Discovery of a new volcanic soil material, “Akahoya,” as an adsorbent for bacterial and viral pathogens and its application to environmental purification

Akahoya is a volcanic soil rich in alumina, primarily deposited in Kyushu, Japan. We have found that Akahoya adsorbs bacteria in the water surrounding cattle grazing areas, suggesting a potential for environmental purification. This study investigated the spectrum of microorganisms adsorbed by Akahoya using a column filled with Akahoya through which a suspension of microorganisms was passed. Shirasu soil, another volcanic soil with a different chemical composition, was used as a control. Akahoya effectively adsorbed a diverse range of microorganisms including <i>Escherichia coli</i>, <i>Campylobacter jejuni</i>, <i>Vibrio parahaemolyticus</i>, <i>Salmonella</i> Enteritidis, <i>Staphylococcus aureus</i>, <i>Clostridium perfringens</i>, spores of <i>Bacillus subtilis</i> and <i>Bacillus anthracis</i>, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), murine norovirus, and avian influenza virus (H3N2), whereas Shirasu soil did not adsorb any of the organisms examined. Moreover, bacteria naturally present in river water, such as aerobic bacteria, total coliforms, and <i>Enterobacteriaceae</i> as indicators of river contamination, as well as <i>E. coli</i> added artificially to sterilized river water, were reduced to below the detection limit (<1 CFU/mL) after being passed through Akahoya. Additionally, the number of viable <i>E. coli</i> continued to decrease after contact with Akahoya for 1 month, suggesting bactericidal effects. Notably, the adsorption of <i>E. coli</i> to Akahoya was influenced by the concentration of phosphate and the pH of the suspension due to the interaction between the surface phosphorylation of organisms and Al₂O₃, the major chemical component of Akahoya. The present results demonstrate the remarkable ability of Akahoya to remove phosphate and microbes, suggesting that Akahoya could be used for water purification processes.IMPORTANCEAlthough a safe and sufficient water supply is essential for the maintenance of hygienic conditions, a major challenge is to develop a comprehensive effective, sustainable, and cost-effective technological approach for the treatment and purification of contaminated water. In this study, we demonstrated that a novel volcanic soil, Akahoya, which has unlimited availability, is a highly effective adsorbent for a wide range of bacterial and viral pathogens, suggesting its potential as a sustainable resource for this purpose. It was suggested that the adsorption of microorganisms on Akahoya was mediated by phosphate groups present on the surface structures of microorganisms, which bind to the alumina component of Akahoya according to the phosphate concentration and pH of the liquid phase. The present findings highlight the exceptional ability of Akahoya to eliminate or reduce phosphate and microorganisms effectively in water purification processes, thus contributing to the development of efficient and sustainable solutions for addressing water pollution challenges.