Aging of plastic caused by biofilm formation in the marine environment

The aging of polymers is becoming ever more important in our understanding of not only their ability to outlast their lifespan but also the way macro-, micro-, and nanoplastics persist in the environment. In this study, commonly used plastic films, exposed to natural sea water from the North Sea, aerobic conditions, and exclusion of ultraviolet radiation through an artificial mesocosm experiment conducted over the last seven years, were analyzed by attenuated total reflection and transmission using a Fourier-transform infrared (FT-IR) spectroscope. The main objective of this study was to investigate the potential of the biofilms on the plastic film surfaces to degrade these polymers through studying any changes in their chemical composition. The scope of this study covers the analysis of poly(ethylene terephthalate) (PET), poly(lactic acid) (PLA), and polystyrene (PS) films. First, the biofilms on the plastic film surfaces were removed, and the films as well as non-exposed films were measured spectroscopically between a wavenumber range of 3600 cm-1 and 900 cm-1. Afterwards, dissimilarities between the spectra of exposed and non-exposed plastic films were calculated based on Euclidean and Bray-Curtis distances and used to find integral ranges to generate false color images. Through evaluating these wavenumber integrals with box-whisker plots and comparing the dissimilarities with principal coordinate analysis, the results would show whether the polymers degraded or not during their time in the mesocosm. Differences in the spectra between the two aging groups, which would indicate the beginning of degradation, were practically nonexistent. Comparing to former studies, no conformity of varying wavenumbers was found. Consequently, it is assumed that there were no chemical aging effects in the last seven years. Finally, this study used polymers, which did not undergo an initial chain breaking, triggered through energetic radiation or higher temperature levels. In the end, it was shown that these plastics have the ability to persevere for a long time in the cold and dark marine ecosystem