Polyethylene or Polyethene is the most common plastic that we see around us 24/7. It has multiple uses (like plastic bags, plastic films, membranes, and containers of different configuration etc.) all of which end up as waste that is not biodegradable and thus a concern for environment and aesthetics.
Annual global production and use of polyethylene is estimated over 80 million tons. Getting rid of this volume of waste in an environment-friendly manner has been an issue of global concern since long. In Japan e.g. it was listed as a $90 billion stake for the researchers to find environmentally acceptable solutions.
Recycling used plastic is one option, the other options being land fill and incineration; landfill being the predominant of all as can be seen in the figure below. However, none of these options meet the satisfaction levels of different stake holders, especially the environmentalists. A 4th and seemingly more acceptable option is to biological dissipate plastics i.e. complete oxidation to carbon dioxide by using live microbes and enzymes therefrom. However, highly aromatic constituents of polyethylene and its variants make it fairly resistant to chemical and biological oxidation.
It is only recently, that a bacterium has been identified that seems to dissipate polyethylene completely. A team (10 members including the lead scientist) of Japanese scientists led by Shosuke Yoshida at the Department of Applied Biology, Kyoto Institute of Technology, Kyoto discovered that among a consortium of organisms feeding on polyethylene, a strain of Ideonella Sakaiensis could almost completely degrade a thin film within 6 weeks at 30 degrees Celcius; 75% of the film surface was oxidized to carbon dioxide at 28°C; an achievement with no previous parallel. The results were published in March 2016 in the scientific magazine “Science” volume 351, pages 1196-1999.
Interestingly, the discovery has been made in Kyoto, a town in Japan that is well known after Kyoto protocol that was signed on December 11, 1997 and implemented on February 16, 2005. The protocol is an international treaty that extends UN Framework Convention on Climate Change (UNFCCC) requiring signatory states to reduce greenhouse gases (GHGs) emissions as a means to mitigate global climate change and warming; carbon dioxide being the main GHG in focus.
The discovery of polyethylene degrading bacterium is undoubtedly a breakthrough being sought since long. While working on and announcing the discovery of a potent bacterium (Ideonella Sakaiensis) for oxidation of polyethylene, the scientists might not have considered fully the implications of their find vis-à-vis Kyoto Protocol. As mentioned at the start, global production of polyethylene is estimated over 80 million tons. Supposing their newly identified bacterium decomposes the whole of it (which has to be the ultimate aim), 230 million tons of carbon dioxide and over 100 million tons of water vapour (again a GHG) will be generated as shown in the figure below.