TERRESTRIAL ECOTOXICITY OF SHORT ALIPHATIC PROTIC IONIC LIQUIDS BREZANA PERIC,*y ESTHER MARTI ´ , y JORDI SIERRA, y ROBERT CRUAN ˜ AS, y MIGUEL IGLESIAS, z § and MARIA ANTONIA GARAUy yLaboratori d’Edafologia, Universitat de Barcelona, Barcelona, Spain zDepartamento de Ingenieria Quı ´mica, Universidad de Santiago de Compostela, Santiago de Compostela, Spain §Departamento de Engenharia Quı ´mica, Universidade Federal da Bahia, Salvador, Brazil (Submitted 2 February 2011; Returned for Revision 14 March 2011; Accepted 22 August 2011) Abstract —A study of the ecotoxicity of different short aliphatic protic ionic liquids (PILs) on terrestrial organisms was conducted. Tests performed within the present study include those assessing the effects of PILs on soil microbial functions (carbon and nitrogen mineralization) and terrestrial plants. The results show that the nominal lowest-observed-adverse-effect concentration (LOAEC) values were 5,000 mg/kg (dry soil) for the plant test in two species (Lolium perenne, Allium cepa), 1,000 mg/kg (dry soil) for the plant test in one species (Raphanus sativus), and 10,000 mg/kg (dry soil) for carbon and nitrogen microbial transformation tests (all concentrations are nominal). Most of the median effective concentration values (EC50) were above 1,000 mg/kg (dry soil). Based on the obtained results, these compounds can be described as nontoxic for soil microbiota and the analyzed plants, and potentially biodegradable in soils, as can be deduced from the respirometric experiment. The toxicity rises with the increase of complexity of the PILs molecule (branch and length of aliphatic chain) among the three PILs analyzed. Environ. Toxicol. Chem. 2011;30:2802–2809. # 2011 SETAC Keywords —Protic ionic liquids Terrestrial ecotoxicity Biodegradability INTRODUCTION Ionic liquids are novel solvents of rising interest as greener alternatives to traditional volatile organic solvents, aimed to facilitate so-called sustainable chemistry. As a consequence of their unusual physical properties, reusability, and apparently environmentally friendly nature, ionic liquids have attracted the interest of industry and academia. In the near future, many new ionic liquids will be developed, but with little data relating to their hazard potential [1]. These chemicals are liquids com- posed entirely of ions; they are salts with a melting point lower than 1008C. The reason for their low melting point lies in the asymmetry of the ions and the important steric hindrance among functional groups [2]. They have a very low vapor pressure, and thus their nonvolatile nature reduces the risk of air pollution and makes them potential green substitutes for volatile organic solvents. Their polarity, hydrophilicity/hydrophobicity, and other properties can be tuned by a suitable combination of cations and anions; therefore, they have been termed designer solvents [1,3]. Two main groups of ionic liquids have been identified: aprotic ionic liquids and protic or Brønsted ionic liquids (PILs). The PILs have a proton available for hydrogen bonding. Common and classical ionic liquids, which belong mainly to the group of aprotic ionic liquids, are designed with bulky organic cations, such as imidazolium, pyridinium, pyr- rolidinium, and quaternary ammonium, with alkyl chain sub- stituents and different inorganic anions. In the last few years, numerous reports have revealed different applications of ionic liquids in terms of separation, catalysis, photochemistry, elec- trosynthesis, lubricants, electrolytes for batteries and dye- sensitized solar cells, as cleaning solvents in applications in which large amounts of solvents are used to clean batch processing equipment, and in minimization of CO 2 /SO 2 emis- sions by removal of SO 2 and CO 2 from natural gas [4–6]. Regarding the fate and effects of ionic liquids in the environ- ment, the water solubility of many ionic liquids is not negli- gible, and the release of ionic liquids into aquatic and terrestrial environments may lead to water and soil pollution and related risks. Several properties of ionic liquids and their effects on aquatic organisms have been investigated [7–12]. However, more research on the effect of protic ionic liquids on soil and sediment organisms is required. Many commonly used ionic liquids are toxic to aquatic and terrestrial organisms, as dem- onstrated by toxicological research studies concerning ionic liquids undertaken in the past decade [13]. A new group of PILs, with different cations and anions from those previously known, has been designed and could have a lesser environmental impact than the former ones, because the new PILs are based on polysubstituted amines and organic anions. Both the cationic and anionic parts of the molecule are organic and present a relatively low molecular weight [14,15]. These new PILs are 2-hydroxyethanolamine formate (2-HEAF), 2-hydroxydiethanolamine propionate (2-HDEAPr), and 2-hydroxytriethanolamine pentanoate (2-HTEAPe). Con- sidering the interest in these substances as more environmen- tally sustainable than volatile organic solvents, one must examine their potential toxicity. The current chemical legis- lation for Registration, Evaluation, Authorization, and Restric- tion of Chemical Substances (REACH) holds suppliers of chemicals responsible for their products. The REACH criteria must be fulfilled for ionic liquids as well, taking into account their possible commercial use [16]. One of the new PILs, 2-HEAF, was found to dissolve many inorganic salts, hydroxylated compounds, and some insoluble polymers such as polyaniline and polypyrrole [17]. Also, 2-HEAF was analyzed as a potential solvent in the preparation of organo- soluble polyanilines with reasonable molecular weights [18,19], for some heterogeneous catalytic hydrogenation processes Environmental Toxicology and Chemistry, Vol. 30, No. 12, pp. 2802–2809, 2011 # 2011 SETAC Printed in the USA DOI: 10.1002/etc.683 * To whom correspondence may be addressed (brezana@hotmail.com). Published online 20 September 2011 in Wiley Online Library (wileyonlinelibrary.com). 2802