Dioxin, patterns and source identification

The primary sources of PCDD and PCDF are chemical, thermal, photochemical and enzymatic reactions. Most of the thermal sources result in emissions into the air. Analyses of air, soil and sediment samples indicate combustion processes as the major sources. Only 2,3,7,8-substituted congeners are found in higher animals such as fish and mammals. There is a discrepancy in profiles between sources and environmental reservoirs, which cannot fully be explained.