Biomedical Engineering Reference
In-Depth Information
effect factor. While the conservative nature of the PNEC concept suits the
purpose of chemical risk assessment, recent expert workshops
103,193,194
have
recommended that the purpose of LCIA is served better with more robust
and less conservative effect parameters. For the concentration at which 50%
of the species are affected, the HC
50
was found suitable.
195-199
It is calculated as
the geometric mean of all the EC
50
values of the species measured and shows
the potentially affected fraction of species exposed above their chronic EC
50
value. Using HC
50
in LCA enables a more robust derivation of freshwater
ecotoxicological effect factors because it is less dependent on the species
tested than the PNEC or on safety factors.
In keeping with the recommendations to use a more robust effect param-
eter, an effect-based chronic PAF approach has been retained as best practice
for comparative assessment, leading to the adoption of the following defini-
tion of freshwater ecotoxicological effect factor (EF) in USEtox:
0.
EF
=
(11.5)
HC50
EC50
Species selection for calculation of HC
50
values should in general aim for
the highest physiological variability, for as many species as possible, repre-
senting as many taxonomic groups as possible. Information on most com-
monly used nanoparticles and on their basic constituents are becoming
available in the literature, the first ecotoxicological tests on common species
having been recently made available. For instance, Lovern al.
200
observed
a significant acute toxicity in
Daphnia magna
when associated with TiO
2
or
C
60
-fullerenes. Haasch et al.
201
showed that the toxicity of the latter can be
influenced by the solvent used to solubilize it. At this time, exposure data
are becoming increasingly available and published.
202,203
It is therefore very
likely that it will be feasible to complement the USEtox HC
50
database of close
to 1000 chemicals (merge of five databases
196
) with HC
50
values for the most
commonly studied nanoparticles.
11.3.4 Nanospecific Interpretation
Understanding and quantifying main uncertainties:
In the rapidly evolv-
ing nanoproduct field, understanding uncertainties and the limitations in
the LCA studies due to missing life cycle stages or impact categories is cru-
cial to properly inform decision making. However, very few of the case stud-
ies provide assessment of uncertainties. Moreover, uncertainties in LCA are
often focused on the sole inventory, whereas large variations between meth-
ods and data also occur in the LCIA step.
It is therefore important for every nano-LCA to provide estimates of
uncertainty and variability of results for nanoproducts and to put them in
perspective compared with the variability across all chemical substances
