Quantification and morphological characterization of plastic litter (0.30–100 mm) in surface waters of off Colombo, west coast of Sri Lanka

This study focused on quantification and morphological characterization of plastics (0.30–100 mm) at seven sites, namely, Uswetakeiyawa, Kerawalapitiya, Dikowita, Modera, Kollupitiya, Bambalapitiya, and Wellawatta along the west coast, off Colombo, in August, October, and November, 2017. Samples were collected by dragging the floating net with a mesh size of 300 μm horizontally at the surface. The collected samples were analyzed using standard methods to quantify the plastics in terms of size, color, and shape. The mean abundance (± SE) of total plastics recovered from off Colombo was 140.34 ± 15.23 items/m 3 (0.30–100 mm) by number and 0.66 ± 0.16 mg/m 3 (1–100 mm) by weight ( n = 63). The significantly higher abundance (± SE) of total plastics (0.30–100 mm) was found at Wellawatta (229.40 ± 46.39 items/m 3 ) and Modera (201.28 ± 62.13 items/m 3 ) than that of other sites ( p < 0.05). Nevertheless, the 99.60% of the plastics collected were small microplastics within the size range of 0.30–1 mm. Only mesoplastics were significantly varied among sites by weight with significantly high abundance in Kerawalapitiya (0.71 ± 0.31 mg/m 3 ) than that of other sites ( p < 0.05). The composition analysis of shape categories indicated that filaments were dominated in coastal area off Colombo with 61% followed by fragments (25%) and films (14%). The color categorization of plastics revealed that colored plastics are predominant with 47% by the number of items followed by white, transparent, and black in off Colombo. According to the results, all study sites are affected by plastic contamination and cause significant health risk on coastal biota. Microplastic contamination level in surface waters acts as a key indicator on high pollution level in the west coast.