On Thursday, September 22, scientists at the University of California San Diego reported in the journal Science of the Total Environment that a type of polyurethane already used in biodegradable land-based products can also break down when immersed in seawater.  This polyurethane is already used as a substitute for plastic in foams and shoes.
The research team performed their experiments at the Ellen Browning Scripps Memorial Pier and Experimental Aquarium.  They cut the polyurethane into cubes similar in size and shape to those naturally formed by EVA plastics.  They wrote that several types of marine bacteria and fungi stick to the polyurethane and break it down to its component chemicals, which they then consume for food.  The polyurethane microbes had already made detectable progress when the scientists checked the samples after four weeks in the water.
"Improper disposal of plastic in the ocean breaks down into microplastics and has become an enormous environmental problem," said study co-author Stephen Mayfield, director of the California Center for Algae Biotechnology. "We've shown that it's absolutely possible to make high performance plastic products that also can degrade in the ocean."
Humans deposit roughly 8 billion kg of plastic in the ocean each year, where it can be mistaken for food by marine organisms.  Natural forces break the plastic into the small pieces that we call microplastic, while larger chunks form near-islands, such as the Great Pacific Garbage Patch.  By mass, about half the patch is commercial fishing waste, such as discarded nets, but reducing the amount of post-consumer plastic in the ocean would still make a considerable dent in the planet's plastic problem.
This type of polyurethane can be used to make flip-flops and parts of other shoes, which make up a large portion of the world's plastic waste.

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Polyurethane plastic substitute can biodegrade in seawater, say scientists