A novel approach reveals that zinc oxide nanoparticles are bioavailable and toxic after dietary exposures

Abstract

If engineered nanomaterials are released into the environment, some are likely to end up associated with the food of animals due to aggregation and sorption processes. However, few studies have considered dietary exposure of nanomaterials. Here we show that zinc (Zn) from isotopically modified ⁶⁷ZnO particles is efficiently assimilated by freshwater snails when ingested with food. The ⁶⁷Zn from nano-sized ⁶⁷ZnO appears as bioavailable as ⁶⁷Zn internalized by diatoms. Apparent agglomeration of the zinc oxide (ZnO) particles did not reduce bioavailability, nor preclude toxicity. In the diet, ZnO nanoparticles damage digestion: snails ate less, defecated less and inefficiently processed the ingested food when exposed to high concentrations of ZnO. It was not clear whether the toxicity was due to the high Zn dose achieved with nanoparticles or to the ZnO nanoparticles themselves. Further study of exposure from nanoparticles in food would greatly benefit assessment of ecological and human health risks.

Keywords::

• Enriched stable isotope tracers
• zinc oxide nanoparticles
• toxic effects
• dietborne exposure
• bioavailability

Acknowledgements

Funding for this work was provided from the Toxic Substances Research Program of the U.S. Geological Survey, the National Research Program (USGS) and by a NERC (UK) grant NE/E01500X/1 under the Environmental Nanoscience Initiative. The authors thank D. J. Cain for his contribution to the experimental design, as well as A. Lorenzi, and A. Kleckner for help with algal cultures. J. Garcia-Alonso is recognized for some of the pictures shown in Table II. The authors also thank Gordon Cressey and Jens Najorka from the Mineral Sciences group at Natural History Museum for their assistance with XRD and Lauren Howard from the EMMA laboratories at Natural History Museum for assistance with SEM/TEM work. Critical comments from Drs Jamie Lead and Valery Forbes are greatly appreciated.

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