Toxicity In Algal Induced By Organic Three-Dimensional Layered Double Hydroxides

With the rapid development of society,nanomaterials have been widely used in the fields of medicine,biosensor and environmental governance due to their unique physical and chemical properties.Layered double hydroxides(LDHs)nanomaterials have attracted extensive attention as adsorbents for wastewater treatment(HG/T 5549-2019)due to their chemical composition tunability of laminates,anion exchange and memory effect.As the problem of environmental pollution has been worse,studies on the use of LDHs to remove environmental pollutants are increasing.It is possible for the excessive use of LDHs to cause its entry into the aquatic ecosystem and there will be potential risks to organisms.However,studies on the biosafety of LDHs to aquatic organisms are few,so it is of great practical significance to study the toxicity and mechanism of LDHs to aquatic organisms.In this paper,three-dimensional layered double hydroxides(3D-LDH)was selected as the representative of LDHS,and the organic three-dimensional layered double hydroxides(O3D-LDH)was successfully prepared by hydrothermal synthesis using sodium dodecyl sulfate(SDS)as soft template.The morphology and structure of O3D-LDH were analyzed by Fourier transform infrared absorption spectrometer(FTIR),X-ray diffraction(XRD),scanning electron microscope(SEM)and transmission electron microscope(TEM),and then the physical and chemical properties of O3D-LDH in BG11 medium were analyzed by particle size analyzer and UV-Vis spectrophotometer.The effects of different concentrations of O3D-LDH on the growth,photosynthetic pigment content,total protein content,malondialdehyde(MDA)content,superoxide dismutase(SOD)and catalase(CAT)activities of Chlorella vulgaris and Scenedesmus obliquus were investigated.To explore the toxicity effects and mechanism of O3D-LDH on Chlorella vulgaris and Scenedesmus obliquus and provide a theoretical basis for ecological risk assessment of O3D-LDH.The main research results of this paper are as follows:(1)The organic three-dimensional layered double hydroxides(O3D-LDH)was successfully prepared.SEM results show that O3D-LDH is a flower-like microsphere formed by the cross agglomeration of a large number of nanosheets.The thickness of the nanosheets is about 65.24 nm,and there are obvious voids between the layers.The results of FTIR?XRD and TEM show that the flower-like morphology of O3D-LDH is tight internal structure and good crystallinity and SDS exists in the product as interlayer anion and outer surface of the sample.(2)The uniformly dispersed O3D-LDH suspension with complete structure was prepared under the conditions of ultrasonic time of 30 min,power of 100 W,frequency of 40 k Hz and temperature of 25?.O3D-LDH suspension was kept constant by oscillation(150 r/min)to avoid settling.In this process,the dissolution of Mg²⁺,Al³⁺and SDS of O3D-LDH were far lower than the theoretical values.(3)O3D-LDH could inhibit the growth of Chlorella vulgaris,and showed a concentration-effect relationship.Under exposing low concentration of O3D-LDH(<75 mg/L),the contents of chlorophyll and carotenoids of Chlorella vulgaris were inhibited to varying degrees,while the activities of SOD and CAT and the content of MDA were increased in different degrees,which indicated that Chlorella vulgaris not only had an impact on photosynthesis,but also had oxidative damage.However,high concentration of O3D-LDH(>75 mg/L)tended to aggregate O3D-LDH,which decreased the concentration of O3D-LDH in direct contact with algal cells and increased the shading effect on Chlorella vulgaris.The toxicity of O3D-LDH to Chlorella vulgaris is mainly due to the shading effect caused by O3D-LDH aggregates and oxidative damage caused by nanosheets.(4)The toxicity effect of O3D-LDH on Scenedesmus obliquus also showed growth inhibition and the toxicity was less than that of Chlorella vulgaris.At low concentration(<75 mg/L),the chlorophyll and carotenoid contents of algae reduced,while the content of MDA and the activities of SOD and CAT increased,indicating that the toxicity mechanism of low concentration O3D-LDH to Scenedesmus obliquus was mainly shading effect and oxidative stress.When exposed to high concentration(>75mg/L),the contents of chlorophyll and carotenoids on Scenedesmus obliquus increased,while the content of MDA and the activities of SOD and CAT decreased gradually,which showed no significant difference compared with the blank group.These results indicated that the toxic mechanism of high concentration of O3D-LDH to Scenedesmus obliquus was mainly the shading effect.