Evaluating the Environmental and Biological Safety of Phosphonium-Based Porous Liquid Systems

Abstract

Porous liquids have emerged as a promising class of advanced materials that combine permanent porosity with fluidity. They are often proposed as “green” alternatives in separations and catalysis, although their biological safety remains underexplored. Here, we present a comprehensive evaluation of the toxicity of two representative porous liquid systems based on methyltriphenylphosphonium bromide ([P1Ph3][Br]) and trihexyltetradecylphosphonium bis(trifluoromethylsulfonyl)amide ([P66614][NTf2]), combined with glycerol and ZIF-8, across a spectrum of biological models. Acute toxicity was assessed in microorganisms (Escherichia coli), aquatic organisms (Daphnia magna, Raphidocelis subcapitata, Artemia franciscana), plants (tomato and oat), and human dermal fibroblasts. While both materials exhibited low cytotoxicity toward human dermal fibroblasts (IC50 > 0.5 mM), notable toxicity emerged in aquatic organisms and bacteria, especially for aromatic [P1Ph3][Br]-based systems (EC50 = 1–10 mg dm–3). The studied multicomponent formulations disrupted microbial growth and inhibited germination even at low concentrations, revealing unexpected phytotoxicity. These contrasting outcomes (limited toxicity toward HDF cells, notable ecotoxicity) highlight the hidden complexity of structure-toxicity relationships in porous liquids. Our findings call for a shift from assumption to evidence in the development of so-called “green” solvents, as functionality must go hand in hand with environmental foresight.