Acute and chronic toxicity to Daphnia magna of colloidal silica nanoparticles in a chemical mechanical planarization slurry after polishing a gallium arsenide wafer

Semiconductor chip manufacturers use slurries of metal oxide nanoparticles (NPs) as abrasives in chemical mechanical planarization (CMP) processes on wafers containing films of III/V semiconducting materials. Assessing the toxicity of these specialized NPs is challenging not only because commercial slurries may contain undefined toxic constituents, but because CMP processes can change the physical and chemical properties of the NPs. Herein, the fresh water flea Daphnia magna (D. magna) was used to assess the effects of Ultra-Sol® 200S CMP slurry containing ~30-nm colloidal silica (c-SiO₂) NPs before (pristine) and after (spent) a GaAs wafer was polished with an extreme arm-pressure of 5 psi. In the acute 96-hour toxicity assessments, both the pristine and spent slurries at 4.0 mg/mL c-SiO₂ NPs had little effect on D. magna morbidity and body sizes. In the chronic 21-day toxicity assessments, neither slurry at 0.10 mg/mL c-SiO₂ NPs was toxic, but both slurries lead to a modest (9–10%) increase in D. magna body sizes and a significant (~2-fold) increase in reproductive output, indicative of a positive hormetic response. Identical increases in D. magna body sizes and reproductive output were observed with a supernatant of the pristine slurry, in the absence of the c-SiO₂ NPs, indicating that soluble material in the pristine supernatant contributed to the hormetic response, which suggests that the soluble material may also contribute to the hormetic response of the spent material.