Nanoplastics Distribution during Ice Formation: Insights into Natural Surface Water Freezing Conditions

The migration characteristics of nanoplastics (NPs) in the natural freezing process are complex and have attracted increasing attention in simulating natural freezing in recent years. However, simulated freezing conditions often fall short of replicating natural freezing processes, and studies on the vertical distribution of NPs remain inadequate. This study established a more realistic simulation of the natural freezing process in surface water by controlling both the air temperature (T₁) and the water temperature (T₂). Additionally, we introduced a new parameter, the local distribution coefficient (K_iw1), to compare with the effective distribution coefficient (K_iw2). The values of K_iw1 and K_iw2 for PS-500 nm were 0.18 and 0.21, respectively, at T₁ = −20 °C and T₂ = 1 °C. The results revealed the NPs concentration differed in ice, near-ice liquid, and far-ice liquid. Both properties of NPs and environmental factors could regulate the vertical distribution of NPs. The findings underscored the importance of freezing temperature regulated by T₁ and T₂, elucidating the roles of various influencing factors on the vertical distribution characteristics of NPs and unraveling the mechanisms of NPs distribution in the ice–water system. This study can provide valuable insights for understanding the migration of NPs in surface water in cold regions.