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Characterization of natural nanomaterial (NNM) physicochemical properties – such as size, size distribution, elemental composition and elemental ratios - is often hindered by lack of methods to disperse NNMs from environmental samples. This study evaluates the effect of extractant composition, pH, and ionic strength on soil NNM extraction in term of recovery and release of primary particles/small aggregate sizes (i.e. , <200 nm). The extracted NNMs were characterized for hydrodynamic diameter and zeta potential by dynamic light scattering and laser Doppler electrophoresis, natural organic matter desorption by UV–Vis spectroscopy, element composition by inductively coupled plasma-mass spectroscopy (ICP-MS), size based elemental distribution by field flow fractionation coupled to ICP-MS, and morphology by transmission electron microscopy. The extracted NNM concentrations increased following the order of NaOH ≤ Na 2 CO 3 < Na 2 C 2 O 4 < Na 4 P 2 O 7. Na 4 P 2 O 7 was the most efficient extractant and results in 2–12 folds higher NNM extraction than other extractants. The Na 4 P 2 O 7 extracted NNMs exhibited narrower size distribution with smaller modal size relative to NaOH, Na 2 CO 3 , Na 2 C 2 O 4 extracted NNMs. Thus, Na 4 P 2 O 7 enhances the extraction of primary NNMs and/or smaller NNM aggregates (i.e. , size <200 nm). Na 4 P 2 O 7 promote soil microaggregates breakup and release of NNMs by reducing free multivalent cation concentration in soil pore water by forming metal-phosphate complexes and by enhancing NNM surface charge via phosphate sorption on NNM surfaces. Additionally, the extracted NNM concentrations increased with the increase in extractant concentration and pH, except at 100 mM where the high ionic strength might have induced NNM aggregation. The improved NNM-extraction will improve the overall understanding of the physicochemical properties of NNMs in environmental systems. This study presents the key properties of NNMs that can be used as background information to differentiate engineered nanomaterials (ENMs) from NNMs in complex environmental media. Unlabelled Image • Efficient extraction of natural nanomaterials from complex environmental matrices • Multimethod approach for characterization of natural nanomaterials from soils • Sodium pyrophosphate to efficiently disperse nanomaterials from soil heteroaggregates • Key nanomaterial properties to discriminate engineered from natural nanomaterials in soils [ABSTRACT FROM AUTHOR]

Atomic force microscopy (AFM) was used to image and quantify natural nanoparticles (prefiltered <25 nm) from three different freshwater sites (Vale Lake, Bailey Brook and Tern Rivers). Four fractions were analysed by AFM; the prefiltered fraction (<25 nm) and three fractions collected after separation of this prefiltered sample by flow field-flow fractionation (FlFFF) which corresponds to material which has size ranges of <4.2 nm, 4.2–15.8 nm and 15.8–32.4 nm, as determined by FlFFF theory. The large majority of materials in all samples appeared as <3 nm nanoparticles, nearly spherical and rich in chromophores active at 254 nm UV, which thus correspond to natural organic matter. However, nanoparticles were also imaged up to slightly more than 25 nm in size, indicating a slight disagreement in sizing between filtration and FlFFF. In addition, some particles in certain fractions were found to be covered with a thin film of less than 0.5–1.0 nm. Substantial differences between sites were observed. [Copyright &y& Elsevier]

• The origin of colloids in streams indicates elemental transport pathways. • Monthly analysis of stream & groundwater, rainwater, throughfall, soil leachate. • Field flow fractionation revealed three fractions in all sample types. • Groundwater derived colloids dominated the stream signal. • Water flux and particle reformation affect the seasonal dynamics of particles. Biogeochemical changes of whole catchments may, at least in part, be deduced from changes in stream water composition. We hypothesized that there are seasonal variations of natural nanoparticles (NNP; 1–100 nm) and fine colloids (<300 nm) in stream water, which differ in origin depending on catchment inflow parameters. To test this hypothesis, we assessed the annual dynamics of the elemental composition of NNP and fine colloids in multiple water compartments, namely in stream water, above and below canopy precipitation, groundwater and lateral subsurface flow from the Conventwald catchment, Germany. In doing so, we monitored meteorological and hydrological parameters, total element loads, and analyzed element concentrations of org C, Al, Si, P, Ca, Mn and Fe by Asymmetric Flow Field Flow Fractionation (AF4). The results showed that colloid element concentrations were < 5 µmol/L. Up to an average of 55% (Fe) of total element concentrations were not truly dissolved but bound to NNP and fine colloids. The colloid patterns showed seasonal variability with highest loads in winter. The presence of groundwater-derived colloidal Ca in stream water showed that groundwater mainly fed the streams throughout the whole year. Overall, the results showed that different water compartments vary in the NNP and fine colloidal composition making them a suitable tool to identify the streams NNP and fine colloid sources. Given the completeness of the dataset with respect to NNP and fine colloids in multiple water compartments of a single forest watershed this study adds to the hitherto underexplored role of NNP and fine colloids in natural forest watersheds. [ABSTRACT FROM AUTHOR]