Bugs can help in plastic fight

City talk | Dr Melody Leung 5 Sep 2018

At a time when plastic pollution is reaching catastrophic levels, scientists have made some discoveries which indicate that digestive enzymes produced by some plastic-eating bugs may provide a solution to complete recycling of plastic.

For instance, in 2015 a scientist from the University of Cantabria in Spain discovered that the larvae of the greater wax moth that consumes bee wax has a certain intestinal digestive bacteria which produces an enzyme that is capable of degrading plastic bags.

Another research team at Beihang University in China used mealworms for experiments.

They found that the larvae survived in good health for a month by consuming nothing but plastic foam.

The team was able to isolate the bacteria Exiguobacterium sp strain YT2 from the mealworms' intestinal tract.

Similar to the greater wax moth larvae's intestinal digestive bacteria, it was this bacterium that digested plastic foam.

While this would seem like the perfect solution to the global issue of plastic pollution, the scientists found that 100 larvae would need a whole month to completely eliminate a plastic shopping bag we get at a supermarket.

In Hong Kong, an average of 1.7 plastic bags are discarded per person per day.

By using a family of four as the basis for calculation, the quantity of plastic bags discarded in one day could only be completely eliminated if 700 larvae were used to consume the bags 24/7 for more than a month.

Separately, Science Magazine reported in 2016 that scientists at Japan's Kyoto Institute of Technology had identified bacteria that could degrade plastic bottles.

And then a group of scientists from the University of Portsmouth in the UK created a mutant enzyme with improved capacity by accident earlier this year. It could break down plastic bottles at a much faster rate.

Compared with breeding insects, it is easier and more economical to cultivate bacteria so scientists hope to extract the bacteria's digestive enzymes to treat plastic waste.

However, if insects were to be removed from this equation, plastic production and elimination is purely a resource-draining process.

Gut bacteria degrade plastic to release nutrients for the insects' use, and then the insects become food for other organisms and this forms nature's enormous cycle.

Breaking the cycle may not be beneficial to humankind in the long run.

Some mushrooms are also good alternatives for decomposing plastic, such as old car tires.

Efforts are being made to grow edible mushrooms from plastic waste.

Although it will still take a while before such products become commercially available, the idea of converting waste into food is certainly an interesting research direction.

HKUST experts have their fingers on the pulse of a new age of science, technology and innovation

Dr Melody Leung, Lecturer, Division of Life Science, HKUST

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