The degradation of disposable plastic bags in the natural environment is a complex process, and different types of plastic bags degrade in different ways and speeds.
Traditional disposable plastic bags are mainly made of petroleum-based plastics such as polyethylene (PE). In the natural environment, they degrade very slowly. First, these plastic bags are affected by light. The ultraviolet rays in the sun can break the chemical bonds in the plastic molecular chain, a process called photo-oxidative degradation. When the chemical bonds are broken, the long-chain molecules of the plastic will gradually break down into smaller fragments. However, this process is extremely slow, and it is only physically broken. The chemical structure of the plastic is still difficult to be decomposed by microorganisms in the natural environment.
Taking the marine environment as an example, the disposable plastic bags floating on the sea surface will gradually break into tiny plastic particles under long-term light and wave washing. These particles are called microplastics, and they can exist in the ocean for years or even decades. Microplastics will spread to every corner with the ocean currents, be eaten by marine organisms by mistake, and then enter the food chain.
For degradable disposable plastic bags, the degradation process is relatively complicated. Biodegradable plastic bags usually contain ingredients that can be decomposed by microorganisms. Under suitable environmental conditions, such as soil or composting environments with sufficient moisture, suitable temperature and microbial communities, microorganisms will secrete enzymes to decompose the organic components of plastic bags. These enzymes can break down plastic molecules into smaller organic compounds, such as carbon dioxide, water and biomass. For example, in a composting environment, microorganisms can break down polylactic acid (PLA) molecules into lactic acid, and then further into carbon dioxide and water.
However, the degradation of degradable plastic bags also requires specific conditions. If the ambient temperature is too low, the humidity is insufficient, or there is a lack of corresponding microbial species, their degradation rate will be greatly slowed down. Moreover, even degradable plastic bags, if discarded in the natural environment at will, may cause certain short-term harm to the environment, such as clogging the drainage system.
