Next-Generation Complex Metal Oxide Nanomaterials Negatively Impact Growth and Development in the Benthic Invertebrate <i>Chironomus riparius</i> upon Settling

Abstract

Most studies of nanomaterial environmental impacts have focused on relatively simple first-generation nanomaterials, including metals or metal oxides (e.g., Ag, ZnO) for which dissolution largely accounts for toxicity. Few studies have considered nanomaterials with more complex compositions, such as complex metal oxides, which represent an emerging class of next-generation nanomaterials used in commercial products at large scales. Importantly, many nanomaterials are not colloidally stable in aqueous environments and will aggregate and settle, yet most studies use pelagic rather than benthic-dwelling organisms. Here we show that exposure of the model benthic species Chironomus riparius to lithium cobalt oxide (Li _xCo_{1- x}O₂, LCO) and lithium nickel manganese cobalt oxide (Li _xNi _yMn _zCo_{1- y- z}O₂, NMC) at 10 and 100 mg·L^-1 caused 30-60% declines in larval growth and a delay of 7-25 d in adult emergence. A correlated 41-48% decline in larval hemoglobin concentration and related gene expression changes suggest a potential adverse outcome pathway. Metal ions released from nanoparticles do not cause equivalent impacts, indicating a nanospecific effect. Nanomaterials settled within 2 days and indicate higher cumulative exposures to sediment organisms than those in the water column, making this a potentially realistic environmental exposure. Differences in toxicity between NMC and LCO indicate compositional tuning may reduce material impact.