Controls on species distribution and biogeochemical cycling in nitrate-contaminated groundwater and surface water, southeastern Australia.

A detailed study of groundwater and surface water nitrate over four seasons across an area of varied landuse provided insights into the mechanisms that underlie accumulation and transport of nitrate. High nitrate concentrations found in a significant percentage of surface water and shallow groundwater samples are due to anthropogenic contamination. Statistics (PCA, ANOVA, parsimonious model and general linear regression) were used to explore the relationship between NO and land use, and confirmed that areas of high NO concentration are associated with dairy pasture and horticulture.

Review: Technical and policy challenges in deep vadose zone remediation of metals and radionuclides.

Contamination in deep vadose zone environments is isolated from exposure so direct contact is not a factor in its risk to human health and the environment. Instead, movement of contamination to the groundwater creates the potential for exposure and risk to receptors. Limiting flux from contaminated vadose zone is key for protection of groundwater resources, thus the deep vadose zone is not necessarily considered a resource requiring restoration.

Isotopic tracking of Hanford 300 area derived uranium in the Columbia River.

Our objectives in this study are to quantify the discharge rate of uranium (U) to the Columbia River from the Hanford Site's 300 Area and to follow that U downriver to constrain its fate. Uranium from the Hanford Site has variable isotopic composition due to nuclear industrial processes carried out at the site. This characteristic makes it possible to use high-precision isotopic measurements of U in environmental samples to identify even trace levels of contaminant U, determine its sources, and estimate discharge rates.

Pathways of aqueous Cr(VI) attenuation in a slightly alkaline oxic subsurface.

Column experiments combined with geochemical modeling, microscopic inspections, spectroscopic interrogations, and wet chemical extractions were used to study sediment-dependent Cr(VI) desorption, physical location, mineral association, and attenuation mechanism(s) in four freshly or naturally aged contaminated sediments exposed to concentrated Cr(VI) waste fluids. Results showed that majority of Cr(VI) mass was easily removed from the sediments (equilibrium site K(d) varied from 0 to 0.33 mL g(-1) and equilibrium site fraction was greater than 95%).

Measurement of helium isotopes in soil gas as an indicator of tritium groundwater contamination.

The focus of this study was to define the shape and extent of tritium groundwater contamination emanating from a legacy burial ground and to identify vadose zone sources of tritium using helium isotopes (3He and 4He) in soil gas. Helium isotopes were measured in soil-gas samples collected from 70 sampling points around the perimeter and downgradient of a burial ground that contains buried radioactive solid waste. The soil-gas samples were analyzed for helium isotopes using rare gas mass spectrometry.

Tracking sources of unsaturated zone and groundwater nitrate contamination using nitrogen and oxygen stable isotopes at the Hanford site, Washington.

The nitrogen and oxygen isotopic compositions of nitrate in pore water extracts from unsaturated zone (UZ) core samples and groundwater samples indicate at least four potential sources of nitrate in groundwaters at the U.S. DOE Hanford Site in south-central Washington.

Identifying the sources of subsurface contamination at the Hanford Site in Washington using high-precision uranium isotopic measurements.

In the mid-1990s, a groundwater plume of uranium (U) was detected in monitoring wells in the B-BX-BY Waste Management Area at the Hanford Site in Washington. This area has been used since the late 1940s to store high-level radioactive waste and other products of U fuel-rod processing. Using multiple-collector ICP source magnetic sector mass spectrometry, high-precision uranium isotopic analyses were conducted of samples of vadose zone contamination and of groundwater.

Metabolic requirement for the inotropic effects of digitalis and BAY K 8644.

The positive inotropic effects of ouabain and of BAY K 8644 are not apparent in rabbit atria suspended in substrate free medium or in a medium containing 5 mM pyruvate. Addition of glucose in graded concentrations (1-11 mM) during continued exposure of the preparations to the inotropic agents yields graded inotropic effects. The possible involvement of the glycolytic pathway to the development of the inotropic effect of ouabain and BAY K 8644 was tested by using inhibitors of glycolysis that act at two different steps.

Blockade of the inotropic effect of Bay K 8644 by cytochalasin-B and phloretin.

1. The positive inotropic effect in rabbit atria and papillary muscles of Bay K 8644 is blocked by cytochalasin-B (Cyto-B) and phloretin, two compounds known to block the facilitated diffusion of glucose. These compounds do not change the concentration-response curve of calcium.

Effects of cytochalasin-B and phloretin on digitalis inotropy.

Phloretin and cytochalasin-B are known to inhibit sugar transport across the cell membrane of many tissues. Both of these agents at concentrations of 100 and 20 microM, respectively, blocked the inotropic effects of ouabain and acetylstrophanthidin (AS) in isolated rabbit atria and papillary muscle preparations. Neither of these agents had any effect of its own on contractile force.

Cytochalasin-B and phloretin depress contraction and relaxation of aortic smooth muscle.

Cytochalasin-B (20 microM) and phloretin (100 microM) blocked by more than 80% the contractile responses to calcium ions in partially depolarized rabbit aortic strips. Both also blocked, but only by approximately 50%, the responses to noradrenaline and histamine in normal calcium medium. The responses to these agonists in calcium-free EGTA medium were also blocked partially.

Electrophysiological effects of ethmozine in perfused rabbit hearts.

His-bundle electrocardiography was used to evaluate the effects of ethmozine on cardiac conduction in isolated perfused rabbit hearts electrically driven at cycle lengths of 320 and 250 ms. There was no significant change in conduction until high concentrations of ethmozine were reached. His-Purkinje and atrioventricular (AV) nodal conduction were slowed significantly at 0.

Ca2+ and the sarcoplasmic reticulum.

The role of the sarcoplasmic reticulum in the regulation of cytosolic calcium is briefly reviewed. A method is described for monitoring calcium efflux from relatively large amounts of SR in a newly designed filtration apparatus using membrane filtration. Two phases of Ca2+ efflux from SR preloaded in the presence of oxalate were observed: an early exponential phase, followed by a phase of constant efflux.

Effect of encainide and its two major metabolites on cardiac conduction.

The effect of encainide and its two major metabolites, O-demethylated encainide (MJ 9444) and 3-O-methoxy encainide (MJ 14030), on cardiac conduction was studied by recording His bundle potentials in isolated perfused rabbit hearts and Purkinje and muscle conduction in vivo in dog hearts after destruction of the atrioventricular node. Both metabolites are 4 to 15 times more potent than encainide in slowing conduction through the atria, the AV-node and the His-Purkinje system of the rabbit heart. They did not differ from each other in potency but MJ 9444 increased the duration and decreased the height of the ventricular potential whereas MJ 14030 had no effect at doses which caused conduction block.

Increase in ventricular fibrillation threshold following blockade of atrioventricular conduction.

The threshold for electrically induced ventricular fibrillation was determined in anesthetized open-chest dogs, before and after blockade of atrioventricular (A-V) conduction. Without exception, the threshold was significantly elevated after creation of the block. The precise mechanism of this effect is not known at this time.

Effect of lidocaine on ventricular conduction in acutely ischemic dog hearts.

The effect of graded doses of lidocaine (1.25-10 mg/kg) on endocardial Purkinje and transmural conduction at different heart rates as well as during extrasystolic stimulation was studied in dogs, 30 min after ligation of the anterior descending coronary artery. The drug had no effect on endocardial conduction within the ischemic zone except at the highest dose.

Absence of supernormal conduction in canine myocardium.

Transmural conduction time, measured as the difference in arrival time of impulses from a distant stimulating site at endocardial and epicardial electrodes near the left ventricular apex, has been reported to decrease when closely coupled extrasystoles are interpolated, indicating that muscle conduction could be supernormal. We have now determined that reduction in transmural conduction time is accounted for completely by the relatively late arrival time of the extrasystolic wave front at the endocardial recording site. The endocardial recording site was activated later than an immediately adjacent site within the wall in two out of eight animals, which could be interpreted as retrograde conduction.

Site of origin of halothane--epinephrine arrhythmia determined by direct and echocardiographic recordings.

A constantly coupled bigeminal arrhythmia was induced in dogs anesthetized with thiopental-halothane by infusion of epinephrine (1 microgram.kg-1.min-1).

Effect of disopyramide and disobutamide on conduction in perfused rabbit hearts.

The effects of disopyramide (DP) and a new antiarrhythmic agent, disobutamide (DB) on cardiac conduction were studied using His bundle recording from modified rabbit Langendorff preparations electrically driven at 3 and 4 Hz. Both disopyramide (4-16 microgram/mL) and disobutamide (1-30 microgram/ml) showed conduction throughout the atrioventricular conduction system, i.e.

Effects of lidocaine on conduction of extrasystoles in the normal canine heart.

The effect of lidocaine on the conduction of extrasystoles was studied in 8 open-chest dogs after atrioventricular nodal block. Simultaneous recording of endocardial and epicardial activation provided separate measures of endocardial (Purkinje) conduction as well as myocardial (muscle) conduction. Lidocaine (1.

Interaction of lidocaine and calcium on the electrical characteristics of rabbit atria.

The interactions of lidocaine (1-5 X 10(-5) M) and calcium ions (1.25-5.0 mM) on electrical characteristics of atrial potentials were determined with standard microelectrode techniques with major reference to the maximum rate of rise of the action potential (Vmax of AP), the time constant of recovery of the rapid sodium carrier (gamma) and repetitive firing due to early extra stimuli (arrhythmia).

The effect of propranolol and dimethylpropranolol on cardiac conduction.

Isolated dog hearts perfused with blood from a donor dogand driven at two heart rates were used to compare the effects of propranolol with those of its quaternary ammonium derivative on atrial, atrioventricular (AV) nodal, and His-Purkinje conduction. Propranolol slowed only AV-nodal conduction, increasing the minimal conduction time and the effect of prematurity, without affecting fatigue. Practolol did not have this effect.

A specific effect of lidocaine and tocainide on ventricular conduction of mid-range extrasystoles.

Lidocaine and tocainide had no effect on ventricular conduction of extrasystoles with coupling intervals longer than 500 msec in isolated blood-perfused dog hearts, but caused interval-related increases in conduction time of extrasystoles in the range of 250--400 msec, here called mid-range extrasystoles (MRE). Quinidine, procainamide, disopyramide, and methyl lidocaine increased conduction times of extrasystoles at all coupling intervals, and no additional slowing of MRE was observed. The slowing of MRE specific to lidocaine and tocainide was confirmed in the intact dog heart.