Transformation of PVP coated silver nanoparticles in a simulated wastewater treatment process and the effect on microbial communities

Extent: 18p.Background: Manufactured silver nanoparticles (AgNPs) are one of the most commonly used nanomaterials in consumer goods and consequently their concentrations in wastewater and hence wastewater treatment plants are predicted to increase. We investigated the fate of AgNPs in sludge that was subjected to aerobic and anaerobic treatment and the impact of AgNPs on microbial processes and communities. The initial identification of AgNPs in sludge was carried out using transmission electron microscopy (TEM) with energy dispersive X-ray (EDX) analysis. The solid phase speciation of silver in sludge and wastewater influent was then examined using X-ray absorption spectroscopy (XAS). The effects of transformed AgNPs (mainly Ag-S phases) on nitrification, wastewater microbial populations and, for the first time, methanogenesis was investigated. Results: Sequencing batch reactor experiments and anaerobic batch tests, both demonstrated that nitrification rate and methane production were not affected by the addition of AgNPs [at 2.5 mg Ag L-1 (4.9 g L-1 total suspended solids, TSS) and 183.6 mg Ag kg -1 (2.9 g kg-1 total solids, TS), respectively]. The low toxicity is most likely due to AgNP sulfidation. XAS analysis showed that sulfur bonded Ag was the dominant Ag species in both aerobic (activated sludge) and anaerobic sludge. In AgNP and AgNO3 spiked aerobic sludge, metallic Ag was detected (~15%). However, after anaerobic digestion, Ag(0) was not detected by XAS analysis. Dominant wastewater microbial populations were not affected by AgNPs as determined by DNA extraction and pyrotag sequencing. However, there was a shift in niche populations in both aerobic and anaerobic sludge, with a shift in AgNP treated sludge compared with controls. This is the first time that the impact of transformed AgNPs (mainly Ag-S phases) on anaerobic digestion has been reported. Conclusions: Silver NPs were transformed to Ag-S phases during activated sludge treatment (prior to anaerobic digestion). Transformed AgNPs, at predicted future Ag wastewater concentrations, did not affect nitrification or methanogenesis. Consequently, AgNPs are very unlikely to affect the efficient functioning of wastewater treatment plants. However, AgNPs may negatively affect sub-dominant wastewater microbial communities.Casey L Doolette, Mike J McLaughlin, Jason K Kirby, Damien J Batstone, Hugh H Harris, Huoqing Ge and Geert Corneli

Plant-available phosphorus in highly concentrated fertilizer bands: effects of soil type, phosphorus form, and coapplied potassium

Phosphorus (P) is increasingly being applied in concentrated bands to satisfy plant nutrient requirements. To quantify changes in plant-available P in the fertosphere of highly concentrated fertilizer bands, we conducted a soil–fertilizer incubation experiment using seven soil types, three highly water-soluble P sources [monocalcium phosphate (MCP), monoammonium phosphate (MAP), and diammonium phosphate (DAP)], and coapplication of potassium chloride (KCl). First, we found that soil properties were important in influencing P availability. For a calcareous soil, availability was generally low irrespective of treatment, presumably due to precipitation of the fertilizer as Ca-P minerals. For all six noncalcareous soils, fertosphere pH was critical in determining potential P availability, with decreasing pH values decreasing availability, presumably due to precipitation of Al- and Fe-P minerals. Second, given the importance of pH, we also found that the form of P supplied (MCP, MAP, or DAP) had a pronounced effect on P availability due to associated changes in fertosphere pH. Finally, we also found that the coapplication of K also decreased P availability in some soils. We conclude that the selection of the P source is of utmost importance when fertilizers are placed as highly concentrated bands and that soil properties also need to be considered

Foliar application of zinc sulfate and zinc EDTA to wheat leaves: differences in mobility, distribution and speciation

Foliar application of zinc (Zn) to crops is an effective way to increase the grain concentration of Zn. However, the development of more efficient foliar Zn fertilisers is limited by a lack of knowledge regarding the distribution, mobility and speciation of Zn in leaves once it is taken up by the plant. We performed an experiment using radiolabelled Zn (65Zn), and in situ time resolved elemental imaging using synchrotron X-ray fluorescence microscopy (XFM), to investigate the behaviour of two commonly used Zn foliar fertilisers (Zn sulfate and ZnEDTA) in wheat (Triticum aestivum) leaves. Both experiments showed that Zn had limited mobility in leaves, movin

Investigating the foliar uptake of zinc from conventional and nano-formulations: a methodological study

Zinc (Zn) deficiency affects half of the world's arable soil and one-third of the world's human population. Application of Zn foliar fertilisers to cereal crops can be an effective way to increase grain Zn content; however, commonly used formulations can scorch the leaf (e.g. soluble Zn salts) or are prohibitively expensive (e.g. chelated Zn, ZnEDTA). Zinc oxide nanoparticles (ZnO-NPs) may offer an efficient and cost-effective alternative, but little is known regarding the mechanisms of Zn uptake and translocation within the plant. Foliar-applied Zn is analytically challenging to detect, locate and quantify, as it is omnipresent. Furthermore, any single analytical technique does not have the detection limit or spatial resolution required. In this study, the uptake and mobility of foliar-applied ZnEDTA, ZnO-NPs and ZnO microparticles (ZnO-MPs) to wheat (Triticum aestivum L.) were investigated using inductively coupled plasma mass spectroscopy (ICP-MS), synchrotron-based X-ray fluorescence microscopy (XFM) and radiotracing techniques using Zn-labelled formulations. The three techniques were compared to highlight limitations and advantages of each. We also report, for the first time, a novel time-resolved in vivo autoradiography imaging technique that can be used to visualise Zn in live plants treated with foliar applications of ZnO-NPs and MPs. The images were supplemented by gamma spectroscopy analysis for quantification. The results of this study provide important insights into the analytical challenges faced when investigating foliar-applied Zn nanofertilisers in plants. Potential solutions using nuclear techniques are also discussed, which in turn may ultimately lead to the development of more efficient foliar fertilisers

Operational taxonomic unit (OTU) sensitivity distributions (OSD) comparing the sensitivity of OTUs to each Ag treatment.

<p>Results are shown for each Ag treatment: (A) ionic Ag (Ag⁺), (B) Ag nanoaparticles (AgNP) and (C) Ag sulfide nanoparticles (Ag₂S-NP). Each data point corresponds to the Ag concentration that decreased the absolute abundance of a specific OTU by 20% (EC₂₀). Data were fitted to a Burr Type III function, where the fitted function is shown in green and 95% confidence intervals are indicated by the blue dashed line.</p