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Silver nanoparticles entering soils via the wastewatersludge-soil pathway pose low risk to plants but elevated Cl concentrations increase Ag bioavailability Peng Wang, Neal W Menzies, Paul Gareth Dennis, Jianhua Guo, Christian Forstner, Ryo Sekine, Enzo Lombi, Peter Kappen, Paul M. Bertsch, and Peter M Kopittke Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.6b01180 • Publication Date (Web): 05 Jul 2016 Downloaded from http://pubs.acs.org on July 6, 2016
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Environmental Science & Technology
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Silver nanoparticles entering soils via the wastewater-sludge-soil pathway pose low risk to
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plants but elevated Cl concentrations increase Ag bioavailability
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Peng Wang,1,2* Neal W. Menzies,2 Paul G. Dennis,2 Jianhua Guo,3 Christian Forstner,2 Ryo
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Sekine,4 Enzo Lombi,4 Peter Kappen,5 Paul M. Bertsch,6 and Peter M. Kopittke2
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Jiangsu, 210095, China
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College of Resources and Environmental Sciences, Nanjing Agricultural University, Nanjing,
School of Agriculture and Food Sciences, The University of Queensland, St. Lucia,
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Queensland, 4072, Australia
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QLD 4072, Australia
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5095, Australia
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Australian Synchrotron, Clayton, Victoria, 3168, Australia
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CSIRO Land and Water, 41 Boggo Road, Ecosciences Precinct, Dutton Park Queensland,
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4102, Australia
Advanced Water Management Centre, The University of Queensland, St Lucia, Brisbane,
Future Industries Institute, University of South Australia, Mawson Lakes, South Australia,
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Correspondence: +61 7 3365 4816,
[email protected] 1 ACS Paragon Plus Environment
Environmental Science & Technology
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Abstract The widespread use of silver nanoparticles (Ag-NPs) results in their movement into
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wastewater treatment facilities and subsequently to agricultural soils via application of
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contaminated sludge. On-route, the chemical properties of Ag may change and further
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alterations are possible upon entry to soil. In the present study, we examined the long-term
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stability and (bio)availability of Ag along the ‘wastewater-sludge-soil’ pathway. Synchrotron-
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based X-ray absorption spectroscopy (XAS) revealed that ca. 99% of Ag added to the sludge
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reactors as either Ag-NPs or AgNO3 was retained in sludge, with ≥ 79% of this being
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transformed to Ag2S, with the majority ( ≥ 87%) remaining in this form even after introduction
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to soils at various pH values and Cl concentrations for up to 400 d. Diffusive gradients in thin
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films (DGT), chemical extraction, and plant uptake experiments indicated that the potential
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(bio)availability of Ag in soil was low but increased markedly in soils with elevated Cl, likely
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due to the formation of soluble AgClx complexes in the soil solution. Although high Cl
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concentrations increased the bioavailability of Ag markedly, plant growth was not reduced in
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any treatment. Our results indicate that Ag-NPs entering soils through the ‘wastewater-sludge-
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soil’ pathway pose low risk to plants due to their conversion to Ag2S in the wastewater
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treatment process, although bioavailability may increase in saline soils or when irrigated with
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high-Cl water.
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Environmental Science & Technology
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INTRODUCTION Silver nanoparticles (NPs,
