Selective phenyl-oxime algicides with low non-target acute toxicity: efficacy against green microalgae vs glutaraldehyde

Abstract Harmful algal blooms (HABs) impair water quality and threaten aquatic life, while common chemical controls (e.g., cooper salts, glutaraldehyde) raise non-target toxicity concerns. We synthesized 31 phenyl-oxime derivatives and quantified algicidal activity as in vivo chlorophyll-reduction in standardized microalgal assays, alongside non-target acute toxicity tests. 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 Scenedesmus rotundus) while showing minimal activity toward Lemna paucicostata. Under matched conditions, KH08 achieved comparable or greater inhibition of green microalgae versus glutaraldehyde, whereas activity against cyanobacteria was modest. Acute-toxicity studies indicated low toxicity to Daphnia magna, Oryzias latipes, Danio rerio, and mice. These data position KH08 as a selective algicide candidate with practical relevance for microalgal control.