Evaluating the effects of deep eutectic solvents on the germination rate and root elongation of Sinapis alba

Deep eutectic solvents (DESs) have gained substantial attention as a new generation of environmentally benign solvents with broad potential across numerous industrial applications. However, their ecological impacts, particularly on biological systems, remain insufficiently explored. This study addresses the limited knowledge regarding the phytotoxic impact of DESs on early plant growth, especially under varying composition and concentration, by investigating their effects on seed germination and root elongation of Sinapis alba . In the present work, several DES formulations were evaluated, including urea: glucose prepared at molar ratios of 1:1 and 2:1 and choline chloride: ascorbic acid (ChCl: AsA) at a molar ratio of 2:1. All samples were characterized by using different techniques, such as FTIR, viscosity, and density. FTIR confirmed strong hydrogen-bond interactions in all DES systems. Density slightly decreased with increasing urea content, and for viscosity measurements, all DESs exhibited non-Newtonian shear-thinning behavior, with the highest viscosity observed for urea: glucose (1:1). The biological effects of their aqueous dilutions of DESs were assessed by studying seed germination and root development in Sinapis alba . The results revealed that, at low concentration (0.1% w/w), urea-based DESs showed moderate inhibition, reducing root growth to 77.99 ± 17.4% and 87.07 ± 19.13% of the control for the 2:1 and 1:1 molar ratios, respectively. At the same time, diluted ChCl: AsA (2:1) exhibited inhibition at the same concentration, reducing root growth to 52.4 ± 11.5% of the control. Complete inhibition was observed at ≥ 5% (w/w) for the urea-based DESs, whereas the ChCl: AsA system produced complete inhibition at ≥ 0.5% (w/w). The stronger inhibitory effect of ChCl: AsA may be associated with its acidic pH (2–4). These findings highlight the importance of evaluating the toxicity of aqueous DES dilutions before their application in agricultural and environmental systems.