The effect of the number of alkyl substituents on imidazolium ionic liquids phytotoxicity and oxidative stress in spring barley and common radish seedlings

• [BMIM][PF6] and [BMMIM][PF6] were characterized by similar phytotoxicity.
• ILs at high concentration were cause oxidative damage in plants.
• The increased level of ILs in soil causes a decrease in content of plant pigments.
• The increased concentration of ILs in the soil increases the activity of POD.
• The common radish revealed the higher tolerance to the ILs as compared to barley.

Increasing amounts of two ILs: 1-butyl-3-methylimidazolium hexafluorophosphate [BMIM][PF6] and 1-butyl-2,3-dimethylimidazolium hexafluorophosphate [BMMIM][PF6], were introduced to soil in which spring barley (Hordeum vulgare) and common radish (Raphanus sativus L. subvar. radicula Pers.) seedlings were cultivated, in order to evaluate the phytotoxicity of ionic liquids with imidazolium cation with two or three alkyl substituents attached. The results of the study i.e. the inhibition of the length of plants and their roots, as well as the yield of fresh weight of plants, clearly showed that differences in the number of substituents did not affect the toxicity of these ILs. Although, radish was more resistant to the applied ionic liquids than barley. Ionic liquids led to a decrease in the content of all assimilation pigments and induced oxidative stress in the plants, as showed by an increase in malondialdehyde (MDA) content, and changes in the level of H2O2 and antioxidant enzymes: superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD). The best biomarkers of oxidative stress in both plants were the changes in chlorophyll content and the increase in POD activity. Both spring barley and radish exposed to [BMIM][PF6] and [BMMIM][PF6] accumulated a large amount of fluoride ions, which further increased the toxicity of these compounds for both plants.

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