Assessment and Validation of a Hygroscopic Growth Model with Different Water Activity Estimation Methods.

Hygroscopic growth models are currently of interest as aids for targeting the deposition of inhaled drug particles in preferred areas of the lung that will maximize their pharmaceutical effect. Mathematical models derived to estimate hygroscopic growth over time have been previously developed but have not been thoroughly validated. For this study, model validation involved a comparison of modeled values to measured values when the growing droplet had reached equilibrium. A second validation process utilized a novel system to measure the growth of a droplet on a microscope coverslip relative to modeled values when the droplet is undergoing the initial rapid growth phase. Various methods currently used to estimate the water activity of the growing droplet, which influences the droplet growth rate, were also compared. Results indicated that a form of the hygroscopic growth model that utilizes coupled-differential equations to estimate droplet diameter and temperature over time was valid throughout droplet growth until it reached its equilibrium size. Accuracy was enhanced with the use of a polynomial expression to estimate water activity relative to the use of a simplified estimate of water activity based on Raoult's Law. Model accuracy was also improved when constraining the film of salt solution surrounding the dissolving salt core at saturation.

Monitoring chemical contaminants in the Gulf of Maine, using sediments and mussels (Mytilus edulis): An evaluation.

The objective of this paper is to determine whether contaminant data on mussels and sediments can be used interchangeably, or not, when assessing the degree of anthropogenic contamination of a water body. To obtain adequate coverage of the entire Gulf of Maine, Bay of Fundy sediment samples were collected, analyzed and combined with similar data from four coastal monitoring programs. This required careful interpretation but provided robust results consistent with published literature. A strong correspondence was found between sediment and mussel concentrations for polycyclic aromatic hydrocarbons, moderate to weak correspondence for polychlorinated biphenyls, and except for mercury and zinc, little to no correspondence was found for metals. We conclude that mussel contaminant data are likely sufficient for providing information on the spatial and temporal distribution of chemical contaminants, in coastal waters, under a broad range of environmental conditions and contaminant levels, and unlike sediments, provide direct information on contaminant bioavailability.

Differences in Particle Deposition Between Members of Imaging-Based Asthma Clusters.

Background: Four computed tomography (CT) imaging-based clusters have been identified in a study of the Severe Asthma Research Program (SARP) cohort and have been significantly correlated with clinical and demographic metrics (J Allergy Clin Immunol 2017; 140:690-700.e8). We used a computational fluid dynamics (CFD) model to investigate air flow and aerosol deposition within imaging archetypes representative of the four clusters. Methods: CFD simulations for air flow and 1-8 µm particle transport were performed using CT-based airway models from two healthy subjects and eight asthma subjects. The subject selection criterion was based on the discriminant imaging-based flow-related variables of J(Total) (average local volume expansion in the total lung) and Dh*(sLLL) (normalized airway hydraulic diameter in the left lower lobe), where reduced J(Total) and Dh*(sLLL) indicate reduced regional ventilation and airway constriction, respectively. The analysis focused on the comparisons between all clusters with respect to healthy subjects, between cluster 2 and cluster 4 (nonsevere and severe asthma clusters with airway constriction) and between cluster 3 and cluster 4 (two severe asthma clusters characterized by normal and constricted airways, respectively). Results: Nonsevere asthma cluster 2 and severe asthma cluster 4 subjects characterized by airway constriction had an increase in the deposition fraction (DF) in the left lower lobe. Constricted flows impinged on distal bifurcations resulting in large depositions. Although both cluster 3 (without constriction) and cluster 4 (with constriction) were severe asthma, they exhibited different particle deposition patterns with increasing particle size. The statistical analysis showed that Dh*(sLLL) plays a more important role in particle deposition than J(Total), and regional flow fraction is correlated with DF among lobes for smaller particles. Conclusions: We demonstrated particle deposition characteristics associated with cluster-specific imaging-based metrics such as airway constriction, which could pertain to the design of future drug delivery improvements.

Photocatalytic degradation of 17α-ethinylestradiol (EE2) in the presence of TiO2-doped zeolite.

Current design limitations and ineffective remediation techniques in wastewater treatment plants have led to concerns about the prevalence of pharmaceutical and personal care products (PPCPs) in receiving waters. A novel photocatalyst, TiO2-doped low-silica X zeolite (TiO2-LSX), was used to study the degradation of the pharmaceutical compound, 17α-ethinylestradiol (EE2). The catalyst was synthesized and characterized using XRD, BET surface analysis, SEM-EDAX, and ICP-OES. The effects of different UV light intensities, initial EE2 concentrations, and catalyst dosages on the EE2 removal efficiency were studied. A higher EE2 removal efficiency was attained with UV-TiO2-LSX when compared with UV-TiO2 or UV alone. The EE2 degradation process followed pseudo-first-order kinetics. A comprehensive empirical model was developed to describe the EE2 degradation kinetics under different conditions using multiple linear regression analysis. The EE2 degradation mechanism was proposed based on molecular calculations, identification of photoproducts using HPLC-MS/MS, and reactive species quenching experiments; the results showed that oxidative degradation pathways initiated by hydroxyl radicals were predominant. This novel TiO2-doped zeolite system provides a promising application for the UV disinfection process in wastewater treatment plants.

Tests of bioaccumulation models for polychlorinated biphenyl compounds: a study of young-of-the-year bluefish in the Hudson River estuary, USA.

A field-based study regarding uptake of polychlorinated biphenyl compounds (PCBs) by young-of-the-year (YOY) bluefish (Pomatomus saltatrix) was initiated to test a steady-state model of bioaccumulation and trophic transfer in a rapidly growing fish. Determination of prey composition as well as size-dependent growth and specific consumption rates for YOY bluefish from separate field and laboratory studies enabled the input of these species-specific parameters into the model. Furthermore, the time and duration of the exposure of YOY bluefish to dissolved PCBs from a well-characterized system (Hudson River, USA) was well known. Patterns of accumulation of individual PCB congeners differed relative to the accumulation of total PCBs, with the greatest net accumulation occurring for the higher-molecular-weight congeners. Comparison of lipid-normalized bioaccumulation factors (BAFs) with the octanol-water partition coefficients of individual PCB congeners revealed bluefish to be above the BAFs predicted by lipid-based equilibrium partitioning, suggesting that uptake from food is an important source of PCBs in YOY bluefish. Comparison of measured BAFs with values predicted by a steady-state, food-chain model showed good first-order agreement.

The influence of sediment resuspension on the degradation of phenanthrene in flow-through microcosms.

The effect of sediment resuspension on the mineralization of phenanthrene was examined in microcosms and sediment slurries. In computer-controlled, flow-through microcosms, 14C-phenanthrene-amended sediments were resuspended into overlying oxic water at frequencies of 12, 4, 1, 0.25 and 0 d(-1). In slurry bottle experiments 14C-phenanthrene-amended sediments were continuously resuspended under oxic (excess air headspace) and anoxic (N2 headspace) conditions and mineralization was measured at periods from 2 h to 7 days. Our main findings were: (1) mineralization rate constants from the microcosms ranged from 0.001 to 0.01 d(-1) and increased with frequency of resuspension, (2) these rates fell between those measured in oxic and anoxic slurries and were predicted within a factor of 2.5 by a model in which mineralization depended on the degree of oxygen exposure, and (3) the phenanthrene-degrading bacterial community was more active in resuspended sediments incubated in the microcosms than in sediments which were not resuspended, or which were stored under refrigeration. We conclude from these experiments that the effects of sediment resuspension on phenanthrene degradation are consistent with a primary role of average oxygen exposure, and also an alteration in the PAH-degrading activity of microbial populations.