Abstract
To date, research on the toxicity and potential environmental impacts of nanomaterials has predominantly focused on relatively simple and single-component materials, whilst more complex nanomaterials are currently entering commercial stages. The current study aimed to assess the long-term and size-dependent (60 and 500 nm) toxicity of a novel core-shell nanostructure consisting of a SiC core and TiO(2) shell (SiC/TiO(2), 5, 25, and 50 mg L(-1)) to the common model organism Daphnia magna. These novel core-shell nanostructures can be categorized as advanced materials. Experiments were conducted under environmentally realistic feeding rations and in the presence of a range of concentrations of humic acid (0.5, 2, 5, and 10 mg L(-1) TOC). The findings show that although effect concentrations of SiC/TiO(2) were several orders of magnitude lower than the current reported environmental concentrations of more abundantly used nanomaterials, humic acid can exacerbate the toxicity of SiC/TiO(2) by reducing aggregation and sedimentation rates. The EC(50) values (mean ± standard error) based on nominal SiC/TiO(2) concentrations for the 60 nm particles were 28.0 ± 11.5 mg L(-1) (TOC 0.5 mg L(-1)), 21.1 ± 3.7 mg L(-1) (TOC 2 mg L(-1)), 18.3 ± 5.4 mg L(-1) (TOC 5 mg L(-1)), and 17.8 ± 2.4 mg L(-1) (TOC 10 mg L(-1)). For the 500 nm particles, the EC50 values were 34.9 ± 16.5 mg L(-1) (TOC 0.5 mg L(-1)), 24.8 ± 5.6 mg L(-1) (TOC 2 mg L(-1)), 28.0 ± 10.0 mg L(-1) (TOC 5 mg L(-1)), and 23.2 ± 4.1 mg L(-1) (TOC 10 mg L(-1)). We argue that fate-driven phenomena are often neglected in effect assessments, whilst environmental factors such as the presence of humic acid may significantly influence the toxicity of nanomaterials.