Page 244 - Materials Chemistry, Second Edition

230 R.K. Rosenbaum et al.

(3) persistence, (4) exposure patterns and bioavailability and (5) toxicity, with the
latter four considered by the characterisation factor.
This shows that toxicity is not the only parameter that determines the potential
ecotoxic impact of a chemical in the environment as it first has to reach and enter a
potential target organism. For example, a substance may be very toxic, but never
reach any organism due to its short lifetime in the environment (e.g. rapid degra-
dation) or because it is not sufficiently mobile to be transported to a target organism
and ends up bound to soil or buried in sediment, in which case it contributes little to
ecotoxic impacts. On the other hand, another substance may not be very toxic, but if
it is emitted in large quantities and over prolonged periods of time or has a strong
environmental persistence, it may still cause an ecotoxic impact.
Chemical emissions into the environment will affect terrestrial, freshwater,
marine and aerial (i.e. flying and gliding animals) ecosystems depending on the
environmental conditions of the place and time of emission and the characteristics
of the substance emitted. They can affect natural organisms in many different ways,
causing increased mortality, reduced mobility, reduced growth or reproduction rate,
mutations, behavioural changes, changes in biomass or photosynthesis, activity etc.

10.11.2 Environmental Mechanism

As shown in Fig. 10.17, the environmental mechanism of ecotoxic impacts of
chemicals in LCA can be divided into four consecutive steps.
1. Fate modelling estimates the increase in concentration in a given environmental
medium due to an emission quantified in the life cycle inventory
2. The exposure model quantifies the chemical’s bioavailability in the different
media by determining the bioavailable fraction out of the total concentration
3. The effect model relates the amount available to an effect on the ecosystem. This
is typically considered a midpoint indicator in LCA, as no distinction between
the severity of observed effects is made (e.g. a temporary/reversible decrease in
mobility and death are given the same importance)
4. Finally, the severity (or damage) model translates the effects on the ecosystem
into an ecosystem population (i.e. biodiversity) change integrated over time and
space
All four parts of this environmental mechanism are accounted for in the defi-
nition of the substance-specific and emission compartment-specific ecotoxicity
characterisation factor CF eco :

CF eco ¼ FF XF eco EF eco SF eco ð10:6Þ
where FF is the fate factor, XF eco the ecosystem exposure factor, EF eco the eco-
toxicity effect factor (midpoint effects), and SF eco the ecosystem severity factor
(endpoint effects). Each of these four elements of the environmental mechanism of