TCDD dioxin. Computer model of a molecule of the dioxin 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Dioxins are a family of toxic by-products of a number of industrial processes. They have no industrial use themselves. They are persistent organic pollutants (POPs) and build up over time in living tissue (bioaccumulation). Long-term high-level exposure can cause birth defects, cancer and a higher risk of diabetes. TCCD is one of the most toxic of the dioxins. It was used in an assassination attempt on the Ukranian politician Viktor Yushchenko in 2004. In this molecule, atoms are shown as balls and are colour coded: carbon (grey), oxygen (red), chlorine (green) and hydrogen (white).