BRIN Finds Microplastics at Depths of 2,450 Metres in Indonesian Waters
Badan Riset dan Inovasi Nasional (BRIN) has disclosed the discovery of microplastics at depths of around 2,450 metres along the main gate of the Indonesian Throughflow (Indonesian Throughflow/ITF). The plastic particles could enter the seafood chain and be consumed by humans.
The finding is published in the international scientific journal Marine Pollution Bulletin in an article titled Vertical Distribution of Microplastic Along the Main Gate of Indonesian Throughflow Pathways (2024). The study was authored by Corry Yanti Manullang, a Senior Researcher at the BRIN Centre for Deep Ocean Research, along with an international collaboration team from Indonesia, Malaysia, the United States, and China.
Arlindo is a major ocean current system linking the Pacific and Indian Oceans through Indonesian waters. It flows through several straits, including the Makassar Strait, the Alas Strait, and the Lombok Strait.
‘This current connects two great oceans, the Pacific and the Indian. In addition to carrying water mass, salt, and nutrients, the current also has the potential to transport small particles such as microplastics,’ Corry said in a statement, quoted on Saturday 7 March 2026.
She noted that research on Arlindo has historically focused more on physical oceanography—temperature, salinity, and current circulation. By contrast, she said, investigations into the distribution of microplastics in the water column, particularly down to sea depth, have been scarce.
‘This study is one of the early efforts to examine the vertical distribution of microplastics down to the deep sea along the Arlindo pathway. So far, most microplastics research in Indonesian waters has concentrated on surface layers or coastal regions,’ she added.
The study was conducted during an oceanographic expedition from January to April 2021 under the international TRIUMPH programme. Samples were collected at 11 monitoring stations spread from Makassar Strait to Lombok Strait.
The research team collected 92 water-column samples at depths ranging from 5 metres to about 2,450 metres. Sampling was conducted using a rosette sampler connected to a CTD system (Conductivity, Temperature, Depth). This equipment enables sampling at exact depths.
‘The sample bottles were lowered into the sea and closed at predetermined depths, for example 50 metres, 200 metres, and thousands of metres,’ Corry explained.
She noted that of the total 872 litres of seawater analysed, researchers found 924 microplastic particles, with an average concentration of about 1.06 particles per litre. Corry said microplastics were found at all study stations, including depths exceeding two kilometres below the surface.
Corry stated that the analysis showed more than 90 per cent of the microplastics were in the form of fibres. This type of particle generally originates from synthetic textiles.
‘The clothes we wear can also shed microplastics. When washed, tiny fibres from synthetic fabrics can detach and end up entering the aquatic system,’ she explained.
In addition to fibres, the researchers identified several polymer types using Raman spectroscopy analysis. These included polyester, polypropylene, and polyurethane, widely used in textiles, packaging, and industrial materials. Corry said the findings indicate the deep sea could act as an accumulation site for microplastics.
‘At certain depths, the Arlindo current is strong enough to carry particles through different water layers,’ she said.
Potential Entry into the Food Chain
Corry added that the team also examined the potential ingestion of these particles by marine organisms. In another study published in Sains Malaysiana titled Ingestion of Microplastics in the Planktonic Copepod from the Indonesian Throughflow Pathways (2024), Corry and colleagues found microplastics inside the bodies of the tiny zooplankton copepods along the Arlindo pathway, which serve as an important food source for various fish species.
In that study, about 6,000 copepod individuals were analysed from several locations along the Arlindo pathway. The results showed 133 microplastic particles inside the bodies of these organisms.
Corry said the average microplastic ingestion rate was about 0.022 particles per individual, equivalent to one particle per 45 copepods.
‘Copepods cannot distinguish between natural food and plastic particles. Whatever comes before them will be eaten,’ Corry said.
The study also showed larger copepods tend to contain more microplastics than smaller ones. She noted this finding is worrisome because copepods are a primary food source for many fish species.
‘Copepods are eaten by small fish, which are then consumed by larger fish, and finally by humans. In other words, microplastics have the potential to move along the food chain up to human consumption,’ she warned.
Corry said research on microplastics in Indonesian seas still needs to be expanded, especially in the deep sea. About 70 per cent of Indonesia’s sea areas have depths greater than 200 metres, so deep-sea research remains relatively limited.
‘The finding that microplastics have already reached depths beyond two kilometres shows that the plastic waste issue is not confined to the coast. This is a problem for the entire marine ecosystem,’ Corry concluded.