Zinc Sulfate Monohydrate (ZnSO₄·H₂O) Toxicity in Medaka Embryos: Impacts of Water Type on Lethal Concentration

Zinc sulfate (ZnSO₄) is widely used in industrial and agricultural applications; however, its release into the environment raises concerns about its potential toxicity to the aquatic ecosystem. This study assesses the acute toxicity of zinc sulfate monohydrate (ZnSO₄·H₂O) on Javanese medaka (Oryzias javanicus) embryos by examining mortality across three water types: pure water, deionized water, and dechlorinated tap water. Embryos were exposed to ZnSO₄ concentrations ranging from 0.1 to 10 mg/L for 96 hours, with mortality recorded at 24, 48, 72, and 96 hours. Mortality increased in a dose- and time-dependent manner, with no deaths observed in control groups. Toxicity was highest in pure water (LC₅₀ = 0.6676 mg/L), followed by dechlorinated tap water (LC₅₀ = 0.9583 mg/L), and lowest in deionized water (LC₅₀ = 1.021 mg/L). Water chemistry significantly influences ZnSO₄ toxicity, as ionic composition affects zinc uptake and its toxic effects. These results underscore the importance of site-specific water quality assessments in aquatic risk assessments. Further studies on long-term sublethal effects and metal bioaccumulation are needed to improve ecotoxicological risk assessments.