Does Plastic Decompose? How Long Does It Take?

It is not a rare occurrence for someone discovering decades-old plastic waste in seafloor and waterway. After all, billions of single-use plastics are used every day, and irresponsible people throw their trash in the river and sea. The more those plastic waste surfaces, the more people realize that that plastic won’t decompose even after being buried for a very long time. So, does plastic decompose?

Does Plastic Decompose?

To answer that question, first, we need to understand the decomposition process. Decomposition is the broken-down process of organic materials, such as paper, wood, and animal carcasses into simple organic compounds. The decomposition process is done in the soil where bacteria resides. The bacteria will break down the organic compound and recycle it as food for the plants. This organic compound that could be broken down by bacteria is called “biodegradable”.

However, plastic is not biodegradable because it’s not an organic compound. Plastic is a synthetic compound made of polyethylene terephthalate (PET) produced by linking unit cells or small building blocks. The building blocks are called monomers, and they are made from a group of atoms from synthetic chemicals or natural product. When assembled, monomers will become sturdy and durable. Thus, bacteria cannot break them, making it extremely hard to decompose plastic.

Sun’s UV light can break PET although it would take forever. Even so, it won’t completely be broken down. The process of UV’s breaking down of plastic is not biodegradation but “photodegradation”.

Unlike biodegradation that completely dissolves organic matter into the soil, photodegradation is a breaking down of PET’s monomers and its turning to microscopic synthetics granule. Even now, scientists are not sure yet if granules could decompose completely.

How Long It Takes for Plastic to Decompose?

Even though it’s not a complete decomposition, it still takes quite a while for plastic to break down into microscopic granule. It also should be noted that the time of plastic decomposition varies depend on the landfill’s condition and plastic’s type. There are seven types of plastic used for products, and each type has its own characteristic.

1. Polyethylene terephthalate- PET(E): It is the most recycled plastic.  Compared to other, PET takes the quickest time to photodegradation and oxidation. As utensils, fruit cups, and plastic bottle, PET takes 450 years to degrade by recycling.
2. High-density polyethylene- HDPE: Compared to the low density one, high-density polyethylene has tougher chemical structure, even when both are Polyethylene-based. As a cling wrap, it takes 450 years to decompose HDPE through landfill. Meanwhile, as a coating for milk cartoon, it takes five years to degrade through recycle.
3. Polyvinyl chloride- PVC: This type of plastic is stable but resistant to chemical breakdown and oxidation. To biodegrade PVC, a certain type of fungus or thermal degradation can be used. As a cling wrap, PVC takes more than 450 years to biodegrade.
4. Low-density polyethylene- LDPE: Still based on polyethylene, LDPE is difficult to biodegrade. As the lining of the coffee cup, LDPE will decompose in 2 years to 20 years.
5. Polypropylene- PP: Polypropylene can not be broken down by acids and bases but can be oxidized. Combined with starch, PP can be biodegraded with microbes. As straws, PP takes 200 to 450 years to degrade through landfill. Meanwhile, it can take more than 1 million years as chip bags since they are combined with aluminum foil.
6. Polystyrene- PS: Like PP, PS can not be broken down by acids and bases. Only mealworms and bacteria called Methanogenic consortia that can biodegrade PS. It is used for Styrofoam, and it takes 500 to more than 1 million years to biodegrade.
7. Other: Mixed plastic or other types of plastics. Plastic degradation time varies.

Therefore, the answer to the question “does plastic decompose?” is quite complicated. However, to make it simple, then yes, plastic decomposes, but it can’t be 100% decomposed. Plastic is mostly decomposed by UV radiation, and it takes two years to more than 1 million years to decompose it.