July 2008
The Southwest Portland Post • 9
FEatuRES
EarthTalk TM
From the Editors of E/The Environmental Magazine
Dear EarthTalk: What are the
environmental pros and cons of
corn-based plastic as an alternative
to conventional petroleum-based
plastic?
-- Laura McInnes,
Glasgow, Scotland
Polylactic acid (PLA), a plastic
substitute made from fermented
plant starch (usually corn) is quickly
becoming a popular alternative to
traditional petroleum-based plas-
tics. As more and more countries
and states follow the lead of China,
Ireland, South Africa, Uganda and
San Francisco in banning plastic
grocery bags responsible for so
much so-called “white pollution”
around the world, PLA is poised
to play a big role as a viable, biode-
gradable replacement.
Proponents also tout the use of
PLA—which is technically “carbon
neutral” in that it comes from re-
newable, carbon-absorbing plants—
as yet another way to reduce our
emissions of greenhouse gases in a
quickly warming world. PLA also
will not emit toxic fumes when
incinerated.
But critics say that PLA is far
from a panacea for dealing with the
world’s plastic waste problem. For
one, although it does biodegrade, it
does so very slowly. According to
Elizabeth Royte, writing in Smith-
sonian, PLA may well break down
into its constituent parts (carbon
dioxide and water) within three
months in a “controlled composting
environment,” that is, an industrial
composting facility heated to 140
degrees Fahrenheit and fed a steady
A cup made from PLA, plastic made from cornstarch. (Bec, courtesy of Flickr)
diet of digestive microbes.
But it will take far longer in a com-
post bin or in a landfill packed so
tightly that no light and little oxygen
are available to assist in the process.
Indeed, analysts estimate that a PLA
bottle could take anywhere from
100 to 1,000 years to decompose in
a landfill.
Another issue with PLA is that,
because it is of different origin
than regular plastic, it must be
kept separate when recycled, lest it
contaminate the recycling stream.
Being plant-based, PLA needs to
head to a composing facility, not a
recycling facility, per se, when it has
out served its usefulness. And that
points to another problem: There are
presently only 113 industrial-grade
composting facilities across the U.S.
Another downside of PLA is that
it is typically made from genetically
modified corn, at least in the U.S.
The largest producer of PLA in the
world is NatureWorks, a subsidiary
of Cargill, which is the world’s larg-
est provider of genetically modified
corn seed.
With increasing demand for corn
to make ethanol fuel let alone PLA,
it’s no wonder that Cargill and oth-
ers have been tampering with genes
to produce higher yields. But the
future costs to the environment and
human health of genetic modifica-
tion are still largely unknown and
could be very high.
While PLA has promise as an
alternative to conventional plastic
once the means of disposal are
worked out, grocery shoppers
could do well to by simply switch
to reusable containers, from cloth
bags, baskets and backpacks for
grocery shopping (most chains
now sell canvas bags for less than a
dollar apiece) to safe, reusable (non-
plastic) bottles for beverages.
As for other types of PLA items—
such as those plastic “clamshells”
that hold cut fruit (and there is
a whole host of industrial and
medical products now made from
PLA)—there is no reason to pass
them by. But until the kinks are
worked out on the disposal and
reprocessing end, PLA may not be
much better than the plain old plas-
tic it’s designed to make obsolete.
CONTACTS: Smithsonian’s “Corn
Plastic to the Rescue,”www.smith-
sonianmag.com/science-nature/
plastic.html; NatureWorks, www.
natureworksllc.com.
Dear EarthTalk: How is it that
hydrogen can replace oil to run our
cars? There seems to be a lot of con-
troversy over whether hydrogen
can really be generated and stored
in such a way to be practical?
-- Stephane Kuziora,
Thunder Bay, ON
The jury is still out on whether
hydrogen will ultimately be our
environmental savior, replacing
the fossil fuels responsible for
global warming and various nag-
ging forms of pollution. Two main
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