| Results |
Effect assessment
Current effect characterisation factors in LCA (CML2 method) are based on PNECs derived from extreme toxicity levels (HC5 of NOECs). Two recommendations are made based on average instead of extreme toxicity levels:
- use the HC50 or geometric mean of available NOEC data;
- base the HC50 upon EC50 values instead of NOEC values from the same chronic ecotoxicity tests.
I n the case of zinc it is recommended to:
- start working with a zinc PNEC of 15.6 instead of 6.6 µg/l for the aquatic environment and a zinc PNEC of 27000 instead of 6700 µg/kg for the terrestrial environment. The proposed values are based on more recent data and replace the LCA-CML database values.
Bioavailability
(right) Figure 1. Schematic overview of the potential corrections on the load of an essential metal in order to account for bioavailability in LCA.
Figure 1 shows the proposed bioavailability correction of metals in LCA in three steps. The present CML method for LCA only accounts for step 2 in the water phase.
The bioavailability correction for zinc has been assessed. No correction can be made for step 1 due to a lack of information. Correction step 2 and step 3 depend on the environmental compartment of concern (see Table 1).
Table 1. Corrected bioavailability of zinc for the three ecotoxicity impact categories (relative to original value).
|
Fractions |
Freshwater |
Marine |
Soil |
|
Soluble (step 1) |
100% * |
100% * |
100% * |
|
Dissolved (step 2) |
100% # |
100% # |
0.04% |
|
Bioavailable (BLM) (step 3) |
60% $ |
100% # |
33% # |
|
Total bioavailable |
60% |
100% |
0.013% | * set to 100% (worst case), lack of available data
# set to 100% (worst case) of a relatively wide range (site specific)
$ average case of a wide range (site specific)
Essentiality
Essentiality could be accounted for in LCA by leaving out the fraction of emissions leading to concentration addition less than the Maximum Permissible Addition (MPA) (see figure 2). Deficiency levels, background concentrations and MPA influence the essentiality correction for metals but depend on species (communities) and geographic locations and scales (local, regional, global). This complex issue needs to be elaborated by a group of experts.
Figure 2. Schematic overview of the deficiency and toxicity curves for essential metals, showing the deficiency and toxicity boundaries, indicating the homeostatic regulation range.
Case study: LCA zinc gutter and downpipe
Characterisation factors for zinc in three ecotoxicity impact categories freshwater ecotoxicity potential (FAETP), marine aquatic ecotoxicity potential (MAETP) and terrestrial ecotoxicity potential (TETP) are adjusted for the two abovementioned modifications types: effect assessment (PNEC) and bioavailability (see Table 2) and subsequently applied in a LCA for zinc gutter and downpipe on a Dutch reference house using the CLM2 method.
Table 2. Corrected characterization factors for zinc for the three ecotoxicity impact categories (relative to original values).
|
Correction |
FAETP |
MAETP |
TETP |
|
Effect (PNEC) |
42% |
42% |
25% |
|
Bioavailability |
60% |
100% |
0.013% |
|
Total |
25.2% |
42.0% |
0.0033% |
The total correction of the characterisation factors on the outcome of the zinc gutter and downpipe LCA is most pronounced for FAETP (65% reduction, followed by TETP (28% reduction) and MAETP (17% reduction). It can be concluded that the influence of both types of modifications is substantial for zinc but strongly varies among the environmental impact categories.
|