High Salinity Alters the Adsorption Behavior of Microplastics towards Typical Pollutants and the Phytotoxicity of Microplastics to Synechococcus

Microplastics (MPs) are ubiquitous in marine environments, and seawater desalination releases large amounts of concentrated saline water. However, little is known about how MPs alter their adsorption behavior towards other pollutants in high-salinity environments. Meanwhile, there is a lack of knowledge about the combined effect of MPs and high salinity on marine phytoplankton. In this work, the impact of high salinity on the adsorption behaviors of two types of MPs (polyethylene MPs (PE-MPs) and polyvinyl chloride MPs (PVC-MPs)) towards three typical water pollutants (Pb2+, 4-chlorophenol, and levofloxacin) was investigated, and the combined effect of MPs and high salinity on Synechococcus was evaluated. The adsorption of Pb2+ and levofloxacin by PE-MPs and PVC-MPs decreased at high salinity, and the adsorption of 4-chlorophenol by PE-MPs also decreased, however, the adsorption of 4-chlorophenol by PVC-MPs increased. The SOD, CAT activities and GSH content of Synechococcus exposed to MPs were increased by the increasing salinity. When the MPs concentration was low, the increase in salinity decreased the content of chlorophyll-a. Our results demonstrated that high salinity significantly changes the adsorption behavior of common pollutants onto MPs and alters the toxic effect of MPs on Synechococcus. This study provides important information necessary for environmental risk assessments with regard to the combined stress of MPs and high salinity, promoting the sustainable development of desalination industries.