Maya Ellison
Plastic is a versatile material that has improved our quality of life, but it has also become a significant environmental concern due to its persistence in the environment. Plastic is designed to be durable, with chemical inertness and physical strength, which makes it challenging for natural processes to break it down. This durability is achieved through strong carbon-carbon bonds in polymers like polypropylene, which are not commonly found in nature. As a result, the microorganisms and enzymes that typically break down organic matter do not recognize or have difficulty metabolizing these bonds. While some biodegradable plastics are being developed, the degradation of traditional plastics can take hundreds to thousands of years, causing harm to the environment through the release of toxic chemicals and microplastics.
| Characteristics | Values |
|---|---|
| Plastic type | Polypropylene, Polyethylene, Polyethylene terephthalate (PET) |
| Plastic composition | Carbon-carbon bonds, Carbon-hydrogen |
| Breakdown method | Photodegradation (UV light), Oxidative degradation |
| Breakdown time | 50-80 years, 500-700 years, 1000 years |
| Biodegradability | Not biodegradable due to complex molecular structure, lack of natural organisms |
| Alternative | Biodegradable plastics (HBP, OBP, bioplastics), plant-based plastics |
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What You'll Learn
Plastic is designed to be hard-wearing
The reason we use plastics is because they are durable and do not break down easily. This makes them ideal for use as containers or structural components. The most common types of polymers in landfills are polypropylene and polyethylene, which consist of only carbon and hydrogen. Most biological processes for degradation involve breaking more complex bonds, such as carbon-oxygen, carbon-nitrogen, and nitrogen-oxygen bonds. Since polyethylene and polypropylene do not contain these more complex bonds, there is no chemical activity that would allow for their breakdown by bacteria or other biological organisms.
The only way plastics can degrade is through photodegradation, which occurs when UV light breaks down the plastic over a long period of time. There are, however, biodegradable plastics available, known as hydro-biodegradable plastics (HBP) and oxo-biodegradable plastics (OBP). These use a catalyst in the material to speed up oxidative degradation, where oxygen in the atmosphere breaks down the plastic.
While biodegradable plastics are available, they are not widely used due to their high cost. However, as demand increases, the price is expected to decrease. In the future, it is hoped that biodegradable plastics will replace plastics derived from fossil fuels.
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Plastic is not organic and so cannot decompose
Plastic is not organic and therefore cannot decompose. Decomposition is a process by which organic materials like wood, animal carcasses, and paper are broken down into simpler organic compounds. In order to decompose, something must be buried in soil, where bacteria can break it down. Decomposed organic material is then recycled into the earth as food for plants, enriched soil, and nourishment for other living things.
Plastic, on the other hand, is derived from petroleum. More specifically, plastic is derived from propylene, a simple chemical component of petroleum. When heated in the presence of a catalyst, propylene forms extremely strong carbon-carbon bonds, resulting in polymers or long chains of monomers called polypropylene. These carbon-carbon bonds are not abundant in nature, and the enzymes in microorganisms that break down biodegradable materials do not recognize them.
While some bacteria have been discovered that can directly break down plastic, most bacteria cannot. This is because plastic is not organic and therefore cannot be metabolized by microorganisms in the same way that organic materials are. The only way for plastics to degrade is through photodegradation, which occurs when UV light breaks down the chemical bonds in plastic. However, this process takes a very long time.
There are, however, new kinds of biodegradable plastics on the market that are designed to be easily broken down by nature. These include plant-based plastics made from corn or sugarcane and petroleum-based plastics with tweaked chemical bonds. In addition, researchers are developing bioplastics that work like regular plastic but can be degraded when people are finished using them.
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Bacteria cannot break down plastic's complex molecular structure
The complex molecular structure of plastics is one of the main reasons why they are hard to break down. Most plastics are polymers, which are made up of long chains of simple molecules bonded together. The strength of these polymer chains is what makes plastics durable and challenging to break down.
Bacteria, which are responsible for breaking down organic matter in nature, typically produce enzymes that break down complex molecules into smaller ones that can be absorbed and utilized by the bacteria. However, the molecular complexity of plastics poses a challenge for bacteria.
Plastics, such as polypropylene and polyethylene, consist primarily of carbon and hydrogen atoms bonded together to form long polymer chains. These polymers lack the complex bonds typically found in biodegradable materials, such as carbon-oxygen, carbon-nitrogen, and nitrogen-oxygen bonds. As a result, bacteria and other biological organisms struggle to break down these polymers.
While some bacteria, such as Ideonella sakaiensis, have been discovered to break down certain types of plastics like polyethylene terephthalate (PET), they are still relatively rare. I. sakaiensis uses enzymes called PETases to break down the PET into smaller molecules, which can then be utilized by the bacterium. However, even with these plastic-degrading bacteria, the process of breaking down plastics is slow and may take weeks or months.
Furthermore, the success of bacteria in breaking down plastics depends on various factors, such as temperature. Certain bacteria work optimally at higher temperatures above 30°C, while others can function at lower temperatures, such as 15°C or potentially as low as 4°C. However, these cold-temperature bacteria are limited in the types of plastics they can digest.
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There are some biodegradable plastics
Plastic pollution is a significant environmental concern, and one of the main reasons for this is that most plastics are not easily biodegradable. However, it is important to note that there are some types of plastics that are biodegradable. These biodegradable plastics are designed to be broken down by microorganisms into water, carbon dioxide, and biomass, reducing their environmental impact.
There are two main types of biodegradable plastics: those made from renewable resources such as corn starch or sugar cane, and those made from traditional petroleum-based resources but with additives that enhance biodegradability. The renewable resource-based plastics are typically composed of polylactic acid (PLA), which is derived from corn starch or sugar cane. These plastics are often used for food packaging and disposable tableware. While they are biodegradable, they do have some limitations, such as a lower melting point and reduced durability compared to traditional plastics.
The second type of biodegradable plastic is made from petroleum-based resources but with added additives. These additives, often referred to as pro-degradant additives, help accelerate the breakdown process. When these plastics are exposed to sunlight, heat, or mechanical stress, the additives help facilitate oxidation, which breaks down the plastic into smaller fragments. However, it is important to note that these fragments may not fully biodegrade and can still persist in the environment.
One example of a biodegradable plastic is polyhydroxyalkanoates (PHA). PHA is a polymer produced by microorganisms that can be processed into a flexible and strong plastic. It is fully biodegradable and has a wide range of applications, including medical devices, packaging, and agricultural products. Another example is polybutylene succinate (PBS), which is made from the condensation polymerization of glycerol and succic acid. PBS has similar properties to polyethylene and can be used in applications such as bags and agricultural mulch films.
It's important to properly manage biodegradable plastics to ensure they effectively break down. This includes ensuring they end up in environments where biodegradation can occur, such as compost facilities or soil. Proper disposal methods, such as industrial composting, are crucial to facilitate the biodegradation process and ensure the benefits of these plastics are realized. Additionally, consumers play a vital role in properly sorting and disposing of biodegradable plastics to contribute to their effective breakdown.
While biodegradable plastics offer a promising solution to the plastic pollution problem, it is essential to use them responsibly and continue researching and developing more sustainable options. Improving the biodegradability of plastics while maintaining their functionality and durability is an ongoing challenge. Furthermore, increasing the accessibility and affordability of biodegradable plastics is crucial to encourage their wider adoption and contribute to a more sustainable future.
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UV light can break down plastic, but slowly
Plastics are hard to break down because they are designed to be chemically inert and physically strong. They are made from complex polymers that consist of many carbon and hydrogen molecules bonded together. Most biological processes for degradation involve breaking more complex carbon-oxygen, carbon-nitrogen, and nitrogen-oxygen bonds, which are not present in plastics. Therefore, there is no chemical activity that would allow for the breakdown of plastics by bacteria or other biological organisms.
However, UV light can break down plastic over time through a process called photodegradation. The high-energy radiation in UV light can cause plastics to degrade by breaking the bonds in the plastic. UVC radiation, in particular, is very aggressive and can tear oxygen molecules apart to generate ozone, which also attacks organic materials like plastics. While UVC radiation from the sun does not reach the Earth's surface due to absorption in the atmosphere, it still contributes to the formation of the ozone layer.
The effects of UV light on plastics can vary, from slight yellowing to the plastic turning into powder and disintegrating. The specific effects depend on the type of plastic and the duration and intensity of UV exposure. For example, polypropylene can lose up to 70% of its strength after just six days of UV exposure. Additionally, UV light can cause changes in the surface layer of plastics, potentially leading to component failure.
While UV light can break down plastics, the process is very slow. Natural plastic degradation through UV light can take hundreds or even thousands of years. During this time, plastic trash can release harmful chemicals into the soil and water or break into tiny bits that can be ingested by animals, fish, and birds, causing environmental damage.
To address the issue of plastic waste, researchers are developing biodegradable materials that function like regular plastic but can degrade when no longer needed. These biodegradable plastics use catalysts to speed up oxidative degradation, where oxygen breaks down the plastic. Additionally, some bacteria have been found to directly break down plastic bags, indicating potential biological mechanisms for plastic degradation.
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Frequently asked questions
Plastics are hard to break down because they are made to be chemically inert, physically strong, and long-lasting. The polymers in plastic have very strong carbon-carbon bonds that are not abundant in nature, so the enzymes in microorganisms that break down biodegradable materials do not recognize these bonds.
Plastics can eventually break down through photodegradation, where UV light breaks down the plastic over a long period of time.
Yes, there are biodegradable plastics called bioplastics that are made to easily biodegrade. Some bioplastics are made from plant-based materials like corn or sugarcane, while others are made from tweaking the chemical bonds of petroleum-based plastics.
