How do contaminants reach the human body?

The waste that is fed into the incinerator, burns. The heat breaks down some of the waste into their chemical constituents. These constituents either react amongst themselves to form new chemicals or remain in their original form.

The chemicals escape along with the smoke via the smokestack, with the flue gases or in the ash.

Ash:

The ash is taken to a dump yard where it is disposed. The contaminants like heavy metals in the ash can either leach into the soil or the ash is carried by the wind and deposited on land, vegetation and water bodies. Animals during foraging on vegetation ingest this contaminated ash.

Humans then consume animal products (for example: milk, meat)

Smoke:

Smoke is carried to long distances by wind. When smoke particles settle down they are consumed during the process of ingestion. This begins with the smallest species, which are then consumed by the larger species and this continues till the top food chain. Thus in every point of the food chain the toxic pollutants from the incinerators are consumed. The levels of intake increase with the size of the animal as it corresponds to its appetite and quantity of consumption of the smaller species.

This is called biomagnification.