Preliminary FDA data suggest that eating
microwave pop corn may expose people to chemicals that
break down to produce PFOA, a suspected carcinogen.
Results of a study by the U.S. Food and Drug Administration
(FDA) published in October reveal that compounds known
to break down into the suspected carcinogen PFOA
(perfluorooctanoic acid) may be served up to millions
of unwitting consumers in bags of microwave popcorn. The
family treat could account for more than 20% of the average
PFOA levels now measured in the blood of the U.S. population.
Most Americans carry 4-5 parts per billion (ppb) of PFOA
in their blood, according to the U.S. EPA's draft PFOA
risk assessment, but its source has been unknown.
Products used in the home are thought to play a role,
including nonstick cookware such as Teflon pans, which
are produced by a process that uses PFOA. But a growing
number of studies, including this one, suggest that nonstick
cookware is not a major source.
The FDA team investigated consumer products that contact
food--nonstick pans, food wraps, and papers--as potential
sources, says FDA chemist Timothy Begley, the study's
lead author. Some of the papers used for packaging food
are treated with grease-repelling fluorotelomer coatings.
Microwave popcorn bags have the most of any food wrappers--
about 4000 milligrams per kilogram (mg/kg) in the coating
or 25 mg per square decimeter of paper, the authors note.
Many of these coatings contain mixtures of long-chain
chemicals that can be metabolized to PFOA, Begley and
colleagues write in their Food Additives & Contaminants
article.
The scientists found that a significant percentage of
the fluorotelomers migrated from the bags to the popcorn
oil, resulting in levels of 3-4 mg/kg. These concentrations
are hundreds of times higher than the amount of PFOA that
could migrate from nonstick cookware the first time it
is heated above 175 °C. Because the surface area of
a microwave popcorn bag is about 1000 square centimeters,
a person consuming a bag's worth could take up to 110
micrograms of fluorotelomers, according to three toxicologists
who performed these calculations on the condition of anonymity.
Toxicologists commonly convert such an exposure into
a human dose by dividing by the average adult body weight,
65 kg. This means that the average dose of fluorotelomers
from each bag of popcorn is 1.7 micrograms per kilogram.
Children who ate a whole bag would get a higher dose.
Scientists don't currently know how readily humans can
metabolize fluorotelomers to PFOA, says University of
Alberta (Canada) biochemist Jonathan Martin. But in a
recent article
in Chemico-Biological Interactions, he reports
that rat liver cells can directly convert 1.4% of fluorotelomer
alcohol to PFOA. Another 7% of the fluorotelomer alcohol
is metabolized to intermediate acids that are also expected
to eventually degrade to PFOA. So a conservative estimate
for the conversion from fluorotelomers to PFOA is 1%.
This means that a person eating a whole bag of popcorn
could take up 0.017 ppb of PFOA.
Given that the average PFOA content of human blood is
about 4 ppb, a person would have to eat about 300 bags
of microwave popcorn over 5-10 years (about a bag a week)
if all the PFOA in their blood came from the snack. Toxicologists
say that 5-10 years is an appropriate timescale for such
a calculation because PFOA is reported to have a long
half-life in humans, about 4 years. Although most people
probably do not eat a bag a week, Americans do wolf down
39 million pounds, or about 156 million bags every year,
according to the Snack Manufacturers Association. Consumption
of just 10 bags of microwave popcorn a year could contribute
about 20% of the average blood PFOA levels, say the scientists
interviewed anonymously for this article.
"This dose is certainly not insignificant",
Martin says. "Scientists should be, and are, considering
polyfluorinated precursors [such as the fluorotelomers]
as a potential human exposure pathway to perfluorinated
acids, including PFOA", he adds.
Microwave popcorn bags probably represent the worst-case
scenario for getting PFOA precursors into foods, Begley
notes. This is because the amount of fluorotelomers in
the coatings is high and because popcorn bags get very
hot-they heat up to more than 200 °C in just a minute
or two. These temperatures significantly increase the
potential for migration of the packaging components to
foods, he says.
Fluorotelomer coatings are not used in all microwave
snack-food packaging. For example, microwavable stuffed
sandwiches like Hot Pockets and microwave pizza do not
use paper coated with fluorotelomers, according to Begley,
who says that he's still conducting research on other
papers and coatings.
Reference
Source 125
November
24, 2005
