Toxicity Of Ionic Liquid With Different Structure On Chlorella Pyrenoidosa

As a new type of organic solvent,ionic liquids?ILs?have been considered as a "green solvent".With mass production and application,they are partially introduced into the environment,resulting in a certain impact of the environmental organisms duing to their efficient stability and poor biodegradability.At present,a large number of literature reported the toxic effects of ILs on organisms?animals,plants,microorganisms and cells,etc.?.The effects of six ILs with different structures on Chlorella pyrenoidosa were studied.The acute toxicity,the effect on photosynthesis,cell structure and oxidative stress were evaluated.The ILs examined in this study included 1-hexyl-3-methylpyridine chloride?C₆[Py]Cl?,1-hexyl-3-methylimidazolium chloride?C₆[MIM]Cl?,1-octyl-3-methylimidazolium chloride?Cg[MIM]Cl?,1-dodecyl-3-methyl Imidazolium chloride?C12[MIM]Cl?,1-dodecyl-2,3-dimethylimidazolium chloride?C12[DMIM]Cl?and 1-hexadecyl-3-methylimidazole Chloride?C16[MIM]Cl?.The results showed that the growth inhibition rate of Chlorella pyrenoidosa increased with increasing ILs concentration,at low concentration of ILs with short carbon chain length,the growth inhibition rate of ILs on algal decreased gradually with the prolongation of exposure time,showing that the growth ability of algae will be restored,but there is no such phenomenon at longer carbon chain length.In contrast,the cell growth is inhibited continuously throughout the experiment in the treatment of high concentration of ILs.The highest toxicity of six ILs appears in 48h.Besides,compared with all EC50,it reveals that the toxicity of ILs increased with the increase of the number of carbon chains,and the impact of imidazolium-based ILs treatment is greater than that of pyridinium-based ILs,the substituted chlorides are larger than the disubstituted chlorine salts.The chlorophyll content and chlorophyll fluorescence intensity are determined afer 96 h.The results shows that the content of chlorophyll a,chlorophyll b and total chlorophyll have an obvious influence by ILs,the chlorophyll content of algal cells have enhancement at low inhibition rate even promote the growth of the concentration,the content of chlorophyll decreased gradually with increasing ILs concentration.Additionally,the the effect of imidazolium-based ILs treatment on chlorophyll is greater than that of pyridinium-based ILs,the substituted chlorides are larger than the disubstituted chlorine salts.Meanwhile,the effects of ILs on the Fv/Fm,Fv/F0 and NPQ of C.pyrenoidosa are showed rising trend with the increase of ILs concentration and light intensity,while F0 and Y???are showed down trend.Finally,the effect of cations on the imidazolium-based ILs is greater than that of pyridine,the substituent imidazolium chloride is larger than that of disubstituted chlorine salts.The effect of ILs on the cell structure of C.pyrenoidosa showed that ILs has a significant effect on the cells,not only changing the shape of cells,but also destroying the structure of cell wall and cell membrane,leading to ILs go into the algal cells,the internal organelles have an impact and damage,which ultimately make the cell metabolism become disorder and cells can not grow normally.Imidazolium-based ILs treatment have higher toxicity than that of pyridinium-based ILs,the substituent imidazolium chloride is larger than that of disubstituted imidazolium chloride salts.A preliminary study of proteomics showed that the number and type of protein in the control group are significantly higher than those in the the treatment group.The synthesis of protein is inhibited and the metabolism of the cells was affected,which affected the normal growth of the cells and led to the death of the cells.There is a positive correlation between six ILs concentration and the content of ROS after exposed for 96 h.The ROS content treated with the imidazolium-based ILs in C.pyrenoidosa is higher than the pyridine-based ILs,the substituent imidazolium chloride is higher than that of disubstituted imidazolium chloride salts.The content of soluble protein increased when exposed to low ILs concentration,and decreased when continuously rising ILs concentration.It is showed that algae cells will be a short time to synthesize a large number of soluble protein to eliminate the external stress at low ILs concentration,but with the further increase in concentration,algal cells are substantially destroyed,the soluble protein content will decline.The activities of SOD and CAT have a same trend to the content of soluble protein,indicating that algae cells increase the content of intracellular ROS when receiving external stress,the intracellular antioxidant defense system will lead to increase the activities of SOD and CAT to eliminate the impact of the outside environment,while SOD and CAT activities are declined in higher concentration,which beyond the recovery level of the cell.