Effect of cobalt-supplemented diets on bioaccumulation,digestive enzyme activities and growth of Cyprinus carpio

Experiments were conducted to determine the effects of excess dietary cobalt (Co) on bioaccumulation, digestive enzyme activities, and growth in freshwater Cyprinus carpio. Four isonitrogenous diets (average crude protein: 35%) were formulated to prepare a control diet (T₁) with no Co, and three Co-supplemented diets with 1 (T₂), 1.5 (T₃), or 2 (T₄)% Co. The results showed that C. carpio fed with T₃ diet showed maximal apparent protein digestibility, feed conversion, protein utilization, and growth. Protease and lipase activities were maximal in the fish group given T₃ diet. Accumulation of Co in different soft and hard tissues of fish did not correlate with levels of Co in the diet. The concentration of Co in the water increased with dietary level, being at a disturbing adverse effect level at 2% dietary Co. Evidence indicates that an additional supply of dietary Co up to a level of 1.5% is a viable option to augment growth of C. carpio, but at higher levels of Co it may be detrimental to fish health and the aquatic ecosystem.     

Complexation of iron by salicylic acid and its effect on atrazine photodegradation in aqueous solution

The photodegradation of atrazine and the photochemical formation of Fe(II) and H₂O₂ in aqueous solutions containing salicylic acid and Fe(III) were studied under simulated sunlight irradiation. Atrazine photolysis followed first-order reaction kinetics, and the rate constant (k) corresponding to the solution of Fe(III)-salicylic acid complex (Fe(III)-SA) was only 0.0153 h^?1, roughly one eighth of the k observed in the Fe(III) alone solution (0.115 h^?1). Compared with Fe(III) solution, the presence of salicylic acid significantly enhanced the formation of Fe(II) but greatly decreased H₂O₂ generation, and their subsequent product, hydroxyl radical (˙OH), was much less, accounting for the low rate of atrazine photodegradation in Fe(III)-SA solution. The interaction of Fe(III) with salicylic acid was analyzed using Fourier-transform infrared (FTIR) spectroscopy and UV-visible absorption, indicating that Fe(III)-salicylic acid complex could be formed by ligand exchange between the hydrogen ions in salicylic acid and Fe(III) ions.     

Fluorescence studies of dye displacement from DNA by chromium(III) complexes: Evidence for cation induced DNA condensations

The interactions of 10 different chromium(III) complexes with isolated calf thymus DNA have been analysed by studying the electronic and fluoresence spectra of intercalated ethidiumbromide. Triply charged cationic complexes including: [Cr(urea)₆]Cl₃.3H₂O, [Cr(1,10‐phenanthroline)₃](ClO₄)₃.2H₂O, [Cr(2,2'‐bipyridyl)₃] (ClO₄)₃.2H₂O, [Cr(ethylendiamine)₃]Cl₃.3.5H₂O and [Cr(NH₃)₆](NO₃)₃ displaced the dye from DNA. Similar effects were observed in experiments using the non‐intercalating dye bisbenzimidazole ("Hoechst 33258"). However, singly charged cationic, anionic and uncharged chromium(III) complexes such as: cis‐[Cr(1,10‐phenanthroline)₂Cl₂]Cl.2H₂O, cis‐[Cr(2,2'‐bipyridyl)₂Cl₂]Cl.2H₂O, [Cr(glutathione)₂]Na₂, [Cr(cysteine)₂]Na.2H₂O and [Cr(glycine)₃] were unable to displace both ethidiumbromide and bisbenzimidazole from DNA. There was no evidence for the formation of co‐ordinate bonds between chromium(III) and DNA for any of the above complexes. The charge and type of ligand are important in controlling the interaction of chromium(III) with isolated DNA in vitro. Our findings indicate that the outer sphere interaction of a chromium(III) complex with DNA is weak and unlikely to be the mechanism by which chromate causes DNA impairments in vivo and in vitro.     

Removal of pentachlorophenol from contaminated soil by catalytic oxidation with iron(III)-porphyrin complexes and potassium monopersulfate

Pentachlorophenol (PCP) in contaminated soil was removed by treatment with aqueous solutions of iron(III)-porphyrin complexes as catalysts and potassium monopersulfate (KHSO₅) as the oxygen donor. The contaminated soils were artificially prepared by spiking PCP to the kaolin and ando soils. Three types of iron(III)-porphyrin complexes, tetra(?p-sulfophenyl) porphineiron(III) (Fe(III)-TPPS), tetra(N-methyl-4-pyridil)porphineiron(III) (Fe(III)-TMPyP) and heme, were examined, and Fe(III)-TPPS was found to be the most effective for removing PCP. Although the sequential addition of KHSO₅ was examined, in an attempt to improve the efficiency of PCP removal, it was not effective. In a preliminary test of various aqueous solutions, the addition of humic acid (HA), with a lower degree of humification, led to a significant enhancement in PCP removal. When HA was added to the soil system, the percentages of PCP removal were increased by up to 10% compared to the absence of HA. Therefore, the addition of HA to the catalytic system was useful in enhancing PCP removal from contaminated soil.     

Hydroxyl radical generation by redox cycling of some chemotherapeutic antibiotics

The anticancer drugs: adriamycin, farmorubicin and mitomycin C greatly enhance the generation of hydroxyl radicals (HO^.) from H₂O₂ in the presence of Co(II) ions (CoCl2) at pH 7.4 and 8, as measured by the deoxyribose assay. Catalase, hydroxyl radical scavengers (mannitol, cysteine, glutathione, thiourea, lactic dehydrogenase) inhibited the degradation of deoxyribose confirming that HO‐radicals are responsible for the degradation of the carbohydrate.     

Efficient adsorption of carbon dioxide and methane on activated carbon prepared from glycerol with potassium acetate

In the context of global warming and the energy crisis, emissions to the atmosphere of greenhouse gases such as carbon dioxide (CO₂) and methane (CH₄) should be reduced, and biomethane from landfill biogas should be recycled. For this, there is a need for affordable technologies to capture carbon dioxide, such as adsorption of biogas on activated carbon produced from industrial wastes. Here we converted glycerol, a largely available by-product from biodiesel production, into activated carbon with the first use of potassium acetate as an activating agent. We studied adsorption of CO₂ and CH₄ on activated carbon. The results show that activated carbon adsorb CO₂ up to 20% activated carbon weight at 250 kPa, and 9% at atmospheric pressure. This is explained by high specific surface areas up to 1115 m²g⁻¹. Moreover, selectivity values up to 10.6 are observed for the separation of CO₂/CH₄. We also found that the equivalent CO₂ emissions from activated carbon synthesis are easily neutralized by their use, even in a small biogas production unit.

     

Removal of arsenic from aqueous solution by two types of nano TiO2 crystals

Titanium dioxide (TiO₂) is a promising sorbent for As removal. There are two main and physico-chemically distinct polymorphs of TiO₂ in nature, namely anatase and rutile. Since the difference of arsenic removal by the two polymorphs of TiO₂ is now well known, study on the arsenic removal efficiency and the underlying mechanism is of great significance in developing new remediation strategies for As-polluted waters. Here batch experiments were carried out in combination with instrumental analysis of X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), and X-ray photoelectron spectroscopy (XPS) to investigate the effects, influential factors and mechanisms of As removal from aqueous solution by two types of nano TiO₂ crystals. The adsorption behavior of anatase and rutile for As(V) and As(III) are well described by Freundlich equations. Anatase had higher As removal efficiency and adsorption capacity than rutile. Solution pH had no influence on the As adsorption of anatase TiO₂, whereas the As removal by rutile TiO₂ was increased by 7?C18% with pH from 4 to 10. Presence of accompanying anions such as phosphate, silicate, nitrate and sulfate, decreased the As(V) and As(III) removal by both crystals, with phosphate being the most effective. However, removal of As by rutile TiO₂ was greatly enhanced in the presence of divalent cations i.e. Ca²⁺ and Mg²⁺. Shading of light decreased the removal of As(V) and As(III) of anatase by 15.5% and 17.5%, respectively, while a slight increase of As removal was observed in the case of Rutile TiO₂. FT-IR characterization of As(V) or As(III)-treated nano TiO₂ crystals indicated that both Ti-O and As-O groups participated in As adsorption. Both FT-IR and XPS analysis demonstrated that As(III) was photooxidated into As(V) when adsorbed by anatase under the light condition. Thus, the effect of crystal types and light condition on As removal should be taken into consideration when nano TiO₂ is applied for As removal from water.     

Toxicokinetics,metabolism, and microsomal studies of chlorpropham in rats

A study on the toxicokinetic behavior, metabolism of chlorpropham, and its effect on cytochrome P₄₅₀ from liver microsomes was carried out in albino rats after a single and consecutive oral administration at 500?mg?kg^?1 body weight for 10 and 20 days. Chlorpropham was detected in the blood at 0.08?h (11.43?±?1.72?µg?mL^?1) reaching a maximum concentration at 2?h (30.90?±?2.55?µg?mL^?1) and a minimum at 48?h (1.95?±?0.20?µg?mL^?1) after a single oral administration of 500?mg?kg^?1. The absorption rate constant (K _a) was 0.66?±?0.48?h^?1. The Vd _area (18.01?±?2.78?L?kg^?1) and t _1/2 β (12.23?±?1.96?h) values suggested a wide distribution and long persistence of the compound in the body, respectively. The higher Cl_R (0.82?±?0.00?L?kg^?1?h^?1) compared to Cl_H (0.18?±?0.02?L?kg^?1?h^?1) value indicated that a major portion of chlorpropham was excreted through the urine (30%) compared to the faeces (2.81%). Chlorpropham residue was detected in all tissues of rat at 0.25?h while its metabolite, meta-chloroaniline was detected in liver, kidney, heart, lung, and spleen tissue at 0.25?h. Meta-chloroaniline was not detected in skeletal muscle, brain, fat, and stomach tissue at any time of the observation period. Maximum concentrations of chlorpropham and meta-chloroaniline were detected at 2?h (except in the spleen), and minimum concentrations of chlorpropham at 24 (heart, lung, spleen, skeletal muscle, and stomach) and 48?h (liver, kidney, brain, and fat tissue) respectively; and meta-chloroaniline at 24?h (except heart and spleen). The tissue half-life of chlorpropham in rat varied from 3.80 to 11.60?h. Repeated oral administration of chlorpropham at 500?mg?kg^?1 for 10 and 20 days caused an induction of the liver microsomal pellet of rat.     

Effective removal of Cobalt(II) ions from aqueous solutions and nuclear industry wastewater using sulfhydryl and carboxyl functionalised magnetite nanocellulose composite: batch adsorption studies

A new adsorbent sulfhydryl and carboxyl functionalized magnetite nanocellulose composite [(MB-IA)-g-MNCC] was synthesized by graft co-polymerization of itaconic acid onto magnetite nanocellulose (MNCC) using EGDMA as cross linking agent and K₂S₂O₈ as free radical initiator. The adsorption occurs maximum in the pH 6.5. The best fitted kinetic model was found to be pseudo-second-order kinetics. Therefore the mechanism of Co(II) adsorption onto (MB-IA)-g-MNCC follows ion exchange followed by complexation. The Langmuir model was the best fitted isotherm model for the adsorption of Co(II) onto the (MB-IA)-g-MNCC. Simulated nuclear power plant coolant water samples were also treated with (MB-IA)-g-MNCC to demonstrate its efficiency for the removal of Co(II) from aqueous solutions in the presence of other metal ions. To recover the adsorbed Co(II) ions and also to regenerate the adsorbent to its original state 0.1?M HCl was used as suitable desorbing agent. Six cycles of adsorption-desorption experiments were conducted and was found that adsorption capacity of (MB-IA)-g-MNCC has been decreased from 97.5% in the first cycle to 84.7% in the sixth cycle. Recovery of Co(II) using 0.1?M HCl decreased from 93.2% in the first cycle to 79.3% in the sixth cycle.

Abbreviations: T: absolute temperature; q_e: amount adsorbed at equilibrium; q_t: amount adsorbed at time t; CELL: cellulose; Co: cobalt; C_e: concentration at equilibrium; C_HCl: concentration of HCl; C_NaOH: concentration of NaOH; C_A: concentrations of acid; C_B: concentrations of base; W_g: dry weight of composite; W_i: dry weight of MNCC; DS: energy dispersive spectra; EGDMA: ethylene glycol dimethacrylate; Ce: equilibrium concentration; K_L: equilibrium constant; F: Faradays constant; FTIR: Fourier transform infrared spectra; ΔG^o: free energy change; K_F: Freundlich adsorption capacity; 1/n: Freundlich constant; R: gas constant; D: grafting density; EC_o: initial concentration; IA: itaconic acid; IA-g-MNCC: itaconic acid-grafted-magnetite nanocellulose composite; b: Langmuir constant; MNCC: magnetite nanocellulose composite; Q⁰: Maximum adsorption capacity; (MB-IA)-g-MNCC: 2-mercaptobenzamide modified itaconic acid-grafted-magnetite nanocellulose composite; NC: nanocellulose; pH_pzc: Point of zero charge; K₂S₂O₈: potassium peroxy sulphate; k₁: pseudo-first-order rate constant; k₂: pseudo-second-order rate constant; SEM: scanning Electron Microscope; b_s: Sips adsorption capacity; Q_s: Sips maximum adsorption capacity; ΔH°: standard enthalpy change; ΔS°: standard entropy change; A: surface area; σ₀: surface charge density; 1/n_s: surface heterogeneity factor; VSM: vibrating sample magnetometer; V: volume of solution; W: weight of (MB-IA)-g-MNCC; M_composite: weight of the composite; XRD: X-ray diffraction     

Complete oxidation of methane on Co3O4-SnO2 catalysts

Co₃O₄-SnO₂ hybrid oxides were prepared by the coprecipitation method and were used to oxidate methane (CH₄) in presence of oxygen. The Co₃O₄-SnO₂ with a molar ratio of Co/(Co + Sn) at 0.75 exhibited the highest catalytic activity among all the Co₃O₄-SnO₂ hybrid oxides. Experimental results showed that the catalysts were considerably stable in the CH₄ combustion reaction, and were verified by X-ray photoelectron spectra (XPS). It was found that Co₃O₄ was the active species, and SnO₂ acted as a support or a promoting component in the Co₃O₄-SnO₂ hybrid oxides. The surface area was not a major factor that affected catalytic activity. The hydrogen temperatureprogrammed reduction (H₂-TPR) results demonstrated that the interaction between cobalt and tin oxides accelerated the mobility of oxygen species of Co₃O₄-SnO₂, leading to higher catalytic activity.     

Kinetics of the oxidation of endocrine disruptor nonylphenol by ferrate(VI)

The kinetics of the oxidation of endocrine disruptor nonylphenol (NP) by potassium ferrate(VI) (K₂FeO₄) in water as a function of pH 8.0–10.9 at 25°C is presented. The observed second-order rate constants, k _obs, decrease with an increase in pH 269–32 M^?1 s^?1. The speciation of Fe(VI) (HFeO ₄ ^? and FeO ₄ ^2? ) and NP (NP–OH and NP–O^?) species was used to explain the pH dependence of the k _obs values. At a dose of 10 mg L^?1 (50 μM) K₂FeO₄, the half-life for the removal of NP by Fe(VI), under water treatment conditions, is less than 1 min.     

Biochemical speciation in chromium genotoxicity

The biochemical speciation of chromium compounds in mammalian cells is discussed with respect to uptake, metabolism, DNA binding and damaging. Whereas soluble hexavalent chromium is taken up rapidly and accumulated intracellularly after its reduction, compounds of trivalent chromium penetrate biomembranes about three orders of magnitude slower. Cr(VI) after its uptake is metabolised by electron donating compounds via Cr(V) to Cr(III) compounds. Chromium from various Cr(III) compounds, but not chromate, binds to chromatin in isolated cell nuclei. The DNA‐protein crosslinks and DNA strand breaks observed in rat liver and kidney after chromate administration are also found in vitro, when Cr(III) compounds (but not chromate) interacts with isolated nuclei. In the Chinese Hamster cell HGPRT mutation assay, three out of four tested Cr(III) complexes were found to be mutagenic. In a direct DNA strand break assay with supercoiled bacteriophage PM 2 DNA, neither chromate nor the four Cr(III) compounds tested caused nicks. However, the combined action of chromate plus glutathione as well as the isolated complex of pentavalent chromium, Na₄Cr(glutathione)₄, did cause DNA breaks. Reactive oxygen species are inferred to be the ultimate DNA nicking agents in this assay. In conclusion there appear to be two mechanisms of chromate genotoxicity; one with direct DNA damage caused by Cr(V) species and one via DNA‐protein crosslinks formed with Cr(III), the final reduction state of chromate.     

Degradation of pentachlorophenol in a contaminated soil suspension using hybrid catalysts prepared via urea�Cformaldehyde polycondensation between iron(III)-tetrakis(p-hydroxyphenyl)porphyrin and humic acid

Hybrid catalysts were synthesized by attaching iron(III)-tetrakis(p-hydroxyphenyl)porphyrin (FeTPP(OH)₄) to humic acid (HA) via urea–formaldehyde polycondensation. FTIR spectra of the prepared catalysts indicated that the catalysts prepared via urea–formaldehyde polycondensation contained cross-links between the phenolic groups of FeTPP(OH)₄ and HA, which contains aliphatic amine functional groups. The prepared catalysts were examined for their ability to catalyze the oxidative degradation of pentachlorophenol (PCP) in a contaminated soil suspension. The levels of PCP degradation and dechlorination for the hybrid catalysts were significantly higher than those for the non-modified catalyst, FeTPP(OH)₄.     

Mechanism of toxicity of ionic copper and copper complexes to algae

The mechanism of toxicity of ionic copper and copper complexes to growth, photosynthesis, respiration, ATP levels and mitochondrial electron-transport chain-activity in two marine diatoms, Nitzschia closterium (Ehrenberg) W. Smith (Hasle, 1964) and Asterionella glacialis Castracane, and one freshwater green alga, Chlorella pyrenoidosa Chick was investigated. Copper ions depressed both cell division and photosynthesis in A. glacialis and C. pyrenoidosa, whereas ionic copper concentrations which were inhibitory to cell division in N. closterium had no effect on photosynthesis, respiration, ATP production, electron transport or membrane ultrastructure. This suggests that in N. closterium, copper does not act on the chloroplast, the mitochondrion, or the cell membrane, since if it did, the above parameters should be affected. Copper-ethylxanthogenate was exceptional amongst the copper complexes in that it stimulated respiration, mitochondrial electrontransport and ATP formation in N. closterium under conditions of strongly inhibited cell division and slightly stimulated photosynthesis. Ionic copper toxicity may result from an intracellular reaction between copper and reduced glutathione (GSH), leading to a lowering of the GSH:GSSG ratio and suppression of mitosis. In addition, copper inhibits the enzyme catalase and reduces cell defence mechanisms against H₂O₂ and oxygen-free radicals. Lipid-soluble copper complexes are more toxic than ionic copper because both the metal and the ligand are introduced into the cell. Toxicity of ionic copper is ameliorated by trivalent metal ions in the growth medium, including those of Mn, Co, Al, Fe and Cr which form a layer of metal (III) hydroxide around the algal cell, adsorb copper and reduce its penetration into the cell. The degree of insolubility of the metal (III) hydroxide is related to its ability to protect against copper toxicity. In addition, manganese and cobalt catalytically scavenge damaging H₂O₂ and superoxide radicals, respectively, produced by the cell.     

Simultaneous measurements of arsenic and sulfide using diffusive gradients in thin films technique (DGT)

Diffusive gradients in thin films technique (DGT) is a dynamically passive sampling technique which has been applied increasingly to the environmental monitoring field. In the preliminary period, the DGT with zirconium hydroxide-silver iodide as the binding phase (ZrO-AgI DGT) has been developed for the determination of sulfide (S(II)). On this basis, this paper developed its determination method for inorganic arsenite (As(III)) to further realize the simultaneous and high-resolution measurements of labile inorganic As and S(II) in sediments. ZrO-AgI binding gel had a strong ability in adsorbing and fixing As(III), showing a linear increase in the initial 12.5 min. After saturation of S(II) on ZrO-AgI binding gel, the adsorption rate and adsorption capacity of As(III) reduced by 8 and 14%, respectively. A stable elution rate (89.1 ± 2.2%) was obtained by extraction of As(III) on the binding gel using a mixture solution of 1.0 M NaOH and 1.0 M H₂O₂ (1:1). The DGT capacity of As(III) determined by the ZrO-AgI DGT was 23.6 μg cm^?2. DGT uptakes of As(III) were independent of pH (4.0–9.0) and ionic strength (0.01–100 mM), and they did not interfere with each other during the uptake process. Simultaneous measurements of labile As and S(II) in four sediment cores of Taihu Lake (China) with ZrO-AgI DGT showed that they had similarly vertical distributions in the top 16-mm layer in one core and in the whole profile up to the 35 mm depth in two cores. It likely reflected a simultaneous release of As and S(II) in sediments by synchronous reduction of As-hosted oxidized iron and sulfate, respectively. The simultaneous decreases of labile As and S(II) from their co-precipitation (e.g., As₂S₃) were not obvious in deeper sediment layer through the measurement with ZrO-AgI DGT.     

Study on increase in toxicity of Schiff bases on microorganism on chelation with metal

New heterochelates of the type [M(L)(SB)(H₂O)] (where M?=?Mn(II), Co(II), Ni(II), Cu(II), Zn(II), and Cd(II), KHL?=?potassium salt of salicylideneglycine and SB?=?thiophene- O -carboxaldeneaniline) have been synthesized. The heterochelates have been characterized on the basis of elemental analyses, electronic spectra, and magnetic measurement analyses. The structural and geometrical conformation has been discussed on the basis of IR spectral data. A thermal study of the complexes has been carried out to ascertain their thermal stability. Magnetic susceptibility measurements and electronic spectral data suggest a six-coordinated octahedral structure for these complexes. The increase in toxicity of the investigated heterochelate metal compounds was tested against three gram-negative bacteria, S. typhi, E. coli, and Serratia marcescens by the disc diffusion method. It is observed that the heterochelates show higher toxicity when compared to the Schiff bases, metal salts, and control (DMSO) due to chelation. The toxicity is also compared to the standard drug tetracycline.     

Investigation of fluorescence characterization and electrochemical behavior on the catalysts of nanosized Pt-Rh/γ-Al2O3 to oxidize gaseous ammonia

This work describes the environmentally friendly technology for oxidation of ammonia (NH₃) to form nitrogen at temperatures range from 423K to 673K by selective catalytic oxidation (SCO) over a nanosized Pt-Rh/γ-Al₂O₃ catalyst prepared by the incipient wetness impregnation method of hexachloroplatinic acid (H₂PtCl₆) and rhodium (III) nitrate (Rh(NO₃)₃) with γ-Al₂O₃ in a tubular fixed-bed flow quartz reactor (TFBR). The characterization of catalysts were thoroughly measured using transmission electron microscopy (TEM), threedimensional excitation-emission fluorescent matrix (EEFM) spectroscopy, UV-Vis absorption, dynamic lightscattering (DLS), zeta potential meter, and cyclic voltammetry (CV). The results demonstrated that at a temperature of 673K and an oxygen content of 4%, approximately 99% of the NH₃ was removed by catalytic oxidation over the nanosized Pt-Rh/γ-Al₂O₃ catalyst. N₂ was the main product in NH₃-SCO process. Further, it reveals that the oxidation of NH₃ was proceeds by the over-oxidation of NH₃ into NO, which was conversely reacted with the NH₃ to yield N₂. Therefore, the application of nanosized Pt-Rh/γ-Al₂O₃ catalyst can significantly enhance the catalytic activity toward NH₃ oxidation. One fluorescent peak for fresh catalyst was different with that of exhausted catalyst. It indicates that EEFM spectroscopy was proven to be an appropriate and effective method to characterize the Pt clusters in intrinsic emission from nanosized Pt-Rh/γ-Al₂O₃ catalyst. Results obtained from the CV may explain the significant catalytic activity of the catalysts.     

Bestimmung von Redoxzonen in einem mineralölbelasteten Grundwasserleiter

Goal and Scope

The goal of this study is the investigation and the grafic presentation of the characteristic redox zonation in a mineral oil contaminated aquifer which will be formed in the plume downstream of the contamination source. Methanogenic conditions, sulfate-reduction, Fe(III)-reduction, Mn(IV)-reduction, nitrate-reduction, aerobic conditions. By that indications type and degree of microbial degradation which is the most important part in Natural Attenuation (NA) processes can be obtained easily.

Methods

Changes of the groundwater parameters Eh, O₂, NO ₃ ^? , SO₄ ^2?, Fe²⁺, Mn²⁺, HCO₃ ^?, Ca²⁺ will be measured upstream, downstream and also in the centre of the plume. The results will be presented in a sequence of special diagrams.

Results and Conclusion

When microbial degradation of hydrocarbons takes place, a microbial community will always use that electron acceptor from which it will gain a maximum of energy by the corresponding redox-reactions. This means as long as oxygen is available this will be used. After its depletion nitrate serves as electron acceptor leading via nitrite to the formation of nitrogen or ammonia. Manganese (IV) and Iron (III) species which are rather insoluble are mainly available from the soil-phase, can act as electron acceptor as next, leading to soluble Manganese (II) and Iron (II) compounds in groundwater. Finally before methanogenic conditions occur sulphate will become a suitable electron acceptor leading to the formation of hydrogen sulphide. All these processes of mineralization of the hydrocarbons will lead to the production of CO₂ and as consequence to an increase of HCO₃ ^? in groundwater changing the calcareous/carbonic acid-equilibrium. By that more soluble Ca(HCO₃)₂ is formed from insoluble CaCO₃, so the concentration from Ca²⁺ will also inerease. Thus, by the action of microorganisms, a typical redox-zonation and changes of other parameters will occur.

Recommendations and Perspective

To follow the changes in time and space of some characteristic groundwater parameters is a simple way to estimate the potential of microbial degradation in a contaminated aquifer considering Natural Attenuation (NA)-processes.     

Induction of gene mutations in salmonella and Drosophila by soluble Cr(Vi) compounds: Synergistic effects of nitrilotriacetic acid

The interaction between NTA and soluble Cr(VI) (K₂Cr₂O₇) was studied by the Ames test on S. typhimurium and the sex‐linked recessive lethal test on D. melanogaster. In both systems a synergistic effect of NTA on Cr(VI) mutagenicity took place at sub‐toxic doses of Cr(VI). The synergism could depend on the action of NTA on intracellular Cr(VI) reduction, as more Cr(VI) was reduced in vitro to Cr(III) by Salmonella and Drosophila protein extracts in the presence of NTA. A similar enhancement of soluble Cr(VI) mutagenicity was produced by low doses of EDTA.     

Blood oxygen-binding characteristics of bigeye tuna (Thunnus obesus), a high-energy-demand teleost that is tolerant of low ambient oxygen

 We found blood from bigeye tuna (Thunnus obesus) to have a significantly higher O₂ affinity than blood from other tunas. Its P₅₀ (partial pressure of oxygen, P_O2 required to reach 50% saturation) was 1.6 to 2.0 kPa (12 to 15 mmHg) when equilibrated with 0.5% CO₂. Previous studies employing similar methodologies found blood from yellowfin tuna (T. albacares), skipjack tuna (Katsuwonus pelamis), and kawakawa (Euthynnus affinis) to have a P₅₀ of 2.8 to 3.1 kPa (21 to 23 mmHg). These observations suggest that bigeye tuna are more tolerant of low ambient oxygen than other tuna species, and support similar conclusions derived from laboratory whole-animal studies, depth-of-capture data, and directly-recorded vertical movements of fish in the open ocean. We also found the O₂ affinity of bigeye tuna blood to be essentially unaffected by a 10 C° open-system temperature change (as is the blood of all tuna species studied to date). The O₂ affinity of bigeye tuna blood was, however, more affected by a 10 C° closed-system temperature change than the blood of any tuna species yet examined. In other words, bigeye tuna blood displayed a significantly enhanced Bohr effect (change in log P₅₀ per unit change in plasma pH at P₅₀) when subjected to the inevitable changes in partial pressure of carbon dioxide (P_CO2) and plasma pH that accompany closed-system temperature shifts, than when subjected to changes in plasma pH accomplished by changing P_CO2 alone. In vivo, the resultant large decrease in O₂ affinity (i.e. the increase in P₅₀) that occurs as the blood of bigeye tuna is warmed during its passage through the vascular counter-current heat exchangers ensures adequate rates of O₂ off-loading in the swimming muscles of this high-energy-demand teleost. Received: 12 March 1999 / Accepted: 18 December 1999