The Toxicology Of Three Imidazolium Chloride Ionic Liquids To Rice Seedlings

Ionic liquids (ILs) are molten salts at room temperature composed by organic cations and organie/inorganic anions. ILs has stable and nonflammable nature which makes them a "green solvents" and become an alternative to replace common organic solvents. Because of its stability in chemistry and thermodynamics, ILs has environmental risks in degradation, residue and ecological efficiency. In this paper, the toxicity of three kinds of ILs with different alkyl chain length to rice seedlings (Ⅱ You023, Otyza saliva saliva L.) was evaluated. The main research includes four parts as follows:(1) The effect of ILs on rice seedling growth was studied. Morphological changes in rice root and stem in different concentrations of ILs treatments could be visibly observed. The ILs included1-octyl-3-methylimidazolium chloride ([OMIM]C1), 1-decyl-3-methylimidazolium chloride ([DMIM]C1) and1-dodecyl-3-methylimidazolium chloride ([C12MIM]Cl). The result showed that in low concentration of ILs treatments (0.1mg/L [OMIM]C1,0.03mg/L[DMIM]C1,0.005mg/L [C12MIM]Cl) the main root length was longer than the control, the rates were6.79%,5.98%and6.56%, respectively. As the ILs concentration increased, the main roots and the stems grew shorter; the number of lateral roots and root hairs were reduced. The weight of the rice root and stem shared the same trend with length. The IC5o,5d for root and stem of [OMIM]C1were0.59mg/L and0.70mg/L, the IC50,5d for root and stem of [DMIM]C1were0.1mg/L and0.15mg/L, the IC50,5d for root and stem of [C12MIM]Cl were0.054mg/L and0.055mg/L. So the results indicated that rice root was more sensitive to ILs than the stem.(2) The effect of ILs on the enzymatic activities in rice roots and leaves were studied. Under the treatment of [OMIM]CI,[DMIM]C1and [C12MIM]Cl, the self-repair of the roots was effected and the activities of superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD) in roots were inhibited seriously. ILs could promote the activities of antioxidant enzyme in rice leaf chloroplasts, mitochondria and cytosol to some extent, but they would decrease when ILs reached higher concentrations. ILs may damage rice seedlings and cause lipid peroxidation in roots and leaves when applied at high concentrations which caused the increase of malondialdehyde (MDA) content. The MDA content in rice roots and leaves at0.8mg/L [OMIM]C1were1.73times and2.30times of the control, and at0.15mg/L [DMIM]C1they were1.90times and4.78times, while at0.08mg/L [C12MIM]C1they were1.97times and3.73times.(3) The effect of ILs on the photosynthesis of rice seedlings was studied. After the analyze of chlorophyll fluorescence parameters determined in rice leaves under the treatment of ILs, the PS II in leaves was damaged, the primary reaction of photosynthesis was inhibited. Moreover, the process of photosynthetic electron transport stopped and the ability of heat dissipation in leaves lost. In all, ILs caused the damage in rice leaves and resulted in the decrease of Hill reaction activity. The inhibition rate of Hill reaction activity at0.8mg/L [OMIM]C1was37.7%, at0.15mg/L [DMIM]C1it was52%and at0.08mg/L [C12MIM]C1it was67.4%. So ILs was toxic to rice photosystem.(4) The effect of ILs on the rice root physiology and dissipation of ILs were studied. Under the treatment of [OMIM]C1,[DMIM]C1and [C12MIM]C1, the respiration of rice roots was inhibited. ILs played a role in damaging the integrity of the plasma membrane and changes of the membrane proteins or lipid composition induce structural damage and alterations in membrane properties. These caused the decrease of root system activity and the increase of root membrane permeability. Ultrastructural studies revealed that0.6mg/L [OMIM]C1had adverse effects on both rice leaf and root cells. The structure of the thylakoid and granum in chloroplasts changed to square and disorganized. The mitochondria became larger, the mitochondrial cristae were vague. And the dissolution of the cristae and stroma showed emptiness in the center of the mitochondria. Golgi vesicle disintegrated and the structure became indistinct. A large number of ribosomes were broken from the surface of the endoplasmic reticulum and the endoplasmic reticulum was expanded. Cultivating rice with different concentrations of [OMIM]C1,[DMIM]C1and [C12MIM]Cl, the concentration of ILs in solvents decreased with time flew. It was mainly caused by the root absorption and biodegradation. The absorb time T1/2was increased with the increase of alkyl chain length of ILs. These indicated that rice roots were damaged irreversibly by the treatment of high concentration of ILs and longer alkyl chain length, and then the ability of absorptive was destroyed.As the alkyl chain length increases, so does the toxicity of the ILs. The toxic order was as [OMIM]C1<PMIM]C1<[C12MIM]C1. In addition, the different time when ILs added to treat rice seedlings was also studied in this paper. The different time to add [OMIM]C1included two ways. One of them was adding [OMIM]C1when rice grew in distilled water until the first leaf stretch completely; the other was adding [OMIM]C1at the very start when the seed begin to grow. The result showed that both two ways affected rice seedlings physiological function and the latter one was much more serious.