by Mohammed Haseeb Nawaz : A marvel technology was introduced for its versatility during World War II and was a major boon to the Allied Forces in the form of plexiglass and lightweight nylon parachutes. This technology soon became a major part of our day to day lives post-1950. Yes, we are talking about PLASTICS (1).
Made of synthetic organic polymers plastics sure have transformed our lives in numerous ways. These have been a better and cheaper alternative to metal in many contexts. From our homes to space, from keeping our food fresh to jumbo jets, plastics are a part of almost everything we use in our day to day lives from car parts to medical devices (1).
The production of plastic has increased at such a rapid pace that nearly half of the plastic that exists now has been generated in the past 15 years. Just to crunch some numbers: since the past 6 decades we’ve been producing plastic at the rate of over 448 million tonnes per year and India alone generates over 25,000 tonnes of plastic waste every day according to CPCB (Central Pollution Control Board). Recently our beloved soft drink company Coca-Cola revealed that it single handedly produces over 128 billion plastic bottles every year ( just one more reason to stop drinking Coke) (1) (2).
So what is the Plastic Problem?
The very nature of plasticity and durability that makes it so good also poses an enormous challenge in disposing of it. Plastic is a synthetic polymer consisting of very long chains of monomers that are made up of links of carbon to carbon bonds often combined with hydrogen and sometimes with nitrogen, fluorine, or chlorine making them strong and durable. This makes plastic highly stable in the environment and up to 500 years. Plastic litters our cities and oceans and affects human and animal health in harmful ways (3) (4).
Most plastic is derived from petroleum, the end product of millions of years of decomposition of once-living organisms. One might therefore argue that plastics should be biodegradable. However, nature doesn’t work that way. The synthetic nature of plastic composition makes the job very difficult for organisms to degrade plastics. For instance, an apple rots over time. Microbes break down the polysaccharides composing the apple and utilize the sugar through their metabolic pathways. When a microorganism encounters plastic with its synthetic carbon bonds, it doesn’t have the proper metabolic pathways to break it down (5).
“Organisms have evolved for over a billion years to attack certain types of bonds that are common in nature,” said Kenneth Peters, an organic geochemist at Stanford University (5). So maybe they need another billion years to evolve in such a way they can break down plastics?.
One such advancement in this regard has been the discovery of a novel bacteria Ideonella sakaiensis 201-F6 which uses Polyethylene terephthalate (PET) as a major energy source and produces two enzymes capable of hydrolyzing PET. These enzymes convert PET efficiently into its two environmentally benign monomers, terephthalic acid, and ethylene glycol (6). Research is currently being carried out to modify these enzymes for a large scale purposes.
The current methods used worldwide to tackle the plastic problem have been based on the three R’s: Reduce, Reuse, Recycle plastics (1).
The strategy involved in this regard has been similar in different countries. One such recycling journey of plastic bottles in the UK is shown below:
However, the extent of recycling depends on the chemical nature of each type of plastic and can be seen below:
The prevailing methods to tackle the situation have been to implement government policies to ban single-use plastics and promote the use of biodegradable plastics made up of renewable natural materials. Poly lactic acid (PLA) is one such biodegradable plastic derived from corn that is being used in medical applications as films. Other materials like Polyhydroxyalkanoate (PHA) derived from bacterial cells and those obtained from cellulose, lignin, and soy have also been developed. But their inefficiency to compete with the property of synthetic plastics has been a major set back (7).
We are currently facing a crisis and recycling only 1/5 of plastics we produce (1). All of this plastic waste is being broken down into micro plastics and surrounding the environment. In time, if we are unable to control this rate of production, we will have to deal with nanoplastics. So the world is in dire need of a fourth R to REFUSE plastics as much as possible.
- National Geographic. https://www.nationalgeographic.com/magazine/2018/06/plastic-planet-waste-pollution-trash-crisis/.