Some of the most unpleasant things are the hardest to get rid of. This tenacious family of chemicals is one such thing. Dioxins are formed primarily from man-made activities, including the burning of waste (particularly plastics) and fuel; from the chlorine bleaching of paper and other products; and from the manufacture of certain chemicals. They are released into the air, travel, then settle into the water and soil, and eventually end up in the food supply, mainly via the systems of livestock, where they bioaccumulate. Most human intake of dioxin comes from food; because these chemicals have been in the environment in large quantities for the last century, all humans have some level of dioxin exposure.

Higher than normal levels of exposure occur occasionally, due to industrial accidents or chemical spills. Dioxins are linked to numerous adverse health effects, including reproductive and endocrine system damage and an increased risk of cancer; the precise level of risk is unclear, as some dioxins are more toxic than others, and it is unknown exactly how much exposure it takes to cause harm. Efforts have been made to reduce dioxin emissions, and levels have been dropping in industrialized nations (where they are highest) for the past 30 years. However, since the chemicals linger in the environment, they aren't likely to disappear anytime soon.

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