Is there a way to degrade plastic?

Is there a way to degrade plastic?

By Huawei Zhou

The problem:

Plastic products have become an essential part of our everyday lives. Recycling is a good way to reuse plastic products, but devising a way to get rid of plastic is of utmost importance. It may come as a shock to know that less than 10% of plastic waste in the US is recycled. So, here’s what happens to the massive amount of non recycled plastic waste.

The plastic problem in numbers:

  • An estimated 275 million metric tons of consumed plastics end up in landfill spots, damaging the environment.
  • Some end up in oceans, killing tens of thousands of marine life animals each year. As published in Science in 2015, 8 million metric tons of plastic enter the oceans as waste each year. By the end of 2025, the estimated cumulative plastic in the ocean will be around 160 million metric tons, which is 100 bags of plastic per foot of coastline over the world.
  • Americans use about 102 billion plastic bags every year.
  • About 31.9 million of metric tons of plastic waste is not disposed of properly.

Without ways to degrade plastic waste, both our land and ocean will be occupied by this hard-to-decompose material.

The solution:

Some research is heading in the direction of biodegradable plastic substitutes that may potentially replace plastics in some applications. However, this will not make all of the plastic waste already polluting the environment disappear. Hence, looking for a way to degrade plastic, i.e. getting rid of it permanently, is what many labs around the world have been studying.

Federica Bertocchini of the Institute of Biomedicine and Biotechnology of Cantabria in Spain recently found out that the larvae of greater wax moth (Galleria mellonella) can degrade polyethylene (PE) bags within 12 hours.

The study claims that:

  • Within 40 minutes, holes start to appear on PE films and ethylene glycol, a signature for biodegredation, was detected.
  • Each worm could create 2.2 holes per hour.
  • With 100 worms, a degradation rate was averaged to be 0.23 mg/cm2h.

Various testing methods including FTIR, HPLC-MS, and AFM were used to support the hypothesis that polyethylene can be chemically broken down to ethylene glycol by these worms, not just physically eaten. Ethylene glycol is an essential product for industrial production of antifreeze. If the exact chemistry of the breakdown process can be understood, replicated enzymes can be produced on an industrial scale to solve the long-standing plastic waste problem.

Despite the fact that the idea of a worm being able to chemically break down polyethylene is alluring, German researchers have casted doubt on the study. In the same journal, the researchers from the Johannes Gutenberg University in Mainz, Germany published an article in the same journal arguing that the methodology of Federica’s paper cannot provide full proof of ethylene glycol’s presence. Weber et al. insisted that the infrared (IR) absorption signal can be from residual protein contamination on the plastic films. The researchers announced that rubbing the plastic bags with a mixture of egg yolk and ground pork can result in the same signals under IR spectroscopy as published in the study of Federica. Weber believes that there is not enough proof for us to think that the magic solution for degradation of plastics has been found.

While it is definitely exciting that the solution for the endlessly accumulating plastic waste problem may be solved soon, it is important that researchers need to obtain sufficient scientific evidence before believing that they have discovered the solution. Federica et al. from Spain may very well have found the enzyme to degrade plastics, although they have not responded to Weber’s arguments. To further prove that plastics can be chemically broken down to useful materials like ethylene glycol, techniques such as carbon labeling may be used to mark whether the plastic has been chemically degraded.

Recommendations:

Many species on earth can potentially digest plastics, either animal or plants, and it may be some time before we can find the magic solution to the current problem. In the meantime, plastic consumption should be cut down with more biodegradable alternatives.

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