Antonia Praetorius

Development of Environmental Fate Models for Engineered Nanoparticles—A Case Study of TiO2 Nanoparticles in the Rhine River

For a proactive risk assessment of engineered nanoparticles (ENPs) it is imperative to derive predicted environmental concentration (PEC) values for ENPs in different environmental compartments; PECs can then be compared to effect thresholds. From the basis of established multimedia environmental fate models for organic pollutants, we develop a new concept of environmental fate modeling for ENPs with process descriptions based on the specific properties of ENPs. Our new fate modeling framework is highly flexible and can be adjusted to different ENPs and various environmental settings. As a first case study, the fate and transport of TiO(2) NPs in the Rhine River is investigated. Predicted TiO(2) NP concentrations lie in the ng/L range in the water compartment and mg/kg in the sediment, which represents the main reservoir for the nanoparticles. We also find that a significant downstream transport of ENPs is possible. A fundamental process, the heteroaggregation between TiO(2) NPs and suspended particulate matter (SPM), is analyzed in more detail. Our modeling results demonstrate the importance of both the SPM properties (concentration, size, density) as well as the affinity of TiO(2) NPs and SPM, characterized by the attachment efficiency, α(het-agg), on the transport potential of ENPs in a surface water system.

Heteroaggregation of Titanium Dioxide Nanoparticles with Model Natural Colloids under Environmentally Relevant Conditions

The heteroaggregation of engineered nanoparticles (ENPs) with natural colloids (NCs), which are ubiquitous in natural surface waters, is a crucial process affecting the environmental transport and fate of ENPs. Attachment efficiencies for heteroaggregation, α hetero, are required as input parameters in environmental fate models to predict ENP concentrations and contribute to ENP risk assessment. Here, we present a novel method for determining α hetero values by using a combination of laser diffraction measurements and aggregation modeling based on the Smoluchowski equation. Titanium dioxide nanoparticles (TiO2 NPs, 15 nm) were used to demonstrate this new approach together with larger silicon dioxide particles (SiO2, 0.5 μm) representing NCs. Heteroaggregation experiments were performed at different environmentally relevant solution conditions. At pH 5 the TiO2 NPs and the SiO2 particles are of opposite charge, resulting in α hetero values close to 1. At pH 8, where all particles are negatively charged, α hetero was strongly affected by the solution conditions, with α hetero ranging from <0.001 at low ionic strength to 1 at conditions with high NaCl or CaCl2 concentrations. The presence of humic acid stabilized the system against heteroaggregation.

The road to nowhere: equilibrium partition coefficients for nanoparticles

Adequate fate descriptors are crucial input parameters in models used to predict the behaviour and transport of a contaminant in the environment and determine predicted environmental concentrations for risk assessment. When new fate models are being developed for emerging contaminants, such as engineered nanoparticles (ENPs), special care has to be applied in adjusting conventional approaches and fate descriptors to a new set of substances. The aim of this paper is to clarify misconceptions about the applicability of equilibrium partition coefficients, such as the octanol–water partition coefficient (Kow) or the soil–water distribution coefficient (Kd), whose application in the context of ENP fate assessment is frequently suggested despite lacking scientific justification. ENPs are present in the environment as thermodynamically unstable suspensions and their behaviour must be represented by kinetically controlled attachment and deposition processes as has been established by colloid science. Here, we illustrate the underlying theories of equilibrium partitioning and kinetically controlled attachment and discuss why the use of any coefficient based on equilibrium partitioning is inadequate for ENPs and can lead to significant errors in ENP fate predictions and risk assessment.

Addressing the complexity of water chemistry in environmental fate modeling for engineered nanoparticles.

Engineered nanoparticle (ENP) fate models developed to date - aimed at predicting ENP concentration in the aqueous environment - have limited applicability because they employ constant environmental conditions along the modeled system or a highly specific environmental representation; both approaches do not show the effects of spatial and/or temporal variability. To address this conceptual gap, we developed a novel modeling strategy that: 1) incorporates spatial variability in environmental conditions in an existing ENP fate model; and 2) analyzes the effect of a wide range of randomly sampled environmental conditions (representing variations in water chemistry). This approach was employed to investigate the transport of nano-TiO2 in the Lower Rhône River (France) under numerous sets of environmental conditions. The predicted spatial concentration profiles of nano-TiO2 were then grouped according to their similarity by using cluster analysis. The analysis resulted in a small number of clusters representing groups of spatial concentration profiles. All clusters show nano-TiO2 accumulation in the sediment layer, supporting results from previous studies. Analysis of the characteristic features of each cluster demonstrated a strong association between the water conditions in regions close to the ENP emission source and the cluster membership of the corresponding spatial concentration profiles. In particular, water compositions favoring heteroaggregation between the ENPs and suspended particulate matter resulted in clusters of low variability. These conditions are, therefore, reliable predictors of the eventual fate of the modeled ENPs. The conclusions from this study are also valid for ENP fate in other large river systems. Our results, therefore, shift the focus of future modeling and experimental research of ENP environmental fate to the water characteristic in regions near the expected ENP emission sources. Under conditions favoring heteroaggregation in these regions, the fate of the ENPs can be readily predicted.

Phenyltin-substituted 9-tungstogermanate and comparison with its tungstosilicate analogue.

Reaction of (C 6H 5)SnCl 3 with Na 10[ A-alpha-GeW 9O 34] in water results in the monomeric, trisubstituted Keggin species [{(C 6H 5)Sn(OH)} 3( A-alpha-GeW 9O 34)] (4-) ( 1), constituting the first organotin derivative of a trilacunary Keggin tungstogermanate. Polyanion 1 could be obtained as two different cesium salts depending on the applied isolation strategy: Cs 3Na[{(C 6H 5)Sn(OH)} 3( A-alpha-GeW 9O 34)].9H 2O ( CsNa-1) and Cs 3[{(C 6H 5)Sn(OH)} 3( A-alpha-HGeW 9O 34)].8H 2O ( Cs-H1). The monomeric phenyltin-containing tungstosilicate [{(C 6H 5)Sn(OH)} 3( A-alpha-SiW 9O 34)] (4-) ( 2) and the dimeric, sandwich-type derivative [{(C 6H 5)Sn(OH)} 3( A-alpha-H 3SiW 9O 34) 2] (8-) ( 3) have also been isolated as the cesium salts Cs 3Na[{(C 6H 5)Sn(OH)} 3( A-alpha-SiW 9O 34)].9H 2O ( CsNa-2), Cs 4[{(C 6H 5)Sn(OH)} 3( A-alpha-SiW 9O 34)].13H 2O ( Cs-2), and Cs 8[{(C 6H 5)Sn(OH)} 3( A-alpha-H 3SiW 9O 34) 2].23H 2O ( Cs-3), respectively. We have investigated in detail the similarities and differences in the reactivity of (C 6H 5)Sn (3+) with [ A-alpha-GeW 9O 34] (10-) vs [ A-alpha-SiW 9O 34] (10-). All five compounds have been characterized in the solid state by means of elemental analysis, infrared spectroscopy, thermogravimetry, and single-crystal X-ray diffraction, representing the first structural analysis for polyanions 1- 3. A full solution characterization of 1 by multinuclear NMR spectroscopy ( (1)H, (13)C, (119)Sn, and (183)W) has also been performed. The monomeric polyanions 1 and 2 are closely associated in the solid state through (Sn)O-H...O t (O t: terminal oxygen atom) hydrogen bonds reinforced by weak C-H...O t contacts to form 2-dimensional ( CsNa-1 and CsNa-2) or 1-dimensional ( Cs-H1) arrangements, and also dimeric entities ( Cs-2) depending on the network of intermolecular interactions.

Detection of Engineered Copper Nanoparticles in Soil Using Single Particle ICP-MS.

Regulatory efforts rely on nanometrology for the development and implementation of laws regarding the incorporation of engineered nanomaterials (ENMs) into industrial and consumer products. Copper is currently one of the most common metals used in the constantly developing and expanding sector of nanotechnology. The use of copper nanoparticles in products, such as agricultural biocides, cosmetics and paints, is increasing. Copper based ENMs will eventually be released to the environment through the use and disposal of nano-enabled products, however, the detection of copper ENMs in environmental samples is a challenging task. Single particle inductively coupled plasma mass spectroscopy (spICP-MS) has been suggested as a powerful tool for routine nanometrology efforts. In this work, we apply a spICP-MS method for the detection of engineered copper nanomaterials in colloidal extracts from natural soil samples. Overall, copper nanoparticles were successfully detected in the soil colloidal extracts and the importance of dwell time, background removal, and sample dilution for method optimization and recovery maximization is highlighted.

Facing complexity through informed simplifications: a research agenda for aquatic exposure assessment of nanoparticles

Exposure assessment of engineered nanoparticles (ENPs) is a challenging task mainly due to the novel properties of these new materials and the complexity caused by a wide range of particle characteristics, ENP-containing products and possible environmental interactions. We here present a research agenda in which we propose to face the complexity associated with ENP exposure assessment through informed and systematic simplifications. Exposure modelling is presented as a method for addressing complexity by identifying processes dominant for the fate of ENPs in the environment and enabling an iterative learning process by studying different emission and fate scenarios. Furthermore, the use of models is important to highlight most pressing research needs. For this reason, we also strongly encourage improved communication and collaboration between modellers and experimental scientists. Feedback between modellers and experimental scientists is crucial in order to understand the big picture of ENP exposure assessment and to establish common research strategies. Through joint research efforts and projects, the field of ENP exposure assessment can greatly improve and significantly contribute to a comprehensive and systematic risk assessment of ENPs.

Single-particle multi-element fingerprinting (spMEF) using inductively-coupled plasma time-of-flight mass spectrometry (ICP-TOFMS) to identify engineered nanoparticles against the elevated natural background in soils

The discrimination of engineered nanoparticles (ENPs) from the natural geogenic background is one of the preeminent challenges for assessing their potential implications. At low ENP concentrations, most conventional analytical techniques are not able to take advantage of inherent differences (e.g. in terms of composition, isotopic signatures, element ratios, structure, shape or surface characteristics) between ENPs and naturally occurring nanoscale particles (NNPs) of similar composition. Here, we present a groundbreaking approach to overcome these limitations and enable the discrimination of man-made ENPs from NNPs through simultaneous detection of multiple elements on an individual particle level. This new analytical approach is accessible by an inductively-coupled plasma time-of-flight mass spectrometer (ICP-TOFMS) operated in single-particle mode. Machine learning is employed to classify ENPs and NNPs based on their unique elemental fingerprints and quantify their concentrations. We demonstrate the applicability of this single-particle multi-element fingerprinting (spMEF) method by distinguishing engineered cerium oxide nanoparticles (CeO2 ENPs) from natural Ce-containing nanoparticles (Ce-NNPs) in soils at environmentally relevant ENP concentrations, orders of magnitude below the natural background.

Microplastic Exposure Assessment in Aquatic Environments: Learning from Similarities and Differences to Engineered Nanoparticles

Microplastics (MPs) have been identified as contaminants of emerging concern in aquatic environments and research into their behavior and fate has been sharply increasing in recent years. Nevertheless, significant gaps remain in our understanding of several crucial aspects of MP exposure and risk assessment, including the quantification of emissions, dominant fate processes, types of analytical tools required for characterization and monitoring, and adequate laboratory protocols for analysis and hazard testing. This Feature aims at identifying transferrable knowledge and experience from engineered nanoparticle (ENP) exposure assessment. This is achieved by comparing ENP and MPs based on their similarities as particulate contaminants, whereas critically discussing specific differences. We also highlight the most pressing research priorities to support an efficient development of tools and methods for MPs environmental risk assessment.

Environmental Fate and Exposure Modeling of Nanomaterials

Different types of engineered nanomaterials (ENMs) are used in a wide range of applications, such as (coated) titanium dioxide (TiO2) nanoparticles (NPs) in sunscreens, silver nanoparticles as biocide in textiles, water disinfection, or wound dressings, and gold nanoparticles as carriers or sensors in medical applications. Because many ENM applications are open, ENMs are released from the systems or devices where they are used. In many cases, ENM releases are to water, either to the sewer system via wastewater from households, hospitals, and industry, or directly to freshwater bodies that receive NPs from, e.g., application of TiO2 NPs in sunscreens. ENMs may also be released to soil, be it with biosolids from wastewater treatment plants, or as components of new types of plant protection products. However, it is currently not well known in what amounts and in what chemical and physical forms ENMs actually reach the environment. This calls for emission estimates and environmental fate assessments of ENMs. We describe the processes that govern the environmental fate of ENMs and how these processes can be represented in environmental fate models for ENMs. Environmental fate models are well-established tools in the risk assessment of organic chemicals, but the process descriptions used for organic chemicals are not suitable for ENMs. We show how new process descriptions can be set up for ENMs, with a particular focus on heteroaggregation of ENMs and natural particulate matter, and present results from several environmental fate models for ENMs, along with a summary of currently available ENM emission data required as input to the models. We also review models used to describe vertical transport of ENMs in soil column experiments and highlight areas for further model development.