A bright future for addressing chemical emissions in life cycle assessment

What you have in your hands or on your screen is a special issue of the International Journal of Life Cycle Assessment dedicated to the impact assessment of chemical emissions occurring along the life cycle of products and services.It counts in total 13 papers on human toxicity and ecotoxicity impacts in life cycle assessment (LCA) and, in particular, on the recently developed international consensus model USEtox.The model was officially launched in May 2010 and has since then been downloaded and applied by users in multiple settings.Since its release, USEtox has been disseminated through the official web page (www.usetox.org),training courses (also accessible as video-streaming-see home page) and incorporation into the major LCA software tools.Its use is encouraged by the United Nations Environment Programme-Society for Environmental Toxicology and Chemistry (UNEP-SETAC) Life Cycle Initiative, and it is under consideration for recommendation as part of the European Commission's ILCD system.A full issue of the journal is dedicated to the further documentation of the model and discussions of experience with its use.Here, we summarize the challenges of assessing chemical impacts in LCA, as identified by the papers in this special issue.Depending on the properties of a chemical, its toxic impacts on human beings and natural organisms and ecosystems can occur through many different mechanisms, e.g.carcinogenicity, neurotoxicity, or endocrine disruption.An emission inventory for a product system easily contains hundreds of substances, and many of these will have the potential to cause toxic impacts depending on the fate and exposure that can follow very diverse routes.Overall, the number of chemicals that are applied in products totals well above 10,000.In principle, all of these may occur as an emission in a life cycle inventory, and they should therefore be covered in the life cycle impact assessment.The coverage with human or ecotoxicity characterization factors of the emission flows in the inventory thus represents a grand challenge.The challenge is further increased by the absence of measurements of key substance properties like toxicity and biodegradability for the majority of all these chemicals.A number of different models for characterization of toxic impacts from chemical emissions have been developed over the last 15 years with differences in scope, modelling principles, and in the characterization factors they provide.The number of substances for which the models provide characterization factors is typically 100-500 substances.This unsatisfactory situation was the background on which a Task Force on Toxic Impacts under the UNEP-SETAC Life Cycle Initiative launched a comparison and harmonization of existing characterization models.