Plastic (Not) Fantastic: Food Containers Leach a Potentially Harmful
Chemical
Is bisphenol A, a major ingredient in many plastics, healthy for
children and other living things?
By David Biello
Scientific American, 19 February 2008
[Link:
http://www.sciam.com/article.cfm?id=plastic-not-fantastic-with-bisphenol-a
]
CHEMICAL LEACHING: When exposed to hot water, plastic
bottles--including baby bottles--leach a chemical that is known to
mimic estrogens in the body.
COURTESY OF THE UNIVERSITY OF CINCINNATI
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 annually.
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 diet."
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
hour.
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 prostate cancer occurrences, altered menstrual cycles and diabetes
in lab mice that were still developing.
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 funded.
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 health issues.
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 says.
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."