Transmission electron microscopy investigation of colloids and particles from landfill leachates

Leachates collected at two (active and closed) municipal solid waste (MSW) landfills were examined for colloids and particles by transmission electron microscopy, energy dispersive spectrometry, selected area electron diffraction and for the chemical compositions of the filtrates after the filtration to 0.1 µm and ultrafiltration to 1 kDa (~ 1 nm). Six groups of colloids/particles in the range 5 nm to 5 µm were determined (in decreasing order of abundance): carbonates, phyllosilicates (clay minerals and micas), quartz, Fe-oxides, organics and others (salts, phosphates). Inorganic colloids/particles in leachates from the active landfill predominantly consist of calcite (CaCO(3)) and minor clay minerals and quartz (SiO(2)). The colloids/particles in the leachates from the closed landfill consist of all the observed groups with dominant phyllosilicates. Whereas calcite, Fe-oxides and phosphates can precipitate directly from the leachates, phyllosilicates and quartz are more probably either derived from the waste or formed by erosion of the geological environment of the landfill. Low amounts of organic colloids/particles were observed, indicating the predominance of organic molecules in the 'truly dissolved' fraction (fulvic compounds). Especially newly formed calcite colloids forming particles of 500 nm and stacking in larger aggregates can bind trace inorganic contaminants (metals/metalloids) and immobilize them in landfill environments.

Engineered nanoparticles and their identification among natural nanoparticles

The more nanotechnology develops, the more likely the release of engineered nanoparticles into the environment becomes. Due to a huge excess of natural nanoparticles, the identification and quantification of engineered nanoparticles pose a big challenge to analysts. Moreover, identification in a qualitative sense and quantification by mass concentration alone are not sufficient, because the potential environmental hazard arising from engineered nanoparticles is controlled by many other properties of the particles. We discuss the most important methods of fractionation and detection of both natural and engineered nanoparticles, with a focus on the chemical nature of the particles, particle concentration, and particle size. Analyses should not rely on only one method; instead, several complementary methods should, if possible, be used. Coupled techniques should be further developed and increasingly applied. Dedicated techniques that are tailored to the search for a particular sort of engineered nanoparticles are more promising than universal approaches that search for any engineered nanoparticles.

Functionalized nanoparticle interactions with polymeric membranes

A series of experiments was performed to measure the retention of a class of functionalized nanoparticles (NPs) on porous (microfiltration and ultrafiltration) membranes. The findings impact engineered water and wastewater treatment using membrane technology, characterization and analytical schemes for NP detection, and the use of NPs in waste treatment scenarios. The NPs studied were composed of silver, titanium dioxide, and gold; had organic coatings to yield either positive or negative surface charge; and were between 2 and 10nm in diameter. NP solutions were applied to polymeric membranes composed of different materials and pore sizes (ranging from ≈ 2 nm [3 kDa molecular weight cutoff] to 0.2 μm). Greater than 99% rejection was observed of positively charged NPs by negatively charged membranes even though pore diameters were up to 20 times the NP diameter; thus, sorption caused rejection. Negatively charged NPs were less well rejected, but behavior was dependent not only on surface functionality but on NP core material (Ag, TiO(2), or Au). NP rejection depended more upon NP properties than membrane properties; all of the negatively charged polymeric membranes behaved similarly. The NP-membrane interaction behavior fell into four categories, which are defined and described here.

Effects of sediment-associated copper to the deposit-feeding snail, Potamopyrgus antipodarum: a comparison of Cu added in aqueous form or as nano- and micro-CuO particles

Increasing use of engineered nanoparticles (NPs) is likely to result in release of these particles to the aquatic environment where the NPs may eventually accumulate in sediment. However, little is known about the potential ecotoxicity of sediment-associated engineered NPs. We here consider the case of metal oxide NPs using CuO to understand if the effects of NPs differ from micron-sized particles of CuO and aqueous Cu (CuCl₂). To address this issue, we compared effects of copper added to the sediment as aqueous Cu, nano- (6 nm) and micro- (<5 μm) CuO particles on the deposit-feeding snail, Potamopyrgus antipodarum. Effects were assessed as mortality, specific growth rate, feeding rate, reproduction, and bioaccumulation after 8 weeks of exposure to nominal concentrations of 0, 30, 60, 120 and 240 μg Cu/g dry weight sediment. The results demonstrate that copper added to sediment as nano-CuO had greater effects on growth, feeding rate, and reproduction of P. antipodarum than copper added as micro-CuO or aqueous Cu. P. antipodarum accumulated more copper in the nano-CuO treatment than in aqueous Cu or micro-CuO treatments, indicating that consideration of metal form may be important when assessing risks of metals to the aquatic environment.

Interactions of gold nanoparticles with freshwater aquatic macrophytes are size and species dependent

The partitioning of 4- and 18-nm gold nanoparticles (AuNPs) to aquatic macrophytes was investigated in vivo with exposure suspension in well water. Three morphologically distinct aquatic macrophytes were studied. Myriophyllum simulans Orch. and Egeria densa Planch. are submerged aquatic vascular plants, whereas Azolla caroliniana Willd. is a free-floating aquatic fern. Because aquatic plants absorb the majority of their nutrients from the water column, it is logical to hypothesize that they may absorb nanomaterials in suspension, potentially facilitating trophic transfer. Each plant was exposed to two different-sized gold nanospheres at a nominal concentration of 250 µg/L AuNPs for 24 h. Macrophytes were harvested at six time points (1, 3, 6, 12, 18, and 24 h), dried, and then analyzed for gold concentration via inductively coupled plasma-mass spectrometry. Concentrations were normalized to whole-plant dry tissue mass. The present study shows that absorption of AuNPs through root uptake was size and species dependent. Electron microscopy revealed that 4- and 18-nm AuNPs adsorbed to the roots of each species. Root tissue was sectioned, and transmission electron microscopy indicated that 4-nm and 18-nm AuNPs were absorbed by A. caroliniana, whereas only 4-nm AuNPs were absorbed by M. simulans. Egeria densa did not absorb AuNPs of either size. Gold nanoparticles were confirmed in tissue by using energy-dispersive X-ray spectroscopy. Absorption of AuNPs by plants may be a function of the salinity tolerance of each species.

New perspectives for in vitro risk assessment of multiwalled carbon nanotubes: application of coculture and bioinformatics

Nanotechnology is a rapidly expanding field with wide application for industrial and medical use; therefore, understanding the toxicity of engineered nanomaterials is critical for their commercialization. While short-term in vivo studies have been performed to understand the toxicity profile of various nanomaterials, there is a current effort to shift toxicological testing from in vivo observational models to predictive and high-throughput in vitro models. However, conventional monoculture results of nanoparticle exposure are often disparate and not predictive of in vivo toxic effects. A coculture system of multiple cell types allows for cross-talk between cells and better mimics the in vivo environment. This review proposes that advanced coculture models, combined with integrated analysis of genome-wide in vivo and in vitro toxicogenomic data, may lead to development of predictive multigene expression-based models to better determine toxicity profiles of nanomaterials and consequent potential human health risk due to exposure to these compounds.

Suppressive effects of natural reduced waters on alloxan-induced apoptosis and type 1 diabetes mellitus

Insulin-producing cells express limited activities of anti-oxidative enzymes. Therefore, reactive oxygen species (ROS) produced in these cells play a crucial role in cytotoxic effects. Furthermore, diabetes mellitus (DM) development is closely linked to higher ROS levels in insulin-producing cells. Hita Tenryosui Water^® (Hita T. W., Hita, Japan) and Nordenau water (Nord. W., Nordenau, Germany), referred to as natural reduced waters (NRWs), scavenge ROS in cultured cells, and therefore, might be a possibility as an alternative to conventional pharmacological agents against DM. Therefore, this study aimed to investigate the role of NRWs in alloxan (ALX)-induced β-cell apoptosis as well as in ALX-induced diabetic mice. NRWs equally suppressed DNA fragmentation levels. Hita T. W. and Nord. W. ameliorated ALX-induced sub-G₁ phase production from approximately 40% of control levels to 8.5 and 11.8%, respectively. NRWs restored serum insulin levels (p < 0.01) and reduced blood glucose levels (p < 0.01) in ALX-induced mice. Hita T. W. restored tissue superoxide dismutase (SOD) (p < 0.05) activity but not tissue catalase activity. Hita T. W. did not elevate SOD or catalase activity in HIT-T15 cells. Nord. W. restored SOD (p < 0.05) and catalase (p < 0.05) activity in both cultured cells and pancreatic tissue to normal levels. Even though variable efficacies were observed between Hita T. W. and Nord. W., both waters suppressed ALX-induced DM development in CD-1 male mice by administering NRWs for 8 weeks. Our results suggest that Hita T. W. and Nord. W. protect against ALX-induced β-cell apoptosis, and prevent the development of ALX-induced DM in experimental animals by regulating ALX-derived ROS generation and elevating anti-oxidative enzymes. Therefore, the two NRWs tested here are promising candidates for the prevention of DM development.

Size distribution and composition of phosphorus in the East Tiao River, China: the significant role of colloids

The environmental risk of aquatic phosphorus (P) critically depends on its mobility and bioavailability, both of which are greatly affected by the size distribution and composition of P. The size distribution (particulate, colloidal and truly dissolved phase) of P, composed of molybdate reactive P (MRP) and molybdate unreactive P (MUP), was determined at twenty-three typical sections of the East Tiao River, China in the plum rain season. Results indicated particulate P was dominant followed by the truly dissolved P, while colloidal P was quantitatively the lowest in the whole river. From upstream to downstream, particulate P sharply increased, along with a slight decrease of truly dissolved P. However, colloidal P remained at a relatively stable level in the whole river, ranging from below detection limit to 0.025 mg L(-1), 0 to 13.4% of total P (TP). Furthermore, colloidal MRP exhibited a rising trend downriver as compared to upriver, with the notable transfer of MRP from the truly dissolved phase to particulate and colloidal phases. Particle concentration effect for colloids, observed in the study of MRP distribution, further corroborated the role of colloids in MRP solid/liquid partitioning. These observations, in this large-scale field investigation, fitted the "colloidal pumping" hypothesis. It may be concluded that colloids act as the intermediate and buffer in the dynamically balanced transfer of P from truly dissolved phase to large particulate phase, having a significant role in size distribution of P.

An assessment of the fate, behaviour and environmental risk associated with sunscreen TiO₂ nanoparticles in UK field scenarios

The fate of Ti was examined in an activated sludge plant serving over 200,000 people. These studies revealed a decrease of 30 to 3.2 μg/L of Ti < 0.45 μm from influent to effluent and a calculated Ti presence of 305 mg/kg DW in wasted sludge. Thus, using sludge as a fertiliser would result in a predicted deposition of up to 250 mg/m² of Ti to soil surfaces using a recommended maximal agricultural application rate. Given the major use of TiO₂ in many industrial and domestic applications where loss to the sewer is possible, this measured Ti was presumed to have been largely TiO₂, a proportion of which will be nanoparticle sized. To assess the behaviour of engineered nanoparticle (ENP) TiO₂ in sewage and toxicology studies, Optisol (Oxonica Materials Ltd) and P25 (Evonik Industries AG), which are representative of forms used in sunscreen and cosmetic products, were used. These revealed a close association of TiO₂ ENPs with activated sludge. Using commercial information on consumption, and removal rates for sewage treatment, predictions were made for river water concentrations for sunscreen TiO₂ ENPs for the Anglian and Thames regions in Southern England. The highest predicted value from these exercises was 8.8 μg/L for the Thames region in which it was assumed that one in four people used the recommended application of sunscreen during a low flow (Q95) period. Ecotoxicological studies using potentially vulnerable species indicated that 1000 μg/L TiO₂ ENP did not affect the viability of a mixed community of river bacteria in the presence of UV light. Direct exposure to TiO₂ ENPs did not impair the immuno-effectiveness of earthworm coelomocyte cells at concentrations greatly above those predicted for sewage sludge.

Titanium in UK rural, agricultural and urban/industrial rivers: geogenic and anthropogenic colloidal/sub-colloidal sources and the significance of within-river retention

Operationally defined dissolved Titanium [Ti] (the <0.45μm filtered fraction) in rivers draining rural, agricultural, urban and industrial land-use types in the UK averaged 2.1μg/l with a range in average of 0.55 to 6.48μg/l. The lowest averages occurred for the upland areas of mid-Wales the highest just downstream of major sewage treatment works (STWs). [Ti] in rainfall and cloud water in mid-Wales averaged 0.2 and 0.7μg/l, respectively. Average, baseflow and stormflow [Ti] were compared with two markers of sewage effluent and thus human population: soluble reactive phosphorus (SRP) and boron (B). While B reflects chemically conservative mixing, SRP declined downstream of STW inputs due to in-stream physico-chemical and biological uptake. The results are related to colloidal and sub-colloidal Ti inputs from urban/industrial conurbations coupled with diffuse background (geological) sources and within-river removal/retention under low flows as a result of processes of aggregation and sedimentation. The urban/industrial inputs increased background [Ti] by up to eleven fold, but the total anthropogenic Ti input might well have been underestimated owing to within-river retention. A baseline survey using cross-flow ultrafiltration revealed that up to 79% of the [Ti] was colloidal/nanoparticulate (>1kDa i.e. >c. 1-2nm) for the rural areas, but as low as 28% for the urban/industrial rivers. This raises fundamental issues of the pollutant inputs of Ti, with the possibility of significant complexation of Ti in the sewage effluents and subsequent breakdown within the rivers, as well as the physical dispersion of fine colloids down to the macro-molecular scale. Although not directly measured, the particulate Ti can make an important contribution to the net Ti flux.

Discovery and characterization of silver sulfide nanoparticles in final sewage sludge products

Nanosized silver sulfide (α-Ag(2)S) particles were identified in the final stage sewage sludge materials of a full-scale municipal wastewater treatment plant using analytical high-resolution transmission electron microscopy. The Ag(2)S nanocrystals are in the size range of 5-20 nm with ellipsoidal shape, and they form very small, loosely packed aggregates. Some of the Ag(2)S nanoparticles (NPs) have excess S on the surface of the sulfide minerals under S-rich environments, resulting in a ratio of Ag to S close to 1. Considering the current extensive production of Ag NPs and their widespread use in consumer products, it is likely that they are entering wastewater streams and the treatment facilities that process this water. This study suggests that in a reduced, S-rich environment, such as the sedimentation processes during wastewater treatment, nanosized silver sulfides are being formed. This field-scale study provides for the first time nanoparticle-level information of the Ag(2)S present in sewage sludge products, and further suggests the role of wastewater treatment processes on transformation of Ag nanoparticles and ionic Ag potentially released from them.

Ecotoxicity of nanoparticles of CuO and ZnO in natural water

The acute toxicity of CuO and ZnO nanoparticles in artificial freshwater (AFW) and in natural waters to crustaceans Daphnia magna and Thamnocephalus platyurus and protozoan Tetrahymena thermophila was compared. The L(E)C(50) values of nanoCuO for both crustaceans in natural water ranged from 90 to 224 mg Cu/l and were about 10-fold lower than L(E)C(50) values of bulk CuO. In all test media, the L(E)C(50) values for both bulk and nanoZnO (1.1-16 mg Zn/l) were considerably lower than those of nanoCuO. The natural waters remarkably (up to 140-fold) decreased the toxicity of nanoCuO (but not that of nanoZnO) to crustaceans depending mainly on the concentration of dissolved organic carbon (DOC). The toxicity of both nanoCuO and nanoZnO was mostly due to the solubilised ions as determined by specific metal-sensing bacteria.

Aggregation and toxicity of titanium dioxide nanoparticles in aquatic environment--a review

The use of nanoparticles--particles with size approximately 1-100 nm is increasing worldwide. This is particularly the case for applications of titanium dioxide nanoparticles (nano-TiO(2)) in consumer products, which have expanded at a fast rate in the last decade. The properties of nano-TiO(2) differ significantly from bulk-TiO(2) of the same composition because of an increase in surface area. A release of nano-TiO(2) from application sources to the aquatic environment may pose possible risks due to their bioavailability and toxicity. The aggregation of nano-TiO(2) plays an important role in the environmental effects of nanoparticles because the size and shape of nanoparticles will determine the magnitude of any potentially toxic effect. Aggregation is affected by pH, ionic strength, and ionic identity (inorganic and organic) of aqueous suspensions and is reviewed in this paper. The current information on the evaluation of ecotoxicological hazards of nano-TiO(2) to bacteria, algae, invertebrates, nematodes, and rainbow trout is also given.

Influence of carboxymethyl cellulose for the transport of titanium dioxide nanoparticles in clean silica and mineral-coated sands

The transport properties of titanium dioxide (anatase polymorph) nanoparticles encapsulated by carboxymethyl cellulose (CMC) were evaluated as a function of changes in the solute chemical properties in clean quartz, amorphous aluminum, and iron hydroxide-coated sands. While pristine anatase TiO2 nanoparticles (ANTNPs) were completely immobile, the presence of CMC significantly enhanced their mobility. The magnitude of the surface charge exhibited by the CMC-coated anatase TiO2 nanoparticles (CMC-ANTNPs) significantly exceeded that of the uncoated ANTNPs, thereby leading to a negative surface charge over the pH range investigated (2-10). The mobility of CMC-ANTNPs was retarded by the presence of amorphous Fe and Al hydroxide, Na+ (30 mM), and Ca2+ (30 mM). Removal of CMC-ANTNPs was more significant in the presence of either Ca2+ or Fe-hydroxide. More retardation and incomplete breakthrough of the CMC-ANTNPs was observed in the mineral-coated sands. This is possibly due to an order of magnitude increase in the surface area of mineral-coated sands compared with the clean quartz sand grains and the potential for chelation between CMC bound to ANTNPs and Fe and Al hydroxides. Chemical-colloidal interactions such as chemicomplexation and ligand exchange were the most important factor controlling mobility of CMC-ANTNPs in mineral-coated sands.

Synthetic TiO2 nanoparticle emission from exterior facades into the aquatic environment

We present direct evidence of the release of synthetic nanoparticles from urban applications into the aquatic environment. We investigated TiO(2) particles as these particles are used in large quantities in exterior paints as whitening pigments and are to some extent also present in the nano-size range. TiO(2) particles were traced from exterior facade paints to the discharge into surface waters. We used a centrifugation based sample preparation which recovers TiO(2) particles between roughly 20 and 300nm. Analytical electron microscopy revealed that TiO(2) particles are detached from new and aged facade paints by natural weather conditions and are then transported by facade runoff and are discharged into natural, receiving waters. Microscopic investigations are confirmed by bulk chemical analysis. By combining results from microscopic investigations with bulk chemical analysis we calculated the number densities of synthetic TiO(2) particles in the runoff.

Nanotechnology, nanotoxicology, and neuroscience

Nanotechnology, which deals with features as small as a 1 billionth of a meter, began to enter into mainstream physical sciences and engineering some 20 years ago. Recent applications of nanoscience include the use of nanoscale materials in electronics, catalysis, and biomedical research. Among these applications, strong interest has been shown to biological processes such as blood coagulation control and multimodal bioimaging, which has brought about a new and exciting research field called nanobiotechnology. Biotechnology, which itself also dates back approximately 30 years, involves the manipulation of macroscopic biological systems such as cells and mice in order to understand why and how molecular level mechanisms affect specific biological functions, e.g., the role of APP (amyloid precursor protein) in Alzheimer's disease (AD). This review aims (1) to introduce key concepts and materials from nanotechnology to a non-physical sciences community; (2) to introduce several state-of-the-art examples of current nanotechnology that were either constructed for use in biological systems or that can, in time, be utilized for biomedical research; (3) to provide recent excerpts in nanotoxicology and multifunctional nanoparticle systems (MFNPSs); and (4) to propose areas in neuroscience that may benefit from research at the interface of neurobiologically important systems and nanostructured materials.

Biotests and Biosensors for Ecotoxicology of Metal Oxide Nanoparticles: A Minireview

Nanotechnologies have become a significant priority worldwide. Several manufactured nanoparticles - particles with one dimension less than 100 nm - are increasingly used in consumer products. At nanosize range, the properties of materials differ substantially from bulk materials of the same composition, mostly due to the increased specific surface area and reactivity, which may lead to increased bioavailability and toxicity. Thus, for the assessment of sustainability of nanotechnologies, hazards of manufactured nanoparticles have to be studied. Despite all the above mentioned, the data on the potential environmental effects of nanoparticles are rare. This mini-review is summarizing the emerging information on different aspects of ecotoxicological hazard of metal oxide nanoparticles, focusing on TiO₂, ZnO and CuO. Various biotests that have been successfully used for evaluation of ecotoxic properties of pollutants to invertebrates, algae and bacteria and now increasingly applied for evaluation of hazard of nanoparticles at different levels of the aquatic food-web are discussed. Knowing the benefits and potential drawbacks of these systems, a suite of tests for evaluation of environmental hazard of nanoparticles is proposed. Special attention is paid to the influence of particle solubility and to recombinant metal-sensing bacteria as powerful tools for quantification of metal bioavailability. Using recombinant metal-specific bacterial biosensors and multitrophic ecotoxicity assays in tandem will create new scientific knowledge on the respective role of ionic species and of particles in toxicity of metal oxide nanoparticles.

Manufactured nanoparticles: an overview of their chemistry, interactions and potential environmental implications

The industrial scale production and wide variety of applications of manufactured nanoparticles (NPs) and their possible release in considerable amounts into the natural aquatic environment have produced an increasing concern among the nanotechnology and environmental science community. In order to address this issue, it is important to understand NP chemistry, preparation, reactivity and possible mechanisms involved in their interaction with the naturally occurring aquatic components, particularly natural colloids and NPs present in the aquatic systems. In this review, an overview of the chemistry of both manufactured and natural aquatic NPs is outlined. This review discusses the physico-chemical aspects of both type of NPs as an essential point to assess possible routes involved in manufactured NP fate in the natural aquatic environment and their toxicity. Key advances related to the characterisation of the manufactured NPs and natural colloids.

The ecotoxicology of nanoparticles and nanomaterials: current status, knowledge gaps, challenges, and future needs

This paper introduces a special issue on the ecotoxicology and environmental chemistry of nanoparticles (NPs), and nanomaterials (NMs), in the journal Ecotoxicology. There are many types of NMs and the scientific community is making observations on NP ecotoxicity to inform the wider debate about the risks and benefits of these materials. Natural NPs have existed in the environment since the beginning of Earth's history, and natural sources can be found in volcanic dust, most natural waters, soils and sediments. Natural NPs are generated by a wide variety of geological and biological processes, and while there is evidence that some natural NPs can be toxic, organisms have also evolved in an environment containing natural NPs. There are concerns that natural nano-scale process could be influenced by the presence of pollution. Manufactured NPs show some complex colloid and aggregation chemistry, which is likely to be affected by particle shape, size, surface area and surface charge, as well as the adsorption properties of the material. Abiotic factors such as pH, ionic strength, water hardness and the presence of organic matter will alter aggregation chemistry; and are expected to influence toxicity. The physico-chemistry is essential to understanding of the fate and behaviour of NPs in the environment, as well as uptake and distribution within organisms, and the interactions of NPs with other pollutants. Data on biological effects show that NPs can be toxic to bacteria, algae, invertebrates and fish species, as well as mammals. However, much of the ecotoxicological data is limited to species used in regulatory testing and freshwater organism. Data on bacteria, terrestrial species, marine species and higher plants is particularly lacking. Detailed investigations of absorption, distribution, metabolism and excretion (ADME) remain to be performed on species from the major phyla, although there are some data on fish. The environmental risk assessment of NMs could be performed using the existing tiered approach and regulatory framework, but with modifications to methodology including chemical characterisation of the materials being used. There are many challenges ahead, and controversies (e.g., reference substances for ecotoxicology), but knowledge transfer from mammalian toxicology, colloid chemistry, as well as material and geological sciences, will enable ecotoxicology studies to move forward in this new multi-disciplinary field.

Nanoparticle analysis and characterization methodologies in environmental risk assessment of engineered nanoparticles

Environmental risk assessments of engineered nanoparticles require thorough characterization of nanoparticles and their aggregates. Furthermore, quantitative analytical methods are required to determine environmental concentrations and enable both effect and exposure assessments. Many methods still need optimization and development, especially for new types of nanoparticles in water, but extensive experience can be gained from the fields of environmental chemistry of natural nanomaterials and from fundamental colloid chemistry. This review briefly describes most methods that are being exploited in nanoecotoxicology for analysis and characterization of nanomaterials. Methodological aspects are discussed in relation to the fields of nanometrology, particle size analysis and analytical chemistry. Differences in both the type of size measures (length, radius, aspect ratio, etc.), and the type of average or distributions afforded by the specific measures are compared. The strengths of single particle methods, such as electron microscopy and atomic force microscopy, with respect to imaging, shape determinations and application to particle process studies are discussed, together with their limitations in terms of counting statistics and sample preparation. Methods based on the measurement of particle populations are discussed in terms of their quantitative analyses, but the necessity of knowing their limitations in size range and concentration range is also considered. The advantage of combining complementary methods is highlighted.

Nanoparticles: structure, properties, preparation and behaviour in environmental media

There is increasing interest and need to develop a deeper understanding of the nature, fate and behaviour of nanoparticles in the environment. This is driven by the increased use of engineered nanoparticles and the increased pressure to commercialise this growing technology. In this review we discuss the key properties of nanoparticles and their preparation and then discuss how these factors can play a role in determining their fate and behaviour in the natural environment. Key focus of the discussion will relate to the surface chemistry of the nanoparticle, which may interact with a range of molecules naturally present in surface waters and sediments. Understanding these factors is a core goal required for understanding the final fate of nanomaterials and predicting which organisms are likely to be exposed to these materials.

Exposure modeling of engineered nanoparticles in the environment

The aim of this study was to use a life-cycle perspective to model the quantities of engineered nanoparticles released into the environment. Three types of nanoparticles were studied: nano silver (nano-Ag), nano TiO2 (nano-TiO2), and carbon nanotubes (CNT). The quantification was based on a substance flow analysis from products to air, soil, and water in Switzerland. The following parameters were used as model inputs: estimated worldwide production volume, allocation of the production volume to product categories, particle release from products, and flow coefficients within the environmental compartments. The predicted environmental concentrations (PEC) were then compared to the predicted no effect concentrations (PNEC) derived from the literature to estimate a possible risk. The expected concentrations of the three nanoparticles in the different environmental compartments vary widely, caused by the different life cycles of the nanoparticle-containing products. The PEC values for nano-TiO2 in water are 0.7--16 microg/L and close to or higher than the PNEC value for nano-TiO2 (< 1 microg/L). The risk quotients (PEC/PNEC) for CNT and nano-Ag were much smaller than one, therefore comprising no reason to expect adverse effects from those particles. The results of this study make it possible for the first time to carry out a quantitative risk assessment of nanoparticles in the environment and suggest further detailed studies of nano-TiO2.

Nanominerals, mineral nanoparticles, and Earth systems

Minerals are more complex than previously thought because of the discovery that their chemical properties vary as a function of particle size when smaller, in at least one dimension, than a few nanometers, to perhaps as much as several tens of nanometers. These variations are most likely due, at least in part, to differences in surface and near-surface atomic structure, as well as crystal shape and surface topography as a function of size in this smallest of size regimes. It has now been established that these variations may make a difference in important geochemical and biogeochemical reactions and kinetics. This recognition is broadening and enriching our view of how minerals influence the hydrosphere, pedosphere, biosphere, and atmosphere.