PCDD/PCDF formation in the chlor-alkali process—laboratory study and comparison with patterns from contaminated sites

Abstract

Studies on the formation of polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) during the electrolysis of sodium chloride solution (brine) using graphite or titanium electrodes were carried out at a laboratory scale. High concentrations of PCDFs but no PCDDs were formed in tests using graphite electrodes. With titanium electrodes, PCDFs were only formed when tar pitch was added and mainly originated from the dibenzofuran present in the tar. For the first time, a detailed assessment of the formation of mono- to octachlorinated PCDD/PCDF from tar pitch was investigated. The assessment included of the chlorination steps proved that PCDFs were formed by successive lateral chlorinated from dibenzofuran to MonoCDFs, DiCDFs, and TriCDFs to form the typical known "chlorine pattern" of TetraCDF to OctaCDF with a dominance of 1,2,7,8- and 2,3,7,8-TetraCDFs, 1,2,3,7,8-PentaCDF, and 1,2,3,4,7,8-HexaCDF as marker congeners. The final homologue distributions depended on reaction time and reaction temperature. In addition, electrolysis with non-chlorinated dibenzo-p-dioxins, dibenzofuran, and biphenyl was carried out. As a result, PCDDs, PCDFs, and PCB were formed at comparable yields. Congener patterns in soil samples from a PCDD/F-contaminated site where chlor-alkali electrolysis had been operated for decades in Japan had identical isomer distribution demonstrating the source and contamination potential and risk of these processes. Therefore, sites where in the past 120 years chlor-alkali electrolysis has been operated or where residues from chlor-alkali production or other chlorine using industries have been disposed should be assessed for their pollution level and exposure relevance. The assessment of total organohalogen content revealed that PCDF is only a small fraction of organohalogens in the contaminated soils. For an appropriate risk assessment, also other chlorinated aromatic compounds such as PCBs or PCNs need to be considered.

Distribution of Polychlorinated Naphthalenes in Sediment From Industrialized Coastal Waters of Korea With the Optimized Cleanup and GC-MS/MS Methods

“…This indicates that these industries could be primary sources of PCN contamination. Previous studies have reported that the metal and non-ferrous smelting processes are major contamination sources of PCNs in the environment (Yamamoto et al, 2018;Hu et al, 2021;Shen et al, 2021). In our study, the highest PCN concentrations were observed in sediment from Daejeong Stream (D1-D4; 6,000 ± 10,400 pg/g dry wt), surrounded by non-ferrous (zinc, copper, and aluminum) industries.…”

Unexpected Dioxin Formation During Digestion of Soil with Oxidizing Acids

“…The congener profiles of digested samples exhibited similar characteristics as those resulting from industrial thermal processes, especially disposal of municipal household waste and sewage treatment plant sludge in cement kilns. , That is, ΣPCDFs ≫ ΣPCDDs, with a significantly higher percentage of ΣCl 4‑6 CDFs. − PCDD/Fs formation upon digestion of soil with aqua regia might also follow a de novo synthesis mechanism with soil minerals functioning as catalysts, which would be similar to fly ash acting as a catalyst in industrial thermal processes. − In addition, the congener profiles of PCDD/Fs in digested samples exhibited similar characteristics as those from chlorine bleaching processes used by wood or non-wood pulp mills, with 2,3,7,8-TCDF having the highest concentration among congeners. − , The chlorination of possible precursors, such as DBF, DBD, and/or other oxygenated aromatic rings (PAH), is considered to be the main process of PCDD/Fs formation during the chlorine bleaching process. − Therefore, the chlorination of possible precursors in soil by the chlorine produced from aqua regia might also account for PCDD/Fs formation. As such, the mechanism of PCDD/Fs formation during soil digestion with aqua regia needed to be further explored.…”

Formation of polychlorinated dibenzo-p-dioxins and furans (PCDD/Fs) in the electrochemical oxidation of polluted waters with pharmaceuticals used against COVID-19

“…Especially if precursors such as chlorinated organic compounds are present, some degradation products more hazardous than the parent compounds such as PCDD/Fs can be formed, as a consequence of the presence of ● OH radicals present in the bulk solution facilitating coupling of aromatic compounds [73] , [116] , [117] . In the presence of elemental chlorine or another chlorinating agent even non-chlorinated organic compounds such as polyaromatic hydrocarbons or phenol can be chlorinated and form PCDD/Fs [118] , [119] . For this reason, the analysis of the PCDD/Fs’s formation has been performed for all the degraded compounds in this study.…”