[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.

[Source Analysis and Risk Assessment of Heavy Metals in Soil of County Scale Based on PMF Model].

This study explores the pollution characteristics, risks, and sources of heavy metals in small-scale areas. Rongcheng District, Jieyang City, Guangdong Province was considered as the study area and enrichment factor (EF), pollution load index (PLI), potential ecological risk index (RI), and US EPA health risk assessment model were used to evaluate its environmental risk. Moreover, the source apportionment of heavy metals was analyzed through correlation analysis, the characteristic of spatial distribution, and a PMF model. The results showed that the mean concentrations of ω(Cr), ω(Hg), ω(As), ω(Pb), ω(Ni), ω(Cd), ω(Cu), and ω(Zn) were 54.87, 0.25, 8.35, 56.00, 15.38, 0.35, 30.56, and 124.23 mg·kg-1, respectively. The mean concentrations of all elements exceeded the local soil background value. In terms of EF level, Cr, As, Pb, and Ni showed negligible accumulation; Zn and Cu showed minor accumulation; and Hg and Cd showed moderate accumulation. The mean value of the pollution load index was 2.37, with a severe pollution level, and the eight elements were in different pollution levels. In total, the study region suffered severe ecological risk, Hg and Cd presented strong ecological risk, and other elements presented slight ecological risk. The non-carcinogenic risks under the three exposure paths were within the acceptable level. The carcinogenic risks (CR) of adults and children were 9.81E-05 and 5.59E-04, respectively, and Cr and As were the main contributors of CR. The results showed that the four sources of heavy metals were transportation sources (37.02%), parent material sources (18.53%), atmospheric deposition sources (26.49%), and industrial sources (17.96%).