Characterization and quantification of microplastics in marine sediments of the Colombian Caribbean.

BACKGROUND: About eight million tons of plastic end up in the oceans every year, with negative impacts including effects on the marine biota, the accumulation of heavy metals and desorption of organic contaminants in marine sediments. METHODS: With the aim of quantifying and characterizing the microplastics (MP) in the marine-coastal and lagoonal environments of two sectors of the Colombian Caribbean, influenced respectively by the Magdalena and Sinú rivers, sediment samples were collected during the 2021 rainy season and the 2022 dry season. The MP pieces (<5 mm) were extracted manually and classified by size (0.3-1.4 mm and 1.4-5.0 mm) and shape (fibers, films, foams and fragments). Moreover, from a total of 2,970 particles, a subset of 54 particles of more than 1.4 mm of both sectors was analyzed via Fourier-Transform Infrared (FTIR) spectrometer. RESULTS: In both the environments, in Magdalena the highest concentrations of MP were found in the dry season (275.56 ± 221.12 MP/kg and 217.78 ± 126.84 MP/kg in lagoonal and marine-coastal, respectively) while in Sinú it was the rainy season when the highest values were reported (208.89 ± 137.56 MP/kg and 135.56 ± 71.45 MP/kg in lagoonal and marine-coastal, respectively). The dominant shape of MP was fibers and the predominant polymer was polypropylene. Although there was no significant effect of season (Permanova, p = 0.0058) nor environment (Permanova, p = 0.0741) there were differences between some in size (Permanova, p = 0.0001) which was noticeable due particles measuring 0.3-1.4 mm exceeded those measuring 1.4-5.0 mm by an order of magnitude. It was not found a clear relation between particle size and MP concentrations.