Page 297 - Materials Chemistry, Second Edition

4.5 Impact Categories, Impact Indicators and Characterisation Factors 281

animals living in the wild by endocrine disruptors or potential side-effects of
GMOs. 329)
2. Ecological systems can also react less sensitively than individuals of a species
The disappearance of only one species in an ecosystem will generally not destroy
the complex interdependency: another species with similar environmental
requirements will replace the extinct one and provide the function of the
former species (occupy an ecological niche). If it is not a remarkable species,
only specialists will be able to perceive the difference.
Ecosystems go through a development from youth to maturity or climax. A perma-
nent biocoenosis develops, according to regional climates and local soils, water and
topographic conditions. Climax ecosystems are therefore highly different from one
another, for example, tropical rain forests, oak and beech mixed woodlands, lakes
in the high mountains or savannah. These spacious ecological systems are called
biomes. In relation to stages of youth and growth, characteristics of climax systems
are:
• huge variety in spatial and functional structuring;
• often interlaced food chains;
• closed nutrient cycles;
• good stability towards small and small stability towards large disturbances from
the outside;
• small net primary production. This means that biomass cannot be extracted
without a major disturbance of the system.
In relation to the stage of youth, stability against small disturbances is based on a
larger flexibility of the complex interdependency in the climax system. With large
disturbances the system needs a very long time to again develop into a climax
ecosystem. If, for example, in a region with tropical rain forest the relatively thin
humus layer due to clear cutting and violent rainfalls is washed away, for a very
long period the tropical rain forest will not develop because of the now changed
local soil and water conditions.

Resumee It is not possible from single species tests to deduce statements con-
cerning ecosystems, it is however done taking into account ‘safety factors’. The
results are NECs, NOECs or PNECs. The values are derived from measured values
(the lowest measured effect concentration; at best only LC values are available
50
on several organisms or for longer durations to be able also to determine chronic
effects). They are usually defined for water as a test environment. For the compart-
ments soil and sediment, there are much less values available; air in ecotoxicity
is only concerned as the recipient and transportation medium. Phytotoxic effects
can be transferred directly by air. In LCA these effects are partly considered by
the impact categories acidification and summer smog. Also global atmospheric
impacts, which in a wider sense are part of ecotoxicity as well, are addressed in
separate impact categories. Scientific ecotoxicology, similarly to human toxicology,

329) Kl¨ opffer et al. (1999) and Kl¨ opffer (1998a, 2001).