| Summary: | The production of chlorine by the chlor-alkali process using graphite electrodes was one of the largest sources of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/PCDFs) in history with estimates in the kg TEQ range for individual factories. In addition, the chlorine production predecessor processes in the former Leblanc soda factories generated large amounts of PCDD/PCDFs, also in kg TEQ range for individual sites. In both processes coal tar, used as pitch binder for electrodes in the chlor-alkali process or tars for sealing chlorine chambers, was the major source for PCDD/PCDFs formation. The complex PAH mixture in the tars which were chlorinated in the processes contained approx. 1% dibenzofuran. Therefore in this study we screened the full range of chlorinated aromatic and heteroaromatic compounds in contaminated soils from former chlor-alkali plants in Germany and Japan as well as from a German Leblanc factory, using high resolution time-of-flight mass spectrometry GC-HR-TOF-MS. At all three sites the full range of unintentionally produced persistent organic pollutants (POPs) listed in the Stockholm Convention (PCDFs, PCDDs, PCBs, PCNs, HCB, HCBD and PeCBz) were present at high ppb levels and TEQ was up to several 100,000 ng/kg soil in hot spot areas. Additionally, a wide range of other polychlorinated (PC-) PAHs (PC-phenanthrene/anthracene, PC-pyrene/fluoranthene, PC-benzo(a)anthracene/chrysene) were detected. Some of these compound classes were present in one to two order of magnitude higher concentrations compared to PCDFs. Furthermore, polychlorinated methyl-dibenzofurans, polychlorinated dimethyl-/ethyl-dibenzofurans, and polychlorinated carbazoles – the N-analogue of dibenzofuran - were detected at levels comparable to PCDFs at all three sites.Polychlorinated benzonitriles were detected in addition to chlorobenzenes as monoaromatic pollutant. Since all three factories have stopped production 50–120 years ago, all detected chlorinated aromatics can be regarded as very persistent. The technologies have been used in several hundred locations globally. These (former) chlorine production sites should be assessed for contamination and their contemporary threat to humans and the environment should be evaluated. The toxicity of most of these polychlorinated PAHs and hetero-PAHs is unknown but due to their related structures, similar toxicity profiles can be expected and need to be investigated. Furthermore, all processes where chlorine and complex organic material are present should be screened for the entire resulting chlorinated pollutant mixture, the detailed fingerprints should be documented, and the overall toxicological risk assessed for individual processes to inform policy making.
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