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The specific properties of nanoparticles can induce toxic or promoting effects on plant growth. We performed a meta-analysis of 173 studies to evaluate the uptake and accumulation of metallic nanoparticles (MNPs) by crops. Studies on the main cereal/vegetable crops (wheat, tomato, bean, maize, rice and cucumber) and Ag, Zn, Ce, Fe, Cu and Ti containing MNPs were mostly found; 63% of the studies used MNPs with size <30 nm, and root application accounted for 84% of all studies. Under root exposure, metal concentrations were reduced by up to 2 orders of magnitude from root through shoot to leaf. Moreover, the uptake preference of MNPs or dissolved metals was element-specific and varied among tissues. Plants accumulated generally higher concentrations of the three essential elements (Cu, Zn and Fe) than of the non-essential ones (Ag, Ce and Ti). Also, foliar application was more efficient than root exposure. Metal concentrations in shoots increased with decreasing particle size for non-essential elements, but showed a variable increase for essential elements as size decreased. Besides, the uptake of MNPs increased with more negative zeta potential (especially for Cu and Zn). Overall, the plant essential elements (Cu, Zn and Fe) were preferred taken up as MNPs, while for non-essential elements (Ag and Ce) uptake as dissolved metals was more common. We conclude that for plant nanofertilizers, foliar application of essential elements as small MNPs might be more efficient for crop uptake than the uptake of dissolved metals. [ABSTRACT FROM AUTHOR]

Soils in hyper‐arid climates, such as the Chilean Atacama Desert, show indications of past and present forms of life despite extreme water limitations. We hypothesize that fog plays a key role in sustaining life. In particular, we assume that fog water is incorporated into soil nutrient cycles, with the inland limit of fog penetration corresponding to the threshold for biological cycling of soil phosphorus (P). We collected topsoil samples (0–10 cm) from each of 54 subsites, including sites in direct adjacency (<10 cm) and in 1 m distance to plants, along an aridity gradient across the Coastal Cordillera. Satellite‐based fog detection revealed that Pacific fog penetrates up to 10 km inland, while inland sites at 10–23 km from the coast rely solely on sporadic rainfall for water supply. To assess biological P cycling we performed sequential P fractionation and determined oxygen isotope of HCl‐extractable inorganic Pδ18OHCl−Pi$$ \mathrm{P}\ \left({\updelta}^{18}{\mathrm{O}}_{\mathrm{HCl}-{\mathrm{P}}_{\mathrm{i}}}\right) $$. Total P (Pt) concentration exponentially increased from 336 mg kg−1 to a maximum of 1021 mg kg−1 in inland areas ≥10 km. With increasing distance from the coast, soil δ18OHCl−Pi$$ {\updelta}^{18}{\mathrm{O}}_{\mathrm{HCl}-{\mathrm{P}}_{\mathrm{i}}} $$ values declined exponentially from 16.6‰ to a constant 9.9‰ for locations ≥10 km inland. Biological cycling of HCl‐Pi near the coast reached a maximum of 76%–100%, which could only be explained by the fact that fog water predominately drives biological P cycling. In inland regions, with minimal rainfall (<5 mm) as single water source, only 24 ± 14% of HCl‐Pi was biologically cycled. We conclude that biological P cycling in the hyper‐arid Atacama Desert is not exclusively but mainly mediated by fog, which thus controls apatite dissolution rates and related occurrence and spread of microbial life in this extreme environment. [ABSTRACT FROM AUTHOR]

It is considered inevitable that the increasing production and application of engineered nanoparticles will lead to their release into the environment. However, the behavior of these materials under environmentally relevant conditions is still only poorly understood. In this study the transport and deposition behavior of engineered surfactant stabilized silver nanoparticles (AgNPs) in water saturated porous media was investigated in transport experiments with glass beads as reference porous medium and in two natural soils under various hydrodynamic and hydrochemical conditions. The transport and retention processes of AgNPs in the porous media were elucidated by inverse modeling and possible particle size changes occurring during the transport through the soil matrix were analyzed with flow field-flow fractionation (FlFFF). A high mobility of AgNPs was observed in loamy sand under low ionic strength (IS) conditions and at high flow rates. The transport was inhibited at low flow rates, at higher IS, in the presence of divalent cations and in a more complex, fine-grained silty loam. The slight decrease of the mean particle size of the AgNPs in almost all experiments indicates size selective filtration processes and enables the exclusion of homoaggregation processes. [ABSTRACT FROM AUTHOR]

Abstract: The effects of soil depth on the colloidal properties and potential release of water-dispersible colloids (WDCs) in an agricultural soil were investigated in batch experiments. Nine soil samples were collected along a trench at different depths (from −7.5cm to −127.5cm) from the TERENO test site located in Selhausen (Germany). A physical gentle soil fractionation confirmed the importance of the solution chemistry in controlling the depth distribution of WDC in the Luvisol soil. A maximal fraction of total clay (fWDC) equal to approx. 45% was released at a depth of −37.5cm to −52.5cm below the surface. This was found to be related to the lowest electrical conductivity of the soil electrolyte phase where Ca2+ concentration played a major role. A rather constant content of metal oxyhydroxide (MO(OH)) accounting for about 10% in WDCs was found along the soil depth after a dithionite-citrate-bicarbonate (DCB) extraction. However, a decrease from 40% to 25% in the contribution of MO(OH) particles to SSA of WDC was calculated along the soil depth. Using photon correlation spectroscopy (PCS) and N2 gas adsorption method, variations were measured in colloidal hydrodynamic diameters (dz) and the mineral specific surface area (SSA) for WDC in water-dispersed and dried states, respectively. A function structure f(np) was defined to relate the particle size variations between the two states along the soil depth. An inverse correlation was established between the particle size variations which assumed that the number of primary particle in the water-dispersed state increases in subsoil samples. The effects of different soil parameters such as pH, organic carbon (OC) coverage at MO(OH) surfaces and humification index (HIX) of dissolved organic carbon (DOC) on the WDC structure variations are discussed. It can be hypothesized that a maximal surface OC coverage at MO(OH) surfaces of WDCs facilitates the release of small particles through electrosteric dispersion in topsoil. Lower pHs and WDC(OC) content would favor the release of large WDC particles in subsoil where an OC content of a more aliphatic character can also facilitate hydrophobic interactions. [Copyright &y& Elsevier]

Abstract: The features of the location of copper ions and the dihalogenated phenol molecules were investigated at their low concentration in the dipalmitoylphosphatidylcholine (DPPC)–water liposomes by using small-angle X-ray scattering (SAXS) and anomalous small-angle X-ray scattering (ASAXS) methods. Only the ASAXS method can provide information about the structural features of the domains rich in these ions and organic guest molecules. The copper ions are mainly located in large domains between the lamellae and only partly in the characteristic periodic water shells of the liposomes. The dihalogenated phenol molecules are embedded in the layers and do not destroy the lamellar arrangement. Their inhomogeneous distribution appears laterally and phase separation occurs. The local structures induced by the copper ions and the dihalogenated phenols were also visualised by freeze-fracture method. [Copyright &y& Elsevier]

The effect of 2,4-dichlorophenol (DCP) was studied on the fully hydrated 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC)—water liposomes. The structure and the thermotropic phase behaviour of the liposomes was examined in the presence of DCP (DCP/DPPC molar ratio, varied from 2×10−2 up to 1) using small- and wide-angle X-ray scattering (SAXS, WAXS) and freeze-fracture electron microscopy. The structural behaviour of the DPPC/DCP/water system was strongly dependent on the concentration of the DCP. In the pretransition range the DCP molecules (at 2×10−2 DCP/DPPC molar ratio) induced the interdigitated phase beside the parent (gel and rippled gel) phases, locally which can be form at higher DCP concentration. When the DCP/DPPC molar ratio was increased the pretransition disappeared and the main transition was shifted to lower temperatures. In the molar ratio range from 2×10−1 up to 5×10−1, a coexistence of different phases was observed in the wide temperature range from 20 up to 40 °C. With a further increase of the DCP/DPPC molar ratio (6×10−1 to 1) only the interdigitated gel phase occurred below 25 °C. A schematic phase diagram of DPPC/DCP/water system was constructed to summarise the results. [Copyright &y& Elsevier]

Engineered nanoparticles (ENPs) present in consumer products are being released into the agricultural systems. There is little information about the direct effect of ENPs on phosphorus (P) availability, which is an essential nutrient for crop growth naturally occurring in agricultural soils. The present study examined the effect of 1, 3, and 5% doses of Cu0 or Ag0 ENPs stabilized with L-ascorbic acid (suspension pH 2–3) on P ad- and desorption in an agricultural Andisol with total organic matter (T-OM) and with partial removal of organic matter (R-OM) by performing batch experiments. Our results showed that the adsorption kinetics data of H2PO4− on T-OM and R-OM soil samples with and without ENPs were adequately described by the pseudo-second-order (PSO) and Elovich models. The adsorption isotherm data of H2PO4− from T-OM and R-OM soil samples following ENPs addition were better fitted by the Langmuir model than the Freundlich model. When the Cu0 or Ag0 ENPs doses were increased, the pH value decreased and H2PO4− adsorption increased on T-OM and R-OM. The H2PO4− desorption (%) was lower with Cu0 ENPs than Ag0 ENPs. Overall, the incorporation of ENPs into Andisols generated an increase in P retention, which may affect agricultural crop production. [ABSTRACT FROM AUTHOR]

• Soil colloids promote the stability of microaggregate occlusion in macroaggregates. • Microaggregate reaggregation is affected by colloidal iron and organic carbon. • Less microaggregate reaggregation with reduced organic carbon concentrations in Luvisols. • Smaller-sized microaggregate structures in presence of colloidal-sized iron. Several beneficial soil functions are linked to aggregates, but how the formation and stability depend on the presence of colloidal- and nanosized (1000–1 nm) bulding blocks is still understood poorly. Here, we sampled subsites from an arable toposequence with 190 and 340 g kg−1 clay, and isolated small soil microaggregates (SMA; <20 µm) from larger macroaggregate units (>250 µm) using an ultrasonic dispersion energy of 60, 250, and 440 J mL−1, respectively. We then allowed these small SMA to reaggregated after chemical removal of organic carbon (OC) as well as of Fe- and Al (hydr)oxides, respectively. The size distribution of the reaggregated small SMA and fine colloids (<0.45 µm) was analyzed via laser diffraction and asymmetric flow field-flow fractionation coupled to inductively coupled plasma mass spectrometry and organic carbon detection, respectively. We found elevated amounts of both finer colloids and stable SMA at subsites with higher clay contents. The size distribution of small SMA was composed of two distinctive fractions including colloids and larger microaggregates with an average size of 5 µm. The removal of Fe with Dithionite-Citrate-Bicarbonate (DCB) shifted the size of the small SMA to a larger equivalent diameter, while removal of OC with NaOCl reduced it. After three wetting and drying cycles, the concentration of colloids declined, whereas the small SMA without chemical pre-treatments reaggregated to particles with larger average diameters up to 10 µm, with the size depending on the clay content. Intriguingly, this gain in size was more pronounced after Fe removal, but it was not affected by OC removal. We suggest that Fe (hydr)oxides impacts the stability of small SMA primarily by being present in small-sized pores and thus cementing the aggregates to smaller size. In contrast, the effect of OC was restricted to the size of colloids, gluing them together to small SMAs within defined size ranges when OC was present but releasing these colloids when OC was absent. [ABSTRACT FROM AUTHOR]

• Low δ 18O HCl-P values were constant with parent material at the driest sites. • δ 18O HCl-P values increase at less arid sites. • δ 18O HCl-P values trace past biological activity in the Atacama Desert. The Atacama Desert (Chile) is one of driest places on Earth, with a hyper-arid climate and less than 2 mm yr−1 precipitation; nevertheless, it has experienced rare periods of sporadic rainfall. These periods shortly enhanced vegetation growth and microbial activity, which must have utilized major nutrients such as phosphorus (P). However, any biological cycling of P involves an oxygen exchange with water, which should now reside in the hyperarid soils as tracer of life. In order to identify such evidences, we performed sequential P fractionation and analyzed the oxygen isotope composition of HCl-extractable phosphate (δ 18O HCl–P) in the surface soil (0–15 cm) of a climatic gradient along the rising alluvial fans of the Central Depression to the Precordillera, Chile. At the driest sites, the δ 18O HCl-P values were constant with depth and deviated from biologically-driven isotopic equilibrium. In contrast, we observed a considerable increase of δ 18O HCl-P values below the soil surface at less arid sites, where some isotope values were even within the range of full isotopic equilibrium with biologically cycled phosphate. For the latter sites, this points to most efficient biological P cycling right below the uppermost surface of the desert. Critically, the absolute concentrations of this biologically cycled P exceeded those of P potentially stored in living microbial cells by at least two orders of magnitude. Therefore, our data provides evidence that δ 18O HCl-P values trace not recent but past biological activity, making it a powerful tool for assessing the existence, pathways and evolution of life in such arid ecosystems on Earth and, thus, potentially on other planets such as Mars. [ABSTRACT FROM AUTHOR]

Despite numerous studies about the change of soil biogeochemical properties by climate alternation driven by elevation, latitude, etc. in arid to hype-arid regions, little is known about soil colloids (1-1000 nm) and nanoparticles (1-100 nm) as nutrient carriers and which events are driving this in such environments. We investigated the size and composition of water dispersible colloids (WDCs) to quantify colloidal bound C and P from three depth profiles in an altitudinal transect in the Atacama Desert (Paposo region) using asymmetric field flow field fractionation (A-FFFF) coupled online to various detectors (ICP-MS, organic carbon detector (OCD) and UV). One of the profiles (A; 200 cm) was located in a semi-arid part and the two others (70 cm depth) in an arid area in the vicinity of each other (B on an abandoned alluvial fan, and C on the more active part of the fan). Three size categories of WDCs were detected based on the FFF results, including nanoparticles from 0.6 to 24 nm, fine colloids from 24 to 210 nm, and medium colloids from 210 to 500 nm. Nanoparticles and soil colloids accounted for up to 60% of the bioavailable P concentration (Olsen P) at the surface layer of profile C. Moreover, the contribution of colloidal Corg to total Corg was 5% at the surface of profile A, with a maximum of 11% at depth of 115 cm, and maximum 1% at the surface layer of both profiles B and C. The size distribution of colloids and their elemental content was significantly different between B and C especially at upper 20 cm. Our results, showing pronounced local differences in soil colloidal properties, suggest that colloidal matter (here mainly C and P) preserved in the Atacama deserts is terrestrial proxy record of both local (e.g. intermittent drainage events) and larger scale (periods of dust input) of environmental changes which have occurred in this part of South America. [ABSTRACT FROM AUTHOR]

The functions of soils are intimately linked to their three‐dimensional pore space and the associated biogeochemical interfaces, mirrored in the complex structure that developed during pedogenesis. Under stress overload, soil disintegrates into smaller compound structures, conventionally named aggregates. Microaggregates (<250 µm) are recognized as the most stable soil structural units. They are built of mineral, organic, and biotic materials, provide habitats for a vast diversity of microorganisms, and are closely involved in the cycling of matter and energy. However, exploring the architecture of soil microaggregates and their linkage to soil functions remains a challenging but demanding scientific endeavor. With the advent of complementary spectromicroscopic and tomographic techniques, we can now assess and visualize the size, composition, and porosity of microaggregates and the spatial arrangement of their interior building units. Their combinations with advanced experimental pedology, multi‐isotope labeling experiments, and computational approaches pave the way to investigate microaggregate turnover and stability, explore their role in element cycling, and unravel the intricate linkage between structure and function. However, spectromicroscopic techniques operate at different scales and resolutions, and have specific requirements for sample preparation and microaggregate isolation; hence, special attention must be paid to both the separation of microaggregates in a reproducible manner and the synopsis of the geography of information that originates from the diverse complementary instrumental techniques. The latter calls for further development of strategies for synlocation and synscaling beyond the present state of correlative analysis. Here, we present examples of recent scientific progress and review both options and challenges of the joint application of cutting‐edge techniques to achieve a sophisticated picture of the properties and functions of soil microaggregates. [ABSTRACT FROM AUTHOR]

[Display omitted] • Different deposition behaviors of co-transport were observed in column and QCM-D. • Ca2+ exhibited a more significant impact on co-transport and deposition than K+. • Divalent cation enhanced the non-DLVO interactions of MWCNTs with BNPs or GNPs. • Ca2+ enhanced straining and competitive blocking in the co-transport in QS. • Ca2+ exhibited a much stronger impact on MWCNTs and GNPs than MWCNTs and BNPs. This work investigates the influence of cation type (Ca2+ as compared to K+) on the co-transport and deposition of functionalized multi-walled carbon nanotubes (MWCNTs) with negatively (bentonite nanoparticles, BNPs) or positively (goethite nanoparticles, GNPs) charged natural nanoparticles under the same ionic strength (IS = 1 mM) conditions. In packed column tests with quartz sand (QS), the co-transport of MWCNTs was slightly increased by BNPs and inhibited by GNPs in both CaCl 2 and KCl solutions, whereas the co-transport of BNPs or GNPs was facilitated by MWCNTs in both solutions. However, the co-transport of MWCNTs in the presence of BNPs or GNPs exhibited a different dependency on the cation type in quartz crystal microbalance with dissipation (QCM-D) tests. No deposition of MWCNTs and BNPs was observed in QCM-D studies in the presence of KCl, while enhanced deposition of MWCNTs and GNPs occurred in this same solution. In contrast, the deposition of both MWCNTs and BNPs or MWCNTs and GNPs increased in QCM-D in the presence of CaCl 2. In both column and QCM-D studies, Ca2+ exhibited a more significant impact on co-transport than K+, especially for MWCNTs with GNPs than BNPs. Results from molecular dynamic simulations, aggregation studies, and interaction energy calculations indicate that non-DLVO interactions (e.g. , H-bonding and cation-π interaction) between two nanoparticles (MWCNTs with BNPs or GNPs) played a non-negligible role in interpreting the deposition and co-transport in the presence of the divalent cation Ca2+. Mathematical modeling of breakthrough curves and retention profiles and aggregation results suggest that both straining and competitive blocking were enhanced and played dominant roles in the co-transport of MWCNTs in the presence of BNPs or GNPs in QS, especially in the presence of Ca2+. This work sheds novel insights on the contribution of divalent cations to interactions between two colloids and their co-transport in porous media. This information is needed to assess the environmental fate and risks of engineered nanoparticles (ENPs) and natural nanoparticles in aquatic and soil environments with abundant divalent cations. [ABSTRACT FROM AUTHOR]

Due to their extreme aridity, high rate of UV irradiation and low soil carbon (C) content, the soils of the Atacama Desert represent one of the world's most hostile environments for microbial life and its survival. Although infrequent, climatic conditions may, however, prevail which temporarily remove these stresses and allow life to briefly flourish. In this study we investigated the response of soil microbial communities to water and C availability across an aridity gradient (semi-arid, arid, hyper-arid) within the Atacama Desert. We simulated the impact of hyper-dry spells, humid fogs and precipitation events on the activation of the microbial community and the subsequent mineralization of low (glucose) and high (plant residues) molecular weight C substrates. Our results showed that mineralization rate followed the trend: semi-arid > arid > hyper-arid. Some glucose mineralization was apparent under hyper-arid conditions (water activity, a w = 0.05), although this was 10-fold slower than under humid conditions and ca. 200-fold slower than under wet conditions. A lag phase in CO 2 production after glucose-C addition in the hyper-arid soils suggested that mineralization was limited by the low microbial biomass in these soils. No lag phase was apparent in the corresponding semi-arid or arid soils. In contrast, the breakdown of the plant residues was initially much slower than for glucose and involved a much longer lag phase in all soils, suggesting that mineralization was limited by low exoenzyme activity, particularly in the humid and hyper-dry soils. Our results also showed that microbial C use efficiency followed the trend: hyper-arid > arid > semi-arid. In conclusion, we have shown that even under hyper-arid conditions, very low levels of microbial activity and C turnover do occur. Further, the microbial communities are capable of rapidly responding to available C once water becomes more abundant, however, this response is both biomass and metabolically limited in hyper-arid soils. [ABSTRACT FROM AUTHOR]

Understanding the physicochemical factors affecting nanoparticle transport in porous media is critical for their environmental application. Water-saturated column experiments were conducted to investigate the effects of input concentration (Co), ionic strength (IS), and sand grain size on the transport of poly(acrylic acid-co-maleic acid) coated magnetite nanoparticles (PAM@MNP). Mass recoveries in the column effluent ranged from 45.2 to 99.3%. The highest relative retention of PAM@MNP was observed for the lowest Co. Smaller Co also resulted in higher relative retention (39.8%) when IS increased to 10 mM. However, relative retention became much less sensitive to solution IS as Co increased. The high mobility is attributed to the PAM coating provoking steric stability of PAM@MNP against homoaggregation. PAM@MNP retention was about 10-fold higher for smaller grain sizes, i.e., 240 µm and 350 µm versus 607 µm. The simulated maximum retained concentration on the solid phase (Smax) and retention rate coefficient (k1) increased with decreasing Co and grain sizes, reflecting higher retention rates at these parameters. The study revealed under various IS for the first time the high mobility premise of polymer-coated magnetite nanoparticles at realistic (<10 mg L−1) environmental concentrations, thereby highlighting an untapped potential for novel environmental PAM@MNP application usage. [ABSTRACT FROM AUTHOR]

The unsaturated zone plays a significant role in protecting groundwater resources from microbial contaminants. The mechanisms governing bacteria transport and retention in aggregated soils are still not fully understood and quantified. This study aims to investigate Pseudomonas fluorescens transport and retention in undisturbed calcareous soils under both saturated and unsaturated conditions. Series of transport experiments with well-controlled suctions and flow rates were performed. The breakthrough curves of bacteria and a nonreactive tracer (Cl-) were obtained. The bacteria were then quantified in different layers of soil. HYDRUS-1D two-site depth-dependent deposition model was employed to simulate transport and retention of bacteria. HYDRUS-1D two-site depth-dependent deposition model fit the observed data well (R2=0.99). Results revealed that the average ratio of detachment to attachment rate was 0.028 and 0.016 under saturated and unsaturated flow conditions, respectively, demonstrating nearly irreversible attachment of cells. Increasing depth dependent-deposition coefficient (k 2) in unsaturated soils was attributed to straining and film straining. The majority of bacteria were deposited nearby the inlet of soil columns, and the rate of retention diminished with depth. Bacterial removal rate was 2.5 times higher under unsaturated than under saturated condition. High removal rate of bacteria under unsaturated flow was attributed to retention of bacteria to film straining, air-water interface, and also attachment to CaCO 3 minerals that contained preferred sites for negatively charged cells. [Display omitted] • We study transport and deposition of bacteria in saturated and unsaturated undisturbed soil. • Transport and retention were well described by two-site kinetic deposition model. • Strong attachment of bacteria was attributed to soil calcium carbonate. • High removal rate of bacteria under unsaturated condition due to straining. [ABSTRACT FROM AUTHOR]

Abstract: Risk assessment of xenobiotics requires a comprehensive understanding of their transformation in the environment. As most of the transformation processes usually involve a redox reaction or a hydrolysis as the first steps of the transformation, we applied an approach that uses an electrochemical cell to investigate model “redox” reactions in aqueous solutions for environmental processes. We investigated the degradation of a variety of xenobiotics from polar to nonpolar and analyzed their degradation products by on-line coupling of electrochemistry with mass spectrometry (EC–MS). Furthermore, we evaluated possible binding reactions with regard to the generation of non-extractable residues with some model substances (catechol, phthalic acid, γ-l-Glutamyl-l-cysteinyl-glycine (GSH) and l-histidine) deduced from a natural organic matter (NOM) structure model and identified possible binding-sites. Whereas typically investigations in soil/water-systems have been applied, we used to our knowledge for the first time a bottom-up approach, starting from the chemicals of interest and different model substances for natural organic matter to evaluate chemical binding mechanisms (or processes) in the EC–MS under redox conditions. Under oxidative conditions, bindings of the xenobiotics with catechol, GSH and histidine were found, but no reactions with the model compound phthalic acid were observed. In general, no chemical binding has yet been found under reductive conditions. In some cases (i.e. benzo[a]anthracene) the oxidation product only underwent a binding reaction, whereas the xenobiotic itself did not undergo any reactions. EC–MS is a promising fast and simple screening method to investigate the environmental behavior of xenobiotics and to evaluate the potential risks of newly synthesized substances. [Copyright &y& Elsevier]

Abstract: A study was conducted to understand the role of cell concentration and metabolic state in the transport and deposition behaviour of Pseudomonas fluorescens with and without substrate addition. Column experiments using the short-pulse technique (pulse was equivalent to 0.028 pore volume) were performed in quartz sand operating under saturated conditions. For comparison, experiments with microspheres and inactive (killed) bacteria were also conducted. The effluent concentrations, the retained particle concentrations and the cell shape were determined by fluorescent microscopy. For the transport of metabolically-active P. fluorescens without substrate addition a bimodal breakthrough curve was observed, which could be explained by the different breakthrough behaviour of the rod-shaped and coccoidal cells of P. fluorescens. The 70:30 rod/coccoid ratio in the influent drastically changed during the transport and it was about 20:80 in the effluent and in the quartz sand packing. It was assumed that the active rod-shaped cells were subjected to shrinkage into coccoidal cells. The change from active rod-shaped cells to coccoidal cells could be explained by oxygen deficiency which occurs in column experiments under saturated conditions. Also the substrate addition led to two consecutive breakthrough peaks and to more bacteria being retained in the column. In general, the presence of substrate made the assumed stress effects more pronounced. In comparison to microspheres and inactive (killed) bacteria, the transport of metabolically-active bacteria with and without substrate addition is affected by differences in physiological state between rod-shaped and the formed stress-resistant coccoidal cells of P. fluorescens. [Copyright &y& Elsevier]

Abstract: The effects of three aminoglycosides (AGs), tobramycin, streptomycin and spectinomycin on 1,2-dipalmitoyl-sn-glycero-3-phosphoethanolamine (DPPE)–1,2-dipalmitoyl-sn-glycero-3-[phospho-rac-1-glycerol] (DPPG)/water systems with 0.05 and 0.2 DPPG/DPPE+DPPG molar fractions were examined by using differential scanning calorimetry (DSC), simultaneous small- and wide-angle X-ray scattering (SWAXS), and freeze-fracture transmission electronmicroscopy (FF-TE) at 10−1 AG/lipid molar ratio in the doped systems. The effects induced by the AGs strongly depend on DPPG/DPPE+DPPG molar fraction. In the presence of the AGs regular lyotropic structures form as opposed to the complex and badly correlated layer structures of the pure 0.2 DPPG/DPPE+DPPG molar fraction system. The investigated AGs possess different structural and thermotropic effects: tobramycin and streptomycin which are true aminoglycosides decrease the main transition enthalpy in both model systems and induce the formation of correlated layer arrangements, while the occurrence of spectinomycin, a non-aminoglycoside aminocyclitol still ranked as an AG, results in a hexagonal phase as it can be deduced from the SAXS patterns and visually observed in the electronmicrographs. [Copyright &y& Elsevier]

Abstract: The effect of the frequently used antibiotic sulfadiazine (SD) was studied on a bacteria membrane mimetic model system by using differential scanning calorimetric (DSC), small- and wide-angle X-ray scattering (SWAXS) and freeze-fracture methods. The membrane model system consisted of dipalmitoylphosphatidylethanolamine (DPPE, 0.8 molar ratio) and dipalmitoylphosphatidylglycerol (DPPG, 0.2 molar ratio). The SD molar ratio (relative to the lipids) was varied between 10−3 and 1. In the presence of SD, two transitions between the gel and liquid crystalline phases appear at 60.5 °C and about at 65 °C. In the temperature domain of the gel phase, the subcell of the chain packing is strongly temperature dependent indicating the increased dominance of the hydration forces during the first transition and the location of SD molecules in the neighbourhood of the polar lipid head groups. The second transition is accompanied by the changes in the nanometer-scale layer arrangements observed by SAXS and in the μm-scale morphology observed by freeze-fracture. Above the temperature of the second transition, the SD-induced metastable structures undergo further formations to produce a more homogeneous state favoured by the geometrical packing of the cylindrical-shaped lipid molecules. [Copyright &y& Elsevier]

Abstract: The influence of sorption on the biodegradation of 2,4-dichlorophenol (DCP) by Ralstonia eutropha was investigated using organoclays. The aim was to examine the suitability of organoclays combined with biodegradation in remediation techniques. Two types of organoclays were used: a dodecyltrimethylammonium montmorillonite, where 89% of the former sodium ions were exchanged by the cationic surfactant (C12-MM), and a dioctadecyldimethylammonium montmorillonite complex (35% exchange of the sodium-ions) (2C18-MM). The organoclays showed high sorption affinity to DCP resulting in the intercalation of DCP into the interlayers of the organoclay. The sorption processes were reversible and completed within minutes. Neither organoclay was inhibitory to R. eutropha degrading fructose. This was different with DCP as sole energy and carbon source. In the presence of DCP C12-MM led to a decrease in cell numbers caused by a coupled effect of DCP and small amounts of free C12 in solution. This was not observed with 2C18-MM, as the concentration of 2C18 in solution was lower because of the lesser degree of exchange (35% compared to 89%). The addition of 2C18-MM enabled complete biodegradation of DCP in initially toxic DCP concentration ranges. Adsorption lowered the DCP concentration to a non-toxic level. Because the sorption process was reversible, DCP was desorbed when R. eutropha reduced the DCP concentration in the liquid phase by biodegradation. The whole amount of DCP—dissolved and initially adsorbed—was degraded as confirmed by oxygen consumption and cell concentration measurements. Organoclays can be very helpful tools in remediation when the exchanged amount of surfactant remains low. They even allow bioremediation under toxic circumstances, as was shown with 2C18-MM. [Copyright &y& Elsevier]

Total counts in soils are usually determined using fluorescent dyes, such as DAPI or Sybr green, due to fluorescence enhancement if they are bound to nucleic acids. Unfortunately, these commonly used dyes stain soil particles as well. Therefore, besides fluorescence enhancement, sufficient spectral differentiation is also required. We present a new procedure that overcomes the problems of visualising bacteria on surfaces in soil and avoids the separation of soil particles to a large extent. Spectral differentiation between bacteria and soil matrix is achieved by using Sytox green and a suboptimal excitation wavelength. Bacteria exhibit a bright green fluorescence, while soil particles fluoresce blue or red. Slight homogenisation and sedimentation of the sand and coarse silt that were too big for microscopic investigations were the only separation steps required. We compared the proposed Sytox green staining with Sybr green staining. The recovery of Sybr green-stained cells amounted to 38%, whereas in samples stained by Sytox green 81% of the spiked cells were counted. Sytox green can also be combined with fluorescence in situ hybridisation (FISH) using deep red dyes such as Cy5. [Copyright &y& Elsevier]

The removal of 2,4-dichlorophenol (DCP) using calcined and modified forms of hydrotalcite (HT) was studied. HT was calcined at 550 ° C for 3 h. The calcined form (HTC) was modified under argon atmosphere using sodium stearate in an amount equivalent to 100% of the theoretical anion exchange capacity of HT. The 3 forms of HT were subjected to X-ray diffraction analysis. It was determined that the peak with characteristic basal spacing d = 7.62 Å corresponding to interlayer carbonate anion disappeared in HTC and a peak with d = 32 Å confirming the adsorption of stearate anion appeared in organo-HT. Adsorption equilibria of DCP on HT and organo-HT were measured using batch equilibration. Adsorption behavior was modeled by the modified Freundlich equation. It was determined that HTC and organo-HT have maximum efficiencies corresponding to certain initial concentrations, i.e. 2.76 mmol/l for HTC and 3.68 mmol/l for organo-HT. At these concentrations, HTC and organo-HT can adsorb 61% and 17% of DCP, respectively. [ABSTRACT FROM AUTHOR]

• In Ap horizons of arable Luvisols, colloids control the aggregation of small soil microaggregates (<20 μm) in wet-dry cycles. • The presence of <450 nm colloids favored the formation of 1–40 μm soil microaggregates. • In absence of <1 μm colloids, >40 μm soil micro- and macroaggregates were preferentially formed. • The particle size is decisive for the aggregate formation under the current experimental condition. In the hierarchical model of soil aggregates, small soil microaggregates (small SMA; <20 μm) are often considered to be fundamental building units at the micron scale. Below which, soil colloids (<1 µm) have recently been proposed as binding agents of (micro)aggregates. However, the way in which soil colloids contribute to the formation and stability of soil micro- and macroaggregates remains largely unknown. For clarification, we evaluated potential impacts of the colloidal content, particularly the <450 nm colloids, on the aggregation of small SMA. Free water stable small SMA and <450 nm colloids were isolated from Ap-horizons of Stagnic Luvisols under different management (cropped and bare fallow). The size-resolved elemental composition of the <450 nm colloids was analyzed by asymmetric flow field-flow fractionation in combination with an inductively coupled plasma mass spectrometer and an organic carbon detector. To vary the colloidal content in small SMA, (1) suspensions containing different amounts of <450 nm colloids were added in small SMA, or (2) <1 µm colloids were removed from small SMA by centrifugation. In the maximum colloidal addition treatment, the mass ratios of added colloids to small SMA were 3.0 and 5.1 wt% for the cropped and bare fallow soil samples, respectively. Aggregation of small SMA with different colloidal amounts was performed in three successive wet-dry cycles. Afterwards, the size distribution of the resulting aggregates was measured by laser diffraction. Our results indicated that, in wet-dry cycles, colloids were important binding agents for the formation of SMA. Their presence, especially those <450 nm, was likely to support the formation of solid bridges during drying at particle contacts of 1–10 µm small SMA, favoring hereby SMA build-up in a relatively small size range of 1–40 µm. In contrast, the absence of <1 μm colloids in small SMA led to a preferential generation of relatively large aggregates in wet-dry cycles, i.e., typically with sizes >40 μm up to 1700 μm in maximum. Our study on aggregation in wet-dry cycles revealed that the colloidal content has a controlling effect on the size distribution of resulting aggregates by acting as a binding agent and provides hereby new insights into the evolvement of aggregate hierarchy in soils. [ABSTRACT FROM AUTHOR]

The concentration of nonionic surfactants like Triton X-100 (TX100) can influence the transport and fate of emerging contaminants (e.g. , carbon nanotubes) in porous media, but limited research has previously addressed this issue. This study investigates the co-transport of functionalized multi-walled carbon nanotubes (MWCNTs) and various concentrations of TX100 in saturated quartz sand (QS). Batch experiments and molecular dynamics simulations were conducted to investigate the interactions between TX100 and MWCNTs. Results indicated that the concentration ratio of MWCNTs and TX100 strongly influences the dispersion of MWCNTs and interaction forces between MWCNTs and QS during the transport. Breakthrough curves of MWCNTs and TX100 and retention profiles of MWCNTs were determined and simulated in column studies. MWCNTs strongly enhanced the retention of TX100 in QS due to the high affinity of TX100 for MWCNTs. Conversely, the concentration of TX100 had a non-monotonic impact on MWCNT retention. The maximum transport of MWCNTs in the QS occurred at an input concentration of TX100 that was lower than the critical micelle concentration. This suggests that the relative importance of factors influencing MWCNTs changed with TX100 sorption. Results from interaction energy calculations and modeling of competitive blocking indicate that the predictive ability of interaction energy calculations and colloid filtration theory may be lost because TX100 mainly altered intermolecular forces between the MWCNT and porous media. This study provides new insights into the co-transport of surfactants and MWCNTs in porous media, which can be useful for environmental applications and risk management. ga1 • The concentration of TX100 had a non-monotonic impact on MWCNT retention. • TX100 influences interaction forces between MWCNTs and QS. • The interactions between MWCNTs and TX100 were calculated by molecular dynamics simulations. • MWCNTs strongly inhibited TX100 transport in QS. • Both breakthrough curves and retention profiles were determined and simulated by HYDRUS 1D. [ABSTRACT FROM AUTHOR]

Light expanded clay aggregates (LECA) have been increasingly used as substrate material for constructed wetlands given their phosphate removal capacity, mechanical strength, hydraulic conductivity and their plant rooting and biofilm growth supporting structure. This review summarizes the current literature on LECA-based constructed wetlands. Removal performances for main wastewater parameters phosphate, nitrogen species, suspended solids and oxygen demand are tabulated. Both, physical and biological water purification processes in LECA wetlands are discussed. Additional emphasis is on design and layout of LECA wetlands for different types of wastewater, under different climatic conditions and to improve treatment performance in general. LECA life cycle considerations include sourcing, production energy demand, reuse and recycling options for spent wetland substrates, for example as soil amendment. Research and development opportunities were identified for structural and compositional LECA modification to obtain tailored substrates for the use in water treatment and specific treatment tasks. Beyond traditional wastewater contaminants the fate of a wider range of contaminants, including organic trace contaminants, needs to be investigated as high Fe, Al and Ca oxides content of LECA substrates provide adsorptive sites that may facilitate further biological interactions of compounds that are otherwise hard to degrade. • Gap/strength analysis of LECA as a substrate material in constructed wetlands. • High Fe, Al, and Ca oxides content underpin LECA pollutant removal and adsorbance. • LECA has indirect effects on parameters controlling biochemical efficiency of CWs. • Technical aspects and optimal design considerations for LECA in different CWs evaluated. • Saturated LECA potential use as soil amendment and fertilizer reviewed. [ABSTRACT FROM AUTHOR]

There is an intimate relationship between microorganisms and the formation and stability of soil microaggregates, realized by the immobilization and occlusion of microorganisms. Little is known about the initial aggregate formation phase and the role of microorganisms in this process under the impact of environmental changes such as wetting and drying. We investigated this initial aggregate formation process of montmorillonite and goethite in combination with two bacterial strains, Pseudomonas protegens strain CHA0 and Gordonia alkanivorans strain MoAcy 2, in the presence or absence of stress conditions in form of wetting and drying cycles for up to eight days. Montmorillonite and goethite formed microaggregates instantaneously, the size of these aggregates being enhanced in the presence of microorganisms, resulting in up to twofold larger aggregates. This increase in aggregate size was strain-dependent. However, the aggregates that developed during the first 48 h broke into smaller structures later on. A microscopic analysis of the microaggregates revealed that notably the larger microaggregates harbored bacteria and that microaggregates had a sheltering effect on living cells, especially when exposed to desiccation stress. Additionally, aggregate formation was analyzed in the presence of a Pseudomonas protegens mutant strain (CHA211) with increased production capability of extracellular polymeric substances (EPS). About fivefold higher survival rates of culturable cells were observed after desiccation for this EPS overproducing mutant strain in comparison to the wild-type. Our results hint at an aggregate formation process characterized by a rapid occlusion of mineral compounds, and, after the addition of microorganisms, the bacterial colonization of small microaggregates, leading to an increase in aggregate size. The further development of the aggregate size distribution varied depending on the presence of microbial taxa and was modulated by environmental conditions like desiccation events. • The presence of bacterial cells increases the size of microaggregates. • Desiccation stress induces the formation of larger microaggregates. • Microaggregates support bacterial survival upon desiccation stress. • Extracellular polymeric substances support bacterial survival upon desiccation stress. [ABSTRACT FROM AUTHOR]

Abstract The roles of graphene oxide (GO) particle geometry, GO surface orientation, surface roughness, and nanoscale chemical heterogeneity on interaction energies, aggregation, retention, and release of GO in porous media were not fully considered in previous studies. Consequently, mechanisms controlling the environmental fate of GO were incompletely or inaccurately quantified. To overcome this limitation, plate-plate interaction energies were modified to account for these factors and used in conjunction with a mathematical model to interpret the results of GO aggregation, retention, and release studies. Calculations revealed that these factors had a large influence on the predicted interaction energy parameters. Similar to previous literature, the secondary minimum was predicted to dominate on smooth, chemically homogeneous surfaces that were oriented parallel to each other, especially at higher ionic strength (IS). Conversely, shallow primary minimum interactions were sometimes predicted to occur on surfaces with nanoscale roughness and chemical heterogeneity due to adsorbed Ca2+ ions, especially when the GO particles were oriented perpendicular to the interacting surface. Experimental results were generally consistent with these predictions and indicated that the primary minimum played a major role in GO retention and the secondary minimum contributed to GO release with IS reduction. Cation exchange (Na+ replacing Ca2+) enhanced GO release with IS reduction when particles were initially deposited in the presence of Ca2+ ions. However, retained GO were always completely recovered into the excess deionized water when the sand pore structure was destroyed during excavation, and this indicates that primary minima were shallow and that the pore structure also played an important role in GO retention. Further evidence for the role of pore structure on GO retention was obtained by conducting experiments in finer textured sand and at higher input concentrations that induced greater aggregation. In both cases, greater GO retention occurred, and retention profiles became more hyperexponential in shape. Graphical abstract Unlabelled Image Highlights • GO interaction depended on GO geometry and orientation, roughness, and adsorbed Ca2+. • GO interacted in a shallow primary minimum under low ionic strength conditions. • Level arms from roughness and grain-grain contacts were important for GO retention. • A mathematical model interpreted the aggregation, retention, and release of GO. [ABSTRACT FROM AUTHOR]

• Fan ages in the Atacama dated to ∼13.6 ka and ∼56.4 ka. • The younger fan with rough surfaces was dominated by nano and fine colloids. • The older fan showed smooth surface but heterogenous size distribution of colloids. • Soil depth distributions pointed to colloidal transport in the younger fan. • Plants enhanced accumulation of nanocolloids with elevated OC and Ca content. As located in one of the oldest and driest deserts on Earth, soils in the Atacama Desert are greatly affected by atmospheric dust deposited on soil surface and the related fate of water-dispersible colloids (WDCs, <300 nm). We hypothesize that formation and content of these WDCs change with topography and age of natural soils. To highlight the processes involved, we investigated a mid-sized and gently (∼5°) sloping alluvial fan system of multi-phase evolution at 1480 m a.s.l. in the Paposo region of the hyper-arid Atacama Desert, which is considered typical for this part of the Coastal Cordillera. Sampling was done along a topographic transect in 11 pits, and assessed the distribution and composition of WDCs by means of asymmetric flow field-flow fractionation (AF4). The younger fan section (optically stimulated luminescence (OSL)-age of ∼13.6 ka) exhibited a pronounced surface roughness and steep slopes. Here, WDCs from the top soils (0–1 cm) free of plants contained nearly 54 ± 7% of medium-sized colloids (MCs, 210–300 nm) with a dominance of Si and Al. The elevated concentrations of fine colloids (FC, 24–210 nm) and particularly nanocolloids (NCs, 0.6–24 nm) was shown in levelled surface soils near shrubs with predominance of organic carbon (OC) and Ca. With higher collodial OC and Ca content in soils near shrubs, more WDC-P was formed concomitantly through increased OC-Ca-P associations. Larger variations in total WDC content were detected in the surface soils of the older fan section, which was dated to ∼56.4 ka. Here, the peaking NC had almost disappeared and thus MC dominated, probably reflecting re-aggregation and wind erosion over longer periods of time across a relatively smooth land surface. The WDCs and WDC-P peaked at 5–10 cm depth in the older fan section, as here a solid mineral/salt layer was present, while in the younger fan section the WDCs were more likely to be translocated from 'permeable' surface into deeper layers, likely reflecting leaching with occasional heavy rainfall. Overall, forms and distribution of WDCs depended on both topographic position and sediment age, thus making colloids as unique tracers of soil development processes during myriad or more years. [ABSTRACT FROM AUTHOR]

As soil microaggregates (<250 μm, SMA) usually withstand long-term tillage, we hypothesized that i) elevated clay contents in arable soil support aggregation already at microaggregate level, leading to ii) increasing organic carbon (SOC) enrichment in smaller SMA size fractions. To test these hypotheses we sampled the topsoil (5–20 cm) of Luvisols with a long history of agricultural management at the Scheyern experiment station (Germany) in quintuplicates from each of five subsites with different clay contents (19–34%). The field-fresh topsoil was fractionated into macroaggregates (8000–250 μm), large SMA (250–20 μm), and small SMA (<20 μm) and the mass distribution was recorded. In addition, the water stable macroaggregates (>250 μm) were dispersed ultrasonically to study occluded SMA and single building units. Finally, we analyzed the size distribution of the small SMA by laser diffraction analysis. The total mass distribution of free and occluded SMA grouped soils into those with small (19, 22, and 24%) and large (32 and 34%) clay contents. The finer textured soils exhibited larger portions of occluded SMA, with a gamma size distribution of small SMA peaking at 6 μm. Yet the occluded small SMA in the finer textured soils showed an additional enrichment of colloids <1 μm. The SOC was indeed enriched in finer fractions, but more in the small SMA of the coarse textured sites than in the finer textured ones, whereas the opposite was true for the large SMA. We conclude, therefore, that elevated contents of clay-sized particles promote SMA formation and stabilization, therewith shifting SOC enrichment from small to larger SMA. [ABSTRACT FROM AUTHOR]

The leaching of P from the upper 20 cm of forest topsoils influences nutrient (re-)cycling and the redistribution of available phosphate and organic P forms. However, the effective leaching of colloids and associated P forms from forest topsoils was so far sparsely investigated. We demonstrated through irrigation experiments with undisturbed mesocosm soil columns, that significant proportions of P leached from acidic forest topsoils were associated with natural colloids. These colloids had a maximum size of 400 nm. By means of Field-flow fractionation the leached soil colloids could be separated into three size fractions. The size and composition was comparable to colloids present in acidic forest streams known from literature. The composition of leached colloids of the three size classes was dominated by organic carbon. Furthermore, these colloids contained large concentrations of P which amounted between 12 and 91% of the totally leached P depending on the type of the forest soil. The fraction of other elements leached with colloids ranged between 1% and 25% (Fe: 1–25%; C org : 3–17%; Al: <4%; Si, Ca, Mn: all <2%). The proportion of colloid–associated P decreased with increasing total P leaching. Leaching of total and colloid-associated P from the forest surface soil did not increase with increasing bulk soil P concentrations and were also not related to tree species. The present study highlighted that colloid-facilitated P leaching can be of higher relevance for the P leaching from forest surface soils than dissolved P and should not be neglected in soil water flux studies. [ABSTRACT FROM AUTHOR]

There is a broad range of carbon based engineered particles including polymer latex particles and carbon black. Also in environmental systems particulate carbon such as humic acids and soot or coal (the latter two summarized as black carbon) is of great importance and is involved in nutrient storage and (re)cycling. Therefore, detailed characterisation of the size distribution and elemental composition of such particles is required to understand the material properties and their environmental relevance. Field flow fractionation (FFF) online with inductively coupled plasma mass spectrometry (ICP-MS) is routinely applied for the characterisation of metal containing particles. However, the far majority of FFF studies relies on UV detection for organic carbon while elemental detection of carbon has hardly been used. Our previous work demonstrated the capability of FFF-ICP-MS for the determination of carbon in fine particulate matter, focusing on humic acid in water samples. The current work investigates the feasibility of carbon detection and quantification in larger particles with sizes up to about 750 nm. For this purpose, latex particle size standards of 21 nm, 100 nm, 250 nm and 740 nm were analysed as well as extracts of charcoal spiked soil. Elemental analysis using combustion techniques was employed as reference for the total carbon content of the samples to establish a mass balance. Recoveries for FFF separation of latex particle standards were in the range from 69% to 83% and in the range from 78% to 104% in flow injection mode. Carbon mass balance calculated from FFF fractionation, ultrafiltration and total content for the extracts from soil and charcoal spiked soil achieved 76% to 105%. Variation of the sampling depth was investigated to check if increased dwell time of the particles in the plasma affects the carbon ionisation and quantification. No significant change of carbon recoveries was observed, yet the signal to noise ratio improved 3-fold. This study provides a method for the analyses of carbon containing particles via FFF-ICP-MS, which allows for the first time the simultaneous measurement of carbon and other nutrients and is hence more timesaving than other methods. [ABSTRACT FROM AUTHOR]

Background and aims: Nanoparticles and colloids affect the mobilisation and availability of phosphorus for plants and microorganisms in soils. We aimed to give a description of colloid sizes and composition from forest soil profiles and to evaluate the size-related quality of colloids for P fixation.Methods: We investigated the size-dependent elemental composition and the P content of water-dispersible colloids (WDC) isolated from five German (beech-dominated) forest soil profiles of varying bulk soil P content by field-flow fractionation (FFF) coupled to various detectors.Results: Three size fractions of WDC were separated: (i) nanoparticles <25 nm (NP) rich in Corg, (ii) fine colloids (25 nm-240 nm; FC) composed mainly of Corg, Fe and Al, probably as associations of Fe- and Al- (hydr)oxides and organic matter, and (iii) medium-sized colloids (240 nm-500 nm; MC), rich in Fe, Al and Si, indicating the presence of phyllosilicates. The P concentration in the overall WDC was up to 16 times higher compared to the bulk soil. The NP content decreased with increasing soil depth while the FC and MC showed a local maximum in the mineral topsoil due to soil acidification, although variant distributions in the subsoil were observed. NP were of great relevance for P binding in the organic surface layers, whereas FC- and MC-associated P dominated in the Ah horizon.Conclusion: The nanoparticles and colloids appeared to be of high relevance as P carriers in the forest surface soils studied, regardless of the bulk soil P content. [ABSTRACT FROM AUTHOR]

Abstract: All soils harbor microaggregates, i.e., compound soil structures smaller than 250 µm. These microaggregates are composed of diverse mineral, organic and biotic materials that are bound together during pedogenesis by various physical, chemical and biological processes. Consequently, microaggregates can withstand strong mechanical and physicochemical stresses and survive slaking in water, allowing them to persist in soils for several decades. Together with the physiochemical heterogeneity of their surfaces, the three‐dimensional structure of microaggregates provides a large variety of ecological niches that contribute to the vast biological diversity found in soils. As reported for larger aggregate units, microaggregates are composed of smaller building units that become more complex with increasing size. In this context, organo‐mineral associations can be considered structural units of soil aggregates and as nanoparticulate fractions of the microaggregates themselves. The mineral phases considered to be the most important as microaggregate forming materials are the clay minerals and Fe‐ and Al‐(hydr)oxides. Within microaggregates, minerals are bound together primarily by physicochemical and chemical interactions involving cementing and gluing agents. The former comprise, among others, carbonates and the short‐range ordered phases of Fe, Mn, and Al. The latter comprise organic materials of diverse origin and probably involve macromolecules and macromolecular mixtures. Work on microaggregate structure and development has largely focused on organic matter stability and turnover. However, little is known concerning the role microaggregates play in the fate of elements like Si, Fe, Al, P, and S. More recently, the role of microaggregates in the formation of microhabitats and the biogeography and diversity of microbial communities has been investigated. Little is known regarding how microaggregates and their properties change in time, which strongly limits our understanding of micro‐scale soil structure dynamics. Similarly, only limited information is available on the mechanical stability of microaggregates, while essentially nothing is known about the flow and transport of fluids and solutes within the micro‐ and nanoporous microaggregate systems. Any quantitative approaches being developed for the modeling of formation, structure and properties of microaggregates are, therefore, in their infancy. We respond to the growing awareness of the importance of microaggregates for the structure, properties and functions of soils by reviewing what is currently known about the formation, composition and turnover of microaggregates. We aim to provide a better understanding of their role in soil function, and to present the major unknowns in current microaggregate research. We propose a harmonized concept for aggregates in soils that explicitly considers the structure and build‐up of microaggregates and the role of organo‐mineral associations. We call for experiments, studies and modeling endeavors that will link information on aggregate forming materials with their functional properties across a range of scales in order to better understand microaggregate formation and turnover. Finally, we hope to inspire a novel cohort of soil scientists that they might focus their research on improving our understanding of the role of microaggregates within the system of aggregates and so help to develop a unified and quantitative concept of aggregation processes in soils. [ABSTRACT FROM AUTHOR]

The release and stability of soil water-dispersible colloids (WDC) in the soil structure are critical for colloid-facilitated soil organic carbon sequestration and contaminants transport. In this study, the potential effects of temperature and associated organic carbon (OC) on the release of WDCs in three silt loam topsoils with the same clay content (~ 20%) under different land uses were investigated. A soil fractionation method was used for simulating the release of colloids from the soil under environmental conditions where mobilization and sedimentation processes occur sequentially. The surface loading of OC has been characterized by the analysis of organic carbon content of WDC with the measurements of the specific surface area (SSA). The effects of fractionation temperature on colloidal properties (e.g., particle size and zeta potential) were systematically investigated and the aggregation kinetics of WDC in salt electrolyte influenced by temperature was assessed by dynamic light scattering (DLS). Experimental results demonstrated that the amount of extracted WDC from three soils decreased when the fractionation temperature increased. A more rapid sedimentation of WDC at higher temperatures outweighed the effect of temperature on WDC mobilization from bulk soil in the shaking step. The sedimentation of WDC at various temperatures indicated that the temperature dependence of the water viscosity ( η ) was a dominate parameter and caused lower efficiency of WDC mass gained at higher temperature according to the Stoke's law. After introducing the factor of η 7 °C / η T , the temperature effect only on WDC mobilization during shaking step could be described and the whole fractionation process could be successfully timely determined along the two shaking and sedimentation steps. Activation energies ( E a ) of about 10 kJ mol − 1 could be now calculated for the WDC mobilization processes from the three topsoils. The associated organic carbon contents of WDC (WDC(OC)) and the mineral surface of WDC blocked by organic carbon ( SSA OC - block ) after various shaking temperatures and shaking time were further determined in order to examine the WDC(OC) effect on the release of WDC from soil matrix. The results demonstrated that the escape of the mobile clay fraction ( F ) from soil at short shaking times is favored by the presence of effective surface loading by an OC layer ( SSA OC - block ), which is known to stabilize its colloidal state through electrosteric effects. The WDC(OC) surface concentration has been also used to estimate the clay-associated OC distribution in the three topsoils. In Ca 2 + solution, an increase of temperature favors the colloidal stability of WDC as measured from the shift of critical coagulation concentration ( CCC ) to higher concentrations of Ca 2 + . In total, the results from this study revealed that temperature and WDC(OC) distribution are critical parameters when considering soil WDC release and stability in natural bulk soils. [ABSTRACT FROM AUTHOR]

Unsaturated column experiments were conducted with an undisturbed loamy sand soil to investigate the influence of flow interruption (FI) and ionic strength (IS) on the transport and retention of surfactant-stabilized silver nanoparticles (AgNP) and the results were compared to those obtained under continuous flow conditions. AgNP concentrations for breakthrough curves (BTCs) and retention profiles (RPs) were analyzed by ICP-MS. Experimental results were simulated by the numerical code HP1 (Hydrus-PhreeqC) with the DLVO theory, extended colloid filtration theory and colloid release model. BTCs of AgNP showed a dramatic drop after FI compared to continuous flow conditions. Evaporation increased due to FI, resulting in increased electrical conductivity of the soil solution, which led to a totally reduced mobility of AgNP. A reduction of IS after FI enhanced AgNP mobility slightly. Here the strongly increased Al and Fe concentration in the effluent suggested that soil colloids facilitated the release of AgNP (cotransport). The numerical model reproduced the measured AgNP BTCs and indicated that attachment to the air-water interface (AWI) occurring during FI was the key process for AgNP retention. [ABSTRACT FROM AUTHOR]

Saturated soil column experiments were conducted to investigate the transport, retention, and release behavior of a low concentration (1 mg L −1 ) of functionalized 14 C-labeled multi-walled carbon nanotubes (MWCNTs) in a natural soil under various solution chemistries. Breakthrough curves (BTCs) for MWCNTS exhibited greater amounts of retardation and retention with increasing solution ionic strength (IS) or in the presence of Ca 2+ in comparison to K + , and retention profiles (RPs) for MWCNTs were hyper-exponential in shape. These BTCs and RPs were well described using the advection-dispersion equation with a term for time- and depth-dependent retention. Fitted values of the retention rate coefficient and the maximum retained concentration of MWCNTs were higher with increasing IS and in the presence of Ca 2+ in comparison to K + . Significant amounts of MWCNT and soil colloid release was observed with a reduction of IS due to expansion of the electrical double layer, especially following cation exchange (when K + displaced Ca 2+ ) that reduced the zeta potential of MWCNTs and the soil. Analysis of MWCNT concentrations in different soil size fractions revealed that >23.6% of the retained MWCNT mass was associated with water-dispersible colloids (WDCs), even though this fraction was only a minor portion of the total soil mass (2.38%). More MWCNTs were retained on the WDC fraction in the presence of Ca 2+ than K + . These findings indicated that some of the released MWCNTs by IS reduction and cation exchange were associated with the released clay fraction, and suggests the potential for facilitated transport of MWCNT by WDCs. [ABSTRACT FROM AUTHOR]

• P increased in all colloidal fractions with long-term cultivation management. • The nanoparticle fraction turned into a complex of OC-Ca-P after cropping management. • Cropping management generates more fine colloidal clays, oxides and associated P. Soil phosphorus (P) is usually hardly present in soluble forms as most of it is strongly bound to minerals. Therefore, transformations of soil colloidal P can play a key role in enhancing soil fertility. Here, we examined water extracts from a chronosequence of soils with 2000 years of paddy rice and 700 years of non-paddy cropping, and fractionated them into <1200 nm, <450 nm, and <3 kDa size fractions using sequential ultrafiltration. Asymmetric-flow field-flow fractionation (AF4) coupled to an organic carbon detector (OCD) and inductively coupled plasma mass spectrometry (ICP-MS) was used for organic carbon and elemental screening in the 3 kDa-450 nm colloidal size range. We found that P increased in all colloidal fractions both with long-term paddy rice and non-paddy managements. Furthermore, P in soil colloids of 3 kDa-450 nm size, as fractionated by AF4, peaked in three size ranges: nanoparticles (NP, ∼3 kDa-20 nm), fine colloids (FC, ∼20–225 nm), and medium-sized colloids (MC, ∼225–450 nm). The NP fraction originally contained mainly P and Ca for tidal wetland (TW), but turned into a complex of OC-Ca-P colloidal forms immediately after onset of arable management, with little temporal change thereafter. Fine colloidal P (FC-P) was detected only after > 50 years for the non-paddy and > 100 years under paddy management, associated with oxides, organic matter and fine clay fragments in the paddy soils and additionally Ca-bound P in the non-paddy ones, respectively. Increasing portions of medium-sized colloidal P appeared after 50 years paddy and non-paddy management, though not exceeding the concentrations of FC-P and with little changes during prolonged arable land use. Overall, after initial formation of FC-P during the first 50–100 years of management, longer term dynamics of colloidal P in these arable soils was fairly independent of paddy or non-paddy managements, but remained closely coupled to the increased presence or generation of fine colloidal clays, oxides and the associated P, thus potentially linking P fertility largely to the dynamics of fine colloids. [ABSTRACT FROM AUTHOR]

Woody encroachment strengthens the retention of OC and P by soil colloids, consequently increasing overall C and P pools in savanna soils. [Display omitted] • P was associated with Ca in < 30 nm colloids, and with OC and Ca in 30–500 nm colloids. • Woody invasion increased colloidal OC and P and their proportions in < 30 nm colloids. • Higher proportions of orthophosphate and -diesters in colloids than bulk soil. • Heavy grazing and fire potentially accelerated the risk of colloidal P loss. • Vegetation type had larger effect on soil colloids than grazing or fire. Soil colloids (diameter < 1000 nm) are comprised mainly of clay minerals and organic matter, and play major roles in determining ion exchange capacity and in regulating key biogeochemical processes. Consequently, it is important to understand how soil colloids and their functions are influenced by land cover and anthropogenic disturbances. In grasslands, savannas, and other dryland ecosystems across the globe, woody plants are encroaching due to livestock grazing, fire suppression, elevated CO 2 concentrations, and climate change. These major land cover changes could influence soil colloidal properties, with implications for soil C, N, and P cycles. We assessed how woody encroachment, livestock grazing, and fire interact to influence soil colloidal properties in a juniper-oak savanna. Surface soils (0–10 cm) from the southern Great Plains (Texas, USA) were collected from long-term treatments differing in grazing intensity (none, moderate, and heavy) and fire history. Within each treatment, soil samples were taken under grass, juniper, and oak canopies. Water dispersible soil colloids (WDC, d < 500 nm) were isolated and analyzed by asymmetric flow field-flow fractionation and their P species by liquid-state 31P-nuclear magnetic resonance spectroscopy (31P NMR). Soil beneath oak and juniper canopies had smaller WDC and elevated colloidal organic carbon (OC) and P concentrations, especially in nanocolloid (<30 nm) and fine colloid (30–160 nm) size fractions. Woody encroachment enriched Ca, Fe, Al, Si and Mg in WDC in the ungrazed control, but not in any of the other grazed or burned areas. Colloidal soil P mainly occurred as orthophosphate and orthophosphate diesters, and was present as OC-Ca-P complexes in fine and medium colloid fractions (30–500 nm), while P in the nanocolloid fraction (<30 nm) was in direct association with Ca. Moderate grazing did not affect the retention of colloidal P, while heavy grazing potentially increased the loss risk of colloidal P. Fire accelerated soil P loss from colloid fractions only in woody areas. Our findings highlight that woody encroachment strengthens the retention of OC and P by soil colloids, consequently increasing overall C and P pools in savanna soils. [ABSTRACT FROM AUTHOR]

Transport and retention behavior of multi-walled carbon nanotubes (MWCNTs) was studied in mixtures of negatively charged quartz sand (QS) and positively charged goethite-coated sand (GQS) to assess the role of chemical heterogeneity. The linear equilibrium sorption model provided a good description of batch results, and the distribution coefficients (KD) drastically increased with the GQS fraction that was electrostatically favorable for retention. Similarly, retention of MWCNTs increased with the GQS fraction in packed column experiments. However, calculated values of KD on GQS were around 2 orders of magnitude smaller in batch than packed column experiments due to differences in lever arms associated with hydrodynamic and adhesive torques at microscopic roughness locations. Furthermore, the fraction of the sand surface area that was favorable for retention (Sf) was much smaller than the GQS fraction because nanoscale roughness produced shallow interactions that were susceptible to removal. These observations indicate that only a minor fraction of the GQS was favorable for MWCNT retention. These same observations held for several different sand sizes. Column breakthrough curves were always well described using an advective-dispersive transport model that included retention and blocking. However, depth-dependent retention also needed to be included to accurately describe the retention profile when the GQS fraction was small. Results from this research indicate that roughness primarily controlled the retention of MWCNTs, although goethite surfaces played an important secondary role. [ABSTRACT FROM AUTHOR]

• Chronological sequence of aggregate formation processes. • Organic gluing agents initiate and accelerate aggregation process. • Minerals stabilize aggregates in the longer term. • Root-mediated processes further stabilize macroaggregates against ultrasonic dispersion. Microaggregates (<250 µm) are key structural subunits of soils. However, their formation processes, rates, and transformation with time are poorly understood. We took advantage of multiple isotope labelling of potential organic gluing agents and inorganic building units to unravel their role in soil aggregation processes being initiated with and without plant growth. We added 13C-labelled extracellular polymeric substances (EPS), 15N-labelled bacteria, 57Fe-labelled goethite, and 29Si-labelled montmorillonite to fine soil <250 µm of an Ap horizon from a Stagnic Luvisol, which was planted with Festuca heteromalla or kept bare in a climate chamber. Samples were taken after 4, 12, and 30 weeks, and separated into free (f) and occluded (o) microaggregates of different sizes (<20 µm, 53–20 µm, 250–53 µm), and in stable macroaggregates (>250 µm) that resisted 60 J mL−1 ultrasonic dispersion. Afterwards, we assessed the C, N, Fe, and Si stable isotope composition in each size fraction. After four weeks we found a rapid build-up of stable macroaggregates comprising almost 50 % of soil mass in the treatment with plants and respective soil rooting, but only 5 % when plants were absent. The formation of these stable macroaggregates proceeded with time. Soil organic carbon (SOC) contents were elevated by 15 % in the large macroaggregates induced by plant growth. However, the recovery of EPS-derived 13C was below 20 % after 4 weeks, indicating rapid turnover in treatments both with and without plants. The remaining EPS-derived C was mainly found in macroaggregates when plants were present and in the occluded small microaggregates (<20 µm) when plants were absent. The excess of bacterial 15N closely followed the pattern of EPS-derived 13C (R2 = 0.72). In contrast to the organic gluing agents, the goethite-57Fe and montmorillonite-29Si were relatively equally distributed across all size fractions. Overall, microaggregates were formed within weeks. Roots enforced this process by stabilizing microaggregates within stable macroaggregates. As time proceeded the labelled organic components decomposed, while the labelled secondary oxides and clay minerals increasingly contributed to aggregate stabilization and turnover at the scale of months and beyond. Consequently, the well-known hierarchical organization of aggregation follows a clear chronological sequence of stabilization and turnover processes. [ABSTRACT FROM AUTHOR]

• Chronological sequence of aggregate formation processes. • Organic gluing agents initiate and accelerate aggregation process. • Minerals stabilize aggregates in the longer term. • Root-mediated processes further stabilize macroaggregates against ultrasonic dispersion. Microaggregates (<250 µm) are key structural subunits of soils. However, their formation processes, rates, and transformation with time are poorly understood. We took advantage of multiple isotope labelling of potential organic gluing agents and inorganic building units to unravel their role in soil aggregation processes being initiated with and without plant growth. We added 13C-labelled extracellular polymeric substances (EPS), 15N-labelled bacteria, 57Fe-labelled goethite, and 29Si-labelled montmorillonite to fine soil <250 µm of an Ap horizon from a Stagnic Luvisol, which was planted with Festuca heteromalla or kept bare in a climate chamber. Samples were taken after 4, 12, and 30 weeks, and separated into free (f) and occluded (o) microaggregates of different sizes (<20 µm, 53–20 µm, 250–53 µm), and in stable macroaggregates (>250 µm) that resisted 60 J mL−1 ultrasonic dispersion. Afterwards, we assessed the C, N, Fe, and Si stable isotope composition in each size fraction. After four weeks we found a rapid build-up of stable macroaggregates comprising almost 50 % of soil mass in the treatment with plants and respective soil rooting, but only 5 % when plants were absent. The formation of these stable macroaggregates proceeded with time. Soil organic carbon (SOC) contents were elevated by 15 % in the large macroaggregates induced by plant growth. However, the recovery of EPS-derived 13C was below 20 % after 4 weeks, indicating rapid turnover in treatments both with and without plants. The remaining EPS-derived C was mainly found in macroaggregates when plants were present and in the occluded small microaggregates (<20 µm) when plants were absent. The excess of bacterial 15N closely followed the pattern of EPS-derived 13C (R2 = 0.72). In contrast to the organic gluing agents, the goethite-57Fe and montmorillonite-29Si were relatively equally distributed across all size fractions. Overall, microaggregates were formed within weeks. Roots enforced this process by stabilizing microaggregates within stable macroaggregates. As time proceeded the labelled organic components decomposed, while the labelled secondary oxides and clay minerals increasingly contributed to aggregate stabilization and turnover at the scale of months and beyond. Consequently, the well-known hierarchical organization of aggregation follows a clear chronological sequence of stabilization and turnover processes. [ABSTRACT FROM AUTHOR]

Reliable and efficient analytical techniques are required for quantitative size-resolved carbon determination of nanoparticles and colloids in complex sample matrices due to the key role of carbon in biological and environmental processes. Field flow fractionation (FFF) online with inductively coupled plasma mass spectrometry (ICP-MS) is a powerful technique for identification and quantification of particle bound metals, but has not been applied for quantitative determination of particulate carbon, yet, due to several challenges. Therefore, our study explores the potential of online particulate carbon detection by ICP-MS to overcome limitations of previously used UV detection or offline total organic carbon measurements. A novel organic carbon detector (OCD) was used as independent sensitive carbon detector to validate the ICP-MS results. Basic validation of organic carbon detection by offline quadrupole and sector-field ICP-MS was performed for fresh water samples using OCD as reference achieving recoveries of 107 ± 16% with Q-ICP-MS and 122 ± 22% with SF-ICP-MS. Limits of detection were 0.6 mg L−1 for Q-ICP-MS, 0.3 mg L−1 for SF-ICP-MS and 0.04 mg L−1 for OCD. The main focus was on comparison of FFF-ICP-MS and FFF-OCD for quantification of particulate carbon in fresh water samples, soil extracts as well as in bovine serum albumin (BSA) as candidate reference standard. Recoveries obtained by FFF-Q-ICP-MS with a flow-injection calibration approach were in a range from 90 to 113% for replicate analyses of fresh water samples compared to FFF-OCD and from 87 to 107% with an alternative post-channel calibration strategy. [ABSTRACT FROM AUTHOR]

Phosphorus (P) is essential for sustainable forest growth, yet the impact of anthropogenic impacts on P leaching losses from forest soils is hardly known. We conducted an irrigation experiment with 128 mesocosms from three forest sites representing a gradient of resin extractable P of the A-horizon. On each site we selected a Fagus sylvatica and a Picea abies managed subsite. We simulated ambient rain (AR), anthropogenic nitrogen input (NI) of 100 kg (ha · a)−1 and forest liming (FL) with a dolomite input of 0.3 Mg (ha · a)−1. Soil solution was extracted from the organic layer, 10 cm depth and 20 cm depth of the mesocosms, and analyzed for molybdate reactive phosphorus (MRP) and molybdate unreactive phosphorus (MUP). Additionally, we separated colloids from the soil solution using Asymmetric Field Flow Fractionation for assessing the colloidal fraction of total element concentrations. NI increased MRP and MUP concentrations for all plots with one exception, while FL decreased MRP and MUP with the exception of another plot. While the irrigation treatments had little impact on the P-richest site, MRP and MUP concentrations changed strongly at the poorer sites. The colloidal fraction of P in the soil solution equaled 38-47% of the total P load. Nitrogen input and liming also affected the Fe, Al, Ca, and Corg contents of the colloidal fraction. [ABSTRACT FROM AUTHOR]

Understanding and quantification of phosphorus (P) fluxes are key requirements for predictions of future forest ecosystems changes as well as for transferring lessons learned from natural ecosystems to croplands and plantations. This review summarizes and evaluates the recent knowledge on mechanisms, magnitude, and relevance by which dissolved and colloidal inorganic and organic P forms can be translocated within or exported from forest ecosystems. Attention is paid to hydrological pathways of P losses at the soil profile and landscape scales, and the subsequent influence of P on aquatic ecosystems. New (unpublished) data from the German Priority Program 1685 ' Ecosystem Nutrition: Forest Strategies for limited Phosphorus Resources' were added to provide up-to-date flux-based information. Nitrogen (N) additions increase the release of water-transportable P forms. Most P found in percolates and pore waters belongs to the so-called dissolved organic P (DOP) fractions, rich in orthophosphate-monoesters and also containing some orthophosphate-diesters. Total solution P concentrations range from ca. 1 to 400 µg P L−1, with large variations among forest stands. Recent sophisticated analyses revealed that large portions of the DOP in forest stream water can comprise natural nanoparticles and fine colloids which under extreme conditions may account for 40-100% of the P losses. Their translocation within preferential flow passes may be rapid, mediated by storm events. The potential total P loss through leaching into subsoils and with streams was found to be less than 50 mg P m−2 a−1, suggesting effects on ecosystems at centennial to millennium scale. All current data are based on selected snapshots only. Quantitative measurements of P fluxes in temperate forest systems are nearly absent in the literature, probably due to main research focus on the C and N cycles. Therefore, we lack complete ecosystem-based assessments of dissolved and colloidal P fluxes within and from temperate forest systems. [ABSTRACT FROM AUTHOR]

Nanoparticles and colloids affect the storage and hence the availability of P in forest ecosystems. We investigated the fine colloids present in forest soils and their association with inorganic and organic P. To differentiate between the different P forms, we performed liquid-state 31P-nucelar magnetic resonance (31P-NMR) measurements on forest bulk soil extracts, on colloid extracts and on the electrolyte phase of their soil suspensions. The 31P-NMR spectra indicated that soil nanoparticles and colloids were more enriched with organic than with inorganic P forms compared to the electrolyte phase. The P concentration was enriched in the colloidal fraction in comparison to the bulk soil and the phosphate diesters were more dominant in the colloidal fraction when compared to the bulk soil. The colloidal P-diester to P-monoester ratios were 2 to 3 times higher in the colloidal fraction than in the bulk soil. In contrast, relatively large percentages of inorganic P were found in the electrolyte phase. [ABSTRACT FROM AUTHOR]

The surface area and pore structure of easily dispersed soil particles < 2 μm in size (water-dispersible colloids, WDCs) are important for carbon sequestration and transport in soil, two processes which are essential for the terrestrial carbon cycling. In this work, we determine the effects of dithionite–citrate–bicarbonate (DCB) extractable metal oxides, and oxalate extractable metal oxides on the specific surface area (SSA) and pore structure of WDCs from silt loam topsoils of three TERENO test sites with a similar clay content (20%) in Germany (arable (Selhausen), grassland (Rollesbroich) and forest (Wuestebach) soils). The N 2 gas-adsorption (− 196 °C), small-angle X-ray scattering (SAXS), dynamic light scattering (DLS) and microelectrophoretic (ME) methods were used and compared. Results show that 1) the SSA of the WDCs from Selhausen, Rollesbroich, and Wuestebach decreased more after DCB treatment (27%, 35%, and 44%) than after oxalate treatment (5%, 14%, and 22%). DCB removed metal oxide nanoparticles from WDCs were found to have diameters ( d p ) ranging from 4 nm to 8 nm and the surface loading ratios on the surface of aluminosilicate residues in WDCs were estimated to be 11% to 22% for three soils where the highest value was found in the acidic forest soil. 2) Pore sizes in the mesopore range (2 nm to 50 nm) were analyzed in the WDC fractions. The results were discussed in terms of accessible open pores for the pristine WDCs and WDC samples from which metal oxide nanoparticles and organic carbon (OC) had been removed. The lower average pore radius ( R p ) measured by the N 2 gas-adsorption method based on the total volume ( V t ) to SSA ratio variations in WDCs without metal oxides compared to WDC with metal oxides indicated a contraction of the porous structure of WDCs due to the presence of metal oxide nanoparticles. The pore size distribution (PSD) analysis showed a sensitive contribution of metal oxide nanoparticles in the low range of pore sizes (< 25 nm) of WDCs. In SAXS measurements, higher surface fractal dimensions ( D s ) were observed in WDCs before the metal oxide's removal, which supports a roughness increase of the interfaces in the presence of nanoparticles. The colloidal characterization of WDCs by the DLS and ME methods shows, at a μm scale, the role of positively charged metal oxide nanoparticles in forming WDCs with a more compact structure by decreasing the particle size ( d z ) and the negative zeta potential ( ζ ). 3) The comparison of R p , k , d z and d p results between different soils also indicates the dependence on the clay mineralogy of WDCs so that the heterocoagulation between kaolinite and illite (clay minerals of different aspect ratios) increases the size of soil mesopores (Rollesbroich). In conclusion, the results of this study clearly show that the combination of the N 2 gas-adsorption, SAXS, DLS and ME methods allows the characterization of soil porosity in the nanometer range where metal oxide nanoparticles contribute to a more compact structure of WDC. [ABSTRACT FROM AUTHOR]

Landfills are used as the primary means for the disposal of municipal solid waste in Canada. In the present study, polybrominated diphenyl ethers (PBDEs) and other flame retardants (FRs) were determined in fresh European starling (Sturnus vulgaris) eggs collected in 2009, 2010, and 2011 from nest boxes established within, adjacent to, and 10 and 40 km distant to five major urban centers across Canada, i.e., Vancouver, British Columbia (BC); Calgary, Alberta (AB); Hamilton, Ontario (ON); Montréal, Québec (QC); and Halifax, Nova Scotia (NS). Nest boxes were located in several land use types: urban industrial areas (districts of industrial activity within city limits), landfill sites (adjacent to cities), and rural (agricultural) sites located 10 and 40 km distant from the major urban centers, as well as a national reference site. Of the 14 PBDE congeners and 16 non-PBDE FR substances determined in the starling eggs, BDE-17, -28, -47, -49, -66, -85, -99, -100, -138, -153, -154, -183, and -209, Dechlorane Plus isomers (anti and syn), and bis(2-ethylhexyl)-3,4,5,6-tetrabromophthalate (BEHTBP) were most frequently quantifiable. The data revealed orders of magnitude greater PBDE concentrations in eggs from starlings nesting in landfill sites (median: 28–280 ng/g wet weight) relative to those from urban industrial and rural environments. However, the percent fractional composition of the PBDE congener patterns did not vary significantly between the types of land uses or between years. Additionally, the median ∑PBDE concentration in eggs from landfill sites and the human population density of the metropolitan region that the landfill serves were highly correlated (r2 = 0.998, p < 0.001). As the first transcontinental effort in assessing FR contamination in Canadian terrestrial ecosystems, the present study strongly suggest that landfills are an important FR source to starlings nesting nearby and that other terrestrial organisms could also be similarly exposed. [ABSTRACT FROM AUTHOR]

Abstract: Saturated sand-packed column experiments were conducted to investigate the influence of physicochemical factors on the transport and retention of surfactant stabilized silver nanoparticles (AgNPs). The normalized concentration in breakthrough curves (BTCs) of AgNPs increased with a decrease in solution ionic strength (IS), and an increase in water velocity, sand grain size, and input concentration (C o ). In contrast to conventional filtration theory, retention profiles (RPs) for AgNPs exhibited uniform, nonmonotonic, or hyperexponential shapes that were sensitive to physicochemical conditions. The experimental BTCs and RPs with uniform or hyperexponential shape were well described using a numerical model that considers time- and depth-dependent retention. The simulated maximum retained concentration on the solid phase (S max) and the retention rate coefficient (k 1) increased with IS and as the grain size and/or C o decreased. The RPs were more hyperexponential in finer textured sand and at lower C o because of their higher values of S max. Conversely, RPs were nonmonotonic or uniform at higher C o and in coarser sand that had lower values of S max, and tended to exhibit higher peak concentrations in the RPs at lower velocities and at higher solution IS. These observations indicate that uniform and nonmonotonic RPs occurred under conditions when S max was approaching filled conditions. Nonmonotonic RPs had peak concentrations at greater distances in the presence of excess amounts of surfactant, suggesting that competition between AgNPs and surfactant diminished S max close to the column inlet. The sensitivity of the nonmonotonic RPs to IS and velocity in coarser textured sand indicates that AgNPs were partially interacting in a secondary minimum. However, elimination of the secondary minimum only produced recovery of a small portion (<10%) of the retained AgNPs. These results imply that AgNPs were largely irreversibly interacting in a primary minimum associated with microscopic heterogeneity. [Copyright &y& Elsevier]