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

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-(1 H -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.