The increasing use of manufactured nanoparticles (NP) in different applications has triggered the need to understand their putative ecotoxicological effects in the environment. Copper oxide nanoparticles (CuO NP) are toxic, and induce oxidative stress and other pathophysiological conditions. The unique properties of NP can change depending on the characteristics of the media they are suspended in, altering the impact on their toxicity to aquatic organisms in different environments. Here, Mozambique tilapia (O. mossambicus) were exposed to flame synthesized CuO NP (0.5 and 5 mg · L(-1)) in two environmental contexts: (a) constant freshwater (FW) and (b) stepwise increase in environmental salinity (SW). Sublethal effects of CuO NP were monitored and used to dermine exposure endpoints. Fish exposed to 5 mg · L(-1) CuO in SW showed an opercular ventilation rate increase, whereas fish exposed to 5 mg · L(-1) in FW showed a milder response. Different effects of CuO NP on antioxidant enzyme activities, accumulation of transcripts for metal-responsive genes, GSH ∶ GSSG ratio, and Cu content in fish gill and liver also demonstrate that additive osmotic stress modulates CuO NP toxicity. We conclude that the toxicity of CuO NP depends on the particular environmental context and that salinity is an important factor for modulating NP toxicity in fish.

The contamination of drinking water with naturally occurring arsenic is a global health threat. Filters that are packed with adsorbent media with a high affinity for arsenic have been used to de-contaminate water - generally iron or aluminium oxides are favored materials. Recently, nanoparticles have been introduced as adsorbent media due to their superior efficiency compared to their bulk counter-parts. An efficient nanoadsorbent should ideally possess high surface area, be easy to synthesize, and most importantly offer a high arsenic removal capacity. Achieving all the key features in a single step synthesis is an engineering challenge. We have successfully engineered such a material in the form of nanochains synthesized via a one step flame synthesis. The ultra-long γ-Fe₂O₃ nanochains possess high surface area (151.12 m² g^-1), large saturation magnetization (77.1 emu g^-1) that aids in their gas phase self-assembly into long chains in an external magnetic field, along with an extraordinary arsenic removal capacity (162 mg.g^-1). A filter made with this material exhibited a relatively low-pressure drop and very little break-through of the iron oxide across the filter.