Waste products

When bacteria decompose sugars they leave some toxins behind--ethyl alcohol being the most famous.

Bacteria are developing to devour plastics. What do they leave behind?

For the PET family, Ideonella sakaiensis is here. Some details are here. The answer seems to be that different colonies of bacteria can eat most stuff all the way down to CO2 and water, but some intermediate compounds are terephthalic acid and ethylene glycol. At least the former isn't very toxic, and since it is solid at room temperatures won't migrate far.

Maybe plastic mines aren't such a wild idea, though purification seems like it would be hard. I don't think I want to be downstream of the ethylene glycol though.