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Determining the potential for accumulation of Ag from Ag2S NPs as an environmentally relevant form of AgNPs in different terrestrial organisms is an essential component of a realistic risk assessment of AgNP emissions to soils. The objectives of this study were first to determine the uptake kinetics of Ag in mealworms (Tenebrio molitor) and woodlice (Porcellio scaber) exposed to Ag2S NPs in a mesocosm test, and second, to check if the obtained toxicokinetics could be predicted by single-species bioaccumulation tests. In the mesocosms, mealworms and woodlice were exposed together with plants and earthworms in soil columns spiked with 10 μg Ag g−1 dry soil as Ag2S NPs or AgNO3. The total Ag concentrations in the biota were measured after 7, 14, and 28 days of exposure. A one-compartment model was used to calculate the Ag uptake and elimination rate constants. Ag from Ag2S NPs appeared to be taken up by the mealworms with significantly different uptake rate constants in the mesocosm compared to single-species tests (K1 = 0.056 and 1.66 g dry soil g−1 dry body weight day−1, respectively), and a significant difference was found for the Ag bioaccumulation factor (BAFk = 0.79 and 0.15 g dry soil g−1 dry body weight, respectively). Woodlice did not accumulate Ag from Ag2S NPs in both tests, but uptake from AgNO3 was significantly slower in mesocosm than in single-species tests (K1 = 0.037 and 0.26 g dry soil g−1 dry body weight day−1, respectively). Our results are of high significance because they show that single-species tests may not be a good predictor for the Ag uptake in mealworms and woodlice in exposure systems having greater levels of biological complexity. Nevertheless, single-species tests could be used as a fast screening approach to assess the potential of a substance to accumulate in biota before more complex tests are conducted.

The advancement of analytical methods for nanoparticle measurements is critical both for the growing industrial exploitation of engineered nanoparticles and for developing robust strategies to understand and control the concentration of nanomaterials in humans and the environment. For high value nanoparticles, the measurement of nanoparticle number concentration in a liquid directly impacts the ability to assess the scale and reproducibility of the production process, it allows optimisation of efficiency and supports regulatory compliance. This measurement is also useful to monitor and control the intentional or accidental release of engineered nanoparticles into the environment at the production plant, as well as by end-users., peer-reviewed

Short, saturated packed columns are used frequently to estimate the attachment efficiency (alpha) of engineered nanomaterials (ENMs) in relatively homogeneous porous media, but a combined experimental and theoretical approach to obtain alpha-values for heterogeneous natural soils has not yet been agreed upon. Accurately determined alpha-values that can be used to study and predict ENM transport in natural soils should vary with ENM and soil properties, but not with experimental settings. We investigated the effect of experimental conditions, and used different methods to obtain soil parameters, essential to calculate alpha. We applied 150 different approaches to determine alpha-values from 52 transport experiments using short columns with 5 different natural soils and 20 and 80 nm gold- or 27 nm silver sulphide ENMs. The choice of column end-filter material and pore size appeared critical to avoid overestimating alpha owing to filter - ENM interactions and/or incomplete saturation of the column. Using a low ionic strength (4.4 x 10-5 mol L-1) artificial rain water as an aqueous medium avoided ENM homo- or heteroaggregation in all soils, as confirmed by single-particle inductively coupled plasma - time of flight mass spectrometry. ENM breakthrough curves could be modelled using colloid filtration theory assuming irreversible attachment only. alpha-Values calculated from this model, having the grain size represented by a single average size, accounting for dispersivity and effective porosity based on a prior inert tracer test, explained up to 42% of the variance in alpha as revealed by partial least squares analysis. However, column length and dispersivity remained as important experimental parameters, which calls for further standardisation efforts of column tests with ENMs in natural soils, preferably cross-validated with batch tests.

Plastic pollution is increasingly perceived as an emerging threat to terrestrial environments, but the spatial and temporal dimension of plastic exposure in soils is poorly understood. Bioturbation displaces microplastics (>1 μm) in soils and likely also nanoplastics (, Environmental Science & Technology, 55 (24), ISSN:0013-936X, ISSN:1520-5851

A novel off-lattice three-dimensional coarse-grained Monte Carlo model is developed to study engineered nanoparticle (ENP) behavior in porous media. Based on individual particle tracking and on the assumption that different physicochemical processes may occur with different probabilities, our model is used to independently evaluate the influence of homoaggregation, attachment and detachment processes on ENP transport and retention inside porous media made of colloidal collectors. The possibility of straining, i.e. trapping of ENPs or aggregates that are too large to pass pore necks, is also included in the model. The overall probability of ENP retention as a function of the above mentioned processes is quantified using functional tests in the form of a alpha(global)(t(ref)) retention parameter. High alpha(global)(t(ref)) values were obtained for moderate probabilities of homoaggregation between ENPs (alpha(ENP-ENP)) and very small probabilities of attachment between ENPs and collectors (alpha(att)), thus indicating the important role of homoaggregation and attachment in ENP retention. Moreover, attaching ENPs and large aggregates was found to cause pore neck enclosure and thus largely contributed to the straining of unbound ENPs. An analysis of depth distribution of retained ENPs revealed that, depending on the dominating conditions, the number of ENPs was decreasing monotonously or exponentially with depth. The introduction of the ENP detachment probability (alpha(det)) from collectors resulted in an increased ENP occurrence at the porous media matrix outlet. It was also found that different sets of alpha(det) and alpha(att) values, reflecting different ENPs and collector physicochemical properties and inter-particle forces, lead to identical alpha(global)(t(ref)) values. This constitutes an important outcome indicating that alpha(global)(t(ref)) values determined from functional tests are not mechanistic but operationally defined parameters and thus cannot be deemed predictive beyond these tests.

International audience; The chemical composition and properties of environmental media determine nanomaterial (NM) transport, fate, biouptake, and organism response. To compare and interpret experimental data, it is essential that sufficient context be provided for describing the physical and chemical characteristics of the setting in which a nanomaterial may be present. While the nanomaterial environmental, health and safety (NanoEHS) field has begun harmonization to allow data comparison and re-use (e.g. using standardized materials, defining a minimum set of required material characterizations), there is limited guidance for standardizing test media. Since most of the NM properties driving environmental behaviour and toxicity are medium-dependent, harmonization of media is critical. A workshop in March 2016 at Duke University identified five categories of test media: aquatic testing media, soil and sediment testing media, biological testing media, engineered systems testing media and product matrix testing media. For each category of test media, a minimum set of medium characteristics to report in all NM tests is recommended. Definitions and detail level of the recommendations for specific standardized media vary across these media categories. This reflects the variation in the maturity of their use as a test medium and associated measurement techniques, variation in utility and relevance of standardizing medium properties, ability to simplify standardizing reporting requirements, and in the availability of established standard reference media. Adoption of these media harmonization recommendations will facilitate the generation of integrated comparable datasets on NM fate and effects. This will in turn allow testing of the predictive utility of functional assay measurements on NMs in relevant media, support investigation of first principles approaches to understand behavioral mechanisms, and support categorization strategies to guide research, commercial development, and policy.

This chapter covers how engineered nanomaterials (ENMs) may enter soils, how they behave in soils, the exposure dynamics this presents to soil organisms, and resulting issues for uptake and food-chain transfer. Special attention is given to summarizing the main issues and the current state of the art for the most important elements of how ENMs act as pollutants in soil, namely: The routes and consequent forms of entry of ENMs from nanoenabled products into soils; the fate and transformations ENMs undergo in soil systems; ENM bioavailability to and interactions with soil biology, including exposure and hazard assessment, toxicokinetics, and trophic transfer.

The quantities of engineered nanoparticles (NP) released to the environment are often influenced by their fate in waste water treatment plants (WWTP). Here, 40 nm silver NP (AgNP) were spiked into a mesocosm simulating the process used at a major municipal WWTP. The evolution of the mass distributions and number concentrations were followed by fast acquisition speed technique single particle inductively coupled mass spectrometry (FAST spICP-MS) using a high-resolution ICP-MS. It was thus possible to detect smaller Ag containing NP than hitherto possible in similar studies. These small particles (ca. 5–10 nm in corresponding metallic Ag equivalent spherical diameter) were possibly dissolved Ag+ precipitated as Ag2S particles. They were detected immediately upon spiking and were stable with respect to aggregation and thus much less removed by the WWTP process compared to the 40 nm AgNP. The results also suggested that any transformation of the latter AgNP occurred without dissolution. Most of these larger AgNP were probably removed by aggregation with large floc particles and subsequent sedimentation with the suspended particulate matter in the simulated WWTP process. The results have implications for differentiating the fate of nanoparticles as a function of size and demonstrate how spICP-MS can reveal such size-dependent fate dynamics.

International audience; High Ca concentrations in complex matrices such as river waters often hamper the detection of titanium nanomaterials (TiO2 NPs) by single particle inductively coupled plasma mass spectrometry (spICPMS), because of isobaric interference of Ca-48 on the most abundant Ti isotope (Ti-48). Several approaches were used to reduce this interference while measuring TiO2 in solutions with different Ca concentrations up to 100 mg L-1. ICP-MS/MS was used with ammonia as the reaction ceLL gas and high resoLution (HR) ICP-MS was used under different resoLution settings. These approaches were compared by measuring different Ti isotopes (Ti-47 and Ti-49). spICPMS data were then treated with a deconvoLution method to filter out dissolved signals and identify the best approach to detect the Lowest possible corresponding spherical size of TiO2 NPs (D,in). ICP-MS/MS aLLowed for an important decrease of the theoretical D-min compared to standard quadrupole ICP-MS, down to 64 nm in uLtrapure water; however the sensitivity was reduced by the reaction gas and increasing Ca concentrations also increased the D-min. The comparably higher sensitivity of HR-ICP-MS aLLowed for theoretically measuring a D-min of 10 nm in uLtrapure water. Combined with the deconvoLution analysis, the highest resoLution mode in HR-ICP-MS Leads to the Lowest D-min at high Ca concentrations, even though significant broadening of the measured mass distributions occurred for TiO2 NPs at Ca concentrations up to 100 mg L-1

The detection capabilities of single particle inductively coupled plasma-mass spectrometry (spICPMS) with respect to particle size and number concentrations are investigated for the case of silver nanoparticles (ca. 20-80 nm). An iterative algorithm was developed where particle measurement events were distinguished as outliers from the more continuous dissolved ion signal if the measured intensity was more than five times the standard deviation of the whole data set. The optimal dwell time for 40-80 nm particles, limiting both incomplete and multiple particle events, was 5 ms. The smallest detectable particle size (ca. 20 nm) is mainly limited by the overlap of particle events and dissolved signal that increases with noise on both signals. The lowest measurable number concentration is limited by the relative frequency of erroneously identified particle events, a limit that can be reduced by acquiring more data points. Finally, the potential of spICPMS for environmental detection of nanoparticles is demonstrated for a wastewater treatment plant effluent sample.

Exposure assessment of engineered nanoparticles (ENPs) in soil and sediment is severely hampered by a lack of understanding of the underlying processes and of the impact of matrix constituents on the fate of ENPs in natural systems, including porewater properties like pH, ionic strength, and presence of naturally occurring (nano)particles. Additional issues such as lack of proper methods for in-situ assessment of ENP speciation, ENP ageing, and agglomeration state, hinder proper exposure assessment. Let alone that the lack does not allow for development of predictive methods for endpoints like transformation and agglomeration potential. This paper discusses current approaches for fate assessment of ENPs in solids dominated media and addresses the most prominent knowledge gaps and how these may be addressed. It is concluded that the key issue to be dealt with, are the attachment and deposition processes that are characteristic for ENPs as opposed to equilibrium-driven partitioning processes of non-particulate organic and inorganic contaminants.

Modeling the environmental fate of nanomaterials (NMs) and their uptake by cells and organisms in the environment is essential to underpin experimental research, develop overarching theories, improve our fundamental understanding of NM exposure and hazard, and thus enable risk assessment of NMs. Here, we critically review the state-of-the-art of the available models that can be applied/adapted to quantify/predict NM fate and uptake in aquatic and terrestrial systems and make recommendations regarding future directions for model development. Fate models have evolved from substance flow analysis models that lack nano-specific processes to more advanced mechanistic models that (at least partially) take nano-specific (typically non-equilibrium, dynamic) processes into account, with a focus on key fate processes such as agglomeration, sedimentation and dissolution. Similarly, NM uptake by organisms is driven by dynamic processes rather than by equilibrium partitioning. Hence, biokinetic models are more suited to model NM uptake, compared with the simple bioaccumulation factors used for organic compounds. Additionally, biokinetic models take speciation processes (e.g. particulate versus ionic uptake) into account, although identifying essential environment-specific processes to include in models remains a challenge. The models developed so far require parameterization, calibration and validation with available data, e.g. field data (if available), or experimental data (e.g. aquatic and terrestrial mesocosms), rather than extension to more complex and sophisticated models that include all possible transformation processes. Collaborative efforts between experimentalists and modelers to generate appropriate ground-truth data would advance the field most rapidly.

Soils are likely to be increasingly exposed to nanoparticles due to growing consumer use of nanoparticles. This has necessitated an investigation into the fate and bioavailability of nanoparticles in natural soils. However, the effect of soil properties on these processes are unknown. To find the dominant properties that determine AgNP retention in natural soils, nonequilibrium retention (K-r) values of polyvinylpyrrolidone (PVP) coated silver nanoparticles (AgNP) were obtained in suspensions of 16 soils having a wide range of physical and chemical properties. The AgNP dissolution was investigated using ultrafiltration, but could only be detected in six soils, possibly due to strong partitioning of dissolved Ag (median K-d 1791 L kg(-1)); a process that increased predominantly with the organic matter content of the soils. When corrected for partitioning, dissolution of AgNP was higher (median 26% of total Ag added as AgNP) in these six soils compared to dissolution in artificial soil solutions. The homocoagulation kinetics of AgNP as a function of increasing NaClO4 concentrations were studied at pH 4 and pH 8, showing that homocoagulation of AgNP is unlikely in the studied soil suspensions. Moreover, Kr values (median value 589 L kg(-1)) only correlated with the soil granulometric clay content and not with parameters that increase the homocoagulation rate, a correlation that suggests that negatively charged AgNP were adsorbed preferentially at positively charged surface sites of clay-sized minerals. Adsorption of negatively charged engineered nanoparticles by Fe and Al oxides and mineral clay edges may thus be an important fate-determining reaction in soils, and possibly also in aquatic systems. Refereed/Peer-reviewed

Application of single particle ICP-MS (spICPMS) for measurement of the size and number concentration, c(p), of nanoparticles is currently hampered by insufficient accuracy. The relative contributions of different types of noise to the overall uncertainty during spICPMS measurements of Ag and Au nanoparticle dispersions were quantified showing that the accuracy of spICPMS is mainly limited by the uncertainty in nebulization efficiency (f(neb)). This uncertainty was improved by correcting f(neb) for analyte partitioning effects during nebulization, and the calculated Ag and Au nanoparticle sizes were in close agreement with sizes determined by scanning electron microscopy. The duration of the particle events was measured, which allowed correction for incomplete particle events and detector dead time, and determination of the effective dwell time for particle counting. The c(p) measured with spICPMS agreed with that measured by counting particles deposited on filters, and calculated from the mass concentration of the analyte.