Acute and chronic toxicity of metal oxide nanoparticles in chemical mechanical planarization slurries with Daphnia magna

Abstract

The semiconductor manufacturing industry uses metal oxide nanoparticles (NPs), including colloidal silica (c-SiO₂), fumed silica (f-SiO₂), ceria (CeO₂), and alumina (Al₂O₃), as abrasives in chemical mechanical planarization (CMP) processes. Assessing the toxicity of NPs used in commercial CMP slurries is difficult because these mixtures may contain undefined toxic constituents. Herein, the fresh water flea Daphnia magna (D. magna) was used to assess the effects of four model CMP slurries that did not contain known toxic additives. In the acute toxicity assessments, the key findings were that c-SiO₂ slurry caused a modest increase in body size indicative of a hormetic stress response, that the Al₂O₃ slurry was toxic to D. magna with a calculated 96 h LC-50 of 1.1 mg mL⁻¹, that the CeO₂ and Al₂O₃ slurries caused significant dose-dependent decreases in body size, and that NP dissolution was not responsible for these responses. In the chronic toxicity assessments, the key findings were that the c-SiO₂ slurry caused a modest increase in reproduction indicative of a hormetic stress response, that the Al₂O₃ slurry lead to a modest increase in morbidity and a significant decrease in body size, and that the CeO₂ and Al₂O₃ slurries caused dose-dependent decreases in reproductive output. The acute and chronic toxicity results demonstrate that different model CMP slurries exert distinct and unpredictable effects on D. magna morbidity, growth, and reproductive output. Especially important is that the CeO₂ and Al₂O₃ slurries reduced D. magna reproduction upon chronic exposure at low applied doses, which could have adverse consequences to aquatic ecosystems.