It depends on the temperature they burn at. You need pretty high heats to combust dioxins, for example, and from some very light skimming of the USA's standards I think you also need various filters and scrubbers for heavy metals (especially mercury which will boil away at these temperatures).

This stuff can be done, but it's expensive. I also don't know how close to 100% it gets even if everything is done properly. And of course to fully remediate this all of the equipment has to be operating properly.