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Substance Flow Analysis for dioxins in Denmark

4. Formation and turnover by miscellaneous human and natural activities

4.1 Fires

It is generally accepted /Cleverly et al 1999, Landesumweltamt Nordrhein-Westfalen 1997/, that accidental fires may be a significant source of dioxin formation. In buildings as well as transport equipment a mixture of materials including chlorine sources (like PVC), organic matters and copper are present, meaning that conditions are appropriate to "de novo synthesis" of dioxins. Many buildings may, furthermore, contain wood preserved by PCP-preservatives that were widely used in Denmark for industrial wood preservation as well as surface preservation/priming of wood before painting up to the late seventies (reference is made to section 2.6.1). Attention should also be paid to the use of brominated flame retardants in plastics, because such plastics in themselves may contain brominated dioxins, and more brominated dioxins may be formed by burning of the flame retarded plastics.

Activity in Denmark

The amount of material burned by accidental fires in Denmark can only be estimated with significant uncertainty. Based on information from /Beredskabsstyrelsen 1999 and Beredskabsstyrelsen 2000/ it may be roughly assumed

	that approx. 2000 large fires take place yearly. A large fire is in this context defined as a fire involving the use of 2 or more fire hoses for fire-fighting and will typically involve a complete house, one or more apartments, or at least part of an industrial complex
	that approx. 6000 medium fires take place yearly. A medium fire is in this context defined as a fire involving the use of 1 fire hose only for fire-fighting and will typically involve a part of a single room in an apartment or house
	that approx. 7000 small fires take place yearly. A small is in this context defined as the fires statistically defined as "extinguished before arrival" , "extinguished by small tools" or "chimney fires" .

Is it furthermore assumed

	that a large fire as a rough average in each case will lead to combustion of 5-10 tonnes of materials equalling the weight of combustible construction materials and furniture and other combustible materials in a typical Danish residential house
	that a medium fire as a rough average in each case will lead to combustion of around 100 kg of materials equalling the weight of some household equipment or pieces of furniture
	that a small fire as a rough average in each case will lead to combustion of around 1-10 kg of materials equalling the content of a paperbasket, a small garden fire or a chimney fire.

Based on these assumptions the total amount of materials combusted by accidental fires annually in Denmark may be roughly estimated at 10-20,000 tonnes.

In this estimate medium and small fires carry no weight that could lead to an underestimate of the importance of especially fires in vehicles, as significant dioxin formation from vehicle fires have been registered. Therefore vehicle fires are estimated separately as follows.

Insurance reports from all Danish insurance companies from 1999 and 2000 on cars and other vehicles characterised as totally damaged by fire (meaning that repair was deemed not feasible) indicate a total number of damaged vehicles of 1535 per year /Forsikrings-oplysningen 2000/. Not all vehicles will actually be completely burned out, for which reason it is deemed fair to compare the 1535 incidents with around 1000 completely burned-out cars.

To these types of fire accidents may be added fires in trains, ships, aeroplanes and equipment containing PCBs. No efforts have been done to quantify these fires and the amount of materials combusted. In general the total volume will be small compared to building fires with the exception of fires in larger passenger liners (e.g. the Scandinavian Star accident) that fortunately is a quite unusual accident. Electrical equipment containing PCBs, e.g. transformers and capacitors, is nowadays banned, although some equipment may still be in operation.

Formation of dioxins

Measurement of dioxin formation related to accidental fires has been carried out in Denmark in 1997 and in May 2000. In 1997 a factory with a stock of approx. 50 tonnes of PVC burned down in Århus. Soil measurements (depth 4 -5 cm) showed dioxin concentrations of 0.2 ng I-TEQ/kg and 0.05 ng I-TEQ/kg for contaminated and reference samples respectively /Vikelsøe 2000/. The accident in May 2000 involved a company north of Copenhagen manufacturing office utilities e.g. based on PVC. The amount of materials consumed by the fire has been estimated at a total of 600 tonnes including 2 tonnes of PVC. During most of the fire the smoke went straight up for several hundred metres. The smoke has been characterised as very heavy and black. Measurements of 6 soot samples were undertaken. One sample from a window at the place of the accident showed a dioxin content of 9 ng I-TEQ/m², whereas 4 other samples taken at distances of 90-450m from the company showed dioxin contents varying from 6 to 1 ng I-TEQ/m². The background level was also determined to 1 ng I-TEQ/m² /Danish EPA 2000a/. The data available are however to a few to allow for a reliable quantification of the dioxin formation and emissions occurred.

Formation of dioxins by accidental fires is generally difficult to quantify and only limited data are available. Generally estimates are based on the content of dioxins in soot samples collected from surfaces on the place of fire and in the vicinity. Based on this approach an estimate for Germany of 81 g I-TEQ/year (estimated margin of uncertainty: 2.5 - 2,500 g I-TEQ/year) has been developed. This estimate covers accidental fires in buildings as well as vehicles. Transferring the German estimate to Danish conditions by the use of per capita calculations, the European Dioxin Inventory states a dioxin emission to air for Denmark of 5.3 g I-TEQ/year /Landesumweltamt Nordrhein-Westfalen 1997/. For the dioxin content of fire residues an estimate for Germany of 139 g I-TEQ/year (estimated margin of uncertainty: 4.3 - 4,300 g I-TEQ/year) has also been developed /Landesumweltamt Nordrhein-Westfalen 1997/. If similar per capita calculations are applied to this figure, the dioxin content of fire residues in Denmark may be estimated at 9.1 g I-TEQ/year.

It should be noted that estimates for emission to air based on soot samples in the vicinity may likely underestimate the total emission to air, as some dioxin may likely be attached to very small particles and transported far.

Another approach could be to utilise the experience from recent investigations of uncontrolled domestic waste burning (reference is made to section 5.3.1), in which domestic waste known to contain 0.2 %, 1% and 7.5 % PVC generated 80 ng I-TEQ/kg respectively 200 ng I-TEQ/kg and 4900 ng I-TEQ/kg waste.

The average content of PVC in houses in Denmark could well be in the range of 0.2-1%, but will be below 7.5%. A figure of 50-1000 ng I-TEQ/kg material and 10,-20,000 tonnes of material would equal a total emission of 0.5-20 g I-TEQ per year.

Vehicles tunnel experiments in Germany (/Wichmann et al 1995/ quoted in /Jensen 1997/) has shown a generation of dioxin of 0.044 and 0.052 mg I-TEQ for two different cars. Assuming these figures to be valid for all 1000 Danish incidents of vehicle fires, the total generation of dioxins by vehicle fires in Denmark may be estimated at approx. 0.05 g I-TEQ/year.

Considering the uncertainties involved in these estimates, and paying respect to the fact that independent assessments methods give results of similar order of magnitude, it is hereby proposed to accept the following estimates for dioxin generation in relation to accidental fires in Denmark:

The estimate for collection with residues is based on the German estimate that the amount of dioxin in fire residues is approximately 70% higher than the amount estimated as emission to air, but the emission to air is likely underestimated.

Dioxin collected with residues will partly be removed as waste that should be assumed dominantly to be directed to landfills, although it cannot be ruled out that some materials like metals and bricks are directed to recycling and left-overs of combustibles may be directed to incineration plants. Some of the dioxin should, however, be assumed to be transported in the smoke by wind and fall-out on land or waters, and others by extinguishing water to the ground and the sewage system.

4.1.2 Other fires

Other fires cover bonfires, camp fires and forest fires. The dominating bonfire event in Denmark is the celebration of midsummer (Skt. Hans) at the 23 June. Camp fires include private fires in gardens and in particular burning of garden waste as well as camp fires in summer camps etc.

At best practice these fires consist of pure wood. But other kinds of waste as plastics or preserved or painted wood may occasionally be included. Camp fires may also be based on driftwood that contains chloride from the sea.

The significance of bonfires (and fireworks - see section 4.4) may be illustrated by British observations that the concentration of dioxins in ambient air increased fourfold during the dominant bonfire event in the UK (/Dyke and Coleman 1995/ quoted in /Dyke et al 1997/).

Landfill or depot fires are a special type of fire that is discussed in section 5.5 and not here.

Activity

No statistics on the number of these fires and the amount of material combusted are available. The following considerations should be regarded as a rough estimate only.

The midsummer bonfire takes place all over Denmark. All cities and villages will have at least one fire and depending on their size often several. In Denmark there are 1421 cities with more than 200 inhabitants /Danmarks Statistik 2000/. Thus, it is reasonable to assume that the number of midsummer bonfires in Denmark come up to somewhat between 5,000 and 20,000 fires. The materials used for these fires will typically be twigs and branches from bushes and trees. Assuming the typical fire to have a size of around 100 m³, of which approx. 5% is wood with a density of 0.8, the total amount of wood combusted may be estimated at 20,000 - 80,000 tonnes/year.

Private fires and in particular burning of garden waste are banned in some districts, but allowed in others. There are 1.4 million houses in Denmark with some kind of garden /Danmarks Statistik 1999/. Assuming that 10% of these burn 10-50 kg of twigs and branches 2-6 times a year, the amount of material combusted may be roughly estimated at 3,000 - 40,000 tonnes/year.

Camp fires are frequent during the summertime in Denmark. The amount of wood consumed, however, are likely less than for burning of garden waste. As a very rough estimate the amount of wood consumed is here assessed to 2,000 – 10,000 tonnes.

Forest fires are seldom in Denmark and should not be expected to cover more than very few hectares per year. Compared to other fires forest fires should be regarded as insignificant for Denmark.

Straw burning on the fields has been banned in Denmark since 1990. However, exemption has been granted to burning of grass seeds, and farmers may occasionally still burn piles of old straws harvested the previous year and left behind on the fields during winter. Neither reliable information about the extent of field burning nor dioxin measurements is available.

Dioxin formation and disposal
No measurements of dioxin formation related to such fires has been carried out in Denmark.

For natural fires the European dioxin inventory (section on UK) proposes emission factors (the very large intervals are due to different assessment methods /Landesumweltamt Nordrhein-Westfalen 1997/):

Attention should also be paid to the experience on wood burning in open fire places and the default emission factors of the European dioxin inventory for domestic wood combustion (reference is made to section 3.3.1):

Considering that the dominant part of the material burned are clean wood, but that other materials may occasionally be involved as well, it is deemed fair to expect the overall picture to be somewhat between a clean wood situation and a slightly contaminated wood situation. An activity of approx. 25,000 – 130,000 tonnes/year burned and an air emission factor of 1-50 m I-TEQ/t equal a total emission of 0.03 – 6.5 g I-TEQ/year.

Residues

/Dyke et al 1997/ assessed dioxin content in residues from bonfire events by referring to measurements of dioxin in ash from a wood stove and soot from a stove burning wood, coal and waste on 75 m I-TEQ/ton and 42048 m I-TEQ/ton respectively. Assuming an amount of ash of approx. 1% of the amount of wood, 25,000 – 130,000 tonnes of wood will result in 250 – 1300 tonnes of ash. Assuming a dioxin content of 75 – 42000 m I-TEQ/t ash, bonfires and the like will result in 0.02 – 55 g I-TEQ/year with ash and other residues that are dominantly is spread on the ground and partly disposed of as waste. It is noted that the high end of this interval may most likely be overestimated. Disposal as waste will primarily be the case for residues from bonfire events. As a rough estimate 50% of the residues is assumed to be spread on the ground and the rest to be disposed of as waste.

4.2 Traffic

Dioxin emission from vehicles is mainly related to chlorine or bromine additives used in leaded gasoline. The use of leaded additives for gasoline in Denmark has now ceased completely. The previous estimate made in /Jensen 97/ of a dioxin emission from vehicles in Denmark of less than 0.2 g I-TEQ/year will still be valid.

This estimate does not include emissions from trains and ships.

The consumption of fuel for such purposes in 1998 was as follows /Energistyrelsen 2000/:

The consumption figures for ships cover inland traffic only.

Based on results from the Dutch national dioxin measurement programme /Bremmer 1994/ estimates the following emissions factor:

No data of trains are available. The emission factor for trains is here assumed to be somewhat between the factors known for ships-gasoil (see above) and diesel vehicles (0 .03 ng I-TEQ/kg fuel /Bremmer 1994/.

Based on these assumptions the total emission from ships and trains in Denmark can be roughly estimated at 1.3 –1.5 g I-TEQ/year, and the total emission from traffic to 1.3 –1.7 g I-TEQ/year.

4.3 Crematories

32 crematories are currently operating in Denmark. All crematories treat flue gasses by afterburning (850° C for one second), without further filtering. The temperature of the off-gases before the chimney will be in the range of 150-400° C /Danish Crematories 2000/.

Approx. 40,000 bodies are cremated yearly. The average mass per creamation (body plus coffin) is 110 kg equalling a total mass of approx. 4,400 t/year /Danish Crematories 2000/.

Measurement of dioxin emission from one crematory in Denmark was carried out in 2000 /dk-TEKNIK 2000/. The oven operated was installed in 1996 and is heated by natural gas. 4 measurements each lasting 6 hours corresponding to the cremation of 4 bodies (1.5 hour/body) were undertaken. The flue gas temperature was approx. 345° C. The air emission reported ranged between 183 and 336 ng I-TEQ/cremation with an average of 283 ng I-TEQ/cremation. The crematory is taken as representative of Danish crematories as per today. Based on these figures the emission to air in Denmark from crematories can be estimated at approx. 0.01 g I-TEQ/year.

It is noted that the European Dioxin inventory assumes a default emission factor for emission to air of 8 mg I-TEQ/cremation and minimum/maximum values of 3 - 40 m g I-TEQ/cremation /Landesumweltamt Nordrhein-Westfalen 1997/.

It is also noted that the air emission of dioxins from cremation in Denmark in a previous report /Jensen, 1997/ has been estimated as 0.16 g I-TEQ/year, mainly based on Dutch investigations (reference is made to /Bremmer et al. 1994/). These investigations also form part of the fundament for the emission factors assumed by the European Dioxin inventory.

No knowledge exists regarding the content of dioxin in ashes from crematories. The dominant route of disposal for ash will be burying in the ground on cemeteries.

4.4 Other activities

A number of other activities that may be suspected to develop dioxins exist in Denmark. The available knowledge related to these activities is presented in the following. Generally the potential for dioxin formation may be assumed to be small, but no precise knowledge is available.

Fireworks

Fireworks should be suspected to develop dioxins, but no measurements seem to be available. The significance of fireworks (and bonfires - see section 4.1.2) may be illustrated by British observations that the concentration of dioxins in ambient air increased fourfold during the dominant bonfire event in the UK (/Dyke and Coleman 1995/ quoted in /Dyke et al 1997/).

Roof cardboard

In Denmark roof cardboard impregnated by bitumen is a common roof covering material, in particular on rather flat roofs. Construction and maintenance of such roofs is normally done by melting layers of roof cardboard together by heating with a gas flame. Formation of dioxins may likely take place by such operations, but no measurements are available.

Other burning/heating operations

Burning/heating operations are used for several activities and might in several cases be the cause of dioxin formation. Examples on such operations include:

	Removal of seed as an alternative to pesticide use.
	Heating of pipes and plates of copper for sanitation or construction purposes.
	Blacksmith activities and similar artisan's work.

Charcoals and charcoal briquettes used in garden grills and cooking in general

Danish investigations on garden grills have confirmed dioxin formation by food preparation on garden grills /dk-TEKNIK 2000/. 4 measurements each involving 2 kg of charcoal (briquettes) used for preparation of approx. 2 kg of meat were carried out. In each test sampling lasted for 2 hours including lighting of charcoal and preparation of meat. In 2 tests oil, salt and pepper was added to the meat in a quantity typical for meat grilling (approx. 15 g of salt per test). In each test 3 paraffin blocks of 18 g/block were used for the lighting process. The dioxin emission observed corresponded to emission factors ranging from 6 to15 ng I-TEQ/kg charcoals. The Danish import of charcoal for grilling and other purposes comes up to approx. 15,000 tonnes/year / Danmarks Statistik 1999a/. Assuming this quantity is used solely for garden grills, the total dioxin emission by garden grilling in Denmark can be estimated at 0.09 - 0.22 g I-TEQ/year. No measurements of the content of dioxins in ash or the grilled meat are available.

It is noted that dioxin formation may well be possible for other cooking operations, e.g. frying.

Smoking

Dioxin formation by cigarette smoking has been confirmed, and smoking is regarded as a source for direct human impact /Jensen 1997/. In an overall context it is likely marginal.

4.5 Summary

The assessments and estimates related to formation and turnover of dioxins by miscellaneous human and natural activities in Denmark by the end of the nineties and presented in section 4.1 to 4.4 are summarised in table 4.1

Table 4.1
Summary of formation and turnover of dioxins by miscellaneous human and natural activities in Denmark

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