Fill a small bucket with warm water.
Sprinkle baking soda over the oxidized plastic.
Dip a sponge in the warm water. Scrub the baking soda into the plastic. The baking soda is slightly abrasive, allowing it to clean the surface of the plastic and remove oxidization. Continue cleaning until all oxidization is removed.
Rinse the item under cool running water. If the plastic item is large, such as a plastic slide or outdoor playhouse, rinse the item with a house.
Combine one part bleach to four parts water in a spray bottle. Coat the surface of the oxidized white plastic with the mixture. Not only does this ensure all oxidation is removed, it also removes and prevents mildew and mold. Only use this mixture on clear and white plastic. It can discolor colored plastic. For colored plastic, replace the bleach with vinegar. Allow the mixture to soak into the plastic for 10 to 20 minutes.
Rinse the item under cool water or with a hose.