Traditional plastics are made with petrochemicals such as oil and natural gases. These are resources that are not renewable and will be scarce if depletion rate is too high from usage such as powering cars and producing plastics.
Plastics take 500 years or even up to 1000 years to degrade. Plastic pollution have been reported to affect 700 marine species and kill 100,000 animals each year. Many animals see plastics as food and ingest plastic litters. As plastic cannot be digested, it stays in the animals and slowly kill them. Even after the animal dies, the same plastic will be released into the sea or environment and the cycle will be repeated. When plastics finally gets degraded, they release toxic substances into the environment which also damages the ecosystem.