Distinct toxic interactions of TiO₂ nanoparticles with four coexisting organochlorine contaminants on algae

Abstract

Engineered nanoparticles are increasingly discharged into the environment. After discharge, these nanoparticles can interact with co-existing organic contaminants, resulting in a phenomena referred to as ‘joint toxicity’. This study evaluated joint toxicities of TiO₂ nanoparticles (TiO₂NPs) with four different (atrazine, hexachlorobenzene, pentachlorobenzene, and 3,3′,4,4′-tetrachlorobiphenyl) organochlorine contaminants (OCs) toward algae (Chlorella pyrenoidosa). The potential mechanisms underlying the joint toxicity were discussed, including TiO₂NPs–OC interactions, effects of TiO₂NPs and OCs on biophysicochemical properties of algae and effects of TiO₂NPs and OCs on each other’s bioaccumulation in algae. The results indicate that coexposure led to a synergistic effect on the joint toxicity for TiO₂NPs–atrazine, antagonistic effect for TiO₂NPs–hexachlorobenzene and TiO₂NPs–3,3',4,4'-tetrachlorobiphenyl, and an additive effect for TiO₂NPs–pentachlorobenzene. There was nearly no adsorption of OCs by TiO₂NPs, and the physicochemical properties of TiO₂NPs were largely unaltered by the presence of OCs. However, both OCs and NPs affected the biophysicochemical properties of algal cells and thereby influenced the cell surface binding and/or internalization. TiO₂NPs significantly increased the bioaccumulation of each OC. However, with the exception of atrazine, the bioaccumulation of TiO₂NPs decreased when used with each OC. The distinct joint toxicity outcomes were a result of the balance between the increased toxicities of OCs (increased bioaccumulations) and the altered toxicity of TiO₂NPs (bioaccumulation can either increase or decrease). These results can significantly improve our understanding of the potential environmental risks associated with NPs.

Keywords:

• Organochlorine contaminants
• nanomaterials
• joint toxicity
• algae

Acknowledgements

This work was supported by the 973 program of China (2014CB441104), the National Key Research and Development Program of China (2017YFA0207000), the National Natural Science Foundation of China (21525728, 21621005, 21337004, and 21477107), the Doctoral Research Startup Project in 2016 of Guizhou Normal University in China and the Science and Technology Foundation of Guizhou Province in China (JZ[2014]2012).

Disclosure statement

The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.