Everyday you consume about 100,000 pieces of microplastic. However, when you die if you open up your body, only about 1000 pieces will be inside.

Overall: microplastics mostly pass harmlessly through any filter we can design. It doesn't stick to anything and it just keeps on moving around. It's a difficult problem.

The first step is capturing microplastics. There isn't a good way to do this. We can capture macro-plastics easier using simple size filters, that's the rescue mission you see where people are pulling out fishing lines, raincoats, plastic bottles, etc. We don't have any good techniques to pull out microplastics. We can use centrifuges, reverse osmosis or solvent extraction - but none of those can scale up to the size of a river or ocean. There are chemical gelling products that sponge up the microplastics almost like running a ball of plasticene over carpet to pick up dirt, but again, really niche stuff that doesn't scale up well.

The second step is sequestration or destruction of the capture material. It's always going to be mixed plastic waste of little recycling value - we don't even recycle easy post-consumer plastics so nobody is going to put energy into environmental plastics. One option is to burn it. Destroys the plastic and converts it to carbon dioxide. Another is landfill, which is really good at trapping solids to deal with later. A more advanced option is anaerobic digestion - where we break the plastic back to it's starting materials or convert it to biogas which can be used as fuel.

The accounting (money, energy, emissions) for this is messy. Maybe you need to fuel up boats and trucks to move all the plastic around, so overall emissions go up. Someone also needs to pay for this work, and maybe that money is better spent elsewhere on bigger problems.

Right now, best targets are reducing the sources. You get significantly higher bang-for-buck.

We can only take out large chunks at the surface. The small stuff goes into the animals and into river and seabed floors. We have a lot of water on this planet. There are bacteria that can break it down but this highlights the issue of plastic recycling. Ideonella sakaiensis can degrade PET and use it as energy but it converts it into carbon dioxide. Then there are a huge array of other plastics.

Taking even a reliably large clean part of plastic and making it back into plastic, when you know the exact material it is (called regrade in plastic moulding terms) degrades the properties. You would normally mix a small percentage of it in with virgin material. But over use means the moulding won’t work. That’s why you see a lot of it used in simple extrusions like decking.

We have too much plastic. We need to reduce its use to important components. Most sea plastic from land sources come from 5 main rivers. Mainly in Asia. So we need to stop throwing it in the sea while we’re at it. That largest contributor to sea plastics is from boats. One easy way to help reduce sea plastic is strangely to not eat fish.

Europe doesn't have as much space as the US and nobody wants landfills near them so for the most part miscellaneous/non-recyclable plastics are just burnt along with other kinds of trash in special facilities that are equipped to handle toxic smokes

plastic is petroleum-based so it burns pretty well and modern incinerators double as power plants

p.s. I suppose you could say it's one kind of chemical transformation...

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