Nano-TiO2 enhances the toxicity of copper in natural water to Daphnia magna

The acute toxicity of engineered nanoparticles (NPs) in aquatic environments at high concentrations has been well-established. This study demonstrates that, at a concentration generally considered to be safe in the environment, nano-TiO2 remarkably enhanced the toxicity of copper to Daphnia magna by increasing the copper bioaccumulation. Specifically, at 2 mg L−1 nano-TiO2, the (LC50) of Cu2+ concentration observed to kill half the population, decreased from 111 μg L−1 to 42 μg L−1. Correspondingly, the level of metallothionein decreased from 135 μg g−1 wet weight to 99 μg g−1 wet weight at a Cu2+ level of 100 μg L−1. The copper was found to be adsorbed onto the nano-TiO2, and ingested and accumulated in the animals, thereby causing toxic injury. The nano-TiO2 may compete for free copper ions with sulfhydryl groups, causing the inhibition of the detoxification by metallothioneins.

Research highlights
► This study demonstrates that, at a concentration generally considered to be safe in the environment, nano-TiO2 remarkably enhanced the toxicity of copper to Daphnia magna.
► The copper was found to be adsorbed onto the nano-TiO2, and ingested and accumulated in the Daphnia magna, thereby causing toxic injury.
► The nano-TiO2 may compete for free copper ions with sulfhydryl groups, causing the inhibition of the detoxification mechanism of metallothionein.