Fate and distribution modelling of metals in life cycle impact assessment

Environmental risk assessment (ERA) and life cycle impact assessment (LCIA) models developed for the assessment of one form of non-ionic organic compounds, here termed species, have gained wide acceptance and use in assessments of chemicals in both ERA and LCIA (single-species approach). However, the aqueous chemistry of metal ions is very different from that of non-ionic organic compounds, since metals speciate into multi-species according to ambient aqueous and geochemical conditions as pH and availability of complexing agents (e.g. dissolved organic matter (DOM), chloride, carbonate). This study demonstrates a new modelling concept being able to perform both single-species assessment (SSA) and multi-species assessment (MSA). By applying multi-species fate modelling, the model has been shown able to account for a change in mobility of metals through coupled regions, caused by complexes formed with ligands such as DOM. It is concluded that single-species models should not be used to characterize the potential ecotoxicological impacts of metals in LCIA. Applying multi-species assessment methods strongly influences the availability of the most bioavailable form-the free metal ion, but it also makes the fate and exposure modelling of metals significantly more dependent on ambient conditions reflecting the very different speciation pattern and behaviour of metals at different sites.