"Sounds nice. Where did you get your chemistry degree?" {sigh} -- so you're not going to post a straight answer, just sharpshoot me and make me look it up myself?
OK, here it is: biodegrade & photodegrade plastics.
"In 2009, researchers from Nihon University in Chiba, Japan, found that plastic in warm ocean water can degrade in as little as a year."
Implying that once the sources of new trash are stopped, the oceans will begin to clean themselves in relatively short time periods.