Effect of Puffing Behavior on Particle Size Distributions and Respiratory Depositions From Pod-Style Electronic Cigarette, or Vaping, Products

The current fourth generation (“pod-style”) electronic cigarette, or vaping, products (EVPs) heat a liquid (“e-liquid”) contained in a reservoir (“pod”) using a battery-powered coil to deliver aerosol into the lungs. A portion of inhaled EVP aerosol is estimated as exhaled, which can present a potential secondhand exposure risk to bystanders. The effects of modifiable factors using either a prefilled disposable or refillable pod-style EVPs on aerosol particle size distribution (PSD) and its respiratory deposition are poorly understood. In this study, the influence of up to six puff profiles (55-, 65-, and 75-ml puff volumes per 6.5 and 7.5 W EVP power settings) on PSD was evaluated using a popular pod-style EVP (JUUL® brand) and a cascade impactor. JUUL® brand EVPs were used to aerosolize the manufacturers' e-liquids in their disposable pods and laboratory prepared “reference e-liquid” (without flavorings or nicotine) in refillable pods. The modeled dosimetry and calculated aerosol mass median aerodynamic diameters (MMADs) were used to estimate regional respiratory deposition. From these results, exhaled fraction of EVP aerosols was calculated as a surrogate of the secondhand exposure potential. Overall, MMADs did not differ among puff profiles, except for 55- and 75-ml volumes at 7.5 W (p < 0.05). For the reference e-liquid, MMADs ranged from 1.02 to 1.23 μm and dosimetry calculations predicted that particles would deposit in the head region (36–41%), in the trachea-bronchial (TB) region (19–21%), and in the pulmonary region (40–43%). For commercial JUUL® e-liquids, MMADs ranged from 0.92 to 1.67 μm and modeling predicted that more particles would deposit in the head region (35–52%) and in the pulmonary region (30–42%). Overall, 30–40% of the particles aerosolized by a pod-style EVP were estimated to deposit in the pulmonary region and 50–70% of the inhaled EVP aerosols could be exhaled; the latter could present an inhalational hazard to bystanders in indoor occupational settings. More research is needed to understand the influence of other modifiable factors on PSD and exposure potential.

Modeled Respiratory Tract Deposition of Aerosolized Oil Diluents Used in Δ9-THC-Based Electronic Cigarette Liquid Products

Electronic cigarette, or vaping, products (EVP) heat liquids (“e-liquids”) that contain substances (licit or illicit) and deliver aerosolized particles into the lungs. Commercially available oils such as Vitamin-E-acetate (VEA), Vitamin E oil, coconut, and medium chain triglycerides (MCT) were often the constituents of e-liquids associated with an e-cigarette, or vaping, product use-associated lung injury (EVALI). The objective of this study was to evaluate the mass-based physical characteristics of the aerosolized e-liquids prepared using these oil diluents. These characteristics were particle size distributions for modeling regional respiratory deposition and puff-based total aerosol mass for estimating the number of particles delivered to the respiratory tract. Four types of e-liquids were prepared by adding terpenes to oil diluents individually: VEA, Vitamin E oil, coconut oil, and MCT. A smoking machine was used to aerosolize each e-liquid at a predetermined puff topography (volume of 55 ml for 3 s with 30-s intervals between puffs). A cascade impactor was used to collect the size-segregated aerosol for calculating the mass median aerodynamic diameter (MMAD) and geometric standard deviation (GSD). The respiratory deposition of EVP aerosols on inhalation was estimated using the Multiple-Path Particle Dosimetry model. From these results, the exhaled fraction of EVP aerosols was calculated as a surrogate of secondhand exposure potential. The MMAD of VEA (0.61 μm) was statistically different compared to MCT (0.38 μm) and coconut oil (0.47 μm) but not to Vitamin E oil (0.58 μm); p < 0.05. Wider aerosol size distribution was observed for VEA (GSD 2.35) and MCT (GSD 2.08) compared with coconut oil (GSD 1.53) and Vitamin E oil (GSD 1.55). Irrespective of the statistical differences between MMADs, dosimetry modeling resulted in the similar regional and lobular deposition of particles for all e-liquids in the respiratory tract. The highest (~0.08 or more) fractional deposition was predicted in the pulmonary region, which is consistent as the site of injury among EVALI cases. Secondhand exposure calculations indicated that a substantial amount of EVP aerosols could be exhaled, which has potential implications for bystanders. The number of EVALI cases has declined with the removal of VEA; however, further research is required to investigate the commonly available commercial ingredients used in e-liquid preparations.

Respirable Coal Mine Dust: A Review of Respiratory Deposition, Regulations and Characterization

In the late 1990s, despite years of efforts to understand and reduce coal worker’s pneumoconiosis (CWP) prevalence from more than 30% in 1970 to less than 4.2%, the level of occurrence among the US coal miners increased unexpectedly. The recent resurgence of lung diseases has raised concerns in the scientific and regulatory communities. In 2014, the United States Mine Safety and Health Administration (MSHA) issued a new dust rule changing the respirable coal mine dust (RCMD) exposure limits, measurement technology, and sampling protocol. The analysis for probable causes for the substantial increase in the CWP incidence rate is rather complicated. This paper aims to conduct a review of RCMD respiratory deposition, health effects, monitoring, regulations, and particle characteristics. The primary sources of RCMD along with the health risks from potential exposure are highlighted, and the current RCMD exposure regulations of the major coal producer countries are compared. A summary of RCMD characterization studies from 1972 to the present is provided. A review of the literature revealed that numerous factors, including geological and mining parameters, advancements in mining practices, particle characteristics, and monitoring approaches are considered to contribute to the recent resurgence of RCMD lung diseases. However, the root causes of the problem are still unknown. The effectiveness of the new dust rules in the United States will probably take years to be correctly assessed. Therefore, future research is needed to understand the relationship between RCMD particle characteristics and lung deposition, and the efficacy of current monitoring practices to measure the true dose of RCMD exposure.

Spatio-temporal variations of PM2.5 and Respiratory Deposition Dose (RDD) before and during different COVID-19 lockdown phases at Delhi, India

<p>Present study explores pre-lockdown (1<sup>st</sup> January-24<sup>th</sup> March, 2020) and during lockdown (25<sup>th</sup> March-20<sup>th</sup> June, 2020) air quality changes in PM<sub>2.5 </sub>along with meteorological effects at megacity- Delhi (28.7041°N, 77.1025°E). Alipur (Rural), Okhla (Industrial) and Pusa Road (Traffic dominant area) experienced mean concentrations (S.D.) of PM<sub>2.5 </sub>as 87.56(±54.06), 124.45(±73.49) and 62.14(±58.64) µg/m<sup>3 </sup>before lockdown(BL; 1<sup>st</sup> January-24<sup>th</sup> March, 2020), while for Lockdown1(L1; 25<sup>th</sup> March-14<sup>th</sup> April, 2020), PM<sub>2.5</sub> decreased drastically as 39.26(±16.31), 38.01(±15.16) and 31.03(±12.79) µg/m<sup>3</sup> and gradually increased during Lockdown2(L2; 15<sup>th</sup> April-3<sup>rd</sup> May, 2020), Lockdown3(L3; : 4<sup>th</sup> May-17<sup>th</sup> May, 2020), Lockdown4(L4; 18<sup>th</sup> May-31<sup>st</sup> May, 2020), respectively. Percentage decrease in PM<sub>2.5 </sub>(-69.46%) correlated with outdoor activities of percentage decrease (-70 to -80%) in L1, from BL phase. Exposure assessment study showed, mean Respiratory Deposition Dose-RDD (S.D.) (µg/hr) for fine particles [Particle diameter (Dp) =0.5 µm] for walk and sit mode during BL, as 27.22(±13.53) and 9.90(±4.91) for Alipur, 30.55(±18.04) and 11.11(±6.56) for Okhla, and 28.67(±14.39) and 10.43(±5.23) for Pusa road, and decreased during L1 as 9.64(±4.00) and 3.50(±1.46) for Alipur, 9.33(±3.72) and 3.39(±1.35) for Okhla, and 7.62(±3.14) and 2.77(±1.14) for Pusa road, respectively. Delhiites were exposed to more fine RDD(walk/sit) before lockdown than during lockdown phases. People in sit mode found less exposed to fine RDD, in comparison to walk condition. The people living indoors were affected by outdoor RDD exposure with windows open condition, while exposed to different indoor pollution sources with windows closed condition during lockdown. Authors suggest avoid use of closed conditioned indoors and ACs; frequent opening of windows to lower the RDD and to minimize the COVID-19 virus transmission via particulates.</p><p>Keywords: PM<sub>2.5</sub>, RDD, COVID-19.</p>