By Kelly A. Reynolds, MSPH, PhD
The widely-debated chemical compound, bisphenol A is in the news again as California lawmakers have proposed a bill to ban the compound from plastic baby bottles and cans of infant formula. Bisphenol A is found in many commercial food storage containers, including water bottles.
Representatives from the U.S. Food and Drug Association state that the current exposure levels of bisphenol A (BPA) in foods is below harmful doses. Judging by the media hype and responses from major retail outlets, consumers are not convinced of BPA’s safety, particularly with regard to exposures in children.
While there is little disagreement that BPA can be toxic, there are many uncertainties as to what levels are ’safe.’ Thus the question remains: what is the risk of BPA in food and water and what evidence is available to evaluate the true health impacts versus the media hype?
The dose makes the poison
Paracelsus, sometimes called the father of toxicology, famously stated “All substances are poisons; there is none which is not a poison. The right dose differentiates a poison from a remedy.”
This 16th century alchemist and physician is credited with the use of chemicals and minerals in medicine. Paracelsus pioneered the idea that humans must have certain balances of minerals in the body but also seemed to realize that beyond a certain threshold value, adverse health effects eventually occurred.
Given that everything is toxic at some dose, how then do we regulate acceptable doses, reaping the benefits and avoiding harm? Numerous studies have been conducted with humans and animals aimed at evaluating tolerable levels of BPA in the body.
Risk assessment modeling has also been used to estimate the health impact of BPA under known and hypothetical exposure scenarios. The science of risk assessment, utilizes four basic steps: 1) hazard identification; 2) dose-response assessment; 3) exposure assessment; and 4) the overall risk characterization.
These mathematical models plug in data from applied studies to forecast current and future outcomes. Information gaps exist, however, complicating risk estimates. Gaps are particularly evident in the exposure and dose-response assessment: how often are people exposed, at what levels (dose), what are the long-term health effects (responses) and can they be effectively measured?
BPA was first synthesized by Russian chemist, Alexander Dianin in 1891. In 1930, the compound was investigated for use as a synthetic estrogen but other chemicals proved more effective. In 1953, scientists found that BPA was useful for the manufacture of polycarbonates.
Today, over six billion pounds of BPA are produced annually. Polycarbonates are used to make CDs, optical lenses, food packages, baby bottles, water bottles, dental sealants and many other household and industrial items. BPA is also a common component of epoxy resins, used in food-contact coatings (e.g., metal cans), PVC pipes and adhesives.
Humans are exposed to BPA via ingestion of contaminated foods. BPA can leach from plastics and coatings into food items. Leaching occurs more readily into foods with high fat or acid content. In addition, the age and treatment (e.g., high heat) of the containers can lead to increased migration to foods.
Strong scientific evidence supports that BPA disrupts the endocrine system, including human hormones and glands that control vital developmental and reproductive processes. Animal studies also show effects to the brain and growth rates in fetuses at very high doses (e.g., >1200 mg/kg/day) but amounts found in foods and beverages are estimated to be hundreds of thousands of times lower.
Part of the concern is that long-term, low-dose health effects in humans are difficult to measure. Questions remain as to how effects in rats or other animal models translate to human health impacts.
In addition, information is lacking on the potential increased susceptibility of sensitive populations. For example, what is the effect of exposure to BPA on fetuses, infants or young children during critical developmental stages?
Furthermore, most laboratory studies focus on health effects related to exposure to a single toxicant and thus little information is known as to the effect of exposures to chemical mixtures. The world we live in today is riddled with environmental toxicants. Thus, information is needed evaluating the synergistic effects of combined chemical exposures over time.
A precautionary approach
Despite the uncertainty of the evidence regarding human risks associated with products containing BPA, politicians, consumers and manufacturers are taking a precautionary approach to safety. The recently proposed bill in California targets protecting children under three years of age, requiring that products designed for this age group contain only trace amounts of BPA.
If passed, California would be the first to set statewide limits. Following the lead of the European Union, San Francisco banned the manufacture, sale and distribution of child care articles and toys with any levels of BPA in 2006, but statewide legislation failed to pass
Conversely, in July of 2008, just weeks before the statewide CA bill was introduced, a scientific panel of the European Food Safety Authority (EFSA) claimed that based on human metabolism of BPA and low exposure levels in foods, there was no significant risk to humans, at any age. This sigh of relief is based on the evidence that humans excrete the compound much more rapidly than rats and thus safety officials argue that rodent models showing increased risk are not representative of the human condition.
The US Food and Drug Administration (US FDA) concurs, but has formed a BPA Task Force to further monitor the issue and gather current and previous research information. The FDA also has funded ongoing research to improve the database on BPA risks.
As new information becomes available, policies may change. But for now, the FDA has made numerous public statements regarding the safety of BPA and minimal exposure levels (typically below the ppb level) in foods.
Based largely on animal studies, BPA limits have been set around the globe. Germany established a safe level for aerosol exposures with employees, where no adverse health effects were observed, at 10 mg/m3. Specific mitigation limits have been set in the European Union, allowing three mg/kg (ppm) to transfer from food storage containers to one kg of food. Japan set a similar standard (2.5 mg/kg).
Previous uncertainties regarding increased effects in infants led the EU to establish a tolerable daily intake level for humans of five mg per kg body weight per day, concluding that reports of adverse effects in rodents at lower levels were not robust or reproducible. The US EPA took a more precautionary approach, suggesting a maximum acceptable dose of 0.05 mg per kg body weight per day.
Studies of where to draw the line at acceptable BPA exposure levels are conflicting. Critics blame these uncertainties on everything from poor study design to intentional bias but virtually all agree that more research is needed.
BPA is thought to be rapidly excreted in humans, but evidence of the compound in placental tissue and amniotic fluid has fueled concern over subtle effects of exposure and long-term exposure risks. Potential long-term impacts such as increased genital abnormalities in children, earlier sexual maturation rates in girls, decreased sperm count in boys, or increased breast cancer in women would be difficult to measure and link to any particular environmental contaminant.
Wal-Mart® and Toys ‘R Us® have agreed to stop selling baby bottles made with BPA next year and major manufacturers of plastic baby bottles have agreed to stop using BPA in their products. Time will tell if BPA is truly a health risk at the current levels we are exposed. Until then, expect continued media hype as consumers demand a more precautionary approach to illness prevention.
References and additional information
- US Department of Health and Human Services. Statement by Norris Alderson, Ph.D. Associate Commissioner for Science Food and Drug Administration. Department of Health and Human Services. FDA on Safety of Bisphenol-A (BPA) before the Subcommittee on Commerce, Trade and Consumer Protection. US House of Representatives. June 10, 2008. Available at: http://www.fda.gov/ola/2008/BPA061008.html
- vom Saal, F.S. et al., (2007) Chapel Hill bisphenol A expert panel consensus statement: Integration of mechanisms, effects in animals and potential to impact human health at current levels of exposure. Reproductive Toxicology. 24(2): 131-138.
About the author
Dr. Kelly A. Reynolds is an associate professor at the University of Arizona College of Public Health. She holds a Master of Science degree in public health (MSPH) from the University of South Florida and a doctorate in microbiology from the University of Arizona. Reynolds has been a member of the WC&P Technical Review Committee since 1997. She can be reached via email at [email protected].