Biological Surface Coating and Molting Inhibition as Mechanisms of TiO2 Nanoparticle Toxicity in Daphnia magna

The production and use of nanoparticles (NP) has steadily increased within the last decade; however, knowledge about risks of NP to human health and ecosystems is still scarce. Common knowledge concerning NP effects on freshwater organisms is largely limited to standard short-term (≤48 h) toxicity tests, which lack both NP fate characterization and an understanding of the mechanisms underlying toxicity. Employing slightly longer exposure times (72 to 96 h), we found that suspensions of nanosized (∼100 nm initial mean diameter) titanium dioxide (nTiO2) led to toxicity in Daphnia magna at nominal concentrations of 3.8 (72-h EC50) and 0.73 mg/L (96-h EC50). However, nTiO2 disappeared quickly from the ISO-medium water phase, resulting in toxicity levels as low as 0.24 mg/L (96-h EC50) based on measured concentrations. Moreover, we showed that nTiO2 (∼100 nm) is significantly more toxic than non-nanosized TiO2 (∼200 nm) prepared from the same stock suspension. Most importantly, we hypothesized a mechanistic chain of events for nTiO2 toxicity in D. magna that involves the coating of the organism surface with nTiO2 combined with a molting disruption. Neonate D. magna (≤6 h) exposed to 2 mg/L nTiO2 exhibited a “biological surface coating” that disappeared within 36 h, during which the first molting was successfully managed by 100% of the exposed organisms. Continued exposure up to 96 h led to a renewed formation of the surface coating and significantly reduced the molting rate to 10%, resulting in 90% mortality. Because coating of aquatic organisms by manmade NP might be ubiquitous in nature, this form of physical NP toxicity might result in widespread negative impacts on environmental health

Bioaccumulation in aquatic systems: methodological approaches, monitoring and assessment

Bioaccumulation, the accumulation of a chemical in an organism relative to its level in the ambient medium, is of major environmental concern. Thus, monitoring chemical concentrations in biota are widely and increasingly used for assessing the chemical status of aquatic ecosystems. In this paper, various scientific and regulatory aspects of bioaccumulation in aquatic systems and the relevant critical issues are discussed. Monitoring chemical concentrations in biota can be used for compliance checking with regulatory directives, for identification of chemical sources or event related environmental risk assessment. Assessing bioaccumulation in the field is challenging since many factors have to be considered that can effect the accumulation of a chemical in an organism. Passive sampling can complement biota monitoring since samplers with standardised partition properties can be used over a wide temporal and geographical range. Bioaccumulation is also assessed for regulation of chemicals of environmental concern whereby mainly data from laboratory studies on fish bioaccumulation are used. Field data can, however, provide additional important information for regulators. Strategies for bioaccumulation assessment still need to be harmonised for different regulations and groups of chemicals. To create awareness for critical issues and to mutually benefit from technical expertise and scientific findings, communication between risk assessment and monitoring communities needs to be improved. Scientists can support the establishment of new monitoring programs for bioaccumulation, e.g. in the frame of the amended European Environmental Quality Standard Directive

Fraction-related quantification of silver nanoparticles via on-line species-unspecific post-channel isotope dilution in combination with asymmetric flow-field-flow fractionation (AF4)/sector field ICP-mass spectrometry (ICP-SF-MS)

Engineered nanoparticles (ENPs) show new and interesting properties leading to an increased use in various application fields and have entered our daily environment (e. g., functionalized clothing, cosmetics, food, medicine). Though on the one hand nanotechnology plays a substantial role in societies' daily life, on the other the presence and behavior of ENPs in organisms and the environment is still unclear to a large extent. Furthermore, comprehensive legislative regulation is still missing. For adequate regulation a clear definition of ENPs is needed. A definition recommendation was released in 2011 by the European Commission (EC) on the basis of size and number of ENPs present within a defined size range. However, straightforward analytical techniques which easily provide information allowing for a decision (based on the EC definition) on the presence and concentration of ENPs in a given sample do not exist yet. A promising tool, offering fraction-related size information on the one hand and allowing for element-specific detection on the other is the coupling of asymmetric flow-field-flow-fractionation (AF4) with inductively coupled plasma-mass spectrometry (ICP-MS). In this work, a new strategy for quantifying silver nanoparticle (AgNP) size fractions (30 nm +/- 2.1 nm, 75 nm +/- 3.9 nm) after base-line AF4 separation relying on on-line ICP-MS detection combined with "post-channel" species-unspecific online isotope dilution (on-line ID) was successfully developed. A limit of detection (LOD) of 0.5 mu g Ag L-1 and a limit of quantification (LOQ) of 1.6 mu g Ag L-1 were achieved by the approach applied. The recovery values for the smaller size-fraction (30 nm) were in the range of 31-41% while for the larger size-fraction (75 nm) in the range of 75-78%. The overall reproducibility (RSDs, peak areas) was in between 3.4-5.4%. Validation of the on-line ID approach was achieved via off-line fraction collection and total silver determination afterwards; a bias of 2.9-16.4% between both approaches was observed indicating that the on-line ID approach is working properly. To the best of the authors' knowledge, this is the first time that species-unspecific (post-channel) on-line ID was combined with AF4/ICP-SF-MS for fraction-related quantification of AgNPs

New Microprofiling and Micro Sampling System for Water Saturated Environmental Boundary Layers

The spatial high resolution of a microprofiling system was combined with the multi element capability of ICP-MS to enable a better understanding of element distributions and related processes across environmental boundary layers. A combination of a microprofiling system with a new micro filtration probe head connected to a pump and a fraction collector (<i>mi</i>croprofiling and micro <i>s</i>ampling <i>sy</i>stem, <i>missy</i>) is presented. This enables for the first time a direct, dynamic, and high resolution automatic sampling of small water volumes (<500 μL) from depth profiles of water saturated matrices (e.g., sediments, soils, biofilms). Different membrane cut-offs are available, and resolutions of a few (matrices with a high physical resistance) to a submillimeter scale (matrices with low physical resistance) can be achieved. In this Article, (i) the modular setups of two <i>missy</i>s are presented; (ii) it is demonstrated how the micro probe heads are manufactured; (iii) background concentrations and recoveries of the system as well as (iv) exemplary results of a sediment water interface are delivered. On the basis of this, potentials, possible sources of errors, and future applications of the new <i>missy</i> are discussed

Metal and Metalloid Size-Fractionation Strategies in Spatial High-Resolution Sediment Pore Water Profiles

Sediment water interfaces (SWIs) are often characterized by steep biogeochemical gradients determining the fate of inorganic and organic substances. Important transport processes at the SWI are sedimentation and resuspension of particulate matter and fluxes of dissolved materials. A <i>mi</i>croprofiling and micro <i>s</i>ampling <i>sy</i>stem (<i>missy</i>), enabling high resolution measurements of sediment parameters in parallel to a direct sampling of sediment pore waters (SPWs), was combined with two fractionation approaches (ultrafiltration (UF) and cloud point extraction (CPE)) to differentiate between colloidal and dissolved fractions at a millimeter scale. An inductively coupled plasma-quadrupole mass spectrometry method established for volumes of 300 μL enabled the combination of the high resolution fractionation with multi-element analyzes. UF and CPE comparably indicated that manganese is predominantly present in dissolved fractions of SPW profiles. Differences found for cobalt and iron showed that the results obtained by size-dependent UF and micelle-mediated CPE do not necessarily coincide, probably due to different fractionation mechanisms. Both methods were identified as suitable for investigating fraction-related element concentrations in SPW along sediment depth profiles at a millimeter scale. The two approaches are discussed with regard to their advantages, limitations, potential sources of errors, further improvements, and potential future applications

Can cloud point-based enrichment, preservation, and detection methods help to bridge gaps in aquatic nanometrology?

Coacervate-based techniques are intensively used in environmental analytical chemistry to enrich and extract different kinds of analytes. Most methods focus on the total content or the speciation of inorganic and organic substances. Size fractionation is less commonly addressed. Within coacervate-based techniques, cloud point extraction (CPE) is characterized by a phase separation of non-ionic surfactants dispersed in an aqueous solution when the respective cloud point temperature is exceeded. In this context, the feature article raises the following question: May CPE in future studies serve as a key tool (i) to enrich and extract nanoparticles (NPs) from complex environmental matrices prior to analyses and (ii) to preserve the colloidal status of unstable environmental samples? With respect to engineered NPs, a significant gap between environmental concentrations and size- and element-specific analytical capabilities is still visible. CPE may support efforts to overcome this "concentration gap" via the analyte enrichment. In addition, most environmental colloidal systems are known to be unstable, dynamic, and sensitive to changes of the environmental conditions during sampling and sample preparation. This delivers a so far unsolved "sample preparation dilemma" in the analytical process. The authors are of the opinion that CPE-based methods have the potential to preserve the colloidal status of these instable samples. Focusing on NPs, this feature article aims to support the discussion on the creation of a convention called the "CPE extractable fraction" by connecting current knowledge on CPE mechanisms and on available applications, via the uncertainties visible and modeling approaches available, with potential future benefits from CPE protocols