Micro- and nanoplastics' transfer in freezing saltwater: Implications for their fate in polar waters

Plastic debris accumulate in the Arctic by way of oceanic and atmospheric circulation. High concentrations of microplastics (1μm to 5 mm) have been measured, and nanoplastics (<1μm) are expected to be abundant as well. However, little is known about the mobility of micro- and nanoplastics at the seawater/ice interface. This study investigates the fate of micro- and nanoplastics during sea ice formation. A novel experimental approach simulates the growth of sea ice by progressively freezing a saline solution. After different durations of freezing, the concentration of NaCl, natural organic matter, microplastics, and nanoplastics was measured in the ice and liquid. Micro- and nanoplastics’ distribution coefficient between saltwater and ice was determined, reflecting their behavior during congelation sea ice growth. The results show that microplastics are retained in ice while nanoplastics are expulsed from it. Furthermore, natural organic matter plays a crucial role in stabilizing nanoplastics at this interface. These results raise new questions concerning the impact of micro- and nanoplastics in fragile polar environments and the analytical strategy to detect them.