Effects Of Three Imidazolium Bromide ILs On Enzyme Activity And The Diversity Of Microbial Community In Soil

Ionic liquids, known as green solvens which is environmentally friendly with excellent performance, have been widely used in many fields of chemistry, have a good prospect of application. Along with the increase in application, however, people come to realize that ionic liquids are not absolutely green, the release in the environment would do harm to the environment. The research into toxicity of different ionic liquids towards various medium may enrich data on ionic liquids, structure-effect relationship model, promote the replacement with lower toxicity ionic liquids to higher toxicity ionic liquids. And is of overreaching importance to the reducing of the environmental hazards.Soil is a complex and dynamic living ecosystem, and certain factors influence its quality and health. In the assessment of soil environment quality, the living and dynamic nature of soil, indicated by such factors as soil enzymes and microorganisms, is usually used as a biomarker. Soil enzymes are involved in catalyzing various reactions and metabolic processes occurring in organic matter metabolism, maintaining soil structure, cycling nutrients,detoxifying pollutants, and producing energy for both microorganisms and plants. In the present study, we chose three typical imidazole bromide ionic liquid with distinct chain length of the side chains connected to the cationic head groups, [C₄mim]Br, [C₆mim]Br and[C₁₀mim]Br, using the enzyme activity photometry method, dilute plate method, Terminal restriction fragment length polymorphism?T-RFLP? and real time-PCR?RT-PCR? technique,to determine the toxicity of ionic liquids to the soil biosystem. The concentrations of[C₄mim]Br and [C₆mim]Br are 0, 1, 10, 100mg/kg, while concentrations of [C₁₀mim]Br are 0,1, 10, 50mg/kg. The indicators include the population of soil culturable bacteria, fungi,actinomycetes; soil enzyme activity such as urease, phosphatase, and ?-glucosidase; diversity of microbial community structure as well as the changes AOA and AOB community quantity.Sampling was done at days 10, 20, 30 and 40, respectively. The results are as follow:?1? All of the three ionic liquids caused decrease in the cultivable microorganisms, and[C₄mim]Br excerts less inhibitory effect. Among the three microorganisms, the toxicity of the three ionic liquids to fungal is more obvious, at the tenth day of the experiment, and existsignificant dose-effect relationship of inhibition. This toxic effect disappeared gradually with prolonged incubation time.The extent of the restrain to microorganisms dealed with[C₁₀mim]Br is largest, and bacteria and fungal numbers didn't recover to the control level at the end of the experiment.?2? Urease activity was stimulated by [C₄mim]Br at the tenth day of the experiment, this effect then gradually disappeared and returned to the control level, urease activity even declined by the end of the test. Whereas, [C₆mim]Br and [C₁₀mim]Br inhibited urease activity and exhibited significant dose-effect relationship. The activities of acid phosphatase and?-glucosidase were stimulated in ionic liquid-spiked soil relative to the control, and this stimulation effected was weaken with the extension of time and the increase of concentration in [C₁₀mim]Br-spiked soil. At the end of the experiment, ?-glucosidase acticity in[C₁₀mim]Br-spiked soil was inhibited, and exhibited obvious change compared with the control.?3? In T-RFLP experiment, we analysed the microbial community structure spectra in the soil afer spiked with ionic liquids [C₄mim]Br, [C₆mim]Br and [C₁₀mim]Br, the maximum fragment length area changes in spectra are 91/92, 138, 141, 148, 292 and 400, we found that their corresponding strain are Bacteroides, Bacillus, Nocardioides, Eubacterium,Mycobacterium and Rhizobium. The ionic liquids lowered Shannon index and Simpson index,and the extent is more obvious with the increase of the length of carbon chain.?4? In present sampling interval and the concentration set, AOB-amo A gene copy number decreased significantly in all the three soil and didn't recover to the control level.Except the treatment group 1mg/kg handled with [C₄mim]Br, the copy number of AOA-amo A gene of any other treatment were noteworthy different with the control level.Ionic liquids exerted irreversible inhibition effect on the expression of ammonia-oxidizing microorganisms.?5? By comparing several indicators,we found that, due to the difference in alkyl chain length, the three ionic liquids present different toxicity. With the extension of alkyl chain length in the imiadazolium cation moiety, the toxicity increase. Among all the indicator in this issue, the amount of AOA-amo A gene copies is most sensitive to ionic liquids.