Silver nanoparticles entering soils via the wastewater-sludge-soil pathway pose low risk to plants but elevated Cl concentrations increase Ag bioavailability (original) (raw)
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Environmental Science and Technology
Long term speciation and lability of silver (Ag-), silver chloride (AgCl-) and silver sulfide nanoparticles (Ag 2 S-NPs) in soil were studied by X-ray absorption spectroscopy (XAS), and newly developed 'nano' Diffusive Gradients in Thin Films (DGT) devices. These nano-DGT devices were designed specifically to avoid confounding effects when measuring element lability in the presence of nanoparticles. The ageing profile and stabilities of the three nanoparticles and AgNO 3 (ionic Ag) in soil were examined at three different soil pH values over a period of up to 7 months. Transformation of ionic Ag, Ag-NP and AgCl-NPs were dependent on pH. AgCl formation and persistence was observed under acidic conditions, whereas sulfur-bound forms of Ag dominated in neutral to alkaline soils. Ag 2 S-NPs were found to be very stable under all conditions tested and remained sulfur bound after 7 months of incubation. Ag lability was characteristically low in soils containing Ag 2 S-NPs. Other forms of Ag were linked to higher DGT-determined lability, and this varied as a function of ageing and related speciation changes as determined by XAS. These results clearly indicate that Ag 2 S-NPs, which are the most environmentally relevant form of Ag that enter soils, are chemically stable and have profoundly low Ag lability over extended periods. This may minimise the long-term risks of Ag toxicity in the soil environment. * 1 The sum of components were not forced to equal 100 % in the LCF analyses. * 2 S-bound percentage is the sum of Ag 2 S, Ag-cysteine and Ag-cystine components.
The Mobility of Silver Nanoparticles and Silver Ions in the Soil‐Plant System
Journal of Environmental Quality, 2019
The widespread use of silver nanoparticles (AgNPs) as a bactericide will ultimately result in their increased concentration in soils. We sought to determine the likely mobility, toxicity, and plant uptake of Ag applied to soil as either AgNPs or Ag+. We measured the solubility, toxicity, and plant uptake of both AgNPs and Ag+ in an immature Pallic soil, a Templeton loamy silt (pH = 5.1), and a granular silt loam (pH = 6.0). The sorption of AgNPs by the test soils was significantly greater than Ag+, and both moieties were more strongly sorbed at lower concentrations and higher pH values. Between pH 4 and 8, distribution coefficient (KD) values increased from <10 up to ∼500 L kg−1 for Ag+, and from 100 to 10,000 L kg−1 for AgNPs. There was strong evidence that our citrate‐coated AgNPs were transformed into Ag+ during the course of the plant growth experiments, and plant responses were similar for both the Ag+ and AgNP treatments. Soil concentrations >100 mg kg−1 significantly re...
Hazard assessment of a silver nanoparticle in soil applied via sewage sludge
Environmental Sciences Europe, 2013
Background: Silver nanoparticles (AgNPs) are widely used in many fields of application and consumer products due to their antibacterial properties. The aim of this study was to prepare a hazard assessment for one specific AgNP in soil, incorporated via sewage sludge (the sewage sludge pathway). The effects of pristine AgNPs on microorganisms, plants and earthworms were first determined in screening tests. Long-term tests over 140 days were then conducted with AgNPs added to soil via sewage sludge. AgNPs were incorporated into the sludge through a simulated sewage treatment plant (STP) over 10 days to allow transformation to occur and also by manual spiking over 2 h. The results of the most sensitive organism from the long-term tests, the soil microorganisms, are presented. Results: The STP simulations confirmed that at environmentally relevant concentrations >90% of AgNPs remain bound to sewage sludge. Effects of AgNPs bound to sewage sludge and added to soil were similar to that of pristine NM-300K after degradation of the sludge. The predicted no-effect concentration for NM-300K in soil of 0.05 mg/kg dry soil determined a maximum threshold of 30 mg/kg dry sludge per application, considering the maximum addition of sewage sludge in Germany (5 tons per hectare every 3 years). Conclusion: At environmentally relevant concentrations, AgNP absorption to sludge and aging in soil (even after transformation) cause toxic effects on soil microorganisms of the terrestrial ecosystem.
Fate of Ag-NPs in Sewage Sludge after Application on Agricultural Soils
The objective of this work was to investigate the fate of silver nanoparticles (Ag-NPs) in a sludge-amended soil cultivated with monocot (Wheat) and dicot (Rape) crop species. A pot experiment was performed with sludges produced in a pilot wastewater treatment plant containing realistic Ag concentrations (18 and 400 mg kg−1, 14 mg kg−1 for the control). Investigations focused on the highest dose treatment. X-ray absorption spectroscopy (XAS) showed that Ag2S was the main species in the sludge and amended soil before and after plant culture. The second most abundant species was an organic and/or amorphous AgS phase whose proportion slightly varied (from 24% to 36%) depending on the conditions. Micro and nano X-ray fluorescence (XRF) showed that Ag was preferentially associated with S-rich particles, including organic fragments, of the sludge and amended soils. Ag was distributed as heteroaggregates with soil components (size ranging from ≤0.5 to 1−3 μm) and as diffused zones likely corresponding to sorbed/complexed Ag species. Nano-XRF evidenced the presence of mixed metallic sulfides. Ag was weakly exchangeable and labile. However, micronutrient mobilization by plant roots and organic matter turnover may induce Ag species interconversion eventually leading to Ag release on longer time scales. Together, these data provide valuable information for risk assessment of sewage sludge application on agricultural soils.
Science of the Total Environment, 2020
Untreated sludge from small-scale on-site domestic wastewater treatment systems (septic tanks) was spiked with 20, 60 and 100 nm silver nanoparticles (Ag-NPs) to investigate Ag-NP behaviour in these systems that are widely distributed in rural areas. In addition, the release of Ag-NPs from a previously spiked clay-rich loam reference soil (LUFA 2.4) was evaluated, in the presence and absence of untreated sludge, to simulate the common practice of sludge disposal by spreading on agricultural land. Single particle ICP-MS was used to determine Ag-NP size distribution and the resultswere compared with total Ag (Ag-NP and ionic) measured in acid digested samples. As documented previously for large municipal scale wastewater treatment plants, Ag-NPs are found to be overwhelmingly (~98%) retained in the sludge in these small-scale systems. The Ag-NP retention efficiency on the LUFA reference soil amended with sludge is approximately 10 times greater than that of LUFA soil alone (in the absence of sludge). For soil spiked with 60 nm Ag-NPs, the calculated average diameter of Ag-NPs in the supernatant, after 24 h was 45±3 nm (dissolution rate 7.2E−06 mol/m2·h for 60 nmAg-NP), smaller than that of supernatant from the combined sludge/soil system (52±2 nm), indicating lower Ag-NP dissolution rates in the sludge-amended soil. This study provides new information about the leachability of Ag-NPs from septic tank sludge and suggests that the effluent and sludge from septic tanks are potential sources of both nano- and dissolved ionic-Ag to environmental waters.
The Influence of Soil Organic Matter on the Uptake of Silver Nanoparticles in a Terrestrial System
— The uptake of silver from silver nanoparticles in soil was investigated in the presence of increasing concentrations of soil organic matter. Especially, the effect of Humus component of soil organic matter on the uptake of Ag from silver nanoparticles was studied. Two insect species, Acheta domesticus and Tenebrio molitor, and two plant species, Helianthus annuus and Sorghum vulgare, were exposed to silver nanoparticles(25 ppm in the presence of increasing concentrations of Humus (0, 1, 5, 10, 15, and 20% Humus) in soil (by weight). The techniques of transmission electron microscopy, dynamic light scattering, and powder X-ray diffraction were used to characterize the silver nanoparticles used in the study. An inductively coupled plasma-optical emission spectrometer was used to measure the levels of silver in test samples. Increasing concentrations of Humus in soil has resulted in an increase in the sulfur content and cation exchange capacity of the soil. A general decrease in the concentrations of silver was observed in Acheta domesticus and both the plant species, as a function of increasing concentrations of Humus in soil. In the case of plant species, the accumulation of silver nanoparticles was predominantly observed in the root tissue. Additionally, the translocation of silver from the roots to other plant tissues was observed in the case of Helianthus annuus. Results from this study suggest that the presence of Humus in soil could possibly decrease the uptake of silver from silver nanoparticles by insect and plant species.
Effects of Dissolved Silver and Silver Nanoparticle on Soil Microorganisms
Journal of Soil and Water Sciences, 2017
Silver nanoparticles (AgNPs) are the most commonly used man-made nanomaterial in consumer products. They are merged into a vast collection of products due to their particular broad-spectrum anti-microbial action. On the other hand, their anti-bacterial properties may pose a significant environmental risk. This study was undertaken to assess whether the risk that AgNPs and dissolved Ag pose to soil microorganisms gained from nano-or dissolved-silver forms. The antimicrobial effect of green manufactured AgNPs (46.2±23.2 nm) and Ag + (as AgNO 3) on soil microbes were studied using disc diffusion assay. Soil microbial growth was assessed by the measurement of inhibitory zone area (mm 2) as a function of different AgNPs and AgNO 3 concentrations, 0.00, 250, 500, 1000 and 2000 mgl-1. The results of antimicrobial effect of AgNPs showed 10 fold of magnitude comparing with Ag + at lower concentrations (250 mgl-1). The theoretical predicted unity of inhibition zone ratio for AgNPs/Ag ions implies that AgNPs equates to about 5 times antimicrobial effects of Ag +. Although the current results confirm that Ag antimicrobial effect is a nano-specific effect, different bacteria isolated from different soils should be used to explore their physico-chemical properties in mitigating AgNPs toxicity effects.
— The bioavailability and uptake of silver from silver nanoparticles in soil was investigated. Two species of insects, Acheta domesticus and Tenebrio molitor, and two species of plants, Helianthus annuus and Sorghum vulgare, were exposed to a range of concentrations of silver nanoparticles in soil. Silver nanoparticles were charactrized by techniques including transmission electron microscopy, dynamic light scattering, and powder X-ray diffraction. The concentration of silver in insects and plants exposed to silver nanoparticles was measured using inductively coupled plasma-optical emission spectrometry. The results suggested an increase in the levels of silver in both insects and plants as a function of increasing concentrations of silver nanoparticles in soil. The translocation of silver to various parts of dicot plants such as stems and leaves was also observed. Such a result was not observed in the case of monocot plants. Results from this study suggests that silver nanoparticles would be available for uptake by insects and plants in terrestrial ecosystems.