Plastics are a major source of pollution in the world's oceans. They can take hundreds of years to decompose, and in the meantime, they can cause significant damage to marine life and ecosystems. One of the ways that plastics break down in the ocean is through exposure to sunlight.
Sunlight breaks down plastics through a process called photodegradation. Photodegradation occurs when ultraviolet (UV) radiation from the sun reacts with the chemical bonds in plastics, causing them to break down. This process can be accelerated by the presence of oxygen, heat, and salt water.
Photodegradation can cause plastics to become brittle and fragmented over time. These small pieces of plastic, known as microplastics, can be ingested by marine life and can cause a variety of health problems. Microplastics can also adsorb toxic chemicals from the water, which can then be transferred to the animals that ingest them.
How Sunlight Breaks Down Plastics
The process of photodegradation begins when UV radiation from the sun strikes the surface of a plastic object. The UV radiation causes the electrons in the plastic's chemical bonds to become excited. This excitation can lead to the formation of free radicals, which are highly reactive molecules that can damage the plastic's structure.
Free radicals can react with other molecules in the plastic, causing the plastic to break down into smaller molecules. These smaller molecules can then be further broken down by UV radiation, leading to the formation of microplastics.
The rate at which plastics photodegrade depends on a number of factors, including the type of plastic, the amount of UV radiation it is exposed to, and the temperature and humidity of the environment.
Types of Plastics That Photodegrade
Not all plastics are equally susceptible to photodegradation. Some plastics, such as polyethylene and polypropylene, are relatively resistant to photodegradation, while others, such as PVC and polystyrene, are more easily degraded.
The chemical structure of a plastic determines its susceptibility to photodegradation. Plastics that contain double bonds between carbon atoms are more likely to photodegrade than plastics that do not contain double bonds.
Environmental Factors that Affect Photodegradation
The rate at which plastics photodegrade is also influenced by environmental factors, such as the amount of UV radiation it is exposed to, the temperature and humidity of the environment, and the presence of oxygen and salt water.
UV radiation is the most important environmental factor that affects photodegradation. The higher the intensity of UV radiation, the faster plastics will photodegrade. UV radiation is strongest in tropical regions and during the summer months.
Temperature and humidity also play a role in photodegradation. Higher temperatures accelerate the rate of photodegradation, while higher humidity can slow down the rate of photodegradation.
Oxygen and salt water can also contribute to photodegradation. Oxygen can react with free radicals to form peroxides, which can further damage the plastic. Salt water can also accelerate the rate of photodegradation by breaking down the plastic's surface.
Conclusion
Photodegradation is a major process that contributes to the breakdown of plastics in the ocean. The rate at which plastics photodegrade depends on a number of factors, including the type of plastic, the amount of UV radiation it is exposed to, and the temperature and humidity of the environment. Photodegradation can cause plastics to become brittle and fragmented over time, leading to the formation of microplastics. Microplastics can be ingested by marine life and can cause a variety of health problems.
