Impact of High Salinity on the Adsorption Behaviors of Polystyrene and Polyamide Microplastics and Alternation of the Toxic Effect toward Synechococcus.

Microplastics (MPs) and concentrated brine are widely present in the coastal area due to accelerated human activities. However, the changes in the adsorption behavior of microplastics for different pollutants under high salinity conditions and their effects on the single/complex behavior of aquatic organisms are not yet clear.. In this work, polystyrene (PS) and polyamide (PA) microplastics were selected to study their effect on the adsorption behavior of three typical water pollutants (Pb²⁺, 4-chlorophenol, and levofloxacin) at high salinity. Furthermore, the individual and combined toxic effects of MPs and high salinity on Synechococcus were primarily explored. Activities of superoxide dismutase and catalase, concentrations of reduced glutathione and chlorophyll-a were employed as toxic indicators. Our results showed that salinity significantly changes the adsorption behavior of the three pollutants onto MPs and alters the toxic effect of MPs. Under the condition of 6% salinity and 10 mg/L MPs, PS-MPs did not significantly affect the cellular metabolism and photosynthetic efficiency of Synechococcus, while PA-MPs showed an evident synergistic effect with the high salinity. Copresence of high salinity with MPs reduced the individual toxic effect of PS-MPs and PA-MPs. This study shows that high salinity seawater can significantly alter the adsorption behavior of microplastics to other pollutants and their toxic effects on organisms. The impact of high-salinity brine on the marine ecology should be considered before construction of desalination projects. [ABSTRACT FROM AUTHOR]