Use and misuse of FTIR spectroscopy for studying the bio-oxidation of plastics

[Display omitted] •Molecular bases for the detection of plastic oxidation by FTIR spectroscopy are reviewed.•A list of IR absorption peaks for oxidized polyethylene (PE) and polystyrene (PS) and their interpretation is given.•Spectra of biological contaminants are presented.•A protocol for cleaning plastics from bio-contaminants while preserving their oxidation state is given.•Simple methods for analyzing the infrared spectra are suggested. Due to massive production, inefficient waste collection, and long lives, plastics have become a source of persistent pollution. Biodegradation is explored as an environmentally friendly remediation method for removing plastics from the environment. Microbial and animal biodegradation methods have been reported in the literature for various plastics. Levels of plastic oxidation are often used as an evidence of degradation and can be measured with great sensitivity by Fourier Transform Infrared (FTIR) spectroscopy. FTIR is highly sensitive to the creation of new CO, CO and OH bonds during oxidation. However, many studies reporting the use of FTIR spectroscopy to evidence plastic oxidation confused the spectral signatures of biomass contamination (CO and CO from lipids, CONH from proteins, O–H from polysaccharides) with plastic oxidation. Here, based on spectra of oxidized plastic and of probable contaminants, we make recommendations for performing and analyzing FTIR measurements properly.