Degrading
plastics revealed as source of greenhouse gases
University of Hawaii
at Manoa
Researchers from the
University of Hawai'i at M'noa School of Ocean and Earth Science and Technology
(SOEST) discovered that several greenhouse gases are emitted as common plastics
degrade in the environment.
Mass production of
plastics started nearly 70 years ago and the production rate is expected to
double over the next two decades.
While serving many applications because of their durability, stability and low cost, plastics have deleterious effects on the environment.
Plastic is known to release a variety of chemicals during degradation, which has a negative impact on organisms and ecosystems.
While serving many applications because of their durability, stability and low cost, plastics have deleterious effects on the environment.
Plastic is known to release a variety of chemicals during degradation, which has a negative impact on organisms and ecosystems.
The study, published in PLOS ONE, reports the unexpected discovery of the
universal production of greenhouse gases methane and ethylene by the most
common plastics when exposed to sunlight.
The science team tested polycarbonate, acrylic, polypropylene, polyethylene terephthalate, polystyrene, high-density polyethylene and low-density polyethylene (LDPE) -- materials used to make food storage, textiles, construction materials, and various plastic goods.
Polyethylene, used in shopping bags, is the most produced and discarded synthetic polymer globally and was found to be the most prolific emitter of both gases.
The science team tested polycarbonate, acrylic, polypropylene, polyethylene terephthalate, polystyrene, high-density polyethylene and low-density polyethylene (LDPE) -- materials used to make food storage, textiles, construction materials, and various plastic goods.
Polyethylene, used in shopping bags, is the most produced and discarded synthetic polymer globally and was found to be the most prolific emitter of both gases.
Additionally, the team
found that the emission rate of the gases from virgin pellets of LDPE increased
during a 212-day experiment and that LDPE debris found in the ocean also
emitted greenhouse gases when exposed to sunlight. Once initiated by solar
radiation, the emission of these gases continued in the dark.
"We attribute the
increased emission of greenhouse gases with time from the virgin pellets to
photo-degradation of the plastic, as well as the formation of a surface layer
marked with fractures, micro-cracks and pits," said lead author
Sarah-Jeanne Royer, a post-doctoral scholar in the Center for Microbial
Oceanography: Research and Education (C-MORE) at the time of this
investigation.
"With time, these defects increase the surface area available for further photo-chemical degradation and therefore contribute to an acceleration of the rate of gas production."
"With time, these defects increase the surface area available for further photo-chemical degradation and therefore contribute to an acceleration of the rate of gas production."
It is also known that
smaller particles, termed 'microplastics,' are eventually produced in the
environment and may further accelerate gas production.
"Plastic
represents a source of climate-relevant trace gases that is expected to
increase as more plastic is produced and accumulated in the environment,"
said David Karl, senior author on the study and SOEST professor with C-MORE.
"This source is not yet budgeted for when assessing global methane and
ethylene cycles, and may be significant."
Greenhouse gases
directly influence climate change -- affecting sea level, global temperatures,
ecosystem health on land and in the ocean, and storms, which increase flooding,
drought, and erosion.
"Considering the
amounts of plastic washing ashore on our coastlines and the amount of plastic
exposed to ambient conditions, our finding provides further evidence that we
need to stop plastic production at the source, especially single use
plastic," said Royer.
Now, Royer is working
to develop estimates of the amount of plastic exposed to the environment in
oceanic and terrestrial regions, globally, in order to constrain the overall
greenhouse gas emissions from plastics.