Interactive Toxicity of Triclosan and Nano-TiO2 to Green Alga Eremosphaera viridis in Lake Erie: A New Perspective Based on Fourier Transform Infrared Spectromicroscopy and Synchrotron-Based X‑ray Fluorescence Imaging

This study explored the toxicity of triclosan in the presence of TiO₂ P25 to the green alga Eremosphaera viridis in Lake Erie. Multiple physicochemical end points were conducted to perform a comprehensive analysis of the toxic effects of individual and combined pollutants. Fourier transform infrared spectromicroscopy and synchrotron-based X-ray fluorescence imaging were first documented to be applied to explore the distribution variation of macromolecules and microelements in single algal cells in interactive toxicity studies. The results were different based on different triclosan concentrations and measurement end points. Comparing with individual pollutants, the toxicity intensified in lipids, proteins, and oxidative stress at 1000 and 4000 μg/L triclosan in the presence of P25. There were increases in dry weight, chlorophyll content, lipids, and catalase content when cells were exposed to P25 and 15.625 μg/L triclosan. The toxicity alleviated when P25 interacted with 62.5 and 250 μg/L triclosan compared with triclosan-only exposure. The reasons could be attributed to the combination of adsorption, biodegradation, and photocatalysis of triclosan by algae and P25, triclosan dispersion by increased biomass, triclosan adherency on algal exudates, and triclosan adsorption site reduction on algae surface owing to P25's taking over. This work provides new insights into the interactive toxicity of nanoparticles and personal care products to freshwater photosynthetic organisms. The findings can help with risk evaluation for predicting outcomes of exposure to mixtures and with prioritizing further studies on joint toxicity.