Civil Engineering Reference
In-Depth Information
Production of timber-impregnating substances and the work at manufacturing
workshops can result in emissions of strong biological poisons into earth, air and
water. For products based on metal salts, the chrome, copper and arsenic used
are heavy metals with large biological amplification capacities. These substances
can quite easily combine with earth particles, but do not combine so easily with
sand, which delays the drainage and spread of the substances to some extent.
Acid rain increases the rate of drainage. In the solvent-based impregnation
industry, vaporized solvents can be released, such as aromates, phenols and dif-
ferent components containing chlorine. These substances, in the same way as
heavy metals, have a capacity for biological amplification and bind much less
with the soil.
In completed buildings creosote-impregnated timber emits, amongst other
things, naphthalene. Considerable concentrations of naphthalene have been
registered inside buildings even when the application has been outdoors
(Gustafsson, 1990). Creosote combined with solar radiation can cause rapid and
serious burning of the skin. A roof treated with creosote can heavily pollute the
garden and groundwater. Pentachlorophenol will emit chlorinated hydrocar-
bons into the air and soil long after impregnation is finished. Permetrine is par-
ticularly poisonous for organisms in water, and can also cause considerable
damage to the human's nervous system, including concentration problems and
general illness. It takes a relatively long time for the emissions to fully break
down.
Water-soluble metal salts are usually stable in buildings. They are, however,
released from exterior surfaces exposed to rain. In Denmark it has been calculat-
ed that a couple of tons of arsenic are washed out in this way annually.
When impregnated timber burns, many of the poisonous substances are
released, including about 80 per cent of the arsenic, so waste must be disposed
of at special tips. Even here, slow draining of poisons into the soil will occur. In
northern Europe there are, at the moment, several hundred thousand tons of cop-
per, chrome and arsenic stored in impregnated timber.
The least dangerous impregnating substances
Ta r
Wood tar is usually extracted from parts of pine that are rich in resin: the bole
and the roots, which are burned to charcoal. It can also be extracted from other
coniferous and deciduous trees. Tar from beech is widely used in mainland
Europe. Modern extraction techniques give a very clear tar - previously, when
burning took place in a charcoal stack, high levels of pitch and particles of car-
bon were included.
