Microfibers in Life Cycle Assessment: Comparing the Physical Effects of Cellulosic and Synthetic Fibers via Characterization Factors Development

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Abstract
Textile clothing is a significant contributor to microfiber pollution in aquatic ecosystems. A large portion of these emissions are cellulosic-based, either natural (e.g., cotton, linen) or semi-synthetic (e.g., viscose, lyocell), which can be ingested by aquatic organisms, posing harmful effects even at environmentally relevant concentrations. Studies comparing the effects of cellulosic and synthetic fibers report conflicting results: some suggest synthetic fibers are more harmful, others the opposite. However, despite their high environmental abundance, the lack of a species sensitivity distribution (SSD) for cellulosic microfibers (CMFs) has prevented comparison of their effects with synthetic microfibers (SMFs). Further, while SMFs have been integrated into Life Cycle Assessment (LCA) through characterization factors (CFs), equivalent CFs for CMFs are missing, due to a lack of an exposure and effect factor (EEF) specific to these fibers. We derived CFs for six CMFs (cotton, linen, viscose, lyocell, rayon, and modal) by combining modelled fate factors in marine water and sediments with an EEF calculated from a hazardous concentration for 20% of species (HC20), using an SSD of EC10eq values. Taxonomically split SSDs were also obtained for further analysis of the mode of action of CMFs and microplastics. The HC20 for CMFs was not significantly different from that of MPs, suggesting similar physical effect mechanisms. Fate modelling indicated lower persistence for CMFs, resulting in CFs one to two orders of magnitude lower than those for SMFs. Computed CFs were applied in an LCA comparing the ecosystem quality impacts of a cotton and a polyester T-shirt while accounting for microfiber emissions. Results show that polyester emissions caused significant impacts compared to other lifecycle impacts, while cotton emissions did not. This work therefore provides the first comparative LCA of a cellulosic and a synthetic textile that considers impacts of microfiber emissions, and computes CFs compatible with different LCIA methods.

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