KIOST researchers find phytoplankton mucus drives microplastic sinking

Researchers at the Korea Institute of Ocean Science and Technology (KIOST) have identified the mechanism that causes microplastics, which are lighter than water, to sink to the deep ocean floor. Through mesocosm experiments conducted in the waters off Geoje, South Korea, a research team led by Dr. Seung-ho Baek discovered that sticky mucus secreted by phytoplankton causes microplastics to clump together, forming heavy aggregates that sink.

The study revealed that the specific type of phytoplankton is more critical to the sinking rate than the total amount of biomass. Diatoms, which grow rapidly and have short lifespans, secrete significant amounts of mucus, leading to a higher sinking rate of microplastics. In contrast, dinoflagellates, which have longer lifespans and secrete less mucus, resulted in lower sinking rates. In experiments, tanks dominated by diatoms saw approximately 34.1% of microplastics sink to the bottom, whereas tanks with higher overall biomass but different species composition saw only 11.6% sink.

Once these aggregates form, they sink at an average rate of 80 meters per day. The findings, published in the journal ‘Water Research’, suggest that predicting the movement and accumulation of microplastics requires considering biological community data alongside physical particle characteristics like size and weight.