Are natural deep eutectic solvents always a sustainable option? A bioassay-based study

Abstract

The traditional use of organic solvents in various branches of industry is being rethought as these compounds very often display high volatility, toxicity and lipophilicity (related to the ability to interact with biological membranes). More recently, developments in the field of Green Chemistry are focusing on the design of more sustainable and cost-effective solvent alternatives like Ionic Liquids (ILs), bio-based solvents and natural deep eutectic solvents (NADESs). The present study aimed at performing an ecotoxicological screening of 15 NADESs using an extensive set of marine and freshwater bioassays, based on different endpoints as the following: immobilization of the crustacean Daphnia magna, growth inhibition of Raphidocelis subcapitata and of Phaeodactylum tricornutum, larval development alterations on the serpulid Ficopomatus enigmaticus and bioluminescence inhibition of Aliivibrio fischeri. What emerged was a general absence of toxicity of all samples. However, both algal assays showed a certain degree of biostimulation, up to over 100% growth increase in respect to controls with 8 out of 15 compounds tested with Raphidocelis subcapitata. Despite NADESs-induced negligible toxicity effects to invertebrates, encouraging their labelling as “sustainable” solvents, the liability of their intentional or accidental release into aquatic systems may represent a serious risk in terms of ecosystem functioning impairments.

Eutectic solvents and low molecular weight gelators for next-generation supramolecular eutectogels: a sustainable chemistry perspective

“…A caveat on the inadequacy of testing protocols for toxicity has been reported, 16 along with the need for an eco-toxicologic evaluation of DESs scored as “non-toxic” after in vitro tests. 17 The overall message emerging from the literature is to evaluate the impact of the solvent within the frame of the process the solvent is involved in – also including the energy balance in manufacturing, purification, removal and disposal of the solvent – rather than naively attempt an absolute ranking. 18,19 (2) (D)ESs are greener than… As remarked above, a solvent's impact should be assessed within the frame of a synthesis or a process adopting suitable green metrics.…”

Greener chemistry in analytical sciences: from green solvents to applications in complex matrices. Current challenges and future perspectives: a critical review

“…125 Recently, an ecotoxicological screening showed that NADESs have negligible toxicity to selected marine and freshwater organisms but some degree of biostimulation, suggesting that the accidental release of these compounds may cause excessive growth of microalgae and thus endanger the environment. 126 These data strongly emphasize that the toxicity, biodegradability, and sustainability of a (NA)DES must be scientifically tested and evaluated on a case-by-case basis before widespread use.…”

On the fate of deep eutectic solvents after their use as reaction media: the CO2 production during downstream and ultimate disposal

“…17,29–32 Last but not least, it must be noted that while classic DES display low-to-moderate toxicities – although more studies are needed including the assessment of wide range of the DES components – there is always the risk of eutrophication if large volumes of DES are accidently disposed in the environment, due to the sudden increase in nutrients, that would trigger large biomass production and oxygen depletion in contaminated areas. 13…”

“…11 In that respect, the rst holistic life cycle cradle-to-grave assessments (LCA) of DES have begun to appear in the open literature. 12 Apart from that, other studies have focused on the sustainability of DES, 13,14 its biocompatibility against several (micro) organisms, [15][16][17][18][19][20][21][22][23] and a few studies also on their biodegradability following standard protocols. 17,21,[24][25][26][27] As a result of these investigations, a more realistic picture of the properties of DES and their (allegedly) greenness has emerged.…”

“…17,[29][30][31][32] Last but not least, it must be noted that while classic DES display low-tomoderate toxicitiesalthough more studies are needed including the assessment of wide range of the DES components there is always the risk of eutrophication if large volumes of DES are accidently disposed in the environment, due to the sudden increase in nutrients, that would trigger large biomass production and oxygen depletion in contaminated areas. 13 Finally, a fundamental but surprisingly largely overlooked aspect is that of DES biodegradability (Fig. 1), presumably because the use of "naturally occurring" compounds implies intrinsically that biodegradability can be taken for granted.…”