A Study On The Toxicity Of Ionic Liquids To Aquatic Organisms

Ionic liquids?ILs?are a new type of solvent composed of relatively large volume,asymmetric organic cations,and a relatively small volume of inorganic anions.They are considered to be environmentally friendly solvents because of their low volatility and excellent water solubility.In recent years,with mass production and application,they are partially introduced into the environment,resulting in a positive impact of the environmental organisms due to their efficient stability and poor biodegradability.Therefore,many studies have questioned the“green solvents”characteristics of ILs and their environmental behavior and ecotoxicity have received widespread attention.In this work,1-butyl-3-methylimidazolium chloride?[C₄mim]Cl?,1-octyl-3-methylimidazoliumnitrate?[C₈mim]NO₃?,1-octyl-3-methylimidazolium chloride?[C₈mim]Cl?,N-octyl-3-metylpyridinium chloride?[C₈mpy]Cl?,N-octyl-3-metylpyridinium bromide?[C₈mpy]Br?and1-dodecyl-3-methylimidazolium chloride([C₁₂Dmim]Cl)were selected as the tested ILs.We aimed to study the acute toxic effects of six ILs with different structures on Chlorella pyrenoidosa?Phaeodactylum tricornutum,Daphnia magna,and Cyprinus carpio.The main results were as follows:?1?The results of acute toxicity revealed that the inhibitory effect on the C.pyrenoidos and P.tricornutum growth rate became stronger with increasing ILs concentrations,which showed a dose-response relationship.The EC₅₀values of three ILs showed that the toxicity of ILs increased with the increase of carbon chain length,which was[C₁₂Dmim]Cl>[C₈mim]Cl>[C₄mim]Cl.The toxicity of the four ILs to this P.tricornutum was in the following decreasing order of:[C₈mpy]Br?[C₈mpy]Cl>[C₈mim]NO₃>[C₈mim]C1,based on the EC₅₀values.The pyridinium-based ILs had higher toxicity than the imidazolium-based ILs because the EC₅₀values of[C₈mpy]Cl were significantly less than that of[C₈mim]Cl.The 24,48,72 and 96 h-EC₅₀values of[C₈mim]Cl for C.protothecoides and P.tricornutum were24.25,8.35,4.72,3.46 mg/L and 93.23,40.74,31.62,33.60 mg/L,respectively.It can be seen that the resistance of P.tricornutum to ILs is significantly greater than that of C.protothecoides.Also,the content of chlorophyll a decreased significantly with the increase of ionic liquid concentration.Through the chlorophyll fluorescence parameters F_v/F_mand?_PSII,the values decreased with the increase of concentrations,which proved that ILs had a destructive effect on the photosynthetic system of microalgae,and the degree of damage increased with the increase of ILs concentration.?2?The soluble protein content,SOD and CAT activities in C.pyrenoidosa and P.tricornutum were measured when they were exposed to different concentrations of ILs for 96 h,which presented that soluble protein content and activities of the two antioxidant enzymes increased firstly,and then decreased with the increase of the ILs concentrations.The ILs could promote the increase of soluble protein content,SOD and CAT activities in the microalgae at low concentrations,the increased contents of soluble protein,SOD and CAT activities could be considered as a self-regulation mechanism in vivo to alleviate the toxic effects of ILs on this alga through producing defensive and protective proteins.When this alga was exposed to high concentrations of ILs,there was a decreased in the contents of soluble protein,SOD and CAT activities may be attributed to the toxicity of ILs exceeding the tolerance range of algal cells,resulting soluble protein synthesis is inhibited.The decreased SOD and CAT activities may be attributed to an excess of ROS.Oxidative stress induced by high concentrations of ILs,exceeding the antioxidant potential of the alga,might lead to irreversible damage.However,the content of malondialdehyde?MDA?in cells increased significantly with the increase of ILs,which indicated that ILs caused lipid peroxidation and oxidative damage to membrane lipid of microalgae cells.?3?To evaluate the biotoxicity of 1-octyl-3-methylimidazolium chloride?[C₈mim]Cl?on D.magna,the sensitivity of D.magna aged different days?1-day-old,2-day-old and 4-day-old?to[C₈mim]Cl was studied through acute toxicity experiments.The results showed that environmental factors have a positive impact on the growth and development of 1-day-old D.magna.There were 1-day-old D.magna found dead after 24h and 48h of exposure.2-day-old D.magna is more sensitive to the toxicity of[C₈mim]Cl;therefore,it is more suitable for evaluating the biological toxicity effects of ILs.At the low concentrations?0.9-18?g/L?,there was no significant variation in mortality.There are almost no D.magna found dead during 21d of exposure.When the concentration was 3.6?g/L,the survival rate of D.magna was significantly increasing,and when its concentration was 18?g/L,the mortality rate reached 100%.Moreover,the first-generation time,first-generation number,exuviate times,total generation times,generation number,and total exuviate times of D.magna it is showed that[C₈mim]Cl had no significant effects on the first generation time,total generation number and times,and total exuviate times,but the ionic liquid significantly inhibited the survival rate and first-generation number were used as indicators to investigate the chronic toxic effects of[C₈mim]Cl on D.magna,suggesting that the survival rate and first-generation number would be the two sensitive indicators for evaluating the chronic toxic effects of[C₈mim]Cl on D.magna.?4?To evaluate the possible toxicity of[C₈mim]Cl?0,30,60,90,120,150,200,and 300 mg/L?on C.carpio,the percentage of the mortality rate was measured.At the low concentrations?0?120 mg/L?,there was no significant variation in mortality.With increasing dosages,the mortality increased remarkably compared with that of the control.For example,the mortality increased by 10,40,and 80%when C.carpio was exposed to 150,200,and 300 mg/L[C₈mim]Cl at 96 h.Moreover,the acute toxicity of[C₈mim]Cl on the organs of C.carpio?eyes,gills,intestines,heart,and kidneys?were determined,the results suggested that[C₈mim]Cl exhibit acute toxicity to C.carpio specific organs causing extensive damage,and in the tissues of this fish was more serious under the exposure of intestine,gill and kidney than that under the eye and heart exposure.The gill,kidney,and intestine of fish are not only the breathing,excretory,digestion,and absorption of nutrients in vivo but also a critical site for intermediary metabolism.Therefore,the organs can also be directly affected by pollutants,triggering antioxidant defense systems,and disturbing their metabolic pathways.The SOD and CAT activities would help to eliminate ROS for protecting the tissues from injury caused by the ILs.The decreased SOD and CAT activities may be attributed to an excess of ROS.And[C₈mim]Cl can induce excessive ROS,inhibit SOD and CAT activities,and then oxidize proteins.Based on the above results,ionic liquids will affect the toxicity of ionic liquids on aquatic organisms and organs,and it was found that the structural compositions of ILs,including cation core,alkyl chain length and short second alkyl chain of the cation,side chain functionalization and type of anion,could affect the degree of their toxicity.Upon entering the ecological environment,these ionic liquids will be absorbed and ingested by the organism.The human body can have toxic effects after consuming these organisms,which contain ionic liquids.Therefore,the toxicity of ionic liquids and the production of new ionic liquids with short carbon chain,multi-function,and low toxicity should be given care.