Page 199 - Materials Chemistry, Second Edition

4.2 Method of Critical Volumes 183

Example

Potential Environmental Impact
An impact is always by definition related and unambiguously assignable to a
cause. The environmental impacts of a product system in its life cycle have their
cause in consumption (inputs) and releases (outputs), which are determined in
the inventory. If, for example, within various processes of a life cycle of a product
+
acids (substance-immanent property: release of H O -ions in aqueous solution
3
and thus decrease of pH value) are released into the air, which thenes reach the
soil and rivers, then acids are the cause for acid rain as well as soil and water
acidification. The decreased pH value can have a set of impacts, like skin damage,
fish mortality, remobilisation of heavy metals and much more. Insofar cause–effect
relationships exist.
As consumptions and releases of the product system which are listed in the
inventory can rarely be assigned to a single definable location, the extent of
damage at a certain place cannot or can only rarely be quantified: Concerning an
environmental impact to be expected, it is a substantial difference whether 1 kg
hydrogen chloride (HCl) eludes within a short time from only one chimney into
the neighbourhood or whether during the entire life cycle of the product small
quantities are released from many plants distributed over a large geographical
area resulting in a 1 kg release, calculated on the overall system and applied to the
fU. As the fU is chosen by convenience, results of the inventory can amount to
a multiple or a fraction of 1 kg. The results of an inventory can therefore not be
correlated to existing concentrations. Two product systems with correctly defined
fUs can however be compared to one another concerning the output ‘HCl into air’.
To adequately account for the uncertainty of the exposition, we speak of
‘potential environmental impacts’ in LCIA. If a differentiated exposition analysis
is accomplished and thus a risk assessment is feasible, this has to be explicitly
described in the context of the impact assessment (see also Section 4.5.3).

4.2
Method of Critical Volumes

The method of critical volumes, although outdated, is shortly appreciated for its
impact on the methodological development, as also on the CML method. It was
8)
suggested for the first time in the famous Swiss ‘BUS report’ in 1984 and contains
an aggregation of the emissions into air and into water in the case of existing
regulations indicating threshold values. The method can also be applied to the soil
compartment but was only rarely used for lack of threshold values. The method
can, in principle, be applied to ground waters also.

8) BUS (1984), BUWAL (1991) and Kl¨ opffer and Renner (1995).