[Effect of Water Components on Aggregation and Sedimentation of Polystyrene Nanoplastics]

The aggregation and sedimentation of micro/nano-plastics significantly affect their migration and distribution in the environment. This study investigated the effects of Na⁺ and natural organic matter （NOM） on the aggregation and sedimentation of polystyrene nano-plastics （PS-NPs） in the aqueous phase. Six types of water， such as seawater， lake water， and domestic sewage， were used to evaluate the above effects and other potential influencing factors. The results indicated that Na⁺ could facilitate the sedimentation of PS-NPs when it was less than 80 mmol·L^-1， whereas it could promote the aggregation and suspension of PS-NPs when the concentration was greater than 80 mmol·L^-1. NOM molecules affected the aggregation and sedimentation of PS-NPs by changing the ζ potential and relative density of particles via forming a multilayer adsorption structure with Na⁺ on the particle surface. It was observed that NOM greater than 10 mg·L^-1 enhanced the dispersion and suspension of PS-NPs， which might have been attributed to the decrease in relative density of the particles as a large amount of NOM was absorbed onto the surface. Compared with synthetic waters， environmental waters enhanced the aggregation of PS-NPs， which may have been related to the amino acid， protein， and other organic macro-molecules in the water.