Chronic Exposure Effects of Silver Nanoparticles on Stream Microbial Decomposer Communities and Ecosystem Functions.

With the accelerated use of silver nanoparticles (AgNP) in commercial products, streams will increasingly serve as recipients of, and repositories for, AgNP. This raises concerns about the potential toxicity of these nanomaterials in the environment. Here we aimed to assess the impacts of chronic AgNP exposure on the metabolic activities and community structure of fungal and bacterial plant litter decomposers as central players in stream ecosystems. Minimal variation in the size and surface charge of AgNP indicated that nanoparticles were rather stable during the experiment. Five days of exposure to 0.05 and 0.5 µM AgNP in microcosms shifted bacterial community structure but had no effect on a suite of microbial metabolic activities, despite silver accumulation in the decomposing leaf litter. After 25 days, however, a broad range of microbial endpoints, as well as rates of litter decomposition, were strongly affected. Declines matched with the total silver concentration in the leaves and were accompanied by changes in fungal and bacterial community structure. These results highlight a distinct sensitivity of litter-associated microbial communities in streams to chronic AgNP exposure, with effects on both microbial functions and community structure resulting in notable ecosystem consequences through impacts on litter decomposition and further biogeochemical processes.

Harmful effects of silver nanoparticles on a complex detrital model system.

The rapid proliferation of silver nanoparticles (AgNP) in industry and the environment requires realistic toxicity assessments based on approaches that consider the biological complexity of ecosystems. Here we assessed the acute toxicity of carbonate-coated AgNP and, for comparison, AgNO3 (Ag(+)) by using a model system consisting of decomposing plant litter and the associated fungal and bacterial decomposers as central players in the functioning of stream ecosystems. Little variation in size and surface charge during the experiment indicated that the AgNP used were essentially stable. AgNP disrupted bacterial growth (≤83% reduction in protein biosynthesis, EC50 = 0.3 µM), clearly affected fungal growth (≤61% reduction in ergosterol synthesis, EC50 = 47 µM) with both endpoints more sensitive to AgNP than to Ag(+). Fungal reproduction, in contrast, was stimulated by AgNP, but not Ag(+), at concentrations up to 25 µM. Both AgNP and Ag(+ )also stimulated extracellular alkaline phosphatase but reduced leucine aminopeptidase, whereas ß-glucosidase was stimulated by AgNP and reduced by Ag(+). Importantly, the provision of cysteine, a chelating ligand that complexes free Ag(+), failed to alleviate AgNP toxicity to microbial growth, clearly demonstrating particle-mediated toxicity independent of the presence of ionic silver. This contrasts with the observed inhibition of leucine aminopeptidase by Ag(+), which accounted for 2-6% of the total silver in treatments receiving AgNP. These results show that although outcomes of AgNP and Ag(+ )exposure assessed by different functional endpoints vary widely, AgNP strongly interferes with bacterial growth and a range of other microbial processes, resulting in severe consequences for natural microbial communities and ecosystem functioning.

Fate of polychlorinated biphenyls in a contaminated lake ecosystem: combining equilibrium passive sampling of sediment and water with total concentration measurements of biota.

Equilibrium sampling devices can be applied to study and monitor the exposure and fate of hydrophobic organic chemicals on a thermodynamic basis. They can be used to determine freely dissolved concentrations and chemical activity ratios and to predict equilibrium partitioning concentrations of hydrophobic organic chemicals in biota lipids. The authors' aim was to assess the equilibrium status of polychlorinated biphenyls (PCBs) in a contaminated lake ecosystem and along its discharge course using equilibrium sampling devices for measurements in sediment and water and by also analyzing biota. The authors used equilibrium sampling devices (silicone rubber and polyethylene [PE]) to determine freely dissolved concentrations and chemical activities of PCBs in the water column and sediment porewater and calculated for both phases the corresponding equilibrium concentrations and chemical activities in model lipids. Overall, the studied ecosystem appeared to be in disequilibrium for the studied phases: sediment, water, and biota. Chemical activities of PCBs were higher in sediment than in water, which implies that the sediment functioned as a partitioning source of PCBs and that net diffusion occurred from the sediment to the water column. Measured lipid-normalized PCB concentrations in biota were generally below equilibrium lipid concentrations relative to the sediment (CLip ⇌Sed ) or water (CLip ⇌W ), indicating that PCB levels in the organisms were below the maximum partitioning levels. The present study shows the application versatility of equilibrium sampling devices in the field and facilitates a thermodynamic understanding of exposure and fate of PCBs in a contaminated lake and its discharge course.

Silver nanoparticle effects on stream periphyton during short-term exposures.

Silver nanoparticles (AgNP) are increasingly used as antimicrobials in consumer products. Subsequently released into aquatic environments, they are likely to come in contact with microbial communities like periphyton, which plays a key role as a primary producer in stream ecosystems. At present, however, very little is known about the effects of nanoparticles on processes mediated by periphyton communities. We assessed the effects of citrate-coated silver nanoparticles and silver ions (dosed as AgNO3) on five functional end points reflecting community and ecosystem-level processes in periphyton: photosynthetic yield, respiration potential, and the activity of three extracellular enzymes. After 2 h of exposure in experimental microcosms, AgNP and AgNO3 inhibited respiration and photosynthesis of periphyton and the activities of two of the three extracellular enzymes. Addition of a chelating ligand that complexes free silver ions indicated that, in most cases, toxicity of AgNP suspensions was caused by Ag(I) dissolved from the particles. However, these suspensions inhibited one of the extracellular enzymes (leucine aminopeptidase), pointing to a specific nanoparticle effect independent of the dissolved Ag(I). Thus, our results show that both silver nanoparticles and silver ions have potential to disrupt basic metabolic functions and enzymatic resource acquisition of stream periphyton.

Intracellular silver accumulation in Chlamydomonas reinhardtii upon exposure to carbonate coated silver nanoparticles and silver nitrate.

The intracellular silver accumulation ({Ag}(in)) upon exposure to carbonate coated silver nanoparticles (AgNP, 0.5-10 µM, average diameter 29 nm) and silver nitrate (20-500 nM) was examined in the wild type and in the cell wall free mutant of the green alga Chlamydomonas reinhardtii at pH 7.5. The {Ag}(in) was measured over time up to 1 h after a wash procedure to remove silver ions (Ag(+)) and AgNP from the algal cell surface. The {Ag}(in) increased with increasing exposure time and with increasing AgNP and AgNO(3) concentrations in the exposure media, reaching steady-state concentrations between 10(-5) and 10(-3) mol L(cell)(-1). According to estimated kinetic parameters, high Ag(+) bioconcentration factors were calculated (>10(3) L L(cell)(-1)). Higher accumulation rate constants were assessed in the cell wall free mutant, indicating a protective role of the cell wall in limiting Ag(+) uptake. The bioavailability of AgNP was calculated to be low in both strains relative to Ag(+), suggesting that AgNP internalization across the cell membrane was limited.

A noninvasive method for assessing impaired diastolic suction in patients with dilated cardiomyopathy.

BACKGROUND: Diastolic suction is a major determinant of early left ventricular filling in animal experiments. However, suction remains incompletely characterized in the clinical setting. METHODS AND RESULTS: First, we validated a method for measuring the spatio-temporal distributions of diastolic intraventricular pressure gradients and differences (DIVPDs) by digital processing color Doppler M-mode recordings. In 4 pigs, the error of peak DIVPD was 0.0+/-0.2 mm Hg (intraclass correlation coefficient, 0.95) compared with micromanometry. Forty patients with dilated cardiomyopathy (DCM) and 20 healthy volunteers were studied at baseline and during dobutamine infusion. A positive DIVPD (toward the apex) originated during isovolumic relaxation, reaching its peak shortly after mitral valve opening. Peak DIVPD was less than half in patients with DCM than in control subjects (1.2+/-0.6 versus 2.5+/-0.8 mm Hg, P<0.001). Dobutamine increased DIVPD in control subjects by 44% (P<0.001) but only by 23% in patients with DCM (P=NS). DIVPDs were the consequence of 2 opposite forces: a driving force caused by local acceleration, and a reversed (opposed to filling) convective force that lowered the total DIVPD by more than one third. In turn, local acceleration correlated with E-wave velocity and ejection fraction, whereas convective deceleration correlated with E-wave velocity and ventriculo:annular disproportion. Convective deceleration was highest among patients showing a restrictive filling pattern. CONCLUSIONS: Patients with DCM show an abnormally low diastolic suction and a blunted capacity to recruit suction with stress. By raising the ventriculo:annular disproportion, chamber remodeling proportionally increases convective deceleration and adversely affects left ventricular filling. These previously unreported mechanisms of diastolic dysfunction can be studied by using Doppler echocardiography.

Doppler-derived ejection intraventricular pressure gradients provide a reliable assessment of left ventricular systolic chamber function.

BACKGROUND: Ejection intraventricular pressure gradients are caused by the systolic force developed by the left ventricle (LV). By postprocessing color Doppler M-mode (CDMM) images, we can measure noninvasively the ejection intraventricular pressure difference (EIVPD) between the LV apex and the outflow tract. This study was designed to assess the value of Doppler-derived EIVPDs as noninvasive indices of systolic chamber function. METHODS AND RESULTS: CDMM images and pressure-volume (conductance) signals were simultaneously acquired in 9 minipigs undergoing pharmacological interventions and acute ischemia. Inertial, convective, and total EIVPD curves were calculated from CDMM recordings. Peak EIVPD closely correlated with indices of systolic function based on the pressure-volume relationship: peak elastance (within-animal R=0.98; between-animals R=0.99), preload recruitable stroke work (within-animal R=0.81; between-animals R=0.86), and peak of the first derivative of pressure corrected for end-diastolic volume (within-animal R=0.88; between-animals R=0.91). The correlation of peak inertial EIVPD with these indices was also high (all R>0.75). Load dependence of EIVPDs was studied in another 5 animals in which consecutive beats obtained during load manipulation were analyzed. During caval occlusion (40% EDV reduction), dP/dtmax, ejection fraction, and stroke volume significantly changed, whereas peak EIVPD remained constant. Aortic occlusion (40% peak LV pressure increase) significantly modified dP/dtmax, ejection fraction, and stroke volume; a nearly significant trend toward decreasing peak EIVPD was observed (P=0.06), whereas inertial EIVPD was unchanged (P=0.6). EIVPD beat-to-beat and interobserver variabilities were 2+/-12% and 5+/-11%, respectively. CONCLUSIONS: Doppler-derived EIVPDs provide quantitative, reproducible, and relatively load-independent indices of global systolic chamber function that correlate closely with currently available reference methods.

Noninvasive assessment of ejection intraventricular pressure gradients.

OBJECTIVES: The study was designed to validate in vivo a new method to measure ejection intraventricular pressure gradients (IVPGs) by processing color M-mode Doppler data and to assess the effects of inotropic interventions on IVPGs in the clinical setting. BACKGROUND: In the absence of obstruction, ejection IVPGs cannot be estimated by Doppler using the simplified Bernoulli equation. METHODS: High-fidelity micromanometers were placed in the left ventricle of eight minipigs, and synchronic Doppler images and pressure signals were obtained during different hemodynamic conditions. Twenty healthy volunteers and 20 dilated cardiomyopathy patients were studied at baseline and during esmolol, dobutamine, and atropine infusion (only dobutamine in patients). RESULTS: Excellent agreement was observed between micromanometer and Doppler methods for measuring instantaneous pressure differences among the apex, the mid-cavity, and the outflow tract (R(intraclass) = 0.98, 0.81, 0.76, and 0.98 for the peak, time-to-peak, peak reverse, and time-to-peak reverse values, respectively; n = 810 beats). Error of the noninvasive method was -0.05 +/- 0.25 mm Hg for the peak pressure difference. Parametrical images demonstrated that IVPGs originate mainly in the mid-ventricle and then propagate to the outflow tract. Both the magnitude and the temporal course of IVPGs were different among volunteers and patients. Inotropic interventions induced significant changes in the apex-outflow tract pressure differences in both populations, whereas atropine had no effect on IVPGs. CONCLUSIONS: For the first time, ejection IVPGs can be accurately visualized and measured by Doppler-echocardiography. Important aspects of the dynamic interaction among myocardial performance, load mechanics, and ejection dynamics can be assessed in the clinical setting using this method.

La función diastólica regional está más conservada en el miocardio viable que en el no viable. Demostración mediante Doppler pulsado tisular realizado en condiciones basales / Regional Diastolic Function is More Preserved in Viable than Non-Viable Myocardium. Demonstration by Pulsed-Wave Doppler. Tissue Imaging in Basal Conditions

Introducción y objetivos. El objetivo del estudio fue analizar mediante Doppler pulsado tisular en condiciones basales las diferencias existentes en la función diastólica regional entre el miocardio viable y no viable. Pacientes y métodos. La población de estudio está formada por 21 pacientes con enfermedad coronaria de tres vasos y alteraciones de la contractilidad segmentaria, a los que se realizaron ecocardiograma transtorácico y Doppler pulsado tisular en condiciones basales y, por un investigador diferente, ecocardiograma de estrés con dobutamina. Resultados. Se estudiaron en total 322 segmentos, de los cuales 140 (43 por ciento) tenían una función sistólica deprimida. De estos 140 segmentos, 52 (37 por ciento) fueron clasificados como hipocinéticos, 80 (57 por ciento) como acinéticos y ocho (6 por ciento) como discinéticos. Durante la administración de dobutamina se observó una mejoría de la contractilidad (segmentos viables) en 67 de los 140 segmentos con disfunción sistólica (48 por ciento), mientras que los restantes 73 (52 por ciento) fueron considerados no viables. Los segmentos viables tenían una mayor velocidad máxima de la onda diastólica precoz e en comparación con los no viables (5,5 ñ 1,9 frente a 4,7 ñ 2,0 cm/s; p = 0,03). La proporción de segmentos con una relación e/a < 1 fue mayor entre los no viables (70 frente al 52 por ciento; p < 0,05). No existieron diferencias en relación con el tiempo de relajación isovolumétrica y la velocidad máxima de la onda a. Aunque la velocidad máxima de la onda sistólica s fue inferior en los segmentos no viables, las diferencias no fueron estadísticamente significativas. Conclusión. Los segmentos miocárdicos viables tienen una función diastólica regional menos alterada que los no viables cuando se estudian con Doppler pulsado tisular en condiciones basales (AU)

Utilidad de las nuevas técnicas de imagen, segundo armónico y contraste en la visualización del borde endocárdico. Análisis de la reproducibilidad en la valoración de la contracción segmentaria / Usefulness of thenew imaging technique, second harmonic with and without contrast in endocardial border visualization. Reliability analysis in segmentarial wall motion assessment

Objetivos. Este estudio intenta determinar si las nuevas técnicas mejoran de manera significativa la resolución del borde endocárdico en pacientes con ventana ultrasónica subóptima y la reproducibilidad en la interpretación de la contracción segmentaria, dependiendo de la técnica empleada y el grado de experiencia del observador. Métodos. Estudiamos un total de 20 pacientes (240 segmentos) consecutivos, con mala ventana ultrasónica, para objetivar si el uso de segundo armónico tisular (2H) o el contraste más segundo armónico (2HC) (Levovist® 4 g i.v.), mejoraba la definición del borde endocárdico, comparado con el modo fundamental (2D).Un total de 4 observadores, con diferentes grados de experiencia, analizaron la contracción segmentaria de 32 pacientes (384 segmentos) consecutivos, para valorar la reproducibilidad del estudio de acuerdo con la técnica empleada. Resultados. La calidad de la imagen fue superior con 2H y 2 HC en comparación con 2D. La diferencia fue mayor en los bordes endocárdicos lateral y apical (0,9 frente a 1,5 y 1 frente a 1,64; p < 0,001) con 2H. Utilizando 2HC, la resolución del borde endocárdico mejoró de manera ligera pero significativa en el ápex en comparación con 2H (1,64 frente a 1,81; p = 0,016).El porcentaje de segmentos valorados para la variabilidad interobservador se incrementa de manera significativa utilizando el segundo armónico y el contraste, siendo la combinación de éstas la que mayor rendimiento alcanza (95 por ciento). La concordancia entre expertos no se modificó de manera significativa. El observador no experto presentaba una concordancia significativamente menor que los expertos; sin embargo, ésta no mejoró a pesar de una mayor calidad del estudio con 2H y 2HC. Conclusiones. a) El segundo armónico tisular y el segundo armónico más contraste mejoran significativamente la visualización del borde endocárdico; b) las nuevas técnicas de imagen mejoran de manera significativa el rendimiento del estudio, sin disminuir el grado de concordancia, y c) la experiencia en la valoración del borde endocárdico es el principal determinante en la variabilidad interobservador (AU)