(340b) High-Throughput Studies for Measuring the Environmental Fate of Polymer Microplastics

One necessary component of the solution to the challenge of plastics in the environment is understanding the rate at which these materials degrade. Despite strong interest, there is little consensus in the community regarding degradation rates, and these rates certainly vary across different environments, necessitating a deep understanding of both material and environmental effects. The field is fundamentally held back by a lack of available data because standardized tests require long testing times and are extremely costly, limiting the number of materials and conditions that can be tested. Herein, we report the adaptation of the clear zone assay from molecular biology to the high-throughput screening of biological effects on polymer microplastic degradation. The clear zone test can overcome long test times of standardized methods and enable a large biodegradation data set to explore structure-property relationships. To demonstrate the utility of this method, we report the synthesis and biodegradation testing of over 1,000 different polyesters. Library design incorporates a wide variety of different chemical functionalities to specifically probe as diverse a chemical space as possible within the class of polyester chemistries. The study of the large library enables us to analyse the impact of a variety of different functional groups on polymer degradation across a large number of polymers, extracting a number of useful trends in chemical structure. This large data set is then analysed using simple regression and random forest classifier (RFC) machine learning methods to attempt to classify polymers as biodegradable or not biodegradable. We explore the relative role of chemical structure as well as property descriptors (i.e. crystallinity) and molar mass in the efficacy of predictions, demonstrating accuracies above 82% for many approaches. Initial work focused on polyesters has now been expanded to polyurethanes, polyamides and a variety of specialized chemistries. As a part of these studies, we have also studied the effects of common catalysts and dyes as polymer formulation ingredients, demonstrating the ability to quantify formulation effects on microplastic fate. Finally, the assay has been extended to a wide variety of organisms, aiming to provide “biodegradation fingerprints” that can be used to predict environmental fate in a wide variety of specific environments.