Sodium montmorillonite and quaternary ammonium organoclays: effect on fungal and bacterial cell growth and survival

Abstract

Clays are composed of alumina, silica, water and sometimes contain metal cations such as Mg2+ or Fe3+. Montmorillonite clays have an unusual crystalline structure; they form as platelets so that an Al3+ octahedron layer is in the middle with two tetrahedral silicate layers on the outside. The plates are turbostratic, meaning that the individual plates have no crystallographic relationship between them. Metal cations can be exchanged easily because of their attraction to the negative charge due to isomorphous substitutions of Mg2+ for Al3+ in the octahedral layer. The clay minerals are only 1 nm in width and up to 1000 nm long. Smectite clays are frequently combined with polymers to create new polymer‐clay nanocomposites with improved characteristics such as increased temperature resistance or strength. Polymer nanocomposites often require that they be surface modified with quaternary ammonium ions to render them compatible with the polymer. These organoclays are becoming more widely studied and utilized as surface bactericides. Two problems are currently associated with this; the nanocomposites may not be persistent or fully effective. In the current study, the toxicity and persistence of Na+ montmorillonite, quaternary ammonium ions, and a clay:quaternary ammonium organoclay in eukaryotic and prokaryotic cells have been investigated. Initial studies using the yeast S. cerevisiae have shown that montmorillonite is not toxic while the quaternary ammonium compound Arquad C‐33W was strongly growth inhibitory.