The detrimental effects of plastic on the environment are widely recognised, but a new study published on August 1 in PLoS ONE, a peer-reviewed scientific journal, now shows plastics may also be contributing to climate change. Preliminary results of the study show that plastics are actually emitting greenhouse gases when exposed to sunlight. Then, once they have been exposed to solar radiation, plastics continue to emit these gases in the dark. The biggest offender was polyethylene, which is used to make plastic bags and is the most produced and discarded synthetic plastic worldwide.
Gases used during the manufacturing process leach out over time and plastics are known to release toxic chemicals during the degradation process, including bisphenol A, facilitated by light, heat, moisture, chemicals, and other environmental elements. To better understand this, lead author of the study, Dr Sarah-Jeanne Royer a postdoctoral researcher at the Center for Microbial Oceanography: Research and Education (C-MORE) in Hawaii, and her colleagues performed experiments on various plastics to assess the type and extent of gas emissions owing to different environmental conditions. They demonstrated that several types of plastic, regularly produced and dispersed across the planet, produce methane and ethylene ― two of the most potent greenhouse gases ― under a variety of environmental conditions.
The study attributed the increased emissions of hydrocarbon gases over time from plastic to photodegradation. One of the biggest factors associated with the rate of degradation was found to be the structure of the polymer and the exposed surface area available for photochemical degradation, which is dictated by shape and size of the plastic object, as well as fractures, micro-cracks, and pits on the surface. In fact, smaller particles called ‘microplastics’ ― tiny pieces of broken down plastic ― eventually form after prolonged environmental exposure and were shown to greatly accelerate gas production.
In other words, as plastic particles degrade in the environment, they become smaller and it is predicted that they will, therefore, produce more hydrocarbon gases per unit mass. Moreover, the driving force behind hydrocarbon gas production via photochemical degradation is the sun, or more specifically, UV rays (2). One final unexpected result of the study was that plastics exposed to land conditions produced even more greenhouse gases than those degrading under ocean conditions.
Plastics started being produced in mass quantities around 70 years ago and it is estimated that more than 8 billion megatonnes of plastic have been manufactured since then. Moreover, plastic production is expected to increase two-fold over the next two decades. While plastics are used in nearly all industries and households since they cheap, durable, and easy to make, this study now points to plastic as a new and previously unrecognized source of two potent greenhouse gases.
Sadly, unless an enormous effort is made within the global community, the majority of plastics will never be recycled (3) and will decay in landfills, forests, and the oceans where they will increasingly continue to produce detrimental greenhouse gases, along with other toxic chemicals that pollute both land and marine environments.
(1) Royer S. et al. Production of methane and ethylene from plastic in the environment. PLoS ONE (2018). DOI: 10.1371/journal.pone.0200574
(2) Andrady A.L. et al. Microplastics in the marine environment. Marine Pollution Bulletin (2011). DOI: 10.1016/j.marpolbul.2011.05.030
(3) Geyer R., Jambeck J.R. and Law K.L. Production, use, and fate of all plastics ever made. Science Advances (2017). DOI: 10.1126/sciadv.1700782
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