Bioaccumulation of silver nanoparticles into Daphnia magna from a freshwater algal diet and the impact of phosphate availability

Abstract

This study assessed the bioavailability, toxicity, and transfer of silver nanoparticles (AgNPs) in comparison with AgNO₃ in two model food chain organisms: the alga Chlamydomonas reinhardtii and the grazing crustacean Daphnia magna. The effects of phosphate, a potential Ag⁺-binding ligand and a determinant of phytoplankton productivity, were evaluated. Nano Ag derived from coated AgNPs and AgNO₃ was accumulated at similar concentrations into microalgae during high phosphate treatment, but AgNO₃ accumulation was increased by low phosphate availability. After feeding on Ag-containing algae, D. magna equally accumulated AgNO₃ and nano-derived Ag. There were significant reductions in feeding when D. magna were fed Ag-contaminated algae, with the AgNO₃, low phosphate-exposed cells being ingested the least. Nutritional quality characteristics including fatty acid and trace nutrient content were similar in all algal samples, indicating that feeding reduction is specifically due to the presence of Ag, with AgNO₃ being more toxic than nano Ag.

Keywords::

• Chlamydomonas reinhardtii
• Daphnia magna
• environmental toxicology
• nanoparticles
• silver

Acknowledgments

We thank Paul Lythgoe (Manchester Analytical Geochemistry Unit, School of Earth, Atmospheric and Environmental Sciences, University of Manchester) for the ICP-MS analysis; Samantha Forbes (Electron Microscope Facility, Faculty of Life Sciences, University of Manchester) for assistance with TEM; Dr. Tom Jowitt (Biomolecular Analysis Facility, Faculty of Life Sciences, University of Manchester) for assistance with the DLS analysis; Robert Clay for performing initial characterization of the AgNPs; Dr. Adam Moolna for performing initial algae AgNP exposure experiments; and Dr. Rachel Webster for discussions on the project. This work was supported in part by a grant from the Leverhulme Trust (grant no. F/00 120/BG) to J.K.P.