Category Archives: risk

What helps you may hurt you (titanium dioxide nanoparticles and orthopedic implants)

From a Sept. 16, 2017 news item on Nanotechnology Now,

Researchers from the Mayo Clinic have proposed that negative cellular responses to titanium-based nanoparticles released from metal implants interfere in bone formation and resorption at the site of repair, resulting in implant loosening and joint pain. [emphasis mine]Their review of recent scientific evidence and call for further research to characterize the biological, physical, and chemical interactions between titanium dioxide nanoparticles and bone-forming cells is published in BioResearch Open Access, a peer-reviewed open access journal from Mary Ann Liebert, Inc., publishers. The article is available free on theBioResearch Open Access website.

A Sept. 14, 2017 Mary Anne Liebert (Publishing) news release, which originated the news item,  mentions the authors,

Jie Yao, Eric Lewallen, PhD, David Lewallen, MD, Andre van Wijnen, PhD, and colleagues from the Mayo Clinic, Rochester, MN and Second Affiliated Hospital of Soochow University, China, coauthored the article entitled “Local Cellular Responses to Titanium Dioxide from Orthopedic Implants The authors examined the results of recently published studies of titanium-based implants, focusing on the direct and indirect effects of titanium dioxide nanoparticles on the viability and behavior of multiple bone-related cell types. They discuss the impact of particle size, aggregation, structure, and the specific extracellular and intracellular (if taken up by the cells) effects of titanium particle exposure.

“The adverse effects of metallic orthopedic particles generated from implants are of significant clinical interest given the large number of procedures carried out each year. This article reviews our current understanding of the clinical issues and highlights areas for future research,” says BioResearch Open Access Editor Jane Taylor, PhD, MRC Centre for Regenerative Medicine, University of Edinburgh, Scotland.

Before getting to the abstract, here’s a link to and a citation for the paper,

Local Cellular Responses to Titanium Dioxide from Orthopedic Implants by Yao, Jie J.; Lewallen, Eric A.; Trousdale, William H.; Xu, Wei; Thaler, Roman; Salib, Christopher G.; Reina, Nicolas; Abdel, Matthew P.; Lewallen, David G.; and van Wijnenm, Andre J.. BioResearch Open Access. July 2017, 6(1): 94-103. Published July 1, 2017

This paper is open access.

Nanoparticles from tattoo inks circulate through your body

English: Tattoo of Hand of Fatima,. Model: Casini. Date: 4 July 2017, 18:13:41. Source : Own work. Author: Stephencdickson.

For those who like their news in video format, there’s this Canadian Broadcasting Corporation (CBC) news item broadcast on Sep. 11, 2017 (after the commercials),

For those who like text and more detail, scientists at the European Synchrotron Radiation Facility (ESRF) have produced a study of the (at the nanoparticle scale) inks in tattoos. From a Sept. 12, 2017 news item on,

The elements that make up the ink in tattoos travel inside the body in micro and nanoparticle forms and reach the lymph nodes, according to a study published in Scientific Reports on 12 September [2017] by scientists from Germany and the ESRF, the European Synchrotron, Grenoble (France). It is the first time researchers have found analytical evidence of the transport of organic and inorganic pigments and toxic element impurities as well as in depth characterization of the pigments ex vivo in tattooed tissues. Two ESRF beamlines were crucial in this breakthrough.

A Sept. 12, 2017 ESRF press release (also on EurkeAlert), which originated the news item, explains further,

The reality is that little is known about the potential impurities in the colour mixture applied to the skin. Most tattoo inks contain organic pigments, but also include preservatives and contaminants like nickel, chromium, manganese or cobalt. Besides carbon black, the second most common ingredient used in tattoo inks is titanium dioxide (TiO2), a white pigment usually applied to create certain shades when mixed with colorants. Delayed healing, along with skin elevation and itching, are often associated with white tattoos, and by consequence with the use of TiO2. TiO2 is also commonly used in food additives, sun screens and paints. Scientists from the ESRF, the German Federal Institute for Risk Assessment, Ludwig-Maximilians University, and the Physikalisch-Technische Bundesanstalt have managed to get a very clear picture on the location of titanium dioxide once it gets in the tissue. This work was done on the ESRF beamlines ID21 and ID16B.

drawing tattookinetics.jpg

Translocation of tattoo particles from skin to lymph nodes. Upon injection of tattoo inks, particles can be either passively transported via blood and lymph fluids or phagocytized by immune cells and subsequently deposited in regional lymph nodes. After healing, particles are present in the dermis and in the sinusoids of the draining lymph nodes. Credits: C. Seim.

The hazards that potentially derive from tattoos were, until now, only investigated by chemical analysis of the inks and their degradation products in vitro. “We already knew that pigments from tattoos would travel to the lymph nodes because of visual evidence: the lymph nodes become tinted with the colour of the tattoo. It is the response of the body to clean the site of entrance of the tattoo. What we didn’t know is that they do it in a nano form, which implies that they may not have the same behaviour as the particles at a micro level. And that is the problem: we don’t know how nanoparticles react”, explains Bernhard Hesse, one of the two first authors of the study (together with Ines Schreiver, from the German Federal Institute for Risk Assessment) and ESRF visiting scientist.


Particle mapping and size distribution of different tattoo pigment elements.  a, d) Ti and the Br containing pigment phthalocyanine green 36 are located next to each other. b, e) Log scale mappings of Ti, Br and Fe in the same areas as displayed in a) and d) reveal primary particle sizes of different pigment species. c, f) Magnifications of the indicated areas in b) and e), respectively. Credits: C. Seim.

X-ray fluorescence measurements on ID21 allowed the team to locate titanium dioxide at the micro and nano range in the skin and the lymphatic environment. They found a broad range of particles with up to several micrometres in size in human skin, but only smaller (nano) particles transported to the lymph nodes. This can lead to the chronic enlargement of the lymph nodes and lifelong exposure. Scientists also used the technique of Fourier transform infrared spectroscopy to assess biomolecular changes in the tissues in the proximity of the tattoo particles.


Ines Schreiver doing experiments on ID16B with Julie Villanova. Credits: B. Hesse.

Altogether the scientists report strong evidence for both migration and long-term deposition of toxic elements and tattoo pigments as well as for conformational alterations of biomolecules that are sometimes linked to cutaneous adversities upon tattooing.

Then next step for the team is to inspect further samples of patients with adverse effects in their tattoos in order to find links with chemical and structural properties of the pigments used to create these tattoos.

Here’s a link to and  a citation for the paper,

Synchrotron-based ν-XRF mapping and μ-FTIR microscopy enable to look into the fate and effects of tattoo pigments in human skin by Ines Schreiver, Bernhard Hesse, Christian Seim, Hiram Castillo-Michel, Julie Villanova, Peter Laux, Nadine Dreiack, Randolf Penning, Remi Tucoulou, Marine Cotte, & Andreas Luch. Scientific Reports 7, Article number: 11395 (2017) doi:10.1038/s41598-017-11721-z Published online: 12 September 2017

This paper is open access.

Measurably fewer nanoparticles in São Paulo’s (Brazil) air after ethanol use

An Aug. 28, 2017 news item on Nanotechnology Now features news about nanoparticles and the environment in São Paulo, Brazil,

When ethanol prices at the pump rise for whatever reason, it becomes economically advantageous for drivers of dual-fuel vehicles to fill up with gasoline. However, the health of the entire population pays a high price: substitution of gasoline for ethanol leads to a 30% increase in the atmospheric concentration of ultrafine particulate matter, which consists of particles with a diameter of less than 50 nanometers (nm).

An Aug. 23, 2017 Fundação de Amparo à Pesquisa do Estado de São Paulo (The São Paulo Research Foundation [FAPESP]) press release, which originated the news item, explains further,

The phenomenon was detected in São Paulo City, Brazil, in a study supported by FAPESP and published in July 2017 in Nature Communications.

“These polluting nanoparticles are so tiny that they behave like gas molecules. When inhaled, they can penetrate the respiratory system’s defensive barriers and reach the pulmonary alveoli, so that potentially toxic substances enter the bloodstream and may increase the incidence of respiratory and cardiovascular problems,” said Paulo Artaxo, Full Professor at the University of São Paulo’s Physics Institute (IF-USP) and a co-author of the study.

Levels of ultrafine particulate matter in the atmosphere are neither monitored nor regulated by environmental agencies not only in Brazil but practically anywhere in the world, according to Artaxo. The São Paulo State Environmental Corporation (CETESB), for example, routinely monitors only solid particles with diameters of 10,000 nm (PM10) and 2,500 nm (PM2.5) – as well as other gaseous pollutants such as ozone (O3), carbon monoxide (CO) and nitrogen dioxide (NO2).

“Between 75% and 80% of the mass of the nanoparticles we measured in this study corresponds to organic compounds emitted by motor vehicles – carbon in different chemical forms. What these compounds are exactly and how they affect health are questions that require further research,” Artaxo said.

He added that a consensus is forming in the United States and Europe based on recent research indicating that these emissions are a potential health hazard and should be regulated. Several US states, such as California, have laws requiring a 20%-30% ethanol blend in gasoline, which also helps reduce emissions of ultrafine particulate matter.


The data analyzed in the study were collected during the period of January-May 2011, when ethanol prices fluctuated sharply compared with gasoline prices, owing to macroeconomic factors such as variations in the international price of sugar (Brazilian ethanol is made from sugarcane).

Collection was performed at the top of a ten-story building belonging to IF-USP in the western part of São Paulo City. According to Artaxo, the site was chosen because it is relatively distant from the main traffic thoroughfares so that the aerosols there are “older” in the sense that they have already interacted with other substances present in the atmosphere.

“Generally speaking, the pollution we inhale every day at home or at work isn’t what comes out of vehicular exhaust pipes but particles already processed in the atmosphere,” he explained. “For this reason, we chose a site that isn’t directly impacted by primary vehicle emissions.”

The study was conducted during Joel Ferreira de Brito’s postdoctoral research, which Artaxo supervised. The model used to analyze the data was developed by Brazilian economist Alberto Salvo, a professor at the National University of Singapore and first author of the article. Franz Geiger, a chemist at Northwestern University in the US, also collaborated.

“We adapted a sophisticated statistical model originally developed for economic analysis and used here for the first time to analyze the chemistry of atmospheric nanoparticles,” Artaxo said. “The main strength of this tool is that it can work with a large number of variables, such as the presence or absence of rainfall, wind direction, traffic intensity, and levels of ozone, carbon monoxide and other pollutants.”

Analyses were performed before, during and after a sharp fluctuation in ethanol prices leading consumers to switch motor fuels in São Paulo City. While no significant changes were detected in levels of inhalable fine particulate matter (PM2.5 and PM10), the study proved in a real, day-to-day situation that choosing ethanol reduces emissions of ultrafine particles. To date, this phenomenon had only been observed in the laboratory.

“These results reinforce the need for public policies to encourage the use of biofuels, as they clearly show that the public lose in health what they save at the pump when opting for gasoline,” Artaxo said.

In São Paulo, a city with 7 million motor vehicles and the largest urban fleet of flexible-fuel cars, it would be feasible to run all buses on biofuel. “We have the technology for this in Brazil – and at a competitive price,” he said.

The fact that the city’s bus fleet still depends on diesel, Artaxo warned, creates an even worse health hazard in the shape of emissions of black carbon, one of the main components of soot and a pollutant that contributes to global warming. Alongside electricity generation, the transportation sector is the largest emitter of pollutants produced by the burning of fossil fuels.

For Artaxo, incentives for electric, hybrid or biofuel vehicles are vital to reduce greenhouse gas emissions. “By incentivizing biofuels, we could solve several problems at once,” he said. “We could combat climate change, reduce harm to health and foster advances in automotive technology by offering a stimulus for auto makers to develop more economical and efficient cars fueled by ethanol.”

Here’s a link to and a citation for the paper,

Reduced ultrafine particle levels in São Paulo’s atmosphere during shifts from gasoline to ethanol use by Alberto Salvo, Joel Brito, Paulo Artaxo, & Franz M. Geiger. Nature Communications 8, Article number: 77 (2017) doi:10.1038/s41467-017-00041-5 Published online: 18 July 2017

This paper is open access.

Getting a more complete picture of aerosol particles at the nanoscale

What is in the air we breathe? In addition to the gases we learned about in school there are particles, not just the dust particles you can see, but micro- and nanoparticles too and scientists would like to know more about them.

An August 23, 2017 news item on Nanowerk features work which may help scientists in their quest,

They may be tiny and invisible, says Xiaoji Xu, but the aerosol particles suspended in gases play a role in cloud formation and environmental pollution and can be detrimental to human health.

Aerosol particles, which are found in haze, dust and vehicle exhaust, measure in the microns. One micron is one-millionth of a meter; a thin human hair is about 30 microns thick.

The particles, says Xu, are among the many materials whose chemical and mechanical properties cannot be fully measured until scientists develop a better method of studying materials at the microscale as well as the much smaller nanoscale (1 nm is one-billionth of a meter).

Xu, an assistant professor of chemistry, has developed such a method and utilized it to perform noninvasive chemical imaging of a variety of materials, as well as mechanical mapping with a spatial resolution of 10 nanometers.

The technique, called peak force infrared (PFIR) microscopy, combines spectroscopy and scanning probe microscopy. In addition to shedding light on aerosol particles, Xu says, PFIR will help scientists study micro- and nanoscale phenomena in a variety of inhomogeneous materials.

The lower portion of this image by Xiaoji Xu’s group shows the operational scheme of peak force infrared (PFIR) microscopy. The upper portion shows the topography of nanoscale PS-b-PMMA polymer islands on a gold substrate. (Image courtesy of Xiaoji Xu)

An August 22, 2017 Lehih University news release by Kurt Pfitzer (also on EurekAlert), which originated the news item, explains the research in more detail (Note: A link has been removed),

“Materials in nature are rarely homogeneous,” says Xu. “Functional polymer materials often consist of nanoscale domains that have specific tasks. Cellular membranes are embedded with proteins that are nanometers in size. Nanoscale defects of materials exist that affect their mechanical and chemical properties.

“PFIR microscopy represents a fundamental breakthrough that will enable multiple innovations in areas ranging from the study of aerosol particles to the investigation of heterogeneous and biological materials,” says Xu.

Xu and his group recently reported their results in an article titled “Nanoscale simultaneous chemical and mechanical imaging via peak force infrared microscopy.” The article was published in Science Advances, a journal of the American Association for the Advancement of Science, which also publishes Science magazine.

The article’s lead author is Le Wang, a Ph.D. student at Lehigh. Coauthors include Xu and Lehigh Ph.D. students Haomin Wang and Devon S. Jakob, as well as Martin Wagner of Bruker Nano in Santa Barbara, Calif., and Yong Yan of the New Jersey Institute of Technology.

“PFIR microscopy enables reliable chemical imaging, the collection of broadband spectra, and simultaneous mechanical mapping in one simple setup with a spatial resolution of ~10 nm,” the group wrote.

“We have investigated three types of representative materials, namely, soft polymers, perovskite crystals and boron nitride nanotubes, all of which provide a strong PFIR resonance for unambiguous nanochemical identification. Many other materials should be suited as well for the multimodal characterization that PFIR microscopy has to offer.

“In summary, PFIR microscopy will provide a powerful analytical tool for explorations at the nanoscale across wide disciplines.”

Xu and Le Wang also published a recent article about the use of PFIR to study aerosols. Titled “Nanoscale spectroscopic and mechanical characterization of individual aerosol particles using peak force infrared microscopy,” the article appeared in an “Emerging Investigators” issue of Chemical Communications, a journal of the Royal Society of Chemistry. Xu was featured as one of the emerging investigators in the issue. The article was coauthored with researchers from the University of Macau and the City University of Hong Kong, both in China.

PFIR simultaneously obtains chemical and mechanical information, says Xu. It enables researchers to analyze a material at various places, and to determine its chemical compositions and mechanical properties at each of these places, at the nanoscale.

“A material is not often homogeneous,” says Xu. “Its mechanical properties can vary from one region to another. Biological systems such as cell walls are inhomogeneous, and so are materials with defects. The features of a cell wall measure about 100 nanometers in size, placing them well within range of PFIR and its capabilities.”

PFIR has several advantages over scanning near-field optical microscopy (SNOM), the current method of measuring material properties, says Xu. First, PFIR obtains a fuller infrared spectrum and a sharper image—6-nm spatial resolution—of a wider variety of materials than does SNOM. SNOM works well with inorganic materials, but does not obtain as strong an infrared signal as the Lehigh technique does from softer materials such as polymers or biological materials.

“Our technique is more robust,” says Xu. “It works better with soft materials, chemical as well as biological.”

The second advantage of PFIR is that it can perform what Xu calls point spectroscopy.

“If there is something of interest chemically on a surface,” Xu says, “I put an AFM [atomic force microscopy] probe to that location to measure the peak-force infrared response.

“It is very difficult to obtain these spectra with current scattering-type scanning near-field optical microscopy. It can be done, but it requires very expensive light sources. Our method uses a narrow-band infrared laser and costs about $100,000. The existing method uses a broadband light source and costs about $300,000.”

A third advantage, says Xu, is that PFIR obtains a mechanical as well as a chemical response from a material.

“No other spectroscopy method can do this,” says Xu. “Is a material rigid or soft? Is it inhomogeneous—is it soft in one area and rigid in another? How does the composition vary from the soft to the rigid areas? A material can be relatively rigid and have one type of chemical composition in one area, and be relatively soft with another type of composition in another area.

“Our method simultaneously obtains chemical and mechanical information. It will be useful for analyzing a material at various places and determining its compositions and mechanical properties at each of these places, at the nanoscale.”

A fourth advantage of PFIR is its size, says Xu.

“We use a table-top laser to get infrared spectra. Ours is a very compact light source, as opposed to the much larger sizes of competing light sources. Our laser is responsible for gathering information concerning chemical composition. We get mechanical information from the AFM [atomic force microscope]. We integrate the two types of measurements into one device to simultaneously obtain two channels of information.”

Although PFIR does not work with liquid samples, says Xu, it can measure the properties of dried biological samples, including cell walls and protein aggregates, achieving a 10-nm spatial resolution without staining or genetic modification.

This looks like very exciting work.

Here are links and citations for both studies mentioned in the news release (the most recently published being cited first),

Nanoscale simultaneous chemical and mechanical imaging via peak force infrared microscopy by Le Wang, Haomin Wang, Martin Wagner, Yong Yan, Devon S. Jakob, and Xiaoji G. Xu. Science Advances 23 Jun 2017: Vol. 3, no. 6, e1700255 DOI: 10.1126/sciadv.1700255

Nanoscale spectroscopic and mechanical characterization of individual aerosol particles using peak force infrared microscopy by Le Wang, Dandan Huang, Chak K. Chan, Yong Jie Li, and Xiaoji G. Xu. Chem. Commun., 2017,53, 7397-7400 DOI: 10.1039/C7CC02301D First published on 16 Jun 2017

The June 23, 2017 paper is open access while the June 16, 2017 paper is behind a paywall.

Burning coal produces harmful titanium dioxide nanoparticles

It turns out that Canada has the fifth largest reserve of coal in the world, according to the Coal in Canada Wikipedia entry (Note: Links have been removed),

Coal reserves in Canada rank fifth largest in the world (following the former Soviet Union, the United States, the People’s Republic of China and Australia) at approximately 10 billion tons, 10% of the world total.[1] This represents more energy than all of the oil and gas in the country combined. The coal industry generates CDN$5 billion annually.[2] Most of Canada’s coal mining occurs in the West of the country.[3] British Columbia operates 10 coal mines, Alberta 9, Saskatchewan 3 and New Brunswick one. Nova Scotia operates several small-scale mines, Westray having closed following the 1992 disaster there.[4]

So, this news from Virginia holds more than the usual interest for me (I’m in British Columbia). From an Aug. 8, 2017 Virginia Tech news release (also on EurekAlert),

Environmental scientists led by the Virginia Tech College of Science have discovered that the burning of coal produces incredibly small particles of a highly unusual form of titanium oxide.

When inhaled, these nanoparticles can enter the lungs and potentially the bloodstream.

The particulates — known as titanium suboxide nanoparticles — are unintentionally produced as coal is burned, creating these tiniest of particles, as small as 100 millionths of a meter [emphasis mine], said the Virginia Tech-led team. When the particles are introduced into the air — unless captured by high-tech particle traps — they can float away from power plant stacks and travel on air currents locally, regionally, and even globally.

As an example of this, these nanoparticles were found on city streets, sidewalks, and in standing water in Shanghai, China.

The findings are published in the latest issue of Nature Communications under team leader Michael F. Hochella Jr., University Distinguished Professor of Geosciences with the College of Science, and Yi Yang, a professor at East China Normal University in Shanghai. Other study participants include Duke University, the University of Kentucky, and Laurentian University in Canada.

“The problem with these nanoparticles is that there is no easy or practical way to prevent their formation during coal burning,” Hochella said, adding that in nations with strong environmental regulations, such as the United States, most of the nanoparticles would be caught by particle traps. Not so in Africa [a continent not a nation], China, or India, where regulations are lax or nonexistent, with coal ash and smoke entering the open air.

“Due to advanced technology used at U.S.-based coal burning power plants, mandated by the Clean Air Act and the Environmental Protection Agency, most of these nanoparticles and other tiny particles are removed before the final emission of the plant’s exhaust gases,” Hochella said. “But in countries where the particles from the coal burning are not nearly so efficiently removed, or removed at all, these titanium suboxide nanoparticles and many other particle types are emitted into the atmosphere, in part resulting in hazy skies that plague many countries, especially in China and India.”

Hochella and his team found these previously unknown nanoparticles not only in coal ash from around the world and in the gaseous waste emissions of coal plants, but on city streets, in soils and storm water ponds, and at wastewater treatment plants.

“I could not believe what I have found at the beginning, because they had been reported so extremely rarely in the natural environment,” said Yang, who once worked as a visiting professor in Virginia Tech’s Department of Geosciences with Hochella. “It took me several months to confirm their occurrence in coal ash samples.”

The newly found titanium suboxide — called Magnéli phases — was once thought rare, found only sparingly on Earth in some meteorites, from a small area of rock formations in western Greenland, and occasionally in moon rocks. The findings by Hochella and his team indicate that these nanoparticles are in fact widespread globally. They are only now being studied for the first time in natural environments using powerful electron microscopes.

Why did the discovery occur now? According to the report, nearly all coal contains traces of the minerals rutile and/or anatase, both “normal,” naturally occurring, and relatively inert titanium oxides, especially in the absence of light. When those minerals are burned in the presence of coal, research found they easily and quickly converted to these unusual titanium suboxide nanoparticles. The nanoparticles then become entrained in the gases that leave the power plant.

When inhaled, the nanoparticles enter deep into the lungs, potentially all the way into the air sacs that move oxygen into our bloodstream during the normal breathing process. While human lung toxicity of these particles is not yet known, a preliminary biotoxicity test by Hochella and Richard Di Giulio, professor of environmental toxicology, and Jessica Brandt, a doctoral candidate, both at Duke University, indicates that the particles do indeed have toxicity potential.

According to the team, further study is clearly needed, especially biotoxicity testing directly relevant to the human lung. Partnering with coal-power plants either in the United States or China would be ideal, said Yang.

More troubling, the study shows that titanium suboxide nanoparticles are biologically active in the dark, making the particles highly suspect. Exact human health effects are yet unknown.

“Future studies will need to very carefully investigate and access the toxicity of titanium suboxide nanoparticles in the human lung, and this could take years, a sobering thought considering its potential danger,” Hochella said.

As the titanium suboxide nanoparticle itself is produced incidentally, Hochella and his team came across the nanoparticle by accident while studying a 2014 coal ash spill in the Dan River, North Carolina. During the study of the downstream movement of toxic metals in the ash in the Dan River, the team discovered and recognized the presence of small amounts of the highly unusual titanium suboxide.

The group later produced the titanium suboxide nanoparticles when burning coal in a lab simulation.

This new potential air pollution health hazard builds on already established findings from the World Health Organization. It estimates that 3.3 million premature deaths occur worldwide per year due to polluted air, Hochella said. In China, 1.6 million premature deaths are estimated annually due to cardiovascular and respiratory injury from air pollution. Most Chinese megacities top 100 severely hazy days each year with particle concentrations two to four times higher than WHO guidelines, Yang said.

Direct health effects on humans is only one factor. Findings of thousands of scientists have determined that the biggest driver of warming of the planet and the resulting climate change is industrial-scale coal burning. The impact of titanium suboxide nanoparticles found in the atmosphere, in addition to greenhouse gases, on animals, water, and plants is not yet known.

They’ve used an unusual unit of measurement, “100 millionths of a meter,” nanoparticles are usually described in nanometers.

Here’s a link to and a citation for the paper,

Discovery and ramifications of incidental Magnéli phase generation and release from industrial coal-burning by Yi Yang, Bo Chen, James Hower, Michael Schindler, Christopher Winkler, Jessica Brandt, Richard Di Giulio, Jianping Ge, Min Liu, Yuhao Fu, Lijun Zhang, Yuru Chen, Shashank Priya, & Michael F. Hochella Jr. Nature Communications 8, Article number: 194 (2017) doi:10.1038/s41467-017-00276-2 Published online: 08 August 2017

This paper is behind a paywall.

This put me in mind of the famous London smog, which one doesn’t hear about much anymore. For anyone not familiar with that phenomenon, here’s more from the Great Smog of London Wikipedia entry (Note: Links have been removed),

The Great Smog of London, or Great Smog of 1952 sometimes called the Big Smoke,[1] was a severe air-pollution event [emphasis mine] that affected the British capital of London in December 1952. A period of cold weather, combined with an anticyclone and windless conditions, collected airborne pollutants – mostly arising from the use of coal [emphasis mine]– to form a thick layer of smog over the city. It lasted from Friday, 5 December to Tuesday, 9 December 1952 and then dispersed quickly when the weather changed.

It caused major disruption by reducing visibility and even penetrating indoor areas, far more severe than previous smog events experienced in the past, called “pea-soupers”. Government medical reports in the following weeks, however, estimated that up until 8 December, 4,000 people had died as a direct result of the smog and 100,000 more were made ill by the smog’s effects on the human respiratory tract. More recent research suggests that the total number of fatalities was considerably greater, about 12,000.[2]

London had suffered since the 1200s from poor air quality,[3] which worsened in the 1600s,[4][5] but the Great Smog is known to be the worst air-pollution event in the history of the United Kingdom,[6] and the most significant in terms of its effect on environmental research, government regulation, and public awareness of the relationship between air quality and health.[2][4] It led to several changes in practices and regulations, including the Clean Air Act 1956. …

DISCmini: world’s smallest handheld nanoparticle counter

DISCmini: a handheld diffusion size classifier for nanoparticle measurement Courtesy: Testo

They’/re claiming this is the world’s smallest in a July 12, 2017 news item on Nanowerk,

Testo, Inc., the world’s leading manufacturer of test and measurement instruments, announces the DiSCmini, the smallest handheld instrument for the measurement of nanoparticle. DiSCmini measures: particle number, average particle diameter and lung-deposited surface area (LDSA) with time resolution and logging at 1 second (1 Hz).

Testo’s DISCmini product page offers a video and more details,

Negative health effects due to nanoparticles appear to correlate particularly well with number concentration or surface. Epidemiological and toxicological studies are still mainly based on total mass, or they use fuzzy proxies like “distance from a busy road” to describe personal exposure, although the health-related effects of particle number concentration are well known. We believe that this contradictory situation is due to the lack of adequate sensors on the market.

This gap is now closed with Testo Particle´s handheld version of the “Diffusion Size Classifier”, testo DiSCmini.  The testo DiSCmini is a portable sensor for the measurement of particle number and average diameter with a time resolution of up to 1 second (1 Hz). The simultaneous capture of number concentration and particle size allows the specification of other characteristic parameters, such as the particles surface (Lung Deposited Surface Area, LDSA). The instrument is battery powered with a lifetime of up to 8 hours; data can be recorded on a memory card, and transferred to a external computer via USB cable.

The testo DiSCmini is particularly efficient for personal exposure monitoring in particle-loaded work space with toxic air contaminants such as diesel soot, welding fumes, or industrial nanomaterials.

The testo DiSCmini is based on the electrical charging of the aerosols. Positive air ions generated in a corona discharge are mixed with the aerosol. The charged particles are then detected in two stages by electrometers. The first detector stage is a pile of steel grids; small particles will preferably deposit on it by diffusion. The second stage is a high-efficiency particle filter which captures all the other particles. The mean particle size can be obtained by analysis of the two currents measured on the stages. The particle count is determined with the total current. The testo DiSCmini detects particles ranging in size from 10 to about 700 nm, while the modal value should lie below 300 nm. The concentration range is from about 1’000 to over 1’000’000 particles per cubic centimetre. The accuracy of the measurement depends on the shape of the particle size distribution and number concentration, and is usually around 15-20% compared to a reference CPC. The unit should be serviced and calibrated once a year.

Unlike other instruments the testo DiSCmini needs neither working liquid of any kind nor radioactive sources. Therefore, it can be operated in any position and over extended periods without requiring a liquid refill. Typical applications include the determination of personal exposure in particle-loaded jobs (diesel soot, welding fumes, industrial nanomaterials) or in vulnerable groups (asthmatics, COPD patients). The development of large area survey grids of ambient air is becoming possible. The small size of  the testo DiSCmini makes the instrument particularly suitable for personal carry-on measurement campaigns. The high measurement frequency of 1 Hz allows the instrument to monitor rapid changes in the aerosol. This feature is particularly interesting to local or defined sources of particle generation. The equipment is designed for situations and applications where quick and easy access to particle number concentration and average diameter is desired.

For anyone interested in the technical specifications, there’s the DISCmini product brochure.

Nanoparticle behaviour in the environment unpredictable

These Swiss researchers took on a fairly massive project according to an April 19, 2017 news item on ScienceDaily,

The nanotech industry is booming. Every year, several thousands of tonnes of man-made nanoparticles are produced worldwide; sooner or later, a certain part of them will end up in bodies of water or soil. But even experts find it difficult to say exactly what happens to them there. It is a complex question, not only because there are many different types of man-made (engineered) nanoparticles, but also because the particles behave differently in the environment depending on the prevailing conditions.

Researchers led by Martin Scheringer, Senior Scientist at the Department of Chemistry and Applied Biosciences, wanted to bring some clarity to this issue. They reviewed 270 scientific studies, and the nearly 1,000 laboratory experiments described in them, looking for patterns in the behaviour of engineered nanoparticles. The goal was to make universal predictions about the behaviour of the particles.

An April 19, 2017ETH Zurich press release by Fabio Bergamin (also on EurekAlert), which originated the news item, elaborates,

Particles attach themselves to everything

However, the researchers found a very mixed picture when they looked at the data. “The situation is more complex than many scientists would previously have predicted,” says Scheringer. “We need to recognise that we can’t draw a uniform picture with the data available to us today.”

Nicole Sani-Kast, a doctoral student in Scheringer’s group and first author of the analysis published in the journal PNAS [Proceedings of the National Academy of Sciences], adds: “Engineered nanoparticles behave very dynamically and are highly reactive. They attach themselves to everything they find: to other nanoparticles in order to form agglomerates, or to other molecules present in the environment.”

Network analysis

To what exactly the particles react, and how quickly, depends on various factors such as the acidity of the water or soil, the concentration of the existing minerals and salts, and above all, the composition of the organic substances dissolved in the water or present in the soil. The fact that the engineered nanoparticles often have a surface coating makes things even more complicated. Depending on the environmental conditions, the particles retain or lose their coating, which in turn influences their reaction behaviour.

To evaluate the results available in the literature, Sani-Kast used a network analysis for the first time in this research field. It is a technique familiar in social research for measuring networks of social relations, and allowed her to show that the data available on engineered nanoparticles is inconsistent, insufficiently diverse and poorly structured.

More method for machine learning

“If more structured, consistent and sufficiently diverse data were available, it may be possible to discover universal patterns using machine learning methods,” says Scheringer, “but we’re not there yet.” Enough structured experimental data must first be available.

“In order for the scientific community to carry out such experiments in a systematic and standardised manner, some kind of coordination is necessary,” adds Sani-Kast, but she is aware that such work is difficult to coordinate. Scientists are generally well known for preferring to explore new methods and conditions rather than routinely performing standardized experiments.

[additional material]

Distinguishing man-made and natural nanoparticles

In addition to the lack of systematic research, there is also a second tangible problem in researching the behaviour of engineered nanoparticles: many engineered nanoparticles consist of chemical compounds that occur naturally in the soil. So far it has been difficult to measure the engineered particles in the environment since it is hard to distinguish them from naturally occurring particles with the same chemical composition.

However, researchers at ETH Zurich’s Department of Chemistry and Applied Biosciences, under the direction of ETH Professor Detlef Günther, have recently established an effective method that makes such a distinction possible in routine investigations. They used a state-of-the-art and highly sensitive mass spectrometry technique (called spICP-TOF mass spectrometry) to determine which chemical elements make up individual nanoparticles in a sample.

In collaboration with scientists from the University of Vienna, the ETH researchers applied the method to soil samples with natural cerium-containing particles, into which they mixed engineered cerium dioxide nanoparticles. Using machine learning methods, which were ideally suited to this particular issue, the researchers were able to identify differences in the chemical fingerprints of the two particle classes. “While artificially produced nanoparticles often consist of a single compound, natural nanoparticles usually still contain a number of additional chemical elements,” explains Alexander Gundlach-Graham, a postdoc in Günther’s group.

The new measuring method is very sensitive: the scientists were able to measure engineered particles in samples with up to one hundred times more natural particles.

The researchers have produced a visualization of their network analysis,

The researchers evaluated the experimental data published in the scientific literature using a network analysis. This analysis reveals which types of nanoparticles (blue) have been studied under which environmental conditions (red). (Visualisations: Thomas Kast)

Here are links and citation for two papers associated with this research,

A network perspective reveals decreasing material diversity in studies on nanoparticle interactions with dissolved organic matter by Nicole Sani-Kast, Jérôme Labille, Patrick Ollivier, Danielle Slomberg, Konrad Hungerbühler, and Martin Scheringer. PNAS 2017, 114: E1756-E1765, DOI: 10.1073/pnas.1608106114

Single-particle multi-element fingerprinting (spMEF) using inductively-coupled plasma time-of-flight mass spectrometry (ICP-TOFMS) to identify engineered nanoparticles against the elevated natural background in soils by Antonia Praetorius, Alexander Gundlach-Graham, Eli Goldberg, Willi Fabienke, Jana Navratilova, Andreas Gondikas, Ralf Kaegi, Detlef Günther, Thilo Hofmann, and Frank von der Kammer. Environonmental Science: Nano 2017, 4: 307-314, DOI: 10.1039/c6en00455e

Both papers are behind a paywall.

Is there a risk of resistance to nanosilver?

Anyone who’s noticed how popular silver has become as an antibacterial, antifungal, or antiviral agent may have wondered if resistance might occur as its use becomes more common. I have two bits on the topic, one from Australia and the other from Canada.


Researchers in Australia don’t have a definitive statement on the issue but are suggesting more caution (from a March 31, 2017 news item on Nanowerk),

Researchers at the University of Technology Sydney [UTS] warn that the broad-spectrum antimicrobial effectiveness of silver is being put at risk by the widespread and inappropriate expansion of nanosilver use in medical and consumer goods.

As well as their use in medical items such as wound dressings and catheters, silver nanoparticles are becoming ubiquitous in everyday items, including toothbrushes and toothpaste, baby bottles and teats, bedding, clothing and household appliances, because of their antibacterial potency and the incorrect assumption that ordinary items should be kept “clean” of microbes.

Nanobiologist Dr Cindy Gunawan, from the ithree institute at UTS and lead researcher on the investigation, said alarm bells should be ringing at the commercialisation of nanosilver use because of a “real threat” that resistance to nanosilver will develop and spread through microorganisms in the human body and the environment.

A March 31 (?), 2017 University of Technology Sydney press release by Fiona McGill, which originated the news item, expands on the theme,

Dr Gunawan and ithree institute director Professor Liz Harry, in collaboration with researchers at UNSW [University of New South Wales] and abroad, investigated more than 140 commercially available medical devices, including wound dressings and tracheal and urinary catheters, and dietary supplements, which are promoted as immunity boosters and consumed by throat or nasal spray.

Their perspective article in the journal ACS Nano concluded that the use of nanosilver in these items could lead to prolonged exposure to bioactive silver in the human body. Such exposure creates the conditions for microbial resistance to develop.

E. coli bacteria. Photo: Flickr/NIAID


The use of silver as an antimicrobial agent dates back centuries. Its ability to destroy pathogens while seemingly having low toxicity on human cells has seen it widely employed, in treating burns or purifying water, for example. More recently, ultra-small (less than 10,000th of a millimetre) silver nanoparticles have been engineered for antimicrobial purposes.  Their commercial appeal lies in superior potency at lower concentrations than “bulk” silver.

“Nanosilver is a proven antimicrobial agent whose reliability is being jeopardised by the commercialisation of people’s fear of bacteria,” Dr Gunawan said.

“Our use of it needs to be far more judicious, in the same way we need to approach antibiotic usage. Nanosilver is a useful tool but we need to be careful, use it wisely and only when the benefit outweighs the risk.

“People need to be made aware of just how widely it is used, but more importantly they need to be made aware that the presence of nanosilver has been shown to cause antimicrobial resistance.”

What is also needed, Dr Gunawan said, is a targeted surveillance strategy to monitor for any occurrence of resistance.

Professor Harry said the findings were a significant contribution to addressing the global antimicrobial resistance crisis.

“This research emphasises the threat posed to our health and that of the environment by the inappropriate use of nanosilver as an antibacterial, particularly in ordinary household and consumer items,” she said.

Here’s a link to and a citation for the paper,

Widespread and Indiscriminate Nanosilver Use: Genuine Potential for Microbial Resistance by Cindy Gunawan, Christopher P. Marquis, Rose Amal, Georgios A. Sotiriou, Scott A. Rice⊥, and Elizabeth J. Harry. ACS Nano, Article ASAP DOI: 10.1021/acsnano.7b01166 Publication Date (Web): March 24, 2017

Copyright © 2017 American Chemical Society

This paper is behind a paywall.

Meanwhile, researchers at the University Calgary (Alberta, Canada) may have discovered what could cause resistance to silver.


This April 25, 2017 news release on EurekAlert is from the Experimental Biology Annual Meeting 2017,

Silver and other metals have been used to fight infections since ancient times. Today, researchers are using sophisticated techniques such as the gene-editing platform Crispr-Cas9 to take a closer look at precisely how silver poisons pathogenic microbes–and when it fails. The work is yielding new insights on how to create effective antimicrobials and avoid the pitfalls of antimicrobial resistance.

Joe Lemire, a postdoctoral fellow at the University of Calgary, will present his work in this area at the American Society for Biochemistry and Molecular Biology annual meeting during the Experimental Biology 2017 meeting, to be held April 22-26 in Chicago.

“Our overarching goal is to deliver the relevant scientific evidence that would aid policymakers in developing guidelines for when and how silver could be used in the clinic to combat and control infectious pathogens,” said Lemire. “With our enhanced mechanistic understanding of silver toxicity, we also aim to develop novel silver-based antimicrobial therapies, and potentially rejuvenate other antibiotic therapies that bacteria have come to resist, via silver-based co-treatment strategies.”

Lemire and his colleagues are using Crispr-Cas9 genome editing to screen for and delete genes that allow certain bacterial species to resist silver’s antimicrobial properties. [emphasis mine] Although previous methods allowed researchers to identify genes that confer antibiotic resistance or tolerance, Crispr-Cas9 is the first technology to allow researchers to cleanly delete these genes from the genome without leaving behind any biochemical markers or “scars.”

The team has discovered many biological pathways involved in silver toxicity and some surprising ways that bacteria avoid succumbing to silver poisoning, Lemire said. While silver is used to control bacteria in many clinical settings and has been incorporated into hundreds of commercial products, gaining a more complete understanding of silver’s antimicrobial properties is necessary if we are to make the most of this ancient remedy for years to come.


Joe Lemire will present this research at 12-2:30 p.m. Tuesday, April 25, [2017] in Hall F, McCormick Place Convention Center (poster B379 939.2) (abstract). Contact the media team for more information or to obtain a free press pass to attend the meeting.

About Experimental Biology 2017

Experimental Biology is an annual meeting comprised of more than 14,000 scientists and exhibitors from six host societies and multiple guest societies. With a mission to share the newest scientific concepts and research findings shaping clinical advances, the meeting offers an unparalleled opportunity for exchange among scientists from across the U.S. and the world who represent dozens of scientific areas, from laboratory to translational to clinical research. #expbio

About the American Society for Biochemistry and Molecular Biology (ASBMB)

ASBMB is a nonprofit scientific and educational organization with more than 12,000 members worldwide. Founded in 1906 to advance the science of biochemistry and molecular biology, the society publishes three peer-reviewed journals, advocates for funding of basic research and education, supports science education at all levels, and promotes the diversity of individuals entering the scientific workforce.

Lemire’s co-authors for the work presented at the 2017 annual meeting are: Kate Chatfield-Reed (The University of Calgary), Lindsay Kalan (Perelman School of Medicine), Natalie Gugala (The University of Calgary), Connor Westersund (The University of Calgary), Henrik Almblad (The University of Calgary), Gordon Chua (The University of Calgary), Raymond Turner (The University of Calgary).

For anyone who wants to pursue this research a little further, the most recent paper I can find is this one from 2015,

Silver oxynitrate: An Unexplored Silver Compound with Antimicrobial and Antibiofilm Activity by Joe A. Lemire, Lindsay Kalan, Alexandru Bradu, and Raymond J. Turner. Antimicrobial Agents and Chemotherapy 05177-14, doi: 10.1128/AAC.05177-14 Accepted manuscript posted online 27 April 2015

This paper appears to be open access.

European Commission has issued evaluation of nanomaterial risk frameworks and tools

Despite complaints that there should have been more, there has been some research into risks where nanomaterials are concerned. While additional research would be welcome, it’s perhaps more imperative that standardized testing and risk frameworks are developed so, for example, carbon nanotube safety research in Japan can be compared with the similar research in the Netherlands, the US, and elsewhere. This March 15, 2017 news item on Nanowerk features some research analyzing risk assessment frameworks and tools in Europe,

A recent study has evaluated frameworks and tools used in Europe to assess the potential health and environmental risks of manufactured nanomaterials. The study identifies a trend towards tools that provide protocols for conducting experiments, which enable more flexible and efficient hazard testing. Among its conclusions, however, it notes that no existing frameworks meet all the study’s evaluation criteria and calls for a new, more comprehensive framework.

A March 9, 2017 news alert in the European Commission’s Science for Environment Policy series, which originated the news item, provides more detail (Note: Links have been removed),

Nanotechnology is identified as a key emerging technology in the EU’s growth strategy, Europe 2020. It has great potential to contribute to innovation and economic growth and many of its applications have already received large investments. However,there are some uncertainties surrounding the environmental, health and safety risks of manufactured nanomaterials. For effective regulation, careful scientific analysis of their potential impacts is needed, as conducted through risk assessment exercises.

This study, conducted under the EU-funded MARINA project1, reviewed existing frameworks and tools for risk assessing manufactured nanomaterials. The researchers define a framework as a ‘conceptual paradigm’ of how a risk assessment should be conducted and understood, and give the REACH chemical safety assessment as an example. Tools are defined as implements used to carry out a specific task or function, such as experimental protocols, computer models or databases.

In all, 12 frameworks and 48 tools were evaluated. These were identified from other studies and projects. The frameworks were assessed against eight criteria which represent different strengths, such as whether they consider properties specific to nanomaterials, whether they consider the entire life cycle of a nanomaterial and whether they include careful planning and prioritise objectives before the risk assessment is conducted.

The tools were assessed against seven criteria, such as ease of use, whether they provide quantitative information and if they clearly communicate uncertainty in their results. The researchers defined the criteria for both frameworks and tools by reviewing other studies and by interviewing staff at organisations who develop tools.

The evaluation was thus able to produce a list of strengths and areas for improvement for the frameworks and tools, based on whether they meet each of the criteria. Among its many findings, the evaluation showed that most of the frameworks stress that ‘problem formulation’, which sets the goals and scope of an assessment during the planning process, is essential to avoid unnecessary testing. In addition, most frameworks consider routes of exposure in the initial stages of assessment, which is beneficial as it can exclude irrelevant exposure routes and avoid unnecessary tests.

However, none of the frameworks met all eight of the criteria. The study therefore recommends that a new, comprehensive framework is developed that meets all criteria. Such a framework is needed to inform regulation, the researchers say, and should integrate human health and environmental factors, and cover all stages of the life cycle of a product containing nanomaterials.

The evaluation of the tools suggested that many of them are designed to screen risks, and not necessarily to support regulatory risk assessment. However, their strengths include a growing trend in quantitative models, which can assess uncertainty; for example, one tool analysed can identify uncertainties in its results that are due to gaps in knowledge about a material’s origin, characteristics and use.

The researchers also identified a growing trend in tools that provide protocols for experiments, such as identifying materials and test hazards, which are reproducible across laboratories. These tools could lead to a shift from expensive case-by-case testing for risk assessment of manufactured nanomaterials towards a more efficient process based on groupings of nanomaterials; and ‘read-across’ methods, where the properties of one material can be inferred without testing, based on the known properties of a similar material. The researchers do note, however, that although read-across methods are well established for chemical substances, they are still being developed for nanomaterials. To improve nanomaterial read-across methods, they suggest that more data are needed on the links between nanomaterials’ specific properties and their biological effects.

That’s all, folks.

The Swiss come to a better understanding of nanomaterials

Just to keep things interesting, after the report suggesting most of the information that the OECD (Organization for Economic Cooperation and Development) has on nanomaterials is of little value for determining risk (see my April 5, 2017 posting for more) the Swiss government has released a report where they claim an improved understanding of nanomaterials than they previously had due to further research into the matter. From an April 6, 2017 news item on Nanowerk,

In the past six years, the [Swiss] National Research Programme “Opportunities and Risks of Nanomaterials” (NRP 64) intensively studied the development, use, behaviour and degradation of engineered nanomaterials, including their impact on humans and on the environment.

Twenty-three research projects on biomedicine, the environment, energy, construction materials and food demonstrated the enormous potential of engineered nanoparticles for numerous applications in industry and medicine. Thanks to these projects we now know a great deal more about the risks associated with nanomaterials and are therefore able to more accurately determine where and how they can be safely used.

An April 6, 2017 Swiss National Science Foundation press release, which originated the news item, expands on the theme,

“One of the specified criteria in the programme was that every project had to examine both the opportunities and the risks, and in some cases this was a major challenge for the researchers,” explains Peter Gehr, President of the NRP 64 Steering Committee.

One development that is nearing industrial application concerns a building material strengthened with nanocellulose that can be used to produce a strong but lightweight insulation material. Successful research was also carried out in the area of energy, where the aim was to find a way to make lithium-ion batteries safer and more efficient.

Promising outlook for nanomedicine

A great deal of potential is predicted for the field of nanomedicine. Nine of the 23 projects in NRP 64 focused on biomedical applications of nanoparticles. These include their use for drug delivery, for example in the fight against viruses, or as immune modulators in a vaccine against asthma. Another promising application concerns the use of nanomagnets for filtering out harmful metallic substances from the blood. One of the projects demonstrated that certain nanoparticles can penetrate the placenta barrier, which points to potential new therapy options. The potential of cartilage and bone substitute materials based on nanocellulose or nanofibres was also studied.

The examination of potential health risks was the focus of NRP 64. A number of projects examined what happens when nanoparticles are inhaled, while two focused on ingestion. One of these investigated whether the human gut is able to absorb iron more efficiently if it is administered in the form of iron nanoparticles in a food additive, while the other studied silicon nanoparticles as they occur in powdered condiments. It was ascertained that further studies will be required in order to determine the doses that can be used without risking an inflammatory reaction in the gut.

What happens to engineered nanomaterials in the environment?

The aim of the seven projects focusing on environmental impact was to gain a better understanding of the toxicity of nanomaterials and their degradability, stability and accumulation in the environment and in biological systems. Here, the research teams monitored how engineered nanoparticles disseminate along their lifecycle, and where they end up or how they can be discarded.

One of the projects established that 95 per cent of silver nanoparticles that are washed out of textiles are collected in sewage treatment plants, while the remaining particles end up in sewage sludge, which in Switzerland is incinerated. In another project a measurement device was developed to determine how aquatic microorganisms react when they come into contact with nanoparticles.

Applying results and making them available to industry

“The findings of the NRP 64 projects form the basis for a safe application of nanomaterials,” says Christoph Studer from the Federal Office of Public Health. “It has become apparent that regulatory instruments such as testing guidelines will have to be adapted at both national and international level.” Studer has been closely monitoring the research programme in his capacity as the Swiss government’s representative in NRP 64. In this context, the precautionary matrix developed by the government is an important instrument by means of which companies can systematically assess the risks associated with the use of nanomaterials in their production processes.

The importance of standardised characterisation and evaluation of engineered nanomaterials was highlighted by the close cooperation among researchers in the programme. “The research network that was built up in the framework of NRP 64 is functioning smoothly and needs to be further nurtured,” says Professor Bernd Nowack from Empa, who headed one of the 23 projects.

The results of NRP 64 show that new key technologies such as the use of nanomaterials need to be closely monitored through basic research due to the lack of data on its long-term effects. As Peter Gehr points out, “We now know a lot more about the risks of nanomaterials and how to keep them under control. However, we need to conduct additional research to learn what happens when humans and the environment are exposed to engineered nanoparticles over longer periods, or what happens a long time after a one-off exposure.”

You can find out more about the Opportunities and Risks of Nanomaterials; National Research Programme (NRP 64) here.