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Ecological effects of ionic liquids on microbial activity of a soil and on tree seed germination

Ionic liquids (ILs) are considered one of the most promising green alternatives to molecular organic solvents. Nevertheless, before a widespread use of these compounds in a determined application, the knowledge of their ecotoxicity and biodegradability must be defined.

In this work the effect of addition of different doses of 1-butil-2,3-dimethylimidazolium trifluoromethanesulfonate, [C4C1C1Im][OTf], on microbial activity of a soil under Pinus pinaster Aiton and on the seed germination of species of P. pinaster , Pinus sylvestris L., Pinus radiata D. Don and Eucalyptus globulus Labill were analyzed. Additionally, seed germination test were also applied to this IL after being subjected to heat treatment.

A microcalorimeter Thermal Activity Monitor (TAM-III) TA-Instruments was used to determine the influence of the addition of four doses (10 %, 25 %, 50 % and 75 %) on the microbial activity of a Galician soil, under P. pinaster. Methodology was widely exposed in previous works [1]. From the data obtained in these experiments, the calculation of microbial growth was performed [2].

Seed germination test of selected species were carried out for several doses of ILs (10 %, 1 %, 0.1 % and 0.01 %). The degradation treatment of the IL was carried out during 24 h in an oven at the temperature of 200 °C. Five replies with 25 seeds per Petri dish were incubated in a Phytotron (Climas AGP890) for every species and treatments. Seeds were maintained for 16 h under light at 24 °C and in the dark for 8 h at 16 °C during 45 days, when the germination was completed in all the species [3, 4].

Results of soil microbial activity and germination obtained for this IL were compared with the corresponding to other ILs, previously studied in our laboratory.  

Dose of 10 % inhibited totally the germination of the four species and dose of 1 % provoked an important reduction with regard to the control, both, for degraded and no-degraded IL. Nevertheless, in spite of all the doses showed differences on calorimetric parameters with regard to control; only the dose of 75 % does not show soil microbial response.

Keywords: ionic liquid, toxicity, soil microbial activity, seed germination