A method for improving Centre for Environmental Studies (CML) characterisation factors for metal (eco)toxicity — the case of zinc gutters and downpipes

Abstract

Background, aim and scope: The environmental impact of building products made from heavy metals has been a topic of discussion for some years. This was fuelled by results of life cycle assessments (LCAs), where the emission of heavy metals strongly effected the results. An issue was that the characterisation factors of the Centre for Environmental Studies (CML) 2000 life cycle impact assessment (LCIA) methodology put too much emphasis on the impact of metal emissions. We adjusted Zn characterisation factors according to the most recent insights in the ecotoxicity of zinc and applied them in an LCA using zinc gutters and downpipes as an example. Materials and methods: The CML 2000 methodology was used to assess the environmental impact of the zinc products. To adjust the Zn characterisation factors, the uniform system for the evaluation of substances (USES)-LCA model and the biotic ligand model were used. Results and discussion: The first correction was based on updating the effect values for zinc. This resulted in a reduction of the characterisation factors for zinc to 42% of their original values. Additional correcting for the bioavailability of zinc leads to final Zn characterisation factors for the freshwater aquatic ecotoxicity potential (FAETP), the marine aquatic ecotoxicity potential (MAETP) and the terrestrial ecotoxicity potential (TETP) of 25%, 42% and 0.006%, respectively, of the original values. The CML 2000 LCIA methodology is based on the predicted no-effect concentration (PNEC) of a substance. PNEC is not value-free as political considerations are used to decide on it. Using a more robust toxicity measure as the hazardous concentration at which 50% of the species is affected (HC50) will provide value-free results. The production of standard high-grade zinc shows main contributions to six of the ten environmental impact categories. The recycling of zinc at the end of the life cycle shows beneficial effects for these same categories. Despite the reduction of the characterisation factor of Zn, the runoff emissions of Zn are still dominant. Conclusions and recommendations: To improve LCA characterisation factors for ecotoxicity in the CML 2000 methodology, it is recommended to use either the geometric mean of the effect data or the HC50. The HC50 should be based upon the EC50 values from chronic ecotoxicity tests. It is proposed to include the bioavailability of metals in LCA in three steps: (1) separate soluble fraction, (2) separate dissolved fraction and (3) separate bioavailable fraction. The issue of essentiality could not be resolved in this study. However, this could be accounted for by leaving out the fraction of the emission below the maximum permissible admission. © 2010 The Author(s).