Dioxins are one of the most toxic groups of chemicals known. Dioxins are chlorine-containing hydrocarbons that are considered extremely toxic carcinogenic agents. The terms 'dioxin' or 'dioxins and furans' generally refers to a group of 210 chlorinated pollutants, chemically known as the polychlorinated dibenzo-p-dioxins and dibenzofurans. Toxic effects include anorexia, hepatotoxicity, chloracne, vascular lesions, and gastric ulcers. Dioxins are by-products of industrial processes involving chlorine and all types of incineration; they are also contained in certain herbicides. Once released into the environment, they are environmentally stable and tend to become associated with sediments or suspended material. Dioxins have the potential to bioaccumulate in the food chain and pose serious risks to ecological and human health. Causes of dioxin production in combustion begin with chlorine compounds in fuel, inadequate supply of combustion air, too low refractory temperatures, and improper mixing of fuel and air.