Evaluation of Biological Effects of Nanoneedle Calcium Carbonate Crystals Used for Water Treatment

Aragonite nanoneedles were synthesized for use in purifying drinking water via a mechano-bactericidal effect, and the biological effects of this aragonite and the calcium carbonate compounds produced during its synthesis were evaluated. Three types of cells (intestinal epithelial-derived Caco-2 cells, keratinocyte-derived HaCaT cells, and macrophage-differentiated THP-1 cells) were exposed to four types of calcium carbonate compound suspensions containing aragonite nanoneedles. No effects on cell viability were observed for any of the cells. However, at a high concentration of 1000 mg/mL, cell membrane damage was observed. In particular, cell membrane damage was observed in THP-1 cells. The acicular calcium carbonate samples also significantly induced IL-8 expression in THP-1 cells. In particular, one of the calcium carbonate compounds significantly promoted the expression of IL-8, TNF-α, MCP-1, and IL-1β. In THP-1 cells, an increase in intracellular calcium levels was also observed. These in vitro results suggest that calcium carbonate-containing aragonite nanoneedles have the potential to induce inflammation. To confirm that inflammation is actually induced in the body, in vivo examinations were performed. These acicular calcium carbonate suspensions were administered intraperitoneally to C57BL/6N mice. Serum cytokines were measured 1 and 3 months later. No significant difference in effect was observed among the samples. Pathological observations also showed no induction of inflammation. These results suggest that acicular calcium carbonate has the potential to induce cytokine secretion by macrophages, but that its in vivo effects are limited. At the levels present in drinking water, the effects of acicular calcium carbonate are likely to be small. These findings pave the way for the application of aragonite nanoneedles in water purification, potentially contributing to the resolution of drinking water challenges, particularly in developing countries.