> break down

If there exists a use of "«break down»" intended to mean "biodegrade", the term remains too close to "crumble".

You would not eat a bottle, but having tiny chunks of plastic around makes "you eat 5 grams of plastic - one credit card - per <period>" fully credible (i.e. you want it to stay big to stay out of the body - you want materials not to shed themselves around). Crumbling plastic just creates microplastic. Which is relevant, because some actors seem to have confused the goals - transforming vs pulverizing.

(See e.g. https://theconversation.com/were-all-ingesting-microplastics... ; https://theconversation.com/youre-eating-microplastics-in-wa... )