Microplastics in seawater and zooplankton: A case study from Terengganu estuary and offshore waters, Malaysia

Widespread accumulation and distribution of microplastics at the sea surface raise concerns as the habitat is a feeding ground for zooplankton. As primary consumers, these organisms are closely connected to microplastic input in the marine food chain. Little comparative information currently exists about this problem in estuary and offshore systems. This study investigates microplastic distribution in the surface water and the potential ingestion of microplastics in selected taxonomic groups of zooplankton from the Terengganu Estuary to offshore waters, Malaysia. In the surface water, three types of microplastics were found (fibres, fragments and pellets). Fibres made up the highest percentage, comprising 80.8% and 73.8% of microplastics in offshore waters and estuaries, respectively. The highest total density of microplastics was found in the Terengganu Estuary (545.8 particles m-3). Microplastics sampled from the offshore waters were identified as polyamide, polyethylene, and polypropylene, which possibly originated from secondary microplastic sources. Two types of microplastics were detected in zooplankton: fibres and fragments. Fibres were the most commonly ingested microplastic type in zooplankton collected from offshore waters (94%) and estuaries (77.7%). The average sizes of ingested fibres and fragments were 361.7 ± 226.8 μm and 96.8 ± 28.1 μm, respectively, with a wider range of sizes ingested observed in offshore waters than in estuaries. The concentration of microplastics in seven zooplankton groups varied from 0.01 ± 0.002 particles ind.-1 (Harpacticoida) to 0.2 ± 0.14 particles ind.-1 (Aphragmophora). Notwithstanding the conformity of our results (increased anthropogenic activities led to greater plastic pollution within the estuary), no significant correlation was observed between the levels of microplastic ingestion and microplastic concentration in the surface water within both areas. Our results provide an important baseline reference on microplastic pollution from estuary to offshore waters, as well as proving that zooplankton act as a repository for microplastic in the marine ecosystem.