The pH-dependent toxicity of triclosan on developing zebrafish (Danio rerio) embryos using metabolomics

Triclosan (TCS) is commonly used in home and personal care products (HPCPs), which causes it to be ubiquitously detected in aquatic environments. The toxicity of triclosan to aquatic organisms can vary at different pH values because the ionization states of TCS affect its bioaccumulation properties. The objective of this study was to examine the pH-dependent toxicity of TCS on embryonic zebrafish (Danio rerio) using a metabolomic profiling method based on gas chromatography-mass spectrometry (GC-MS). Exposure experiments were conducted on zebrafish embryos at three pH conditions (6, 7, and 8) and two TCS concentrations (30 mu g/L and 300 mu g/L). Metabolic profiles were obtained by extracting intracellular metabolites. Univariate (One-way ANOVA) and multivariate (PLS-DA) analyses were conducted to determine the metabolomic changes in TCS-treated embryos. Changes in the metabolic profile revealed that interference in biological pathways were induced by mostly ionized TCS (low pH) and high TCS concentrations. Also, fold changes in metabolite profiles showed that the TCS toxicity was a function of pH. Metabolites including urea, D-glucose, D-galactose, phenylalanine, L-glutamic acid, citric acid, and phosphoric acid showed significant changes under different pH conditions (p-value < 0.05). Our metabolomics study revealed that the responses of metabolites to TCS toxicity were pH-dependent. The differences of the responses could be attributed to the bioaccumulation capability of TCS, which increased as the ionized TCS proportion increased under low pH conditions.