Friederike Lang

The fate of silver nanoparticles in soil solution--Sorption of solutes and aggregation.

Nanoparticles enter soils through various pathways. In the soil, they undergo various interactions with the solution and the solid phase. We tested the following hypotheses using batch experiments: i) the colloidal stability of Ag NP increases through sorption of soil-borne dissolved organic matter (DOM) and thus inhibits aggregation; ii) the presence of DOM suppresses Ag oxidation; iii) the surface charge of Ag NP governs sorption onto soil particles. Citrate-stabilized and bare Ag NPs were equilibrated with (colloid-free) soil solution extracted from a floodplain soil for 24h. Nanoparticles were removed through centrifugation. Concentrations of free Ag ions and DOC, the specific UV absorbance at a wavelength of 254 nm, and the absorption ratio α254/α410 were determined in the supernatant. Nanoparticle aggregation was studied using time-resolved dynamic light scattering (DLS) measurement following the addition of soil solution and 1.5mM Ca(2+) solution. To study the effect of surface charge on the adsorption of Ag NP onto soil particles, bare and citrate-stabilized Ag NP, differing in the zeta potential, were equilibrated with silt at a solid-to-solution ratio of 1:10 and an initial Ag concentration range of 30 to 320 μg/L. Results showed that bare Ag NPs sorb organic matter, with short-chained organic matter being preferentially adsorbed over long-chained, aromatic organic matter. Stabilizing effects of organic matter only come into play at higher Ag NP concentrations. Soil solution inhibits the release of Ag(+) ions, presumably due to organic matter coatings. Sorption to silt particles was very similar for the two particle types, suggesting that the surface charge does not control Ag NP sorption. Besides, sorption was much lower than in comparable studies with sand and glass surfaces.

Mobilization of soluble and dispersible lead, arsenic, and antimony in a polluted, organic-rich soil - effects of pH increase and counterion valency.

Liming is a common technique suggested for the stabilization of shooting range sites. We investigated the effect of an increase in pH on the mobilization of soluble and dispersible (colloidal) Pb, As, and Sb. Our hypothesis was that the addition of divalent cations counteracts the pH-induced mobilization of soluble and colloidal metal(loid)s. We determined soluble (operationally defined as the fraction < 10 nm obtained after centrifugation) and dispersible (filter cut-off 1200 nm) As, Pb, Sb, Fe, and C(org) concentrations in the filtered suspensions of batch extracts of topsoil samples (C(org): 8%) from a former shooting range site following a pH increase to values between 3.5 and 7 by adding a monovalent (KOH) or a divalent (Ca(OH)(2)) base. In the Ca(OH)(2)-treated samples, dissolved metal(loid) concentrations were 62 to 98% lower than those titrated with KOH to similar pH. Similarly, Ca reduced the concentration of dispersible Pb by 95%, but had little or no impact on dispersible As and Sb. We conclude that the counterion valency controls the mobility of metal(loid)s by affecting the mobility and sorption capacity of the sorbents (e.g., colloids, organic matter).

Immobilisation of molybdate by iron oxides: effects of organic coatings

Abstract It has been suggested that molybdate penetrates into micropores and interdomains of iron oxides. This process will cause immobilisation of molybdate. The influence of organic matter that may occlude the pores by adsorptive cover has not yet been examined. Thus, the aim of our study is to elucidate the role of organic coatings around iron oxides for intraparticular molybdate diffusion. We used two synthetic goethites of different crystallinity (specific surface G13: 13 m 2 g −1 and G83: 83 m 2 g −1 ), in pure form and equilibrated with dissolved organic matter (DOM), that has been extracted from forest floor samples. The iron oxide samples that were characterised by N 2 adsorption, X-ray diffraction analysis and scanning electron microscopy were preincubated with molybdate solution (5 g iron oxide l −1 , 0.2 mM molybdate, pH 4) for 12, 24 and 48 h. To follow the molybdate immobilisation, molybdate desorption kinetics (desorption periods 0.5–48 h) were determined with ion exchange resins in batch systems after the different incubation times. In addition, the preincubated iron oxides were examined by XPS. Fractional coverage of DOM-treated iron oxides estimated according to the enthalpy of N 2 adsorption was 0.33 m 2 m −2 for G83 and 1.19 m 2 m −2 for G13. The pore volume of G13 decreased after DOM treatment. Furthermore, SEM images show that DOM treatment results in microaggregation of the iron oxides. A combination of the first-order equation and a diffusion term was applicable to the Mo desorption data of both, the pure and the DOM-treated iron oxides. Desorbability and apparent diffusion constants of molybdate decreased with increasing residence time. However, the decrease was less distinct for the DOM treated than for the pure goethites. The Mo/Fe XPS ratios of the iron oxides indicate that in the presence of organic matter a higher percentage of molybdate is sorbed to outer surfaces. The results confirm the hypothesis that molybdate diffuses into the pores of iron oxides. Organic coatings slow down the molybdate immobilisation probably by decreasing the accessibility of diffusion pathways. This mechanism may be relevant even at low molybdate and C concentrations, where no competition effect of sorbed organic molecules can be observed.

Phosphorus depletion in forest soils shapes bacterial communities towards phosphorus recycling systems

Phosphorus (P) is an important macronutrient for all biota on earth but similarly a finite resource. Microorganisms play on both sides of the fence as they effectively mineralize organic and solubilize precipitated forms of soil phosphorus but conversely also take up and immobilize P. Therefore, we analysed the role of microbes in two beech forest soils with high and low P content by direct sequencing of metagenomic deoxyribonucleic acid. For inorganic P solubilization, a significantly higher microbial potential was detected in the P-rich soil. This trait especially referred to Candidatus Solibacter usiatus, likewise one of the dominating species in the data sets. A higher microbial potential for efficient phosphate uptake systems (pstSCAB) was detected in the P-depleted soil. Genes involved in P starvation response regulation (phoB, phoR) were prevalent in both soils. This underlines the importance of effective phosphate (Pho) regulon control for microorganisms to use alternative P sources during phosphate limitation. Predicted genes were primarily harboured by Rhizobiales, Actinomycetales and Acidobacteriales.

Effects of 100 years wastewater irrigation on resistance genes, class 1 integrons and IncP-1 plasmids in Mexican soil

Long-term irrigation with untreated wastewater can lead to an accumulation of antibiotic substances and antibiotic resistance genes in soil. However, little is known so far about effects of wastewater, applied for decades, on the abundance of IncP-1 plasmids and class 1 integrons which may contribute to the accumulation and spread of resistance genes in the environment, and their correlation with heavy metal concentrations. Therefore, a chronosequence of soils that were irrigated with wastewater from 0 to 100 years was sampled in the Mezquital Valley in Mexico in the dry season. The total community DNA was extracted and the absolute and relative abundance (relative to 16S rRNA genes) of antibiotic resistance genes (tet(W), tet(Q), aadA), class 1 integrons (intI1), quaternary ammonium compound resistance genes (qacE+qacEΔ1) and IncP-1 plasmids (korB) were quantified by real-time PCR. Except for intI1 and qacE+qacEΔ1 the abundances of selected genes were below the detection limit in non-irrigated soil. Confirming the results of a previous study, the absolute abundance of 16S rRNA genes in the samples increased significantly over time (linear regression model, p < 0.05) suggesting an increase in bacterial biomass due to repeated irrigation with wastewater. Correspondingly, all tested antibiotic resistance genes as well as intI1 and korB significantly increased in abundance over the period of 100 years of irrigation. In parallel, concentrations of the heavy metals Zn, Cu, Pb, Ni, and Cr significantly increased. However, no significant positive correlations were observed between the relative abundance of selected genes and years of irrigation, indicating no enrichment in the soil bacterial community due to repeated wastewater irrigation or due to a potential co-selection by increasing concentrations of heavy metals.

Guadiamar toxic flood: Factors that govern heavy metal distribution in soils.

The remaining soil contamination after the removal of thesludge and the affected topsoil was studied in the northernpart of the Guadiamar river valley affected by the Aznalcóllartoxic spill. The easily soluble (NH4NO3-extraction)and the oxidisable fraction (H2O2/HNO3-extraction)were analysed in samples of two calcareous and two non-calcareoussoils. Correlations between soil properties and heavy metal concentrations were tested with special respect to depth distribution. The spatial distributions of the easily soluble and the oxidisable fraction were highly skewed in both examineddepths (0–20 and 20–40 cm). Easily soluble heavymetal concentrations of a high percentage of samples exceededthresholds that have been given in the German soil protectionlaw particularly in the non-calcareous soils. Within the soillayers of the non-calcareous soils, the pH seems to control theeasily soluble concentrations. However no relation between thepH and depth distribution of heavy metals within the profilescould be found. Physical properties, which determine partlypenetration depth of the sludge and soil mixing caused by theremoval may be the more important factors. Accordingly, highheavy metal concentrations are to be expected even in thesubsoils of clayey sites. As heavy metal concentrations in theoxidisable fraction are still high, further oxidationaccompanied by pH lowering has to be expected. Thus, thestudied soils show a significant risk potential of availableheavy metals even after the removal of the sludge.

Molybdenum fractions and mobilization kinetics in acid forest soils

We extracted molybdenum (Mo) from eight acid forest soils (19 A, E, and B horizons) in NE-Bavaria and from one site in the Ore Mountains, using (1) anion exchange-resin, (2) 0.2 M ammonium oxalate, and (3) ascorbic acid/ammonium oxalate. The Mo concentrations in the anion exchange-resin fraction varied between 5 and 28 μg kg-1. Oxalate-extractable Mo ranged from 44 to 407 μg kg-1 and after reduction of iron (Fe) with ascorbic acid, 135 to 1071 μg Mo kg-1 were extracted. The lowest concentrations of Mo were measured in acid and sesquioxide impoverished E horizons. The total concentrations of Mo in spruce needles correlated with ion exchange resin extractable Mo, indicating that this fraction represents Mo readily available to plants. The Mo and Fe dissolution kinetics during oxalate extraction were studied on 8 of the soil samples to obtain further information on Mo mobilization. Oxalate extractable iron (Feo) was mobilized within a few hours. A first order equation was applicable to the Fe dissolution kinetics with the rate constants ranging between 0.9 and 9.0 h-1. The mobilization of Mo occurred in two distinct stages. An initially rapid dissolution was followed by a further increase in extractable Mo but with slower kinetics. A combined first order-diffusion equation was found to be appropriate for modelling the results. The first order rate constants for Mo mobilization ranged from 0.6 to 11.4 h-1. However, correlations between the rates of reaction of Mo and Fe could not be established, indicating that Mo is either not distributed equally along Fe minerals or that there is another pool, possibly the organic substance of the soil, from which Mo is extractable by oxalate. Molybdan-Fraktionen und -Freisetzungs- kinetik in sauren Waldboden Wir extrahierten Molybdan (Mo) mittels (1) Anionenaustauscherharz, (2) 0,2 M Ammoniumoxalat und (3) Ascorbinsaure/Ammoniumoxalat aus sauren Waldboden (19 A-, E- und B-Horizonte) von insgesamt 9 Standorten im Fichtelgebirge, Frankenwald und Erzgebirge. Die Mo-Gehalte im Harzextrakt lagen zwischen 5 und 28 μg kg-1 oxalatextrahierbares Mo betrug 44 bis 407 μg kg-1 und nach Reduktion kristalliner Eisenoxide mit Ascorbinsaure wurden Gehalte von 135 bis 1071 μg Mo kg-1 extrahiert. Niedrige Mo-Gehalte traten in sauren und sesquioxidarmen Eluvialhorizonten auf. Zusammenhange zwischen Austauscherharz-extrahierbarem Mo und den Mo-Nadelgehalten von Fichten deuten darauf hin, das diese Fraktion ein Mas fur die Mo-Pflanzenverfugbarkeit darstellt. Um weitere Aufschlusse uber die Mo-Mobilitat zu erhalten, wurde an 8 Bodenproben die Freisetzungskinetic von Mo und Eisen (Fe) bei der Extraktion mit 0,2 M Ammoniumoxalat untersucht. Das gesamte oxalatlosliche Fe (Feo) wurde innerhalb weniger Stunden mobilisiert. Die Kinetik folgt dem Modell 1. Ordnung mit Geschwindigkeitskonstanten (k) zwischen 0,9 und 9,0 h-1. Molybdan wird zunachst ebenfalls rasch mobilisiert (k: 0,6—11,4 h-1). Jedoch ist die Mo-Losungskinetik von einem vermutlich diffusionsgesteuerten Mobilisierungsprozes uberlagert. So lies sich die Mo-Freisetzung durch ein kombiniertes Modell beschreiben, das Auflosung und Diffusion Rechnung tragt. Obwohl die Geschwindigkeitskonstanten der Fe- und Mo-Mobilisierung eine vergleichbare Spanne abdecken, korrelieren sie nicht. Dies deutet darauf hin, das Mo entweder nicht gleichmasig auf die Fe-Oxide verteilt ist, oder das mit der Oxalat-Extraktion noch ein weiterer leicht mobilisierbarer Mo-Pool, moglicherweise die organische Substanz, erfast wird.

Novel oligonucleotide primers reveal a high diversity of microbes which drive phosphorous turnover in soil

Phosphorus (P) is of central importance for cellular life but likewise a limiting macronutrient in numerous environments. Certainly microorganisms have proven their ability to increase the phosphorus bioavailability by mineralization of organic-P and solubilization of inorganic-P. On the other hand they efficiently take up P and compete with other biota for phosphorus. However the actual microbial community that is associated to the turnover of this crucial macronutrient in different ecosystems remains largely anonymous especially taking effects of seasonality and spatial heterogeneity into account. In this study seven oligonucleotide primers are presented which target genes coding for microbial acid and alkaline phosphatases (phoN, phoD), phytases (appA), phosphonatases (phnX) as well as the quinoprotein glucose dehydrogenase (gcd) and different P transporters (pitA, pstS). Illumina amplicon sequencing of soil genomic DNA underlined the high rate of primer specificity towards the respective target gene which usually ranged between 98% and 100% (phoN: 87%). As expected the primers amplified genes from a broad diversity of distinct microorganisms. Using DNA from a beech dominated forest soil, the highest microbial diversity was detected for the alkaline phosphatase (phoD) gene which was amplified from 15 distinct phyla respectively 81 families. Noteworthy the primers also allowed amplification of phoD from 6 fungal orders. The genes coding for acid phosphatase (phoN) and the quinoprotein glucose dehydrogenase (gcd) were amplified from 20 respectively 17 different microbial orders. In comparison the phytase and phosphonatase (appA, phnX) primers covered 13 bacterial orders from 2 different phyla respectively. Although the amplified microbial diversity was apparently limited both primers reliably detected all orders that contributed to the P turnover in the investigated soil as revealed by a previous metagenomic approach. Genes that code for microbial P transporter (pitA, pstS) were amplified from 13 respectively 9 distinct microbial orders. Accordingly the introduced primers represent a valuable tool for further analysis of the microbial community involved in the turnover of phosphorus in soils but most likely also in other environments.

Organic phosphorus in the terrestrial environment: a perspective on the state of the art and future priorities

BackgroundThe dynamics of phosphorus (P) in the environment is important for regulating nutrient cycles in natural and managed ecosystems and an integral part in assessing biological resilience against environmental change. Organic P (Po) compounds play key roles in biological and ecosystems function in the terrestrial environment being critical to cell function, growth and reproduction.ScopeWe asked a group of experts to consider the global issues associated with Po in the terrestrial environment, methodological strengths and weaknesses, benefits to be gained from understanding the Po cycle, and to set priorities for Po research.ConclusionsWe identified seven key opportunities for Po research including: the need for integrated, quality controlled and functionally based methodologies; assessment of stoichiometry with other elements in organic matter; understanding the dynamics of Po in natural and managed systems; the role of microorganisms in controlling Po cycles; the implications of nanoparticles in the environment and the need for better modelling and communication of the research. Each priority is discussed and a statement of intent for the Po research community is made that highlights there are key contributions to be made toward understanding biogeochemical cycles, dynamics and function of natural ecosystems and the management of agricultural systems.

Engineered nanoparticles in soils and waters.

Over the last decade, the variety and number of products and techniques based on the use or the addition of engineered nanoparticles has increased dramatically. This includes among others the use of e.g. silver, titanium dioxide, or other nanoparticles in amultitude of personal care products, clothing, colors, and other consumer products (Schaumann et al., 2015-in this issue), and their direct application in the environment, e.g., for site remediation (Fajardo et al., 2015-in this issue; Schöftner et al., 2015-in this issue) or drinking water treatment (Simeonidis et al., 2015-in this issue). It is widely accepted that such nanoparticles can enter aquatic and terrestrial ecosystems and may impact biotic and abiotic processes in those environments (Schaumannet al., 2015-in this issue). The environmental relevance was recognized longer than a decade ago, and in contrast to the situation for other innovativematerials and compounds, the research on potential environmental impacts of engineered nanoparticles has actually started before first negative environmental effects were reported. The pioneer researchers were challenged by limited analytical access to the nanoparticles and demanding experiments arising from the distinctive features of these emerging materials. Not only the chemical composition, but also specific particle characteristics determine their mobility, chemical affinity and biological effects. Even today, it is still highly challenging to detect nanoparticles in environmental matrices and distinguish them from an omnipresent natural colloidal background. The presentations and discussions on the International Workshop Nanoparticles in Soils and Waters: Fate, Transport and Effects, held 11th–13th March, 2014 in Landau in der Pfalz, Germany, with 81 participants from 15 countries, 32 oral and 29 poster presentations (Schaumann, 2014), led to a common agreement that it is reasonable and required to summarize and critically discuss current approaches and research activities in a special issue on engineered nanoparticles in soils and waters. This special issue is a collection of 18 publications, part of which is based on presentations during the workshop in Landau. The publications cover awide spectrumof relevant issues related to engineered nanoparticles in the environment: they (i) stand for the current state of knowledge, (ii) demonstrate actual approaches to experimentally investigate fate and biological effects of six representatives of engineered nanoparticles: Ag, AgCl, TiO2, zerovalent iron, magnetite and copper oxide and (iii) present new approaches for characterizing and modeling fate, effects and the life cycle of nanoparticles. As a large part of engineered nanoparticles enter the environment via wastewater, they will pass waste water treatment systems, which then serve as hotspots for their transformation determining the colloidal speciation and the chemical status of the nanoparticles released from the wastewater treatment plants. This is central for silver (Kaegi et al., 2015-in this issue), but also for other oxidic and metallic nanoparticles (Schaumann et al., 2015-in this issue). Also use activities for products containing