Environmental Impact of β-Cyclodextrin Complexes with Herbicides: A Study on Solubility and Toxicity

Formulation strategies that modify the physicochemical behavior of herbicides may influence their environmental fate and toxicity. In this context, this study investigates the effect of β-cyclodextrin (β-CD) complexation on the solubility and aquatic toxicity of chlorpropham (CLP), monuron (MON), and propanil (PRO), herbicides still in use in different parts of the world and frequently detected in aquatic environments at concentrations ranging from ng/L to µg/L. The solubility enhancement mediated by β-cyclodextrin was explored using UV-Vis and NMR spectroscopy, evaluating the impact of complexation on herbicides' water solubility. Ecotoxicological evaluations were performed in Raphidocelis subcapitata (R. subcapitata) and Brachionus calyciflorus (B. calyciflorus), representing primary producers and consumers. Acute toxicity in B. calyciflorus significantly increased following complexation, with LC50 values decreasing from 178.09 µM (CLP), 32.32 µM (MON), and 20.77 µM (PRO) to 4.89, 2.55, and 2.29 µM, respectively. Chronic exposure further confirmed heightened sensitivity in rotifers (EC50: 0.04 µM for β-CD: MON; 0.02 µM for β-CD:PRO). R. subcapitata exhibited higher sensitivity to CLP (EC50: 2.57 µM), consistent with its mitosis inhibition mechanism. Risk Quotient (RQ) analysis, based on current environmental concentrations, revealed an ecotoxicological concern for MON and PRO. Overall, our study indicates that although β-cyclodextrin enhances herbicides solubility, it may also increase their bioavailability and toxicity underlining the necessity to evaluate a novel formulation not only from the point of view of the efficacy enhancement.