They can be burned safely in an incinerator. Ad hoc burning can produce very toxic chemicals, though, including dioxins, hydrogen cyanide, vinyl chloride and furans. It could release lead. It depends on the type of plastic (PVC? Polyethylene? Polypropylene?). This is why it’s troubling to see people burning bags of trash and tossing in plastic bags and soda bottles as if they magically disappear.

This is a good rundown: https://www.directplastics.co.uk/about_plastics/post/whats-i...

MIT says... https://engineering.mit.edu/engage/ask-an-engineer/can-we-sa...

“When plastic is burned, it releases dangerous chemicals such as hydrochloric acid, sulfur dioxide, dioxins, furans and heavy metals, as well as particulate.”

To be fair, aren't soda bottles and plastic usually PET, which should not release nasty stuff? Or am I just misinformed?

See TehCorwiz' response below. It seems it never is JUST plastic.

PET and PP seem to be cleaner than styrenes, ABS or PVC but best I can gather PET releases antimony when burned.

Even putting aside the heavy metals, the assumption that they burn into CO2 is a hard one to accomplish in fact.

Done improperly, you end up with a very snokey, sooty smoke.

Done properly, you’re dealing with very high T, which is hard, and NOx production.

But, assuming you’re doing a good job... burn baby burn!

(Just separate out the per-fluorinates - HF is nasty)

Plastics often are doped with heavy metals like molybdenum to affect mechanical properties like wear resistance, or bromine for fire resistance. Neither of which you want in your lungs.