| The pollution of microplastics(MPs)in the ocean has raised many concerns around the world.As an important part of the marine ecosystem,macroalgae have the ability to capture microplastics from the aquatic environment.Hainan Island have bred a wealth of seaweed resources,but no one have revealed the existence characteristics of microplastics in coastal macroalgae.In addition,the response of macroalgae to microplastics is an important step in assessing the risk of marine microplastics,but there are few studies have addressed this issue.This topic mainly include: 1)Investigated the distribution characteristics of microplastics in two dominant macroalgae,Betaphycus gelatinus and Sargassum polycystum,in the seaweed culture area of Qizi Bay,Hainan.The status of microplastic pollution in Qizi Bay was analyzed and the potential of macroalgae to capture microplastics in situ was evaluated.2)Investigated the shortterm and long-term toxicological effects of different concentrations of microplastics on Caulerpa lentilifera,Gracilaria tenuistipitata and B.gelatinus.The effect of PS on the structure of epiphytic bacterial community on the surface of B.gelatinus was studied by using the high-throughput sequencing technology.3)The adhesion process of microplastics on the surface of algae was simulated,and the effects of dewatering,washing and combined decontamination procedures on the removal of microplastics were studied.The decontamination process of microplastics was optimized by orthogonal test.The research results are as follows:(1)Microplastics was widely distributed in Hawei Bay,mainly in the form of fiber.B.gelatinus and S.polycystum have strong ability to enrich microplastics,and the abundance of microplastics on their surface was 184 times and 244 times that of seawater,respectively.The highest detection rate of microplastics in seawater and S.polycystum was Polyamide(PA),while the highest detection rate of microplastics in B.gelatinus was polyethylene terephthalate(PET).There were significant differences in the particle size of the microplastics between the seawater and the macroalgae.The microplastics in the seawater was mainly 0-500 μm size,while the microplastics in the macroalgae was mainly 1500-2000 μm size.(2)In the short-term toxicology experiment,PS had no effect on B.gelatinus regardless of concentration.The growth,chlorophyll-a content,Fv/Fm and total photosynthetic oxygen release rate of C.lentilifera were significantly inhibited by PS.The higher concentration of PS,the stronger inhibitory effect of C.lentilifera.The negative effects of PS on C.lentilifera were only observed at high concentrations(100mg/L).There was no effect of PA on the growth and metabolic processes of the three macroalgae.In the long-term toxicology experiment,B.gelatinus showed a strong tolerance to microplastic stress.The inhibitory effect of high concentration PS on G.tenuistipitata was temporary,and with the extension of culture time(6 weeks),G.tenuistipitata resumed to its normal growth state.The C.lentilifera has been inhibited by high concentration of PS for a long time.In addition,we found that the bacterial community structure on the surface of B.gelatinus was affected by microplastics.After two weeks of cultivation in PS,compared with the blank control group,the relative abundance of Vibrionaceae＿vibrio and Hirschia has decreased,while the relative abundance of Desulfovibrio has increased.(3)After reaching adsorption equilibrium,microplastics adhered to the surface of macroalgae were observed by microscope.We found that the density of microplastics on the surface of G.tenuistipitata was significantly higher than that of B.gelatinus and C.lentilifera,which might be related to the higher EPS content of G.tenuistipitata.After the decontamination procedure(dewatering,washing and the combined decontamination procedures),the density of microplastics adhering to the surface of macroalgae was significantly reduced.The decontamination effect of washing on microplastics is better than that of dewatering,and the combination of dewatering and washing method has the highest removal rate of microplastics.The orthogonal test showed that the elution time had a significant impact on the desorption rate of microplastics,and the optimal washing conditions were elution time of 8 hours,elution water volume of 40 m L,and elution revolution speed of 50 rpm.No matter how the washing conditions change,the microplastics on the algae surface cannot be completely removed.Microplastics with weak adhesion are eluted,while with strong adhesion force stays on the surface of macroalgae. |
