[mikro2nd]

The trouble with that notion is this: imagining that a plastic-based ecosystem arises (horrifying thought!) it means that there are life-forms capable of deriving energy from plastics, breaking them down. That makes plastics useless to us humans, because any time we try to use plastics for all the things we currently do with them, those life-forms are going to come along and attack, break down the stuff we deem "useful plastics"; the critters will make no distinction between nurdles lost on the beach and the plastics holding your car/house/clothes/aeroplane together. i.e. It's Game Over for plastics use.

[cglace]

That's not necessarily true. There is an ecosystem for breaking down wood, and my house is framed in wood.

[FrustratedMonky]

Termites are a good example.

They are a natural way to break down wood. And they can eat your house. Thus we have come up with ways to mitigate them. Now there is an entire industry around preventing termites, fixing termite damage, etc..

So, the problem is, we find some microbe that eats plastics. Boom, now we have a new problem, we need an entire industry to prevent them from eating the plastics we don't want them to eat. Think of traveling with your laptop, 'oops, got a little bit of plastic eating microbe, guess i'm buying a new laptop'