Set of Small Molecule Polyurethane (PU) Model Substrates: Ecotoxicity Evaluation and Identification of PU Degrading Biocatalysts

Polyurethanes (PUs) are an exceedingly heterogeneous group of plastic polymers, widely used in a variety of industries from construction to medical implants. In the past decades, we have witnessed the accumulation of PU waste and its detrimental environmental impacts. PUs have been identified as one of the most toxic polymers leaching hazardous compounds derived both from the polymer itself and the additives used in production. Further environmental impact assessment, identification and characterization of substances derived from PU materials and establishing efficient degradation strategies are crucial. Thus, a selection of eight synthetic model compounds which represent partial PU hydrolysis products were synthesized and characterized both in terms of toxicity and suitability to be used as substrates for the identification of novel biocatalysts for PU biodegradation. Overall, the compounds exhibited low in vitro cytotoxicity against a healthy human fibroblast cell line and virtually no toxic effect on the nematode Caenorhabditis elegans up to 500 mu g mL(-1), and two of the substrates showed moderate aquatic ecotoxicity with EC50 values 53 mu g mL(-1) and 45 mu g mL(-1), respectively, on Aliivibrio fischeri. The compounds were successfully applied to study the mechanism of ester and urethane bond cleaving preference of known plastic-degrading enzymes and were used to single out a novel PU-degrading biocatalyst, Amycolatopsis mediterranei ISP5501, among 220 microbial strains. A. mediterranei ISP5501 can also degrade commercially available polyether and polyester PU materials, reducing the average molecular number of the polymer up to 13.5%. This study uncovered a biocatalyst capable of degrading different types of PUs and identified potential enzymes responsible as a key step in developing biotechnological process for PU waste treatment options.

Automated summary

Polyurethanes (PUs) are widely used plastic polymers in various industries, but their accumulation as waste and the associated environmental impacts have raised concerns. This study synthesized and characterized synthetic compounds representing partial PU hydrolysis products to assess their toxicity and suitability for identifying biocatalysts for PU biodegradation. The compounds showed low in vitro cytotoxicity and low toxic effects on the nematode C. elegans. Two compounds exhibited moderate aquatic ecotoxicity. They were also used to study the cleaving preference of known plastic-degrading enzymes and to identify a novel PU-degrading biocatalyst, Amycolatopsis mediterranei ISP5501. This study highlights the potential of biotechnological processes for PU waste treatment.