My favourite journal. Enjoy.
February 19, 2008
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
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_
(http://www.sciam.com/article.cfm?id=how-are-polymers-made) 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_
(http://www.sciam.com/article.cfm?id=bringing-cancer-to-dinner-table-breast-cancer-cells-grow-under-influence-fish-flesh) 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_
(http://energycommerce.house.gov/Investigations/Bisphenol.shtml) 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_
(http://www.sciam.com/article.cfm?id=bringing-cancer-to-dinner-table-breast-cancer-cells-grow-under-influence-fish-flesh) to which humans are
routinely exposed, from soy to _antibacterial ingredients in some soaps_
(http://www.sciam.com/article.cfm?id=strange-but-true-antibacterial-products-may-do-more-h
arm-than-good) . 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."
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