Page 238 - Materials Chemistry, Second Edition

222 4 Life Cycle Impact Assessment

With energetic raw materials reference energies must be specified. Different
resources store exergy in different forms of energy, such as chemical, thermal,
kinetic, potential and nuclear energy. Which form is to be assigned to a specific
material, and so on, depends on the use of the resource 113) :
• chemical exergy for all material resources, biomass, water and fossil fuels (all
materials with exception of the reference compounds in a reference state – these
obtain the value zero);
• thermal exergy for geothermal energy (no material transfer);
• kinetic exergy for wind energy (wind generator);
• potential exergy for water in hydro-electric power plants;
• nuclear exergy for nuclear fission in nuclear power stations;
• radiating exergy for solar radiation (solar panel).
According to this listing, exergy is allocated to both scarce resources (some material
resources, water in many parts of the world, potential energy for conventional water
power) as well as to those with practically unlimited reserves (solar radiation, wind
energy). Therefore a CExD as scarceness indicator for energy resources is only of
limited use. This valuation might vary for material resources because here a large
dilution, which implies a large expenditure for the mining, must be included in
the result.
Due to missing experience with CExD in real LCA, this indicator should be
regarded as a highly interesting area of research within the impact assessment.
Exergy values suitable for the setting up of characterisation factors can be extracted
from the quoted work papers and have already been integrated into the ecoinvent
data base.

4.5.1.4 Consumption of Biotic Resources
Biotic resources are living natural beings and communities, which grow without
direct human effort, reproduce and have a specific function within the natural
ecological systems. 114) To these belong the fish of the seas, rainforests (more
general: natural forests), and their plants and animals, not products of agriculture
and forestry plus related techniques like commercial aquaculture (‘fish farms’), all
kinds of plantation economy, keeping of domestic cattle, and so on. The reason
for this separation is the general system boundary of LCA: The technosphere is
separated from the ecosphere, and all anthropogenic activities are based within the
technosphere. The environment is by this definition everything that is not part of
the technosphere.
Biotic resources are mostly, but not always regenerative. For example, tropical
rain forests cannot be sustainably cultivated because it is already heavily damaged
by the building of roads necessary for development, and hence, tropical wood from
primary forests cannot be regarded as regenerative. Game in the wild is a border
line case in cultural forests, for example, in the high mountains. This game, fit

113) B¨ osch et al. (2007).
114) M¨ uller-Wenk (2002a).