Combined toxicity of fluorescent silica nanoparticles with cadmium in Ceriodaphnia dubia: Interactive effects of natural organic matter and green algae feeding

The environmental risks of silica nanoparticles (SiNP) reported in the literature are contradictory and bring into question its safety for use in consumer applications. Organisms are never exposed to NPs alone in the real environment, while studies of the combined toxicity of SiNP are limited. To address this, we compared the acute toxicity of fluorescent core-shell SiNPs alone and in mixtures with Cd²⁺ to Ceriodaphnia dubia in the absence and presence of NOM. We identified biodistribution and feeding behaviour in addition to the traditional endpoints. NOM increased the colloidal stability of SiNPs in reconstituted water. In immobility tests, no significant effects were observed from Cd²⁺ exposure with NOM and varying concentrations of SiNPs. A similar pattern of curve dose-response was observed for varying concentrations of SiNPs and increasing Cd²⁺ concentration and constant NOM. Fluorescence microscopy verified a dose-dependent bioaccumulation of SiNPs in C. dubia. Co-exposure to 10 mg L⁻¹ SiNP with NOM and Cd²⁺ resulted in a stimulated stress feeding response at the lower Cd²⁺ concentrations which declined at the higher dose due to a functional impairment of the digestive tract. Alterations in feeding behaviour and the increasing bioaccumulation of SiNP indicate a potential ecological risk for Ceriodaphnia dubia from the mixture exposure.