This study revisits the activity of two enzymes, a bacterial catalase-peroxidase from Klebsiella sp. (KlebCP) and a hexamerin from Galleria mellonella saliva ("Ceres"), reported to degrade polyethylene (PE) and poly(vinyl chloride) (PVC). The researchers attempted to replicate previous studies but found no evidence of enzymatic degradation of PE or PVC under various conditions. They showed that the original results may have been misinterpreted, with the observed signals likely due to protein contamination rather than true enzymatic degradation. KlebCP, while active in oxidizing a model substrate, did not cause oxidation or deconstruction of PVC. Similarly, "Ceres" did not show activity on PE, and FTIR analysis indicated that the signals previously interpreted as oxidation were from protein contamination. The study highlights the need for caution in interpreting claims of enzymatic degradation of non-hydrolyzable plastics, emphasizing the importance of rigorous experimental validation and control. The results suggest that the enzymes in question do not effectively degrade PE or PVC, and the reported degradation may be due to contamination or misinterpretation of data. The study underscores the challenges in biodegrading non-hydrolyzable plastics and the need for standardized analytical methods and controls in future research.This study revisits the activity of two enzymes, a bacterial catalase-peroxidase from Klebsiella sp. (KlebCP) and a hexamerin from Galleria mellonella saliva ("Ceres"), reported to degrade polyethylene (PE) and poly(vinyl chloride) (PVC). The researchers attempted to replicate previous studies but found no evidence of enzymatic degradation of PE or PVC under various conditions. They showed that the original results may have been misinterpreted, with the observed signals likely due to protein contamination rather than true enzymatic degradation. KlebCP, while active in oxidizing a model substrate, did not cause oxidation or deconstruction of PVC. Similarly, "Ceres" did not show activity on PE, and FTIR analysis indicated that the signals previously interpreted as oxidation were from protein contamination. The study highlights the need for caution in interpreting claims of enzymatic degradation of non-hydrolyzable plastics, emphasizing the importance of rigorous experimental validation and control. The results suggest that the enzymes in question do not effectively degrade PE or PVC, and the reported degradation may be due to contamination or misinterpretation of data. The study underscores the challenges in biodegrading non-hydrolyzable plastics and the need for standardized analytical methods and controls in future research.