There are 75 PCDD congeners , differing in the number and location of chlorine atoms , and seven of them are especially toxic , the most dangerous being 2 , 3 , 7 , 8 - Tetrachlorodibenzodioxin ( TCDD )
PCDDs are derivatives of dibenzo - p - dioxin .
There are 75 derivatives congeners , differing in the number and location of chlorine atoms , and seven of them are especially toxic , the most dangerous being 2 , 3 , 7 , 8 - Tetrachlorodibenzodioxin ( TCDD )
PCDDs are derivatives of dibenzo - p - dioxin .