Mohammed Baalousha

Aggregation and surface properties of iron oxide nanoparticles: Influence of ph and natural organic matter

The interactions between unpurified manufactured nanoparticles (NPs; iron oxide NPs, approximately 7 nm) and standard Suwannee River humic acid (SRHA) were investigated under a range of environmentally relevant conditions. At low pH, approximately 35% of the total iron was in the dissolved phase (< 1 kDa), present from the initial synthesis, whereas at pH more than 4, this concentration was negligible because of the formation of new particles via hydrolysis. Dynamic light scattering results indicated that extensive aggregation of NPs began at approximately pH 5 to 6 and reached a maximum at approximately pH 8.5, whereas with added SRHA, aggregation was shifted to lower pH values of 4 to 5 and was affected by SRHA concentration. Aggregation could be explained mainly by charge neutralization. Further, more detailed investigations by flow field-flow fractionation and transmission-electron microscopy were performed under a more restricted set of conditions (pH 2-6) to examine the aggregation process. Results indicated the formation of SRHA surface coating on iron oxide NPs of approximately 1 nm and the increase in thickness of this coating with the increase of SRHA concentration. Iron oxide NPs were shown to form increasingly large aggregates with increases in both pH (from 2 to 6) and SRHA concentration (from 0 to 25 mg/L). The structure and aggregation mechanism of these aggregates were found to be both pH and SRHA concentration dependent, with open, porous aggregates in the absence of SRHA and compact aggregates in the presence of SRHA.

Effects of Aqueous Exposure to Silver Nanoparticles of Different Sizes in Rainbow Trout

Despite increasing application of silver nanoparticles (NPs) in industry and consumer products, there is still little known about their potential toxicity, particularly to organisms in aquatic environments. To investigate the fate and effects of silver NPs in fish, rainbow trout (Oncorhynchus mykiss) were exposed via the water to commercial silver particles of three nominal sizes: 10 nm (N(10)), 35 nm (N(35)), and 600-1600 nm (N(Bulk)), and to silver nitrate for 10 days. Uptake into the gills, liver, and kidneys was quantified by inductively coupled plasma-optical emission spectrometry, and levels of lipid peroxidation in gills, liver, and blood were determined by measurements of thiobarbituric acid reactive substances. Expression of a suite of genes, namely cyp1a2, cyp3a45, hsp70a, gpx, and g6pd, known to be involved in a range of toxicological response to xenobiotics was analyzed in the gills and liver using real-time PCR. Uptake of silver particles from the water into the tissues of exposed fish was low but nevertheless occurred for current estimated environmental exposures. Of the silver particles tested, N(10) were found to be the most highly concentrated within gill tissues and N(10) and N(Bulk) were the most highly concentrated in liver. There were no effects on lipid peroxidation in any of the tissues analyzed for any of the silver particles tested, and this is likely due to the low uptake rates. However, exposure to N(10) particles was found to induce expression of cyp1a2 in the gills, suggesting a possible increase in oxidative metabolism in this tissue.

Flow field-flow fractionation for the analysis and characterization of natural colloids and manufactured nanoparticles in environmental systems: A critical review

The use of flow field flow fractionation (FlFFF) for the separation and characterization of natural colloids and nanoparticles has increased in the last few decades. More recently, it has become a popular method for the characterization of manufactured nanoparticles. Unlike conventional filtration methods, FlFFF provides a continuous and high-resolution separation of nanoparticles as a function of their diffusion coefficient, hence the interest for use in determining particle size distribution. Moreover, when coupled to other detectors such as inductively coupled plasma-mass spectroscopy, light scattering, UV-absorbance, fluorescence, transmission electron microscopy, and atomic force microscopy, FlFFF provides a wealth of information on particle properties including, size, shape, structural parameters, chemical composition and particle-contaminant association. This paper will critically review the application of FlFFF for the characterization of natural colloids and natural and manufactured nanoparticles. Emphasis will be given to the detection systems that can be used to characterize the nanoparticles eluted from the FlFFF system, the obtained information and advantages and limitation of FlFFF compared to other fractionation and particle sizing techniques. This review will help users understand (i) the theoretical principles and experimental consideration of the FlFFF, (ii) the range of analytical tools that can be used to further characterize the nanoparticles after fractionation by FlFFF, (iii) how FlFFF results are compared to other analytical techniques and (iv) the range of applications of FlFFF for natural and manufactured NPs.

Aggregation and dispersion of silver nanoparticles in exposure media for aquatic toxicity tests

Silver nanoparticles (AgNPs) are currently being very widely used in industry, mainly because of their anti-bacterial properties, with applications in many areas. Once released into the environment, the mobility, bioavailability, and toxicity of AgNPs in any ecosystem are dominated by colloidal stability. There have been studies on the stability or the aggregation of various nanoparticles (NPs) under a range of environmental conditions, but there is little information on fully characterised AgNPs in media used in (eco)toxicity studies. In this study, monodisperse 7, 10 and 20 nm citrate-stabilised AgNPs were synthesised, characterised and then fractionated and sized by flow field-flow fractionation (FFF) and measured with dynamic light scattering (DLS) in different dilutions of the media recommended by OECD for Daphnia magna (water flea) toxicity testing. Stability of NPs was assessed over 24 h, and less so over 21 days, similar time periods to the OECD acute and chronic toxicity tests for D. magna. All particles aggregated quickly in the media with high ionic strength (media1), resulting in a loss of colour from the solution. The size of particles could be measured by DLS in most cases after 24h, although a fractogram by FFF could not be obtained due to aggregation and polydispersity of the sample. After diluting the media by a factor of 2, 5 or 10, aggregation was reduced, although the smallest NPs were unstable under all media conditions. Media diluted up to 10-fold in the absence of AgNPs did not induce any loss of mobility or fecundity in D. magna. These results confirm that standard OECD media causes aggregation of AgNPs, which result in changes in organism exposure levels and the nature of the exposed particles compared to exposure to fully dispersed particles. Setting aside questions of dose metrics, significant and substantial reduction in concentration over exposure period suggests that literature data are in the main improperly interpreted and nanoparticles are likely to have far greater biological effects than suggested thus far by poorly controlled exposures. We recommend that the standard OECD media is diluted by a factor of ca. 10 for use with these NPs and this test media, which reduces AgNP aggregation without affecting the viability of the text organism.

Effect of monovalent and divalent cations, anions and fulvic acid on aggregation of citrate-coated silver nanoparticles

The dynamic nature of nanoparticle (NP) aggregation behavior is of paramount interest to many current studies in environmental and toxicological nanoscience. The present study seeks to elucidate the influence that different electrolytes have on the aggregation of citrate-coated silver NPs (cit-AgNPs). The use of both UV-vis spectroscopy and dynamic light scattering (DLS, both z-average hydrodynamic diameter (z-dh) and size distribution analysis data) allowed improvement in the data quality and interpretation as compared to other studies using only DLS and reporting solely the z-dh, as the change in the z-dh can be related to analytical errors and uncertainties rather than only aggregation or dissolution of NPs. Divalent cations (CaCl2, Ca(NO3)2, CaSO4, MgCl2 and MgSO4) have stronger influence (ca. 50-65 fold) on aggregation of cit-AgNPs as compared to monovalent cations (NaCl, NaNO3, Na2SO4), as expected. For electrolytes with monovalent cations, there was no specific ion effect of nitrate and sulfate anions. However, the addition of chloride anions resulted in enhanced apparent aggregation, possibly due to the formation of AgCl NPs that sorb/attach to the surface of cit-AgNPs. Suwannee River fulvic acid enhances the stability of cit-AgNPs and shifts the critical coagulation concentrations to higher electrolyte concentrations for all types of electrolytes. Aggregation kinetics in the presence of mixture of monovalent and divalent cations is additive and controlled by the dominant cations. An empirical formula (αmixture=αNa+(50 to 65)Ca) is proposed that reproduces the effect of mixtures of electrolytes in the presence of humic substances and cations that can be used to help predict the aggregation behavior of cit-AgNPs in environmental and ecotoxicological media.

Physico-chemical behaviour and algal toxicity of nanoparticulate CeO2 in freshwater

In assessing the risks posed by nanomaterials in the environment, the overriding research challenges are to determine if nanomaterials are more toxic than the bulk forms of the same material, and the extent to which toxicity is governed by particle size and reactivity. In this study, the toxicity of nanoparticulate CeO2 (nominally 10-20 nm) to the freshwater alga Pseudokirchneriella subcapitata was compared to the same material at the micron size (nominally <5 µm). Growth inhibition experiments revealed inhibitory concentration values, giving 50% reduction in algal growth rate after 72 h (IC50), of 10.3 ± 1.7 and 66 ± 22 mg L −1 for the nanoparticles and bulk materials respectively. Cells exposed to CeO2 particles were permeable to the DNA-binding dye SYTOX ® Green in a concentration-dependent manner indicating damage to the cell membrane. Screening assays to assess the oxidative activity of the particles showed that the light illumination conditions used during standard assays are sufficient to stimulate photocatalytic activity of CeO2 particles, causing the generation of hydroxyl radicals and peroxidation of a model plant fatty acid. No oxidative activity or lipid peroxidation was observed in the dark. These findings indicate that inhibitory mode of action of CeO2 to P. subcapitata is mediated by a cell-particle interaction causing membrane damage. The effect is most likely photochemically induced and is enhanced for the nanoparticulate form of the CeO2.

Interspecies comparisons on the uptake and toxicity of silver and cerium dioxide nanoparticles

An increasing number and quantity of manufactured nanoparticles are entering the environment as the diversity of their applications increases, and this will lead to the exposure of both humans and wildlife. However, little is known regarding their potential health effects. We compared the potential biological effects of silver (Ag; nominally 35 and 600-1,600 nm) and cerium dioxide (CeO(2;) nominally <25 nm and 1-5 µm) particles in a range of cell (human hepatocyte and intestinal and fish hepatocyte) and animal (Daphnia magna, Cyprinus carpio) models to assess possible commonalities in toxicity across taxa. A variety of analytical techniques were employed to characterize the particles and investigate their biological uptake. Silver particles were more toxic than CeO(2) in all test systems, and an equivalent mass dose of Ag nanoparticles was more toxic than larger micro-sized material. Cellular uptake of all materials tested was shown in C3A hepatocytes and Caco-2 intestinal cells, and for Ag, into the intestine, liver, gallbladder, and gills of carp exposed via the water. The commonalities in toxicity of these particle types across diverse biological systems suggest that cross-species extrapolations may be possible for metal nanoparticle test development in the future. Our findings also suggest transport of particles through the gastrointestinal barrier, which is likely to be an important uptake route when assessing particle risk.

Modeling nanomaterial environmental fate in aquatic systems.

Mathematical models improve our fundamental understanding of the environmental behavior, fate, and transport of engineered nanomaterials (NMs, chemical substances or materials roughly 1-100 nm in size) and facilitate risk assessment and management activities. Although todays large-scale environmental fate models for NMs are a considerable improvement over early efforts, a gap still remains between the experimental research performed to date on the environmental fate of NMs and its incorporation into models. This article provides an introduction to the current state of the science in modeling the fate and behavior of NMs in aquatic environments. We address the strengths and weaknesses of existing fate models, identify the challenges facing researchers in developing and validating these models, and offer a perspective on how these challenges can be addressed through the combined efforts of modelers and experimentalists.

Characterization of cerium oxide nanoparticles—Part 1: Size measurements

The present study gives an overview of some of the major aspects for consideration in the characterization of nanomaterials (NMs). Part 1 focuses on the measurement of particle size and size-related parameters using several analytical techniques such as transmission electron microscopy, atomic force microscopy, dynamic light scattering, X-ray diffraction, and Brunauer, Emmett, and Teller surface area measurements as applied to commercially available cerium oxide nanoparticles (NPs) and microparticles (MPs). Part 2 (see companion paper) considers nonsize-related characterization and analysis. The results are discussed in relation to the nature of the sample and preparation, and the analytical principles, limitations, and advantages of each technique. Accurate information on the particle size of the different fractions of a sample can be obtained by using a combination of different types of microscopy, spectroscopy, separation, and other techniques; this should inform ecotoxicological and environmental studies. The good agreement between the measured primary particle size of the NPs (~15 nm) by atomic force microscopy, transmission electron microscopy, X-ray diffraction, and Brunauer, Emmett, and Teller suggests that the primary particles are formed of semispherical single crystals. For MPs, all measurements agree that they are large particles in the range above the NPs (100 nm), with some difference between the measured sizes, possibly as a result of polydispersity effects. Additionally, our findings suggest that atomic force microscopy and transmission electron microscopy prepared by centrifugation methods provide consistent data at low concentrations when dynamic light scattering fails.

Transformations of citrate and Tween coated silver nanoparticles reacted with Na2S

Silver nanoparticles (Ag NPs) are susceptible to transformations in environmental and biological media such as aggregation, oxidation, dissolution, chlorination, sulfidation, formation/replacement of surface coatings following interaction with natural organic matter (NOM). This paper investigates the impact of surface coating and Suwannee River fulvic acid (SRFA) on the transformations and behavior of Ag NPs (citrate coated and Tween coated; cit-Ag NPs and Tween-Ag NPs, respectively), following reaction with different concentrations of Na2S solution (as a source of sulfide species, H2S and HS(-)). These transformations and the dominant mechanisms of transformations were investigated using UV-vis and scanning transmission electron microscopy coupled with electron energy loss spectroscopy. Here, we have shown that Ag NP surface coating impacts their dissolution following dilution in ultrahigh purity water, with higher extent of dissolution of Tween-Ag NPs compared with cit-Ag NPs. Tween-Ag NPs are susceptible to dissolution following their sulfidation at low S/Ag molar ratio. Suwannee River fulvic acid (SRFA) slows down the dissolution of Tween-Ag NPs at low sulfide concentrations and reduces the aggregation of cit-Ag NP in the presence of sodium sulfide. Sulfidation appears to occur by direct interaction of sulfide species with Ag NPs rather than by indirect reaction of sulfide with dissolved Ag species subsequent to dissolution. Furthermore, the sulfidation process results in the formation of partially sulfidized Ag NPs containing unreacted (metallic) subgrains at the edge of the NPs for Tween-Ag NPs in the presence of high sulfide concentration (2000nM Na2S), which occurred to less extent at lower Na2S concentration for Tween-Ag NPs and at all concentrations of Na2S for cit-Ag NPs. Thus, sulfidized Ag NPs may preserve some of the properties of the Ag NPs such as their potential to shed Ag(+) ions and their toxic potential of Ag NPs.