Plastic lasts forever. The older it gets the more dangerous it gets. Plastic slowly breaks down, it is very hard to repair (requiring very toxic glues and specialist equipment). Plastic has slowly replaced traditional materials such as metal and wood. Also, our dependance on plastic has eroded cultural skills in the use of natural materials. Few people now can mend their clothes or shoes, make a water vessel or fix a simple basket. Refuse to buy plastic and search biodegradable alternative. Or simply live with less.
Recently a lot of research has been invested in trying to find ways to break the plastic back into useful carbon molecules. There are now some known nylon-eating bacteria and the guts of creatures such as mealworms and waxworms have shown to increase effectiveness. But this does not give us cause to keep using plastic, we have mountains of plastic waste to try to clean up first.
Lets keep focusing on alternatives to plastic. Here is a great mind-map about why and how to go plastic-free.