Abstract
Nanomaterials (NMs) are thermodynamically unstable by nature, and exposure of soil organisms to NMs in the terrestrial environment cannot be assumed constant. Thus, steady-state conditions may not apply to NMs, and bioaccumulation modeling for uptake should follow a dynamic approach. The one-compartment model allows the uptake and elimination of a chemical to be determined, while also permitting changes in exposure and growth to be taken into account. The aim of the present study was to investigate the accumulation of Ag from different Ag NM types (20 nm Ag0 NMs, 50 nm Ag0 NMs, and 25 nm Ag2 S NMs) in the crop plant wheat (Triticum aestivum). Seeds were emerged in contaminated soils (3 or 10 mg Ag/kg dry soil, nominal) and plants grown for up to 42 d postemergence. Plant roots and shoots were collected after 1, 7, 14, 21, and 42 d postemergence; and total Ag was measured. Soil porewater Ag concentrations were also measured at each sampling time. Using the plant growth rates in the different treatments and the changing porewater concentrations as parameters, the one-compartment model was used to estimate the uptake and elimination of Ag from the plant tissues. The best fit of the model to the data included growth rate and porewater concentration decline, while showing elimination of Ag to be close to zero. Uptake was highest for Ag0 NMs, and size did not influence their uptake rates. Accumulation of Ag from Ag2 S NMs was lower, as reflected by the lower porewater concentrations. Environ Toxicol Chem 2021;40:1861-1872. © 2021 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.
Highlights
Silver nanomaterials (Ag NMs) are used in numerous consumer products and are expected to be released to soils through the application of sewage sludge to agricultural soils following wastewater treatment
To investigate plant accumulation of NMs as a dynamic process, and how these processes apply to different Ag forms and sizes, this study examines the kinetics of Ag uptake into wheat over early growth stages, from three different Ag NMs, pristine NMs of two different sizes (20 nm and 50 nm) and an aged NM form Ag2S (25 nm)
In order to distinguish between the higher and lower concentrations for each of the Ag treatments the nominal concentrations 3 and 10 mg Ag/kg are referred to as ‘low’ and ‘high’, respectively, hereafter. 3.3 Porewater concentrations Markedly higher porewater Ag concentrations were found after 42 days postemergence compared to the starting time point in both the low and high treatments of the pristine NMs (20 and 50 nm NMs)
Summary
Silver nanomaterials (Ag NMs) are used in numerous consumer products and are expected to be released to soils through the application of sewage sludge to agricultural soils following wastewater treatment. Often considered barely soluble and scarcely bioavailable, accumulation of Ag2S NMs in plants has been reported in several studies, both in hydroponic (Stegemeier et al 2015; Pradas del Real et al 2017; Wang et al 2017) and soil exposures (Doolette et al 2015; Judy et al 2015; Wu et al 2018; Pradas del Real et al 2016; Schlich et al 2018) These studies have found low translocation of Ag from roots to shoots and conclude that uptake largely depends on particle characteristics, as well as the plant species. The majority of these studies investigated accumulation at a single time point, and only a few measured Ag in the porewater or available/extractable Ag in the soils to understand how NM fate and speciation in soils affects uptake
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