To clean up microplastics from the oceans, we could use genetically engineered fish and bacteria. The fish would have an organ for storing plastic, which could be a modified appendix (because fish have those, right?), as well as gut bacteria (because fish have those, right?) designed to concentrate the plastic particles and move them into that organ.
Anyway, we release these fish. Then, as in the original idea [link], we put a bounty on them, but with the condition that they're returned alive. The ones that come in have the plastic extracted, measured, and recycled. Those that collected the most plastic are bred to form the next generation. Over time, this should result in fish and bacteria optimized for collecting plastic.
I expect this will result in better collection of microplastic pollution than the original idea, which seems to me that it would only work for macroplastic.
N/A [2019-07-01]-- notexactly, Jul 01 2019 Fish For Plastic by [theircompetitor]. The inspiration for this idea [notexactly, Jul 01 2019] random, halfbakery