PULLMAN – WSU reproductive biologist Patricia A. Hunt has been named one of the top 50 researchers of 2007 by Scientific American for her work showing a potential threat to human health posed by bisphenol A (BPA), a component of the polycarbonate plastics used to make food and beverage containers.
“There’s been so much good work in this area in the past year that to be singled out is really an honor,” said Hunt after learning of her selection.
The “SciAm 50” list, as it is called, includes companies and research institutes as well as individual scientists. It was announced in the popular science magazine’s January issue. The entire list is available online at www.sciam.com/article.cfm?id=sciam-50-2007 and the description of Hunt’s work, under the heading “Fighting Toxins in the Home,” is available at www.sciam.com/article.cfm?id=sciam-50-fighting-toxins-at-home.
Working with mice, Hunt discovered that environmentally relevant levels of BPA—amounts that humans routinely encounter when they consume food or beverages from containers made of polycarbonate or lined with a BPA-based resin —led to high rates of chromosome abnormalities in developing oocytes (the cells that will become eggs). She traced the abnormalities to a failure of the chromosomes to be distributed properly to the early oocyte’s daughter cells.
In Hunt’s tests, 40 percent of the eggs that developed from BPA-exposed oocytes had either too many chromosomes or too few. (The normal rate of chromosomal abnormalities in mice is one to two percent.) In mice, such chromosomal abnormalities almost always cause death of the embryo. In humans, depending on which chromosomes are affected, they lead to miscarriage, death soon after birth or conditions such as Down syndrome and Turner syndrome.
Another notable aspect of Hunt’s work on BPA is that a single brief exposure to the substance can affect three generations. If an adult female is exposed, her eggs that are close to ovulating are affected; those that suffer chromosome abnormalities will not go on to produce healthy offspring. If the adult female is already pregnant when she is exposed, the embryos she is carrying are affected.
Oocytes begin to develop very early in female embryos; by the time a girl (or female mouse) is born, all the oocytes she will ever have have already gone through important stages of their developmental. If they encountered BPA during their early development in the embryo, the damage will have already been done.
“It’s amazing,” said Hunt. “We can disrupt everything with this little pulse of BPA in this critical window of development. You hit the mom, you’re hitting her daughter or her son, and if it’s a daughter, you’re hitting her developing eggs, which will be the grandchildren. So by exposing the mom you’re affecting the likelihoodthat the grandchildren are going to be chromosomally abnormal.”
Hunt’s findings alarmed consumer groups and parents of young children. Baby formula is often packaged in cans lined with a resin containing BPA, and many cups and bottles made for babies and toddlers are made of polycarbonate. Such items are often billed as being able to survive microwaving and being put through a dishwasher cycle, but in fact, said Hunt, polycarbonate does not survive those events intact. Polycarbonate is a polymer, a long chain of BPA molecules bound together. A variety of conditions, including heat (as in a microwave or dishwasher) and high pH (as in bleach-based cleaning solutions), can damage the polymer, causing it to leach BPA.
That is how Hunt first discovered the link between polycarbonate and BPA exposure. Two years ago, her research team saw a sudden increase in chromosomal abnormalities during studies of mouse eggs from normal, young adult females. They eventually traced the effects to polycarbonate cages and water bottles, which had been damaged by being washed with the wrong cleaning agent.
“We literally saw a night and day difference,” Hunt said. “We ran the experiment one week and the control data were normal. The next week, data from the same control animals were completely different and unlike anything we had seen before.”
Spurred by the findings of Hunt and other researchers in the field, manufacturers of baby bottles and drinking cups have begun to shift away from polycarbonate and toward safer substances, as described in a recent article in Newsweek magazine (www.newsweek.com/id/84533/output). On Jan. 17, the Committee on Energy and Commerce of the United States House of Representatives announced it will investigate the use of BPA, “particularly in products intended for use by infants and children.” (http://energycommerce.house.gov/Investigations/Bisphenol.shtml)
Hunt is Meyer Distinguished Professor in Washington State University’s Center for Reproductive Biology and School of Molecular Biosciences. Her research focus is the process of egg formation in mammals, and how mistakes in the process lead to chromosomal abnormalities. She has been particularly interested in the role of the mother’s age in the development of chromosome problems.
