Environmental Factor, January 2007, National Institute of Environmental Health Sciences
Expert Panel Debates Health Risks of BPA
By John Peterson
Fifty of the country's leading environmental health experts gathered at the Chapel Hill Sheraton November 28-29 to debate the potential health risks of bisphenol A (BPA), an environmental contaminant that has come under increasing scientific scrutiny. Sponsored by NIEHS, the National Institute of Dental and Craniofacial Research, the U.S. Environmental Protection Agency and Commonweal, the expert panel was convened to examine the recent literature on BPA and come to some conclusions regarding its effects on wildlife, laboratory animals and human populations.
BPA is a man-made chemical used in the production of polycarbonate plastics, epoxy resins for dental sealants and container linings, and many consumer products such as toys, baby bottles, eyeglass lenses and medical tubing. Each year manufacturers worldwide produce more than 6 billion pounds of the chemical.
The exposure of wildlife and humans to BPA is a concern, say the expert panel members. The compound is an endocrine-disrupting chemical that mimics the effects of estrogen and other naturally occurring hormones in the body, potentially leading to changes in growth, development and reproduction.
Lou Guillette, Ph.D., professor of zoology at the University of Florida and head of the wildlife panel, presented data from studies on fish showing that BPA exposure can result in feminization of male sex organs, reduction in sperm motility and a delay in the timing of ovulation and spawning. Researchers have also observed BPA-induced gonadal changes in birds and reptiles.
To illustrate the extent of BPA in the environment, Guillette produced a sample of ocean water, collected a thousand miles off the California coast, which contained hundreds of small and mid-sized pieces of floating debris. "As BPA enters the marine environment through biodegradation, there is the potential for bioaccumulation of the compound in fish and other wildlife," said Guillette.
Data collected by Frederick vom Saal, Ph.D., an endocrinologist with the University of Missouri, and other researchers shows that low-dose administration of BPA produces a wide spectrum of developmental and reproductive effects in mammals. These effects include an increase in aggressive behavior in male rats, early onset of sexual maturation in female mice, changes in mammary gland development in the offspring of treated dams, and a decrease in testosterone levels and sperm production in male rats.
Gail Prins, Ph.D., professor of physiology at the University of Illinois at Chicago, presented some recent evidence suggesting that BPA exposure early in life may increase cancer susceptibility years later. According to Prins, laboratory rats given BPA during the first five days of life were much more sensitive during adulthood to the carcinogenic activity of estradiol. "This study suggests that an environmental reprogramming of a normal response, combined with subsequent exposure to a cancer-causing agent, can work together to promote cancer," said Prins.
Concerning the potential health consequences of BPA exposure, panel experts debated such issues as the degree to which the results of in vitro studies can be used to predict effects in laboratory animals and whether data collected on animals relates to the question of human health effects. "The fact that the effects seen in wildlife are very similar to those observed in laboratory animals suggests that these kinds of changes might be occurring in humans," said Wade Welshons, Ph.D., associate professor at the College of Veterinary Medicine, University of Missouri-Columbia.
Retha Newbold, a biologist with the Developmental Endocrinology Studies Group at NIEHS and a conference participant, argued that carefully designed epidemiology studies must be conducted and evaluated. Only then can researchers make definitive conclusions about the effects of BPA in humans. "The current data we have from wildlife and laboratory animal studies is not sufficient evidence that BPA increases cancer risk in humans," Newbold concluded.
"This was a very stimulating meeting," says Jerry Heindel, program administrator at NIEHS and one of the meeting organizers. "This is the first time a group of experts has examined all of the published literature on a particular environmental agent and developed a consensus statement based on the strength of the data. This information will be valuable not only to scientists, but also to risk assessors and the general public, who want to know if what they are exposed to can cause harm."
Expert Panel's Consensus Statements On Bisphenol A
The unique conference format included expert panel presentations based on white paper reports prepared by the participants in advance of the meeting. The presentations were divided into five subject areas -- effects on wildlife, in vitro studies, laboratory animal experiments, data on human exposures and cancer. Following morning breakout sessions in which the groups finalized their reports, each group presented a brief overview of the published literature in its assigned area of expertise. Presenters were also asked to rank each observation as either confident, likely but requiring confirmation, or needing additional research, based on the strength of the available data, and create consensus statements on the compound:
- BPA interacts with and modulates estrogen receptors
- Prenatal and neonatal BPA exposure in animals results in organizational changes in the prostate, breast, testis and brain
- Sensitivity to BPA varies extensively with life stage
- Adult exposures cannot be presumed to predict the results of developmental exposure
- Circulating levels of BPA in humans exceed the BPA levels extrapolated from acute exposure studies in laboratory animals
- There are compelling data to support the low-dose effects of BPA in wildlife and animal studies