These compounds may be found on crops near industrial facilities where both chlorinated organic compounds and elevated temperatures exist. Elevated levels can also be found in meat, dairy, and poultry products through contaminated feed. These compounds are persistent in the environment, and several congeners are toxic. Specifically, those with chlorine substitution at all four corners resulting in a co-planar shaped molecule are identified as toxic to humans. A total of 17 of the 210 dioxin/furan congeners and 12 of the 207 PCB congeners are co-planar. Following extraction and cleanup, GC coupled with high resolution mass spectrometry (HRMS) is necessary to properly measure these toxic co-planar congeners.