Microplastics have been detected in deep-sea animals collected from hydrothermal vents more than 2,000 meters below the ocean surface, showing that even remote chemosynthetic ecosystems are connected to surface-derived plastic pollution.
The study, led by researchers at the Korea Research Institute of Bioscience and Biotechnology (KRIBB) in collaboration with the Korea Institute of Ocean Science and Technology (KIOST), compared vent fauna from the North Fiji Basin in the southwestern Pacific Ocean and the Central Indian Ridge in the Indian Ocean. The team analyzed provannid snails and modiolid mussels, using mitochondrial COI DNA barcoding to identify species before dissecting specimens into gills, muscle and mantle tissue, and internal organs.
The analytical workflow combined hydrogen peroxide digestion, density separation, filtration, stereomicroscopic screening, and Fourier transform infrared (FTIR) microscopy. Suspected particles larger than 20 µm were selected for FTIR analysis, with polymer identity assigned by matching spectra against reference libraries. Blank and background controls were included throughout to monitor possible procedural or airborne contamination.
Microplastics were detected in 92 percent of the animals examined, corresponding to 11 of 12 specimens. In total, the team identified 40 particles, most of them fragments rather than fibers. Polystyrene was the dominant polymer, followed by acrylonitrile and polyethylene.
The tissue-resolved analysis showed that feeding behavior influenced where particles accumulated. In grazing Alviniconcha snails, microplastics were concentrated mainly in internal organs, including the gut and digestive gland, consistent with ingestion from microbial mats on vent surfaces. In filter-feeding Bathymodiolus mussels, particles were distributed more evenly across tissues, consistent with continuous exposure to suspended material in the water column.
Regional differences were also apparent. Animals from the Indian Ocean carried higher microplastic loads and a broader polymer profile than those from the southwestern Pacific, pointing to differences in surface inputs, riverine plastic discharge, ocean circulation, and particle transport to the deep seafloor.
“Plastic pollution has now spread even to deep-sea hydrothermal vent ecosystems that were once considered among the most isolated environments on Earth,” said corresponding author Se-Joo Kim in the team’s press release. “Our findings provide important scientific evidence for establishing future deep-sea environmental monitoring systems and conservation policies.”
Because FTIR microscopy does not capture particles below about 20 µm, the authors note that reported counts may underestimate total exposure. They suggest that microplastic monitoring should be incorporated into future deep-sea environmental assessments, particularly in vent fields being considered for mineral resource development.
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