The Effect Of Exopolymeric Substances On The Algal Toxicity And Bioaccumulation Of Nanoparticles

With the rapid development of nanotechnology,more and more nanopariticles(NPs)are discharged into the environment during production,using,and disposing,potentially threatening planktons like algae and affecting the safety of entire aquatic ecosystem.Algae can secrete high-molecular polymers,named extracellular polymeric substances(EPS),which would interact with NPs and affect their biological effect.But the specific mechanisms are still unclear.We extracted and characterized the EPS of Chlorella Pyrenoidosa,studied the effects of EPS on the algal bioaccumulation and toxicity of Ag nanoparticles(AgNPs)and TiO2 nanoparticles(TiO2-NPs).The obtained results mainly include:(1)EPS of Chlorella Pyrenoidosa were mainly consisted of proteins and polysaccharides,containing large amounts of amino,carboxyl,hydroxyl and other active groups.The EPS could combine with AgNPs and TiO2-NPs and change their physicochemical properties,such as UV spectra of AgNPs,Ag+ release from AgNPs,and zeta potentials and hydrodynamic sizes of TiO2-NPs.(2)NPs could not only be adsorbed on the surface of algal cells,but also be internalizated into the algal cells.EPS on the algal surface could increase the cell adsorption of NPs,but inhibit the cell internalization of NPs.(3)EPS could combine with AgNPs and Ag+,inhibit the cell internalization,and alleviate the algal toxicity of AgNPs.Compared with rutile TiO2-NPs,anatase TiO2-NPs had stronger heteroagglomeration with algae,thus causing higher oxidative stress and toxicity to algae.EPS could inhibit the direct contact to the algal cell wall/membrane and algal internalization of TiO2-NPs,reduce the oxidative stress,and thus alleviate the algal toxicity.