Microplastics ingestion in zooplankton in tropical estuarine fronts of Terengganu, Malaysia.

Microplastics are ubiquitous in aquatic environments and pose a risk of trophic transfer ingestion in the marine food chain. Tropical estuaries, which have high primary productivity, also act as a conduit for anthropogenic pollutants enter to the ocean. We conducted a spatiotemporal survey in the microtidal Kuala Terengganu estuary during the southwest monsoon (May and August) in 2022. In this work, 15 stations across three zones (plume, front, and shelf) were sampled by collecting zooplankton using a submersible pump and filtering through a 60 μm mesh. The zooplankton were taxonomically identified and treated with an alkaline digestion, and the recovered ingested microplastics were subsequently characterized morphologically and chemically using SEM-EDS and FTIR. Microplastics were dominated by fragments (98.6%) and polyamide (PA) (66.7%). The ingestion incidence ranged from 0.002 to 0.032 particles ind.-1 with no significant differences among stations or sampling events. The frontal region exhibited a higher potential intake of microplastics by zooplankton (10.57-271.23 particles m-3) during high tide compared to the other regions. This was reflected in the elevated microplastic abundance in the water at the frontal zone, where the abundance ratio was 0.8 to 4.1 times higher than in surrounding areas. Copepods accounted for 83% of microplastic ingestions, with Temora sp. showing the highest species-level incidence (2.0 particles ind.-1) and Oithona sp. showing the high potential intake of microplastic (96.56 particles m-3). Overall, these results indicate measurable microplastic bioavailability to estuarine zooplankton in the Kuala Terengganu estuary and highlight the need for continued monitoring of microplastic exposure and potential trophic transfer in tropical estuaries.