Annex 51 Complementary information to source category 7h Leather Refining
Solid wastes generated by the leather can be classified as follows:
- Wastes from untanned hides/skins (trimmings, fleshing wastes);
- Wastes from tanned leather (shaving wastes, buffing dust); and
- Wastes from dyed and finished leather (trimmings from leather).
In addition to carrying chemicals directly required for or generated by leather production processes, leather production wastes also contain chemicals that are incidental to those processes, such as biocides. For example, in the analysis of eleven organochlorine biocides in raw hides from Europe, America and ten Africa countries, none were found in the European and American hides but one or more were found in 63% of the African hides (Font and Marsal 1998). Indeed, lindane and its residues were found in 56% of the African samples, with concentrations as high as 258 mg/kg. It is evident, however, that other organochlorines occur in European leather production. For example, three different chlorophenols, some at concentrations as high as 500 mg/kg, were measured in “wet blue” leather samples from Italy (Favaro et al. 2008). HCB was detected at a concentration of 3.3 μg/L in a composite sample of wastewater discharged from 100 small and big leather industrial units in India (Kumar et al. 2008). These three studies suggest that organochlorines may be common, if not ubiquitous, contaminants in the wastewater, wastewater treatment sludge and other solid wastes of leather production.
Leather wastes have high calorific values (4500-5000 kcal/kg). However, they also have salt content as high as 2.5% (Ozgunay et al. 2007), and, as indicated earlier, potentially significant levels of organochlorine chemicals. Both sources of chlorine – salt and organochlorine chemicals – may exacerbate PCDD/PCDF formation and release if such wastes are incinerated. For example, combustion of footwear leather waste in a semi-pilot scale incinerator was accompanied by PCDD/PCDF concentrations of 0.841 and 0.355 ng TEQ/Nm3 in the flue gas (Godinho et al. 2009).
In contrast to textiles, once PCDD/PCDF-contaminated PCP is applied to leather, neither PCDD/PCDF nor PCP is easily removed by washing processes. In leather “breast-wallets” concentrations of PCDD/PCDF up to 430 ng I-TEQ/kg, in leather shoes up to 6,400 ng I-TEQ/kg were found (Malisch 1994). Although in many countries, the use of PCP has decreased, at least in shoes, the PCDD/PCDF concentrations did not decrease and in Germany, peak concentrations of 2,100 and 3,000 ng I-TEQ/kg were detected in leather shoes bought in 1991. In the year 1996, highly elevated concentrations continued to exist (Klasmeier and McLachlan 1997). For leather goods, the PCP concentrations correlate with PCDD/PCDF concentrations at least qualitatively. The homologue and congener profiles and patterns strongly indicate that PCP is the source of the dioxin contamination.
The continued use of PCP is evidenced by a case in Germany in which a PCP concentration of >2000 mg/kg was found in a leather jacket, following the discovery of high PCP levels in the plasma of a child and her parents (Heudorf et al. 2003). In 2007, Hedman et al. (2007) found that leather and textiles accounted for 90-95% of total PCDD/PCDF in source-separated combustible domestic waste in Sweden.
A more detailed discussion of leather production processes can be found in the BAT&BEP Guidelines.
Derivation of emission factors
Emission factors for PCDD/PCDF releases to air, water, land, and residues could not be derived due to lack of information. However, it is important to note, to the extent possible, the quantities, methods of treatment, and fate of wastewater, treated wastewater effluents, wastewater treatment sludge, and other solid wastes since PCDD/PCDF releases to water and residues could be high. If wastewater treatment sludge and/or other wastes are applied to land or incinerated or otherwise combusted, this should also be noted since release to air, land and in residues could be high.
EFProduct of 1,000 μg TEQ/t is presented as a reasonable upper limit value, based on values reported in existing studies.
EFProduct of 10 μg TEQ/t is presented as a reasonable lower limit value, based on values reported in existing studies.