| As an emerging pollutant,microplastics widely exist in the marine environment,and their impact on marine ecology has attracted global attention.In recent years,with the rapid increase in the number of desalination plants,a large amount of concentrated brine has entered the environment,causing the salinity of the receiving sea area to increase.However,it is currently unclear how the adsorption performance of microplastics on environmental pollutants and their biological effects will change under high salinity conditions.We took four kinds of microplastics,polystyrene(PS),polyethylene(PE),polyamide(PA),and polyvinyl chloride(PVC),which were widely present in the water environment,as the research objects,and analyzed their effects under high salinity conditions Changes in the adsorption performance of different types of pollutants and related mechanisms.We also selected Synechococcus,which plays an important role in the marine ecological environment,as the tested species,and explored the toxic effects of microplastics on marine organisms under high salinity.The main findings were as follows:We selected Pb,4-chlorophenol and levofloxacin as representatives of heavy metals,organochlorine pollutants and personal care products(PPCPs),respectively,and studied the adsorption performance of microplastics on three pollutants under high salt conditions.The results showed that the adsorption process of four kinds of microplastics on Pb conformed to the pseudo-second order kinetic and Langmuir isotherm adsorption.The main mechanism of adsorption was electrostatic force,and the adsorption capacity of microplastics on Pb was reduced under high salinity conditions.The adsorption process of the four microplastics on 4-chlorophenol conformed to the pseudo-second-order kinetics and Freundlich isotherm adsorption.The adsorption mechanism was hydrophobic.The high salinity increased the equilibrium adsorption capacity of PS and PVC,and reduced the adsorption of PE and PA.quantity.The adsorption process of the four microplastics on levofloxacin conformed to the pseudo-second-order kinetics and Freundlich isotherm adsorption.The adsorption mechanism was hydrogen bonding between functional groups.High salinity reduced the equilibrium adsorption capacity of the four microplastics on levofloxacin.Secondly,we studied the single and compound toxic effects of microplastics and salinity on Synechococcus.The results showed that different concentrations of PS,PE,PA(10 mg/L,50 mg/L,500 mg/L)affectted the activity of Synechococcus metabolic enzymes and the level of chlorophyll.The inhibitory effect increased with the increase of the concentration of microplastics.Low concentration of PVC did not significantly inhibit the growth of Synechococcus,while high concentration of PVC induced oxidative stress in Synechococcus.High salinity affectted the cell metabolism and chlorophyll content of Synechococcus,and the degree of influence increased with the increase of salinity.Under 10 mg/L PS and PE stress,high salinity(6%)had no significant effect on the metabolism and photosynthetic efficiency of Synechococcus cells.Under the stress of 10 mg/L of PA and PVC,the toxic effectted of microplastics and high salinity showed a synergistic effect,and the cell metabolism and chlorophyll levels of Synechococcus were significantly inhibited.Under the condition of 500 mg/L microplastic exposure,high salinity reduced the toxic effect of PS,PE and PA on Synechococcus,but promoted the toxic effect of PVC on Synechococcus.This study showed that high-salinity seawater could significantly change the adsorption behavior of microplastics to other pollutants and their toxic effects on organisms.In the planning and layout of seawater desalination projects,the impact of high-salt wastewater on the ecological environment of some coastal areas should be considered,and the environmental risk impact assessment work should be done to provide scientific guarantee for the sustainable development of the seawater desalination industry. |
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