Textural and chemical characteristics of micro plastics in coastal sediments along the southeast coast of Sri Lanka: implications for possible sources

Abstract

At present Microplastics (MPs) have been recognized as one of the most critical and emerging sources of marine pollution with a significant impact on marine and coastal biota. The current study aimed to comprehend MP pollution along the Southeastern coast of Sri Lanka by investigating their spatial distribution, morphology, composition and possible sources. For the study, 23 coastal sediment samples were collected from straight beaches and 8 samples were collected from lagoon areas of the Southeast coast extending from Kalmunai to Panama. About 5 kg of surface sediments were collected from the wrack line to the berm zone at each sampling site. The MPs were isolated by density separation using 1.20 g/ml NaCl solutions. The amount, shape, and colour of isolated MPs were analyzed on the petrographic microscope. The Scanning Electron Microscope (SEM) and Fourier Transform Infrared (FTIR) Spectroscope were employed to investigate their morphology and chemical composition respectively. The results indicated the presence of both mesoscopic- and microscopicsized plastics in the studied sediments. The MPs occurred in five morphological categories; fibers (86.77%), flakes (6.61%), fragments (3.58%), foams (1.93%), and films (1.10%), and nine various colours. The SEM images demonstrated the presence of different weathering surfaces such as scratches, pores, protrusions, grooves, pits, and scales in these MPs. These weathered surfaces may have been formed due to mechanical abrasion, chemical reactions, photodegradation, and microbial degradation. The FTIR analysis revealed that the main polymer compositions of MPs are polyethylene and polystyrene. The distribution of MPs along the coast varied greatly (from 0 to 45 MPs 500 g-1 ) and shows the highest amount in lagoon environments (>20 MP 500 g -1 ) indicating land-derived sources of MPs. An in-depth textural and compositional characterization of MPs, and their spatial distribution investigations will advance the understanding of MP pollution in the Southeastern coast of Sri Lanka.