RESUMEN
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 ï¼NOMï¼ on the aggregation and sedimentation of polystyrene nano-plastics ï¼PS-NPsï¼ in the aqueous phase. Six types of waterï¼ such as seawaterï¼ lake waterï¼ and domestic sewageï¼ 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-1ï¼ 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-NPsï¼ 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 watersï¼ environmental waters enhanced the aggregation of PS-NPsï¼ which may have been related to the amino acidï¼ proteinï¼ and other organic macro-molecules in the water.