Frederick S. vom Saal, Catherine A. Richter, Rachel R. Ruhlen, Susan C. Nagel, and Wade V. Welshons
Mammalian embryonic development is epigenetic in that hormonal signals not only control the timing of gene expression but also set the activity of genes and thus the functioning of organs and homeostatic systems for the remainder of life. Variation in endogenous hormones (e.g., estradiol and testosterone), which regulate the development of organs (vom Saal 1989), or disruption of the activity of these hormones during development by chemicals can lead to permanent changes in organ structure and function. Adult exposure to endocrine-disrupting chemicals can lead to transient changes in organ function that can disrupt experiments.
Polycarbonate cages and water bottles are manufactured by polymerizing the chemical bisphenol A, which was initially considered for use as an estrogenic drug before being used to manufacture polycarbonate in the 1950s (Dodds and Lawson 1936). More than 50 published studies have shown effects of developmental as well as adult exposure to bisphenol A on a wide variety of traits in mollusks, insects, fish, frogs, rats, and mice. Polycarbonate cages have been commonly used to house rodents and aquatic animals in laboratory experiments. What was not appreciated by scientists using these cages until recently is that after repeated washings the rate of leaching of bisphenol A increases dramatically and can reach levels that can alter traits in animals. Howdeshell and coworkers reported that a small but detectable amount of bisphenol A leached out of new polycarbonate animal cages into water at room temperature, and the rate of leaching was more than 1000 times greater (> 300 µg/L) in old, visibly