Peroxidase-like activity of widely-used commercial inorganic pigments induces oxidative stress and antibiotic degradation: Implications for health risks

Inorganic pigments, which often contain significant amounts of nanoparticles, are crucial chemicals for human life. They are produced in massive quantities and widely used in consumer products, food, and pharmaceuticals. Herein, we reported that a variety of commonly used commercial inorganic pigments possess peroxidase-like activity, catalyzing hydrogen peroxide (H 2 O 2 ) decomposition into reactive oxygen species, primarily hydroxyl radical ( OH) and superoxide radical anion (O 2 − ). The catalytic activity of inorganic pigments exhibits saturation kinetics as described by the Michaelis-Menten model, with optimal pH and temperature conditions that can be found in the human body. The enzyme-mimicking activity is strongly correlated with the formation of OH ( R 2  = 0.98), indicating the radical-mediated reaction pathway. The peroxidase-like activity of inorganic pigments can induce significant oxidative stress at health-relevant H 2 O 2 concentrations (3–30 μM), as demonstrated by the ascorbic acid assay. Additionally, the peroxidase-like activity of inorganic pigments is able to mediate the oxidation of tetracycline, with oxidation rate constants positively correlated with the pigments' peroxidase-like activity. The discovery of peroxidase-like activity of commercial inorganic pigments sheds light on the reported oxidative stress exerted by these pigments and has important implications for the health risk assessment of inorganic food and pharmaceutical colorants, as well as colored consumer products.