Challenges in Exposure Modeling of Nanoparticles in Aquatic Environments

Managing the potential environmental risks of nanoparticles requires methods to link nanoparticle properties with macro-scale risks. This study outlines challenges in exposure modeling of nanoparticles in aquatic environments, such as the role of natural organic matter, natural colloids, fractal dimensions of agglomerates, coatings and doping of particles, and uncertainties regarding nanoparticle emissions to aquatic environments. The pros and cons of the exposure indicators mass concentration, particle number concentration, and surface area are discussed. By applying colloid chemistry kinetic equations describing particle agglomeration and sedimentation for the case of titanium dioxide nanoparticles, a limited exposure assessment including some of the factors mentioned is conducted with particle number concentration as the exposure indicator. The results of the modeling indicate that sedimentation, shear flows, and settling are of less importance with regard to particle number based predicted environmental concentrations. The inflow of nanoparticles to the water compartment had a significant impact in the model, and the collision efficiency (which is affected by natural organic matter) was shown to greatly affect model output. Implications for exposure modeling, regulation and science are discussed. A broad spectrum of scientific disciplines must be engaged in the development of exposure models where nano-level properties are linked to macro-scale risk

Size dependence of silver nanoparticle removal in a wastewater treatment plant mesocosm measured by FAST single particle ICP-MS

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

Are We Speaking the Same Language? Recommendations for a Definition and Categorization Framework for Plastic Debris

Embargo until 04 Jan 2020The accumulation of plastic litter in natural environments is a global issue. Concerns over potential negative impacts on the economy, wildlife, and human health provide strong incentives for improving the sustainable use of plastics. Despite the many voices raised on the issue, we lack a consensus on how to define and categorize plastic debris. This is evident for microplastics, where inconsistent size classes are used and where the materials to be included are under debate. While this is inherent in an emerging research field, an ambiguous terminology results in confusion and miscommunication that may compromise progress in research and mitigation measures. Therefore, we need to be explicit on what exactly we consider plastic debris. Thus, we critically discuss the advantages and disadvantages of a unified terminology, propose a definition and categorization framework, and highlight areas of uncertainty. Going beyond size classes, our framework includes physicochemical properties (polymer composition, solid state, solubility) as defining criteria and size, shape, color, and origin as classifiers for categorization. Acknowledging the rapid evolution of our knowledge on plastic pollution, our framework will promote consensus building within the scientific and regulatory community based on a solid scientific foundation.acceptedVersio

Selective incorporation of dissolved organic matter (DOM) during sea ice formation

This study investigated the incorporation of DOM from seawater into >2 day-old sea ice in tanks filled with seawater alone or amended with DOM extracted from the microalga, Chlorella vulgaris. Optical properties, including chromophoric DOM (CDOM) absorption and fluorescence, as well as concentrations of dissolved organic carbon (DOC), dissolved organic nitrogen (DON), dissolved carbohydrates (dCHOs) and dissolved uronic acids (dUAs) were measured. Enrichment factors (EFs), calculated from salinity-normalized concentrations of DOM in bulk ice, brine and frost flowers relative to under-ice water, were generally >1. The enrichment factors varied for different DOM fractions: EFs were the lowest for humic-like DOM (1.0–1.39) and highest for amino acid-like DOM (1.10–3.94). Enrichment was generally highest in frost flowers with there being less enrichment in bulk ice and brine. Size exclusion chromatography indicated that there was a shift towards smaller molecules in the molecular size distribution of DOM in the samples collected from newly formed ice compared to seawater. Spectral slope coefficients did not reveal any consistent differences between seawater and ice samples. We conclude that DOM is incorporated to sea ice relatively more than inorganic solutes during initial formation of sea ice and the degree of the enrichment depends on the chemical composition of DO

Effects of silver nanoparticles on freshwater microbial communities

Nanoparticles (NPs) display special chemical properties because of their size, shape, composition and electronic structure. These properties lend NPs their functionality, but may also lead to toxic effects. Due to their widespread use in consumer products an exposure of the aquatic environment to NPs is anticipated and already proven in first analytical surveys. Especially metal/metaloxide NPs are widely used, of which silver nanoparticles (AgNPs) have gained considerable attention due to their broad microbiocidal properties. This implies a specific hazard for exposed aquatic primary producers (algae) and bacteria. In a case study with AgNPs, the toxicity to natural freshwater microbial communities was determined. The microbial communities were exposed to AgNPs of different sizes (10, 20, 40 and 50 nm) as well as different coatings (non-coated, citrate coated) in concentrations from 0.1 - 5000 nmol/L expcept for one silver nanoparticle type (50 nm, uncoated) which was tested in a range from 100 - 10 000 nmol/L. The selected silver nanoparticles were all purchased from commercial producers and distributers (Amepox, British Biocell, NanoTrade, Tedpella). To distinguish between particle related effects and effects caused by free silver ions silver nitrate was tested as a reference in corresponding total silver concentrations. The effects on the algal parts of the community was studied through pigment profile analysis with HPLC. The bacterial community composition was analysed by metabolic profiling on so called ecologplates[TRADEMARK] containing different carbon sources with a redox dye responding to respiration with colour change. The metabolic activity i.e. the colour change was detected as absorbance and was measured over time in several intervals for a total time period of 96 hours. Inhibition of growth detected as decrease in total biomass was seen in both bacterial and algal communities. All experiments were backed up by analytical measurements, measuring the total silver content, dissolved Ag+ (ultrafiltration) and particle size distribution (Nanosight)

Effects of selected silver nanoparticles on freshwater microbial communities

Due to their widespread use in consumer products an exposure of the aquatic environment to nanoparticles (NPs) is most likely. Especially metal/metaloxide NPs are widely used, of which silver nanoparticles (AgNPs) have gained considerable attention due to their broad microbiocidal properties implying a specific hazard for exposed aquatic algae and bacteria.In a case study with selected AgNPs (different sizes (10, 20 and 40 nm), and different coatings (citrate coated, non-coated)), the toxicity to natural freshwater microbial communities was determined. To distinguish between particle related effects and effects caused by free silver ions silver nitrate (AgNO3) was tested as a reference. The effects on the algal part of the community was studied through pigment profiling with HPLC. The bacterial community composition was analysed by metabolic profiling (ecologplates™). Inhibition of growth detected as a decrease in total biomass was seen in both bacterial and algal communities, for some cases in the range of environmentally realistic concentrations. Differences in toxicity could be determined for the different particles with AgNO3 being for almost all cases the most toxic compound with one excpetion. All experiments were backed up by analytical measurements (total silver content, dissolved silver (ultrafiltration), particle size distribution (Nanosight))