Effects of hydrophobicity of titanium dioxide nanoparticles and exposure scenarios on copper uptake and toxicity in Daphnia magna

Abstract

Titanium dioxide (TiO2) nanoparticles (NPs) encounter heavy metals in the environment under different scenarios. However, the mechanism of their joint toxicity effects on Daphnia magna remains vague. This study assessed the effects of hydrophobicity of TiO2 NPs (TDONPs) and exposure scenarios on copper uptake and toxicity in Daphnia magna. In the individual exposure scenario, hydrophilic and hydrophobic TDONPs both showed no acute toxicity to Daphnia magna, whereas individual Cu2+ exposure resulted in a 30% mortality rate. Co-exposure and sequential exposure to the two types of TDONP and Cu2+ resulted in mortality rates of 40%–50%. The mechanisms of the increased Cu2+ toxicity caused by hydrophilic and hydrophobic TDONP were different. In the presence of hydrophobic TDONPs, the Cu toxicity could be attributed to the increased bioaccumulation of Cu and Ti, leading to high oxidative stress injury. The Cu toxicity due to hydrophilic TDONPs could be induced by intensified intestinal membrane damage. The obtained data suggest that the hydrophobicity of the TDONPs plays a critical role in regulating the toxicity of Cu2+.