Abstract:
Microplastic (MP) pollution has become a major environmental concern affecting aquatic ecosystems.
Mangrove-associated estuaries are important sinks for microplastics due to inputs from both riverine
and marine sources, exposing fish communities to contamination. This study investigated the
occurrence and characteristics of microplastics in three fish species collected from the mangroveassociated Kalu River estuary, Sri Lanka, in April 2024. Three fish species: Oreochromis mossambicus,
Etroplus suratensis, and Heteropneustes fossilis were collected from the local fishermen from the Kalu
River estuary. Three individuals of each species (n=3) were analyzed. MPs were extracted from muscle
digested using 30% potassium hydroxide (KOH), followed by density separation with saturated sodium
chloride (NaCl). The extracted particles were filtered through 1.2µm glass fiber filters and examined
under a stereomicroscope for enumeration and characterization as colour, shape, and type of
microplastics. Microplastics were detected in all examined fish species, confirming the widespread
occurrence of plastic contamination in edible fish tissues. H. fossilis exhibited the highest mean
microplastic abundance (0.47±0.09 MPs/g), followed by O. mossambicus (0.42±0.11 MPs/g) and E.
suratensis (0.40±0.05 MPs/g). Filament-shaped particles were the predominant morphology,
accounting for 71.9% of the identified microplastics, followed by irregular (26.3%) and round particles
(1.8%). Regarding microplastic types, fibers were the most dominant category, representing 62.1% of
the total identified particles, followed by films (19.0%) and fragments (17.2%). The most dominant
microplastic colour was blue (34.5%), followed by black (32.8%), transparent (15.5%), green (8.6%),
red (5.2%), and other colours (3.4%). The predominance of filamentous microplastics indicates that
synthetic textile fibers and fishing-related materials are likely the primary sources of contamination in
the Kalu River. The presence of microplastics in edible fish tissues highlights the potential for trophic
transfer and human dietary exposure. These findings provide baseline evidence of freshwater fish
contamination in Sri Lanka and underscore the need for sustained monitoring and effective management
strategies to mitigate plastic pollution in inland aquatic ecosystems.
