Hormones are chemical messengers that circulate in the blood and regulate many critical biological functions through intricate signaling mechanisms. In addition to the sex hormones estrogen, progesterone, and testosterone, there are others, such as thyroid hormone, insulin, melatonin, and cortisone. Endocrine disruptors (EDs) are chemicals that mimic or block hormones or otherwise interfere with normal hormone activity, often at extremely small doses. Evidence for endocrine disruption comes from studies of animals, humans, and laboratory cell cultures. Chemicals released into the environment have dramatically affected the reproductive success and development of wildlife by interfering with sex hormones. Humans are intentionally or inadvertently exposed to EDs in the workplace, home, and community and during medical care. Evidence of adverse health effects is overwhelming in some instances but only suggestive in others.
As early as the 1930s, studies in laboratory animals demonstrated estrogenic properties of a number of synthetic chemicals. Among them was bisphenol-A, now widely used in some plastics, resins, and dental sealants. 1 Estrogen-like effects of the pesticide DDT in chickens were reported in 1950. 2 In 1962, Rachel Carson's Silent Spring alerted the world to the harmful effects of pesticides on wildlife reproduction. She described a cascade of events resulting in contamination of the food chain, decline of egg survival, and destruction of populations of songbirds. Although unrecognized as hormone disruption at the time, that