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Disclaimer—This paper partially fulfills a writing requirement for first year (freshman) engineering students at the University
of Pittsburgh Swanson School of Engineering. This paper is a student, not a professional, paper. This paper is based on publicly
available information and may not provide complete analyses of all relevant data. If this paper is used for any purpose other
than these authors’ partial fulfillment of a writing requirement for first year (freshman) engineering students at the University
of Pittsburgh Swanson School of Engineering, the user does so at his or her own risk.
PLASTIC: A FOE TO ECOLOGY, A FEAST TO NEWFOUND BACTERIA
Brian McMinn ([email protected])
FROM PISCES TO PLASTIC
Humanity is about to out-produce the forces of
nature by filling the seas with its own creation: plastic. It
is projected by [1] that, within the next 35 years, fish will
be out massed by plastic in the world’s oceans [1]. Even
today, the oceans are not too far behind that mark.
It is imperative that the oceans stay behind that
mark. Per [2], oceans overwhelmed by plastic pollutants
are dangerous to sea life and humans on land [2]. The
chemicals released and physical presence of these
resilient particles threaten the seas as hot spots of
biodiversity.
Many solutions for the disposal of plastics have
proven ineffective. Reducing plastic usage can cause
more damage to the environment, due to the efficiency
created by plastic [3]. Recycling is another misleading
option, since much of what is sent to recycling centers
lands in a landfill [4]. The slow decay rates of plastics
prohibit landfills from being a viable option and the
toxicity of their components bar the expansive use of
cheap incinerators [Columbia blog]. The ineffectiveness
of all these common disposal methods for plastic has
been prodding scientists and engineers to devise another,
more effective way to eliminate these useful, yet
destructive materials.
Those physical and industrial methods have been
ineffective, so academia has looked to nature for complex
chemical solutions to the disposal problem. One place
they have found a solution is in certain fungi. Fusarium
fungi can produce enzymes that can degrade plastics into
constituent molecules that are much safer for the
environment [5]. However, since they are parasitic to
plants, these fungi cannot be used in practice. Therefore,
there is a need for another, safer method.
Knowing that Fusarium can metabolize some
plastics, scientists and environmental engineers
suspected that other organisms could have the same
capabilities. As seen in the magazine Materials World,
Japanese scientists from the Kyoto Institute of
Technology have recently discovered bacteria that can
metabolize polyethylene terephthalate (PET), a versatile
petrochemical utilized in synthetic textiles, plastic water
bottles, and other commonly disposed plastics [4]. The
University of Pittsburgh, Swanson School of Engineering 1
Submission Date- 10.04.2016
researchers believe “these results will bring us closer to
achieving an ideal model for PET recycling” and, in
achieving this model, plastic use will be more sustainable
[3]. Natalie Daniels, writer for Materials World
magazine, also sees this technology as one that could
combat the problem of plastic on the shores [4]. This
biological innovation is a step in a novel direction for
waste management. There has yet to be an industrial,
biological plastic disposal venture of this scale, and it
seems that the biological plastic degradation could be
used in conjunction with older methods to improve
plastic disposal. The proposed hybrid landfills could
allow for safe, timely disposal of plastics [4]. A solution
superior to its precedents, bacteria that decay plastics
could alleviate the destruction caused by environmentally
introduced petrochemicals without constant upkeep and
without adding to the damage.
PLASTIC POLLUTION: AN
ECOLOGIST’S NIGHTMARE
With patches of plastic “garbage” the size of Texas
in the Pacific Ocean confirmed by the journal Plastics
Engineering, this bacterial solution could not have come
at a better time [1]. Since the development of cheap
plastics, their durability has made their disposal a
challenge. Now that we have the technology to see the
effects of our poor disposal across oceans, the scale of the
pollution is significant. In a trawling mission across the
Pacific, Hayden K. Webb et. al. of Swinburne University
of Technology found plastic debris in every ten-degree
latitudinal belt [2]. This shows that petrochemicals are a
universal ailment to the waters of the world.
The plastics are not just thinly spread, either. The
mass of microplastics -- plastic chunks smaller than five
millimeters long -- is six times greater than that of the
world’s zooplankton --a vital food source for thousands
of marine species [2]. Many of those marine species eat
small objects indiscriminately. As those unfussy eaters,
be they krill, filter feeders, or larger zooplankton, are
eaten, the plastic sticks around in the larger animal’s
digestive systems. This magnifies the problem. Small as
well as large marine life are affected, suffering from
starvation or malnutrition along with hormonal problems
Brian McMinn
caused by the degradation of plastics [2]. Though humans
are usually unaffected by the travel of these particles up
the food chain, the ecological repercussions of
microplastics affect edible fish and other desirable
wildlife.
Plastics and their chemical components can still be
a direct threat to humans in high doses. If ingested, says
[6, plastics can degrade into toxic substances or release
high concentrations of environmental toxins [6].
Substances from plastics can be found in seafood at
higher concentrations that affect fish eaters [n]. These
toxins can be deleterious to human health. So, as the
problem of plastic pollution continues to heighten, a
solution must be found to mitigate these dangers.
entire third of what ends up in the recycling bin ends up
in a landfill or in the ocean as harmful, toxic pollution.
CURRENT PLASTIC DISPOSAL
METHODS
WHAT BEST NURTURES NATURE
Landfill and Incinerators
The landfills where most plastic lands are not a
sustainable or entirely safe solution to petrochemical
disposal. Plastic occupying landfills will not decay
quickly like natural waste, but can remain for over a
thousand years [7]. Not only does this slow
decomposition take up space, it also slowly leeches
toxins into the soil that can be transferred into the
watershed and the ocean. Currently, the clear majority of
plastics have this noxious fate due to negligent disposal
and inefficient recycling procedures.
Fungi
Under the right circumstances, life finds ways to be
productive using harmful and toxic conditions and
chemicals. A plastic comprised of harmful compounds,
PET, has been degraded by different types of fungi in the
past. Fusarium oxysporum and F. solani, two filamentous
fungal species, says[5], have been grown on media
enriched with minerals and PET yarn. The fungi use
enzymes to break down the plastics into safe monomers
and carbon dioxide to be used for their own growth.
Once an organism with the proper enzymes to
digest the hardy PET is found, there are simple methods
of byproduct repurpose and disposal. Depending on the
efficacy of the enzymes, the leftover PET could be
collected and recycled like it is now. The degraded
humus digested by the fungus or other organism could
also be repurposed in ornamental gardens or other
organic purposes [5]. Solutions like Fusarium fungi are
not poisonous, so they could be used near people.
Both types of fungi, though not toxic to humans, can
be harmful to plants, being of the same genus as blight
and Fusarium wilt, making them unideal candidates for
PET degradation [8]. The PET yarn medium must also be
prepared for the Fusarium species to effectively reduce
the plastic. Also, Fusarium oxysporum can penetrate
soils and attack plants, so the generated humus from the
PET would be pathogenic and unusable until sterilized
[8]. These fungi create more problems than solutions.
Reducing Plastic Usage
While plastic waste is an issue, the use of plastic can
actually benefit the environment. By using plastics, says
[5], costs of transporting bulkier materials are drastically
diminished [5]. This reduction saves further use of other
petrochemicals as fuel, thus diminishing overall
pollution.
Aside from lower shipping costs, perishable goods
can be stored longer due to the protection of plastics.
Longer storage means less waste. A study by Turner et.
al. in 2015 showed plastic packaging decreased wasted
cucumbers, meats, and garden cress by 3.8%, 16%, and
39.6%, respectively [5]. Reductions in food waste save
pollution caused by transportation and preparation and
are usually more effective than eliminating plastic
packaging. The same study calculated that the average
supermarket’s carbon footprint is only made of five
percent packaging materials and for the average
consumer it is one percent [5]. Packaging is dwarfed by
the huge amounts of food waste and fuel burned for both
supermarkets and personal consumption. Therefore, the
solution is not to eliminate plastic, but to eliminate waste.
Recycling
The common conception is that recycling is the
solution to eliminating plastic waste. However, recycling
is only minimally effective. According to [4], only five
percent of plastics are recycled, meaning most of the
plastic items you toss in either municipality bin are not
going to get a second life as a new water bottle[4]. Single
stream recycling -- the most common method that places
all recyclables in the same bin -- is only 68% efficient for
plastics, according to [7] [7]. From that figure, almost an
Bacteria
Using benign bacteria instead of fungi could solve
those problems. A team from the Kyoto Institute of
Technology including Shosuke Yoshida, Kazumi Hiraga,
and Toshihiko Takehana found many microbes
responsible for degrading large amounts PET. The most
efficient was bacteria called Ideonella sakeiensis; it was
responsible for breaking down three times more material
than all the other microbes combined [4].
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Brian McMinn
The process it takes to break down PET uses two
enzymes: PETase and MHETase. These two proteins
catalyze a reaction that converts PET into the
environmentally harmless chemicals terephthalic acid
and ethylene glycol. Both safe chemicals can be further
reduced into carbon dioxide and water by more common
enzymes [4].
Thin sheets of PET can be completely degraded in
a manner of weeks by this process, accelerating the
process of PET degradation by thousands of years[4].
Using layers of PET, I. sakeiensis can eliminate large
quantities of the plastic. This biotechnology can augment
currently used methods of PET disposal and increase
their efficiency.
Bacteria are indiscriminate; they will degrade PET
regardless of contamination. In this way, I. sakeiensis is
superior to recycling, which can only reuse plastics that
are sufficiently clean and sorted. Since bacteria can be
grown easily, this technology is perfectly scalable,
reducing the need to decrease plastic usage. The bacteria
could also be added to landfills to accelerate the decay of
disposed plastics. Also, I. sakeiensis is not malicious to
plants; its byproducts can, therefore, be used
horticulturally. The discovery of I. sakeiensis has
potential to work alongside of or improve nearly all
previous methods of plastic remediation.
look for bacteria that decompose other plastics or bacteria
that break down PET more effectively. Collectively,
plastics will become less of an environmental problem,
due to these advancements. Now that the idea of
bacterially enhanced plastic degradation exists, there can
be more discoveries in that field.
As a future engineer, this new field has exciting
prospects. Within four years, this technology should be
budding and in the final stages of development. This
means that engineers like myself will be among the first
to utilize and understand the nuances of biological plastic
remediation. This also means that solutions to
petrochemical pollutions are on the forefront of science.
As someone who is likely to live well into this century, it
is comforting to know that there are options for
environmental repair beyond physical trash collection
and supply side remedies like reduced plastic use,
recycling and landfills. These bacteria can lead to a
cleaner environment for the foreseeable future.
BACTERIA FOR A CLEANER PLANET
Ideonella sakeiensis are bacteria that have the
potential to revolutionize plastic disposal. Since it
degrades plastic in a low waste, natural process that
utilizes enzymes over industry, biological remediation
for plastic PET, with 3.1 million tons produced annually
in North America alone, is a plastic that is in desperate
need of environmental remediation [11]. When plastics
are introduced to thriving ecosystems, they falter,
decreasing the effectiveness of human economic and
social activities. With biological plastic remediation,
landfills will become less toxic and more efficient;
oceans will become less contaminated and more robust.
Engineers can achieve an ideal method of PET recycling
with these bacteria, and the theories put toward that ideal
can advance other plastic recycling methods. That
positive feedback loop is one step toward cleaning up the
planet for ourselves and for future generations.
THE FUTURE OF BACTERIAL PLASTIC
DEGRADATION
The major topic of research now is not how I.
sakeiensis can improve the efficacy other fields but how
other fields can improve the efficacy of I. sakeiensis.
Currently, scientists and environmental engineers are
looking to accelerate the PET reduction further while
scaling up the biotechnology. [4] says genetic
engineering could be used to increase the production of
PETase and MHETase, making each bacterium more
efficient at decomposing the plastic [4]. These more
efficient bacteria would be introduced to landfills to
further speed up the ages-long process of plastic
decomposition.
Gene splicing involving CRISPR-Cas9 -- a
biotechnology that can alter the genome of a living
organism -- could also be used to place the PETase and
MHETase production traits into sea-dwelling bacteria
[10]. If many bacteria in the ocean carry these enzymes,
the South Pacific Garbage Patch could be reduced over
time without a major clean-up operation. Waterborne
plastic-degrading bacteria could also contribute to the
reduction of microplastics suspended in the ocean,
stemming tide of PET in the ocean.
Engineers can use the principals learned from this
biotechnology to explore the capabilities of other
microbes and plastic reduction systems. Researchers will
SOURCES
[1] N. Daniels. "Plant-based biodegradable water bottle
fights plastic waste." Materials World Magazine. Date of
publication
05.01.2016.
Accessed
10.29.2016
http://www.iom3.org/materials-worldmagazine/news/2016/may/01/plantbased-biodegradablewater-bottle-fights-plastic-waste.
[2] H. K. Webb, J. Arnott, E. Ivanova. "Plastic
Degradation and Its Environmental Implications with
Special Reference to Poly(ethylene terephthalate)".
Swinburne University of Technology. Date of
publication
01.06.2016.
Accessed
10.28.2016.
http://www.mdpi.com/2073-4360/5/1/1/htm.
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Brian McMinn
[3] S. Frost. "Packaging innovations, more packaging
means less waste." Materials World Magazine. Date of
publication 04.01.2016. Accessed 10.29.2016.
[4] C. Morawski. "Single-stream Uncovered." Resource
Recycling Magazine. Date of publication 02.2012.
Accessed
10.28.2016.
http://www.containerrecycling.org/assets/pdfs/media/2010-2SingleStreamUncovered.pdf.
[5] R. Cho. "What Happens to All That Plastic?".
Columbia University Earth Institute. Date of publication
01.21.2012. Accessed 10.28.2016.
[6] S. Yoshida, K. Hiraga, T. Takehana et. al. "A
bacterium that degrades and assimilates poly(ethylene
terephthalate)." Science Magazine. Date of publication.
03.11.2016. Accessed 10.28.2016. Vol. 351 Issue 6278,
p. 1196-1199
[7] M. Eriksen, A. Cummins, N. Maximenko et. al.
"Plastic pollution in the South Pacific Gyre." Plastics
Engineering. Date of publication 05.2013. Accessed
10.28.2016.
[8] C. M. Rochman, E. Hoh, B.T. Hentschel, S. Kaye.
"Long-Term Field Measurement of Sorption of Organic
Contaminants." The American Chemical Society. Date of
publication 12.27.2012. Accessed 10.28.2016.
[9] D. Campbell. "Fusarium oxysporum." Biodiversity
Heritage Library. Date of publication 03.2013. Accessed
10.28.2016.
http://eol.org/pages/187980/hierarchy_entries/57331216
/overview.
[10] A. Reis. "CRISPR/Cas9 and Targeted Genome
Editing: A New Era in Molecular Biology." New
England Biolabs Expressions. Date of publication
01.2014. Accessed 10.28.2016.
[11] "PET By the Numbers." Petra PET Resin
Association. Date of publication 03.2015. Accessed
10.28.2016.
ACKNOWLEDGMENTS
I would like to thank Karlee Williston at the writing
center for all her help and editions on this paper. She
provided excellent stylistic guidance. Also Louis Fillman
was an inspiration to my paper. I would also like to thank
caffeine. Without caffeine, I would have passed out well
before I finished this essay.
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