They mix together. Air too flows from one place to another. And they stay around a long time. Many of these chemicals take a very long time to break down in the body. DDT for example has a half-life of 57 years in temperate zones.
Hormones get their name from the Greek word meaning 'to urge on'.
They are chemical messengers produced and released into the bloodstream by organs known as the endocrine glands. These include the testicles, the ovaries, the pancreas, the adrenal glands, the thyroid, the parathyroid and the thymus. These play a crucial role in helping the foetus to grow in the womb, in the development of the baby and young child, and in the sexual development of both male and female. Endocrine-disrupting chemicals interfere with these hormones, most crucially at the stage when the baby is developing in the womb. But they can also mimic the hormone or block or stimulate its action in adults.