What are dioxins and why they harmfu?

Dioxin and  related compounds,i.e. polychlorinated  dibenzo-p-dioxin  (PCDDs), polychlorinated  dibenzofurans  (PCDFs)  and polychlorinated biphenyls (PCBs), are halogenated aromatic compounds which are industrial pollutants that persist in the environment.  In addition to cancer, dioxins have been linked to adverse human health effects such as developmental, immunologic  and endocrine toxicity. The major environmental  sources of dioxin and  dioxin-like compounds (referred  to  simply as "dioxins")  are emissions from combustion, incineration, any industrial processes using chlorine, paper mills, fireplaces, grass fires etc. The aerial transport of these emissions is  the primary  pathway dioxins enter the terrestrial environment and food  chain.