Assessing PET and PE degradation in the Adriatic Sea using plastic bottles and sealing rings from Fishing for Litter

Fishing for Litter (FfL) is one of the various measures enacted to limit the presence of waste in the marine environment (marine litter (ML)) and consists in the concurrent collection of litter items during fishing activities and the subsequent disposal in suitable facilities on land. The present work reports an investigation about plastic marine litter collected during FfL activities, focusing on plastic water bottles, some of which still showing the expiry date. This allowed to study in detail the degradation of two different polymers in the marine environment: polyethylene terephthalate (PET) and polyethylene (PE), constituting the body/neck and the cap/sealing ring, respectively, of the same closed bottles. The PE components of drinking bottles have been rarely paid attention in the literature. Both infrared and Raman spectroscopy, with the assistance of multivariate statistical analysis by means of principal component analysis (PCA), were employed. This set of techniques allowed to identify various degradation processes in different PET and PE sections, due to both the mechanical stresses applied during their molding and the photochemical degradation in the sea. Whereas the degradation index of the PET sections (CEGI) did not correlate with bottle age, the here proposed indexes Carboxyl-Ester Index/Carboxyl-Ester Deconvoluted Index actually did for PE. Three different levels of degradation could be defined for the dated bottles. Subsequently, this classification was also extended to the non-dated ones. This approach could be useful to establish degradation of PET and PE items in collected ML fractions.