Removal of microplastics via tannic acid-mediated coagulation and in vitro impact assessment

Microplastics are distributed in oceans worldwide, and the negative effects of microplastics on the environment and human health are increasing. Generally, three methods are employed to remove microplastics: filtration, biological degradation, and coagulation. Of these methods, filtration is the most commonly used but depends on the filter size or degree of microplastic coagulation. Although Fe- or Al-salts are generally used for coagulation via electrostatic interactions between metal ion and microplastics, their microplastic removal efficiency is less than 40%, and the smaller the size of microplastics, the lower is the removal efficiency. In order to improve the removal efficiency, metal–phenolic coordinate bonds were newly utilized for microplastic coagulation. Plant-derived tannic acid contributed to interfacial bridging between the microplastics and Fe(3+). Using 0.5 μm polystyrene beads as model microplastics, a removal efficiency of more than 90% within 5 min was achieved. Since microplastics mostly accumulate in the gut of animals, rat intestine IEC18 cells exposed to purified water from the microbead suspension were risk assessed, revealing that water purified using the coagulation-based method reduced oxidative stress and inflammatory cytokines to levels similar to those in cells exposed to water without microbeads.