Organic Carbon Linkage with Soil Colloidal Phosphorus at Regional and Field Scales: Insights from Size Fractionation of Fine Particles

Nano and colloidal particles (1–1000 nm) play important roles in phosphorus (P) migration and loss from agricultural soils; however, little is known about their relative distribution in arable crop soils under varying agricultural geolandscapes at the regional scale. Surface soils (0–20 cm depth) were collected from 15 agricultural fields, including two sites with different carbon input strategies, in Zhejiang Province, China, and water-dispersible nanocolloids (0.6–25 nm), fine colloids (25–160 nm), and medium colloids (160–500 nm) were separated and analyzed using the asymmetrical flow field flow fractionation technique. Three levels of fine-colloidal P content (3583–6142, 859–2612, and 514–653 μg kg–1) were identified at the regional scale. The nanocolloidal fraction correlated with organic carbon (Corg) and calcium (Ca), and the fine colloidal fraction with Corg, silicon (Si), aluminum (Al), and iron (Fe). Significant linear relationships existed between colloidal P and Corg, Si, Al, Fe, and Ca and for nanocolloidal P with Ca. The organic carbon controlled colloidal P saturation, which in turn affected the P carrier ability of colloids. Field-scale organic carbon inputs did not change the overall morphological trends in size fractions of water-dispersible colloids. However, they significantly affected the peak concentration in each of the nano-, fine-, and medium-colloidal P fractions. Application of chemical fertilizer with carbon-based solid manure and/or modified biochar reduced the soil nano-, fine-, and medium-colloidal P content by 30–40%; however,the application of chemical fertilizer with biogas slurry boosted colloidal P formation. This study provides a deep and novel understanding of the forms and composition of colloidal P in agricultural soils and highlights their spatial regulation by soil characteristics and carbon inputs

Process sequence of soil aggregate formation disentangled through multi-isotope labelling

Microaggregates (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

Novel multiple sclerosis susceptibility loci implicated in epigenetic regulation.

We conducted a genome-wide association study (GWAS) on multiple sclerosis (MS) susceptibility in German cohorts with 4888 cases and 10,395 controls. In addition to associations within the major histocompatibility complex (MHC) region, 15 non-MHC loci reached genome-wide significance. Four of these loci are novel MS susceptibility loci. They map to the genes L3MBTL3, MAZ, ERG, and SHMT1. The lead variant at SHMT1 was replicated in an independent Sardinian cohort. Products of the genes L3MBTL3, MAZ, and ERG play important roles in immune cell regulation. SHMT1 encodes a serine hydroxymethyltransferase catalyzing the transfer of a carbon unit to the folate cycle. This reaction is required for regulation of methylation homeostasis, which is important for establishment and maintenance of epigenetic signatures. Our GWAS approach in a defined population with limited genetic substructure detected associations not found in larger, more heterogeneous cohorts, thus providing new clues regarding MS pathogenesis

Development of a novel online sequential extraction method for the characterisation of fine dust sources using inductively coupled plasma mass spectrometric detection

Multi-elemental analysis in combination with statistical models has the potential to support the apportionment of numerous sources of airborne dust. Lack of selectivity can be overcome by the application of sequential extraction schemes. However, classical offline extraction schemes are designed for >0.5 g of sample and are not suitable for particulate matter in (sub-)mg range.Therefore, a novel online sequential extraction (OSE) scheme was developed based on the well-established Tessier and BCR schemes. The solvent composition (deionised water, ammonium nitrate, acetic acid and hydroxylammonium chloride) was adapted to allow direct online introduction of the extracts into sector-field inductively coupled plasma mass spectrometry (ICP-MS). The OSE setup was optimised regarding sample containment, flow rates, transfer lines and ICP-MS transient data recording. Four model dust source samples (soil, coal, mine overburden and road dust) were screened by OSE for elemental fractionation patterns. Characteristic fractograms were obtained demonstrating the difference in mobility of the investigated elements Na, Mg, Al, K, Ca, V, Cr, Mn, Co, Ni, Cu, Zn, Rb, Sr, Cd, Ba and Pb in the chosen sample matrices. Results for the road dust, a very fine and homogenous matrix, showed high repeatability with most relative standard deviations from quadruplicate analysis <10%. Standard deviations for the other model samples were partly higher due to lower homogeneity of these matrices at the applied sample mass of only 5 mg.Verification of the elemental fractionation via the novel OSE was performed for the road dust model sample. A flow injection setup was applied to check the accuracy of the applied post-cartridge calibration approach. Recoveries for the QC standard were 90% with SD 4%. Bracketing the OSE runs with flow injection of the QC standard demonstrated the stability of the OSE operation over several days of measurement. Variation of the sample mass revealed a significant increase of the extracted mass fractions at lower mass of 2 mg. The results of this optimised road dust OSE data set were compared to offline sequential extractions of the same sample. Average recovery for the first fraction (water-soluble) was 87% with SD 21% indicating comparable extraction efficiency by OSE. Recoveries for the other extraction steps were partly lower due to lower reagent concentrations and much shorter extraction times. However, the OSE provided repeatable results matching the extraction pattern of the offline extraction. Overall, the summed extracted mass fractions of all 4 OSE extraction steps equalled 72% of the same fractions obtained with offline extraction. Considering the operationally defined character of all sequential extraction schemes these results demonstrate the reliability of OSE for elemental fractionation of fine particulate samples at mg range sample mass

ICP-MS for the analysis at the nanoscale – a tutorial review

This tutorial review focuses on the use of ICP-MS based techniques for the analysis of metal-containing nanoparticles and colloids. Within the first part the capabilities of “stand alone” ICP-MS for the analysis of total metal contents and the suitability of stable isotopes for nanoparticle tracking (stable isotope labelling and naturally occurring variation in isotope ratios) are introduced (Chapter 3). Special focus was given on single particle ICP-MS (sp-ICP-MS) mode (Chapter 4). Upon a brief introduction into the theoretical concept, critical aspects such as calibration strategies, dwell time as well as ionic background were discussed and practical advice is given. References to current data assessment sheets are provided. Furthermore, a brief chapter on general sample preparation aspects is included within the first part (Chapter 2). The second part is dedicated to fractionation/separation systems, such as field-flow fractionation (FFF), hydrodynamic chromatography (HDC), high performance liquid chromatography (HPLC) and capillary electrophoresis (CE) coupled on-line with ICP-MS detection for metal-based nanoparticle and colloid analysis (Chapter 5). Each section starts with an introduction into the theoretical concept of the respective fractionation/separation system, followed by practical hints regarding method development (e.g. selection of appropriate carrier/mobile phase, membrane/stationary phase) as well as critical aspects and limitations. Particular attention is payed to laser ablation ICP-MS (LA-ICP-MS) for spatially resolved nanoparticle analysis. Each section concludes with selected application examples of the respective analytical technique from the most relevant fields of nanoparticle use or exposure (consumer products, food, medicine and environment), highlighting the performance of each technique in metal-based nanoparticle analysis. Chapter 6 is dedicated to aspects of quality assurance. Various critical points regarding method development and validation, mass balance, size calibration and quantification from the previous sections are revisited, discussed and practical advice is given. Finally, the authors provide some concluding remarks and future perspectives (Chapter 7). Furthermore, a flow-chart is included as a “hands-on” overview on all ICP-MS based techniques discussed within this tutorial review intended as a “method-decision tool” for users

A novel approach for determination of the dissolved and the particulate fractions in aqueous samples by flow field flow fractionation via online monitoring of both the cross flow and the detector flow using ICP-MS

Size resolved elemental characterisation of nanoparticles and colloids is routinely performed via flow field flow fractionation online with inductively coupled plasma mass spectrometry (ICP-MS) for a variety of sample matrices. However, low molecular weight elemental species (i.e. the dissolved fraction in the context of this study) pass with the cross flow through the membrane of the separation channel and thus escape detection. The lack of information on the dissolved fraction is a significant disadvantage compared to centrifugal field flow fractionation and chromatographic techniques. This fraction is relevant to determine the ratio of free and particle bound nutrients or toxicologically relevant elemental species, to establish the dissolution rate of non-stabilised (nano)particles and to establish a mass balance for quality control of the fractionation results. Fraction collection of the cross flow followed by off-line elemental analysis is rarely performed to determine the dissolved fraction because of delayed elution through the frit of the channel, dilution and elevated blank levels for some elements. Therefore, a novel approach was developed in this study enabling the online monitoring of the dissolved fraction in the cross flow. A special interface was constructed to convert the discontinuous cross flow into a continuous flow to the ICP-MS. Two frit materials, ceramic and steel, were investigated to overcome the challenges of the interaction of dissolved elemental species with the frit and to improve recovery. Quantification was performed both for aqueous standard solutions and for environmental water samples using ultrafiltration as a reference method. Finally, a combined method including monitoring of the dissolved fraction in the cross flow and the particulate fractions in the detector flow was established. Comparison of the dissolved fraction obtained with the new method and via ultrafiltration indicates the suitability of the developed approach for environmental water samples with mean recoveries in the range of 87% to 120% for Ca, Mg and Si. In the case of Al and P the dissolved fraction is in the low μg L−1 range resulting in partially elevated recoveries but their concentrations match within their confidence intervals