Characterization modelling of aquatic ecotoxicity from metal emission to be applied in Life Cycle Impact Assessment

Following the Apeldoorn Declaration (Aboussouan et al. 2004) and Clearwater Consensus (Diamond et al. 2010), Gandhi et al. (2010) developed a new method to calculate metals Characterization Factor (CF) in freshwater and applied it on six metals, considering metals speciation and its impacts on bioavailability.

However, ecotoxicity of several metals that commonly appear in Life Cycle Inventory (LCI) have not yet been characterized in freshwater by the novel method. Ecotoxicity CF in marine ecosystem has received even less attention. In the previous Life Cycle Impact Assessment (LCIA) model, marine CF is either lacking (e.g.

USEtox, IMPACT 2002+), or derived by applying freshwater ecotoxicity data and ignoring metal speciation (e.g. USES-LCA). Moreover, the connection between freshwater and seawater, the estuary, which may act as a metal filter, is missing in the framework. To solve the problems mentioned above, this Ph.D. project aims at developing aquatic CFs for metals, including freshwater CF for 14 metals (Al(III), Ba, Be, Cd, Co, Cr(III), Cs, Cu(II), Fe(II), Fe(III), Mn(II), Ni, Pb, Sr and Zn) and marine CF for nine metals (Cd, Co, Cr(III), Cu, Fe(III), Mn, Ni, Pb and Zn) both for emission to seawater and for emission to freshwater.

The work builds on the method developed by Gandhi et al. (2010), accounting metals speciation and its impact on bioavailability but expands to ensure a broader coverage of metals and to cover the marine environment in addition to freshwater ecosystems. Metals speciation varies in different water chemistries.

Thus for each metal spatially differentiated freshwater CF was developed in seven different EU freshwater archetypes. Considering that emission location is often unknown in Life Cycle Assessment (LCA) studies, different averaging principles were tested on the spatially differentiated freshwater CFs to derive generic freshwater CFs, and the best approach was identified.

For similar reasons, spatially differentiated marine CF was developed first for 64 Large Marine Ecosystems (LMEs) covering all coastal seawaters in the whole world. Based on the spatially differentiated marine CFs, several generic CFs were developed applying different averaging principles and the generic marine CF most suitable for use in LCA was recommended.

The new sets of generic metal CFs were then applied in a case study, to test the impacts of new CFs when assessing Freshwater Ecotoxicity (FE) and Marine Ecotoxicity (ME) Impact Score (IS). CF was calculated as the product of Fate Factor (FF), Bioavailability Factor (BF) and Effect Factor (EF). The multimedia fate model embedded in USEtox (Rosenbaum et al. 2008) was modified and applied to calculate FF.

The chemical speciation model WHAM VII (Tipping et al. 2011) was used to calculate BF and partitioning coefficients for use in the calculation of FF, and the Free Ion Activitiy Model (FIAM) was adopted to derive EF. The resulting freshwater CF shows up to 2-6 orders of magnitude variations across freshwater archetypes for metals that form stable hydroxides in slightly alkaline waters (Al(III), Be, Cr(III), Cu(II) and Fe(III)), but it varies less than one order of magnitude for the other metals (Ba, Cd, Co, Cs, Fe(II), Mn(II), Ni, Pb, Sr and Zn), showing a much lower relevance of water archetype differentiation.

In slightly acidic water, Al(III) and Cu(II) have the highest CF of all the investigated metals, while Cd has the highest CF in other water types. The emission weighted freshwater CF was recommended to be applied as site-generic CF in the LCA studies where emission location and water chemistry of the receiving freshwater is unknown.

In marine ecosystems, the variation of marine CFs is up to 3-4 orders of magnitude for each metal cross LMEs, mainly caused by the variation in the residence time of seawater in each LME. In all LMEs the highest CF was observed for Cd, Pb or Zn. Fe has a true zero CF in all LMEs, since it is argued that it will not act as a toxic agent at the concentrations that occur in coastal seawaters, but rather as an essential nutrient to biota.

For all metals investigated, the highest CF was observed in the LMEs that have the longest residence times and correspondingly the lowest CF appears in the LMEs with the shortest residence times. Marine CF for Cd, Co, Mn, Ni and Zn emitted to freshwater is less than half an order of magnitude lower than marine CF for the same metals emitted to seawater.

The difference is largely due to metal removal in the freshwater compartment on the way to the coast, with a minor contribution from estuary removal. For the metals that have strong tendency to complex with particles (e.g. Cr, Cu and Pb), the difference between the two marine CFs is 1.5 orders of magnitude.

Here estuary removal noticeably reduces the fraction of metals that be transported to seawater by 25%-65%. Compared with freshwater CF, marine CF emitted to seawater shows a similar range for Cd, Co, Cr, Mn, Ni and Zn. But for Cu, freshwater CF is slightly higher than marine CF emitted to seawater, while for Pb freshwater CF is 1-4 orders of magnitude lower than marine CF emitted to seawater, depending on archetypes and LMEs.

For marine CFs both emitted to freshwater and seawater, weighting by the annual estuary discharge was recommended as averaging principle to calculate the sitegeneric CF to be applied in LCA studies where emission location is unknown. Compared with freshwater CFs calculated with the default parameter settings and databases in USES-LCA and USEtox, the recommended site-generic freshwater CFs in this study are mostly higher or similar, within ~2 orders of magnitude difference.

The recommended site-generic marine CFs for emission to seawater in this study are 1-4 orders of magnitude lower compared with the USES-LCA default CF with an egalitarian perspective except for Pb, for which the USESLCA CF is similar to the value found in this study. Marine CFs for emission to freshwater in this study are 1-2 orders of magnitude lower than USES-LCA CFs for Co, Cr, Cu and Ni.

For the rest of the investigated metals the CFs are similar or slightly higher than previous values. By applying the new CFs on a smartphone inventory, FE and ME IS were calculated. Metals still dominant toxicity impacts even with the revised CFs. Compared with IS calculated by default USES-LCA and USEtox CFs, the new ecotoxicity IS is 1.5 orders of magnitude higher in freshwater and half an order of magnitude lower in marine water.

The uncertainty of IS caused by ignoring emission location is two orders of magnitude, indicating that the difference between IS calculated with new CFs and previous CFs is modest. A number of relevant improvements on the developed method are discussed, mainly focusing on alternative metal speciation models, which may allow expanding the coverage of metals further, and an update of the ecotoxicity data.

For future research, it is recommended to develop ecotoxicity CF for sediment both in freshwater and marine ecosystem, to complement the framework of ecotoxicity impacts in the aquatic ecosystem in LCIA.