Agglomeration behaviour of titanium dioxide nanoparticles in river waters: A multi-method approach combining light scattering and field-flow fractionation techniques

© 2015 Elsevier Ltd. Titanium dioxide nanoparticles (TiO2 NPs) are currently one of the most prolifically used nanomaterials, resulting in an increasing likelihood of release to the environment. This is of concern as the potential toxicity of TiO2 NPs has been investigated in several recent studies. Research into their fate and behaviour once entering the environment is urgently needed to support risk assessment and policy development. In this study, we used a multi-method approach combining light scattering and field-flow fractionation techniques to assess both the aggregation behaviour and aggregate structure of TiO2 NPs in different river waters. Results showed that both the aggregate size and surface-adsorbed dissolved organic matter (DOM) were strongly related to the initial DOM concentration of the tested waters (i.e. R2>0.90) suggesting that aggregation of TiO2 NPs is controlled by the presence and concentration of DOM. The conformation of the formed aggregates was also found to be strongly related to the surface-adsorbed DOM (i.e. R2>0.95) with increasing surface-adsorbed DOM leading to more compact structures. Finally, the concentration of TiO2 NPs remaining in the supernatant after sedimentation of the larger aggregates was found to decrease proportionally with both increasing IS and decreasing DOM concentration, resulting in more than 95% sedimentation in the highest IS sample

Assessing the aggregation behaviour of iron oxide nanoparticles under relevant environmental conditions using a multi-method approach

Iron nanoparticles are becoming increasingly popular for the treatment of contaminated soil and groundwater; however, their mobility and reactivity in subsurface environments are significantly affected by their tendency to aggregate. Assessing their stability under environmental conditions is crucial for determining their environmental fate. A multi-method approach (including different size-measurement techniques and the DLVO theory) was used to thoroughly characterise the behaviour of iron oxide nanoparticles (Fe2O3NPs) under environmentally relevant conditions. Although recent studies have demonstrated the importance of using a multi-method approach when characterising nanoparticles, the majority of current studies continue to use a single-method approach.Under some soil conditions (i.e. pH 7, 10mM NaCl and 2mM CaCl2) and increasing particle concentration, Fe2O3NPs underwent extensive aggregation to form large aggregates (>1μm). Coating the nanoparticles with dissolved organic matter (DOM) was investigated as an alternative "green" solution to overcoming the aggregation issue instead of using the more commonly proposed polyelectrolytes. At high concentrations, DOM effectively covered the surface of the Fe2O3NPs, thereby conferring negative surface charge on the particles across a wide range of pH values. This provided electrostatic stabilisation and considerably reduced the particle aggregation effect. DOM-coated Fe2O3NPs also proved to be more stable under high ionic strength conditions. The presence of CaCl2, however, even at low concentrations, induced the aggregation of DOM-coated Fe2O3NPs, mainly via charge neutralisation and bridging. This has significant implications in regards to the reactivity and fate of these materials in the environment. © 2013 Elsevier Ltd

Uptake and distribution of nickel and other metals in the hyperaccumulator Berkheya coddii

Berkheya coddii is a fast-growing, high biomass nickel (Ni) hyperaccumulator plant that has recently attracted attention for its possible use in the phytoextraction of Ni. The mechanisms of Ni accumulation, however, are not well understood in this plant. Plants were grown hydroponically in varying Ni concentrations to assess the uptake and distribution of Ni, and other metals, at the whole plant level. X-ray microanalyses (EDXA) of frozen hydrated tissues were conducted to determine the distribution of Ni at the cellular level in the leaves. Most Ni was found in the shoots, especially in the leaves. Leaf Ni concentration increased with age, whereas older stem sections had lower Ni concentrations than new growth. EDXA analyses revealed that the cuticle of the upper epidermis had a significantly higher Ni concentration than the rest of the leaf. The Ni concentrations in the other leaf tissues were not significantly different. This pattern of distribution contrasts sharply with some other hyperaccumulator species that commonly show a preferential accumulation of Ni and other metals in the vacuoles of the epidermal cells

Chemical considerations in the interpretation of toxicity of metals in soil

Extended abstract.Enzo Lombi, Mike J. McLaughlin and Rebecca E. Hamo

Long-term natural attenuation of Cu added to soils predicted by soil pH and time

Extended abstract.Yibing Ma, Enzo Lombi, Annette L. Nolan, Mike J. McLaughli

Challenges of polymer‐based pH sensing in soil

OnlinePublIt is well established that plants need a range of soil nutrients to grow. In farming, these nutrients are generally added to the soil in the form of fertilizers. However, depending on the soil conditions (such as temperature, water content, pH, and soil type), nutrients may not be in the right form for plant uptake. Determining the availability of nutrients in the soil for plant growth is therefore critical for the yield and productivity of modern farming. A considerable amount of research and knowledge has been developed that shows the importance of the soil pH on the availability (or not) of nutrients. Furthermore, pH plays a crucial role in controlling the availability of potential toxic elements, such as aluminum and manganese. This review article discusses recent research aimed at real‐time and continuous soil pH measurement in‐situ. More specifically, it focuses on the development of polymer materials that will ultimately enable pH measurements for the specific application of in‐ground pH sensing. Given the breadth of the polymeric sensor research field, this review has a narrowed focus on optical and electrochemical transduction methods.Esmat Ebadati, Eliza Switalska, Enzo Lombi, Stephen C. Warren-Smith, Drew Evan

Trace metal distribution in colloid size fractions from biosolids amended soils – using a modified multistage tangential flow ultrafiltration system

Extended abstract.Hayley M. Castlehouse, Jason Kirby, Enzo Lombi, Mike J. McLaughli

Arsenic distribution and speciation in the fronds of the hyperaccumulator Pteris vittata

Pteris vittata is the first plant reported to be a hyperaccumulator of arsenic (As), and little is known about the mechanisms of As hyperaccumulation in this plant. Arsenic distribution at the whole plant (fronds) and cellular level was investigated using chemical analyses and energy dispersive X-ray microanalyses (EDXA). Speciation of As in the fronds was determined using X-ray absorption near edge spectroscopy (XANES) analyses. The majority of As was found in the pinnae (96% of total As). The concentration of As in pinnae decreased from the base to the apex of the fronds. Arsenic concentrations in spores and midribs were much lower than in the pinnae. EDXA analyses revealed that As was compartmentalized mainly in the upper and lower epidermal cells, probably in the vacuoles. The distribution pattern of potassium was similar to As, whereas other elements (Ca, Cl, K, Mg, P and S) were distributed differently. XANES analyses showed that approximately 75% of the As in fronds was present in the As(III) oxidation state and the remaining as As(V)

Speciation and distribution of thallium in Iberis Intermedia: an in-vivo synchrotron study

Extended abstract.Enzo Lombi, Kirk Scheckel, Steve Rock, Mike McLaughlin, Rebecca Hamo