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USEtox—the UNEP-SETAC toxicity model: recommended characterisation factors for human toxicity and freshwater ecotoxicity in life cycle impact assessment

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Abstract

Background, aim and scope

In 2005, a comprehensive comparison of life cycle impact assessment toxicity characterisation models was initiated by the United Nations Environment Program (UNEP)–Society for Environmental Toxicology and Chemistry (SETAC) Life Cycle Initiative, directly involving the model developers of CalTOX, IMPACT 2002, USES-LCA, BETR, EDIP, WATSON and EcoSense. In this paper, we describe this model comparison process and its results—in particular the scientific consensus model developed by the model developers. The main objectives of this effort were (1) to identify specific sources of differences between the models’ results and structure, (2) to detect the indispensable model components and (3) to build a scientific consensus model from them, representing recommended practice.

Materials and methods

A chemical test set of 45 organics covering a wide range of property combinations was selected for this purpose. All models used this set. In three workshops, the model comparison participants identified key fate, exposure and effect issues via comparison of the final characterisation factors and selected intermediate outputs for fate, human exposure and toxic effects for the test set applied to all models.

Results

Through this process, we were able to reduce inter-model variation from an initial range of up to 13 orders of magnitude down to no more than two orders of magnitude for any substance. This led to the development of USEtox, a scientific consensus model that contains only the most influential model elements. These were, for example, process formulations accounting for intermittent rain, defining a closed or open system environment or nesting an urban box in a continental box.

Discussion

The precision of the new characterisation factors (CFs) is within a factor of 100–1,000 for human health and 10–100 for freshwater ecotoxicity of all other models compared to 12 orders of magnitude variation between the CFs of each model, respectively. The achieved reduction of inter-model variability by up to 11 orders of magnitude is a significant improvement.

Conclusions

USEtox provides a parsimonious and transparent tool for human health and ecosystem CF estimates. Based on a referenced database, it has now been used to calculate CFs for several thousand substances and forms the basis of the recommendations from UNEP-SETAC’s Life Cycle Initiative regarding characterisation of toxic impacts in life cycle assessment.

Recommendations and perspectives

We provide both recommended and interim (not recommended and to be used with caution) characterisation factors for human health and freshwater ecotoxicity impacts. After a process of consensus building among stakeholders on a broad scale as well as several improvements regarding a wider and easier applicability of the model, USEtox will become available to practitioners for the calculation of further CFs.

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Notes

  1. The following procedure has been applied: (1) selecting those (665) chemicals from the list of 5,019 substances that had a pK a value listed, (2) scoring substances that can donate a proton ‘a’ and those that can accept a proton as ‘b’, (3) calculating the fraction of the substance that is expected to be present in its original, neutral form at pH 7 and (4) flagging acids with pK a <6 and bases with pK a >8 ‘F’ [note that these are the substances with F(neutral) <10%]. Chemicals that are listed as salts need special attention. If the K ow listed for these chemicals pertain to the salt form, the K ow may be used to estimate K p. If it pertains to the conjugated acid or base, it needs to be corrected: Neglecting the possible contribution of the ionic form to hydrophobicity, we can use the product F(neutral) × K ow as a basis for estimating K aw, K p and BCF.

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Acknowledgement

Most of the work for this project was carried out on a voluntary basis and financed by in-kind contributions from the authors’ home institutions which are therefore gratefully acknowledged. The work was performed under the auspices of the UNEP-SETAC Life Cycle Initiative which also provided logistic and financial support and facilitated stakeholder consultations. The financial support from ACC (American Chemical Council) and ICMM (International Council on Mining and Metals) is also gratefully acknowledged. A number of persons have contributed to the process and success of the model comparison and scientific consensus model development. The authors are grateful for the participation of Miriam Diamond, Louise Deschênes, Bill Adams, Andrea Russel, Jeroen Guinée, Pierre-Yves Robidoux, Stefanie Hellweg, Evangelia Demou, Stig Irving Olsen, Cécile Bulle, Sau Soon Chen, Manuel Olivera, Julian Marshall, Bert-Droste Franke, Peter Fantke, Oleg Travnikov, Dick de Zwart, Peter Chapman, Kees van Gestel and Thomas H. Slone.

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Correspondence to Ralph K. Rosenbaum.

Electronic supplementary material

Below is the link to the electronic supplementary materialSupporting information A set of supporting information is available online, accompanying this paper. It comprises a full list of recommended and interim CFs, including a selection of intermediary parameters: intake fractions (inhalation, ingestion), effect factors (cancer, non-cancer, freshwater ecotoxicity), fate factors (air, water, soil), etc. in Excel format. The complete chemical data base and the model are available through the authors and might become accessible via the internet (under www.usetox.com) in the future. Further, an overview of the general qualitative model-analysis criteria and a brief summary of the qualitative analysis results are included in the supporting information.

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Rosenbaum, R.K., Bachmann, T.M., Gold, L.S. et al. USEtox—the UNEP-SETAC toxicity model: recommended characterisation factors for human toxicity and freshwater ecotoxicity in life cycle impact assessment. Int J Life Cycle Assess 13, 532–546 (2008). https://doi.org/10.1007/s11367-008-0038-4

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