Caracterização da degradação de microplásticos em ecossistemas marinhos fluminenses através de técnicas de isótopos estáveis, infravermelho e microscopia eletrônica de varredura

Abstract

Understanding the degradation process of microplastics (MPs) - plastics smaller than 5 mm - is crucial for assessing the impact of these emerging contaminants in marine environments. This study specifically evaluated the degradation of polyethylene (PE), polypropylene (PP), and polystyrene (PS) microplastics exposed to both in situ environ- mental conditions and three laboratory scenarios. MPs were subjected to degradation for 112 days at Cabo Frio Island in Arraial do Cabo and for 140 days in Guanabara Bay in Niterói (both located in Rio de Janeiro, RJ) at a depth of 1 to 1.5 m. This allowed for a comparison between environments with different levels of eutrophication. In a controlled environment, MPs were exposed for 210 days in laboratory experiments. To assess the degradation of MPs, Fourier Transform Infrared Spectroscopy (FTIR) and Elemental Analysis-Isotope Ratio Mass Spectrometry (EA-IRMS) techniques were applied. These methods allowed for the calculation of degradation indices and the com- parison of changes in chemical bonding structures. Carbonyl bond indices were calculated using peaks of interest in the FTIR spectra, which indicated changes in chemical bonding structures (specifically carbonyl groups, 1509 - 1780 cm −1 ). Additionally, a Scanning Electron Microscope (SEM) was used to evaluate morphological changes in the MPs. SEM results indicated an increase in the surface roughness of the polymers, including the appearance of grooves. According to EA-IRMS analyses, all samples showed carbon isotopic fractionation, with δ 13 C values differing from the initial ones. Notably, in the more polluted environment, there was an increase in biofilm formation, the development of MP clusters, and a higher presence of carbonyl groups, according to FTIR results. In contrast, changes in degradation indices in samples exposed only to ultrapure water suggested that hydrolysis was a more significant factor in this process. One result that was obtained by correlating FTIR and EA-IRMS techniques was identifying trends for PE and PP that relate the increase in the carbonyl index to the enrichment of 13 C.