Soil pH effects on the comparative toxicity of dissolved zinc, non-nano and nano ZnO to the earthworm Eisenia fetida

Abstract

To determine how soil properties influence nanoparticle (NP) fate, bioavailability and toxicity, this study compared the toxicity of nano zinc oxide (ZnO NPs), non-nano ZnO and ionic ZnCl₂ to the earthworm Eisenia fetida in a natural soil at three pH levels. NP characterisation indicated that reaction with the soil media greatly controls ZnO properties. Three main conclusions were drawn. First that Zn toxicity, especially for reproduction, was influenced by pH for all Zn forms. This can be linked to the influence of pH on Zn dissolution. Secondly, that ZnO fate, toxicity and bioaccumulation were similar (including relationships with pH) for both ZnO forms, indicating the absence of NP-specific effects. Finally, earthworm Zn concentrations were higher in worms exposed to ZnO compared to ZnCl₂, despite the greater toxicity of the ionic form. This observation suggests the importance of considering the relationship between uptake and toxicity in nanotoxicology studies.

Keywords::

• zinc oxide
• nanoparticle
• nanotoxicology
• soil pH
• earthworms

Acknowledgements

The authors would like to acknowledge Rudo A. Verweij at the Vrije University of Amsterdam, for help and guidance with metal analysis and Birgitte Boje Rasmussen at the University of Copenhagen for performing soil characterisation analysis. The RECETO Ph.D. school is acknowledged for additional funding of Miss L. R. Heggelund via the RECETO Scolar Stipend. Dr. M. Diez-Ortiz is supported by a Marie Curie Intra-European Fellowship within the 7th European Community Framework Programme (call reference FP7-PEOPLE-2010-IEF, 273207 Nano-Ecotoxicity). The NanoFATE, Project CP-FP 247739 (2010-2014) under the 7th Framework Programme of the European Commission (FP7-NMP-ENV-2009, Theme 4), coordinated by C. Svendsen; www.nanofate.eu is acknowledged for financial support.