What are the poisons in cigarettes?

The same, or equivalent, "poisons"are present in tobacco as in any other plant.

All plants may absorb naturally produced chemicals, such as arsenic and polonium-210, from the environment. Similarly, all plants may absorb "poisons" from man-made pollution or the fertillisers, etc. used to grow them. At the same time, all plants get contaminated with the "poisons" used in their processing. All plants also naturally produce "poisons" to deter predators, to encourage reproduction, etc.

Everything is "poisonous" in the appropriate dose, even water and oxygen.