Nanosized titanium dioxide elevates toxicity of cationic metals species for Daphnia – have aging and natural organic matter an unexpected impact?

Abstract

In aquatic ecosystems, nanosized titanium dioxide particles (nTiO₂) likely interact with natural organic matter (NOM) and may alter the ecotoxicity of co-occurring metals. The magnitude of changes in toxicity may be modulated by the duration of interactions (i.e. aging) between these factors. As those interactions are hardly addressed in literature, the present study aimed at assessing the impact of aging durations (0, 1, 3 and 6 days) on metals with mainly cationic (silver (Ag), cadmium (Cd)) or anionic (arsenic (As)) toxic ions in combination with three nTiO₂ levels (0.0, 0.6 and 3.0 mg/L) and two NOM levels (0 versus 8 mg TOC/L). The interaction of these factors was additionally investigated for two aging scenarios: in one scenario nTiO₂ were aged together with one of the metals, while in other scenario metals were added to aged nTiO₂. Subsequently, their combined acute effects on Daphnia magna were assessed. The results uncovered that nTiO₂ elevate the toxicity of metals with mainly cationic species (i.e. Ag⁺ and Cd²⁺) with the effect size depending on their valence electron. Contrary, nTiO₂ have no impact on the metal with mainly anionic species (i.e. HAsO₄²⁻). Furthermore, NOM reduced metal toxicity only for Ag and aging duration had a limited impact on the test outcome suggesting that relevant interactions between metal and nTiO₂ occur rather quick (below 24 h). These findings suggest that the charge of metals’ most toxic species is the determining factor for its interaction with nanoparticles and the resulting ecotoxicological effect assessment.

Keywords:

• Aging
• nanoparticles
• natural organic matter
• toxic metal species
• ecotoxicity

Correction Statement

This article has been corrected with minor changes. These changes do not impact the academic content of the article.

Acknowledgments

The authors are thankful to Therese Bürgi for her support in the laboratory, Wolfgang Fey for ICP-OES analysis and Carsten Schilde for providing the nTiO₂ dispersion. We are also thankful to Frank Seitz, Katharina Berkes and Cyril Chenwi Neba for their support.

Disclosure statement

The authors declare that they have no conflict of interest.

Additional information

Funding

We would also like to thank the German Academic Exchange Service [Grant No. 57299294] and Slovenian Research Agency (Research Program Chemical Engineering [P2-0191]) for the financial support.