Characterization factors for zinc terrestrial ecotoxicity including speciation

Purpose

Ignoring metal speciation in the determination of characterization factors (CFs) in life cycle assessment (LCA) could significantly alter the validity of LCA results since toxicity is directly linked to bioavailability.

Methods

Zinc terrestrial ecotoxicity CFs are obtained using modified USEtox fate factors, WHAM 6.0-derived bioavailable factors, and effect factors calculated using the assessment of mean impact (AMI) method with available terrestrial ecotoxicity data. Soil archetypes created using influent soil properties on Zn speciation (soil texture, pH, cation exchange capacity, organic matter and carbonate contents) are used to group soils of the world into a more manageable spatial resolution for LCA. An aggregated global CF value is obtained using population density as a Zn emission proxy. Results are presented in a world map to facilitate use.

Results and discussion

When using soluble Zn as the bioavailable fraction, CF values vary over 1.76 orders of magnitude, indicating that a single aggregated value could reasonably be used for the world. When using true solution Zn, CFs cover 14 orders of magnitude. To represent this variability, 518 archetypes and 13 groups of archetypes were created. Aggregated global default values are 4.58 potentially affected fraction of species (PAF) m³·day kg^?1 for soluble Zn and 1.45 PAF m³·day kg^?1 for true solution Zn. These values are respectively 28 and 88 times lower than the Zn terrestrial CF in IMPACT 2002 (128 PAF m³·day kg^?1).

Conclusions

The CFs obtained for Zn, except for soluble Zn, are at least 2 orders of magnitude lower than current CFs. However, they must be tested in case studies to measure the impact of including Zn speciation in the CF definition of terrestrial ecotoxicity.