Evaluation of herbicide toxicity to Lemna minor L. and Azolla caroliniana Willd.

Long-residual herbicides can negatively impact aquatic ecosystems through surface runoff and leaching. This study evaluated the acute toxicity of indaziflam, sulfentrazone, clomazone, and tebuthiuron on Lemna minor and Azolla caroliniana. Experiments were conducted in the laboratory using a completely randomized design (CRD) with six concentrations of each herbicide across four replicates. The study assessed the concentration causing acute effects in 50% of the organisms (EC₅₀), the effects on fresh weight (g), and the risk quotient (RQ). For L. minor, EC₅₀ values were 0.41, 0.73, 0.12, and 0.21 mg L⁻¹ for clomazone, sulfentrazone, indaziflam, and tebuthiuron, respectively; and for A. caroliniana, the values were 3.26, 0.51, 0.11, and 0.71 mg L⁻¹, respectively. All tested herbicides were classified as highly toxic to macrophyte species, except for clomazone, which was categorized as 'moderately toxic' for A. caroliniana. Moreover, these herbicides significantly reduced fresh weight even at the lowest concentrations.