Glass bottles in the ocean get chemical and mechanical weathering pretty quickly, being ground away to sand on the order of decades. (https://en.wikipedia.org/w

Glass bottles in the ocean get chemical and mechanical weathering pretty quickly, being ground away to sand on the order of decades. (https://en.wikipedia.org/wiki/Sea_glass https://en.wikipedia.org/wiki/Sea_glass) You can also simply put them through a crusher/pulverize two or three times to turn them back into sand. I'm not really sure intact glass is a big environmental problem though. Animals could get stuck in intact bottles or cut themselves on sharp glass, but otherwise I believe glass is nontoxic, generally quite inert, and as far as nature is concerned indistinguishable from other naturally occurring minerals (obsidian in particular comes to mind.)