## 1 Introduction  
Ionic liquids (ILs) are generally defined as low-melting organic salts, often described as liquid below 100 \({}^{\circ}\)C, and represent a relatively new class of chemical compounds [1]. They exhibit a variety of useful physico-chemical properties, including very low volatility, high thermal, chemical and electrochemical stability, a wide liquid range and varying lipophilicity. Some of these characteristics are sought-after, environmentally favorable attributes, which has led to frequent proposal for ILs as more sustainable alternatives in numerous applications [2]. Successful uses of ILs were reported in the fields of solvent extraction and separation [3; 4], organic synthesis [5], electrochemistry [6], among many others. Their versatile properties enable numerous applications ranging from carbon dioxide (CO\({}_{2}\)) capture [7] to their use as a drug carrier in the pharmaceutical industry [8]. An increasing number of studies has also exploited these properties to extract heavy metals, in the desire to improve the applicability and sustainability of traditional methods [9]. In this regard, the synthesis of task-specific ionic liquids (TSILs) has received growing interest because they can be \"tailored\" to meet the intended properties: Introducing metal-chelating functional groups to either the respective cation or anion can fine-tune the affinity of the ILs towards metal ions, improving the efficacies in the extraction processes [10]. Incorporating anions with functional groups has proved to be successful in extracting various heavy metals or trace elements. For instance, ILs with a Sulphur functionality, e.g., thiosalcylate, thioglycolate or thiocyanate groups, showed a high affinity towards copper, silver, cadmium, platinum or mercury [11; 12; 13]. Meeting the claim of ILs as \"green\" solvents, starting with their production, involved proposing enhanced synthesis routes achieving higher yields and fewer byproducts while avoiding environmentally harmful chemicals [14; 15]. Regarding green applicability, however, the liquid-liquid extraction of metals from aqueous phases revealed a major drawback: partial dissolution of the ILs during extraction, so-called leaching [9]. Moreover, the prevalent extraction mechanism can also decompose the IL: excellent extraction capabilities can be accomplished through a cation-exchange mechanism, which considerably limits the practicability of ILs in liquid-liquid extraction [16]. Utilizing more hydrophobic ILs, e.g., by increasing the length of alkyl chains on the cation, combined with a strongly coordinating, functional anion, enables a shift from ion exchange to neutral extraction mechanisms, thus improving the leaching behavior [17]. However, even using highly hydrophobic ILs cannot guarantee the complete inhibition of ion exchange [18]. The antimicrobial activity of quaternary ammonium compounds has long been known, and imidazolium-based ILs, for example, were recently tested for their antibiofilm activity [19]. Accordingly, this inevitable (even if only partial) loss of the ILs during extraction requires a stronger focus on their hazard potential [20]. The regularly attributed green status of ILs is mainly derived from their non-volatile nature, ignoring their potential bioactivity [21], which represents an often-neglected parameter in the optimization of TSILs [22]. For example, the hydrolysis of fluorinated anions and the subsequent toxicity makes ILs based on fluorinated anions inadequate for use in extraction processes [21; 23]. Recent work has therefore highlighted both the ecotoxicity and degradability of ILs [21; 24]. [PERSON] et al. [25] investigated the in vitro cytotoxicity of various TSILs using human breast cancer cells. The authors showed a positive correlation between alkyl chain length and cytotoxicity. Determining the ecotoxicity through algal growth assays proved to be another useful tool, because this approach is easy to perform, and algae are important primary producers.