Plastics Status
Polymers derived from fossil fuels are widely used in people's daily lives. They mainly include polyethylene (PE)， polypropylene (PP)， polyvinyl chloride (PVC), polyurethane (PUR)， polyamide (PA), polyethylene terephthalate (PET)， and other types.
Plastics Europe reports that global production of plastics has increased from 1.5 million tonnes per year in 1950 to an estimated 275 million tonnes in 2010 and 359 million tonnes in 2018. Countries with coastal regions dump between 4.8 and 12.7 million tonnes of waste annually into the ocean.
Millions of tonnes of waste accumulate in the world's oceans every year. In 2014, researchers published the first oceanographic study to investigate the amount of plastic waste near the surface of the world's oceans. Up to 5.25 tillion, floating plastic particles weighing around 244,000 tonnes were observed on or near the ocean surface.
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As synthetic plastics are primarily non-biodegradable, they persist in the natural environment, often taking decades or centuries to break down. Many single-use plastic products and packaging materials are typically sent directly to landfill or incinerated, resulting in environmental pollution and waste of resources.
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The dangers of plastic pollution
Plastic pollution can kill marine mammals when entangled in objects such as fishing gear. Alternatively, they can ingest plastics by using them as food. Plastics are not nutritious and are indigestible. They can also increase the concentration of pollutants in the surrounding seawater by up to a million times. As a result, species that ingest plastics may, in turn, ingest these concentrated pollutants. Another study reported that ingesting plastic pellets selected from Tokyo Bay by seabirds led to a significant increase in polychlorinated biphenyI (PCB) levels in their prefrontal gland oil. PCBs are a lubricant and insulating material that is now widely banned.
Image source: Encyclopaedia Britannica, Inc./Christine McCabe
Plastic pollution on land can cause intestinal blockage and death in animals, including he Californian condor, which was found to have plastic in its stomach. In addition, plastic pollution can affect human health, as it is reported to contain plastic additives that are detectable in all humans and disrupt the endocrine system. Phthalates mimic androgens and are therefore called anti-androgens; bisphenol A mimics the natural female hormone estrogen; and polybrominated diphenyl ethers block thyroid hormones with anti- androgenic consequences. Chemicals that disrupt hormones impact women 0 childbearing age and children, who are usually more vulnerable.
There is a growing public awareness of the severe consequences of plastic pollution. As a result, governments and the public are adopting novel measures to combat the problem, such as the use of biodegradable plastics and the emphasis on the 'zero waste' philosophy. As a result, the biodegradation of plastic waste through synthetic biology is an area of active research. It would reduce plastic pollution and support the sustainable use of plastic waste materials.
PET: the most used plastic
Polyethylene terephthalate (PET) is one of the most widely used artificial polymers. I comprises terephthalic acid (TPA) ester bonded to ethylene glycol (EG). PET is a well- known material for producing water bottles and fabrics due to its transparency, flexibility, and resistance to natural degradation processes. Annual production of PET is estimated at over 50 million tonnes. Vast amounts of PET are in landfills and pollute the oceans, creating a significant environmental burden.
Current treatment
In recent years, there has been an increasing public and scientific focus on the disposal of PET waste. Due to their ease of operation, the traditional methods of disposing of PET waste are incineration and landfill. However, incineration produces harmful gases, and landfills contaminate the soil and take a long time to decompose.
Currently, the industry uses several methods to recycle PET scrap. The primary recycling method is extrusion, where the scrap material is reclaimed and converted into the original products. However, recycling poses a significant challenge due to the variety of materials contained in PET scraps, such as polymers, paper, pigments, metals, and adhesives used in plastic packaging materials. Another recycling approach is mechanical recycling, in which PET waste is processed into pellets by separating the polymer from the contaminants. Despite its advantages, mechanical recycling is complicated by the demanding nature of PET waste and contamination, as the temperature generated during metting triggers photo-oxidation and vice versa, leading to mechanical stress. As a result, manufacturers do not use this method to produce high-quality products.
Chemical recycling is the third recycling technique. Chemical recycling recovers the petrochemical compounds in PET waste, which can be used to make PET products or other synthetic chemicals. One of the advantages of chemical recycling is that it reverses he energy-intensive pooling that occurs during the initial PET production process. PET waste can be converted by hydrolysis, methanolysis, and glycolytic depolymerization into PET resin or other unsaturated polyesters, which provide feedstocks for a wide range of products. Quality specifications for food packaging limit the use of recycled PET. Biological processes are greener and gentler than traditional and industrial techniques. They can reduce the generation of PET waste by recovering petroleum-based feedstocks, terephthalic acid (TPA), and ethylene glycol (EG).
Synthetic biology offers the opportunity to develop and incorporate complex biological designs into novel systems. Multiplexed signal processing enables the efficient degradation of plastics with dynamic degradation in varying environmental conditions while converting them into high-value-added commodities, providing a solution to plastic pollution and turning plastic into treasure. Significantly, this type of biotechnology is cost- effective because it can effectively degrade plastics and convert them into higher-value commodities. Synthetic biology degradation is, therefore, at the heart of the future of biodegradation.