On the other hand (having no idea about the subject) I can imagine that the fact that plastics can't be broken down so easily is part of the reason why we find it so useful, for example to protect foods.

"bacteria haven't evolved the correct enzymes"

Yet. The results might not be that great for humanity either. Especially if the bacteria get, shall we say, overly eager and efficient?... and plentiful.

That said, there's plenty of obscure bacteria having a decent stab at the problem and having a good time. Humans are helping them along as well.

Like all decently powerful tools there's a possibility for harm and hope.

I am inclined to prefer the scenario where plastic is more readily decomposed, rather the situation where we are in now, where plastic is entering the food chain and organisms, including ourselves.

Other than climate change, I think plastic pollution is the issue of our time.

This is a fiction book about the aftermath of an oil spill, developing enzymes to digest the hydrocarbons and how it all then gets a bit out of control..

https://www.goodreads.com/book/show/86452.Ill_Wind

Sounds like on of Neal Stephenson's books: https://www.nealstephenson.com/zodiac.html

Reminds me of Doomwatch:The Plastic Eaters, from 1970.

See https://en.wikipedia.org/wiki/Doomwatch

OR more dramatically, good ole ICE-9 from Cat's Cradle

> Why are there so few natural decomposers of plastics?

Because plastics weren't naturally occurring. Give it time.

Maybe a lot of time. The main reason we have cheap coal is from nature failing to find a solution to break down lignin during the Carboniferous period (and really particularly during the Carboniferous rainforest collapse) hundreds of millions of years ago.

Sometimes nature is very slow. Like geological timescales.

Lignin can be broken down in aerobic conditions by peroxidase and a series of other fungal enzymes, it only forms those energy dense forms under anaerobic conditions and probably requires high pressures. The reason it is so difficult and only breaks down through oxidation is because it is quite complex, unlike the homogenous polymer chains of plastic that have many repeating monomers.

https://www.researchgate.net/figure/Chemical-structure-of-li...

>Why is a molecules with high energy density so difficult to break down?

Generally, even if a given reaction is energetically favourable, if the activation energy or enabling conditions for the reaction to occur are high/rare respectively, then the rate of the energetically favourable reaction will be slow.

It's like water in a cup; sure it would prefer to be on the ground, but absent something tipping the cup over, it'll stay inside the current local energy minima without any complaints.