Omar Khalid
Plastic is a synthetic compound made of polyethylene terephthalate (PET) and is produced by linking unit cells or small building blocks called monomers. Its carbon bonds are not the same as the chemical bonds found in nature, making it harder and more energy-intensive to break down. Burying plastic in landfills is a common practice, but it can take anywhere from 20 to 500 years for plastic to decompose, depending on the material and structure. For example, single-use plastic grocery bags take about two decades to break down, while plastic water bottles made with PET are estimated to take approximately 450 years. The rate of decomposition also depends on the landfill's condition and sunlight exposure, as UV light plays a crucial role in breaking down plastic through photodegradation. While some biodegradable plastics and plastic-eating bacteria have been developed, the challenge of effectively managing plastic waste remains a pressing issue for our planet.
| Characteristics | Values |
|---|---|
| Decomposition time | Anywhere from 20 to 500 years, or even more, depending on the type of plastic and the environment |
| Factors affecting decomposition | Sunlight exposure, landfill conditions, recycling process, type of plastic |
| Plastic in landfills | Expected to last hundreds of years |
| Plastic in the ocean | Can degrade in as little as a year |
| Plastic bag decomposition | From a couple of weeks to a million years |
| Plastic bottle decomposition | Approximately 450 years |
| Biodegradability | Not biodegradable, but certain types of bacteria can break it down |
| Alternative plastics | Biodegradable plastics or bioplastics, plant-based plastics |
| Disintegration products | Carbon, carbon dioxide, or other carbon compounds |
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What You'll Learn
Plastic-eating bacteria
Plastic is a synthetic compound made of polyethylene terephthalate (PET) produced by linking unit cells or small building blocks called monomers. When assembled, these monomers become sturdy and durable, making it extremely hard for bacteria to break them down.
In 2008, Daniel Burd, a student at Waterloo Collegiate Institute, demonstrated that certain types of bacteria can break down plastic. His research earned him the top prize at the Canada-wide Science Fair. Researchers have since confirmed Burd's findings and identified several other plastic-eating bacteria.
In 2001, a group of Japanese scientists discovered a slimy film of bacteria in the trenches of a rubbish dump that had been breaking down plastic bottles, toys, and other waste. The bacteria harvested the carbon in the plastic for energy, which they used to grow, move, and divide into more plastic-hungry bacteria. The scientists named the bacterium Ideonella sakaiensis, after the city of Sakai, where it was found. They also described a specific enzyme that the bacterium was producing, which allowed it to break down PET, the most common plastic found in clothing and packaging.
Since 2021, a French company named Carbios has been using a bacterial enzyme to process about 250 kg of PET plastic waste every day, breaking it down into precursor molecules that can be used to make new plastic. This has brought us much closer to achieving infinitely recyclable plastic.
Other researchers have also developed a plastic-eating E. coli that can efficiently turn PET waste into adipic acid, which is used to make nylon materials, drugs, and fragrances.
While these developments are promising, it is important to note that the practical applications of these plastic-eating bacteria have been limited. The only effective way to break down plastic currently is through photodegradation, which requires sunlight.
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Decomposition time varies
There are seven types of plastic used for products, each with its own characteristics and decomposition timeline. Polyethylene terephthalate (PET) is the most recycled type of plastic and also the quickest to photodegrade and oxidize. However, it still takes approximately 450 years for a PET plastic bottle to decompose in a landfill. In contrast, low-density polyethylene (LDPE), such as the lining of a coffee cup, will decompose in 2 to 20 years. Polyvinyl chloride (PVC) is stable and resistant to chemical breakdown and oxidation, requiring either a specific type of fungus or thermal degradation for biodegradation, which can take over 450 years. Polypropylene (PP) cannot be broken down by acids or bases but can be oxidized or biodegraded with the help of microbes when combined with starch. As straws, PP takes 200 to 450 years to degrade in a landfill, but when used as chip bags and combined with aluminum foil, it can take over 1 million years to decompose. Polystyrene (PS) shares similarities with PP in terms of acid and base resistance, and its biodegradation is facilitated by mealworms and bacteria called Methanogenic consortia.
The decomposition process for plastics is different from that of organic materials. Organic materials, such as paper, wood, and animal carcasses, are broken down by bacteria in the soil into simple organic compounds. However, bacteria cannot break down the carbon bonds in plastic, making it challenging for plastic to biodegrade. Instead, plastic undergoes photodegradation, where UV rays from sunlight break down the molecular bonds, turning large pieces of plastic into smaller ones over time. This process can be accelerated by exposing plastic waste to sunlight in landfills.
The environment in which plastic is disposed of also influences its decomposition rate. For example, plastic in the ocean can degrade more rapidly due to constant motion and exposure to UV light. In 2009, researchers from Nihon University in Japan found that plastic in warm ocean water could degrade in as little as a year. In contrast, buried plastics in landfills may rarely come into contact with sunlight, prolonging their decomposition. Additionally, the presence of certain types of bacteria or fungi can facilitate the biodegradation of specific plastics, such as polypropylene and polystyrene.
While some plastics are designed to be biodegradable, they still face challenges in practical applications. Biodegradable plastics, or bioplastics, are not derived from nature but can easily biodegrade due to their modified chemical bonds. Plant-based plastics made from corn or sugarcane are also being developed to address the issue of plastic waste. However, even with these advancements, the complete decomposition of plastic, especially in buried forms, remains a complex and time-consuming process.
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Photodegradation
Plastic buried in landfills rarely comes into contact with sunlight, which is essential for photodegradation. This means that plastic buried underground can take anywhere from 20 to 500 years to decompose, depending on the type of plastic and environmental conditions. For example, plastic bags can take about two decades to break down, while plastic water bottles made from polyethylene terephthalate (PET), a common plastic type, can take approximately 450 years to fully degrade.
The intensity of UV radiation affects the rate of photodegradation. Factors such as shade, cloud cover, and geographic location influence the amount of UV radiation that reaches a plastic object. Additionally, biofouling, which is the accumulation of microorganisms, can hinder photodegradation by reducing sunlight penetration. This process can cause plastic debris in the ocean to sink, further reducing the effectiveness of photodegradation.
To enhance photodegradation, engineers can manipulate the molecular structure of plastics or integrate additives to make them more light-sensitive. Additives such as ketone carbonyl, carbon monoxide carbonyl, and metal blends can initiate a two-stage degradation process. In the first stage, these additives absorb UV light and create weak links in the polymer chains, making the plastic weaker over time.
While photodegradable plastics can be beneficial in situations involving littering, they also have potential drawbacks. These plastics can end up in the food chain when consumed by other organisms. Additionally, photodegradable plastics may not be a comprehensive solution to plastic waste, as they require sunlight exposure, which is often lacking in landfills. As a result, reusing and recycling plastics remain the most effective strategies for managing plastic waste.
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Biodegradable plastics
Plastic is a synthetic compound made of polyethylene terephthalate (PET) produced by linking unit cells or small building blocks called monomers. These monomers are made from a group of atoms from synthetic chemicals or natural products. When assembled, monomers will become sturdy and durable, making it difficult for bacteria to break them down.
However, in 2008, Daniel Burd, a student at Waterloo Collegiate Institute, demonstrated that certain types of bacteria could break down plastic. Researchers have since confirmed Burd's findings and identified several other plastic-eating bacteria.
Polylactic acid (PLA), a plastic made from corn, decomposes into water and carbon dioxide in 47 to 90 days—four times faster than a PET-based bag floating in the ocean. However, conditions have to be just right to achieve these results. PLA breaks down most efficiently in commercial composting facilities at high temperatures. When buried in a landfill, a plastic bag made from corn may remain intact just as long as a plastic bag made from oil or natural gas.
A 2009 study found that biodegradable plastics were financially viable only in the context of specific regulations that limit the usage of conventional plastics. Compostable plastic bags disintegrated when exposed to air and the sea but were still present after being buried in the soil for more than two years. Biodegradable plastic bags are seen by some as a sustainable solution, but they still take a considerable amount of time to break down.
There is also concern that another greenhouse gas, methane, might be released when biodegradable plastics degrade in an anaerobic landfill environment.
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Plastic in landfills
Plastic is not biodegradable because it is not an organic compound. Unlike wood, grass, and food scraps, which undergo biodegradation and are transformed by bacteria in the soil into other useful compounds, plastic does not break down in the same way. In fact, bacteria cannot break down plastic at all, making it extremely challenging to decompose.
The only natural way for plastic to break down is through photodegradation, which requires exposure to sunlight, specifically ultraviolet (UV) radiation. Over time, UV rays can break the bonds holding the long molecular chains of plastic together, causing the plastic to degrade into smaller pieces. However, plastic buried in landfills rarely comes into contact with sunlight, significantly slowing down the degradation process.
The time it takes for plastic to decompose in landfills varies depending on the type of plastic and the specific conditions of the landfill. Some types of plastic, such as polyethylene terephthalate (PET), commonly used in plastic water bottles, can take up to 450 years to fully break down in landfills. Other types of plastic, like single-use plastic bags, may take around two decades to degrade.
The slow decomposition of plastic in landfills has significant environmental implications. Plastic pollution can harm natural habitats and release toxins into the soil. Additionally, as plastic degrades, it can break down into microplastics, which are tiny particles that can be ingested by animals and even make their way into the human body through the food chain.
To address the issue of plastic in landfills, there has been a growing focus on developing biodegradable plastics or bioplastics. These new types of plastic are designed to be easily biodegradable, either through specific chemical bonds or by using plant-based materials such as corn or sugarcane. While these alternatives offer promising solutions, the challenge remains to implement effective waste treatment processes that can handle the large volume of plastic waste already present in landfills.
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Frequently asked questions
It depends on the type of plastic and the conditions of the landfill. Plastic tends to break down into smaller particles until they are too small to be seen, but it does not biodegrade like organic matter. Plastic buried in a landfill rarely sees the light of day, so it can take anywhere from 20 to 500 years to decompose.
The rate of decomposition depends on the type of plastic, the presence of UV light or bacteria, and the landfill conditions.
Organic matter, such as paper, wood, and food scraps, undergoes biodegradation, where bacteria in the soil break down the material into simple organic compounds. Plastic, on the other hand, does not biodegrade because it is not an organic compound, and its chemical bonds are harder to break down.
Biodegradable plastics, or bioplastics, are designed to easily biodegrade. Plant-based plastics made from corn or sugarcane are examples of bioplastics. Additionally, plastics in the ocean can degrade faster due to constant motion and UV light exposure.
Plastic water bottles made with PET can take approximately 450 years to break down, while single-use plastic bags take about two decades. Plastic straws can take 200 to 450 years, and chip bags combined with aluminum foil can take over a million years.
