Soil components mitigate the antimicrobial effects of silver nanoparticles towards a beneficial soil bacterium, Pseudomonas chlororaphis O6 (original) (raw)
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Environmental Sciences Europe, 2018
Background: The growing production and use of engineered AgNP in industry and private households make increasing concentrations of AgNP in the environment unavoidable. Although we already know the harmful effects of AgNP on pivotal bacterial driven soil functions, information about the impact of silver nanoparticles (AgNP) on the soil bacterial community structure is rare. Hence, the aim of this study was to reveal the long-term effects of AgNP on major soil bacterial phyla in a loamy soil. The study was conducted as a laboratory incubation experiment over a period of 1 year using a loamy soil and AgNP concentrations ranging from 0.01 to 1 mg AgNP/kg soil. Effects were quantified using the taxon-specific 16S rRNA qPCR. Results: The short-term exposure of AgNP at environmentally relevant concentration of 0.01 mg AgNP/kg caused significant positive effects on Acidobacteria (44.0%), Actinobacteria (21.1%) and Bacteroidetes (14.6%), whereas beta-Proteobacteria population was minimized by 14.2% relative to the control (p ≤ 0.05). After 1 year of exposure to 0.01 mg AgNP/kg diminished Acidobacteria (p = 0.007), Bacteroidetes (p = 0.005) and beta-Proteobacteria (p = 0.000) by 14.5, 10.1 and 13.9%, respectively. Actino-and alpha-Proteobacteria were statistically unaffected by AgNP treatments after 1-year exposure. Furthermore, a statistically significant regression and correlation analysis between silver toxicity and exposure time confirmed loamy soils as a sink for silver nanoparticles and their concomitant silver ions. Conclusions: Even very low concentrations of AgNP may cause disadvantages for the autotrophic ammonia oxidation (nitrification), the organic carbon transformation and the chitin degradation in soils by exerting harmful effects on the liable bacterial phyla.
2012
Silver nanoparticles (AgNPs) are increasingly being integrated into a wide range of consumer products, such as air filters, washing machines, and textiles, due to their antimicrobial properties [1]. However, despite the beneficial applications of AgNPs in consumer products, it is likely that their use will facilitate the release of AgNPs into wastewater treatment plants, thereby possibly negatively impacting key microorganisms involved in nutrient removal. For this reason, it is important to characterize the effects of AgNPs in natural and engineered systems and to measure the antimicrobial effect of AgNPs on wastewater microorganisms. Polyvinyl alcohol coated AgNPs have already been linked to decreased nitrifying activity and it is important to determine if AgNPs coated with other materials follow similar trends [2]. Furthermore, it is likely that with repeated exposure to AgNPs, microbial communities could evolve and develop resistance to Ag. Thus, a long-term effect of Ag nanoparticle exposure could be a reduction of the efficacy of such products in a similar fashion to the development of microbial antibiotic resistance [3]. Therefore, it is critical that the impacts of these materials be ascertained in wastewater treatment systems to prevent long-term negative effects. The objectives of this dissertation were to: 1) characterize the effect of several different AgNPs on the ammonia oxidizing bacterium (AOB) Nitrosomonas europaea and investigate possible mechanisms for toxicity, 2) test the effects of consumer product AgNPs on a wide range of heterotrophic bacteria, 3) evaluate the effects of AgNPs on analyses using T-RFLP conclude that soil bacterial communities will be altered if Ag and AgNP spiked biosolids are land applied. Overall, distinct shifts in microbial community were observed in Ag treated samples after 1 d that were statistically different from the biosolids and no biosolids controls. After 50 d, the AgNP induced clustering was not as obvious, possibly because the communities had time to adapt to environmental changes. T-RFLP fragments were used to identify which species of bacteria were present using ribosomal database matching. Fragment matching indicated that the Proteobacteria community decreased initially and Firmicutes become more dominant. We did not ix observe any decrease in diversity, but rather an increase, possibly due to the bacteria supplemented by the biosolids slurry, which appears to be more diverse than the natural soil microbial community. Denitrifying bacteria, which are important for nitrogen cycling in soil, may have been negatively impacted AgNPs since they fall under the Proteobacteria phylum. Overall, this dissertation asserts that AgNPs have a toxic effect on bacteria, which can be even more than pure Ag as AgNO 3 , due to their unique physical and chemical properties like size, Stern layer charge, coating composition, and stability. Based on the types of AgNP used in consumer products, it may be possible to predict which AgNPs may be more detrimental wastewater treatment, but not all AgNPs will have the same effect. AgNPs at concentrations of 0.2 to 2 ppm were shown to be inhibitory to nitrifying bacteria, heterotrophic bacteria, and the mixed microbial community found in wastewater SBRs. Consumer product AgNPs were also proven to be of concern to environmental engineers since their toxicity was at level or sometimes higher than laboratory made AgNPs. Future studies regarding AgNPs should include an investigation of the prevalence of Ag resistance in wastewater to assess how resilient wastewater microbes are to Ag. The results obtained herein should also be expanded to other types of AgNPs and microorganisms of ecological importance. x Dedication This dissertation is dedicated to my parents, Samir and Linda Arnaout, for their undying support and love. Thank you for never letting me give up my career aspirations and for always offering me advice and encouragement. I wouldn't be in this place in my life without you.
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.
Environmental Sciences Europe
Background: Increasing exposure to engineered inorganic nanoparticles takes actually place in both terrestric and aquatic ecosystems worldwide. Although we already know harmful effects of AgNP on the soil bacterial community, information about the impact of the factors functionalization, concentration, exposure time, and soil texture on the AgNP effect expression are still rare. Hence, in this study, three soils of different grain size were exposed for up to 90 days to bare and functionalized AgNP in concentrations ranging from 0.01 to 1.00 mg/kg soil dry weight. Effects on soil microbial community were quantified by various biological parameters, including 16S rRNA gene, photometric, and fluorescence analyses. Results: Multivariate data analysis revealed significant effects of AgNP exposure for all factors and factor combinations investigated. Analysis of individual factors (silver species, concentration, exposure time, soil texture) in the unifactorial ANOVA explained the largest part of the variance compared to the error variance. In depth analysis of factor combinations revealed even better explanation of variance. For the biological parameters assessed in this study, the matching of soil texture and silver species, and the matching of soil texture and exposure time were the two most relevant factor combinations. The factor AgNP concentration contributed to a lower extent to the effect expression compared to silver species, exposure time and physico-chemical composition of soil. Conclusions: The factors functionalization, concentration, exposure time, and soil texture significantly impacted the effect expression of AgNP on the soil microbial community. Especially long-term exposure scenarios are strongly needed for the reliable environmental impact assessment of AgNP exposure in various soil types.
Environmental science & technology, 2016
The widespread use of silver nanoparticles (Ag-NPs) results in their movement into wastewater treatment facilities and subsequently to agricultural soils via application of contaminated sludge. On-route, the chemical properties of Ag may change and further alterations are possible upon entry to soil. In the present study, we examined the long-term stability and (bio)availability of Ag along the 'wastewater-sludge-soil' pathway. Synchrotron-based X-ray absorption spectroscopy (XAS) revealed that ca. 99% of Ag added to the sludge reactors as either Ag-NPs or AgNO3 was retained in sludge, with ≥ 79% of this being transformed to Ag2S, with the majority ( ≥ 87%) remaining in this form even after introduction to soils at various pH values and Cl concentrations for up to 400 d. Diffusive gradients in thin films (DGT), chemical extraction, and plant uptake experiments indicated that the potential (bio)availability of Ag in soil was low but increased markedly in soils with elevated C...
Environmental Pollution, 2015
We investigated the effects of silver nanomaterials (AgNMs) on five well-characterized soils with distinct physicochemical properties using two standardized test systems. The carbon transformation test (OECD 217) showed minimal sensitivity whereas the ammonia oxidizing bacteria test (ISO 15685) showed extreme sensitivity over 28 days of exposure. AgNM toxicity was compared with the physicochemical properties of the soils, revealing that toxicity declined with increasing clay content and increasing pH. AgNM toxicity did not appear to be affected by the organic carbon content of the soil. Our results showed that AgNM toxicity cannot be attributed to any single soil property but depends on the same parameters that determine the toxicity of conventional chemicals. Recommendations in the test guidelines for soil ecotoxicity studies are therefore applicable to AgNMs as well as conventional chemicals.
Geoderma, 2017
The extensive use of silver nanoparticles (AgNPs) in consumer and medical products leads inevitably to release of such particles into environment and soil resources. This study was conducted to provide evidences for biological effects of AgNPs in two calcareous soils with different textures and salinity levels. Basal respiration (BR) and substrate-induced respiration (SIR), as indicators of soil microbial activity and biomass, respectively, were determined in the calcareous soils spiked with a dilution series of AgNPs and AgNO 3. Urease and alkaline phosphatase activities were also measured in the spiked and control soils. Finally, dose-response approach was used to model the sensitivity of the soil biological properties to AgNPs and AgNO 3 contamination. The results revealed that the effects of AgNPs and AgNO 3 on the soil respiration and enzyme activities depended on Ag dose and soil type. For instance, soil respiration was not affected or even stimulated by low doses of AgNPs and AgNO 3 , but negatively affected by high doses (N 20 mg Ag kg −1). Soil urease and phosphatase activities were generally inhibited in the presence of AgNPs and AgNO 3 , though in low Ag concentrations there was no inhibition or even stimulation. Generally, the ecological dose (ED) values of AgNPs were smaller than those of AgNO 3 , suggesting that AgNPs have more negative effects than AgNO 3 on the soil microbial and enzyme activities, at the same level of Ag dose. The results also revealed that suppression of microbial and enzyme activities by AgNPs and Ag ions are greater in the soil with lower clay content and ionic strength.
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.