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-TiO(2) remarkably enhanced the toxicity of copper to Daphnia magna by increasing the copper bioaccumulation. Specifically, at 2 mg L(-1) nano-TiO(2), the (LC(50)) of Cu(2+) 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 Cu(2+) level of 100 μg L(-1). The copper was found to be adsorbed onto the nano-TiO(2), and ingested and accumulated in the animals, thereby causing toxic injury. The nano-TiO(2) may compete for free copper ions with sulfhydryl groups, causing the inhibition of the detoxification by metallothioneins.