues in the endocrinology division had initially discovered a protein in yeast that binds with estrogen, which they thought might be a primitive estrogen receptor, and if yeast had such an estrogen receptor, then there must be a yeast hormone. The team was hunting for such a hormone when they saw that some substance was indeed binding to the yeast receptor. But the researchers soon realized the estrogenic effect was due to a contaminant rather than a hormone. They determined that the contaminant was bisphenol-A and that the source of the contamination was the polycarbonate lab flasks used to sterilize the water used in the experiments.

In a 1993 paper, the Stanford team reported their discovery and their discussions with the manufacturer of polycarbonate, GE Plastics Company. Apparently aware that polycarbonate will leach, particularly if exposed to high temperatures and caustic cleaners, the company had developed a special washing regimen that they thought had eliminated the problem. In working with the company, however, the researchers discovered that GE could not detect bisphenol-A in samples sent by the Stanford lab-samples that were causing proliferation in estrogen-responsive breast cancer cells. The problem proved to be the detection limit in GE's chemical assay-a limit of ten parts per billion. The Stanford team found that two to five parts per billion of bisphenol-A was enough to prompt an estrogenic response in cells in the lab.

Though bisphenol-A is two thousand times less potent than estrogen, notes Feldman, "it still has activity in the parts per billion range." Feldman is cautious, however, about making people alarmed about plastics. "We don't know enough yet to make this into a public health crisis." He adds, however, that the accidental discovery about polycarbonate raises a host of questions that need to be answered. The Stanford paper shows that bisphenol-A prompts an estrogen response in cells in a lab. The next logical question, he says, is whether it prompts the same response when given in water to an animal.






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