Dioxins are a group of substances consisting of 7 polychlorinated dibenzo-p-dioxins (PCDDs) and 10 dibenzofurans (PCDFs) with dioxin-like activity. These substances are lipophilic (fat-soluble) and are classified as persistent organic pollutants. Depending on the degree of chlorination (from 1 to 8 chlorine atoms) and the substitution positions, the group of PCDDs can form 75 different congeners, and PCDFs can form 135 different congeners. These congeners can be distinguished from one another.