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Background, aim, and scope A new trend driven by climate change concerns is the interest to label consumer products with a carbon footprint (CF) number. Here, we present a study that examines the uncertainty in the estimated CFs of a liquid and a compact powder detergent and how the uncertainty varies with the type of comparison one wishes to make. Materials and methods A simplified CF model for detergents, encompassing all life cycle stages, has been used for the calculation of CFs. The CFs for the two detergents were compared under three different cases: (1) a situation where most of life cycle assessment (LCA) system is similar, (2) a situation where the LCA background systems may be different but certain choices with regard to system boundaries are standardized, and (3) a situation where the LCA background system, choices of system boundaries, and foreground system may also be different. Uncertainty in the CFs was calculated for each of the three comparison situations using a stepwise sensitivity/uncertainty analysis approach. Results The stepwise approach makes it possible to obtain reliable uncertainty estimates without the need to have very good uncertainty descriptions for every input parameter. Only a few input parameters were found to drive the uncertainty of the CF values. For case 1, the uncertainties in the difference between the CF of the ultraliquid and compact powder products are very small. The CF of compact powder is always larger than that of the ultraliquid product. In case 3, the uncertainties become much larger, such that in 23% of the cases, a CF comparison would wrongly indicate that the compact powder product has a lower CF than the ultraliquid product. Case 2 falls between the extremes of cases 1 and 3. Discussion One of the challenges of developing userfriendly CF methods based on the ISO 14040 framework is to ensure a high level of comparability of CF values, such that misleading or oversimplified conclusions can be avoided. Our analysis shows how the uncertainty margins around the calculation of a CF for a set of given products will broaden as the assessment moves from an "internal" comparison to a comparison with data from third parties where there is no specific information how these data have been obtained. CF calculations based on internal comparisons can lead to very clear distinctions between products and illustrate the utility of a CF tool to optimize the environmental performance of products using difference analysis. Conclusions CF calculations for products can only provide a fair comparison if the LCA background system used for the two products is the same and exactly the same choices in the foreground system are made. In practice, this would

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Cleaning products have long been a focus of efforts to improve sustainability and assure safety for the aquatic environment when disposed of after use. The latter is addressed at ingredient level through environmental risk assessment, including in formal frameworks such as REACH. Nevertheless, in the context of programs to improve overall sustainability, stakeholders demand both environmental safety assurance and progress at product level. Current product-level approaches for aquatic toxicity (e.g., USEtox TM , Critical Dilution Volume) can be seen as predominantly hazard-based. The more logical approach would be risk-based, because ecotoxicity is generally threshold-dependent and hazard-based assessment produces conflicts with risk-based learnings. The development of a risk-based approach to assess formulated products is described: the International Association for Soaps, Detergents and Maintenance Products (A.I.S.E.) Charter Environmental Safety Check (ESC), which is consistent with the scientific principles underlying REACH. This is implemented through a simple spreadsheet tool and internal database of ingredient parameters including predicted no-effect concentration (PNEC) and removal rate. A novel feature is applying market volume information for both product types and ingredients to permit a risk-based calculation.To pass the ESC check, the projected environmental safety ratio (PESR) for each ingredient as formulated and dosed (unless cleared by a published risk assessment or exempted as inherently low risk) must be less than 1. The advantages of a risk-based approach are discussed. The strengths and limitations of various possible approaches to standard-setting, product-ranking and driving continuous improvement in respect of potential ecotoxic impacts on the aquatic environment are considered. It is proposed that as ecotoxicity is generally accepted to be threshold-dependent, with no effect below the threshold, the most constructive approach to continuous improvement of sustainability with regard to ecotoxicity is to focus efforts on instances where the safety margins for ingredients as used in specific products are narrow. This necessitates a risk-based approach.

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