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Substance Flow Analysis for dioxins in Denmark

6. Total picture for Denmark

6.1 Formation and consumption

The dioxin brought into circulation in the Danish society and emitted to the environment in Denmark partly originates from processes taking place in Denmark and partly from raw materials extracted and manufactured in Denmark or imported to Denmark.

Table 6.1 summarises the available estimates regarding formation of chlorinated dioxins in Denmark and the extent to which these estimates are based on Danish investigations or literature values.

The calculation of formation of dioxins by each activity or process takes into account the amount emitted to air and water as well as the amount collected and disposed of with waste products. Formation does in principle also include the amount created in the products manufactured, but no information has been available to allow estimates of these quantities that to the best of knowledge regarding chlorinated dioxins are also insignificant in Denmark, but could well be important to brominated dioxins in plastics containing brominated flame retardants.

The total formation of chlorinated dioxins in Denmark in 1998-99 is estimated at 90-830 g I-TEQ/year. The most important activity is waste treatment and disposal activities of which municipal waste incineration is the dominant source for dioxin generation. Several other activities are, however, also adding significantly to the total formation. These activities include steel reclamation, coal and biomass combustion and fires, both accidental fires and other fires like the dominant Danish bonfire event – Sct. Hans Evening (Midsummer Day).

The formation of dioxins is widespread in the society, as it e.g. is connected to all types of combustion processes. It is noted that for several activities the formation cannot be quantified due to lack of data. It is, however, believed that the results presented in this report cover all major activities relevant in this context.

The large intervals given for most activities in table 6.1 reflect the uncertainty of the estimates. These uncertainties are partly related to the absence of reliable Danish data making it necessary in many cases to rely on international literature data. As dioxin formation is extremely process specific, this calls for a very critical attitude to all available data and in particular to whether the data available are representative to the process in question. However, the uncertainties also reflect the fact that for several important activities, e.g. fires, the knowledge available is actually inadequate, and the estimates presented may in reality only be justified by the need for obtaining an impression of the significance of such activities. It would be fair to conclude that dealing with dioxins is a matter of dealing with a host of uncertainties.

To make the picture complete, it is also necessary to consider the amount of dioxins brought into circulation by raw materials extracted and manufactured in Denmark or imported to Denmark. In table 6.2 the available estimates on this topic are summarised.

As stated in table 6.2 around 10 –1110 g I-TEQ/year should be expected to be in circulation of chlorinated dioxins alone. To this figure may be added brominated dioxins that are primarily brought into circulation by the use of brominated flame retardants in plastics.

The dominant part of this quantity will most likely be destroyed by heating or incineration processes, thus never being emitted to the environment. This is the case for dioxins in clay that are dominantly used for tiles, bricks and insulation materials manufactured of high-temperature processes. This is also the case for the dominant part of brominated dioxins, as they should be expected as plastics to be directed to municipal waste incineration.

However, this fate is certainly not the case for all types of products. Dioxins in feedstuff will partly be re-circulated to farmland by manure, dioxins in paper and cardboard will likely continue to be re-circulated for paper/cardboard manufacturing and preserved wood and leather may to some extent remain in the society, and slowly release dioxins to air by evaporation.

The assessment of the consumption of dioxins by products should for many reasons be regarded as premature. An important reason is that so far insignificant efforts internationally have been devoted to products, and measurements are generally few and old and in no way systematic. The recognition of the presence of dioxins in natural clay is mainly due to a larger investigation reported recently. The question naturally arises whether dioxins might not be present in other sedimentary materials like e.g. lime or chalk. Despite these uncertainties, it is deemed relevant to bring forward these estimates in order to illustrate the magnitude of the dioxin flows in question.

6.2 Emissions to the environment

Table 6.3 summarises the estimates made with respect to emissions to the environment and quantities directed to depots in Denmark.

Emissions to air

Concerning emission to air the total emission is estimated at 19 -170 g I-TEQ/year or as a best estimate, assuming uncertainties to compensate each other, to around 95 g I-TEQ/year. The dominant sources include:

	Municipal waste incineration
	Biomass combustion (in particular combustion in wood stoves and farm boilers)
	Evaporation from PCP-preserved wood
	Fires
	Steel and aluminium reclamation

In 1999 incineration of chemical waste was a significant source as well, but the contribution from this source is likely to be heavily reduced in 2000 due to redesign of ovens and installation of dioxin filters. Other sources for emission that could be significant include cable scrap reclamation, lime and cement manufacturing, traffic, and landfills that in this context cover fires in temporary depots for combustible waste.

Concerning municipal waste incineration more plants are in the process of installing special dioxin filters, and the dioxin emission to air should thus be expected to decrease in the near future. The choice has been made to report emission from waste incineration as an interval reflecting the assumed interval of uncertainty rather than as a calculated best estimate based on average figures, as the number of measurements available from Danish plants are still relatively few, and it is debatable to what extent the measurements available actually reflect the total emission. This discussion is elaborated at the end of this section and is in reality relevant to all sources of formation and emission of dioxins.

Biomass combustion in small units without flue gas cleaning like wood stoves, farm boilers and stoker boilers is deemed an important source although the estimates are subject to significant uncertainty. For wood stoves it is known that burning of pure wood only is hardly a serious problem. However, adding other materials like paper, milk cartons, plastics or treated wood into the stove should be believed to promote dioxin formation e.g. due to the use of copper pigments in such materials. Considering that around 370,000 wood stoves are being used in Denmark by households, one should be prepared to accept a high level of variation with respect to the materials burned. With respect to the use of treated wood attention should e.g. be paid to the fact that very few people – if any – are able, without measurements, to determine whether the disposable pallet cut to pieces to be used as firewood has actually been treated with PCP or not. One may also discuss how many Danes actually have knowledge enough to care.

Concerning farm boilers existing measurements have shown high variation of dioxin emission, and there is certainly a need for a better understanding of the factors causing this variation. As for wood stoves, one should be prepared to accept that also farm boilers are used for a number of other materials besides pure straw.

The contribution from other larger biomass combustion plants equipped with flue gas cleaning seems to be small compared to wood stoves, farm boilers and stoker boilers. In this context the larger plants should be expected to benefit from considerably better control of the materials burned and of operations in general. However, the number of measurements carried out so far is still small and may not necessarily be representative to the total number of plants in operation.

Concerning evaporation from PCP-preserved wood the dominant part of the emission is due to old construction wood (from before 1980) in houses etc. all over Denmark. This emission will continue, until the wood in question has been naturally replaced. This should be expected to take place within the next 20 years, in which period the emission will gradually decrease. However, emission from PCP-preserved materials will continue to take place, as long as PCP is produced and used in the world. Dioxins are a natural contaminant in PCP and the increasing globalisation ensures that chemical substances used for industrial production in other regions of the world to some extent also will end up in Denmark.

Table 6.3
Estimated emissions/losses to the environment and depots in Denmark 1998-99

Accidental fires etc. are a source recognised, but not quantified in most dioxin inventories, as the factual knowledge available is small and all estimates thus are highly uncertain. The basic problem is that it is difficult to undertake realistic experiments or to undertake actual measurements of the emission to air. Still the significance of fires for dioxin formation and emission should not be underestimated. It should be noted, that fires cover accidental fires in building, vehicles etc. for which a mixture of many different materials containing all the elements needed for dioxin formation are present, as well as bonfires, garden fires etc. dominantly based on pure wood but occasionally involving other materials, too.

Steel and aluminium reclamation together with incineration of chemical waste and perhaps also cable scrap reclamation, cement and lime manufacturing are examples of single plant sources that should be considered significant at least in the perspective that one is dealing with the emission from a single plant. Whether or not chemical industries like manufacturing of pesticides and pharmaceuticals should be included in this focus, remains to be proven, as available measurements are both old and incomplete or non-existing. It should be noted that emissions from these companies can always be debated, based on the fact that spot measurements - even based on a standard procedure of 6-hours sampling - will normally not represent the total emission from such plants, and little experience exist to allow the importance of deviating process conditions to be assessed. This issue is further elaborated below. Concerning the estimated emission from steel reclamation in Denmark, the choice has been made to rely mainly on the company’s own measurements.

A special source developed in Denmark in the last years is fires in temporary depots of combustible waste awaiting adequate incineration capacity to be established. This source is in table 6.3 included under "landfills". The comments relevant to this source correspond to a large extent to the comments given above on accidental fires etc.

The very large ranges given for most emissions reflect to the best judgement of the authors of this report the uncertainty actually related to the estimates presented. An issue, however, not necessarily fully covered by the ranges presented, is the consequences of deviating process conditions. As dioxin formation is extremely process dependent and the actual formation may differ considerably from "normal" process conditions to "deviating" process conditions, deviating process conditions may contribute significantly to the total dioxin formation and emission. E.g. even if deviating process conditions only rules 5% of the total operation time for a specific plant the dioxin formation during this time could perhaps be 10-100 times higher than under normal process conditions. It is the impression of the authors that most of the emission factors reported reflect normal process conditions and thus do not include the consequences of deviating process conditions. In this report the consequences of deviating process condition have been considered in relation to steel reclamation and to one municipal waste incineration plant. Only little factual knowledge is available on this issue, but the significance to the total emission should not be overlooked.

Emissions to water

The total emission to the water environment is estimated at 0.3 – 1.4 g I-TEQ/year based on very few samples. The estimate should accordingly be regarded as very uncertain. Based on the knowledge available the most important source for dioxins in Danish waste and storm water seems to be atmospheric deposition (reference is made to table 5.5), but congener profiles of sludge correspond better to profiles of textiles. It must be concluded that knowledge is limited and any definite conclusions on this issue should be taken as premature.

Emissions to soil

The total direct emission of dioxins to the soil environment is estimated at 1.3-54 g I-TEQ/year. The dominant sources are:

	Ash from biomass combustion (wood stoves and farm boilers)
	Residues from miscellaneous fires
	Manure from domestic animals applied to farmland.

Other minor sources seem to be the use of pesticides and sewage sludge. It is, however, strongly emphasised that all estimates apart from sewage sludge are highly uncertain, as they are generally based on very few data of which most originates from foreign investigations. One must be prepared to accept that further and more detailed investigations could change the picture considerably. E.g. knowledge of the content of dioxins in pesticides should be regarded as almost non-existing and more detailed investigations could perhaps identify pesticides as a significant source.

The focus on ash from wood stoves relates to that ash may frequently be directed to garden composts or directly spread on the soil in gardens. Similar behaviour should be expected for farmers operating farm boilers.

Residues from fires deal with ash etc. from other fires than accidental fires – e.g. garden fires and bonfires - not removed from the place of the fire and in time mixed into the soil.

Manure from domestic animals is generally applied to farmland and will contain dioxins originating from the feedstuff. As detailed investigations of the turnover of dioxins in the Danish agricultural sector are not available, the estimated supply should be regarded as a rough first estimate indicating the relevant order of magnitude.

Losses to depots

The total quantity of dioxins directed to landfills and other types of depots in Denmark is estimated at 38 – 420 g I-TEQ/year. Again municipal waste incineration stands out as the dominant source. However, neither residues from coal combustion, biomass combustion nor fires should be overlooked. The significant quantities of dioxins ending on landfills naturally call for more knowledge of what is actually happening to dioxins on landfills.

Previous estimates

The figures presented in table 6.3 may be compared to previous estimates of dioxin emissions in Denmark presented in table 6.4. The main differences between the previous estimates and the present are due to the following:

	That the previous estimates have generally been expressed as "best estimates" giving relatively little consideration to the significant uncertainties connected to the estimates.
	That the present estimates have included a number of sources previously not quantified, e.g. fires and PCP-treated wood
	That the present estimates benefit from the significant knowledge developed internationally and in Denmark in the recent years and e.g. has included all measurements known to be available from Denmark.

Other differences may be due to different interpretation of the available data. It should e.g. be noted, how the estimates of biomass consumption and in particular wood stoves fluctuate.

The benefit of including uncertainties in the estimates and operating with intervals instead of "best estimates" becomes clear, when comparing to the atmospheric deposition. A significant difference between estimated total emissions to air and estimated total atmospheric deposition has for long been recognised internationally (reference is e.g. made to /Brzuzy & Hites 1996 and Landesumweltamt Nordrhein-Westfalen 1997/) and is also illustrated in the figures given in table 6.4. On the contrary the balance for Denmark presented in figure 6.1 indicates that Danish emissions are reasonably balanced with atmospheric deposition on the Danish land area. This could be taken as an indication of the fact that dioxin inventories are generally underestimating emissions and that giving proper attention to the significant uncertainties related to emission estimates may provide at least a part of the explanation of the difference generally noted between emissions and deposition.

Apart from steel reclamation and waste incineration, no specific trend in dioxin emissions should be noted. The Danish steel reclamation plant has based on the company’s own estimate for dioxin emission seemingly succeeded in reducing emissions considerable whereas Danish waste incineration plants are in the process of speeding up installations of special dioxin filters. For other plants and activities the focus on dioxin emissions in Denmark have so far been limited.

6.3 Substance flow balance for Denmark

The available knowledge and assessments on the flow of chlorinated dioxins in Denmark in 1998-99 have been compiled and illustrated in figure 6.1.

Figure 6.1 Se her!
Balance for chlorinated dioxins Denmark 1998-99 (all figures in g I-TEQ/year)

Input to the Danish society

The Danish society receives dioxin by products imported to Denmark and by raw materials extracted from nature. The products in question are mainly materials like wood, leather and textiles preserved by pentachlorophenol, but also clay, paper/cardboard and feedstuff. The raw materials extracted are clay and clay-like materials that are mainly used for manufacturing purposes besides fish, grass and animals that mainly are turned into feedstuff and food products.

Export from the Danish Society

From Denmark is exported a number of items containing dioxins, mainly residues from waste and coal combustion, but also residues from manufacturing processes, like filter dust from steel reclamation. To this can be added small amounts of dioxin in exported feedstuff, clay and paper/cardboard etc.

Formation and destruction

Significant formation and destruction of dioxins is believed to take place in the Danish society. Formation is related to manufacturing, energy production and waste treatment and miscellaneous other processes as elaborated in the previous sections. Destruction is related to high-temperature manufacturing of products based on clay, besides that thermal waste treatment like incineration of municipal waste and sewage sludge is believed to destroy – more or less – the dioxins present in the waste materials treated. Attention should be paid to the possibility that recycling of materials like coal fly ash and paper sludge for cement manufacturing also should imply destruction of the dioxins present in the recycled materials. To this may be added the unknown amount of dioxins in special dioxin filters assumed to be destructed by incineration in the plants own ovens/kilns. Whereas the destruction capacity of such thermal processes should be recognised, it should, however, not be forgotten that at the same time many of the processes – in particular municipal waste incineration – belong to the dominant sources for dioxin formation.

It should be noted that destruction for the time being might well be larger than formation, as the stock of dioxins in use in products in the Danish society should be expected to be decreasing (reference is made to the section on stock building below).

Recycling

Recycling of dioxins present in paper and cardboard will take place.

Emissions to the environment

From the Danish society emissions will take place both to air, soil and water as elaborated in the previous sections.

Stock building

A stock of dioxins in the Danish society exists in the form of dioxins in PCP-treated wood. The size of this stock per 1999 is roughly estimated at 100 – 5,000 g I-TEQ. The stock should be assumed slowly to decrease due to replacement of the wood in question as well as evaporation of dioxins from the wood corresponding to the fact that the use of PCP in Denmark is now banned.

Balance for air

Whereas Denmark emits dioxins to the air, Denmark also receives dioxin from the air by atmospheric deposition. The deposition on the Danish land area is estimated at 16-160 g I-TEQ/year assuming a total land area of 43,100 km² and a deposition of 1-10 pg I-TEQ/mē per day (reference is made to section 2.4.4). A deposition rate of 250 pg I-TEQ/ mē per year based on calculations on long-range transport of dioxins/furans (also reference to section 2.4.4) would correspond to a total deposition on the Danish land area of 11 g I-TEQ/year.

The Danish marine internal waters are assumed to cover 38,000 km² and will certainly also receive deposition that has however not been estimated due to lack of data. As an immediate conclusion it can be judged that a reasonable balance between the estimated emission and the calculated deposition seems to exist, assuming that the deposition on Danish internal waters is small compared to the deposition on the Danish land area. It is emphasised that the estimate of atmospheric deposition on the Danish land area is based on measurements from Germany (the Hamburg region), as no investigations so far have been undertaken in Denmark. The general experience with respect to airborne pollution considering the prevalent wind directions is that the emission generated in Denmark to some extent will be a source of deposition in Sweden. Denmark is on the other hand exposed to deposition caused by emissions in other parts of Europe like Germany, Belgium and the UK.

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