Effects of exposure pathways on the accumulation and phytotoxicity of silver nanoparticles in soybean and rice

Abstract

The widespread use of silver nanoparticles (AgNPs) raises concerns both about their accumulation in crops and human exposure via crop consumption. Plants take up AgNPs through their leaves and roots, but foliar uptake has been largely ignored. To better understand AgNPs–plant interactions, we compared the uptake, phytotoxicity and size distribution of AgNPs in soybean and rice following root versus foliar exposure. At similar AgNP application levels, foliar exposure led to 17–200 times more Ag bioaccumulation than root exposure. Root but not foliar exposure significantly reduced plant biomass, while root exposure increased the malondialdehyde and H₂O₂ contents of leaves to a larger extent than did foliar exposure. Following either root or foliar exposure, Ag-containing NPs larger (36.0–48.9 nm) than the originally dosed NPs (17–18 nm) were detected within leaves. These particles were detected using a newly developed macerozyme R-10 tissue extraction method followed by single-particle inductively coupled plasma mass spectrometry. In response to foliar exposure, these NPs were stored in the cell wall and plamalemma of leaves. NPs were also detected in planta following Ag ion exposure, indicating their in vivo formation. Leaf-to-leaf and root-to-leaf translocation of NPs in planta was observed but the former did not alter the size distribution of the NPs. Our observations point to the possibility that fruits, seeds and other edible parts may become contaminated by translocation processes in plants exposed to AgNPs. These results are an important contribution to improve the risk assessment of NPs under environmental exposure scenarios.

Keywords:

• Silver nanoparticles
• foliar exposure
• root exposure
• particle size
• spICP-MS

Acknowledgements

We thank Prof. Miao Aijun from Nanjing University for comments on the manuscript and Zhou Zhiping for EDS analysis. We thank the anonymous reviewers for their comments. We also thank the National Natural Science Foundation of China (No. 41430752 and 41301559) and the Natural Science Foundation of Jiangsu Province (BK20131041) for funding this research. Part of this study was supported by Hunan 2011 Collaborative Innovation Center of New Chemical Technologies for Environmental Benignity and Efficient Resource Utilization. NexION 300 ICP-MS was provided by PerkinElmer, China.

Disclosure statement

The authors report no conflicts of interest with other organizations or individuals regarding the content or publication of this paper.

Additional information

Funding

We thank the anonymous reviewers for their comments. We also thank the National Natural Science Foundation of China (No. 41430752 and 41301559) and the Natural Science Foundation of Jiangsu Province (BK20131041) for funding this research. Part of this study was supported by Hunan 2011 Collaborative Innovation Center of New Chemical Technologies for Environmental Benignity and Efficient Resource Utilization. NexION 300 ICP-MS was provided by PerkinElmer, China.