That's an excellent question. Thank you for asking that.
Some of these are unique to the incinerator process, especially the most highly dangerous of them all, known as furans and dioxins. These only exist from incinerators; that's the only place that we know of them coming from. They are the most highly dangerous, poisonous cancer-producing substances.
The others do exist, but are released very rapidly from incinerators. This is why, if I'm asked why we don't put our waste into an incinerator, burn it, and get rid of it quickly instead of putting it into a landfill where it will seep out into the water, in order to shock people I've sometimes said that I would rather see our waste dumped into Lake Ontario than see it incinerated. Now, I am not advocating that we do that with our waste, but if we dumped it into Lake Ontario it would seep out, and if we put it into landfill without any protection, into a raw hole in the ground without a covering, it would seep out, but it would seep out over months or years, and probably many years, whereas when we incinerate, it's out in a fraction of a second.
These others—mercury, lead, cadmium, chromium, and so on—do exist and they will seep out into the water over time, but not nearly as fast. Also, as mentioned, some of the most important poisons don't exist except from an incinerator.