Certain processes for the manufacture of chlorine have been associated with high formation and releases of PCDD/PCDF and other unintentional POPs (Weber et al. 2008a,b). In addition to well-documented releases from the chlor-alkali process (Otto et al. 2006), earlier chlorine production using the Weldon or Deacon process has also resulted in PCDD/PCDF contaminated sites (Balzer et al. 2007, 2008).

I. Chlor-alkali production

The manufacture of chlorine using graphite anodes generates PCDD/PCDF contamination of the residues. Contamination levels close to 4 mg TEQ/kg in chloralkali residues have been reported; contaminated soil samples ranged from 0.15 μg I-TEQ/kg to 23.1 μg I-TEQ/kg (She and Hagenmaier 1994, Otto et al. 2006). The only chlor-alkali production site for which a PCDD/PCDF inventory has been published was operated in Rheinfelden/Germany. The deposited residues and contaminated soils were estimated to contain a total of 8.5 kg I-TEQ PCDD/PCDF from residues of the chloralkali process (see example 10aI).

Chlorine was produced almost exclusively using graphite anodes until it was gradually replaced by metal anodes and other technologies starting with the 1970s. The graphite residue was highly contaminated with PCDF, PCN and other chlorinated PAHs mainly from the reaction between chlorine and the pitch binder (Takasuga et al. 2009). In developing regions, graphite anodes have been used until recently and might possibly still be in use.

Primary locations for contamination from these operations include soil and, if leaching has occurred, neighbouring compartments and eventually sediments of nearby rivers. High concentrations of mercury are relevant indicators for contamination with PCDD/PCDF as well. Barium levels in the deposited chlor-alkali residues were also found to be a useful and inexpensive monitoring parameter for tracking contamination of residues and deposits. This approach has been used for screening and mapping a German site impacted by widespread chlor-alkali residues (Otto et al. 2006; see example 10aI).

II. Leblanc process and associated chlorine/bleach production

High concentrations of PCDF (and minor concentrations of PCDD) were formed by Leblanc Soda and associated processes. PCDD/PCDF levels of up to 500 µg TEQ/kg have been reported in deposits from a former German Leblanc factory (Balzer et al. 2007, 2008; see example 10aII). The Leblanc process was extensively used until early 20th century to produce sal soda/sodium carbonate (Na2CO3) from sodium chloride (NaCl). The waste from this process (HCl) was recycled in some facilities by oxidation to produce chlorine/calcium hypochlorite (bleaching powder) either via manganese oxide (Weldon process) or by CuCl2 catalysts (Deacon process) (Weber et al. 2008a,b, Encyclopaedia Britannica 1911). The major source of PCDD/PCDF precursors was coal tar which was used as a filler and surface protection material. In addition to PCDD/PCDF, other unintentionally produced POPs and chlorinated aromatic compounds were formed (Takasuga et al. 2009, Bogdal et al. 2009).

Leblanc factories were predominantly operated in the UK, France and Germany with a few facilities in other European countries (Balzer et al. 2008; see example 10aII). For inventories of former Leblanc factory sites, it is important to assess if the factory recycled HCl to chlorine/bleach, as recycling would be associated with high PCDD/PCDF levels in the wastes and likely contamination of the land where these wastes were deposited. In addition, PCDD/PCDF contamination has been found in areas where Leblanc ovens have been operated and since demolished (Balzer et al. 2008).

The largest PCDD/PCDF contaminated sites and hotspots have been generated by the production and application of chlorinated organics. For some production processes, other unintentionally produced POPs were/are major residues. Furthermore, considerable quantities of product, either remaining in the residues or as faulty batches, were deposited on or close to the production sites. A prime example is lindane/HCHs, with only approximately 15% of the total mass emerging as product, and the remaining 85% representing HCH waste isomers, dumped in the vicinity of the production facilities. The production of DDT and endosulfan also generate large amounts of wastes containing POPs which have often been landfilled. Wastes from the organochlorine industry are now destroyed in BAT/BEP incinerators in developed regions. However, these wastes were often landfilled or dumped until the 1970s/1980s. In developing regions, such wastes might still be landfilled nowadays.

The inventory of such production sites and related contaminated sites should consider:

• The former and current production portfolio should be assessed for chemicals containing or possibly containing PCDD/PCDF, HCB or other unintentionally produced POPs (see Annex 2 and example 10bIII). The highest concentrations of PCDD/PCDF are expected to be associated with the production of chlorinated phenols, their derivatives, and other chlorinated aromatic compounds. However the production of non-aromatic chemicals like chlorinated solvents has also generated wastes containing unintentional POPs e.g. 10,000 tons of unintentionally produced HCB from single production sites (Weber et al. 2011b).
• Former and current management practices for waste residues should be reviewed and an inventory of related production sites, stockpiles and landfills should be developed (see examples 10bII and 10bIII).
• Contamination with PCDD/PCDF of buildings and soil is likely to be found at current or former production sites of chlorinated organics.
• If wastewater was discharged into receiving waters, sediments and floodplains of entire river systems or bays can be contaminated (see example 10bI).
• If wastewater has been allowed to settle in ponds, sediment or sludge from these settling ponds can contain high concentrations of PCDD/PCDF.

I. Production sites of chlorophenol

High concentrations of PCDD/PCDF can be expected at sites where chlorinated phenols were produced. In the case of Times Beach, USA, were production residues were spread, contaminated soils have been reported as having concentrations of up to 33,000,000 ng TEQ/kg (Rappe 1984). Levels around factories can be as high as 200,000 ng TEQ/kg (di Domenico et al. 1982). Where production residues have been released via water discharge, sediments can be polluted with tens of kg TEQ (Verta et al. 2008; see example 10bI). PCDD/PCDF in related deposits are reported to total 7.7 kg TEQ for a PCP production facility in Germany (Otto et al. 2006; see example 10bI) and 22.3 kg from a 2,4,5-T production site also located in Germany (Götz et al. 2012).

II. Former lindane production where HCH waste isomers have been recycled

In the production of lindane (gamma-HCH), approximately 85% HCH waste isomers are formed in the chlorination step of benzene as unintentionally produced POPs (Vijgen et al. 2011). The active gamma-isomer used to be separated and the remaining 85 to 90% waste isomers, consisting mainly of alpha-HCH and some beta, delta and epsilon-HCH, were dumped. This practice has generated the largest international POPs stockpile, estimated at 4 to 7 million tons, often dumped in the vicinity of the factories (Vijgen et al. 2011). To avoid such dumping, waste isomers have been recycled at some production sites (Vijgen et al. 2011; see example 10bII). Recycling of HCH by thermal decomposition to produce technical tri/tetrachlorbenzene generated highly contaminated residues containing 1.4 to 13% PCDD/PCDF with I-TEQ in the high ppm range (90 to 610 ppm) (Vijgen et al. 2011, Zheng et al. 1999). The total PCDD/PCDF amount in registered waste disposed of by a German factory was estimated to be between 333 and 854 kg PCDD/PCDF I-TEQ (53 -102 tons total PCDD/PCDF) (Götz et al. 2012; see example 10bII). Since the recycling of HCH waste has been carried out at several lindane production sites, related contamination can also be expected at these sites (Vijgen et al. 2011).

III. (Former) production sites of other chemicals known or suspected to contain PCDD/PCDF or other unintentional POPs

A wide range of production residues from organochlorine chemicals can be considered to be contaminated with PCDD/PCDF or other unintentionally produced POPs (see Annex 2). Some data may be available for levels in products (see Source Group 7), however data on levels of PCDD/PCDF or other unintentionally produced POPs in the residues have not been published. Emission factors for most residues are currently not available and will depend on the specific technologies used. Detailed data for the inventory need to be generated for the individual sites including information on the (former) products and intermediates and the respective management and disposal procedures. These production sites and related deposits can be inventoried as potentially contaminated with PCDD/PCDF, noting that “further assessment is necessary”. As an example, an inventory has been compiled for the production wastes generated and landfilled by the Basel Chemical Industry (see example 10bIII).

IV. Production sites of chlorinated solvents and other “HCB waste”

In the production of certain solvents (e.g. carbon tetrachloride, tetrachloroethene, trichlorobenzenes, trichloroethene, trichlorotoluenes), large amount of wastes containing HCB as a prime contaminant (“HCB waste”) are generated (Jacoff et al. 1986, Jones et al. 2005). For one facility, an emission factor of 1.8% was calculated on the basis of the solvents produced (see example 10bIV; Weber et al. 2011b). Other studies have estimated that 4% of “HCB waste” is generated from tetrachloroethene production. For some solvent production, it is reported that individual factories have deposited or stored some 10,000 tons HCB waste (Weber et al. 2011a,b). Some of these wastes also contained relevant levels of PeCB (see example 10bIV).

For an inventory of deposits and dumps from solvent production, the following steps are recommended:

• Establish the total quantities of organochlorine solvent produced at the site.
• Establish whether specific factors for factory-generated wastes or data on the total deposited wastes are available. Otherwise a factor of 2% “HCB waste” for the solvents mentioned above can be used.
• Assess the waste management practices over time i.e. the time over which the wastes have been deposited, when improved treatment/destruction capacity for production residues was added.
• Mapp and assess the deposits, associated contamination and related risks.

HCB is also the prime unintentional POP contaminant in the production of certain pesticides (e.g. PCNB, PCP, dacthal, daconil, hexachlorcyclopentadiene) (Jacoff et al. 1986) and of tetrachlorophthalic acid and related dyes such as chlorinated phthalocyanines (Government of Japan 2007). A similar approach to the assessment of “HCB waste” from solvents can be used for these sites.

V. (Former) PCB and PCB-containing materials/equipment production

PCB and PCB-containing materials (varnish/paints, sealants, etc.) were produced at chemical plants, and PCB-containing equipment at electrotechnical plants. According to Fedorov (1993) and Ishankulov (2008), annual releases of PCB into the environment from production processes of PCB-containing capacitors at the Ust-Kamenogorsk plant in Kazakhstan generated some 188-227 tons PCB (10-12% of the total PCB used). These releases lead to significant environmental contamination with PCB and PCDD/PCDF, in particular at production sites. These sites can thus be treated as potential hot spots. In addition, storage sites of solid waste and sewage sludge from such facilities are also potential hot spots.

The procedure for revealing such hot spots includes the steps described below:

• A compilation of a list of enterprises where PCB and PCB-containing materials/equipment have been produced;
• Collection of general information about the enterprises (location, the area occupied by the plant, production timeframe, volume of PCB production or PCB used, volume of PCB-containing waste, waste water and sewage sludge, emissions via these vectors, etc.);
• Localization of dumps of PCB-containing waste and sewage sludge storage;
• Collect information on PCB leakages, monitoring of POPs content in the environment, etc;
• Estimation of PCDD/PCDF discharges into the environment based on PCB leakages data.

These sites include locations where pesticides and other chemicals containing PCDD/PCDF have been applied. Dioxin-containing herbicides/pesticides such as 2,4,5-T, 2,4-D, PCP or others have been applied in agriculture or for clearing vegetation. In Vietnam, spraying of the defoliant Agent Orange and other 2,4,5-T/2,4-D containing agents during 1963-1970 caused extensive environmental contamination and human exposure (Schecter 1994, Allen 2004) releasing some 366 kg TEQ (Stellmann et al. 2003). A comprehensive inventory for historic agricultural pesticide use (mainly PCP and CNP) has been established for Japan and is estimated at 460 kg TEQ, having migrated partly from agricultural fields to river sediments and sea (see example 10c). The human milk contamination measured in Japan today is correlated to former pesticide use (Tawara et al. 2006, Weber et al. 2008a,b).

The use of other organochlorine chemicals having resulted in large contaminated sites are e.g. solvents such as tetrachloethene or trichlorethene, which can be contaminated with HCB and PeCB.

For establishing a country inventory, either own PCDD/PCDF data measured from historic pesticides and other chemicals, or emission factors established by other studies might be used (see example 10c). The impacted areas and nearby river systems should be included in the inventory. PCDD/PCDF levels in grazing animals and milk, or in fish in the affected water systems might be assessed.

Saw mills and timber manufacturing sites are often associated with the use of pentachlorophenol. Soils and sediments can be contaminated with PCDD/PCDF as these industries use large volumes of water and are often located close to rivers. The application of PCP in Sweden, for example, has released between 5 and 50 kg TEQ on these sites, and a further 200 kg TEQ in the product (Swedish EPA 2005). As PCP and PCP-Na have a much higher water solubility and shorter half-lives, the concentration of PCP in soils or sediments can only give approximate indications of PCDD/PCDF contamination.

Inventories can be established using former application quantities and contamination levels. In addition to an inventory of PCP application sites, a rough inventory of former PCP use and related PCDD/PCDF in treated wood might be established.

PCDD/PCDF and other unintentionally produced POPs containing chemicals like PCP, chloranil and certain dyes have been, and sometimes still are, used in this sector. Contaminated sites or hotspots can be expected at production sites where these chemicals have been stored, used and discharged. In particular, adjacent sediments and waste deposits are likely to be contaminated. Areas where sludges from production or from wastewater treatment have been applied can also be contaminated and should be included in the inventory.

The use of PCB has generated a large number of sites and hotspots contaminated with PCDF and dioxin-like PCB via production, use in industries, releases from equipment and open applications (see examples 10fI and 10fII). Commercial mixtures of PCB contain dioxin-like PCB, non-dioxin-like PCB and PCDF, with a major TEQ contribution (> 90%) from dioxin-like PCB (Takasuga et al. 2005). PCDF releases can only be estimated based on of the amount of PCB leaked. For this assessment, the total TEQ of PCDF and dioxin-like PCB needs to be considered. With the increasing age of the equipment and longer time of operation, PCDF concentrations in equipment fillings increase, and in the case of high thermal stress (fire event, short circuit) PCDF become the main TEQ contributor.

About 60% of the total volume of PCB was used as dielectric fluids in transformers and power capacitors globally (Breivik et al. 2007, Willis 2000). The open uses of PCB, largely as sealants and paints in buildings and in industrial installations, can be considered as hotspots.

If the transformers and capacitors are in a good condition and well maintained, with no leakage, PCB and PCDF are not released into the environment. Once the equipment is leaking, PCDF together with PCB and possibly PeCB will subsequently be released into the surroundings, in soils and sediments. PCB can serve as an indicator for PCDF contamination.

Sites with PCB-containing equipment in use or storage should be treated as potential hotspots. The number of such sites per country may be rather large (see example 10fI; Kukharchyk and Kakareka 2008).

The main tasks for inventorying PCB-contaminated sites and hotspots are:

• Identification/localization of sites where PCB-containing transformers and capacitors are in use or stored, including damaged equipment and PCB waste and sites of open PCB application;
• Identification of PCB leakage;
• Development of the hotspot list;
• Assessment of volumes of PCB leakage and releases of PCDD/PCDF;
• Assessment of PCDD/PCDF concentrations in
  • PCB transformers/capacitors from producers where PCDF levels are currently unknown;
  • Sites where transformer fires, short circuits or other fires involving PCB have occurred.

The identification and assessment can be performed based on a tiered approach as presented below.

1. Baseline approach

The basis for hotspots accounting is the national inventory of PCB according to Annex A, Part II of the Stockholm Convention. All sites where PCB-containing equipment can be found in use or storage are treated as hotspots. The baseline approach allows the assessment of the total number of potential hotspots, total volumes of PCB and PCDD/PCDF in PCB-containing equipment, as well as potential leakages of PCB and PCDD/PCDF into the environment, using the results of the national PCB inventory.

To differentiate between lower and higher chlorinated PCB congeners, as needed for estimating PCDD/PCDF releases, it can generally be assumed that capacitors are filled with lower chlorinated PCB, while transformers include higher chlorinated PCB with associated PCDD/PCDF levels (Table II.10.1).

For a preliminary assessment of PCB releases into the environment, emission factors given in the EMEP/EEA Atmospheric Emission Inventory Guidebook (2009) may be used (Table II.10.1). Using data on the volumes of lower and higher chlorinated PCB and PCDD/PCDF content in PCB liquids (Table II.10.2), it is possible to estimate PCDD/PCDF and dioxin-like PCB content in PCB equipment and their environmental releases.

Table II.10.1 PCB release factors from electrical equipment

10f	PCB Filled Transformers and Capacitors	PCB release, kg/t dielectric fluid	Country or region
1	Transformers	0.06	Europe
		0.3	North America
		0.3	CIS countries
2	Capacitors	1.6	Europe
		4.2	North America
		2.0	CIS countries

Table II.10.2 Concentrations of PCDD/PCDF and dioxin-like PCB in unused commercial PCB

PCB type	PCDD/PCDF in unused commercial PCB (µg TEQ/t product)	Dioxin-like PCB (µg TEQ/t product)*
Low chlorinated, e.g., Clophen A30, Aroclor 1242	7000 - 15 000	1,900,000-3,500,000
Medium chlorinated, e.g., Clophen A40, Aroclor 1248; KC-400; KC-500	23000 - 70 000	12,000,000-16,000,000
Medium chlorinated, e.g., Clophen A50, Aroclor 1254	300 000	12,000,000-16,000,000
KC-600; KC-1000	22,000	4,100,000 - 10,000,000
High chlorinated, e.g., Clophen A60, Aroclor 1260	1 500 000	4,100,000 - 10,000,000

* Data for dioxin-like TEQ in low, medium and high chlorinated PCB are derived from PCB mixtures (Takasuga et al. 2005).

If the results of the PCB inventory contain detailed PCB data per site and a clear indication of sites, the list of potential hotspots should be compiled. It should contain the details of the location, coordinates, facility name, type and number of PCB-containing equipment, volume of PCB and the state of the equipment. This list can then serve as a basis for further investigation of hotspots.

2. Detailed approach

The detailed approach is used when the results of the national PCB inventory are partial, inaccurate or not applicable for the identification of hotspots. In such cases, additional questionnaires are sent to governmental bodies, state offices or directly to facilities which hold or operate PCB-containing equipment. In addition to usual questions on the number of PCB-filled equipment, the questionnaires should also enquire on PCB leaks, accidents involving such equipment, description of sites with PCB, results of analysis of PCB in soils and water etc.

3. Comprehensive approach

Through the comprehensive approach, in addition to the results of the national PCB inventory and/or questionnaires to owners of PCB-filled equipment, special investigations of PCB-filled equipment or storage sites are organised, including on-site inspection, soil and other media sampling and analysis, estimation of polluted areas, volumes of leakages, PCB stocks in soil, depth of pollution, risk assessment etc. During the first stages, priority should be given to sites with the largest stocks of PCB-filled equipment, sites with accidents and significant leakages and sites with the highest risk of water and soil pollution.

The results of such a comprehensive inventory allow the preparation of a detailed register of hotspots, with the indication of their prioritisation for remediation measures.

As for the presentation of results of the hotspot inventory (applying the baseline and detailed approach), these can be included in the relevant Excel file (in source group 10); the number of identified hotspots, volumes of PCB in equipment (and distribution between lower and higher chlorinated congeners) are needed as input to estimate PCDD/PCDF releases from these sources. For the comprehensive inventory, separate reports are prepared.

In addition to organochlorine industry, chlorine was/is used in a range of other industries, resulting in PCDD/PCDF containing residues and releases. For example, pulp and paper sludge from bleach process using elemental chlorine have been highly contaminated with PCDD/PCDF and other chlorinated compounds. The application of such sludges to land or through dumping of sludges resulted in hot spots or contaminated land (see example 10g).

Elemental chlorine either remains in the final product (e.g. HCl, NaOCl, ClO2, phosphorous chlorides or metal chlorides) or is simply used in the process (e.g. titanium dioxide, magnesium or silicon) (Stringer and Johnston 2001). For some of these processes, high PCDD/PCDF formation and release potential has been documented. Contaminated sites have been assessed worldwide, e.g. magnesium production in Norway which polluted several fjords and associated food webs with an estimated total PCDD/PCDF release between 50 and 100 kg TEQ (Knutzen and Oehme 1989). The production of titanium dioxide using chlorine process can also generate PCDD/PCDF in the order of kg/year (Wenborn et al. 1999).

For an inventory of contaminated sites from processes using chlorine e.g. production of pulp and paper, magnesium production, TiO2, former releases of these productions, impacted sediments and deposits of residues should be considered.

Emissions from non-BAT incinerators can result in the contamination of milk, eggs or vegetables in the surroundings of incinerators (Liem et al. 1991, Schmid et al. 2003, DiGangi and Petrlík 2005, Watson 2001). In particular, non-BAT incinerators that process organochlorine products, especially PCDD/PCDF precursors (PCB, chlorophenols, chlorobenzenes and other chlorinated aromatics), can result in high emissions of PCDD/PCDFs with considerable impacts on the local environment (Holmes et al. 1994, 1998). Only a limited number of cases of PCDD/PCDF contaminated sites from waste incinerators have been documented to date, showing that release vectors from incinerators - air, solids and water - can lead to PCDD/PCDF contaminated sites if not appropriately managed and controlled (see example 10h). The areas around incinerators can also be contaminated from spills of hazardous chemicals treated/destroyed in these facilities.

For the inventory of PCDD/PCDF contaminated sites from incinerators (and other thermal facilities), (former) management practices and disposal of ashes (in particular fly ash and APC residues) and water release from wet scrubbers should be assessed. Contaminated sites via deposition from air releases are only expected for non-BAT incinerators which emit high PCDD/PCDF levels over extended time periods. In addition to soil measurements, PCDD/PCDF levels in eggs or cow’s milk in the vicinity of the incinerator are potentially good indicators of the contamination status.

A limited number of PCDD/PCDF contaminated sites associated with metal industries have been documented. Typically, toxic heavy metals represent the key contaminants for sites associated with these industries, while PCDD/PCDF are generally regarded as minor by-products.

Releases from primary metal production processes can cause PCDD/PCDF contaminated sites via distribution of metal industry slag, as recorded in Germany. In this case, more than 400,000 tons of slag from a specific primary copper production process, which was highly contaminated with PCDD/PCDF (10,000 to 100,000 ng TEQ/kg), was used as a surface cover for more than 1,000 sports fields, playgrounds and pavements in Germany and neighbouring countries (Ballschmiter and Bacher 1996, Theisen et al. 1993). PCDD/PCDF contaminated sites around a sinter plant in Italy have also resulted in restrictions on grazing (Diletti et al. 2009). Emissions from a secondary copper smelter in Rastatt/Germany contaminated surrounding soils, including residential areas, with PCDD/PCDF levels above the German limit values for contaminated soils (Hagenmaier et al. 1992).

For the inventory of PCDD/PCDF (and heavy metal) hotspots and contaminated sites, the air releases over years/decades should be considered as well as the management and disposal of ashes.

Fires can produce soot and residues with elevated concentrations of PCDD/PCDF (see also category 6b). High levels of contamination result from fires where chlorinated aromatic compounds are burned such as PCB transformer fires or fires of pesticide stocks or other organochlorine stockpiles. Fires in buildings with flame retardant material or high level of PVC can also result in high PCDD/PCDF releases and deposition, normally concentrated in the soot (see example 10j). The soot should thus be collected and disposed of properly as hazardous waste.

Sediments from harbours or downstream of industrial discharge pipelines from any of the above-listed industrial activities can be contaminated with PCDD/PCDF, HCB and other pollutants like heavy metals. Very often, to maintain access through channels, these sediments are dredged and deposited on land. This activity only removes PCDD/PCDF contamination from its location and from the aquatic environment, and transfers the same level of contamination to another location with potentially new exposures. When inventories of dredging activities are established, the deposition of sediments on areas used for agriculture and residential housing should be highlighted and possibly assessed for levels of contamination.

Rivers with a history of PCDD/PCDF contamination can have PCDD/PCDF contaminated floodplains in addition to polluted sediments. Since floodplains are often used for grazing or in agriculture, the inventory and management of impacted floodplains should be performed to prevent human exposure (see example 10k).

Where PCDD/PCDF containing products or residues have been disposed of, there is a probability that these contaminants will be released into the environment. PCDD/PCDF are relatively immobile in dumps or landfills as long as there are no organic co-deposits facilitating leaching or seepage water capable of mobilizing the contamination. Of particular importance is the remobilization of PCDD/PCDF-containing deposits if such landfills or dumps are excavated due to remediation measures or for mining purposes (see category 9a; see example 10l).

Chemical or otherwise hazardous landfills containing PCDD/PCDF are sometimes secured by engineering measures. Because of their persistence, PCDD/PCDF and other unintentionally produced POPs will persist in landfills for many decades or centuries (Balzer et al. 2008). Over these extended time frames, engineered landfill systems, including liners, gas and leachate collection systems will inevitably degrade and lose their structural integrity and capability to contain persistent contaminants (Allen 2001, Weber et al. 2011a).

Landfills and deposits should thus be inventoried and included in a database. In a systematic inventory of landfills/dumps within a country, the specific presence of PCDD/PCDF and other unintentional POPs should be included.

Ball clay and kaolinic clays in different regions in the world can contain PCDD/PCDF with a specific OCDD dominated pattern (Ferrario et al. 2007, Horii et al. 2011). A first global inventory has been established by Horii et al. (2011). Typical for all samples is the almost total absence of PCDF, and the nearly identical congener/isomer distribution throughout all geographies. Thus, PCDD appear to have been formed by natural processes possibly millions of years ago (Ferrario et al. 2007, Horii et al. 2011). Kaolin samples from Africa have also been found to contain elevated levels of PCDD (Hoogenboom et al. 2011). Studies also show that the relative high levels of PCDD/PCDF in human milk samples from Congo and Ivory Coast are due to the use of the clay during pregnancy (see example 10m). PCDD/PCDF in ball/kaolinic clays, in particular from quarries where clays are used for human consumption or as animal feed additive, should thus be included in the inventory.