Mutant 59: The Plastic Eaters, a 1971 British sci-fi environmental disaster novel written by medical scientist Kit Pedler and television screenwriter Gerry Davis.

No wikipedia page, but goodreads has it here:

https://www.goodreads.com/book/show/99852816-mutant-59

That wasn’t it; I just found it, it’s called Ill Wind by Kevin J Anderson