The Facts about Bisphenol A (BPA)

By ACSH Staff — Jan 04, 2005

This 2005 report by the American Council on Science and Health reviews the evidence and finds that low doses of bisphenol A (BPA) aren't a threat to human health.

Based on the longer article "Bisphenol A: A Scientific Evaluation," written for ACSH by Michael Kamrin, Ph.D. and published on Medscape General Medicine on September 3, 2004 and available at :http://www.medscape.com/viewarticle/484739?src=search.

The American Council on Science and Health gratefully acknowledges the comments and contributions of the following individuals, who reviewed all or part of this work.

Larry Beeson, Dr.P.H.
Loma Linda University

Robert Brent, M.D., Ph.D.
Jefferson Medical College

Charles R. Curtis
The Ohio State University

Alan R. Kristal, Dr.P.H.
University of Washington

Joseph D. Rosen, Ph.D.
Rutgers University

Charles R. Santerre, Ph.D.
Purdue University

Patrick J. Shea, Ph.D.
University of Nebraska -- Lincoln

Anne M. Smith, Ph.D., R.D., L.D.
The Ohio State University

Miles Weinberger, M.D.
University of Iowa

Summary

Concerns have been raised about the safety of bisphenol A, a substance used in the manufacture of many consumer products, including some types of plastic bottles. Research has shown, however, that the amounts of bisphenol A that may migrate into food and beverages from plastic containers are extremely small and well within acceptable limits that are set by various regulatory agencies. Suspicions that exposure to bisphenol A at very low doses might cause harmful effects that do not occur at higher doses have not been confirmed by further research. There is no need for concern about the current, very low levels of human exposure to bisphenol A from plastic bottles and other consumer products.

What Is Bisphenol A?

Bisphenol A is an industrial chemical that is used in the manufacture of polycarbonate plastic. Polycarbonate plastic is light in weight, durable, shatter-resistant, and heat resistant; thus, it is well suited for a variety of uses. Several types of products that come into contact with food or beverages -- including infant feeding bottles, some brands of water bottles carried by sports enthusiasts, reusable five-gallon water bottles, returnable beverage bottles, plastic dinnerware, and plastic food storage containers -- may be made of polycarbonate. Polycarbonate is also used in other types of consumer products, such as eyeglass lenses, electrical equipment, cell phones, automobiles, medical equipment, household appliances, sports safety equipment, CDs, and DVDs.

Bisphenol A is also used in the manufacture of epoxy resins. These resins are used in a variety of protective coatings, including the coatings that line food and beverage cans. They are also used in the manufacture of paints, adhesives, floorings, and printed circuit boards. Similar resins are used in some dental composites (filling materials) and sealants.

How Are People Exposed to Bisphenol A?

The principal way in which consumers may be exposed to bisphenol A is through food and beverages. Traces of bisphenol A may migrate into foods or beverages from polycarbonate containers or from cans lined with epoxy resins.

How Much Bisphenol A Are People Exposed To?

Researchers have performed several types of investigations in an effort to find out how much bisphenol A people are exposed to. They have conducted tests to see how much bisphenol A migrates into foods or beverages from polycarbonate containers or cans lined with epoxy resins under the usual conditions of use and combined the results of these tests with estimates of the amounts of different types of foods and beverages consumed by people of different ages. Other researchers have used a different approach, measuring people's urinary levels of bisphenol A and of substances that may be formed from it and combining these results with information on how bisphenol A is handled by the human body.

Based on this research, the best estimates of the daily intake of bisphenol A range from about one one-thousandth (0.001) to one-tenth (0.1) of a microgram per kilogram of the person s body weight per day. (Exposures are usually expressed in terms of body weight because it takes less of a substance to produce an effect in a smaller person than in a larger person.) The data indicate that exposures are similar in for infants, children, and adults magnitude (when corrected for differences in body weight).

Is the Amount of Bisphenol A That People Are Exposed to a Cause for Concern?

To determine whether there is cause for concern about people's exposure to any substance, it is necessary to have the answers to two questions: 1) How much of the substance are people exposed to? 2) At what levels of exposure do harmful effects occur? It is important to recognize that practically all substances -- even substances that are essential for life, such as oxygen and vitamins -- can have harmful effects at high doses.

The only direct evidence about the effects of bisphenol A in humans comes from the experiences of workers who were exposed to the substance on the job. As a result of long-term exposure to high levels of bisphenol A in the air at their workplaces, some of these individuals experienced irritation of the eyes, respiratory tract, and skin. These symptoms, however, resulted from inhaling bisphenol A, not from ingesting it in foods and beverages, and thus the experiences of workers who were exposed to bisphenol A on the job are not applicable to the experiences of the general public.

Because no direct information is available on the effects of human exposure to bisphenol A in foods and beverages, it is necessary to make use of data from studies in experimental animals. In studies conducted by the U.S. National Toxicology Program, harmful effects, especially a reduction in body weight, were found in mice and rats only when the amount of bisphenol A fed to the animals exceeded 50,000 micrograms (50 milligrams) per kilogram of body weight per day. Lower doses did not harm the rodents. When bisphenol A was fed to pregnant animals, the offspring were harmed only by doses that were high enough to also cause toxicity in the mother. Bisphenol A is not carcinogenic (cancer-causing) in experimental animals, and although the results of various tests have not been entirely consistent, the overall scientific evidence indicates that it does not cause mutations (genetic damage).

Because the amount of a substance that is needed to produce a harmful effect may differ between humans and test animals, and because individual humans may differ in their sensitivity to a substance, it is customary to use a substantial safety factor when applying the results of studies in experimental animals to the human situation. Using this approach, the U.S. Environmental Protection Agency (EPA) calculated its human acceptable daily intake level (known as the Reference Dose or RfD) of bisphenol A by dividing the rodent "lowest effect" level of 50,000 micrograms per kilogram of body weight per day by 1000 to obtain an RfD of 50 micrograms per kilogram body weight per day. Using slightly different assumptions, the European Commission Scientific Committee on Food calculated an acceptable daily intake level of 10 micrograms per kilogram body weight per day. Comparing these values with exposure estimates indicates that the amounts considered acceptable by government agencies are 100 to 500 times higher than the highest estimated human exposure levels. Thus, a substantial margin of safety exists between current levels of exposure to bisphenol A and levels that might be harmful.

In actuality, the margin of safety is likely to be even greater than the government agencies' calculations would indicate. As mentioned earlier, when government agencies calculate acceptable intake levels, they assume that humans may be more sensitive to a substance than experimental animals are. In the case of bisphenol A, however, there is evidence that the opposite is true. Humans break down and excrete bisphenol A more rapidly and completely than rodents do and thus are likely to be less sensitive than rodents to this substance.

Are Low Doses of Bisphenol A Harmful?

Concerns have recently been raised about the possibility that low doses of bisphenol A might have detrimental effects on reproduction and development that do not occur at higher doses. This idea is contrary to fundamental principles of toxicology (the science of poisons). The harmful effects of toxic substances increase with dose rather than decreasing. Effects seen at low doses of a substance may differ from those seen at high doses, but those seen at high doses are more intense. This is evident from common experience. For example, consumption of a relatively small amount of alcohol can cause a feeling of relaxation; larger amounts cause intoxication, with obvious symptoms such as slurred speech and impaired coordination; and still larger amounts cause unconsciousness. This type of pattern, with higher doses causing more severe symptoms, is to be expected. What would be unexpected would be if small or moderate amounts of alcohol caused mild symptoms of intoxication but larger amounts had no effect at all. Such a pattern would be contrary to both common experience and scientific principles.

The idea that bisphenol A might be harmful at low doses but not at higher doses came from the results of a few animal experiments, in which some adverse effects were observed in groups of animals that received low doses. Other animal experiments, however, including some that involved much larger numbers of animals, have not confirmed the existence of low-dose effects.

The suggested rationale for the proposed low-dose effects of bisphenol A is that this substance might be able to act as a hormone disruptor or modulator, mimicking the effects of the female hormone estrogen. Some experimental evidence indicates that bisphenol A does indeed bind weakly to the body s receptor for estrogen. However, estrogenic effects of bisphenol A are unlikely to occur to any meaningful extent in humans because the human body rapidly transforms bisphenol A into a byproduct that does not bind to the estrogen receptor. Moreover, if bisphenol A did have estrogenic effects, we would expect those effects to become increasingly evident as the dose of bisphenol A increases, not to disappear at higher doses.

Scientists consider the results of experiments to be valid only if they can be verified by further research. If a finding cannot be reproduced, it is probably erroneous. The findings of low-dose effects of bisphenol A have not proven to be reproducible. They are most likely attributable to random chance or to some difficulty that occurred during a specific experiment, rather than to a true effect of bisphenol A.

The U.S. National Toxicology Program and the European Commission Scientific Committee on Toxicity, Ecotoxicity, and the Environment have convened independent scientific panels to examine the evidence on possible low-dose effects of bisphenol A. Both panels concluded that reproducible low-dose effects have not been established.

Conclusion

The current, very low levels of exposure to bisphenol A from plastic bottles and other consumer products do not pose a hazard to human health.

References

This booklet is a summary of the following scientific paper:

Kamrin MA, Bisphenol A: A scientific evaluation, Medscape General Medicine, September 3, 2004. Available online at http://www.medscape.com/viewarticle/484739 (You must register with the site to read this article. Registration is free.)

For those who wish to examine the scientific evidence in detail, the following additional references may also be helpful:

Gray GM, Cohen JT, Cunha G, et al., Weight of the evidence evaluation of low-dose reproductive and developmental effects of bisphenol A. Hum Ecol Risk Assess 2004;10:875-921.

Integrated Risk Information System (IRIS). Bisphenol A. United States Environmental Protection Agency, Office of Research and Development, National Center for Environmental Assessment. Washington, DC. Available at:http://www.epa.gov/iris/subst/0356.htm

National Toxicology Program. The National Toxicology Program endocrine disruptors low-dose peer review final report, August, 2001. US Department of Health and Human Services, National Institute of Environmental Health Sciences. Research Triangle Park, NC. Available at: http://ntp-server.niehs.nih.gov/

Volkel W, Colnot T, Csanady GA, Filser JG, Dekant W. Metabolism and kinetics of bisphenol A in humans at low doses following oral administration. Chem Res Toxicol 2002;15:1281-1287.

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