ABSTRACT
Manganese oxides are widespread in the environment and their surface reactivity has the potential to modifythe geochemical behavior of uranium. We have investigated the effect of different concentrations of U and Mn on the coupled biogeochemical oxidation-reduction reactions of U and Mn. Experiments conducted in the presence of Mn(II)-oxidizing spores from Bacillus sp. strain SG-1 and 5% headspace oxygen show that the Mn oxides produced by these spores can rapidly oxidize UO2. Thirty to fifty times more UO2 is oxidized in the presence of Mn oxides compared to Mn oxide free controls. As a consequence of this U02 oxidation, Mn oxides are reduced to soluble Mn(II) that can be reoxidized by SG-1 spores. SG-1 spores cannot directly oxidize U02, but U02 oxidation proceeds rapidly with Mn(II) concentrations of <5 microM. The rate of UO2 oxidation is equal to the rate of MnO2 reduction with UO2 oxidation controlled by the initial concentrations of UO2, dissolved Mn(II) (in systems with spores), or Mn(IV) oxides (in systems containing preformed MnO2). U(VI) and UO2 decrease the Mn(II) oxidation rate in different ways by inhibiting the Mn(II)-oxidizing enzyme or decreasing the available Mn(II). These results emphasize the need to consider the impact of Mn(II)-oxidizing bacteria when predicting the potential for U02 oxidation in the subsurface.
Subject(s)
Bacillus/drug effects , Bacillus/metabolism , Manganese/metabolism , Manganese/pharmacology , Spores, Bacterial/metabolism , Uranium Compounds/metabolism , Uranium/pharmacology , Biodegradation, Environmental/drug effects , Catalysis/drug effects , Environment , Kinetics , Manganese Compounds/metabolism , Oxidation-Reduction/drug effects , Oxides/metabolism , Spores, Bacterial/drug effectsABSTRACT
In the present investigation the changes in energy levels or caloric concentrations of Penaeus indicus postlarvae (PL) were determined after exposure to acute and sublethal concen- trations of lead. The biochemical constituents such as carbo- hydrates, proteins, and lipids were estimated in PL exposed to LC(5) (0.1495), LC(10) (0.3488), LC(25) (1.4660), and LC(50) (7.223 ppm) of lead for 48h. The effect of sublethal concentration (1.44 ppm) of lead was also studied on the above biochemical constituents at intervals of 24, 48, and 96 h, and 10 and 30 days. The caloric concentrations as well as biochemical constituents of the PL demonstrated a decrease on exposure to lead but proteins and lipids decreased to a maximum extent compared to carbohydrates. Moreover, acute concentrations were found to be more effective than sublethal lead. An increasing trend in the ratios of carbohydrate/protein and carbohydrate/lipid was observed during acute and sublethal exposure to lead, indicating more utilization of protein and lipid. Therefore, measuring the caloric concentration in PL of P. indicus can be used to evaluate the physiological effects of combating lead toxicity.
Subject(s)
Energy Metabolism/drug effects , Lead/toxicity , Penaeidae/physiology , Water Pollutants/toxicity , Animals , Carbohydrate Metabolism , Lethal Dose 50 , Lipid Metabolism , Proteins/metabolismABSTRACT
The estuaries and backwaters that are the potential breeding grounds of penaeid shrimps are subject to heavy metal pollution through industrial effluents and domestic sewage. In the present investigation, laboratory experiments were conducted to study the acute toxicity of lead on tolerance, oxygen consumption, ammonia-N excretion, and metal accumulation in Penaeus indicus postlarvae. Static bioassay tests were employed to determine tolerance limits. Oxygen consumption, ammonia-N excretion, and metal accumulation were determined in postlarvae by exposing them to different concentrations of lead for a period of 48 h. Oxygen consumption measurements were made by using a respiratory chamber equipped with an oxygen electrode and ammonia-N was determined with trione (dichloro-S-triamine 2,4,6(1H,3H,5H-trione)). Accumulation of metal was estimated by wet-ash method. The LC50 value for 96 h was 7.223 ppm and the regression equation Y=4.1638+0.9738X with correlation coefficient of 0.9613 was obtained by probit method. A decrease in oxygen consumption and ammonia-N excretion was observed in postlarvae with increasing concentration of lead. A concentration-dependent accumulation of metal was noticed in these postlarvae. Modifications in O:N ratios of postlarvae suggest that lead accumulation might have altered utilization patterns.
