Mission planet clean-up

New discoveries offer hope but it's a long road from lab to industrial processes

We produce over 300 million tons of assorted plastics every year. Most of this consists of stuff that is thrown away after use. Unfortunately, plastic garbage isn’t easily decomposed. A water bottle made of PET (polyethylene terephthalate) takes 450 years or longer, to decompose naturally. About a million such bottles are sold, every minute. 

This immunity to biodegradation is precisely why plastics are considered miracle materials and used for many purposes. Plastic of different types is ideal for packing food, medicines and anything else that has to be protected from the environment.  

But that immunity is also why there is a region of the Pacific Ocean, the so-called  Great Pacific Garbage Patch, which is thrice the size of France and entirely covered with floating plastic. Floating plastic trash is estimated to kill over 100,000 seals, turtles, dolphins and whales annually. Closer to home, we know the harm plastic does to cows and buffaloes.  Micro-particles contaminate water supply and food as well. 

So, what can one do about plastic disposal? Ideally it would not escape into the environment. Indeed, there are many parts of the world where plastic packaging have been banned. But it is produced in such large quantities and used in so many applications, this doesn’t seem a practical solution. 

The latest plan to clean up the Great Pacific Garbage Patch (GPGP) consists of creating a system of floating plastic nets, each covering around 9,200 square km. These nets will trap the floating garbage for collection by ships that can take it to land for disposal. The inventor of this system, 23-year-old Dutchman, Boyan Slat, has launched a company, Ocean Cleanup. The cleanup is scheduled to launch in July. Slat hopes that the GPGP can be cleared by 2050. 

But even if the world’s oceans can be cleared of plastic, that still leaves the problem of exactly how to dispose of the collected plastic. One approach involves recycling — that is, reusing already manufactured plastic again, rather than producing new plastic. This is expensive and energy-intensive and it effectively depends on responsible behaviour from consumers. 

Other more biological approaches involve exotic experiments such as breeding waxworms, caterpillars which eat beeswax and seem to be able to digest plastics. The intrinsically elegant solution would be to find and cultivate strains of fungi and bacteria that can eat plastic — in other words, make it biodegradable. This has been mooted for decades. But it's hard to do this in practice. 

Plastics consist of polymers. That is, long thin molecules are made by linking the same single molecule ( a “monomer”) again and again to itself. The basic building material is carbon. The feedstock for making plastics is derived from crude oil, or natural gas.

Most bacteria eat natural carbon-based materials. But plastics are artificial.  The first plastics were created only about a century ago and usage became common only after World War II. Bacterial evolution hasn’t had much time to catch up. 

PET is among the most difficult types of plastic to decompose. However, there may be a potential breakthrough. In 2016, Japanese scientists in Kyoto discovered that a bacteria, Ideonella sakaiensis. could eat PET. Importantly, they isolated the enzyme that this bacteria uses for breaking down PET into two environmentally benign chemicals, terephthalic acid and ethylene glycol.  They named the enzyme PETase and also managed to isolate the genes necessary for producing this enzyme. 

Now, another group of researchers significantly improved the enzyme’s effectiveness, more or less by accident. A group consisting of researchers from the University of Portsmouth (UK) and the US Department of Energy’s National Renewable Energy Laboratory examined the enzyme by hitting with massive bursts of x-rays.

They also tinkered with the PETase structure. The resulting mutant PETase turned out to about 20 per cent more efficient at eating PET. They have filed patents on the new mutant enzyme, which can degrade PET in a few days. Assuming that this mutant PETase can be produced in industrial quantities, it could be used to used to breakdown used PET items into basic chemicals. 

It is often a long road from lab results to generic industrial processes. However, this discovery offers hope that plastic pollution can now be tackled in new ways that can help clean up our planet.