Historically, the first observations of contamination with PCDD/PCDF were from the manufacture of chlorinated phenols and their derivatives. PCDD/PCDF can be formed in chemical processes where chlorine is involved. The following processes have been identified as sources of PCDD and PCDF with a decreasing probability of generating PCDD/PCDF from top to bottom:
Manufacture of chlorinated phenols and their derivatives,
Manufacture of chlorinated aromatics and their derivatives,
Manufacture of chlorinated aliphatic chemicals,
Manufacture of chlorinated catalysts and inorganic chemicals.
Within the chemical industry sector, the most critical parts in the manufacturing processes are the oxychlorination process to manufacture ethylene dichloride (EDC), which is usually found as part of the manufacture of chlorinated organics.
It should be noted that the conditions, which favor the formation of PCDD/PCDF in wet chemical industrial processes are different from those that favor the formation of PCDD/PCDF in thermal processes. For chemical manufacturing processes involving chlorine, the generation of PCDD and PCDF is favored if one or several of the conditions below apply (for further information on formation mechanisms of PCDD/PCDF, see UNEP Chemicals 2003a, NATO/CCMS 1992b):
High temperatures (>150°C)
Alkaline conditions (especially during purification)
UV radiation or other radical starters.
The following subsections list products which have been found to contain PCDD and PCDF or the process of their manufacture has been associated with the formation of PCDD/PCDF. It should be noted that some countries have published lists of chemicals that must be tested for PCDD/PCDF before being placed on the market. Such lists include many chemicals that were or are suspect of containing PCDD/PCDF concentrations above certain limits. For most of the chemicals, the PCDD/PCDF concentrations are below the threshold. Several chemicals are intermediates in the manufacture of other chemicals; the PCDD/PCDF contamination of these intermediates is either transferred to the final product (e.g., in the case of the chloranil-based dye pigments, old process) or will be found in production residues (and then mostly associated with the residues from the oxychlorination process).
In all cases where plants are identified to manufacture the chemicals listed in the following subsections, it is recommended to characterize the processes in place by starting with the raw materials and conditions applied through purification steps applied and ending with amounts and treatment of residues from the process (e.g., what type of treatment is applied to effluents and how much residue is produced – where does it go). The main uses and customers for the products and any available data on levels of PCDD/PCDF in products, residues and effluents will help in compiling the inventory.
Since the design of the processes and the handling of effluents and residues has such a profound effect on the formation of PCDD/PCDF and any releases to the environment, it is not possible to provide default emission factors for the different processes discussed in this section. The suggested approach for assessing releases from the chemical industry is to identify production facilities for the chemicals listed, to detail the processes used, the purification applied, the production and treatment of residues and by-products. Further, it is important to know about the fate of the residues (landfill, by-product recovery, incineration, etc.). As many of these chemicals may be used in formulations, these should be identified as well as the uses for each product. It may be possible to assess in general terms the flow of PCDD/PCDF in the product and also to identify entry points to the environment. Any information on the disposal of materials treated with the chemicals will be valuable, too.
Some of the chemicals may not be produced in the country but may be imported as final products (i.e. formulations) or intermediates. In other cases, products may be imported which have been subject to treatment with one of the chemicals (e.g., wood treated with PCP). Imports should be noted and quantified if possible and the uses noted. On the other hand, there may be plants in a country, where chemicals listed in this section are synthesized for export (only). Whereas the potential PCDD/PCDF releases occurring during the production phase should be accounted in the country’s inventory, the PCDD/PCDF releases associated with the use or the disposal of these chemicals should show up in the recipient country.
PCDD/PCDF emission factors are listed for different activities in the following sections. Detailed information on how these emission factors have been derived can be found in Annex 48.5
Owners/operators of the relevant facilities (by questionnaires);
State, provincial, national and/or international agencies that gather centralized statistical information.
Data quality rating is provided for the default emission factors
Pentachlorophenol (PCP) and Sodium Pentachlorophenate (PCP-Na)
Pentachlorophenol (PCP) and sodium pentachlorophenate (PCP-Na) are pesticides and used as a preservative for e.g., wood (indoor and outdoor), leather, textiles (including cotton or wool). Pentachlorophenol (PCP) is a chlorinated hydrocarbon insecticide and fungicide. It is used primarily to protect timber from fungal rot and wood-boring insects. PCP products are very toxic to plants and are used as pre-harvest defoliants and general herbicides. Technical mixtures containing PCP or PCP-Na have been marketed under numerous trade names.
The predominant use of PCP was as wood preservative at least until the end of the 1980s. In the USA, 95-98% of American PCP production is used directly or indirectly in wood treatment. Data from Canada (95%) and Germany (61%) confirm the main use of PCP as a wood preservative. In Germany, however, considerable amounts of PCP were used by the textile (13%), leather (5%), mineral oil (6%), and glue (6%) industries in 1983 (WHO 1987).
The sodium salt of pentachlorophenol (PCP-Na) is utilized primarily in aqueous solution. It is used as an antifungal and antibacterial, and has applications in the following areas:
a wood preservative (fungicide and anti-blueing agent),
an agent for the impregnation of industrial textiles (fungicide),
bactericide in tanning and the paper pulp industry,
a molluscicide in the treatment of industrial water, in particular cooling water, and sometimes as
a sterilizing agent.
Because of its toxicity, PCP has been made subject to various restrictions in more than thirty countries.
Pentachlorophenol contains dangerous impurities including up to 0.1% of PCDD/PCDF and 1-5% of polychlorinated phenoxyphenols. PCDD/PCDF are emitted when products treated with PCP are exposed to the sun and when they are improperly burned at the end of their useful life. PCP in sewage sludge is also a source of PCDD/PCDF (EC 1996).
There are three major processes for the commercial production of pentachlorophenol (NATO/CCMS 1992a):
The most common method is the direct chlorination of phenol with chlorine gas in the presence of a catalyst. The reaction results in the formation of byproducts such as hydrogen, hydrogen chloride and PCDD/PCDF.
Hydrolysis of hexachlorobenzene with sodium hydroxide. PCDD/PCDF are formed as unwanted byproducts. This process was used only in Germany.
In China, PCP is manufactured via thermolysis of hexachlorocyclohexane (HCH) (Wu 1999).
Overall, there are two processes to manufacture PCP-Na:
Hydrolysis of hexachlorobenzene (HCB) with sodium hydroxide. This process was applied in Germany until 1984 (then, method (2) with PCP as the starting material has been used).
Dissolution of PCP in sodium hydroxide. After filtration, the PCP-Na solution is being concentrated.
Normally, the PCDD/PCDF contamination in PCP-Na is lower as in the PCP as some contamination is eliminated through the filtration process.
The contamination of PCP and PCP-Na with PCDD and PCDF varies from some μg I-TEQ/kg to 1-2 mg I-TEQ/kg depending on the manufacturing process and the compound. Today many countries have banned the use of pentachlorophenol and its sodium salt. In the EU, Directive 91/173/EEC prohibits the marketing and use of pentachlorophenol and its salts and esters in a concentration equal to or greater than 0.1% by mass in substances and preparations. However, four exceptions are given. The use of pentachlorophenol and its compounds in industrial installations is permitted:
as a synthesizing and/or processing agent in industrial processes;
for the in situ treatment of buildings of cultural and historic interest (subject to individual authorization by the Member State concerned).
In any event, PCP used as such or as a constituent of preparations must have a total Cl6DD (hexachlorodibenzo-para-dioxin) content of less than four parts per million (4 ppm). Remaining principal uses are the high-pressure treatment of (telephone) poles, railroad ties, and wooden fences (see source group 10).
A considerable flow of PCP into a country may occur through the imports of the chemical substance itself as well as of PCP-treated products such as wood (also as furniture) or textiles and leather. Tracing these flows can be very difficult.
The default emission factor for PCP manufactured via processes (1) or (2) described above is 2,000,000 μg TEQ/t product (200 μg TEQ/kg product). The Chinese production line will give an emission factor of 800,000 μg TEQ/t.
The default emission factor for PCP-Na is 500 μg TEQ/t product. Note: Santl et al. (1994) detected 3,400 μg TEQ/kg in a PCP-Na sample from France in the year 1992.
Emissions of PCDD/PCDF to air from materials treated with PCP are difficult to quantify and may be controlled by site-specific factors and releases from the disposal of PCP-containing materials by combustion can lead to high emissions of PCDD/PCDF, which cannot be adequately addressed here. However, the impact on the emission factors when combusting PCP-contaminated wood can be seen in 3d Household heating and cooking with biomass and also contributes to higher emissions in uncontrolled burning processes (see 6b Waste burning and accidental fires).