Use of nanomaterials in the European construction industry and some occupational health aspects thereof

In the European construction industry in 2009, the use of engineered nanoparticles appears to be confined to a limited number of products, predominantly coatings, cement and concrete. A survey among representatives of workers and employers from 14 EU countries suggests a high level of ignorance about the availability and use of nanomaterials for the construction industry and the safety aspects thereof. Barriers for a large-scale acceptance of products containing engineered nanoparticles (nanoproducts) are high costs, uncertainties about long-term technical material performance, as well as uncertainties about health risks of nanoproducts. Workplace measurements suggest a modest exposure of construction workers to nanoparticles (NPs) associated with the use of nanoproducts. The measured particles were within a size range of 20–300 nm, with the median diameter below 53 nm. Positive assignment of this exposure to the nanoproduct or to additional sources of ultrafine particles, like the electrical equipment used was not possible within the scope of this study and requires further research. Exposures were below the nano reference values proposed on the basis of a precautionary approach.     

Emission measurement and safety assessment for the production process of silicon nanoparticles in a pilot-scale facility

Emission into the workplace was measured for the production process of silicon nanoparticles in a pilot-scale facility at the Institute of Energy and Environmental Technology e.V. (IUTA). The silicon nanoparticles were produced in a hot-wall reactor and consisted of primary particles around 60 nm in diameter. We employed real-time aerosol instruments to measure particle number and lung-deposited surface area concentrations and size distribution; airborne particles were also collected for off-line electron microscopic analysis. Emission of silicon nanoparticles was not detected during the processes of synthesis, collection, and bagging. This was attributed to the completely closed production system and other safety measures against particle release which will be discussed briefly. Emission of silicon nanoparticles significantly above the detection limit was only observed during the cleaning process when the production system was open and manually cleaned. The majority of the detected particles was in the size range of 100–400 nm and were silicon nanoparticle agglomerates first deposited in the tubing then re-suspended during the cleaning process. Appropriate personal protection equipment is recommended for safety protection of the workers during cleaning.     

Evaluation of environmental filtration control of engineered nanoparticles using the Harvard Versatile Engineered Nanomaterial Generation System (VENGES)

Applying engineering controls to airborne engineered nanoparticles (ENPs) is critical to prevent environmental releases and worker exposure. This study evaluated the effectiveness of two air sampling and six air cleaning fabric filters at collecting ENPs using industrially relevant flame-made engineered nanoparticles generated using a versatile engineered nanomaterial generation system (VENGES), recently designed and constructed at Harvard University. VENGES has the ability to generate metal and metal oxide exposure atmospheres while controlling important particle properties such as primary particle size, aerosol size distribution, and agglomeration state. For this study, amorphous SiO₂ ENPs with a 15.4 nm primary particle size were generated and diluted with HEPA-filtered air. The aerosol was passed through the filter samples at two different filtration face velocities (2.3 and 3.5 m/min). Particle concentrations as a function of particle size were measured upstream and downstream of the filters using a specially designed filter test system to evaluate filtration efficiency. Real time instruments (FMPS and APS) were used to measure particle concentration for diameters from 5 to 20,000 nm. Membrane-coated fabric filters were found to have enhanced nanoparticle collection efficiency by 20–46 % points compared to non-coated fabric and could provide collection efficiency above 95 %.     

Experimental evaluation of individual protection devices against different types of nanoaerosols: graphite,TiO<Subscript>2,</Subscript> and Pt

In this study different conventional individual protection devices, well-qualified for submicron particles were tested for different types of polydispersed nanoaerosols of TiO₂, Pt, and graphite. The electrical mobility diameters of the generated particles are ranging from 9 to 19 nm for Pt, 9 to 90 nm for TiO₂, and 15 to 90 nm for graphite. Toward this purpose, two specific test benches were used: one for the filter-based devices which are tested under a controlled air flow, and the other one for protective clothing and gloves under diffusion and without air flow. Different types of nanoaerosols, such as TiO₂, Pt, and graphite, were generated. Electrostatic and HEPA (High Efficiency Particle Air) filters have shown the highest efficiency for graphite nanoparticles. The main hypothesis for explaining this effect is that electrostatic forces could enhance the graphite nanoparticles capture. Air-tight fabrics made of non-woven textile seem much more efficient in protecting workers against Pt, and TiO₂ nanoparticles than cotton and polypropylene. With regard to protective clothing, no obvious effect linked to the aerosol type was observed. Gloves are found very efficient for TiO₂ and Pt nanoaerosols. Therefore, no effect of aerosol on the protection efficiency of gloves was evidenced.     

Size-tuneable synthesis of nickel nanoparticles

A facile method is described for synthesising nickel nanoparticles via the thermal decomposition of an organometallic precursor in the presence of excess n-trioctylphosphine as a capping ligand. For the first time, alkylamines with different chain lengths were employed as size-limiting agents in this synthesis. A direct correlation is demonstrated between the size of the alkylamine ligands used and the mean diameter of the nickel nanoparticles obtained. The use of bulky oleylamine as a size-limiting agent over a reaction period of 30 min led to the growth of nickel nanoparticles with a mean diameter of 2.8 ± 0.9 nm. The employment of less bulky N,N-dimethylhexadecylamine groups led to the growth of nickel nanoparticles with a mean diameter of 4.4 ± 0.9 nm. By increasing the reaction time from 30 to 240 min, while employing oleylamine as the size-limiting agent, the mean diameter of the nickel nanoparticles was increased from 2.8 ± 0.9 to 5.1 ± 0.7 nm. Decreasing the amount of capping ligand present in the reaction system allowed further growth of the nickel nanoparticles to 17.8 ± 1.3 nm. The size, structure and morphology of the nanoparticles synthesised were characterised by transmission electron microscopy and powder X-ray diffraction; while magnetic measurements indicated that the particles were superparamagnetic in nature.     

Electrochemical method for the synthesis of silver nanoparticles

The article deals with a novel electrochemical method of preparing long-lived silver nanoparticles suspended in aqueous solution as well as silver powders. The method does not involve the use of any chemical stabilising agents. The morphology of the silver nanoparticles obtained was studied using transmission electron microscopy, scanning electron microscopy, atomic force microscopy and dynamic light scattering measurements. Silver nanoparticles suspended in water solution that were produced by the present technique are nearly spherical and their size distribution lies in the range of 2 to 20 nm, the average size being about 7 nm. Silver nanoparticles synthesised by the proposed method were sufficiently stable for more than 7 years even under ambient conditions. Silver crystal growth on the surface of the cathode in the electrochemical process used was shown to result in micron-sized structures consisting of agglomerated silver nanoparticles with the sizes below 40 nm.     

Cytotoxic evaluation of N-isopropylacrylamide monomers and temperature-sensitive poly(N-isopropylacrylamide) nanoparticles

The objective of this research project is to investigate the biocompatibility of N-isopropylacrylamide (NIPAAm) monomers and poly(N-isopropylacrylamide) (PNIPAAm) nanoparticles in vitro. PNIPAAm nanoparticles of different sizes were synthesized and characterized by transmission electron microscopy and dynamic light scattering. Cytotoxicity studies using MTS assays were conducted on fibroblasts, smooth muscle cells, and endothelial cells. In addition, the concentration of NIPAAm monomers remaining on PNIPAAm nanoparticles was determined using bromination and spectrophotometry. The cytotoxicity results did not show a significant difference in cell survival when cells were exposed to different particle sizes (100, 300, and 500 nm). Dose studies showed that all three cell types exposed to 100 nm PNIPAAm nanoparticles at concentrations less than or equal to 5 mg/mL were compatible, while cells exposed to NIPAAm monomers exhibited toxicity even at very low concentrations. We also found that 1 mg/mL concentration of 100 nm PNIPAAm nanoparticles was cytocompatible for 4 days, whereas NIPAAm monomers were cytotoxic after 24 h of exposure. Photomicrographs showed altered morphology in cells exposed to NIPAAm monomers, while cells exposed to PNIPAAm nanoparticles maintained their normal morphology. Finally, a very low concentration of NIPAAm monomers remained on the PNIPAAm nanoparticles after synthesis and dialysis. Our results demonstrate that NIPAAm monomers are cytotoxic, whereas PNIPAAm nanoparticles are compatible at 5 mg/mL concentration or below for fibrobasts, smooth muscle cells, and endothelial cells.     

Study of iron oxide nanoparticles in soil for remediation of arsenic

There is a growing interest in the use of nanoparticles for environmental applications due to their unique physical and chemical properties. One possible application is the removal of contaminants from water. In this study, the use of iron oxide nanoparticles (19.3 nm magnetite and 37.0 nm hematite) were examined to remove arsenate and arsenite through column studies. The columns contained 1.5 or 15 wt% iron oxide nanoparticles and soil. Arsenic experiments were conducted with 1.5 wt% iron oxides at 1.5 and 6 mL/h with initial arsenate and arsenite concentrations of 100 μg/L. Arsenic release occurred after 400 PV, and 100% release was reached. A long-term study was conducted with 15 wt% magnetite nanoparticles in soil at 0.3 mL/h with an initial arsenate concentration of 100 μg/L. A negligible arsenate concentration occurred for 3559.6 pore volumes (PVs) (132.1 d). Eventually, the arsenate concentration reached about 20% after 9884.1 PV (207.9 d). A retardation factor of about 6742 was calculated indicating strong adsorption of arsenic to the magnetite nanoparticles in the column. Also, increased adsorption was observed after flow interruption. Other experiments showed that arsenic and 12 other metals (V, Cr, Co, Mn, Se, Mo, Cd, Pb, Sb, Tl, Th, U) could be simultaneously removed by the iron oxide nanoparticles in soil. Effluent concentrations were less than 10% for six out of the 12 metals. Desorption experiment showed partial irreversible sorption of arsenic to the iron oxide nanoparticle surface. Strong adsorption, large retardation factor, and resistant desorption suggest that magnetite and hematite nanoparticles have the potential to be used to remove arsenic in sandy soil possibly through in situ techniques.     

A hypothetical model for predicting the toxicity of high aspect ratio nanoparticles (HARN)

The ability to predict nanoparticle (dimensional structures which are less than 100 nm in size) toxicity through the use of a suitable model is an important goal if nanoparticles are to be regulated in terms of exposures and toxicological effects. Recently, a model to predict toxicity of nanoparticles with high aspect ratio has been put forward by a consortium of scientists. The High aspect ratio nanoparticles (HARN) model is a platform that relates the physical dimensions of HARN (specifically length and diameter ratio) and biopersistence to their toxicity in biological environments. Potentially, this model is of great public health and economic importance, as it can be used as a tool to not only predict toxicological activity but can be used to classify the toxicity of various fibrous nanoparticles, without the need to carry out time-consuming and expensive toxicology studies. However, this model of toxicity is currently hypothetical in nature and is based solely on drawing similarities in its dimensional geometry with that of asbestos and synthetic vitreous fibres. The aim of this review is two-fold: (a) to present findings from past literature, on the physicochemical property and pathogenicity bioassay testing of HARN (b) to identify some of the challenges and future research steps crucial before the HARN model can be accepted as a predictive model. By presenting what has been done, we are able to identify scientific challenges and research directions that are needed for the HARN model to gain public acceptance. Our recommendations for future research includes the need to: (a) accurately link physicochemical data with corresponding pathogenicity assay data, through the use of suitable reference standards and standardised protocols, (b) develop better tools/techniques for physicochemical characterisation, (c) to develop better ways of monitoring HARN in the workplace, (d) to reliably measure dose exposure levels, in order to support future epidemiological studies.     

Measurement of filtration efficiency of Nuclepore filters challenged with polystyrene latex nanoparticles: experiments and modeling

Membrane filtration has been demonstrated to be effective for the removal of liquid-borne nanoparticles (NPs). Such technique can be applied to purify and disinfect drinking water as well as remove NPs in highly pure chemicals used in the industries. This study aims to study the filtration process of a model membrane filter, the Nuclepore filter. Experiments were carried out using standard filtration tools and the nanoparticle tracking analysis (NTA) technique was used to measure particle (50–500 nm) concentration upstream and downstream of the filter to determine the filtration efficiency. The NTA technique has been calibrated using 150-nm polystyrene latex particles to determine its accuracy of particle concentration measurement. Measurements were found reliable within a certain concentration limit (about 10⁸–10¹⁰ particles/cm³), which is dependent on the camera settings during the measurement. Experimental results are comparable with previously published data obtained using the aerosolization method, validating the capability of the NTA technique. The capillary tube model modified from that developed for aerosol filtration was found to be useful to represent the experimental results, when a sticking coefficient of 0.15 is incorporated. This suggests that only 15% of the particle collisions with the filter results in successful attachment. The small sticking coefficient found can be explained by the unfavorable surface interactions between the particles and the filter medium.     

Experimental study of nanoparticles penetration through commercial filter media

In this study, nanoparticle penetration was measured with a wide range of filter media using silver nanoparticles from 3 nm to 20 nm at three different face velocities in order to define nanoparticle filtration characteristics of commercial fibrous filter media. The silver particles were generated by heating a pure silver powder source via an electric furnace with a temperature of 870°C, which was found to be the optimal temperature for generating an adequate amount of silver nanoparticles for the size range specified above. After size classification using a nano-DMA, the particle counts were measured by an Ultrafine Condensation Particle Counter (UCPC) both upstream and downstream of the test filter to determine the nanoparticle penetration for each specific particle size. Particle sampling time continued long enough to detect more than 10⁵ counts at the upstream and 10 counts at the downstream sampling point so that 99.99% efficiency can be detected with the high efficiency filter. The results show a very high uniformity with small error bars for all filter media tested in this study. The particle penetration decreases continuously down to 3 nm as expected from the classical filtration theory, and together with a companion modeling paper by␣Wang et al. in this same issue, we found no significant evidence of nanoparticle thermal rebound down to 3 nm.     

Inter-laboratory performance between two nanoparticle air filtration systems using scanning mobility particle analyzers

The performance of two aerosol testing systems, at two different laboratories (University of Nebraska Medical Center—UNMC and 3M Company), was compared to evaluate which calibration procedures minimized variability in filter testing of nanoparticles. Both charged electret and uncharged flat-web fibrous filters were used with Scanning Mobility Particle Sizers to give upstream and downstream size distributions and calculate filter penetration. Challenge aerosols were polydisperse nanoparticles of sodium chloride (NaCl) ranging from approximately 10–300 nm and monodisperse polystyrene latex (PSL) spheres of preselected sizes, including 40, 60, 100, and 200 nm. The implementation of optimized procedures resulted in comparable filtration performance at the two testing sites with challenges of NaCl particles and PSL spheres. The penetration results for the uncharged filter were nearly identical for both challenges, while lower penetration through the charged filter was observed with NaCl aerosol, probably due to differences in NaCl and PSL dielectric constants. Results showed that reproducible, comparable nanoparticle filtration data could be achieved between two separate laboratories when sources of error and proper calibration procedures were addressed.     

Cytotoxicity and drug release behavior of PNIPAM grafted on silica-coated iron oxide nanoparticles

The nanoparticles containing thermosensitive and magnetic properties were investigated for their potential use as a novel drug carrier for targeted and controlled release drug delivery system. These thermosensitive and magnetic nanoparticles were prepared by grafting thermosensitive poly (N-isopropylacrylamide) (PNIPAM) on the surface of silica (SiO₂)-coated Fe₃O₄ nanoparticles with the particle size of 18.8 ± 1.6 nm. Adsorption and desorption behavior of bovine serum albumin (BSA) on the surface of PNIPAM-grafted SiO₂/Fe₃O₄ nanoparticles was studied, and the results indicated that these nanoparticles were able to absorb protein at temperature above the lower critical solution temperature (LCST) and to be desorbed below the LCST. Cytotoxicity studies conducted on Chinese hamster ovary (CHO-K1) cells using methyl tetrazolium (MTT) assays revealed that cell viability of 1 mg/mL PNIPAM-grafted nanoparticles was slightly decreased after 24 h of incubation as compared to the lower concentration of nanoparticles. Furthermore, the concentration of 0.5 mg/mL PNIPAM-grafted nanoparticles was totally biocompatible for 48 h, but had low cytotoxicity after 72 h of incubation. These PNIPAM-grafted nanoparticles did not induce morphological change in their cellularity after exposure for 24 and 108 h. These results demonstrate that PNIPAM-grafted nanoparticles are biocompatible and have potential use as drug carriers.     

Evaluation of antibacterial activities of silver nanoparticles green-synthesized using pineapple leaf (Ananas comosus)

Pineapple leaf was used in this study for the synthesis of silver nanoparticles based on the search for sustainable synthetic means. Indeed, this offered an economical and sustainable synthetic route relative to expensive and toxic chemical methods. The leaf extract was used and the corresponding nanoparticles obtained were subjected to UV–vis analysis at different times. The UV–vis was used to monitor the silver nanoparticle formation through sampling at time intervals. The formation of silver nanoparticles was apparently displayed within 2 min with evidence of surface plasmon bands (SPB) between 440 and 460 nm. The crystals was equally characterized using FTIR, X-ray diffraction methods and TEM. The different results obtained suggested the appearance of silver nanoparticles (SNPs) as determined by the process parameters with a particle size of 12.4 nm. The sample was further screened against Staphylococcus aureus, Streptococcus pneumoniae, Proteus mirabilis and Escherichia coli using Gentamicin as control. From the results, there is evidence of inhibition towards bacteria growth. It can now be inferred from the studies that biosynthesis of nanoparticles could be a gateway to our numerous health issues.     

Extracellular biosynthesis of monodispersed gold nanoparticles by a SAM capping route

Monodispersed gold nanoparticles capped with a self-assembled monolayer of dodecanethiol were biosynthesized extracellularly by an efficient, simple, and environmental friendly procedure, which involved the use of Bacillus megatherium D01 as the reducing agent and the use of dodecanethiol as the capping ligand at 26 °C. The kinetics of gold nanoparticle formation was followed by transmission electron microscope (TEM) and UV-vis spectroscopy. It was shown that reaction time was an important parameter in controlling the morphology of gold nanoparticles. The effect of thiol on the shape, size, and dispersity of gold nanoparticles was also studied. The results showed that the presence of thiol during the biosynthesis could induce the formation of small size gold nanoparticles (<2.5 nm), hold the shape of spherical nanoparticles, and promote the monodispersity of nanoparticles. Through the modulation of reaction time and the use of thiol, monodispersed spherical gold nanoparticles capped with thiol of 1.9 ± 0.8 nm size were formed by using Bacillus megatherium D01.     

Fabrication of silver nanoparticles in a continuous flow,low temperature microwave-assisted polyol process

The performed experiments showed that continuous microwave-assisted polyol synthesis at about 70 °C is a viable process to give silver nanoparticles with a narrow size distribution in bulk amounts. The increase of silver precursor concentration in reaction system from 0.0097 to 0.0389 M resulted in the formation of fine nanoparticles 5–10 nm in size, in addition to the larger ones 30–100 nm, and that changed the pattern of particle size distribution from monomodal to bimodal. The effect of specific process variables was found to be the same in the continuous process as in batch operation. An aqueous glycerol solution was found suitable for use as both solvent and reducing agent.     

FITC Labeled Silica Nanoparticles as Efficient Cell Tags: Uptake and Photostability Study in Endothelial Cells

The use of fluorescent nanomaterials has gained great importance in the field of medical imaging. Many traditional imaging technologies have been reported utilizing dyes in the past. These methods face drawbacks due to non-specific accumulation and photobleaching of dyes. We studied the uptake and internalization of two different sized (30 nm and 100 nm) FITC labeled silica nanoparticles in Human umbilical vein endothelial cell line. These nanomaterials show high biocompatability and are highly photostable inside live cells for increased period of time in comparison to the dye alone. To our knowledge, we report for the first time the use of 30 nm fluorescent silica nanoparticles as efficient endothelial tags along with the well studied 100 nm particles. We also have emphasized the good photostability of these materials in live cells.     

Structuring of Surfaces with Gold Nanoparticles by Using Bessel‐Like Beams

Here, the structuring of surfaces with gold nanoparticles by using Bessel‐like beam array is demonstrated. The experimental results show that the fabricated microring structures containing gold nanoparticles have a surface plasmon resonance in the spectral range of 520–540 nm, which can be tuned by selecting the laser treatment parameters. Fabricated microring structures exhibit a lower light transmittance comparing with the randomly distributed gold nanoparticles for wavelengths 500–570 nm due to the growth in the size of nanoparticles. In the spectral range of 600–700 nm, the light transmittance through microring structures is higher compared with the randomly distributed gold nanoparticles because of the removal of gold nanoparticles as gold has high reflectivity for wavelengths longer than 600 nm. The demonstrated method enables an easy fabrication of microring structures having tunable plasmonic properties.     

Toxicity of amorphous silica nanoparticles in mouse keratinocytes

The present study was designed to examine the uptake, localization, and the cytotoxic effects of well-dispersed amorphous silica nanoparticles in mouse keratinocytes (HEL-30). Mouse keratinocytes were exposed for 24 h to various concentrations of amorphous silica nanoparticles in homogeneous suspensions of average size distribution (30, 48, 118, and 535 nm SiO₂) and then assessed for uptake and biochemical changes. Results of transmission electron microscopy revealed all sizes of silica were taken up into the cells and localized into the cytoplasm. The lactate dehydrogenase (LDH) assay shows LDH leakage was dose- and size-dependent with exposure to 30 and 48 nm nanoparticles. However, no LDH leakage was observed for either 118 or 535 nm nanoparticles. The mitochondrial viability assay (MTT) showed significant toxicity for 30 and 48 nm at high concentrations (100 μg/mL) compared to the 118 and 535 nm particles. Further studies were carried out to investigate if cellular reduced GSH and mitochondria membrane potential are involved in the mechanism of SiO₂ toxicity. The redox potential of cells (GSH) was reduced significantly at concentrations of 50, 100, and 200 μg/mL at 30 nm nanoparticle exposures. However, silica nanoparticles larger than 30 nm showed no changes in GSH levels. Reactive oxygen species (ROS) formation did not show any significant change between controls and the exposed cells. In summary, amorphous silica nanoparticles below 100 nm induced cytotoxicity suggest size of the particles is critical to produce biological effects.     

Anti-solvent precipitation for the preparation of nobiletin nano-particles under ultrasonication-cis/reverse homogenization

In order to address the issue of nobiletin's limited bioavailability, nobiletin nanoparticles (NNP) were created for the first time in this research employing an anti-solvent under ultrasonication-cis/reverse homogenization. Dimethyl sulfoxide (DMSO) was used as the solvent and deionized water as the anti-solvent to create the nobiletin solution. The optimal surfactant dose of surfactant dose of 0.43%; an ultrasonic period of 8.1 min, ultrasonic at a temperature of 64 °C and a solution concentration of 8.33 mg/mL, the method was optimized to obtain the minimum NNP diameter of 199.89 ± 0.02 nm. A dual optimization process of response surface PBD and BBD was used to minimize the size of HNP particles. Additionally, scanning electron microscopy revealed that the specific surface area of the NNP dramatically increased with the reduction of NNP particle size, and dissolving studies indicated the solubility and dissolution studies showed that NNP had substantially greater solubility and dissolution rates than raw nobiletin per unit time; as a result, the NNP produced by anti-solvent precipitation with a twofold homogenization system supported by ultrasound had a realistic potential for growth.