Emission factors of unintentional HCB and PeCBz and their correlation with PCDD/PCDF

Hexachlorobenzene (HCB) and pentachlorobenzene (PeCBz) have been listed as unintentional POPs in the annex of the Stockholm Convention and thus, attracted attention by government and researchers. Since the intentional production and use has ceased in most countries, the unintentional releases to the environment have increased. This study gathered 206 and 78 emission factors (EFs) of unintentional HCB and PeCBz from scientific publications and governmental reports, respectively. Most of the EFs referred to the release vector "air" (EF_Air) and to a less extent to "product" (EF_Product). EFs were proposed for different source categories/classes used in the Toolkit according to the technologies that released the HCB or PeCBz. Overall, lowest and highest EF_Air for HCB were found in the metallurgical industry range from 1 μg/t in well controlled plants (coke, iron and steel) up to 40,000 μg/t (secondary zinc). EFs for PeCBz were in similar order of magnitude. Due to lack of data, EFs to water, land or residue cannot be proposed. Using linear regression and statistical analysis such as Pearson correlation, we found strongest correlation of EF_Air between HCB and PeCBz (R² = 0.79, P < 0.01) and weaker, but still significant, correlations for EF_Air between PCDD/PCDFTEQ and HCB (R² = 0.56; P < 0.01) or PeCBz (R² = 0.31 P < 0.01) for various thermal processes.