Bisphenol A (BPA) is a ubiquitous
compound in plastics. First synthesized in 1891, the chemical has become a key
building block of plastics from polycarbonate
to polyester; in the U.S. alone more than 2.3
billion pounds (1.04 million metric tons) of the stuff is manufactured
Since at least 1936 it has been known that BPA mimics estrogens, binding to
the same receptors throughout the human body as natural female hormones. And
tests have shown that the chemical can promote human
breast cancer cell growth as well as decrease sperm count in rats, among other effects. These findings have raised
questions about the potential health risks of BPA, especially in the wake of
hosts of studies showing that it leaches from plastics and resins when they are
exposed to hard use or high temperatures (as in microwaves or dishwashers).
The U.S. Centers for Disease Control (CDC) found traces of BPA in nearly all
of the urine samples it collected in 2004 as part of an effort to gauge the
prevalence of various chemicals in the human body. It appeared at levels
ranging from 33 to 80 nanograms (a nanogram is one billionth of a gram) per
kilogram of body weight in any given day, levels 1,000 times lower than the 50
micrograms (one millionth of a gram) per kilogram of bodyweight per day
considered safe by the U.S. Environmental Protection Agency (EPA) and the
European Union's (E.U.) European Food Safety Authority (EFSA).
Studies suggest that BPA does not linger in the body
for more than a few days because, once ingested, it is broken down into
glucuronide, a waste product that is easily excreted. Yet, the CDC found
glucuronide in most urine samples, suggesting constant exposure to it.
"There is low-level exposure but regular low-level exposure," says
chemist Steven Hentges, executive director of the polycarbonate / BPA global
group of the American Chemistry Council. "It presumably is in our
BPA is routinely used to line cans to prevent
corrosion and food contamination; it also makes plastic cups and baby
and other bottles transparent and shatterproof. When the polycarbonate plastics
and epoxy resins made from the chemical are exposed to hot liquids, BPA leaches out 55 times faster
than it does under normal
conditions, according to a new study by Scott Belcher, an endocrine
biologist at the University of Cincinnati. "When we added boiling water [to
bottles made from polycarbonate] and allowed it to cool, the rate [of leakage]
was greatly increased," he says, to a level as high as 32 nanograms per
A recent report in the journal Reproductive Toxicology found that
humans must be exposed to levels of BPA at least 10 times what the EPA has
deemed safe because of the amount of the chemical detected in tissue and blood
samples. "If, as some evidence indicates, humans metabolize BPA more
rapidly than rodents," wrote study author Laura Vandenberg, a
developmental biologist at Tufts University in Boston, "then
human daily exposure would have to be even higher to be sufficient to produce
the levels observed in human serum."
The CDC data shows that 93 percent of 2,157 people between the ages of six
and 85 tested had detectable levels of BPA's by-product in their urine.
"Children had higher levels than adolescents and adolescents had higher
levels than adults," says endocrinologist Retha Newbold of the U.S.
National Institute of Environmental Health Sciences, who found that BPA impairs
fertility in female mice. "In animals, BPA can cause permanent effects after very short periods of
exposure. It doesn't have to remain in the body to have an effect."
But experts are split on the potential health hazards to humans. The Food
and Drug Administration has approved its use and the EPA does not consider it
cause for concern.* One U.S. National Institutes of Health (NIH) panel agreed, but another team of
government scientists last year found
that the amount of BPA present in humans exceeds levels that have caused ill
effects in animals. They also found that adults' ability to tolerate it does
not preclude damaging effects in infants and children.
"It is the unborn baby and children that investigators are most worried
about," Newbold says, noting that BPA was linked to increased breast and
occurrences, altered menstrual cycles and diabetes in lab mice that were still
Fred vom Saal, a reproductive biologist at the University of
Missouri–Columbia, warns that babies likely face the "highest
exposure" in human populations, because both baby bottles and infant
formula cans likely leach BPA. "In animal studies,
the levels that cause harm happen at 10 times below what is common in the U.S."
says vom Saal, who also headed the NIH panel that concluded the chemical may
pose risks to humans.
Amid growing concern, Rep. John Dingell (D–Mich.) chairman of the House
Committee on Energy and Commerce, has launched
an investigation into BPA, sending letters last month to the FDA and seven
manufacturers of infant products sold in the U.S. requesting information on any
BPA safety tests as well as specific levels in the baby goods. The companies
that make Similac, Earth's Best and Good Start have already responded,
confirming that they coat the inside of their cans with BPA but that analyses
did not detect it in the contents. They also emphasize that FDA has approved
BPA for such use.
"Based on the studies reviewed by FDA, adverse effects occur in animals
only at levels of BPA that are far higher orders of magnitude than those to
which infants or adults are exposed," says FDA spokeswoman Stephanie
Kwisnek. "Therefore, FDA sees no reason to ban or otherwise restrict the
uses now authorized at this time."
FDA first approved BPA as a food container in 1963 because no ill effects
from its use had been shown. When Congress passed a law—the Toxic Substances
Control Act of 1976—mandating that the EPA conduct or review safety studies on
new chemicals before giving them the nod, compounds like BPA were already on
the market. Therefore, they were not subject to the new rules nor required to
undergo additional testing unless specific concerns had been raised (such as in
the case of PCBs). "The science that exists today supports the safety of
BPA," ACC's Hentges says, based largely on research his organization has
But other studies since 1976 have shown that small doses (less than one part
per billion) of estrogenlike chemicals, such as BPA, may be damaging. "In
fetal mouse prostate you can stimulate receptors with estradiol at about two
tenths of a part per trillion, and with BPA at a thousand times higher,"
vom Saal says. "That's still 10 times lower than what a six-year-old
has." In other words, children six years of age were found to have higher
levels of BPA's by-product glucuronide in their urine
than did mice dosed with the chemical that later developed cancer and other
Further complicating the issue is the stew of other
estrogen-mimicking chemicals to which humans are routinely exposed, from soy to antibacterial
ingredients in some soaps. The effects of such chemical mixtures are not
known but scientists say they may serve to enhance the ill effects of one
another. "The assumption that natural estrogens are somehow immediately
good for you and these chemicals are immediately bad," Belcher says,
"is probably not a reasonable assumption to make."
The chemical industry argues that unless BPA is proved to have ill effects
it should continue to be manufactured and used, because it is cheap, lightweight,
shatterproof and offers other features that are hard to match. "There is
no alternative for either of those materials [polycarbonate plastics and epoxy
resins] that would simply drop in where those materials are used," Hentges
Not so, says vom Saal, who notes that there are
plenty of other materials, such as polyethylene and polypropylene plastics,
that would be fine substitutes in at least some applications. "There are a
whole variety of different kinds of plastic materials and glass," he says.
"They are all more stable than polycarbonate."
Concern over BPA is not confined only to the U.S. Japanese
manufacturers began to use natural resin instead of BPA to line cans in 1997
after Japanese scientists showed that it was leaching out of baby bottles. A
subsequent study there that measured levels in urine in 1999 found that they
had dropped significantly.
A new E.U. law (Registration, Evaluation, Authorization and Restriction of
Chemical Substances, or REACH), which took effect last year, requires that
chemicals, such as BPA, be proved safe. Currently, though, it continues to be
used in Europe; the EFSA last year found no reason for alarm based on rodent
studies. European scientists cited multigenerational rat studies as reassuring
and noted that mouse studies may be flawed because the tiny rodent is more
susceptible to estrogens.
For now, U.S. scientists with concerns about BPA recommend that anyone
sharing those worries avoid using products made from it: Polycarbonate plastic
is clear or colored and typically marked with a number 7 on the bottom, and
canned foods such as soups can be purchased in cardboard cartons instead.
If canned goods or clear plastic bottles are a must, such containers should
never be microwaved, used to store heated liquids or foods, or washed in hot
water (either by hand or in much hotter dishwashers). "These are fantastic
products and they work well … [but] based on my knowledge of the scientific
data, there is reason for caution," Belcher says. "I have made a
decision for myself not to use them."
* This is based on a study done for the EPA by a company
paid by the plastics industry.