Polyvinyl chloride releases dioxin when burned. This is an undeniable scientific fact.
So does firewood. ANY relatively "low temperature" fire in which the substance burning contains chlorine (which is everything that lives), emits some level of CHLORINATED dioxin. It's the CHLORINATED stuff that is supposed to be bad, but the fools at the EPA wrote the rules so that the non-chlorinated species are also "banned". And for God's sake, NEVER burn seawater driftwood. Look up an article entitled "Trace Chemistries of Fire".