Harmful algal blooms (HABs) threaten water quality and aquatic life, yet many chemical controls raise concerns about non-target toxicity. There is a need for selective algicides that effectively inhibit target microalgae while minimizing impacts on non-target organisms and the environment. We synthesized 31 phenyl-oxime derivatives and quantified algicidal activity against the green microalga Scenedesmus rotundus (hereafter Scero) using in vivo chlorophyll-reduction assays alongside non-target acute-toxicity tests against Lemna paucicostata (hereafter LEMPA) and three non-target animal species. A lead compound, (E)-1-(4-bromo-1,1’-biphenyl-4-yl)-2-(1H-1,2,4-triazol-1-yl)ethan-1-one O-benzyl oxime (KH08), strongly inhibited green microalgae, notably Scero, while showing minimal activity toward LEMPA. Under matched conditions, KH08 achieved comparable or greater inhibition than glutaraldehyde for green microalgae, whereas its activity against cyanobacteria was strain-dependent: sub-micromolar inhibition was observed against Microcystis aeruginosa (FBCC strain), while three other cyanobacterial strains remained largely insensitive at concentrations up to 5.0 μM. Acute toxicity was low under our test conditions (Daphnia magna EC₅₀ 3.11–4.80 mg/L; fish LC₅₀ > 2.0 mg/L; mouse LD₅₀ > 2000 mg/kg). Collectively, these findings position KH08 as a selective algicide candidate with practical relevance for microalgal control and motivate further evaluation under environmentally realistic scenarios.
Kim et al. (Sun,) studied this question.