Page 249 - Materials Chemistry, Second Edition

10 Life Cycle Impact Assessment 235

The HC50 value can be determined from the SSD curve but is often, more
conveniently, calculated as the geometric mean of the EC50 values per species s,
respectively:

1 X
log HC50 ¼ log EC50 s ð10:8Þ
n s
s
where n s is the number of species.
A damage model, incorporating the severity of the effect, goes even further
along the cause–effect chain and quantifies how many species are disappearing
(instead of ‘just’ affected) from a given ecosystem. Disappearance may be caused
by mortality, reduced proliferation or migration, for example.

10.11.3 Emissions and Main Sources

Chemicals are a main pillar of our industrialised economy, they are used in virtually
any product around the globe and therefore numerous, used in large quantities and
emitted from nearly all processes that an LCI may contain. Ecotoxity is very
different from any other (non-toxicity) impact category when it comes to the
number of potentially relevant elementary flows. Whereas no other (non-toxicity)
impact category—with the exception of photochemical ozone formation—exceeds
100 contributing elementary flows (and related characterisation factors), the toxicity
categories are facing the challenge of having to characterise several tens of thou-
sands of chemicals with huge differences in their abilities to cause toxic impacts.
The CAS registry currently (end of 2016) contains more than 124 million unique
organic and inorganic structures (www.cas.org/about-cas/cas-fact-sheets) of which
roughly 200,000 may play an industrial role as reflected by the ever increasing
number of more than 123,000 substances registered in the European Classification
and Labelling Inventory Database which contains REACH (Registration,
Evaluation, Authorisation and Restriction of Chemical substances) registrations and
CLP (Classification, Labelling and Packaging of substances and mixtures) notifi-
cations so far received by the European Chemicals Agency (ECHA: http://echa.
europa.eu/information-on-chemicals/cl-inventory-database). Current LCIA models
cover around 3000 substances for aquatic ecotoxicity.

10.11.4 Existing Characterisation Models

Characterisation methods like EDIP account for fate and exposure relying on key
properties of the chemical applied to empirical models. Mechanistic models and
methodologies have been published accounting for fate, exposure and effects