Effects And Mechanisms Of Polystyrene Microplastics On The Growth Of Phaeodactylum Tricornutum Bohlin

Plastics are the most common organic synthetic polymer material in daily life.Every year,a large amount of plastic waste enters the ocean and becomes small and fine plastic particles under the action of external forces,which poses a serious threat to the marine ecological environment and human health.In recent years,offshore eutrophication has intensified,and harmful red tides have frequently occurred.Microplastics,as a major kind of emerging pollutants in the marine environment,may participate in or interfere with the production and dissipation of red tides.Therefore,it is necessary to study the influence of microplastics on the growth of red tide algae.However,there are still few reports.In this study,Phaeodactylum tricornutum Bohlin,a common red tide alga in the ocean,was used as the research object to prepare primary and hygrothermal aging polystyrene microplastics(p MPs).The two types of microplastics were studied at the concentration of 0,10,20,50 and the 100 mg/L and the initial algae density of 10~5and 10~6cell/m L on algal cell growth,photosynthetic pigment content and chlorophyll fluorescence parameters,in order to provide theoretical basis and data support for analyzing the possible impact of the presence of polystyrene microplastics on the occurrence of red tides in the seawater environment.Primary p MPs had an inhibitory effect on the growth of P.tricornutum with low initial algal density,and the inhibitory rate increased with the increase of exposure concentration,and had an stimulating effect on P.tricornutum with high initial algal density,and the stimulation rate also increased with microplastics concentration increasing.The effect of hygrothermal aging p MPs on P.tricornutum was less than that of primary p MPs.Hygrothermal aging p MPs inhibited the synthesis of chlorophyll a in P.tricornutum cells compared to primary p MPs.The effects of two types of microplastics on the content of chlorophyll c and carotenoids in algal cells are not obvious.Therefore,chlorophyll a may be an important target site for microplastics to damage algal cells.The high concentration of primary p MPs inhibited the maximum photochemical efficiency(Fv/Fm)of P.tricornutum photosystem?(PS?),and the inhibitory effect on Fv/Fm was not significant at low concentrations;The hygrothermal aging p MPs inhibited Fv/Fm to a greater extent than the primary p MPs.The photoprotective capability(NPQ)and photosynthetic activity(Qp)had a certain adaptation mechanism to the stress of two types of polystyrene microplastics;The change rule of Qp was consistent with the change rule of growth.There were obvious changes of the number of times required to reduce the electron acceptor Q_Aof the PSII(N),the degree of openness of the PSII reaction center(?o),the quantum yield for electron transfer(?Eo)and the energy for electron transfer(ETo/RC)under the action of two types of microplastics,especially when the microplastics undergo hygrothermal aging treatment,the above parameter values were significantly reduced relative to the primary polystyrene microplastics.Under the action of primary p MPs,there was no significant change the of Q_Areduction rate(Mo),the energy required to completely reduce the electron acceptor Q_Aof the PSII(Sm),the photosynthetic efficiency(?Po),the quantum ratio used by the reaction center for heat dissipation(?Do),light energy absorbed by the reaction center(ABS/RC),energy captured by the reaction center for reducing Q_A(TRo/RC)and energy dissipated in the reaction center(DIo/RC).There was no significant change in Mo,?Po,?Eo,?Do,?o,TRo/RC and ETo/RC after the action of hygrothermal polystyrene microplastics.