A commonly overlooked and largely unknown aspect of assessing the environmental and biological safety of engineered nanomaterials is the transformation of these materials in aqueous systems. Complex metal oxides are an important class of materials for use in catalysis, energy storage, and water purification. However, the potential impact of nano complex mexal oxides onthe environment upon improper disposal is not well understood. We present a comprehensive analysis of the interaction of an environmentally relevant oxyanion, phosphate, with the complex metal oxide nanomaterial, lithium cobalt oxide. Our results show that adsorption of phosphate to the surface of these materials drastically impacts their surface charge, rendering them more stable in aqueous systems. The adsorbed phosphate remains on the surface over significant periods of time, suggesting that desorption is not kinetically favored. The implications of this interaction may be increased dispersability and bioavailability of these materials in environmental water systems.