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Cleaner Technology Projects in Denmark 1997
Træbeskyttelsesmidler og imprægneret træ
Arbejdsrapport nr. 57, 1997, Miljøstyrelsen
In the report a mass flow analysis has been carried out for wood impregnated with
preservatives and for some of the most important substances. Regarding active substances
arsenic, cobber, chrome, tributylene and creosote were chosen. As representative
substances from the impregnation methods, pressure-, vacuum-, and surface impregnation were chosen. The substances’
health- and environmental toxicity is shortly described at the same time as possible
exposure situations are stated.
A couple of the substances, arsenic and creosote, are no longer used in Denmark,
but since the report also deals with the development of the amount of waste in impregnated
wood, and that these substances were previously used and are still imported in impregnated
wood, they are included.
By comparing the collected information on production, import and export, use and
disposal of wood impregnation substances and impregnated wood, a mass balance for 1992 has
been made. The mass balance has been divided in two parts: one part for the impregnated
wood, and the other for the used active substances.
The annual consumption of impregnated wood in Denmark is approx. 117.000 tons based on
1992 figures. The consumption is growing approx. 3% per year. The annual import and export
of impregnated wood is roughly the same when calculate din weight, but do not correspond
to each other with regards to the contents of impregnation substances and active
substances.
Pressure- and vacuum impregnated wood has an estimated lifespan of more than 32 years.
It is estimated that in 1992 8.000 tons impregnated wood was disposed of. This figure
must be used with caution since it is subject to a significant insecurity. Impregnated
wood is primarily disposed of via waste incineration or in waste disposal sites. But an
unknown quantity does end in private incineration or is re-cycled. With regards to the
latter the lifespan is increased an unknown number of years.
It is estimated that 2.7 mill. Tons impregnated wood has accumulated in Denmark in
1992. This quantity is presently beginning decay to waste. Within the frame of this
project it has not been possible to examine what matters and active substances the
accumulated wood contains.
The dominating method of impregnation is pressure impregnation. Provided that the
guidelines from the Environment Agencies for establishing and operating industrial
impregnation plants (vacuum – and pressure impregnation) are respected, these only
allow a very small amount of loss to the surroundings. However there is the de-steaming of
fluctuant organic combinations (FOC) from vacuum impregnation. There will also be
emissions of FOCs from the surface treatment matters that are solvent based.
It is approximated that in 1992 in the use phase, 1014 tons of metal from pressure
impregnated wood was released to the environment, and that 33 tons active substances
(˜ 6,6 tons of metal) from vacuum impregnated wood was released. A very cautious
estimate of the waste to the surroundings from surface treated wood is maximum 2 tons
active substances in 1992.
The active substances in the impregnated wood that was consumed in Denmark in 1992 came
partly from wood impregnate din Denmark and partly from imported wood or wood products.
This gave the following picture of active-substance consumption, either used a lone or in
combination with each other (figures are approximate figures): 222 tons chrome, 221 tons
cobber, 50 tons arsenic, 110 tons creosote, 14,5 tons TBTN/TBTO (˜ 4,2 tons tin) and
over 425 tons other active substances.
Active substances containing arsenic that were supplied to the Danish market in 1992
came almost exclusively from import. Correspondingly creosote was only found in imported
wood since impregnation against wood destructive fungus and insects is forbidden in
Denmark. With regards to the remaining substances, import and export has only a limited
significance for the actual amount found in the used wood.
The health risk is largest in impregnated wood where there is a risk of exposure
through breathing, where the active substances come in contact with the skin, or via the
organic solvents in the production phase and by handling and working with the wood. If the
work environment laws are followed the risk is though minimal.
The most important potential sources of pollution of the outer environment of the
impregnation plant are the handling of chemicals, spillage, accidents or through washout.
The latter can result in heavy local pollution. The more diffuse pollution,
individual’s handling of chemicals and washout from used impregnated wood can be
alarming, but at present there is no general view of these situations. If the impregnated
wood is used or stored in large quantities, a large accumulation of active substances in
the environment from washouts and decomposed wood can be expected.
Impregnated wood must be treated as dangerous waste and be deposited at controlled
waste disposal sites or burnt in controlled incineration plants.
Author/ institution
Ole Christian Hansen, Henriette Færgemann og Susanne Møller, Denmark’s
Technological University, Lotte Kau Andersen and Christian Poll, Environmental Technique.
This report is subsidised by the National Council for Recycling and Cleaner Technology
ISSN no. 0908-9195
ISBN no. 87-7810-803-9
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