Phenol nitration upon oxidation of nitrite by Mn(III,IV) (hydr)oxides

An interesting aspect of the chemistry of nitrite is the possibility for this compound to interact with other environmental factors and many oxidising species, which results in the oxidation of nitrite to nitrogen dioxide. This is a potentially interesting process that can lead to the formation of nitroaromatic compounds in the environment. In previous papers we have shown that nitrite can interact with dissolved Fe(III) and nitrate under irradiation, Fenton and heterogeneous photo-Fenton reagents, and semiconductor oxides such as TiO2, alpha-Fe2O3, and beta-FeOOH under irradiation. This paper reports on the interaction between nitrite/nitrous acid and the Mn(III,IV) (hydr)oxides beta-MnO2 and gamma-MnOOH, both in neutral solution under irradiation and in acidic conditions in the dark. beta-MnO2 and gamma-MnOOH originate from the oxidation of Mn(II) and play a key role in the redox cycling of manganese in the environment. These Mn(III,IV) (hydr)oxides show some photocatalytic activity, and they can act as thermal oxidants at acidic pH. The photoinduced oxidation of nitrite and the thermal oxidation of nitrous acid by Mn(III,IV) (hydr)oxides yield nitrogen dioxide and lead to the formation of nitrophenols in the presence of phenol. These processes can take place at the water-sediment or water-colloid interface in natural waters and on the surface of atmospheric particulate. Furthermore, the phenol/gamma-MnOOH/HNO2 system in dark acidic solution is an interesting model due to the formation of phenoxyl radical upon phenol monoelectronic oxidation by gamma-MnOOH. The kinetics of nitrophenol generation under such conditions indicates that phenol nitration is unlikely to take place upon reaction between phenoxyl and *NO2 and suggests a solution to a literature debate on the subject.     

Azo-dyes photocatalytic degradation in aqueous suspension of TiO2 under solar irradiation

The photodegradation of two common and very stable azo-dyes, i.e. methyl-orange (C₁₄H₁₄N₃SO₃Na) and orange II (C₁₆H₁₁N₂SO₄Na), is reported. The photocatalytic oxidation was carried out in aqueous suspensions of polycrystalline TiO₂ irradiated by sunlight. Compound parabolic collectors, installed at the “Plataforma Solar de Almería” (PSA, Spain) were used as the photoreactors and two identical reacting systems allowed to perform photoreactivity runs for the two dyes at the same time and under the same irradiation conditions. The disappearance of colour and substrates together with the abatement of total organic carbon content was monitored. The main sulfonate-containing intermediates were found to be in lower number in respect to those obtained under artificial irradiation. In particular there were no more evidence of the presence of hydroxylated transients. The dependence of dye photooxidation rate on: (i) substrate concentration; (ii) catalyst amount; and (iii) initial pH was investigated. The influence of the presence of strong oxidant species (H₂O₂, S₂O₈²⁻) and some ions (Cl⁻, SO₄²⁻) on the process was also studied.     

Fetal echocardiography using transvaginal and transabdominal probes during the first period of pregnancy: A comparative study

The authors compare the diagnostic possibilities of fetal transabdominal echocardiography versus transvaginal echocardiography. A larger diagnostic capacity is verified in different gestation ages with transvaginal probe between the 11th and 14th week of gestation. The results are emphasized by colour Doppler.     

Preservation of ancient DNA in thermally damaged archaeological bone

Evolutionary biologists are increasingly relying on ancient DNA from archaeological animal bones to study processes such as domestication and population dispersals. As many animal bones found on archaeological sites are likely to have been cooked, the potential for DNA preservation must be carefully considered to maximise the chance of amplification success. Here, we assess the preservation of mitochondrial DNA in a medieval cattle bone assemblage from Coppergate, York, UK. These bones have variable degrees of thermal alterations to bone collagen fibrils, indicative of cooking. Our results show that DNA preservation is not reliant on the presence of intact collagen fibrils. In fact, a greater number of template molecules could be extracted from bones with damaged collagen. We conclude that moderate heating of bone may enhance the retention of DNA fragments. Our results also indicate that ancient DNA preservation is highly variable, even within a relatively recent assemblage from contexts conducive to organic preservation, and that diagenetic parameters based on protein diagenesis are not always useful for predicting ancient DNA survival.     

Alpha-male paternity in elephant seals

The aim of this study was to assess paternity of males that dominated mating in harems at northern (Mirounga angustirostris) and southern (M. leonina) elephant seal rookeries using DNA fingerprinting and microsatellite DNA analysis. Southern alpha males had greater reproductive success than most northern alphas at similar-sized harems. Comparison of the relatedness between pups within harems also suggested that fewer males achieved matings in the southern elephant seal population. This was consistent with behavioral observations that suggest greater competition for mates in northern elephant seal harems. Reproductive success was consistent with estimates of mating success in some cases, but lower than expected for some northern elephant seal alpha males. A lower reproductive success than predicted from mating behavior may arise from a variety of factors including sperm competition, male sperm depletion from frequent mating, or reduced fertility. The alternatives are discussed in the context of environmental and historical factors. Received: 17 August 1998 / Received in revised form: 28 March 1999 / Accepted: 30 May 1999     

Applicability of the Arrhenius model for ammonia oxidizing bacteria subjected to temperature time gradients

The aim of this work is to identify the range of applicability of Arrhenius type temperature dependence for Ammonia Oxidizing Bacteria (AOB) subjected to temperature time gradients through continuous titrimetric tests. An innovative online differential titrimetric technique was used to continuously monitor the maximum biologic ammonia oxidation rate of the biomass selected in a pilot scale membrane bioreactor, as a function of temperature time gradients. The monitoring technique is based on the measurement of alkalinity and hydrogen peroxide consumption rates in two parallel reactors operated in non-limiting substrate conditions for AOB; both reactors were continuously fed with mixed liquor and in one of them AOB were inhibited with allylthiourea. The effects of temperature decrease rates in the range 1 to 4°C·h⁻¹ were evaluated by controlling the titrimetric reactor in the temperature range 10°C–20°C. The dependence of growth kinetics on temperature time gradients and the range of applicability of Arrhenius model for temperature dependency of AOB growth kinetics were assessed. The Arrhenius model was found to be accurate only with temperature gradients lower than 2°C·h⁻¹. The estimated Arrhenius coefficients (θ) were shown to increase from 1.07 to 1.6 when the temperature decrease rate reached 4°C·h⁻¹.     

Performance of some biotic indices in the real variable world: A case study at different spatial scales in North-Western Mediterranean Sea

The aim of this study was to analyse the variability of four different benthic biotic indices (AMBI, BENTIX, H′, M-AMBI) in two marine coastal areas of the North-Western Mediterranean Sea. In each coastal area, 36 replicates were randomly selected according to a hierarchical sampling design, which allowed estimating the variance components of the indices associated with four different spatial scales (ranging from metres to kilometres). All the analyses were performed at two different sampling periods in order to evaluate if the observed trends were consistent over the time. The variance components of the four indices revealed complex trends and different patterns in the two sampling periods. These results highlighted that independently from the employed index, a rigorous and appropriate sampling design taking into account different scales should always be used in order to avoid erroneous classifications and to develop effective monitoring programs.     

Binary mixtures of azinphos-methyl oxon and chlorpyrifos oxon produce in vitro synergistic cholinesterase inhibition in Planorbarius corneus

In this study, the cholinesterase (ChE) and carboxylesterase (CES) activities present in whole organism homogenates from Planorbarius corneus and their in vitro sensitivity to organophosphorous (OP) pesticides were studied. Firstly, a characterization of ChE and CES activities using different substrates and selective inhibitors was performed. Secondly, the effects of azinphos-methyl oxon (AZM-oxon) and chlorpyrifos oxon (CPF-oxon), the active oxygen analogs of the OP insecticides AZM and CPF, on ChE and CES activities were evaluated. Finally, it was analyzed whether binary mixtures of the pesticide oxons cause additive, antagonistic or synergistic ChE inhibition in P. corneus homogenates. The results showed that the extracts of P. corneus preferentially hydrolyzed acetylthiocholine (AcSCh) over propionylthiocholine (PrSCh) and butyrylthiocholine (BuSCh). Besides, AcSCh hydrolyzing activity was inhibited by low concentrations of BW284c51, a selective inhibitor of AChE activity, and also by high concentrations of substrate. These facts suggest the presence of a typical AChE activity in this species. However, the different dose-response curves observed with BW284c51 when using PrSCh or BuSCh instead of AcSCh suggest the presence of at least another ChE activity. This would probably correspond to an atypical BuChE. Regarding CES activity, the highest specific activity was obtained when using 2-naphthyl acetate (2-NA), followed by 1-naphthyl acetate (1-NA); p-nitrophenyl acetate (p-NPA), and p-nitrophenyl butyrate (p-NPB). The comparison of the IC(50) values revealed that, regardless of the substrate used, CES activity was approximately one order of magnitude more sensitive to AZM-oxon than ChE activity. Although ChE activity was very sensitive to CPF-oxon, CES activity measured with 1-NA, 2-NA, and p-NPA was poorly inhibited by this pesticide. In contrast, CES activity measured with p-NPB was equally sensitive to CPF-oxon than ChE activity. Several specific binary combinations of AZM-oxon and CPF-oxon caused a synergistic effect on the ChE inhibition in P. corneus homogenates. The degree of synergism tended to increase as the ratio of AZM-oxon to CPF-oxon decreased. These results suggest that synergism is likely to occur in P. corneus snails exposed in vivo to binary mixtures of the OPs AZM and CPF.     

Factors affecting the growth rates of ammonium and nitrite oxidizing bacteria

The maximum specific growth rates of both ammonium oxidizing bacteria (AOB) and nitrite oxidizing bacteria (NOB) were investigated under varying aerobic solids retention time (SRT_a) and in the presence/absence of anoxic (alternating) conditions. Two bench SBRs, reactor R1 and R2, were run in parallel for 150 d. Reactor R1 was operated in aerobic conditions while R2 operated in alternating anoxic/aerobic conditions. The feed (synthetic wastewater), temperature, hydraulic retention time and mixing were identical in both reactors. The SRT_a in both reactors was, sequentially, set at four values: 5, 4, 3 and 2 d.Kinetic tests with the biomasses from both reactors were carried out to estimate the maximum specific growth rates (μ_max) at each tested SRT_a and decay rates, in both aerobic and anoxic conditions. The kinetic parameters of nitrifier were estimated through the calibration of a two step nitrification-denitrification activated sludge model.The results point to a slightly higher μ_max,AOB and μ_max,NOB in alternating conditions, while both μ_max,AOB and μ_max,NOB were shown not to vary in the tested range of SRT_a (from 2 to 5 d) at 20 °C. They were relatively high when compared to literature data: 1.05 d⁻¹ < μ_max,AOB < 1.4 d⁻¹ and 0.91 d⁻¹ < μ_max,NOB < 1.31 d⁻¹. The decay coefficients of both AOB and NOB were much higher in aerobic (from 0.22 d⁻¹ to 0.28 d⁻¹) than in anoxic (0.04 d⁻¹ to 0.16 d⁻¹) conditions both in R1 and R2, which explained the higher nitrification rates observed in the alternating reactor.