Capacity of a Red Cabbage (Brassica oleracea var. capitata) Cyanidin to Neutralize Sodium Hypochlorite Toxicity in Daphnia magna Straus

Abstract

Residual sodium hypochlorite (NaClO) discharged after disinfection may adversely affect aquatic organisms. This study examined whether anthocyanins extracted from red cabbage (Brassica oleracea var. capitata f. rubra) could reduce NaClO concentration and attenuate its toxicity to Daphnia magna. Anthocyanins were extracted using methanol and 2% hydrochloric acid (80:20), concentrated, purified and separated by column chromatography. Thin-layer chromatography was used to characterise the fractions. NaClO concentration was measured by iodometric titration, while acute toxicity was evaluated through 24-hour D. magna viability assays conducted in triplicate. The extraction yield was 4.59% (w/w). Of 15 coloured fractions, fraction 3 exhibited a retention factor of 69.23%, consistent with its tentative identification as cyanidin. The estimated 24-hour median lethal concentration (LC₅₀) of NaClO was 0.11 mg/L. Fraction 3 caused no observed mortality at the concentrations evaluated in the extract-only bioassays. Addition of 0.02 mg/L of the cyanidin-rich fraction reduced the measured NaClO concentration in an initial 0.11 mg/L solution by up to 93%. In combined-exposure bioassays, the tested extract concentrations were associated with complete D. magna survival after 24 hours. These findings suggest that the cyanidin-rich fraction may reduce NaClO-associated acute toxicity under the experimental conditions. More specific chemical characterisation and evaluation in complex water matrices are needed to establish its wider applicability.