Supplementary file 1_Modeling marine microplastic emissions in Life Cycle Assessment: characterization factors for biodegradable polymers and their application in a textile case study.docx

IntroductionWith the continuous increase of plastics production, it is imperative to carefully examine their environmental profile through Life Cycle Assessment (LCA). However, current LCA modeling is not considering the potential impacts of plastic emissions on the biosphere. To integrate plastic emissions into LCA, characterization factors are needed that commonly consist of three elements: a fate factor, an exposure factor, and an effect factor. In this context, fate factors quantify the distribution and longevity of plastics in the environment. Research on these fate factors is still limited, especially for biodegradable polymers. Hence, the main objective of this research was to determine the fate factors of biodegradable polymers [poly (lactic acid), poly (butylene succinate), and poly (ε-caprolactam)] based on primary experimental data for the marine environment.
MethodsThe validity of former research is tested by comparing the degradation evolution of i. macro- and microplastic particles, ii. two different grades of the polymer, and iii. different temperature levels. The degradation data are obtained by monitoring the oxygen consumption over a period of six months in natural seawater. The determined degradation rates are combined with sedimentation, resuspension, and deep burial rates to obtain fate factors. These fate factors are used to develop polymer-specific characterization factors. The resulting characterization factors are tested in an LCA case study of a synthetic sports shirt made from biodegradable polymer fibers. It allows to assess the relative importance of microplastic impacts compared to other life cycle impacts.
Results and discussionComparing the resulting specific surface degradation rates indicates that microplastic degradation rates could be overestimated when using macroplastic degradation data. Pertaining to the case study, the results show that the impact on ecosystem quality by microplastic emissions could account for up to 30% of the total endpoint category. Overall, this work aims to foster interdisciplinary collaboration to leverage the accuracy of LCA studies and thus provide guidance for novel material development.

引言
随着塑料产量的持续增长，通过生命周期评估（Life Cycle Assessment, LCA）深入探究其环境全貌已成为当务之急。然而当前的LCA建模尚未考虑塑料排放对生物圈的潜在影响。若要将塑料排放纳入LCA框架，需构建包含三要素的表征因子：归趋因子、暴露因子与效应因子。在此语境下，归趋因子用于量化塑料在环境中的分布与留存时长。目前针对此类归趋因子的研究仍较为匮乏，针对生物降解聚合物的相关研究尤甚。因此本研究的核心目标，是基于海洋环境的原始实验数据，确定三类生物降解聚合物的归趋因子：聚乳酸、聚丁二酸丁二醇酯以及聚ε-己内酰胺。

研究方法
本研究通过对比以下三类对象的降解演化过程，验证既往研究的有效性：一、宏塑料与微塑料颗粒；二、两种不同品级的聚合物；三、不同温度条件。降解数据通过在天然海水中为期六个月的耗氧量监测获取。将测定得到的降解速率与沉降、再悬浮及深埋速率相结合，即可得到归趋因子。利用这些归趋因子可构建针对特定聚合物的表征因子。将所得表征因子应用于一项以生物降解聚合物纤维制备的合成运动衫的LCA案例研究中进行验证，借此可评估微塑料影响相较于其他生命周期影响的相对重要性。

结果与讨论
对比所得的比表面降解速率后可见，若采用宏塑料降解数据，微塑料的降解速率可能被高估。就本次案例研究而言，结果表明微塑料排放对生态系统质量的影响可高达总终点影响类别的30%。总体而言，本研究旨在推动跨学科合作，以提升LCA研究的准确性，进而为新型材料的开发提供指导。