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BACKGROUND: Quantifying the dose and distribution of tobacco smoke in the respiratory system is critical for understanding its toxicity, addiction potential, and health impacts. Epidemiologic studies indicate that the incidence of lung tumors varies across different lung regions, suggesting there may be a heterogeneous deposition of smoke particles leading to greater health risks in specific regions. Despite this, few studies have examined the lobar spatial distribution of inhaled particles from tobacco smoke. This gap in knowledge, coupled with the growing popularity of little cigars among youth, underscores the need for additional research with little cigars. RESULTS: In our study, we analyzed the lobar deposition in rat lungs of smoke particles from combusted regular and mentholated Swisher Sweets little cigars. Twelve-week-old male and female Sprague-Dawley rats were exposed to smoke particles at a concentration of 84 ± 5 mg/m3 for 2 h, after which individual lung lobes were examined. We utilized Inductively Coupled Plasma Mass Spectrometry to quantify lobar chromium concentrations, serving as a smoke particle tracer. Our findings demonstrated an overall higher particle deposition from regular little cigars than from the mentholated ones. Higher particle deposition fraction was observed in the left and caudal lobes than other lobes. We also observed sex-based differences in the normalized deposition fractions among lobes. Animal study results were compared with the multi-path particle dosimetry (MPPD) model predictions, which showed that the model overestimated particle deposition in certain lung regions. CONCLUSIONS: Our findings revealed that the particle deposition varied between different little cigar products. The results demonstrated a heterogenous deposition pattern, with higher particle deposition observed in the left and caudal lobes, especially with the mentholated little cigars. Additionally, we identified disparities between our measurements and the MPPD model. This discrepancy highlights the need to enhance the accuracy of models before extrapolating animal study results to human lung deposition. Overall, our study provides valuable insights for estimating the dose of little cigars during smoking for toxicity research.

The particle number concentration (PNC), particulate matter (PM1) and black carbon (BC) mass concentration limits are not available from standard air quality monitoring networks as well as for indoor level standards in many countries. Total personal exposure is often disproportionately affected by the relatively short amount of time spent in office spaces and commuting trips. In this study, real-time measurements of PNC, PM1, and BC mass concentrations in the office and during commuting trips were performed to assess real-time employee personal exposure. Urban environments are very complex due to the different emission sources and their emission activities; therefore, a combination of mobile and stationary measurements allows for a better understanding of their dynamics and employee exposure, constituting a better predictor of health effects. Mobile measurements at the street level showed that the BC mass concentrations were the highest during peak hours, reaching up to 7.14 µg/m3 at hotspots. The hourly mean BC mass concentration in March 2022 at the urban background station ranged from 0.30 to 9.01 µg/m3, with traffic-related BC (BCtr) accounting for 66% of the total BC mass concentration. The highest minute deposition dose of BC (MDDBC) occurred during the morning rush hour at 53 ng/min and in the evening at 26 ng/min. These findings reveal the impact of traffic exhaust emissions on aerosol particles, particularly on fine particles. Marked differences were found between the MDDBC in the office and the vehicle micro-environment. The deposition dose in the office micro-environment was 11 ng/min. The results from the multi-path particle dosimetry model indicate that almost half of the inhaled BC mass 39.2% was deposited in the lowest part of the respiratory system, the lung-pulmonary region. [ABSTRACT FROM AUTHOR]

This study correlates computational predictions with in vivo and in vitro experimental results of inhaled fine and ultrafine particulate matter (PM) transport, dissemination, and deposition in the human respiratory airways. Epidemiological studies suggest that workplace exposure to anthropogenic pollutant PMs is a risk factor for increased susceptibility to acute bronchopulmonary illnesses. However, investigations on detailed human inhalation and PM transport processes are restrictive from time, cost, and ethical perspectives. Computational simulation based on the Multiple Path Particle Dosimetry (MPPD) model was employed to quantify the risks associated with workplace exposure of these PMs. Here, the physical, mechanical, and electrical properties of PMs of carbon black (CB) and ultrafine particles (UFPs) from wire-cut electrical discharge machining (WEDM), with mass median aerodynamic diameter (CMAD) in the range of 1 nm to 1000 nm, were used as input parameters of MPPD. Additionally, it mimicked occupational workers’ age, body mass index, and oronasal-combinational nose and mouth breathing exposure time. The deposition results were compared with several vivo and in vitro experimental data reported in the literature, and satisfactory agreements were found. For example, a total lung dose of CB-PMs of 100 nm is the highest (28%), while a 380 nm dose is the lowest (15%). Afterward, deposition increases with particle size, reaching 26% for 1000 nm. In the case of WEDM-UFPs, about 98% of all 1.0 nm inhaled particles remain in the lung. Subsequently, the deposition dose decreases with the particle size and reaches up to 28% for 100 nm particles. Approximately 51% of deposited WEDM-UFPs are of CMAD ≤ 5 nm. The images of lung geometry also observed the maximum deposited mass and mass flux rate in the head, tracheobronchial, and pulmonary airways. [ABSTRACT FROM AUTHOR]

Abstract Background Quantifying the dose and distribution of tobacco smoke in the respiratory system is critical for understanding its toxicity, addiction potential, and health impacts. Epidemiologic studies indicate that the incidence of lung tumors varies across different lung regions, suggesting there may be a heterogeneous deposition of smoke particles leading to greater health risks in specific regions. Despite this, few studies have examined the lobar spatial distribution of inhaled particles from tobacco smoke. This gap in knowledge, coupled with the growing popularity of little cigars among youth, underscores the need for additional research with little cigars. Results In our study, we analyzed the lobar deposition in rat lungs of smoke particles from combusted regular and mentholated Swisher Sweets little cigars. Twelve-week-old male and female Sprague-Dawley rats were exposed to smoke particles at a concentration of 84 ± 5 mg/m3 for 2 h, after which individual lung lobes were examined. We utilized Inductively Coupled Plasma Mass Spectrometry to quantify lobar chromium concentrations, serving as a smoke particle tracer. Our findings demonstrated an overall higher particle deposition from regular little cigars than from the mentholated ones. Higher particle deposition fraction was observed in the left and caudal lobes than other lobes. We also observed sex-based differences in the normalized deposition fractions among lobes. Animal study results were compared with the multi-path particle dosimetry (MPPD) model predictions, which showed that the model overestimated particle deposition in certain lung regions. Conclusions Our findings revealed that the particle deposition varied between different little cigar products. The results demonstrated a heterogenous deposition pattern, with higher particle deposition observed in the left and caudal lobes, especially with the mentholated little cigars. Additionally, we identified disparities between our measurements and the MPPD model. This discrepancy highlights the need to enhance the accuracy of models before extrapolating animal study results to human lung deposition. Overall, our study provides valuable insights for estimating the dose of little cigars during smoking for toxicity research.

Household air pollution has been identified as a global threat in recent decades. The partial combustion of solid fuel is a leading reason for indoor pollution in middle- and low-income countries and has been estimated to cause around 3.5 million death per year globally. Women become the most vulnerable to these household air pollution due to their exceptional physical possessions and higher exposure duration. The current study aims to identify the possible exposure conditions of indoor air pollution in women. The study starts with a questionnaire survey to assess the health-related issues distinguishing women further leading to the sampling of air pollutants in the kitchen area of different homes (n=10) bifurcated on the basis of the nature of the family. Further, the concentration obtained was utilized for health risk assessment using ICRP and MPPD modelling techniques. The concentration trend observed shows a higher concentration of particulate matter in joint family kitchens. According to MPPD modelling the highest deposition as determined was for PM2.5 and the fraction distributed was 55.9% in the head region, 6.7% in the tracheobronchial region and 37.2% in the pulmonary region. The lowest deposition was obtained for PM0.5 with the highest deposition fraction obtained for the pulmonary region (61.1%) followed by the head region(21.45%) and the tracheobronchial region (17.3%). Precisely, the present study gives a clear picture about lung deposition of particulate matter present in an indoor setting specifically in women. Also, it throws light upon different sources and scenarios regarding indoor air pollution prevailing among the population.

Scientific research confirms the harmful effects of airborne cyanobacteria and microalgae. However, determining human exposure to these microorganisms remains a challenge. The six-stage Tisch impactor was used to collect bioaerosols from April to September 2020 in the coastal zone of the southern Baltic. The MPPD model was used for estimation of regional, lobar, and generation deposition of microorganisms in human respiratory tract. The mass deposition fraction of cyanobacteria and microalgae in the head region gradually increased with the aerosol size. The maximum deposition fractions in the trachea, bronchial, and the pulmonary region were found for particles between 2.1 and 3.3 μm. The contribution of cyanobacteria and microalgae was the highest in the head region. The majority of microorganisms found in pulmonary region dominated in particles smaller than 2.1 μm. Exposure to the ambient bioaerosols may have an adverse impact on the human health in the region of southern Baltic Sea. [Display omitted] • Bioaerosol deposition pattern in human airways was studied in Baltic coastal zone. • Multiple Path Particle Dosimetry Model was used. • In pulmonary regions majority of microorganisms was in aerosols <2.1 μm in diameter. • In acinar and peripheral airways highest mass deposition of smallest particles • Highest deposition of bioaerosols in the right lower lobe of the lungs was found. [ABSTRACT FROM AUTHOR]

To examine the trends of particulate matter with aerodynamic diameter ≤2.5 µm (PM2.5) and its elemental constituents during two distinct seasons at a site away from the city center of Delhi and the National Capital Region (Delhi-NCR) of India, this unique study aimed at the development of source-receptor-effect linkages. This research paper presents results of occurrence, long-range transport (LRT), source apportionment, and human health impact assessment of 24 PM2.5-bound trace elements (Al, Ba, Bi, Ca, Cd, Co, Cr, Cu, Fe, Ga, K, Li, Mg, Mn, Na, Ni, Pb, S, Se, Si, Te, Tl, Zn, and Zr). The concentration of PM2.5 during winter (296 ± 45 μg/m3) was significantly higher than in summer (114 ± 48 μg/m3) and exceeded 24 h Indian standard on most of the measurement days. The seasonal concentration ratios (winter/summer) of individual elements varied from 1.7 (Si) to 5.9 (Tl). The backward trajectory of air masses showed that transboundary transport of pollutants occurred in the downwind direction during winter, indicating that this remote site was affected by transported particulates and local activities. The principal component analysis–absolute principal component score (PCA-APCS) model confirmed five significant sources, vehicles (22.3%), soil/road dust (23.1%), coal combustion (20.9%), open burning (13.8%), and other industries (10.2%) responsible for particulate emission. The results from the multiple path particle dosimetry model (MPPD) showed higher deposition of particulates in the human respiratory system occurred during winter (44%) than in summer (40%). The elements with crustal sources of origin had a higher deposition fraction in the head region (0.27 for Si) compared to elements of anthropogenic sources (0.13 for Li). The excess lifetime carcinogenic risk (ELCR) under winter episodic events increased significantly at 128 × 10−6 compared to the summer non-episodic period at 41 × 10−6.

Ultrafine particles (UFPs) usually explosive growth during new particle formation (NPF) events. However, the risk of exposure to UFPs on NPF days has been ignored due to the prevalence of mass-based air quality standards. In this study, the daily deposited doses, i.e., the daily deposited particle number dose (DPNd), mass dose (DPMd), and surface area dose (DPSd), of ambient particles in the human respiratory tract in Beijing were evaluated based on the particle number size distribution (3 nm-10 µm) from June 2018 to May 2019 utilizing a Multiple-Path Particle Dosimetry Model (MPPD) after the hygroscopic growth of particles in the respiratory tract had been accounted for. Our observations showed a high frequency (72.6%) of NPF on excellent air quality days, with daily mean PM2.5 concentrations less than 35 μg m−3. The daily DPNd on excellent air quality days was comparable with that on polluted days, although the DPMd on excellent air quality days was as low as 15.6% of that on polluted days. The DPNd on NPF days was ~1.3 times that on non-NPF days. The DPNd in respiratory tract regions decreased in the order: tracheobronchial (TB) > pulmonary (PUL) > extrathoracic (ET) on NPF days, while it was PUL > TB > ET on non-NPF days. The number of deposited nucleation mode particles, which were deposited mainly in the TB region (45%), was 2 times higher on NPF days than that on non-NPF days. Our results demonstrated that the deposition potential due to UFPs in terms of particle number concentrations is high in Beijing regardless of the aerosol mass concentration. More toxicological studies related to UFPs on NPF days, especially those targeting tracheobronchial and pulmonary impairment, are required in the future.

During the synthesis of engineered nanomaterials (ENMs), various occupational exposures occur, leading to health consequences. To date, there is paucity of studies focused on modeling the deposition of nanoparticles emitted from ENMs synthesis processes. This study aimed to characterise and assess exposure to gold (AuNPs) and silver nanoparticles (AgNPs) during a synthesis process in a research laboratory in South Africa. AuNPs and AgNPs synthesis processes were monitored for an hour in a laboratory using a Scanning Mobility Particle Sizer. The monitoring was conducted at a height of 1.2–1.5 m (m) and 1.5 m away from the hood, assuming a 30 cm (cm) breathing circumference zone. Each synthesis process was monitored thrice to generate reliable point estimates, which were used to assess exposure over 8 hours. A time-weighted average concentration was calculated and compared to the derived 8-h occupational exposure limit (OEL) for AgNPs (0.19 μg/m3) and the proposed provisional nano reference value for AuNPs (20,000 particles/cm3). The Multiple-Path Particle Dosimetry model was used to calculate the deposition and retention of both AuNPs and AgNPs. NPs emitted during the synthesis process were dominant in the nuclei (79% for AuNPs and 54% for AgNPs), followed by the Aitken (12% for AuNPs and 29% for AgNPs), with fewer particles in the accumulation mode (9.2% for AuNPs and 17% for AgNPs). AuNPs and AgNPs generated during the synthesis process were determined at 1617.3 ± 102 cm3 (0.046 μg/m3) and 2,687 cm3 ± 620 (0.077 μg/m3), respectively. For the three exposure scenarios, none exceeded the occupational exposure limit for both AuNPs (provisional) and AgNPs (OEL). Workers in the synthesis laboratory are exposed to a concentration below the recommended occupational exposure limit for silver and the proposed provisional nano reference value for gold. Although, the concentrations to which laboratory workers are exposed to are below safe levels, the assessment of the lung deposition patterns indicate a high particle lung retention which raise concerns about long term safety of workers.

As a part of their occupation, workers at toll stations are exposed to traffic emissions during the working shift, which sometimes stretches to 12 h. To assess the exposure and subsequent health risk of these workers, a study was performed on a highway toll station in India. PM 1 , PM 2.5 , PM 10 , BC and UFP concentration were determined inside a toll collectors' cabin and outside in a free-flowing traffic section (125 m from the toll cabin). The concentrations varied in the following range: PM 1 (40.69–226.13 μg m−3), PM 2.5 (49.71–247.36 μg m−3), PM 10 (83.15–458.14 μg m−3) and BC (2.1–87.5 μg m−3) and UFP: 101–53705 pt cm−3. The mean concentration inside the cabin was 1.34 (PM 1), 1.35 (PM 2.5), 1.16 (PM 10) and 2.91 (BC) times the concentration outside for the summer season. The corresponding levels in the winter season were 1.14 (PM 1), 1.11 (PM 2.5), 1.11 (PM 10), 2.50 (BC) and 1.82 (UFP). In addition to the exhaust emission, the non-exhaust emissions such as resuspension of crustal particles, fly ash and bioaerosols were identified. Using the Multiple Path Particle Dosimetry model for two groups - adults (18–21 years) and adults (21+ years), it was estimated that the pulmonary deposition of in-cabin workers were 50% (PM 2.5) −75% (PM 1) higher than the workers outside the cabin. Particle mass deposition was found to be higher for adults (21+ years) than adults (18–21 years) for both the seasons. The study quantitatively assessed the health risk faced by the workers in terms of exposure concentration and deposition in respiratory tract. More such studies at different traffic mix and climate can provide better estimates of health risk of toll workers that can be used to devise appropriate strategies for control of it. [Display omitted] • Concentrations of PM, BC and UFP were measured at a highway toll plaza. • Measurements were carried out inside the toll cabin and outside at a free section. • Besides exhaust emission, resuspended PM, fly ash and bioaerosols were identified. • In-cabin workers are exposed to 50–75% higher pulmonary deposition. • Toll plazas can be removed on highways by using satellite-based toll collection. [ABSTRACT FROM AUTHOR]

Abstract Particulate matter (PM) is crucial among six criteria air pollutants, and it is frequently associated with human morbidity and mortality. According to the aerodynamic diameter, PM is classified as coarse (PM 10) and fine (PM 2.5). PM with these smaller sizes can easily enter and get deposited in the human airways. This deposited PM fraction commences the development of respiratory diseases such as asthma, chronic obstructive pulmonary disease, and even cancer. Thus, the quantification of PM deposition and its clearance in the human airway are essential for evaluating health risks. This study aims to investigate the size-segregated PM (PM 10 , PM 2.5, and PM 1) deposition in human lungs. Size-segregated PM is collected using the Grimm portable environmental dust monitor during winter season near an arterial road located in Chennai city of Tamil Nadu state, India. Multiple-Path Particle Dosimetry (MPPD) Model version 3.04 is utilized for quantifying PM deposition. In MPPD, airway structures of infants (3 and 28 months), children (3, 8, 9 and 14 years) and adults (18 and 21 years) are considered for the study. The values of PM concentration, body orientation, breathing scenario, tidal volume, pause fraction, inspiration fraction, and breathing frequency are specified in the MPPD for quantifying PM depositions. Results showed that 8-year children and 28 months infant groups are recorded with maximum and minimum size-segregated PM deposition respectively. The coarse particles (PM 10) are primarily deposited in the head (55–95%) and tracheobronchial (3–44%) regions whereas fine particles (PM 2.5 and PM 1) depositions are observed maximum in the head (36–63%) and pulmonary (28.2–52.7%) regions. Except for the adult age group, PM 2.5 has the maximum deposition percentage in tracheobronchial and pulmonary regions. In the case of lobar depositions, lower lobes receive maximum deposition (66.4%) than the upper (27.2%) and middle lobes (6.4%). PM 2.5 dominated the deposition in all five lobes of infant, children, and adults. The clearance rate of deposited PM is high in the tracheobronchial region whereas it is low in the pulmonary region. This study also concludes that PM 2.5 is the important size fraction in lung deposition. Further, the study results can be used for human health risk assessments such as oxidative potential and toxicity of deposited PM. Highlights • Total, regional and lobar depositions of PM in eight human airways are quantified. • Maximum PM deposition is observed in children airways (8 and 9 years old). • PM 10 highly deposited in Head and TB regions. • PM 2.5 and PM 1 have the maximum deposition in the alveolar region. • PM 2.5 mass deposition in first 16 generations increases with age. [ABSTRACT FROM AUTHOR]

Morphology and chemical composition altogether determine the fate of atmospheric particulate matter(PM) deposition and inhalation. Site-wise(#20 sites) and cumulative variations in morphology and chemical composition of PM 5 in Delhi showed dominance of non-spherical (sharp-edged, angular and flattened) particles followed by spherical ones, rich in elements like C, O, S, N, Al, Si, Cu, Ca, Na, Cl, Fe, Ni, Cr, Zn, Hg, Pb, Mo, etc. having potential health effects. #2650 individual particles analyzed for the morphological parameters like aspect ratio(AR), circularity factor(CIR), surface equivalent radius(SER) and area. Dominant AR and SER values found between ≥1–1.60 and > 0–0.50 μm, respectively showing dominance of non-spherical and fine-size particles in Delhi. The Multiple Path Particle Dosimetry (MPPD) Model used to study variations in deposition potential (regional deposition, lobar deposition, mass deposition and mass flux) of different PM sizes (PM 0.4 , PM 1 , PM 2.5 and PM 5) at different AR values which suggested that AR is an important input parameter of health models to get realistic and unbiased output health data. In addition, study revealed higher coarse particles deposition in the head region affecting upper respiratory tract with their non-spherical shapes whereas higher fine particles deposition in TB and pulmonary regions affecting inner parts of the lungs. [Display omitted] • Morphology and chemical composition of individual and bulk PM 5 particles analyzed on #20 sites in Delhi. • AR, CIR, SER and area of #2650 individual particles showed dominance of non-spherical and fine size particles in Delhi. • Deposition potential of ultrafine, fine and coarse particles studied using MPPD Model. • Effect of aspect ratio input on MPPD model output studied. [ABSTRACT FROM AUTHOR]

Dosimetric models are essential tools to refine inhalation risk assessments based on local respiratory effects. Dosimetric adjustments to account for differences in aerosol particle size and respiratory tract deposition and/or clearance among rodents, workers, and the general public can be applied to experimentally- and epidemiologically-determined points of departure (PODs) to calculate size-selected (e.g., PM 10 , inhalable aerosol fraction, respirable aerosol fraction) equivalent concentrations (e.g., HEC or human equivalent concentration; REC or rodent equivalent concentration). A modified POD (e.g., HEC) can then feed into existing frameworks for the derivation of occupational or ambient air concentration limits or reference concentrations. HECs that are expressed in terms of aerosol particle sizes experienced by humans but are derived from animal studies allow proper comparison of exposure levels and associated health effects in animals and humans. This can inform differences in responsiveness between animals and humans, based on the same deposited or retained doses and can also allow the use of both data sources in an integrated weight of evidence approach for hazard and risk assessment purposes. Whenever possible, default values should be replaced by substance-specific and target population-specific parameters. Assumptions and sources of uncertainty need to be clearly reported. [ABSTRACT FROM AUTHOR]

This study aims to simulate depositions of size-segregated particles in human airway in Beijing, China during seasons when fine particulate matter concentrations are high (December 2011 and April 2012). Particle size distributions (5.6–560 nm, electrical mobility diameter) near a major road in Beijing were measured by the TSI Fast Mobility Particle Sizer (FMPS). The information of size distributions provided by FMPS was applied in the Multiple-Path Particle Dosimetry model (MPPD) to quantify number and mass depositions of particles in human airway including extrathoracic (ET), tracheobronchial (TB), and pulmonary (PUL) regions of exposed Chinese in Beijing. Our results show that under ambient conditions, particle number concentration (NC) deposition in PUL is the highest in the three major regions of human airway. The total particle NC deposition in human airway in winter is higher than that in spring, especially for ultrafine particles (1.8 times higher) while particle mass concentration (MC) deposition is higher in spring. Although particle MC in clean days are much lower than that in heavily polluted days, total particle NC deposition in human airway in clean days is comparable to that in heavily polluted days. NC deposition for nucleation mode particles (10–20 nm, aerodynamic diameter) in clean days is higher than that in heavily polluted days. MC deposition for accumulation mode particles (100–641 nm, aerodynamic diameter) in heavily polluted days is much higher than that in clean days, while that of nucleation mode is negligible. The temporal variation shows that the arithmetic mean and the median values of particle NC and MC depositions in the evening are both the highest, followed by morning and noon, and it is most likely due to increased contribution from traffic emissions. [ABSTRACT FROM AUTHOR]

Ultrafine particles (UFPs) usually explosive growth during new particle formation (NPF) events. However, the risk of exposure to UFPs on NPF days has been ignored due to the prevalence of mass-based air quality standards. In this study, the daily deposited doses, i.e., the daily deposited particle number dose (D PNd), mass dose (D PMd), and surface area dose (D PSd), of ambient particles in the human respiratory tract in Beijing were evaluated based on the particle number size distribution (3 nm-10 µm) from June 2018 to May 2019 utilizing a Multiple-Path Particle Dosimetry Model (MPPD) after the hygroscopic growth of particles in the respiratory tract had been accounted for. Our observations showed a high frequency (72.6%) of NPF on excellent air quality days, with daily mean PM 2.5 concentrations less than 35 μg m−3. The daily D PNd on excellent air quality days was comparable with that on polluted days, although the D PMd on excellent air quality days was as low as 15.6% of that on polluted days. The D PNd on NPF days was ~1.3 times that on non-NPF days. The D PNd in respiratory tract regions decreased in the order: tracheobronchial (TB) > pulmonary (PUL) > extrathoracic (ET) on NPF days, while it was PUL > TB > ET on non-NPF days. The number of deposited nucleation mode particles, which were deposited mainly in the TB region (45%), was 2 times higher on NPF days than that on non-NPF days. Our results demonstrated that the deposition potential due to UFPs in terms of particle number concentrations is high in Beijing regardless of the aerosol mass concentration. More toxicological studies related to UFPs on NPF days, especially those targeting tracheobronchial and pulmonary impairment, are required in the future. [Display omitted] • Deposited number dose on excellent days are comparable with that on polluted days. • New particle formation (NPF) leads to high deposited number dose on excellent days. • Deposited nucleation mode particles are doubled from non-NPF days to NPF days. • Tracheobronchial region is the most readily affected part by new particle formation. [ABSTRACT FROM AUTHOR]

Abstract: Inhalation animal studies usually employ homogeneous aerosols of small particle diameter. By contrast, workers are usually exposed to coarser and more heterogeneous aerosols. The particle size distribution of an aerosol will determine the deposited fraction of inhaled particles in the various regions of the respiratory tract in rodents and humans. The deposited, and subsequently retained, doses in these regions correlate closely with long-term toxic effects. Yet, differences in deposited doses between animals and humans due to particle size differences of aerosols have not been consistently taken into account in risk assessment. This paper describes an approach to calculate equivalent human concentrations (EHC) for respiratory tract effects after inhalation using workplace particle size information. Worker’s exposure to the EHC results in the same deposited dose in the respiratory tract as achieved in animals exposed to the experimental particle size distribution. Example data for nickel compounds demonstrate that exposure levels used in the rat studies are equivalent to 4–11-fold higher levels of human workplace exposures. This approach is equally applicable to other metal/inorganic particulates that exert adverse effects on the respiratory tract after inhalation. Dosimetric extrapolation should be a first step in the derivation of limit values based on animal local respiratory effects. [Copyright &y& Elsevier]

This paper, one of several in a special issue of the Journal of Aerosol Science on "Inhaled Aerosol Dosimetry", covers selected methods for defining the respiratory tract anatomy required as input to inhaled aerosol deposition models, along with some applications and challenges. "Anatomy" refers to the study of biological structures and to the structures themselves. Quantitative anatomical data obtained by morphometric measurements are used in inhaled aerosol deposition dose models. The equations used in modeling calculations define the needed specific quantitative anatomy input, whether the model is deterministic, stochastic, semi-empirical, or computational fluid dynamics based. Replica airway casts are widely used for defining airway morphology, and for making hollow models to validate deposition calculations. The parameters measured on casts, e.g., airway lengths, diameters, branching and gravity angles, alveolar shapes, and generational linkages do not capture some important airway details, such as bifurcation shapes, airway motion, deviations from airway smoothness, and non-uniform airway tube diameters. These details can affect inhaled aerosol fates. Advances in methods for scanning airways in living subjects or in non-dissected excised lungs have overcome many of the problems associated with replica cast morphometry, but limitations remain with respect to providing linked airway regions, capturing airway motion, and resolving fine structural detail. There are also needs for cast measurements and scans that represent additional animal species and normal variations within species and individuals. Other methods for defining airway anatomy, such as serial sectioning of fixed or frozen tissue, planar x-ray imaging, and bolus aerosol inhalation, also provide useful airway anatomical data. Along with advances in aerosol dynamics, the current state of understanding airway anatomy is adequate for modeling many medical and environmental exposure cases. However, it appears that advances in understanding respiratory tract anatomy and physiology have lagged behind advances in the quality of aerosol science used in current inhaled aerosol deposition models, with the exception of dynamic and/or multi-component aerosol systems (e.g., cigarette smoke). Accordingly, for anatomists and aerosol scientists working on inhaled aerosol dose models both challenges and opportunities lie ahead for addressing remaining anatomical issues of concern. • Airway anatomy is required as input in inhaled aerosol models. • Anatomical information for dose models comes from a variety of methods. • Scanning methods are used to discover living airway anatomy. • New exposure scenarios may require new knowledge of airway structures. [ABSTRACT FROM AUTHOR]