Page 270 - Materials Chemistry, Second Edition

254 4 Life Cycle Impact Assessment

4.5.2.5 Acidification
The inclusion of the impact category ‘acidification’ can be related to the following
environmental problem areas:
• acidification of unbuffered waters
• damage to forests
• acidification of soils.

In the first case which has particularly been observed within the crystalline region
of South Scandinavia, 229) a direct causal chain can be presumed between emissions
and impact. In the south of Norway and Sweden, freshwater lakes on granite
bedrock were transformed into diluted acids as a result of acid precipitation. Under
the influence of acids, Al 3+ ions, which are toxic for aquatic organism, dissolve
from aluminium silicates. These ions are absent at normal pH levels (about
5.5–6; unbuffered equilibrium with CO of the troposphere). Aluminium ions, the
2
acid itself and possibly further dissolved products extinguish most organisms of
these usually shallow lakes. In Scandinavia a chemical analysis of precipitation at
different times showed a relation between the direction of the wind and the acid load.
Highest loads always occurred with winds from Great Britain and the Continent.
Acidification was caused mainly by European power plants. A misleading ‘policy of
high chimneys’ only aimed at a dilution of pollutants. Improvements in cleansing
technology slowly improved the air quality, especially with regard to SO .
2
An acidification of waters that can be observed in Scandinavia is typical for all
scarcely buffered surface waters, partly and indirectly also for groundwater of the
crystalline rock, which come into contact with air masses from industrial areas.
Part of the acid-forming gases also originates from agriculture. To these, belongs
the base ammonia, which by oxidation is transformed into NO ,which in the
x
end reacts with water in an oxidising environment to become nitric acid. NH 3
+
and NH , respectively, which enter soil and waters, are oxidised by bacterial
4
nitrification and contribute to acidification.
A second environmental area related to acidification is the so-called novel
damage to the forest. While direct damage to vegetation by acid gases has been
known for 150 a 230) – so to speak acute phytotoxic impacts by high concentration
of acid gases – these novel damages have only been studied since around 1970.
In Germany, a political issue of forest decline was initialised by an article in
the magazine ‘Der Spiegel’ in 1980; only 3 a later a special report of a board
of environmental experts on the subject of forest decline and air pollution was
published. 231) A first hypothesis by Professor Ulrich 232) was similar to the one
explaining the impacts of acidification of lakes: a discharge of toxic ions into the
soils of the forests, implying a damage to mycorrhiza (symbiotic association between
a fungus and the roots of plants), nitrogen over-fertilisation of low nutrient forest
soils, and so on. This rather mono-causal interpretation could not be maintained as

229) Fabian (1992, Section 4.2).
230) Stoklasa (1923).
231) RSU (1983).
232) Ulrich (1984).