Naturally occurring highly chlorinated organic compounds in soils with elevated OCDD concentration

Elevated octachlorodibenzo-p-dioxin (OCDD) levels have been repeatedly reported in different regions. To date, several hypotheses exist on its origin; however, none of them may be accepted as a universal mechanism. The purpose of this study was to investigate, using a non-target HPLC-HRAM MS-MS/MS approach, what other polyhalogenated organic compounds are present in highly OCDD contaminated soils. More than a 100 highly chlorinated compounds belonging to seven structurally distinct classes were detected and identified in Vietnamese soils. Several compounds had molecular formulas matching those of some natural antibiotics, while others are reported for the first time. Some of the compounds occurred in soils regardless of the OCDD level, while others were intrinsic to the OCDD hotspot and the surrounding area. The great diversity of compound structures with a limited number of isomers and the absence of obvious anthropogenic precursors suggests the presence of a number of natural, probably biogenic, processes leading to their formation and provide further evidence for the OCDD natural origin.