title: Sorption to dissolved humic acid and its impacts on the toxicity of imidazolium based ionic liquids.
abstract: Two typical ionic liquids (ILs), 1-butyl-3-methylimidazolium chloride ([C4MIM]Cl) and 1-octyl-3-methylimidazolium chloride ([C8MIM]Cl), are demonstrated to associate strongly with dissolved organic matter (DOM) with distribution coefficients (KDOC) in the range of 10(4.2) to 10(4.6) for Aldrich humic acid (used as model DOM). With the increase of humic acid concentration to 11 μg/mL DOC (dissolved organic carbon), the free fraction (ratio of freely dissolved to total concentration) of [C4MIM]Cl and [C8MIM]Cl reduced to about 0.85 and 0.79, respectively. This reduction of freely dissolved concentration gave rise to remarkable reduction of bioavailability and toxicity of the two ILs. MTT assay with HepG2 cell lines showed that the EC50 values were 459 μmol/L for [C4MIM]Cl and 12 μmol/L for [C8MIM]Cl, respectively, and the cell viability increased about 50% in the presence of trace amount of humic acid (1 μg/mL DOC). The SOS/umu test indicated mutagenicity for [C4MIM]Cl at levels above 664 μmol/L, and the genotoxicity was diminished with the addition of trace humic acid (0.00000374-0.374 μg/mL DOC). The studied ILs showed acute toxicity toward model fish medaka with a 96 h median lethal concentration (LC50) of 2254 μmol/L for [C4MIM]Cl and 366 μmol/L for [C8MIM]Cl. The addition of humic acid (5.49 μg/mL DOC for [C8MIM]Cl, 1.37 μg/mL DOC for [C4MIM]Cl) to IL solutions reduced the death rate of medaka to a minimum value of ∼25% of that at zero DOC. Our results suggest that DOM may play an important role in determining the environmental fate and toxicity of imidazolium-based ILs, and its effects should be taken into account in assessing the environmental risk of ILs.
authors.affiliation: State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China.
authors.forename: Zhen
authors.initials: Z
authors.lastname: Zhang
authors.forename: Jing-fu
authors.initials: JF
authors.lastname: Liu
authors.forename: Xiao-qiang
authors.initials: XQ
authors.lastname: Cai
authors.forename: Wei-wei
authors.initials: WW
authors.lastname: Jiang
authors.forename: Wen-ru
authors.initials: WR
authors.lastname: Luo
authors.forename: Gui-bin
authors.initials: GB
authors.lastname: Jiang
mesh_terms: D000818:Animals; D001881:Borates / Q000737:chemistry / Q000633:toxicity*; D056945:Hep G2 Cells; D006801:Humans; D006812:Humic Substances; D007093:Imidazoles / Q000737:chemistry / Q000633:toxicity*; D052578:Ionic Liquids; D009990:Oryzias; D012486:Salmonella typhimurium; D018675:Toxicity Tests; D014874:Water Pollutants, Chemical / Q000633:toxicity
chemical_list: C528768:1-octyl-3-methylimidazolium; D001881:Borates; D006812:Humic Substances; D007093:Imidazoles; D052578:Ionic Liquids; D014874:Water Pollutants, Chemical; C502841:1-butyl-3-methylimidazolium chloride