2,4,6-Trichlorophenyl-4’-nitrophenyl ether (CNP) or chloronitrofen has been used as an alternative for pentachlorophenol with intensive applications in rice paddies in Japan. CNP has been found to contain high concentrations of PCDD and PCDF. Especially, batches produces in the 1970s and early 1980s had contamination in the range of 240 to 540 μg TEQ/kg; later productions showed lower concentrations in the range of 400 ng TEQ/kg (Masunaga et al. 2001). There is no further information on the synthesis and what might have caused the decrease in the contamination level in the more recent batches.
The emission factors for CNP is 300,000 μg TEQ/t using old technologies and 400 μg TEQ/t with new technology.
PCDD/PCDF formation concerns only trichlorobenzene, in a specific process, which does not exist any longer today (Source: EURO CHLOR). Mono- and dichlorobenzenes are produced commercially by the direct chlorination of benzene in the liquid phase in the presence of a Lewis acid catalyst such as ferric chloride (FeCl3) or oxychlorination of benzene with HCl in the presence of oxygen (NATO/CCMS 1990, EHC 1991). 1,4-Dichlorobenzene (p-DCB) is one of the chemicals used to make mothballs, commonly called paramoth. As such it has been used as a deodorant for garbage and restrooms, as well as an insecticide for control of fruit borers and ants. It may be applied to tobacco seed beds for blue mold control, for the control of peach tree borer, and mildew and mold on leather and fabrics (HSDB 2004).
The formation of PCDD/PCDF is not obvious from the reaction mechanisms mentioned above but probably occurs during purification where alkaline conditions are often used.
Early PCDD/PCDF analyses performed in the 1980s were not capable to analyze congener-specific concentrations of 2,3,7,8-substituted congeners and thus, in the 1990 NATO/CCMS report, only homologue data were provided, which do not allow to assign an emission factor as TEQ. Recently, PCDD/PCDF concentrations on TEQ basis have been reported in chlorobenzenes (Liu et al. 2004; Table 61). Six samples have been collected from the production process of dichlorobenzenes (o-DCB and p-DCB) and trichlorobenzene (124- TCB); the samples S4, S5, and S6 represent the purified products from the Chinese manufacturer synthesized via chlorination of benzene and chlorobenzene with a Friedel-Crafts catalyst (FeCl3) (Yanzh Pesticide Co., Ltd.).
Table X: Concentrations of PCDD/PCDF in chlorobenzenes (Liu et al. 2004)
Intermediate: mixture of DCB after distillation and separation from monochlorobenzene
p-DCB: after distillation and crystallization (98.1%)
o-DCB: after distillation and crystallization
Purified 1,2,4-trichlorobenzene (124-TCB)
From the above results, the default emission factors as shown in Table X will be derived. It should be noted that the emission factors in the residues relate to the mass of these residues generated in the production of di- and trichlorobenzene. It can be seen that most of the PCDD/PCDF is left in these heavy ends (sample S3). Their releases should be estimated only if the residues are taken out of the process and be disposed of. In cases where the residues are being used as raw materials into other synthesis processes, these concentrations will not be reflected in the national release inventory.