Answer: D. They are never produced in the natural environment.
Step-by-step explanation:
Dioxins are toxic chemicals that are produced when chlorine based compounds are burnt with hydrocarbon such as oil, wood or coal.
High levels are found in the environment in places such as
soil, sediments and food but low levels are found in plant.
Dioxins can stay in the human body for long time because of their chemical stability and it's ability to be absorbed by fat tissue.