Microplastics in beach sand and potential contamination of planktivorous fish Sardinella gibbosa inhabiting in coastal waters of Negombo, Sri Lanka

Microplastic pollution has become the most significant marine environmental concern. There has been a surge of information on microplastic contamination in various marine environments worldwide. However, the level of microplastic contamination in marine environments is just begun to understand in Sri Lanka. The present study looked at the microplastic contamination level in the beach sand of Pitipana, Catamaran, and Dūwana beaches along the coast of Negombo, Sri Lanka. Sampling was conducted bi-monthly from March to November in 2017. Beach sand samples were collected from the surface (0-1cm) and subsurface (10-11cm) layers and three regions representing the low-tide, high-tide, and vegetation line of each beach. Sand samples were filtered through 5mm and 1mm sieve-set, and particles greater than 5mm were discarded since they are not considered microplastics. Particles retained in 1mm sieve and the filtrate were collected separately. Microplastics were density separated and categorized into two size classes as 1-5mm and smaller than 1mm. Microplastics in the 1-5mm size-class were categorized as fiber, foam, fragment, and pellet. Microplastics <1mm were subjected to FTIR spectroscopy and identified based on the polymer type. Further, goldstrip sardine, Sardinella gibbosa samples were obtained from the coastal waters of Pitipana and tested for possible microplastic contamination in commercial fishes. Results revealed that the Pitipana beach sand was highly contaminated with 1-5mm category microplastics reporting a mean abundance (±SD) value of 7.2±7.66 particles/m3 by number compared to other sites. The fragment was the dominant type found in Catamaran and Dūwana beaches, while foam was the predominant type in Pitipana beach. However, pellets were not recorded in any of the sites sampled. Polyvinyl chloride (PVC) was the major polymer type recorded in Pitipana beach sand, and polyester was dominant in Dūwana and Catamaran beaches. The FTIR spectra revealed the presence of polyethylene and polypropylene in gut contents of Sardinella gibbosa, suggesting contamination of microplastics in planktivorous fish and potential for accumulation along the trophic chain.