Exposure to engineered nanoparticles: Model and measurements for accident situations in laboratories

Predicting accidental release of engineered nanomaterials to the environment

Challenges in distinguishing between natural and engineered nanomaterials (ENMs) and the lack of historical records on ENM accidents have hampered attempts to estimate the accidental release and associated environmental impacts of ENMs. Building on knowledge from the nuclear power industry, we provide an assessment of the likelihood of accidental release rates of ENMs within the next 10 and 30 years. We evaluate risk predictive methodology and compare the results with empirical evidence, which enables us to propose modelling approaches to estimate accidental release risk probabilities. Results from two independent modelling approaches based on either assigning 0.5% of reported accidents to ENM-releasing accidents (M1) or based on an evaluation of expert opinions (M2) correlate well and predict severe accidental release of 7% (M1) in the next 10 years and of 10% and 20% for M2 and M1, respectively, in the next 30 years. We discuss the relevance of these results in a regulatory context.

Transient and continuous effects of indoor human movement on nanoparticle concentrations in a sitting person's breathing zone

Particle concentration in a sitting person's breathing zone can be influenced by human movement around the person, and the transient and continuous effects may differ. In this study, a set of full-scale experiments was conducted to sample the nanoparticle concentration in the breathing zone of a sitting thermal breathing manikin (STBM). The transient fluctuation of the nanoparticle concentration was recorded continuously and analyzed. The results showed that when a manikin moved (at 1 m/s) past the STBM, the nanoparticle concentration in the STBM's breathing zone decreased and reached its lowest after the standing manikin had passed, decreasing 37.6 (±5.7) % compared with the peak value. The average concentration in the STBM's breathing zone during influence periods was 5.18 (±0.99) % less than that during non-influence Periods (NP). This finding reflected the fact that the transient inhalation (over several seconds) of the STBM may be reduced by manikin movement. On the other hand, the exposure of the STBM increased 2.88 (±1.24) % when there was a continuously moving manikin compared with the stable state in a 10-min observation. This finding may be explained by the fuller mix of indoor air and nanoparticles caused by manikin movement, as well as the increase of nanoparticle suspension time. The difference in the transient and continuous effects of the manikin movement on the STBM's exposure shows the importance of considering these effects separately in different scenarios.

NanoSafe III: A User Friendly Safety Management System for Nanomaterials in Laboratories and Small Facilities

Research in nanoscience continues to bring forward a steady stream of new nanomaterials and processes that are being developed and marketed. While scientific committees and expert groups deal with the harmonization of terminology and legal challenges, risk assessors in research labs continue to have to deal with the gap between regulations and rapidly developing information. The risk assessment of nanomaterial processes is currently slow and tedious because it is performed on a material-by-material basis. Safety data sheets are rarely available for (new) nanomaterials, and even when they are, they often lack nano-specific information. Exposure estimations or measurements are difficult to perform and require sophisticated and expensive equipment and personal expertise. The use of banding-based risk assessment tools for laboratory environments is an efficient way to evaluate the occupational risks associated with nanomaterials. Herein, we present an updated version of our risk assessment tool for working with nanomaterials based on a three-step control banding approach and the precautionary principle. The first step is to determine the hazard band of the nanomaterial. A decision tree allows the assignment of the material to one of three bands based on known or expected effects on human health. In the second step, the work exposure is evaluated and the processes are classified into three "nano" levels for each specific hazard band. The work exposure is estimated using a laboratory exposure model. The result of this calculation in combination with recommended occupational exposure limits (rOEL) for nanomaterials and an additional safety factor gives the final "nano" level. Finally, we update the technical, organizational, and personal protective measures to allow nanomaterial processes to be established in research environments.

Inappropriate use of ozone generators and their sales status: questionnaire survey of healthcare providers and investigation of online sales

Ozone generators have attracted attention as a result of the spread of severe acute respiratory syndrome coronavirus-2. In a questionnaire survey targeting healthcare facilities, 20 (91%) used ozone generators in patient areas, and five (23%) used them in indoor spaces occupied by people. A search for ozone generators on the Amazon Japan website revealed that 76% of products lacked information on ozone emission rate, coverage area and/or use time. These results suggest that ozone generators may be used inappropriately in hospitals and clinics, and have been sold to the general public without adequate information for assessing their safety and efficacy.

A review on in vivo and in vitro nanotoxicological studies in plants: A headlight for future targets

Owing to the unique properties and useful applications in numerous fields, nanomaterials (NMs) received a great attention. The mass production of NMs has raised major concern for the environment. Recently, some altered growth patterns in plants have been reported due to the plant-NMs interactions. However, for NMs safe applications in agriculture and medicine, a comprehensive understanding of bio-nano interactions is crucial. The main goal of this review article is to summarize the results of the toxicological studies that have shown the in vitro and in vivo interactions of NMs with plants. The toxicity mechanisms are briefly discussed in plants as the defense mechanism works to overcome the stress caused by NMs implications. Indeed, the impact of NMs on plants varies significantly with many factors including physicochemical properties of NMs, culture media, and plant species. To investigate the impacts, dose metrics is an important analysis for assaying toxicity and is discussed in the present article to broadly open up different aspects of nanotoxicological investigations. To access reliable quantification and measurement in laboratories, standardized methodologies are crucial for precise dose delivery of NMs to plants during exposure. Altogether, the information is significant to researchers to describe restrictions and future perspectives.

Evacuation characteristics of released airborne TiO2 nanomaterial particles under different ventilation rates in a confined environment

A specially designed 32 m³ airtight chamber that allows the implementation of various ventilation strategies was utilised to study the evacuation characteristics of airborne sub-micron particles generated from TiO₂ nanopowder in a potential indoor accidental release situation. Following the release using a heated line from a nebuliser system, the spatial and temporal variations in particle number concentration were recorded by three condensation particle counters (CPCs) distributed at specific locations in the chamber. A differential mobility spectrometer was co-located with one of the CPCs for the measurement of particle size distributions (PSDs). The different modal groups present within the measured PSDs were determined through a log₁₀-normal fitting program. Of the ventilation rates evaluated, the greatest relative improvement in particle concentration and clearance time occurred at the highest rate (12 air changes per hour, ACH). At the same time, indications of cross-contamination from regions with strong mixing conditions to regions where mixing was poor, were obtained showing that the latter could operate as particle traps where localised poor ventilation might occur. However, reducing the ventilation rate led to: i) an increase of leftover particles in the air of the chamber when the cleaning process had been completed, and more specifically to an increased ratio of ultrafine particles over fine ones, resulting in the potentially dangerous accumulation of contaminants with high exposure hazards, ii) a decrease in ventilation efficiency, which at low evacuation rates became independent of distance from the inlet diffuser, iii) slower clearance of resuspended particles, with the lowest efficiency at the moderate ventilation rate.

Review of measurement techniques and methods for assessing personal exposure to airborne nanomaterials in workplaces

Exposure to airborne agents needs to be assessed in the personal breathing zone by the use of personal measurement equipment. Specific measurement devices for assessing personal exposure to airborne nanomaterials have only become available in the recent years. They can be differentiated into direct-reading personal monitors and personal samplers that collect the airborne nanomaterials for subsequent analyses. This article presents a review of the available personal monitors and samplers and summarizes the available literature regarding their accuracy, comparability and field applicability. Due to the novelty of the instruments, the number of published studies is still relatively low. Where applicable, literature data is therefore complemented with published and unpublished results from the recently finished nanoIndEx project. The presented data show that the samplers and monitors are robust and ready for field use with sufficient accuracy and comparability. However, several limitations apply, e.g. regarding the particle size range of the personal monitors and their in general lower accuracy and comparability compared with their stationary counterparts. The decision whether a personal monitor or a personal sampler shall be preferred depends strongly on the question to tackle. In many cases, a combination of a personal monitor and a personal sampler may be the best choice to obtain conclusive results.

Understanding workers' exposure: Systematic review and data-analysis of emission potential for NOAA

Exposure assessment for nano-objects, and their aggregates and agglomerates (NOAA), has evolved from explorative research toward more comprehensive exposure assessment, providing data to further develop currently used conservative control banding (CB) tools for risk assessment. This study aims to provide an overview of current knowledge on emission potential of NOAA across the occupational life cycle stages by a systematic review and subsequently use the results in a data analysis. Relevant parameters that influence emission were collected from peer-reviewed literature with a focus on the four source domains (SD) in the source-receptor conceptual framework for NOAA. To make the reviewed exposure data comparable, we applied an approach to normalize for workplace circumstances and measurement location, resulting in comparable "surrogate" emission levels. Finally, descriptive statistics were performed. During the synthesis of nanoparticles (SD1), mechanical reduction and gas phase synthesis resulted in the highest emission compared to wet chemistry and chemical vapor condensation. For the handling and transfer of bulk manufactured nanomaterial powders (SD2) the emission could be differentiated for five activity classes: (1) harvesting; (2) dumping; (3); mixing; (4) cleaning of a reactor; and (5) transferring. Additionally, SD2 was subdivided by the handled amount with cleaning further subdivided by energy level. Harvesting and dumping resulted in the highest emissions. Regarding processes with liquids (SD3b), it was possible to distinguish emissions for spraying (propellant gas, (high) pressure and pump), sonication and brushing/rolling. The highest emissions observed in SD3b were for propellant gas spraying and pressure spraying. The highest emissions for the handling of nano-articles (SD4) were found to nano-sized particles (including NOAA) for grinding. This study provides a valuable overview of emission assessments performed in the workplace during the occupational handling of NOAA. Analyses were made per source domain to derive emission levels which can be used for models to quantitatively predict the exposure.

Occupational Exposure to Nano-Objects and Their Agglomerates and Aggregates Across Various Life Cycle Stages; A Broad-Scale Exposure Study

BACKGROUND

Occupational exposure to manufactured nano-objects and their agglomerates, and aggregates (NOAA) has been described in several workplace air monitoring studies. However, data pooling for general conclusions and exposure estimates are hampered by limited exposure data across the occupational life cycle of NOAA and a lack in comparability between the methods of collecting and analysing the data. By applying a consistent method of collecting and analysing the workplace exposure data, this study aimed to provide information about the occupational NOAA exposure levels across various life cycle stages of NOAA in the Netherlands which can also be used for multi-purpose use.

METHODS

Personal/near field task-based exposure data was collected using a multi-source exposure assessment method collecting real time particle number concentration, particle size distribution (PSD), filter-based samples for morphological, and elemental analysis and detailed contextual information. A decision logic was followed allowing a consistent and objective way of analysing the exposure data.

RESULTS

In total, 46 measurement surveys were conducted at 15 companies covering 18 different exposure situations across various occupational life cycle stages of NOAA. Highest activity-effect levels were found during replacement of big bags (<1000-76000 # cm(-3)), mixing/dumping of powders manually (<1000-52000 # cm(-3)) and mechanically (<1000-100000 # cm(-3)), and spraying of liquid (2000-800000 # cm(-3)) showing a high variability between and within the various exposure situations. In general, a limited change in PSD was found during the activity compared to the background.

CONCLUSIONS

This broad-scale exposure study gives a comprehensive overview of the NOAA exposure situations in the Netherlands and an indication of the levels of occupational exposure to NOAA across various life cycle of NOAA. The collected workplace exposure data and contextual information will serve as basis for future pooling of data and modelling of worker exposure.

A laboratory study of the performance of the handheld diffusion size classifier (DiSCmini) for various aerosols in the 15-400 nm range

In addition to chemical composition, particle concentration and size are among the main parameters used to characterize exposure to airborne ultrafine or nanoparticles. To assess occupational inhalation exposure, real-time instruments are recommended in recent strategies published. Among portable devices for personal exposure assessment in the workplace, DiSCmini (Matter Aerosol AG, Switzerland) has been identified as a potential candidate with its capacity to measure the airborne nanoparticle concentration and average particle size with good time-resolution. Monodisperse and polydisperse test nanoaerosols of varying compositions and morphologies were produced in the laboratory using the CAIMAN facility. These aerosols covered a range of particle sizes between 15 and 400 nm and number concentrations from 700 to 840,000 cm(-3). The aerosols were used to investigate the behavior of DiSCmini, comparing experimental data to reference data. In spite of a slight tendency to underestimate particle size, all particle diameters, number concentrations and surface area concentrations measured were in the same order of magnitude as reference data. Furthermore, no significant effect due to particle composition or morphology was noted.

Effect of particle agglomeration in nanotoxicology

The emission of engineered nanoparticles (ENPs) into the environment in increasing quantity and variety raises a general concern regarding potential effects on human health. Compared with soluble substances, ENPs exhibit additional dimensions of complexity, that is, they exist not only in various sizes, shapes and chemical compositions but also in different degrees of agglomeration. The effect of the latter is the topic of this review in which we explore and discuss the role of agglomeration on toxicity, including the fate of nanomaterials after their release and the biological effects they may induce. In-depth investigations of the effect of ENP agglomeration on human health are still rare, but it may be stated that outside the body ENP agglomeration greatly reduces human exposure. After uptake, agglomeration of ENPs reduces translocation across primary barriers such as lungs, skin or the gastrointestinal tract, preventing exposure of "secondary" organs. In analogy, also cellular ENP uptake and intracellular distribution are affected by agglomeration. However, agglomeration may represent a risk factor if it occurs after translocation across the primary barriers, and ENPs are able to accumulate within the tissue and thus reduce clearance efficiency.

Exposure Assessment of a High-energy Tensile Test With Large Carbon Fiber Reinforced Polymer Cables

This study investigated the particle and fiber release from two carbon fiber reinforced polymer cables that underwent high-energy tensile tests until rupture. The failing event was the source of a large amount of dust whereof a part was suspected to be containing possibly respirable fibers that could cause adverse health effects. The released fibers were suspected to migrate through small openings to the experiment control room and also to an adjacent machine hall where workers were active. To investigate the fiber release and exposure risk of the affected workers, the generated particles were measured with aerosol devices to obtain the particle size and particle concentrations. Furthermore, particles were collected on filter samples to investigate the particle shape and the fiber concentration. Three situations were monitored for the control room and the machine hall: the background concentrations, the impact of the cable failure, and the venting of the exposed rooms afterward. The results showed four important findings: The cable failure caused the release of respirable fibers with diameters below 3 μm and an average length of 13.9 μm; the released particles did migrate to the control room and to the machine hall; the measured peak fiber concentration of 0.76 fibers/cm(3) and the overall fiber concentration of 0.07 fibers/cm(3) in the control room were below the Permissible Exposure Limit (PEL) for fibers without indication of carcinogenicity; and the venting of the rooms was fast and effective. Even though respirable fibers were released, the low fiber concentration and effective venting indicated that the suspected health risks from the experiment on the affected workers was low. However, the effect of long-term exposure is not known therefore additional control measures are recommended.

Development of a self-cleaning dispersion and exposure chamber: application to the monitoring of simulated accidents involving the generation of airborne nanoparticles

The release of hazardous nanoparticulate matter in accidental situations was simulated in a specially designed 13-m(3) stainless steel airtight chamber, which allowed the dispersion analysis of airborne matter in a practically particle-free environment (less than 2 #/cm(3)) and in presence of background atmospheric aerosols. A fast recovering of the initial situation was achieved by means of a tandem HEPA-filtered air and deionized water system. Both unintended spilling of silica-based nanoparticulate powders and continuous emission of 100-nm SiO2 nanoparticles were used as aerosol generation events. The emission of airborne nanoparticles was analyzed in terms of particle number concentrations (PNC), size distributions and source strengths. The emission of nanoparticulate aerosols reached peak PNC for particles in the range from 5 nm to 1 μm with source strengths about 10(8) #/h in a background-filled environment and 10(10) #/h in a practically particle-free atmosphere. No agglomeration was noticed for the released nanoparticles, suggesting that PNC was low enough to prevent coagulation and that particle diameters were over 80 nm. Results indicate that emitted matter was within the range of the most penetrating particle sizes and with source strengths similar to accidental scenarios.

Unintended emission of nanoparticle aerosols during common laboratory handling operations

Common laboratory operations such as pouring, mashing in an agate mortar, transferring with a spatula, have been assessed as potential sources for emission of engineered nanoparticles in simulated occupational environments. Also, the accidental spilling from an elevated location has been considered. For workplace operations, masses of 1500 or 500mg of three dry-state engineered nanoparticles (SiO2, TiO2 and Ce-TiO2) with all dimensions under 30nm, and one fibrous nanomaterial (MWCNT) with diameter under 10nm and length about 1.5μm were used. The measured number emission factors (NEF) for every operation and material in this work were in the range of 10(5) #s(-1). The traceability of emitted nanoparticles has been improved using Ce-doping on TiO2 nanoparticles. With this traceable material it was possible to show that generated aerosol nanoparticles are rapidly associated with background particles to form large-sized aerosol agglomerates.

From nanoobject release of (Bio)nanomaterials to exposure

An increasing variety of different nanostructured materials including bionanomaterials are used. During synthesis, but also during use of nanostructured materials along their life-cycle, nanostructured materials and engineered nano-objects (ENO) – may be released into the environment. They will follow different exposure pathways and create an exposure concentration at the point of different biological systems, especially human beings. The inhalation pathway is of greatest importance with regard to health issues. The exposure concentration together with the breathing conditions integrated over time leads to the dose of the deposited material, which is of greatest interest for different effect studies. We discuss in this paper the kind of nanostructured material released from bionanomaterials into the environment. A large part of existing exposure studies in the literature is critically considered. A strategy is proposed to investigate in a more effective way the ENO-release from nanostructured materials as the first step of the exposure pathway. The release – exposure relationship as well as exposure – dose relationship for the case of inhalation is described leading to the possibility of tracing and ideally a complete balancing from ENO-release to dose. In the end the still needed activities for ENO-control methods in the environment are summarized.

Comparison of the DiSCmini aerosol monitor to a handheld condensation particle counter and a scanning mobility particle sizer for submicrometer sodium chloride and metal aerosols

We evaluated the robust, lightweight DiSCmini (DM) aerosol monitor for its ability to measure the concentration and mean diameter of submicrometer aerosols. Tests were conducted with monodispersed and polydispersed aerosols composed of two particle types (sodium chloride [NaCl] and spark-generated metal particles, which simulate particles found in welding fume) at three different steady-state concentration ranges (Low, <10(3); Medium, 10(3)-10(4); and High, >10(4) particles/cm(3)). Particle number concentration, lung deposited surface area (LDSA) concentration, and mean size measured with the DM were compared with those measured with reference instruments, a scanning mobility particle sizer (SMPS), and a handheld condensation particle counter (CPC). Particle number concentrations measured with the DM were within 16% of those measured by the CPC for polydispersed aerosols. Poorer agreement was observed for monodispersed aerosols (±35% for most tests and +101% for 300-nm NaCl). LDSA concentrations measured by the DM were 96% to 155% of those estimated with the SMPS. The geometric mean diameters measured with the DM were within 30% of those measured with the SMPS for monodispersed aerosols and within 25% for polydispersed aerosols (except for the case when the aerosol contained a substantial number of particles larger than 300 nm). The accuracy of the DM is reasonable for particles smaller than 300 nm, but caution should be exercised when particles larger than 300 nm are present. [Supplementary materials are available for this article. Go to the publisher's online edition of the Journal of Occupational and Environmental Hygiene for the following free supplemental resources: manufacturer-reported capabilities of instruments used, and information from the SMPS measurements for polydispersed test particles.].

Co-release of hexabromocyclododecane (HBCD) and Nano- and microparticles from thermal cutting of polystyrene foams

Polystyrene foam is a very important insulation material, and hexabromocyclododecane (HBCD) is frequently used as its flame retardant. HBCD is persistent, bioaccumulative, and toxic, and therefore workplace exposure and environmental emission should be avoided. In this study, we investigated the co-release of HBCD and aerosol particles during the thermal cutting of expanded polystyrene foam (EPS) and extruded polystyrene foam (XPS). The generated particles were simultaneously measured by a fast mobility particle sizer (FMPS) and collected by a cascade impactor (NanoMoudi). In the breathing zone of a cutting worker, the number concentration of aerosol particles was above 1 × 10(12) particles m(-3), and the air concentration of HBCD was more than 50 μg m(-3). Most of the released HBCD was partitioned into particles with an aerodynamic diameter at the nanometer scale. The average concentrations of HBCD in these submicrometer particles generated from the thermal cutting of EPS and XPS were 13 times and 15 times higher than the concentrations in raw foams, respectively. An occupational exposure assessment indicated that more than 60% of HBCD and 70% of particles deposited in the lung of cutting worker would be allocated to the alveolar region. The potential subchronic (or chronic) toxicity jointly caused by the particles and HBCD calls for future studies.