Pursuant to Article 5 of the Convention, the following unintentional POPs are listed in Annex C:

• Polychlorinated dibenzo-p-dioxins (PCDD),
• Polychlorinated dibenzofurans (PCDF),
• Polychlorinated biphenyls (PCB),
• Hexachlorobenzene (HCB), and
• Pentachlorobenzene (PeCBz).

Among these, PCDD and PCDF (also collectively referred to as PCDD/PCDF) have never been used as commercial products, nor were intentionally manufactured for any reason other than laboratory purposes. PCB, HCB and PeCBz are also unintentionally formed, usually from the same sources that produce PCDD/PCDF. However, unlike PCDD/PCDF, they have also been manufactured and used for specific purposes, their intentional production and use being by far higher than the unintentional formation and release.

PCDD/PCDF releases are accompanied by releases of other unintentional POPs, which can be minimized or eliminated by the same measures that are used to address PCDD/PCDF releases. When a comprehensive inventory of PCDD/PCDF is elaborated, it allows to identify priority sources, set measures and develop action plans to minimize releases of all unintentional POPs.

It is thus recommended, for practical reasons, that inventory activities be focused on PCDD/PCDF, as these substances are indicative of the presence of other unintentional POPs. They are considered to constitute a sufficient basis for identifying and prioritizing sources of all such substances as well as for devising applicable control measures for all Annex C POPs and for evaluating their efficacy.

Only in the context of research or other projects it is advisable to analyze emissions of all unintentional POPs listed in Annex C in order to produce useful information for the purpose of deriving emission factors.

In addition to emission factors for PCDD/PCDF, the Toolkit also contains emission factors for other POPs when such information is available. Typically, emission factors are provided for the five release vectors, i.e., air (EFAir), water (EFWater), land (EFLand), product (EFProduct), and residue (EFResidue).

The purpose of the “Toolkit for Identification and Quantification of Releases of Dioxins, Furans and Other Unintentional POPs” is to support Parties in preparing PCDD/PCDF inventories that are consistent in format and content, ensuring that it is possible to compare results, identify priorities, mark progress and follow changes over time at the country level, and at the regional and global levels. Towards this end, the Toolkit provides the following “tools”:

• A simple but comprehensive procedure for identifying sources of PCDD/PCDF, including but not limited to the source categories listed in Annex C, Parts II and III;
• Guidance on gathering basic information on the design, operation and/or expected performance of sources that supports their classification and the assignment of appropriate default emission factors;
• Default emission factors – values for the quantity of PCDD/PCDF, expressed as TEQ, released to each vector per unit of activity (e.g., µg TEQ per ton of material produced, per ton of fuel burned, etc.) that have been assigned for each class within the source categories. For the other unintentional POPs, mass concentrations will be assigned as appropriate;
• Guidance on acquiring data and related information to estimate national values for annual activity rates for source categories and/or classes within source categories, e.g., tons per year of waste burned, tons per year of feed material processed, tons per year of product produced, etc.; and
• A spreadsheet to list all source groups, source categories and their associated classes and emission factors, for the five release vectors. This spreadsheet will automatically calculate annual PCDD/PCDF releases from all source categories in a given country or region where national activity data are entered.

The emission factors can be modified in the spreadsheet, i.e., countries may use their own emission factors instead of the default ones, preferably using the same units to ensure comparability of results. Countries can also insert new source categories or classes by adding extra lines into the worksheet to better reflect national circumstances.

The Toolkit is divided into three parts: Part I contains four chapters providing general guidance, Part II contains default emission factors for nine of the ten source groups, and Part III provides complementary information, including 53 annexes and 11 example inventories.

Part I

Chapter 1 - Introduction and Overview summarizes the obligations of Parties under Article 5 and Annex C of the Stockholm Convention, describes the purpose and structure of the Toolkit and the chemicals listed in Annex C, including a brief overview of their formation and sources.

Chapter 2 - Identification of PCDD/PCDF Sources and Estimation of Releases addresses the identification of sources and provides general guidance on gathering information that will allow for 1) sources to be identified and catalogued according to the source category and class to facilitate the selection of the most appropriate default emission factors, and 2) guidance to determine activity rates for each of the classes within each source category.

Chapter 3 - Reporting of Releases explains how to undertake inventory updates and revisions as well as projections of future releases. Finally, the reporting format under Article 15 of the Convention is described.

Chapter 4 - Data Quality provides information on the inventory data quality criteria along with guidance on possible quality assurance and quality control measures and a simple approach to characterize the quality of the inventory results.

Part II

1 – Waste Incineration addresses seven source categories of waste incinerators, the classes within each category and the default emission factors for each class.

2 – Ferrous and Non-Ferrous Metal Production addresses twelve source categories for the production of metals and metal alloys including recycling operations, the classes within each category and the default emission factors for each class.

3 – Heat and Power Generation addresses five source categories of large and small installations using fossil fuels, biomass or gas, the classes within each category and the default emission factors for each class.

4 – Production of Mineral Products addresses seven source categories of processes to manufacture mineral products, the classes within each category and the default emission factors for each class.

5 – Transport addresses four source categories including road and ship transport, the classes within each category and the default emission factors for each class.

6 – Open Burning Processes addresses two source categories of burning biomass or waste without technical equipment, the classes within each category and the default emission factors for each class.

7 – Production and Use of Chemicals and Consumer Goods addresses five source categories of various industrial activities, the classes within each category and the default emission factors for each class.

8 – Miscellaneous addresses an array of five source categories that do not match the description of any other source group, the classes within each category and the default emission factors for each class.

9 – Disposal addresses five source categories related to waste disposal, the classes within each category and the default emission factors for each class.

10 – Hot Spots addresses thirteen source categories that should only be noted in the inventory, where possible, since these categories cannot be further classified and no default emission factors can be designated.

Part III

The following annexes provide complementary information:

Annex 1 - Table of TEFs

Annex 2 - Guidance on identifying sources of PCDD/PCDF

Annex 3 - Questionnaires

Annex 4 - Compilation of all emission factors

Annex 5 - Reporting of releases

Annex 6 - Usage of units in air emissions

Annex 7 - Per capita/GDP emissions

Annex 8 - Data quality

Annexes 9 to 53 provide complementary information to source groups 1-10 and the source categories included in the respective groups.

Eleven example inventories are also included in Part III to illustrate the process of update and revision of inventories, as well as specific examples of inventories for source groups 1-10.

The Toolkit (current version updating and amending edition 2, which was published in 2005) is presented in an electronic version (web-based and CD-ROM). The electronic version of the Toolkit has been developed to increase the availability, portability and storage of information. It delivers the Toolkit’s content in an interactive and dynamic manner. The information is organized in a user-friendly multi-layer structure according to the level of complexity, where information elements are arranged according to the relevance for the inventory process:

• The first layer contains key elements of the Toolkit and essential information for the development of the inventory;
• The second layer of complementary information or additional explanatory material is included in annexes and example inventories accessible via hyperlinks;
• Further complementary information is accessible via pop-up windows;
• Cross-referencing within the Toolkit sections is done via internal links; and
• External links are used to reference outside resources.

Among other features, the web-based tool also offers access to interactive features including a search tool and Excel files for calculating releases. The user is therefore given flexibility in accessing the content of the Toolkit to meet specific information requirements.

The Toolkit has been assembled for the purpose of assisting each country in identifying and quantifying sources of unintentional POPs that are located within the country’s borders and estimating releases from those sources.

Sources of POPs releases are of four general types, three of which are active, ongoing processes, and one is a legacy of historic activities:

• Chemical production processes, e.g., facilities or production units that produce chlorinated phenols or in which certain other chlorinated chemicals are manufactured, or that produce pulp and paper using elemental chlorine for chemical bleaching;
• Thermal and combustion processes, e.g., waste incineration, combustion of solid and liquid fuels, or production of metals in thermal processes;
• Biogenic processes in which PCDD/PCDF may be formed from precursors – manufactured chemicals such as pentachlorophenol that are structurally closely related precursors of PCDD/PCDF.
• Reservoir sources such as historic dumps containing PCDD/PCDF and other POPs-contaminated wastes, and soils and sediments in which POPs have accumulated over time.

The Toolkit presents information on each of the unintentional POPs source categories listed in Annex C, some additional source categories, and a strategy for identifying new source categories. It describes a step-by-step process to estimate PCDD/PCDF releases from each source category to the following environmental media:

• Air,
• Water (surface and ground water, including marine and estuarine water), and
• Land (surface soils),

and to these process outputs:

• Products (such as chemical formulations, including pesticides or consumer goods such as paper, textiles, etc.);
• Residues (including certain liquid wastes, sludge, and solid residues, which are handled and disposed of as waste or may be recycled).

Combustion Processes

PCDD/PCDF and other unintentional POPs can be formed in combustion processes when their component elements – carbon, oxygen, hydrogen, and chlorine – are present and combustion temperatures range between 200°C and 900°C (De Fre and Rymen 1989). Two primary mechanisms for PCDD/PCDF formation during combustion have been proposed:

• De novo formation, in which non-extractable carbon-based structures that fundamentally differ from the PCDD/PCDF undergo transformations and reactions to form PCDD/PCDF; and
• Precursor formation/reactions in which hydrocarbon fragments undergo cyclization or incomplete oxidation to form chemicals that share structural similarities with PCDD/PCDF and that undergo further reactions to finally form PCDD/PCDF.

PCDD/PCDF formation via these mechanisms can take place homogeneously (molecules react entirely in the gas phase or in the solid phase) or heterogeneously (the reactions take place between gas phase molecules and surfaces).

PCDD/PCDF can also be destroyed during combustion when temperatures are sufficiently high, residence times are adequate and mixing in the combustion zone is sufficiently thorough. However, combustion gases must also be rapidly cooled in the post-combustion zone in order to minimize the formation of new PCDD/PCDF in this phase. Variables known to influence PCDD/PCDF formation in combustion processes include the following:

• Technology: Poor combustion, poor mixing in the combustion chamber, poorly designed and managed post-combustion chambers, and inadequate air pollution control devices are associated with increased PCDD/PCDF formation.
• Temperature: Formation has been reported in post-combustion zones and air pollution control devices at temperatures ranging from 200°C to 650°C, with the greatest formation occurring between 200°C and 450°C and peaking at about 300°C;
• Metals: Formation is catalyzed by metals including copper, iron, zinc, aluminum, chromium, and manganese;
• Sulphur and nitrogen: Chemicals containing sulphur and nitrogen have the potential to inhibit the formation of PCDD/PCDF in certain conditions, but may give rise to other undesirable by-products;
• Chlorine: Chlorine must be present. Whether chlorine is present as organic, inorganic or elemental in the materials combusted is relatively negligible. However, its presence in fly ash or in its elemental form in the gas phase may be especially important.

Other variables and combinations of conditions also affect PCDD/PCDF formation. For example, while simulating the burning of household waste in a metal barrel inside a burn hut, Gullet et al. (1999) reported greater PCDD/PCDF formation with 1) increased chlorine in the waste, independent of the original form of the chlorine – organic or inorganic; 2) higher humidity; 3) increased waste load; and 4) higher levels of catalytic metals.

Industrial-Chemical Processes

As with combustion processes, carbon, hydrogen, oxygen, and chlorine must also be present for PCDD/PCDF to form in industrial-chemical processes. In chemical manufacturing processes, PCDD/PCDF formation may be favored if one or more of the following conditions apply (NATO/CCMS 1992, Hutzinger and Fiedler 1988):

• Elevated temperatures (>150°C);
• Alkaline conditions (especially during purification);
• Metal catalysis;
• Ultraviolet radiation or substances that generate radicals.

Among chlorine-containing chemicals, the following groups have been associated with the formation of PCDD/PCDF as byproducts during their production:

• Chlorinated phenols and their derivatives,
• Chlorinated aromatics and their derivatives,
• Chlorinated aliphatic chemicals,
• Chlorinated catalysts and inorganic chemicals.

PCDD/PCDF can be also formed as byproducts of some chemicals that do not contain chlorine when some form of chlorine is present or used during their production.

Application of Toxic Equivalents (TEQ)

Taken as a whole, PCDD and PCDF are a group of 210 tricyclic, chlorine-containing aromatic chemicals; there are 75 congeners of PCDD and 135 congeners of PCDF possible. PCDD and PCDF typically occur as mixtures. The most toxic compounds have chlorines in the 2, 3, 7 and 8 positions; they have been assigned a toxicity equivalency factor (TEF) based on the relative potency of each congener in comparison to the most toxic congener, 2,3,7,8-tetrachlorodibenzo-p-dioxin. In total, there are 17 congeners in which chlorine atoms occur at the 2, 3, 7, and 8 positions. Mixtures of these congeners are often evaluated and reported as a single number called toxic equivalent (TEQ). To determine the TEQ of a mixture, the mass concentration of each congener is analytically determined, multiplied with the assigned TEF, and the products summed. The first scheme, derived by the Committee on the Challenges of Modern Society of the North Atlantic Treaty Organization in 1988 and called I-TEFs, covered 17 PCDD/PCDF. Subsequent revisions of TEFs have been coordinated by the World Health Organization (WHO) in 1997 and 2005. These revisions also included 12 dioxin-like polychlorinated biphenyls (dl-PCB). For PCB, the compounds having the highest toxicity are those in which the molecule can assume a planar configuration, analogous to that of PCDD/PCDF.

To estimate PCDD/PCDF releases in inventories, the Convention requires that the most advanced TEFs are used. These are, at present, the WHO-TEFs established by a WHO/IPCS expert meeting in 2005 (van den Berg et al. 2006) (see Annex 1). However, these have not yet been recognized or adopted by the Conference of the Parties. For the purpose of the Toolkit and its “order-of-magnitude” estimates of emission factors, the differences between the WHO-TEFs (either from 1998 or 2005) and the international TEFs (I-TEFs) previously established by the Committee on the Challenges of Modern Society of the North Atlantic Treaty Organization in 1988 are negligible. Therefore, the TEF-scheme accompanying the emission factors is not specified in the Toolkit. When reference is made to measured values, the TEF scheme used should be included.

An inventory can provide valuable information on the magnitude of releases to each environmental medium and in products and residues. It can highlight sources for possible impacts but it cannot provide an accurate guide to the relative impact of these releases on human or ecosystem exposure since the fate of PCDD/ PCDF varies considerably from one release source to another. The main purpose is to identify sources of unintentional POPs, prioritize them and undertake measures to prevent the formation and reduce or eliminate releases of unintentional POPs. Furthermore, measures taken to address PCDD/PCDF releases are equally suitable for other unintentional POPs.

The default emission factors presented in the Toolkit are best estimates derived from experimental results at well-documented sources (i.e., taking into account technology, process characteristics and operating practices) or otherwise based on expert judgment. The results obtained for processes with similar characteristics are then aggregated into one emission factor representing "order of magnitude" release estimates, which do not describe accurately PCDD/PCDF releases from individual plants/facilities.

The default emission factors are assigned data quality ranks to enable an informed approach to estimating PCDD/PCDF releases. They should be applied with the specified level of confidence only when matching a specific situation in certain national circumstances. Annex 8 provides more information on data quality issues related to both emission factors and activity rates.

Most importantly, the Toolkit offers focused guidance on inventorying sources and releases of unintentional POPs. The Toolkit is based on systematic expert consultation, and can thus be considered as the most comprehensive and up-to-date compilation of emission factors for unintentional POPs.