Continuum-based models and concepts for the transport of nanoparticles in saturated porous media: A state-of-the-science review

Environmental applications of nanoparticles (NP) increasingly result in widespread NP distribution within porous media where they are subject to various concurrent transport mechanisms including irreversible deposition, attachment/detachment (equilibrium or kinetic), agglomeration, physical straining, site-blocking, ripening, and size exclusion. Fundamental research in NP transport is typically conducted at small scale, and theoretical mechanistic modeling of particle transport in porous media faces challenges when considering the simultaneous effects of transport mechanisms. Continuum modeling approaches, in contrast, are scalable across various scales ranging from column experiments to aquifer. They have also been able to successfully describe the simultaneous occurrence of various transport mechanisms of NP in porous media such as blocking/straining or agglomeration/deposition/detachment. However, the diversity of model equations developed by different authors and the lack of effective approaches for their validation present obstacles to the successful robust application of these models for describing or predicting NP transport phenomena. This review aims to describe consistently all the important NP transport mechanisms along with their representative mathematical continuum models as found in the current scientific literature. Detailed characterizations of each transport phenomenon in regards to their manifestation in the column experiment outcomes, i.e., breakthrough curve (BTC) and residual concentration profile (RCP), are presented to facilitate future interpretations of BTCs and RCPs. The review highlights two NP transport mechanisms, agglomeration and size exclusion, which are potentially of great importance in controlling the fate and transport of NP in the subsurface media yet have been widely neglected in many existing modeling studies. A critical limitation of the continuum modeling approach is the number of parameters used upon application to larger scales and when a series of transport mechanisms are involved. We investigate the use of simplifying assumptions, such as the equilibrium assumption, in modeling the attachment/detachment mechanisms within a continuum modelling framework. While acknowledging criticisms about the use of this assumption for NP deposition on a mechanistic (process) basis, we found that its use as a description of dynamic deposition behavior in a continuum model yields broadly similar results to those arising from a kinetic model. Furthermore, we show that in two dimensional (2-D) continuum models the modeling efficiency based on the Akaike information criterion (AIC) is enhanced for equilibrium vs kinetic with no significant reduction in model performance. This is because fewer parameters are needed for the equilibrium model compared to the kinetic model. Two major transport regimes are identified in the transport of NP within porous media. The first regime is characterized by higher particle-surface attachment affinity than particle-particle attachment affinity, and operative transport mechanisms of physicochemical filtration, blocking, and physical retention. The second regime is characterized by the domination of particle-particle attachment tendency over particle-surface affinity. In this regime although physicochemical filtration as well as straining may still be operative, ripening is predominant together with agglomeration and further subsequent retention. In both regimes careful assessment of NP fate and transport is necessary since certain combinations of concurrent transport phenomena leading to large migration distances are possible in either case

Hepatitis B Surface Antigenemia at Birth : A Long-Term Follow-up Study

Objective: To investigate the prevalence and outcome of hepatitis B surface antigenemia in newborns of hepatitis B e antigen (HBeAg)-positive hepatits B surface antigen (HBsAg) carrier mothers under the current immunoprophylaxis program . Study design: From 1984 to 1993, 665 high-risk newborns born to HBeAg-positive HBsAg carrier mothers were prospectively recruited. The newborns were tested for HBsAg soon after birth, before hepatitis B immune globulin administration. All newborns received hepatitis B immune globulin within 24 hours after birth plus subsequent hepatitis B vaccination. Those who were seropositive for HBsAg at birth were regularly followed up for their hepatitis B virus (HBV) markers, liver function profiles, and α-fetoprotein levels from 1984 to 1996. Results: Sixteen (2.4%) of the 665 subjects were found to be seropositive for HBsAg at birth, and all remained HBsAg- positive at 6 months of age. Twelve of the 16 received long- term follow-up care, and all were confirmed to have chronic HBV infection. Of the 12,2 had HBeAg seroconversion, and 1 had alanine aminotransferase flares without HBeAg seroconversion. Delayed appearance of hepatitis B core antibody (anti-HBc) occurred in 2 without alanine aminotransferase elevation. Conclusions: Current immunoprophylaxis strategy does not protect newborns with surface antigenemia, apparently acquired inutero, from becoming HBV carriers. Immunologic attempts to eliminate HBV may occur in carrier children infected in utero, despite their profound immune tolerance to HBV

Tumor Necrosis Factor-α and Interleukin-10 in Viral and Bacterial Gastroenteritis in Children

Gastroenteritis is a common cause of hospitalization and is associated with high morbidity in children. C-reactive protein (CRP), tumor necrosis factor-α (TNF-α) and interleukin-10 (IL-10) are primary mediators of inflammation, and have been implicated in many infectious and non-infectious inflammatory diseases. The main objective of this study was to identify serum markers in viral and bacterial gastroenteritis. Methods: Thirty-one patients admitted to a pediatric infection ward with gastroenteritis and definite pathogens were enrolled in the study: 17 patients had viral gastroenteritis and 14 bacterial gastroenteritis. Serum levels of TNF-α, IL-10 and CRP were measured in these 31 patients, and in a control group of 15 healthy children. Results: Serum concentrations of TNF-α and CRP were significantly greater in patients with bacterial gastroenteritis than in patients with viral gastroenteritis and healthy controls (p < 0.001). Concentrations of IL-10 were increased, but not significantly, in patients with viral or bacterial gastroenteritis (p = 0.577 vs controls). Regarding diagnosis, the measurement of TNF-α and CRP levels was 78.6% and 92.0% sensitive, respectively; and 88.2% and 58.8% specific, respectively. Conclusion: Serum TNF-α concentration may be a useful marker for distinguishing between viral and bacterial gastroenteritis

A Model for Predicting Risk of Serious Bacterial Infection in Febrile Infants Younger Than 3 Months of Age

BackgroundThe objective of this study was to construct a model for predicting the risk of serious bacterial infection (SBI) in febrile infants.MethodsA total of 135 febrile infants younger than 3 months of age who met the inclusion criteria were assessed on the following: physical appearance, complete blood count, serum C-reactive protein (CRP), urinalysis, stool smears for white blood cell (WBC) count if diarrhea was apparent, and blood and urine cultures. Chest X-rays were performed if respiratory symptoms were evident. Cerebrospinal fluid was analyzed if central nervous system infection was suspected.ResultsOf the 135 infants, 34 were diagnosed with SBI. Data from 99 infants were used to construct a model for predicting SBI by multivariate logistic regression. Sex (male), spun urine WBC count (≥ 10 per high-powered field [400 ×]) and CRP (≥ 3.6 mg/L) were significantly related to SBI. A probability cut-off of 0.265 was selected, where values below and above the cut-off reflected low and high SBI risk respectively. Data from the remaining 36 infants were used to test model validity. Both sensitivity and specificity were 77.8% for predicting SBI using this model.ConclusionThese findings suggest that sex, serum CRP concentration and spun urine WBC count can be used to accurately predict SBI in febrile infants aged less than 3 months of age. [J Chin Med Assoc 2009;72(10):521–526

Moderate postnatal hyperoxia accelerates lung growth and attenuates pulmonary hypertension in infant rats after exposure to intra-amniotic endotoxin

To determine the separate and interactive effects of fetal inflammation and neonatal hyperoxia on the developing lung, we hypothesized that: 1) antenatal endotoxin (ETX) causes sustained abnormalities of infant lung structure; and 2) postnatal hyperoxia augments the adverse effects of antenatal ETX on infant lung growth. Escherichia coli ETX or saline (SA) was injected into amniotic sacs in pregnant Sprague-Dawley rats at 20 days of gestation. Pups were delivered 2 days later and raised in room air (RA) or moderate hyperoxia (O2, 80% O2 at Denver's altitude, ∼65% O2 at sea level) from birth through 14 days of age. Heart and lung tissues were harvested for measurements. Intra-amniotic ETX caused right ventricular hypertrophy (RVH) and decreased lung vascular endothelial growth factor (VEGF) and VEGF receptor-2 (VEGFR-2) protein contents at birth. In ETX-exposed rats (ETX-RA), alveolarization and vessel density were decreased, pulmonary vascular wall thickness percentage was increased, and RVH was persistent throughout the study period compared with controls (SA-RA). After antenatal ETX, moderate hyperoxia increased lung VEGF and VEGFR-2 protein contents in ETX-O2 rats and improved their alveolar and vascular structure and RVH compared with ETX-RA rats. In contrast, severe hyperoxia (≥95% O2 at Denver's altitude) further reduced lung vessel density after intra-amniotic ETX exposure. We conclude that intra-amniotic ETX induces fetal pulmonary hypertension and causes persistent abnormalities of lung structure with sustained pulmonary hypertension in infant rats. Moreover, moderate postnatal hyperoxia after antenatal ETX restores lung growth and prevents pulmonary hypertension during infancy