Page 299 - Materials Chemistry, Second Edition

4.5 Impact Categories, Impact Indicators and Characterisation Factors 283

If the reference of OELs leads to a relative weighting of the HTP of substances, a
formal relative weighting concerning the documented NECs is similarly obtained.
The difference is that usually a large data background is consulted for the derivation
of limit and indicative values for the protection of the human health. NEC and NOEC
values on the other hand usually bear no relation to the complex interdependencies
in ecosystems, (see discussion on the protection goal above) but were determined
for single organisms. Nevertheless it is a first step towards a relative weighting of
the ecotoxicity. A further disadvantage of the simple weighting is the neglect of
persistence and bioaccumulation of compounds, which should be determined in an
extra score or at least in a list from the inventory. Otherwise the most toxic persistent
environmental chemicals often without a high acute toxicity would by aggregation
not (or not sufficiently) be considered. 334) Substances with a very high ecotoxicity
−1
(LC < 1 μgl ) dominate the result. Contrary to human toxicity, which only refers
50
to humans, biologically speaking to a single species gives rise to a predicament, as
described in Sections 4.5.3.3.1 and 4.5.3.3.2 for ecotoxicity, as to the exact objective
of the protection goal and to the choice of the impact indicator, which describes
the damaging impacts. Simple characterisations according to Equation 4.31 will
therefore only be recommendable for simple LCAs and must be justified within
the ‘goal and scope’.

4.5.3.3.4 Inclusion of Persistence and Distribution into Quantification An inclusion
of substance properties, which describe transport, distribution and degradation,
requires more subtle structured impact indicators. These must include a fate
factor (F) according to the formula described in the paragraph on human toxicity
(Equation 4.30):
m
S = E F M n (4.30)
i i i i
S i nm score of a substance i for compartment m, the release originating in
compartment n
E effect factor (for (target) compartment m)
F fate (distribution from compartment n to m and degradation)
M mass (entry of substance i into compartment n per fU).

Reciprocal NOEC, which are known for the regarded compartment m (water, soil
and sediment) and preferably have been evaluated, can be used. Values that have
been determined for multiple species and have been averaged are more meaningful
than those of a single species. 335)
Modelling necessary for the computation of fate factors are state of the art 336) ,the
problem being boundary conditions like the size of compartments (global or local),
selected transfer and degradation models as well as numbers for degradation and

334) Stephenson (1977), Frische et al. (1982), Kl¨ opffer (1989, 1994a, 2001), M¨ uller-Herold (1996),
Scheringer (1999) and Kl¨ opffer and Wagner (2007a,b).
335) Larsen and Hauschild (2007a,b).
336) Mackay (1991), Trapp and Matthies (1996, 1998), Fenner et al. (2005) and Kl¨ opffer (2012b)