The Toxic Effect And Cell Distribution Of ZnO Nanoparticles On Chlorella Vulgaris Under The Presence Of Different-charged Surfactants

The environmental behavior and biological effects of nanoparticles are one of the hotspots in the environmental field in recent years.Due to the complexity of the water environment,nanoparticles will inevitably coexist with other pollutants after entering the water environment.The charged species in aqueous environments can alter the physicochemical properties,accumulation,and distribution of solubel nanoparticles,thereby affecting their toxicity on aquatic life.As primary producers in the aquatic ecological environment,algae are one of the most vulnerable aquatic indicator organisms to nanoparticles,so they are often used as model organisms to evaluate the biological effects of nanoparticles.The research on the environmental behavior and toxic effects of different charged pollutants on nanoparticles will help to deeply understand the impact of nanoparticles on organisms and potential ecological risks in different charged water environments.These results will provide more accurate and authentic evidence of the biological effects of nanoparticles in aqueous environments with different charged species.This study investigated the toxicity of zinc oxide nanoparticles（nZnO）on Chlorella vulgaris（C.vulgaris）under the stress of three different-charged surfactants,including the cationic surfactant cetyltrimethyl ammonium chloride（CTAC）,anionic surfactant sodium dodecyl benzene sulfonate（SDBS）,and nonionic surfactant octyl phenoxy polyethoxyethanol（TX-100）.Meanwhile,we determined the effect of these surfactants on the properties of nZnO(potential,particle size,dissolution of Zn²⁺,etc.)and the intracellular distribution of Zn.The research conclusions of this paper are as follows:（1）The combined toxicity of nZnO/CTAC,nZnO/SDBS and nZnO/TX-100composite system to C.vulgaris were antagonistic,synergistic and antagonistic,respectively.The calculated 96 h-EC₅₀values of nZnO/0.2 mg/L CTAC and nZnO/0.3mg/L CTAC to C.vulgaris were 1.8 and 2.9 mg/L,respectively;The 96 h-EC₅₀values of nZnO/20 mg/L SDBS,nZnO/0.3 mg/L SDBS to C.vulgaris were 1.2 and 1.8 mg/L,respectively;The 96 h-EC₅₀values of nZnO/100 mg/L TX-100,nZnO/0.3 mg/L TX-100 to C.vulgaris were 2.8 and 4.9 mg/L,respectively.（2）Cationic CTAC can be adsorbed on the surface of nZnO through electrostatic and hydrophobic interactions,reducing the negative charge but increasing the hydrophobicity of nZnO,and promoted the agglomeration of nZnO but inhibited the dissolution of Zn²⁺.Anionic SDBS can adsorb on the surface of nZnO through hydrophobic interaction,promoted the dispersion and dissolution of nZnO,and increased intracellular accumulation of Zn²⁺.Non-ionic TX-100 had no significant effect on the potential Zn²⁺dissolution of nZnO,but significantly enhanced the hydrophobicity of nZnO.Fourier transform infrared spectroscopy further proved that CTAC,SDBS,TX-100 can be adsorbed on the nZnO.Comparing the changes in the interfacial.tension of surfactants.in the presence and.absence of nZnO,we obtained that nZnO reduces the interfacial tension of the three surfactants.（3）The cell membrane hydrophobicity of C.vulgaris could be significantly improved under the stress of three surfactants,and the degree of influence was CTAC>TX-100>SDBS.By comparing the ZnCl₂/surfactant composite system,it could be seen that both the particle and the ion of nZnO can have toxic effects,and the ion has a greater toxicity effect than the particle.The Zn element in the nZnO/CTAC composite system tends to be distributed on the cells surface,and in the nZnO/SDBS composite system tends to be distributed in inteacellular.Furthermore,nonionic TX-100 exhibited no significant effect on the cell distribution of Zn²⁺and decreased intracellular accumulation of granular nZnO.