Dioxin sources to the aquatic environment: Re-assessing dioxins in industrial processes and possible emissions to the aquatic

Releases of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/PCDFs) from industrial or thermal processes to the aquatic environment are considered small compared to emissions to air today. However, industrial processes have occasionally released PCDD/PCDFs into local aquatic environments. . PCDD/PCDF formation and releases were re-examined based on investigations conducted before the introduction of water quality regulations in Japan. Emphasis was given to PCDD/PCDF formation in various industrial processes such as the manufacture of acetylene and caprolactam.In acetylene production, PCDD/PCDFs are formed in the oxidative process using chlorine to remove impurities, with PCDFs formed with the particular chlorine pattern with 1,2,7,8-TetraCDF, 2,3,7,8-TetraCDFs and 1,2,3,4,7,8-HexaCDF as maker congeners and low PCDDs levels. This indicates that acetylene production residues contain organochlorines.In caprolactam production, formation of PCDD/PCDFs in the cyclohexane photonitrosation process has been confirmed and the emission factor for PCDD/PCDF releases to water from for caprolactam manufacture was estimated with an emission factor for releases to the aquatic environment of 0.25 ± 0.04 μg-TEQ/t.A range of additional processes with PCDD/PCDF release were also found during the Japanese survey. Overall, the formation processes were placed in two categories: A) chemical synthesis processes and B) flue gas treatment of high temperature processes. The final effluent water met the PCDD/PCDF limits by applying advanced treatment for PCDD/PCDF removal such as activated carbon treatment. The survey shows that industrial processes involving elemental chlorine or other processes that facilitate chlorination or use chlorinating chemicals should be assessed and controlled for PCDD/PCDFs and other unintentional POPs releases to water. In such surveys, chemicals from the chlorine and organochlorine industry should also be assessed for PCDD/PCDFs and other unintentional POPs contamination as proposed by the UNEP Toolkit. The current study can contribute to the Stockholm Convention implementation of Article 5 of the Stockholm Convention to take measures to reduce the release of UPOPs from anthropogenic sources with the goal of their continuing minimization and, where feasible, ultimate elimination.