Ionic liquids as emerging environmental contaminants: a critical review of fate, toxicity mechanisms, and sustainable design strategies

Ionic liquids (ILs) are increasingly detected in various environments, raising profound concerns regarding their ecological impacts and long-term sustainability. While their tunability offers immense application potential, it concurrently introduces complex and unpredictable environmental risks that are not yet fully understood. This review provides a comprehensive synthesis and analysis of the multifaceted environmental footprint of ILs. We systematically elucidate the fundamental molecular mechanisms underpinning their ecotoxicity, framing IL ions as exogenous ligands that disrupt biological systems through membrane permeabilization, coordination-driven inhibition of metalloenzymes, and intercalation with genetic material. A particular focus is placed on tracing the environmental fate and behaviour of ILs. Furthermore, the review critically evaluates the burgeoning role of quantitative structure-toxicity relationship (QSTR) models and machine learning in advancing from retrospective hazard assessment to prospective risk prediction. By integrating mechanistic insights with fate analysis and computational toxicology, we consolidate a forward-looking framework for the rational design of greener ILs. The review concludes by identifying critical knowledge gaps - such as the implications of long-term low-dose exposure, mixture toxicity effects, and the environmental impact of transformation products - and proposes essential research directions to steer the sustainable development and regulated application of this versatile class of chemicals.