Degrading plastics emit greenhouse gases: Study

Several greenhouse gases are emitted as common plastics degrade in the environment, according to a study.

Greenhouse gases directly influence climate change - affecting sea level, global temperatures, ecosystem health on land and in the ocean, and storms, which increase flooding and drought, said researchers at the University of Hawaii at Manoa.

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 the journal PLOS ONE, found that most common plastics, when exposed to sunlight, produce greenhouse gases methane and ethylene.

The 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 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 Sarah-Jeanne Royer, a post-doctoral scholar at the University of Hawaii at Manoa.

"With time, these defects increase the surface area available for further photochemical degradation and therefore contribute to an acceleration of the rate of gas production," Royer said.

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.

"This source is not yet budgeted for when assessing global methane and ethylene cycles, and may be significant," Karl said.