I have to disagree heavily there. Thermic plastic disposal is standard in many developed countries and cleaning of combustion exhaust gases is an established and reliable technology.

It just costs money and requires regulatory oversight, that some countries like to cut on.

You gave heavy metals as an example. No mushroom can clean away heavy metals. They can only break down molecular components. Heavy metals are one of the compounds why thermal disposal is necessary. You can wash the heavy metals out of the exhaust gas, concentrate them and then store them in more dedicated facilities, e.g. old salt mines.