[waterhouse]

More generally regarding poisons, see https://en.wikipedia.org/wiki/Mithridatism . TLDR: YMMV.

"Mithridatism is not effective against all types of poison. Immunity is generally only possible with biologically complex types which the immune system can respond to. Depending on the toxin, the practice can lead to the lethal accumulation of a poison in the body. Results depend on how each poison is processed by the body."

"A minor exception is cyanide, which can be metabolized by the liver. The enzyme rhodanese converts the cyanide into the much less toxic thiocyanate.[12] This process allows humans to ingest small amounts of cyanide in food like apple seeds and survive small amounts of cyanide gas from fires and cigarettes. However, one cannot effectively condition the liver against cyanide, unlike alcohol. Relatively larger amounts of cyanide are still highly lethal because, while the body can produce more rhodanese, the process also requires large amounts of sulfur-containing substrates."

Our immune, metabolic, and other systems are built to be adaptable, and some things are easy to adapt to, but other things are difficult or impossible for them to adapt to.

[SideburnsOfDoom]

While that deals with deliberate poisoning, when it comes to environmental contaminants such as lead and other heavy metals, or PM10s from vehicle exhausts, the other by-products of coal power stations and wood fires etc. I suspect that long-term exposure to these is not something where "you can build a tolerance" is a useful framing at all. Even if you technically do, it's irrelevant to the harm caused over time to whole populations.