Spatial and PMF analysis of particle size distributions simultaneously measured at four locations at the roadside of highways.

In urban areas, particulate matter emitted from vehicles directly affects the health of citizens near roads. Thus, in this study, particle size distribution was measured by the horizontal and vertical distances along a highway road with heavy traffic to characterize the dispersion phenomena of particulate matter emitted from vehicles. In addition, the contribution of pollution sources was analyzed using a source-receptor model. A concentration gradient was observed in which the concentration decreased with the increase in the distance from the road when the wind blew from the road to the monitoring locations. The concentration was slightly higher within 50 m of the road when the wind blows parallel to the road, and similar concentrations were found at the other monitoring locations further away from the roads. In particular, the higher the turbulence intensity of the wind, the lower is the concentration gradient coefficient because of the more enhanced mixing and dispersion. A positive matrix factorization (PMF) model with the measured particle size distribution data in the range of 9-300 nm resulted in a contribution of about 70 % (number) and 20 % (mass) to particle concentrations because of six types of vehicles including LPG, two gasoline vehicles (GDI, MPI), and three diesel vehicles with 3rd, 4th, and 5th emission classes. It showed a decrease in the vehicular contribution as the distance from the road increased. Particle number concentrations decreased with increasing altitude up to 30 m above the ground. The results of this study can be useful in deriving generalized gradient equations of particle concentrations exposed by distance and wind direction at the roadside using traffic and meteorological conditions and for establishing environmental policies, such as roadside exposure assessment, in the future. A CAPSULE ABSTRACT: Dispersion of particles emitted from vehicles on a busy highway was characterized by roadside measurements of horizontal and vertical profiles of particle size distributions measured at four locations. The source profiles and contributions were estimated by major sources using a source-receptor model such as PMF.

Accurate measurements of particle emissions from a three-dimensional printer using a chamber test with a mixer-installed sampling system.

Recently, three-dimensional (3D) printing has attracted attention as a new manufacturing technology. However, there is lack of data and regulations regarding the emissions of ultrafine particles from 3D printers. Therefore, we investigated particle emissions from a 3D printer using a chamber system. The test system was improved by installing a developed mixer for accurate measurement. Without a mixer, the particle concentration was unstable depending on the sampling point; however, reliable data with good uniformity were obtained by installing a mixer. Using the test system with a mixer, we investigated particle emissions from a 3D printer during operation. Filaments made each of acrylonitrile butadiene styrene (ABS) and polylactic acid (PLA) were used as the printing material. The effects of nozzle temperature and printing time were investigated. Compared to the effect of the printing time, the nozzle temperature had greater impact on the particle emissions. The dominant particle size for the emissions from a 3D printer is less than 10 nm, and the particle concentration decreased with increasing particle size.

Biokinetics of subacutely co-inhaled same size gold and silver nanoparticles.

BACKGROUND: Toxicokinetics of nanomaterials, including studies on the absorption, distribution, metabolism, and elimination of nanomaterials, are essential in assessing their potential health effects. The fate of nanomaterials after inhalation exposure to multiple nanomaterials is not clearly understood. METHODS: Male Sprague-Dawley rats were exposed to similar sizes of silver nanoparticles (AgNPs, 10.86 nm) and gold nanoparticles (AuNPs, 10.82 nm) for 28 days (6-h/day, 5-days/week for four weeks) either with separate NP inhalation exposures or with combined co-exposure in a nose-only inhalation system. Mass concentrations sampled from the breathing zone were AuNP 19.34 ± 2.55 µg/m3 and AgNP 17.38 ± 1.88 µg/m3 for separate exposure and AuNP 8.20 µg/m3 and AgNP 8.99 µg/m3 for co-exposure. Lung retention and clearance were previously determined on day 1 (6-h) of exposure (E-1) and on post-exposure days 1, 7, and 28 (PEO-1, PEO-7, and PEO-28, respectively). In addition, the fate of nanoparticles, including translocation and elimination from the lung to the major organs, were determined during the post-exposure observation period. RESULTS: AuNP was translocated to the extrapulmonary organs, including the liver, kidney, spleen, testis, epididymis, olfactory bulb, hilar and brachial lymph nodes, and brain after subacute inhalation and showed biopersistence regardless of AuNP single exposure or AuNP + AgNP co-exposure, showing similar elimination half-time. In contrast, Ag was translocated to the tissues and rapidly eliminated from the tissues regardless of AuNP co-exposure. Ag was continually accumulated in the olfactory bulb and brain and persistent until PEO-28. CONCLUSION: Our co-exposure study of AuNP and AgNP indicated that soluble AgNP and insoluble AuNP translocated differently, showing soluble AgNP could be dissolved into Ag ion to translocate to the extrapulmonary organs and rapidly removed from most organs except the brain and olfactory bulb. Insoluble AuNPs were continually translocated to the extrapulmonary organs, and they were not eliminated rapidly.

The Acute and Short-Term Inhalation of Carbon Nanofiber in Sprague-Dawley Rats.

The inhalation toxicity of carbon nanofibers (CNFs) is not clearly known due to relatively few related studies reported. An acute inhalation study and short-term inhalation study (5 days) were therefore conducted using Sprague-Dawley rats. In the acute inhalation study, the rats were grouped and exposed to a fresh air control or to low (0.238 ± 0.197), moderate (1.935 ± 0.159), or high (24.696 ± 6.336 mg/m3) CNF concentrations for 6 h and thereafter sacrificed at 14 days. For the short-term inhalation study, the rats were grouped and exposed to a fresh air control or low (0.593 ± 0.019), moderate (2.487 ± 0.213), or high (10.345 ± 0.541 mg/m3) CNF concentrations for 6 h/day for 5 days and sacrificed at 1, 3, and 21 days post-exposure. No mortality was observed in the acute inhalation study. Thus, the CNF LC50 was higher than 25 mg/m3. No significant body or organ weight changes were noted during the 5 days short-term inhalation study or during the post-exposure period. No significant effects of toxicological importance were observed in the hematological, blood biochemical, and coagulation tests. In addition, the bronchoalveolar lavage (BAL) fluid cell differential counts and BAL inflammatory markers showed no CNF-exposure-relevant changes. The histopathological examination also found no CNF-exposure-relevant histopathological lesions. Thus, neither acute nor 5 days inhalation exposure to CNFs induced any noticeable toxicological responses.

Application of an aerosol electrical mobility spectrum analyzer: Charged-particle polarity ratio measurement in the Antarctic and Arctic regions.

An aerosol electrical mobility spectrum analyzer (AEMSA), developed at Hanyang University, was employed to investigate the particle charge characteristics in the Antarctic and Arctic regions. The particle charge characteristics in these areas were compared with the charging state in Ansan, South Korea, located in the midlatitude, where artificial factors, such as human activity, urbanization, and traffic, might result in a higher total concentration. Furthermore, in Ansan, South Korea, the charged-particle polarity ratio was very stable and was close to 1. However, notably different particle charge characteristics were obtained in the Antarctic and Arctic regions. The imbalance between the numbers of positively and negatively charged particles was evident, resulting in more positive charges on the atmospheric particles. On average, the positively charged particle concentrations in the Antarctic and Arctic areas were 1.4 and 2.8 times higher, respectively, compared with the negatively charged particles. The developed AEMSA system and the findings of this study provide useful information on the characteristics of atmospheric aerosols in the Antarctic and Arctic regions and can be further utilized to study particle formation mechanisms.

Estimate of the critical exposure time based on 70 confirmed COVID-19 cases.

The transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) occurs via contact with contaminated surfaces and inhalation of large airborne droplets and aerosols. As growing evidence of airborne SARS-CoV-2 transmission has been reported worldwide, ventilation is an effective method of reducing the infection probability of SARS-CoV-2. This leads to such questions as "What is a sufficient ventilation rate for avoiding the risk of COVID-19 infection?" Therefore, this study evaluates the critical ventilation rates according to room size and exposure time when a susceptible person is in the same room as an infector. The analytical results were based on data obtained from 70 confirmed COVID-19 cases transmitted in confined spaces without an operational ventilation system. The results reveal that even with active ventilation (20 h-1 air exchange rate), the critical exposure time for a susceptible person with a COVID-19 infector in a small space of 20 m3 is less than 1 h. For other cases (different space sizes), the estimated air exchange rates for avoiding the risk of infection are generally higher than various requirements for good indoor air quality. The findings of this study will provide guidelines for determining sufficient ventilation rates to protect against the highly contagious COVID-19.

Lung retention and particokinetics of silver and gold nanoparticles in rats following subacute inhalation co-exposure.

BACKGROUND: Inhalation exposure to nanomaterials in workplaces can include a mixture of multiple nanoparticles. Such ambient nanoparticles can be of high dissolution or low dissolution in vivo and we wished to determine whether co-exposure to particles with different dissolution rates affects their biokinetics. METHODS AND RESULTS: Rats were exposed to biosoluble silver nanoparticles (AgNPs, 10.86 nm) and to biopersistent gold nanoparticles (AuNPs, 10.82 nm) for 28 days (6-h/day, 5-days/week for 4 weeks) either with separate NP inhalation exposures or with combined co-exposure. The separate NPs mass concentrations estimated by the differential mobility analyzer system (DMAS) were determined to be 17.68 ± 1.69 µg/m3 for AuNP and 10.12 ± 0.71 µg/m3 for AgNP. In addition, mass concentrations analyzed by atomic absorption spectrometer (AAS) via filter sampling were for AuNP 19.34 ± 2.55 µg/m3 and AgNP 17.38 ± 1.88 µg/m3 for separate exposure and AuNP 8.20 ± 1.05 µg/m3 and AgNP 8.99 ± 1.77 µg/m3 for co-exposure. Lung retention and clearance were determined on day 1 (6-h) of exposure (E-1) and on post-exposure days 1, 7, and 28 (PEO-1, PEO-7, and PEO-28, respectively). While the AgNP and AuNP deposition rates were determined to be similar due to the similarity of NP size of both aerosols, the retention half-times and clearance rates differed due to the difference in dissolution rates. Thus, when comparing the lung burdens following separate exposures, the AgNP retention was 10 times less than the AuNP retention at 6-h (E-1), and 69, 89, and 121 times lower less than the AuNP retention at PEO-1, PEO-7, and PEO-28, respectively. In the case of AuNP+AgNP co-exposure, the retained AgNP lung burden was 14 times less than the retained AuNP lung burden at E-1, and 26, 43, and 55 times less than the retained AuNP lung burden at PEO-1, PEO-7, and PEO-28, respectively. The retention of AuNP was not affected by the presence of AgNP, but AgNP retention was influenced in the presence of AuNP starting at 24 h after the first day of post day of exposure. The clearance of AgNPs of the separate exposure showed 2 phases; fast (T1/2 3.1 days) and slow (T1/2 48.5 days), while the clearance of AuNPs only showed one phase (T1/2 .81.5 days). For the co-exposure of AuNPs+AgNPs, the clearance of AgNPs also showed 2 phases; fast (T1/2 2.2 days) and slow (T1/2 28.4 days), while the clearance of AuNPs consistently showed one phase (T1/2 54.2 days). The percentage of Ag lung burden in the fast and slow clearing lung compartment was different between separate and combined exposure. For the combined exposure, the slow and fast compartments were each 50% of the lung burden. For the single exposure, 1/3 of the lung burden was cleared by the fast rate and 2/3 of the lung burden by the slow rate. CONCLUSIONS: The clearance of AgNPs follows a two- phase model of fast and slow dissolution rates while the clearance of AuNPs could be described by a one- phase model with a longer half-time. The co-exposure of AuNPs+AgNPs showed that the clearance of AgNPs was altered by the presence of AuNPs perhaps due to some interaction between AgNP and AuNP affecting dissolution and/or mechanical clearance of AgNP in vivo.

Even lobar deposition of poorly soluble gold nanoparticles (AuNPs) is similar to that of soluble silver nanoparticles (AgNPs).

BACKGROUND: Information on particle deposition, retention, and clearance is important when evaluating the risk of inhaled nanomaterials to human health. The revised Organization Economic Cooperation and Development (OECD) inhalation toxicity test guidelines now require lung burden measurements of nanomaterials after rodent subacute and sub-chronic inhalation exposure (OECD 412, OECD 413) to inform on lung clearance behavior and translocation after exposure and during post-exposure observation (PEO). Lung burden measurements are particularly relevant when the testing chemical is a solid poorly soluble nanomaterial. Previously, the current authors showed that total retained lung burden of inhaled soluble silver nanoparticles (AgNPs) could be effectively measured using any individual lung lobe. METHODS AND RESULTS: Accordingly, the current study investigated the evenness of deposition/retention of poorly soluble gold nanoparticles (AuNPs) after 1 and 5 days of inhalation exposure. Rats were exposed nose-only for 1 or 5 days (6 h/day) to an aerosol of 11 nm well-dispersed AuNPs. Thereafter, the five lung lobes were separated and the gold concentrations measured using an inductively coupled plasma-mass spectrophotometer (ICP-MS). The results showed no statistically significant difference in the AuNP deposition/retention among the different lung lobes in terms of the gold mass per gram of lung tissue. CONCLUSIONS: Thus, it would seem that any rat lung lobe can be used for the lung burden analysis after short or long-term NP inhalation, while the other lobes can be used for collecting and analyzing the bronchoalveolar lavage fluid (BALF) and for the histopathological analysis. Therefore, combining the lung burden measurement, histopathological tissue preparation, and BALF assay from one rat can minimize the number of animals used and maximize the number of endpoints measured.

Using miniaturised scanning mobility particle sizers to observe size distribution patterns of quasi-ultrafine aerosols inhaled during city commuting.

Portable miniaturised scanning mobility particle sizer (SMPS) instruments measuring atmospheric particles within the 10-241 nm size range were used to track particle number size distributions and concentrations during near-simultaneous pedestrian, bicycle, bus, car, tram and subway commuting journeys in Barcelona, Spain on 4th-6th July 2018. The majority of particles in this size range were <100 nm, with k-means cluster analysis identifying peaks at 15-22 nm, 30-40 nm, and 45-75 nm. Around 10-25% of the particles measured however were >100 nm (especially in the subway environment) and so lie outside the commonly defined range of "ultrafine" particles (UFP, or <100 nm particles). The study demonstrated in detail how personal exposure to quasi-UFP (QUFP, <241 nm), most of which present in the city streets are produced by road traffic, varies greatly depending on the transport mode and route chosen. Proximity to fresh traffic exhaust sources, such as in a car with open windows, on-road cycling, walking downwind of busy roads, or in a subway station contaminated by roadside air, enhances commuter exposure to particles <30 nm in size. In contrast, travelling inside air-conditioned bus or tram offers greater protection to the commuter from high concentrations of fresh exhaust. Ultrafine number size distributions in traffic-contaminated city air typically peak in the size range 30-70 nm, but they can be shifted to finer sizes not only by increased content of fresh proximal exhaust emissions but also by bursts of new particle formation (NPF) events in the city. One such afternoon photochemical nucleation NPF event was identified during our Barcelona study and recognised in different transport modes, including underground in the subway system. The integration of static urban background air monitoring station information with particle number concentration and size distribution data obtained from portable miniaturised SMPS instruments during commuting journeys opens new approaches to investigating city air quality by offering a level of detail not previously available.

Mode of silver clearance following 28-day inhalation exposure to silver nanoparticles determined from lung burden assessment including post-exposure observation periods.

Recently revised OECD inhalation toxicity testing guidelines require measurements of lung burden immediately after and for periods following exposure for nanomaterials. Lung burden is a function of pulmonary deposition and retention of nanoparticles. Using lung burden studies as per OECD guidelines, it may be possible to assess clearance mechanisms of nanoparticles. In this study, male rats were exposed to silver nanoparticle (AgNP) aerosols (18.1-19.6 nm) generated from a spark generator. Exposure groups consisted of (1) control (fresh air), (2) low (31.2 ± 8.5 µg/m3), (3) moderate (81.8 ± 11.4 µg/m3), and (4) high concentrations (115.6 ± 30.5 µg/m3). Rats were exposed for 6-h/day, 5-days/week for 4 weeks (28-days) based on the revised OECD test guideline 412. Bronchoalveolar lavage (BAL) fluids were collected on post-exposure observation (PEO)-1 and PEO-7 days and analyzed for inflammatory cells and inflammatory biomarkers. The lung burdens of Ag from AgNPs were measured on PEO-1, PEO-7, and PEO-28 days to obtain quantitative mass concentrations per lung. Differential counting of blood cells and inflammatory biomarkers in BAL fluid and histopathological evaluation of lung tissue indicated that exposure to the high concentrations of AgNP aerosol induced inflammation at PEO-1, slowly resolved at PEO-7 and completely resolved at PEO-28 days. Lung burden measurement suggested that Ag from AgNPs was cleared through two different modes; fast and slow clearance. The fast clearance component was concentration-dependent with half-times ranging from two to four days and clearance rates of 0.35-0.17/day-1 from low to high concentrations. The slow clearance had half-times of 100, 57, and 76 days and clearance rates of 0.009, 0.012, and 0.007/day-1 for the high, moderate and low concentration exposure. The exact mechanism of clearance is not known currently. The fast clearance component which was concentration-dependent could be dependent on the dissolution of AgNPs and the slow clearance would be due to slow clearance of the low dissolution AgNPs secondary particles originating from silver ions reacting with biogenic anions. These secondary AgNPs might be cleared by mechanisms other than dissolution such as mucociliary escalation, translocation to the lymphatic system or other organs.

Extensive evaluation and classification of low-cost dust sensors in laboratory using a newly developed test method.

An extensive evaluation of low-cost dust sensors was performed using an exponentially decaying particle concentration. A total of 264 sensors including 27 sensors with light-emitting diodes (LEDs) and 237 sensors with laser lighting sources were tested. Those tested sensors were classified into 4 groups based on the deviation from the reference data obtained by a reference instrument. The response linearities of all the tested samples for PM1 , PM2.5 , and PM10 were in excellent agreement with the reference instrument, except a few samples. For the measurements of PM1 and PM2.5 , the lighting source, that is, LED or laser, did not show any significant difference in overall sensor performance. However, LED-based sensors did not perform well for PM10 measurements. The 32, 24, and 16% of all the tested sensors for PM1 , PM2.5 , and PM10 measurement, respectively, are in the category of Class 1 (reference instrument reading ± 20%) requirement. The performance of the low-cost dust sensors for PM10 measurement was relatively less satisfactory.

28-Day inhalation toxicity study with evaluation of lung deposition and retention of tangled multi-walled carbon nanotubes.

Lung deposition and retention measurements are now required by the newly revised OECD inhalation toxicity testing guidelines 412 and 413 when evaluating the clearance and biopersistence of poorly soluble nanomaterials, such as multi-walled carbon nanotubes (MWCNTs). However, evaluating the lung deposition concentration is challenging with certain nanomaterials, such as carbon-based and iron-based nanomaterials, as it is difficult to differentiate them from endogenous elements. Therefore, the current 28-day inhalation toxicity study investigated the lung retention kinetics of tangled MWCNTs. Male Sprague Dawley rats were exposed to MWCNTs at 0, 0.257, 1.439, and 4.253 mg/m3 for 28 days (6 h/day, 5 days/week, 4 weeks). Thereafter, the rats were sacrificed at day 1, 7, and 28 post-exposure and the pulmonary inflammatory response evaluated by analyzing the bronchoalveolar lavage fluid. Plus, the blood biochemistry, hematology, and histopathology of the lungs were also examined. The lung deposition and retention of MWCNTs were determined based on the elemental carbon content in the lungs after tissue digestion. The number of polymorphonuclear cells and LDH concentration were both found to be significantly higher with the medium and high concentrations (1.439 and 4.253 mg/m3) and dose dependent. The estimated retention half-life for the high concentration (4.253 mg/m3) was about 35 days. The results of this study indicate that tangled MWCNTs seem to have a relatively shorter retention half-life when compared to previous reports on rigid MWCNTs, and the no-observed adverse effect level (NOAEL) for the tested tangled MWCNTs was 0.257 mg/m3 in a previous rat 28-day subacute inhalation toxicity study.

Measurements of atmospheric aerosol vertical distribution above North China Plain using hexacopter.

In this study, a novel setup was developed to measure the vertical profile of particle number size distribution (PNSD) and meteorological parameters by using hexacopter equipped with a portable instrument package including a custom-built scanning mobility particle sizer, an optical particle counter and temperature and relative humidity (RH) sensors. By using this setup, a field experiment was carried out to investigate the vertical profiles of RH, temperature, PNSD ranged from 8 to 245 nm, and particle number concentration with the diameter ranges of 0.3-0.5 µm and 0.5-1.0 µm from the ground up to 300 m above ground level in a rural site of the North China Plain. New particle formation (NPF) event in a vertical scale was observed during the daytime cruises. The newly formed particles showed a heterogeneous vertical distribution, indicating the inhomogeneous occurrence of the NPF event vertically. During the daytime, the vertical variations in number concentration of particles larger than 0.3 µm was not obvious, while, showed a tendency to decrease associated with the increasing altitude in the evening. The newly-developed unmanned aerial vehicle research platform could be applied to study the vertical NPF events and transport processes of air pollutants within the atmospheric boundary layer and urban canopy, and to monitor source emissions with the purpose of environment management.

Lobar evenness of deposition/retention in rat lungs of inhaled silver nanoparticles: an approach for reducing animal use while maximizing endpoints.

BACKGROUND: Information on particle deposition, retention and clearance are important for the evaluation of the risk of inhaled nanomaterials to human health. Recent revised OECD inhalation toxicity test guidelines require to evaluate the lung burden of nanomaterials after rodent subacute and subchronic inhalation exposure (OECD 412, OECD 413). These revised test guidelines require additional post-exposure observation (PEO) periods that include lung burden measurements that can inform on lung clearance behavior and translocation. The latter being particularly relevant when the testing chemical is a solid poorly soluble nanomaterial. Therefore, in the spirit of 3 R's, we investigated whether measurement of retained lung burden of inhaled nanoparticles (NPs) in individual lung lobes is sufficient to determine retained lung burden in the total lung. If it is possible to use only one lobe, it will reduce animal use and maximize the number of endpoints evaluated. RESULTS: To achieve these goals, rats were exposed nose-only for 1 or 5 days (6 h/day) to an aerosol of 20 nm well-dispersed silver nanoparticles (AgNPs), which is the desired particle diameter resulting in maximum deposition in the pulmonary region when inhaled as singlets. After exposure, the five lung lobes were separated and silver concentration was measured using inductively coupled plasma-mass spectrophotometer (ICP-MS). The results showed that the retention of deposited silver nanoparticle in the different lung lobes did not show any statistically significant difference among lung lobes in terms of silver mass per gram lung lobe. This novel finding of evenness of retention/deposition of inhaled 20 nm NPs in rats for all five lobes in terms of mass per unit tissue weight contrasts with earlier studies reporting greater apical lobe deposition of inhaled micro-particles in rodents. The difference is most likely due to preferred and efficient deposition of inhaled NPs by diffusion vs. additional deposition by sedimentation and impaction for micron-sized particles. CONCLUSION: AgNPs following acute inhalation by rats are evenly retained in each lung lobe in terms of mass per unit lung tissue weight. Accordingly, we suggest sampling any of the rat lung lobes for lung burden analysis can be used to determine deposited or retained total lung burden after short-term inhalation of NPs and using the other lobes for collecting and analyzing bronchoalveolar lavage fluid (BALF) and for histopathological analysis. Therefore, by combining lung burden measurement, histopathological tissue preparation, and BALF assay in the same rat will reduce the number of animals used and maximize the number of endpoints measured.

Tissue distribution of gold and silver after subacute intravenous injection of co-administered gold and silver nanoparticles of similar sizes.

Gold (AuNPs, 12.8 nm) and silver nanoparticles (AgNPs, 10 nm), mixed or separate, were injected into the caudal vein of male Sprague-Dawley rats for 4 weeks. The rats were allowed to recover for further 4 weeks to examine the differences in AuNP/AgNP tissue distribution and clearance. The size distribution of injected AuNPs and AgNPs were not statistically different. The dose groups (five males per group for the administration and three males for the recovery) consisted of seven divisions, i.e., control, AgNPs (with a low dose of 10 µg/kg/day, and, a high dose of 100 µg/kg/day), AuNPs (with a low dose of 10 µg/kg/day, and, a high dose of 100 µg/kg/day), as well as mixed AgNPs/AuNPs (with a low dose of 10/10 µg/kg/day, and a high dose of 100/100 µg/kg/day). The AgNPs accumulated in a dose-dependent manner in the liver, spleen, kidneys, lung, brain, testis or blood. Au concentration increased also in a dose-dependent manner in the liver, kidneys, spleen and lungs, but not in the brain, testis and blood. Ag concentration in the tissues increased dose-dependently after 4 weeks of AgNP/AuNP mixed administration, but to a much lower extent than those observed when they were administered separately. Ag concentration in the tissues after 4 weeks of AgNP/AuNP mixed administration cleared dose-dependently after 4 weeks of recovery. Au concentration in the tissues increased dose-dependently after 4 weeks of AgNp/AuNP mixed administration, while Au concentration in the tissues did not clear as seen in Ag after 4 weeks recovery. Au concentration showed biopersistency or accumulation in the liver, kidneys, spleen and brain of the 4 weeks of recovery. In conclusion, AgNPs and AuNPs showed different toxicokinetic properties and the mixed administration of AgNPs with AuNPs resulted in mutual reduction of their tissue distribution which appeared to be due to competitive inhibition. Furthermore, this subacute intravenous injection study has suggested that these nanoparticles were distributed to the organs in particulate instead of ionic forms.

Subacute inhalation toxicity study of synthetic amorphous silica nanoparticles in Sprague-Dawley rats.

Synthetic amorphous silica nanoparticles (SiNPs) are one of the most applied nanomaterials and are widely used in a broad variety of industrial and biomedical fields. However, no recent long-term inhalation studies evaluating the toxicity of SiNPs are available and results of acute studies are limited. Thus, we conducted a subacute inhalation toxicity study of SiNPs in Sprague-Dawley rats using a nose-only inhalation system. Rats were separated into four groups and target concentrations selected in this study were as follows: control (fresh air), low- (0.407 ± 0.066 mg/m3), middle- (1.439 ± 0.177 mg/m3) and high-concentration group (5.386 ± 0.729 mg/m3), respectively. The rats were exposed to SiNPs for four consecutive weeks (6 hr/day, 5 days/week) except for control group of rats which received filtered fresh air. After 28-days of inhalation exposure to SiNPs, rats were sacrificed after recovery periods of one, seven and 28 days. Although there were minimal toxic changes such as temporary decrease of body weight after exposure, increased levels of red blood cells (RBCs) and hemoglobin (Hb) concentration, the lung histopathological findings and inflammatory markers in bronchoalveolar lavage (BAL) fluid including polymorphonuclear (PMN) leukocyte, lactate dehydrogenase (LDH), albumin and protein did not show significant changes at any recovery period. The results of this study suggest that the subacute inhalation of SiNPs had no toxic effects on the lung of rats at the concentrations and selected time points used in this study.

Testing of Nanoparticle Release from a Composite Containing Nanomaterial Using a Chamber System.

With the rapid development of nanotechnology as one of the most important technologies in the 21st century, interest in the safety of consumer products containing nanomaterials is also increasing. Evaluating the nanomaterial release from products containing nanomaterials is a crucial step in assessing the safety of these products, and has resulted in several international efforts to develop consistent and reliable technologies for standardizing the evaluation of nanomaterial release. In this study, the release of nanomaterials from products containing nanomaterials is evaluated using a chamber system that includes a condensation particle counter, optical particle counter, and sampling ports to collect filter samples for electron microscopy analysis. The proposed chamber system is tested using an abrasor and disc-type nanocomposite material specimens to determine whether the nanomaterial release is repeatable and consistent within an acceptable range. The test results indicate that the total number of particles in each test is within 20% from the average after several trials. The release trends are similar and they show very good repeatability. Therefore, the proposed chamber system can be effectively used for nanomaterial release testing of products containing nanomaterials.

Exposure monitoring of graphene nanoplatelets manufacturing workplaces.

Graphenes have emerged as a highly promising, two-dimensional engineered nanomaterial that can possibly substitute carbon nanotubes. They are being explored in numerous R&D and industrial applications in laboratories across the globe, leading to possible human and environmental exposures to them. Yet, there are no published data on graphene exposures in occupational settings and no readily available methods for their detection and quantitation exist. This study investigates for the first time the potential exposure of workers and research personnel to graphenes in two research facilities and evaluates the status of the control measures. One facility manufactures graphene using graphite exfoliation and chemical vapor deposition (CVD), while the other facility grows graphene on a copper plate using CVD, which is then transferred to a polyethylene terephthalate (PET) sheet. Graphene exposures and process emissions were investigated for three tasks - CVD growth, exfoliation, and transfer - using a multi-metric approach, which utilizes several direct reading instruments, integrated sampling, and chemical and morphological analysis. Real-time instruments included a dust monitor, condensation particle counter (CPC), nanoparticle surface area monitor, scanning mobility particle sizer, and an aethalometer. Morphologically, graphenes and other nanostructures released from the work process were investigated using a transmission electron microscope (TEM). Graphenes were quantified in airborne respirable samples as elemental carbon via thermo-optical analysis. The mass concentrations of total suspended particulate at Workplaces A and B were very low, and elemental carbon concentrations were mostly below the detection limit, indicating very low exposure to graphene or any other particles. The real-time monitoring, especially the aethalometer, showed a good response to the released black carbon, providing a signature of the graphene released during the opening of the CVD reactor at Workplace A. The TEM observation of the samples obtained from Workplaces A and B showed graphene-like structures and aggregated/agglomerated carbon structures. Taken together, the current findings on common scenarios (exfoliation, CVD growth, and transfer), while not inclusive of all graphene manufacturing processes, indicate very minimal graphene or particle exposure at facilities manufacturing graphenes with good manufacturing practices.

28-Day inhalation toxicity of graphene nanoplatelets in Sprague-Dawley rats.

Graphene, a two-dimensional engineered nanomaterial, is now being used in many applications, such as electronics, biological engineering, filtration, lightweight and strong nanocomposite materials, and energy storage. However, there is a lack of information on the potential health effects of graphene in humans based on inhalation, the primary engineered nanomaterial exposure pathway in workplaces. Thus, an inhalation toxicology study of graphene was conducted using a nose-only inhalation system for 28 days (6 h/day and 5 days/week) with male Sprague-Dawley rats that were then allowed to recover for 1-, 28-, and 90-day post-exposure period. Animals were separated into 4 groups (control, low, moderate, and high) with 15 male rats (5 rats per time point) in each group. The measured mass concentrations for the low, moderate, and high exposure groups were 0.12, 0.47, and 1.88 mg/m(3), respectively, very close to target concentrations of 0.125, 0.5, and 2 mg/m(3). Airborne graphene exposure was monitored using several real-time instrumentation over 10 nm to 20 µm for size distribution and number concentration. The total and respirable elemental carbon concentrations were also measured using filter sampling. Graphene in the air and biological media was traced using transmission electron microscopy. In addition to mortality and clinical observations, the body weights and food consumption were recorded weekly. At the end of the study, the rats were subjected to a full necropsy, blood samples were collected for blood biochemical tests, and the organ weights were measured. No dose-dependent effects were recorded for the body weights, organ weights, bronchoalveolar lavage fluid inflammatory markers, and blood biochemical parameters at 1-day post-exposure and 28-day post-exposure. The inhaled graphenes were mostly ingested by macrophages. No distinct lung pathology was observed at the 1-, 28- and 90-day post-exposure. The inhaled graphene was translocated to lung lymph nodes. The results of this 28-day graphene inhalation study suggest low toxicity and a NOAEL of no less than 1.88 mg/m(3).

Case study on risk evaluation of printed electronics using nanosilver ink.

BACKGROUND: With the ever-increasing development of nanotechnology, our society is being surrounded by possible risks related to exposure to manufactured nanomaterials. The consumer market already includes many products that contain silver nanoparticles (AgNPs), including various household products, such as yoga mats, cutting boards, running shirts, and socks. There is a growing concern over the release of AgNPs in workplaces related to the manufacture and application of nanomaterials. OBJECTIVE: This study investigated the release of AgNPs during the operation of a printed electronics printer. METHODS: Using an exposure simulation chamber, a nanoparticle collector, scanning mobility particle sizer (SMPS), condensation particle counter (CPC), dust monitor, and mixed cellulose ester (MCE) filters are all connected to measure the AgNP exposure levels when operating a printed electronics printer. RESULTS: A very small amount of AgNPs was released during the operation of the printed electronics printer, and the number of AgNPs inside the exposure simulation chamber was lower than that outside background. In addition, when evaluating the potential risks for consumers and workers using a margin of exposure (MOE) approach and target MOE of 1000, the operational results far exceeded the target MOE in this simulation study and in a previous workplace exposure study. CONCLUSION: The overall results indicate a no-risk concern level in the case of printed electronics using nanosilver ink.