Substance Flow Analysis for dioxins in Denmark
Summary and conclusions
This study has tried to develop – to the extent possible – an updated and complete picture of the dioxin circulation in the Danish society based on the knowledge available. The formation of chlorinated dioxins in Denmark in 1998-99 has been estimated at 90 – 830 g I-TEQ/year, whereas the emissions to the environment have been estimated at:
| Air: | 19 – 170 | g I-TEQ/year |
| Water: | 0.3 - 1.4 | g I-TEQ/year |
| Soil: | 1.3 – 54 | g I-TEQ/year |
| Depots: | 38 – 420 | g I-TEQ/year |
As contaminants in various products and materials chlorinated dioxins are furthermore imported to Denmark and extracted from the nature around us, as dioxins can be found both in clay, fish, animals and vegetation due to historical and ongoing contamination. The estimate for emission of dioxins to air is in reasonable balance with the estimated atmospheric deposition on the Danish land area of 16 - 160 g I-TEQ/year.
Formation of dioxins in Denmark is almost entirely related to combustion processes. Combustion process is in this context used for any process leading to combustion of organic matter present, including processes such as wood and straw burning, waste incineration, fires, cement manufacturing and steel reclamation. Formation of dioxins is thus widespread in the society.
Formation of dioxins is highly influenced by local process conditions including raw materials and temperature pattern in flue gas emission systems. Estimating formation and emissions is a matter of dealing with a host of uncertainties. The large ranges of formation and emissions stated above reflect the uncertainties related to the estimates.
Background and objectives
This study has been initiated by the Danish EPA in November 1999 in order to improve the existing understanding of the circulation of dioxins in the Danish society.
The objectives of the study have been to integrate the present knowledge of dioxins related to Denmark into the frame work of substance flow analysis and as part of this process to reconsider the knowledge so far reported from Denmark paying respect to the significant amount of knowledge made internationally available during the nineties.
Previous studies on emissions of dioxins in Denmark have been published in 1995 and 1997.
The study
This study has been carried out in accordance with the paradigm of substance flow analysis of the Danish Environmental Protection Agency. The knowledge presented is based on data from Statistics Denmark, the literature, and public institutions as well as from private organisation and companies. In the analysis, all the information has been held together to describe the flow of dioxins through the Danish society.
As dioxin analyses are relatively costly, the number of measurements available to Danish plants is limited. It has thus been necessary for most processes to rely on emission factors developed abroad. In adopting such figures it has been assumed more correct to use minimum and maximum figures instead of average figures, as average figures generally give a false impression of the accuracy of the estimates presented. The same approach has in some cases been adopted also for processes for which Danish measurements actually exist, e.g. for municipal waste incineration. One of the problems addressed by this approach – at least partly – is the fact that dioxin formation and emission may differ considerably from "normal" process conditions to "deviating" process conditions, and that deviating process conditions could contribute significantly to the total dioxin formation and emission. Most measurements available should be assumed to reflect normal process conditions and do not necessarily give a reliable picture of the total emission from the individual plants.
Main conclusions
The main conclusions of the study are:
 | The total Danish formation of chlorinated dioxins in 1998-99 is estimated at 90 – 830 g I-TEQ/year. The dominant source is municipal waste incineration. Other significant sources also include coal and biomass combustion and fires, both accidental fires and others. Most chlorinated dioxins formed by processes in Denmark are emitted to the environment. A minor part is exported with residues like coal fly ash and filter dust from Denmark. |
| Denmark also receives chlorinated dioxins by products imported to Denmark and by raw materials extracted from nature. The import by products is estimated at 3.4 – 106 g I-TEQ/year and is partly related to import of products like wood, leather and textiles treated by pentachlorophenol (PCP) abroad, as chlorinated dioxins are contaminants in PCP. Chlorinated dioxins are also imported with products like clay, paper/cardboard and feedstuff. Raw materials extracted from nature in Denmark accounts for 5 - 1010 g I-TEQ/year dominantly in clay but also in fish, grass and animals used for food and feedstuff. |
| The total Danish emission of chlorinated dioxins to air in 1998-99 is estimated at 19-170 g I-TEQ/year. The dominant sources include municipal waste incineration, biomass combustion in small units without flue gas cleaning like wood stoves and farm boilers, evaporation from PCP-treated wood in use in Denmark, fires, steel and aluminium reclamation. Other sources of emission that could be significant are cable scrap reclamation, lime and cement manufacturing, traffic and landfills that in this context cover fires in temporary depots for combustible waste. 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 kilns and installation of dioxin filters. |
| The total Danish emission to water in 1998-99 is estimated at 0.3 – 1.4 g I-TEQ/year. The dominant source seems to be atmospheric deposition, but congener profiles for sewage sludge correspond better to textiles than to atmospheric deposition. The knowledge is limited, and any definite conclusions on this issue should be taken as premature. |
| The total direct emission of chlorinated dioxins to the soil environment is estimated at 1.3-54 g I-TEQ/year. The dominant sources are deemed to be ash from biomass combustion in wood stoves and farm boilers applied directly to soil, residues from miscellaneous fires (garden fires, bonfires etc.) not removed from the place of the fire and by time mixed into soil, and manure from domestic animals applied to farmland. |
| The total quantity of chlorinated 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. |
| 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 of dioxin emission apparently succeeded in reducing emissions considerably, 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 has so far been limited. |
| A significant destruction of chlorinated dioxins corresponding to 13 – 1465 g I-TEQ/year is assumed to take place. The 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 are believed to destroy – more or less – the dioxins present in the waste materials treated. It should be stressed 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 due to the temperatures involved by cement manufacturing. To this an unknown amount of dioxins in special dioxin filters burned in the ovens/kilns at the plant, from where they were used can be added. |
| It must be recognised that the plants effective in destruction of dioxins at the same time may belong to the dominant sources of dioxin formation. For municipal waste incineration the overall picture is that the amount of dioxins emitted by flue gas and incineration residues is significantly higher than the amount assumed to be destroyed. Municipal waste incineration should be regarded as the most important source for dioxin formation and emission in Denmark. |
| A stock of chlorinated dioxins in the Danish society exists in the form of dioxins in PCP-treated wood. The stock is mainly due to the widespread use of PCP as wood preservative that took place in Denmark from 1950 to 1978. By 1999 the size of this stock was roughly estimated at 100 – 5,000 g I-TEQ. The stock should be assumed slowly decreasing due to replacement of the wood in question as well as evaporation of dioxins from the wood, as the use of PCP in Denmark is now banned. The wood replaced is assumed directed to incineration. |
| Another group of dioxins is the brominated dioxins. No measurements for brominated dioxins have been undertaken in Denmark and only relatively few internationally, as analytical procedures are still in the process of being developed. Denmark is importing an estimated 2 – 60 g I-TEQ/year of brominated dioxins as contaminants in plastics containing brominated flame retardants. To the extent such plastics are exposed to accidental fires or further processing, e.g. recycling, further formation of brominated dioxins may take place. Brominated dioxins in plastics are likely to be destroyed by waste incineration, but formation of brominated dioxins as well as mixed brominated/chlorinated dioxins may take place by flue gas cleaning and emission processes parallel to formation of chlorinated dioxins. |