Page 94 - Materials Chemistry, Second Edition

76 LIFE CYCLE ASSESSMENT HANDBOOK

In practice many methods do not report the endpoint level (case of skin
cancer), which is an interim result but reported in a damage units. These
damage models can have units of Disability Adjusted Life Years (DALYs), an
aggregation of environmental impacts, monetary value, or other aggregated
damage units.
Even though the remainder of the environmental mechanism from mid-
point to endpoint to damages describes the link to environmentally relevant
endpoint indicators, this sometimes occurs at the expenses of the compre-
hensive nature of the midpoint, and likely resulting in higher uncertainty.
In certain categories, providing methodological approaches that character-
ize the environmental mechanism closer to endpoints and damages does not
provide additional distinction of differences in impact between substances.
However, a model between damage and midpoint may add relevance (either
in a quantitative or qualitative manner - in cases where quantification of
endpoints is difficult to impossible), and this relevance may be added for
all substances in the same way This could also enable us to compare the
outcomes of different midpoint categories using models based on natural
science instead of weighting factors based on social science. In a midpoint
model it seems wise to minimize the unnecessary uncertainty by choosing
a midpoint indicator as early as possible in the environmental chain where
all substances are unified in an indicator yet the five criteria are still satisfied:
comprehensiveness, relevance/reproducibility, transparency, validity and
compatibility (see Section 1).
The second group of impact categories, illustrated in Figure 4.5, may not
have a common midpoint and are comprised of different environmental mech-
anisms. Examples of the second type of impact categories which are almost
always represented at an aggregated level (either at damage or midpoint level)
include human toxicity and ecotoxicity, where interim human health endpoints
that may be aggregated include neurological, reproductive, respiratory, and
cardiovascular health endpoints. The aggregation may be in units of DALYs,
monetary value, or a unitless score which is based on the relative human toxic-
ity potency after including the fate, transport, and toxicity of the substances
and comparing to a reference substance.
The ILCD Handbook suggests considering the following points (EC-JRC
2010a):

1. For the first group of impact categories described above, the goal
of damage modeling is to make results in different midpoint cat-
egories comparable, and sometimes to arrive to a single score,
or smaller number of environmental scores. It can then replace
or support weighting practices in the midpoint approaches. The
choice to stay at the midpoint level or go to the damage level is
left to the user.
2. When the decision has been made to go to the damage level on an
impact category of the first type (e.g., global climate change), care
must be taken to ensure comprehensiveness. For example, while