But why put them in the hole? If you have no clean burning, the filter mostly gets carbon, which can be burned again. Some plastics like PVC release HCl, so you need to scrub that, but the result is harmless table salt. The biggest issue is formation of dioxins, so you need to have a high flame temperature to make sure everything burns clean. Otherwise dust etc. could contain heavy metals, but that is not directly from the plastic.
Why is it a global day but only at one specific location?